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Sample records for bond dissociation energy

  1. Bond dissociation energies and bond orders for some astrophysical molecules

    NASA Astrophysics Data System (ADS)

    Reddy, R. R.; Viswanath, R.

    1989-06-01

    The bond dissociation energies for various astrophysically important diatomic molecules have been determined using a formula in which bond dissociation energies are the sum of the geometric average of the component bond energies and 32.058 times the Pauling electronegativity difference. Bond orders are estimated according to the formula of Reddy et al. (1985, 1987). The results confirm the definition of bond order given by Politzer (1969). The estimated bond energies are found to agree well with previous values and to give an error of 8 percent, as compared to the error of 26.8 percent found using Pauling's (1960) equation.

  2. The Bond Dissociation Energies of 1-Butene

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R. (Technical Monitor)

    1994-01-01

    The bond dissociation energies of 1-butene and several calibration systems are computed using the G2(MP2) approach. The agreement between the calibration systems and experiment is very good. The computed values for 1-butene are compared with calibration systems and the agreement between the computed results for 1-butene and the "rule of thumb" values from the smaller systems is remarkably good.

  3. Bond Dissociation Energies of Organic Molecules

    E-print Network

    Ellison, Barney

    . Introduction The making and breaking of bonds is the basis of all chemical transformation. A sound knowledge to understanding chemical processes.1 The energy required for homolytic bond cleavage at 298 K corresponds of chemical reactions for which experimental bond en- thalpies are available. One must be cautious, however

  4. Theoretical study of the bond dissociation energies of methanol

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Walch, Stephen P.

    1992-01-01

    A theoretical study of the bond dissociation energies for H2O and CH3OH is presented. The C-H and O-H bond energies are computed accurately with the modified coupled-pair functional method using a large basis set. For these bonds, an accuracy of +/- 2 kcal/mol is achieved, which is consistent with the C-H and C-C single bond energies of other molecules. The C-O bond is much more difficult to compute accurately because it requires higher levels of correlation treatment and more extensive one-particle basis sets.

  5. Estimation of Bond Dissociation Energies and Radical Stabilization Energies by ESR Spectroscopy

    E-print Network

    Brocks, Jochen J.

    Estimation of Bond Dissociation Energies and Radical Stabilization Energies by ESR Spectroscopy stabilization enthalpies (RSE) and with BDE(C-H), the C-H bond dissociation energies for the corresponding stabilization energies and bond dissociation enthalpies (BDE) are useful for the prediction or inter- pretation

  6. The dissociative bond.

    PubMed

    Gordon, Nirit

    2013-01-01

    Dissociation leaves a psychic void and a lingering sense of psychic absence. How do 2 people bond while they are both suffering from dissociation? The author explores the notion of a dissociative bond that occurs in the aftermath of trauma--a bond that holds at its core an understanding and shared detachment from the self. Such a bond is confined to unspoken terms that are established in the relational unconscious. The author proposes understanding the dissociative bond as a transitional space that may not lead to full integration of dissociated knowledge yet offers some healing. This is exemplified by R. Prince's (2009) clinical case study. A relational perspective is adopted, focusing on the intersubjective aspects of a dyadic relationship. In the dissociative bond, recognition of the need to experience mutual dissociation can accommodate a psychic state that yearns for relationship when the psyche cannot fully confront past wounds. Such a bond speaks to the need to reestablish a sense of human relatedness and connection when both parties in the relationship suffer from disconnection. This bond is bound to a silence that becomes both a means of protection against the horror of traumatic memory and a way to convey unspoken gestures toward the other. PMID:23282044

  7. Model energy landscapes and the force-induced dissociation of ligand-receptor bonds.

    PubMed Central

    Strunz, T; Oroszlan, K; Schumakovitch, I; Güntherodt, H; Hegner, M

    2000-01-01

    We discuss models for the force-induced dissociation of a ligand-receptor bond, occurring in the context of cell adhesion or single molecule unbinding force measurements. We consider a bond with a structured energy landscape which is modeled by a network of force dependent transition rates between intermediate states. The behavior of a model with only one intermediate state and a model describing a molecular zipper is studied. We calculate the bond lifetime as a function of an applied force and unbinding forces under an increasing applied load and determine the relationship between both quantities. The dissociation via an intermediate state can lead to distinct functional relations of the bond lifetime on force. One possibility is the occurrence of three force regimes where the lifetime of the bond is determined by different transitions within the energy landscape. This case can be related to recent experimental observations of the force-induced dissociation of single avidin-biotin bonds. PMID:10968985

  8. The computation of C-C and N-N bond dissociation energies for singly, doubly, and triply bonded systems

    NASA Technical Reports Server (NTRS)

    Langhoff, Stephen R.; Bauschlicher, Charles W., Jr.; Taylor, Peter R.

    1989-01-01

    The bond dissociation energies (D sub e) of C2H2, C2H4, C2H6, N2, N2H2, and N2H4 are studied at various levels of correlation treatment. The convergence of D sub e with respect to the one particle basis is studied at the single reference modified coupled-pair functional (MCPF) level. At all levels of correlation treatment, the errors in the bond dissociation energies increase with the degree of multiple bond character. The multireference configuration interaction (MRCI) D sub e values, corrected for an estimate of higher excitations, are in excellent agreement with those determined using the size extensive averaged coupled pair functional (ACPF) method. It was found that the full valence complete active space self consistent field (CASSCF)/MRCI calculations are reproduced very well by MRCI calculations based on a CASSCF calculation that includes in the active space only those electrons involved in the C-C or N-N bonds. To achieve chemical accuracy (1 kcal/mole) for the D sub e values of the doubly bonded species C2H4 and N2H2 requires one particle basis sets including up through h angular momentum functions (l = 5) and a multireference treatment of electron correlation: still higher levels of calculation are required to achieve chemical accuracy for the triply bonded species C2H2 and N2.

  9. The effect of bond functions on dissociation energies

    NASA Technical Reports Server (NTRS)

    Bauschlicher, C. W., Jr.

    1985-01-01

    The procedure employing bond functions recently suggested by Wright and Buenker has been applied to the N2 X 1 Sigma g + potential curve within the CAS SCF + MRSD CI treatment of electron correlation. The basis set used herein is identical to that employed by these authors in their SCF + CI calculations. The De and and the shape of the resulting potential curve, as judged by the computed vibrational levels, is not so accurate as would be expected from the results reported by Wright and Buenker (1984). The results indicate that using the CI superposition errors associated with bond functions to cancel basis set incompleteness depends on the treatment of the electron correlation.

  10. Theoretical study of the C-H bond dissociation energy of acetylene

    NASA Technical Reports Server (NTRS)

    Taylor, Peter R.; Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

    1990-01-01

    The authors present a theoretical study of the convergence of the C-H bond dissociation energy (D sub o) of acetylene with respect to both the one- and n-particle spaces. Their best estimate for D sub o of 130.1 plus or minus 1.0 kcal/mole is slightly below previous theoretical estimates, but substantially above the value determined using Stark anticrossing spectroscopy that is asserted to be an upper bound.

  11. The computation of C-C and N-N bond dissociation energies for singly, doubly, and triply bonded systems

    NASA Technical Reports Server (NTRS)

    Langhoff, Stephen R.; Bauschlicher, Charles W., Jr.; Taylor, Peter R.

    1991-01-01

    The bond dissociation energies (De) of C2H2, C2H4, C2H6, N2, N2H2, and N2H4 are studied at various levels of correlation treatment. The convergence of De with respect to the one-particle basis is studied at the single-reference modified coupled-pair-functional (MCPF)level. At all levels of correlation treatment, the errors in the bond dissociation energies increase with the degree of multiple bond character. The multireference configuration-interaction (MRCI) De values, corrected for an estimate of higher excitations, are in excellent agreement with those determined using the size-extensive averaged-coupled-pair-functional (ACPF) method. The full-valence complete-active-space self-consistent-field (CASSCF)/MRCI calculations are reproduced very well by MRCI calculations based on a CASSCF calculation that includes in the active space only those electrons involved in the C-C or N-N bonds.

  12. Theoretical study of the bond dissociation energies of propyne (C3H4)

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

    1992-01-01

    The C-C and C-H bond dissociation energies (BDEs) of propyne have been computed using the modified coupled-pair functional method. Due to hyperconjugation, the C-C and methyl C-H single bonds are stronger and weaker, respectively than those in ethane. The acetylenic C-H and C triple bond C BDEs are larger and smaller, respectively, than in acetylene, also as a result of the hyperconjugation. Our best estimate of 92.5 +/- 2 kcal/mol for the methyl C-H BDE in propyne is slightly larger than the experimental value. For the acetylenic C-H BDE in propyne we predict 135.9 +/- 2 kcal/mol.

  13. Theoretical study of the C-H bond dissociation energy of C2H

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

    1990-01-01

    A theoretical study of the convergence of the C-H bond dissociation energy D(0) in C2H with respect to both the one- and n-particle spaces is presented. The calculated C-H bond energies of C2H2 and C2H4, which are in excellent agreement with experiment, are used for calibration. The best estimate for D(0) of 112.4 + or - 2.0 kcal/mol is slightly below the recent experimental value of 116.3 + or - 2.6 kcal/mol, but substantially above a previous theoretical estimate of 102 kcal/mol. The remaining discrepancy with experiment may reflect primarily the uncertainty in the experimental D(0) value of C2 required in the analysis.

  14. Prediction of the bond lengths, vibrational frequencies, and bond dissociation energy of octahedral seaborgium hexacarbonyl, Sg(CO){sub 6}

    SciTech Connect

    Nash, C.S.; Bursten, B.E.

    1999-11-24

    The recent syntheses of several new elements (including the recent reports of elements 116 and 118), coupled with the controversy surrounding the naming of elements 104--109, have stimulated a great interest in the chemistry of the transactinide elements. This contribution addresses hypothetical hexacarbonyl complex of seaborgium (Sg, element 106), which is predicted to be a 6d-block transition element with six valence electrons, analogous to Cr, Mo, and W. The authors have previously predicted that, if it were to exist, Sg(CO){sub 6} would exhibit metal-carbonyl bonding that is very similar to that in Cr(CO){sub 6}, Mo(CO){sub 6}, and W(CO){sub 6}, and quite unlike that of the unknown valence isoelectronic actinide complex U(CO){sub 6}. This finding is in accord with the scant experimental data available for Sg. The relativistic DV-X{alpha} method used in the earlier paper facilitated the analysis of the molecular orbitals of Sg(CO){sub 6}, but did not allow for the calculation of total-energy properties, such as bond lengths and vibrational frequencies. Here the authors will use the superior methodology they have applied to other transactinide molecules to compare the bond lengths, vibrational frequencies, and CO dissociation energy of hypothetical Sg(CO){sub 6} to those of Mo(CO){sub 6} and W(CO){sub 6}.

  15. Bond Dissociation Energies for Substituted Polycyclic Aromatic Hydrocarbons and Their Cations

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W.; Langhoff, Stephen R.; Arnold, James O. (Technical Monitor)

    1998-01-01

    The B3LYP/4-31G approach is used to compute bond energies for a series of substituted benzene, naphthalene, and anthracene molecules and their cations. The benzene bond energies are compared with experiment. The trends in the bond energies are discussed. The ionization energies are also reported and compared with available experiments.

  16. Bond Dissociation Energies of the Tungsten Fluorides and Their Singly-Charged Ions: A Density Functional Survey

    NASA Technical Reports Server (NTRS)

    Dyall, Kenneth G.; Arnold, James (Technical Monitor)

    1999-01-01

    The dissociation of WF6 and the related singly-charged cations and anions into the lower fluorides and fluorine atoms has been investigated theoretically using density functional theory (B3LYP) and relativistic effective core potentials, with estimates of spin-orbit effects included using a simple model. The inclusion of spin-orbit is essential for a correct description of the thermochemistry. The total atomization energy of the neutral and anionic WF6 is reproduced to within 25 kcal/mol, but comparison of individual bond dissociation energies with available experimental data shows discrepancies of up to 10 kcal/mol. The results are nevertheless useful to help resolve discrepancies in experimental data and provide estimates of missing data.

  17. Bond-Specific Dissociation Following Excitation Energy Transfer for Distance Constraint Determination in the Gas Phase

    PubMed Central

    2015-01-01

    Herein, we report chemistry that enables excitation energy transfer (EET) to be accurately measured via action spectroscopy on gaseous ions in an ion trap. It is demonstrated that EET between tryptophan or tyrosine and a disulfide bond leads to excited state, homolytic fragmentation of the disulfide bond. This phenomenon exhibits a tight distance dependence, which is consistent with Dexter exchange transfer. The extent of fragmentation of the disulfide bond can be used to determine the distance between the chromophore and disulfide bond. The chemistry is well suited for the examination of protein structure in the gas phase because native amino acids can serve as the donor/acceptor moieties. Furthermore, both tyrosine and tryptophan exhibit unique action spectra, meaning that the identity of the donating chromophore can be easily determined in addition to the distance between donor/acceptor. Application of the method to the Trpcage miniprotein reveals distance constraints that are consistent with a native-like fold for the +2 charge state in the gas phase. This structure is stabilized by several salt bridges, which have also been observed to be important previously in proteins that retain native-like structures in the gas phase. The ability of this method to measure specific distance constraints, potentially at numerous positions if combined with site-directed mutagenesis, significantly enhances our ability to examine protein structure in the gas phase. PMID:25174489

  18. Theoretical study of the C-H bond dissociation energies of CH4, C2H2, C2H4, and H2C2O

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.

    1991-01-01

    The successive C-H bond dissociation energies of CH4, C2H2, C2H4, and H2C2O (ketene) are determined using large-basis sets and a high level of correlation treatment. For CH4, C2H2, and C2H4 the computed values are in excellent agreement with experiment. Using these results, the values 107.9 + or - 2.0 and 96.7 + or - 2.0 kcal/mol are recommended for the C-H bond dissociation energies of H2C2O and HC2O, respectively.

  19. On the Enthalpy of Formation of Hydroxyl Radical and Gas-Phase Bond Dissociation Energies of Water and Hydroxyl

    SciTech Connect

    Ruscic, Branko; Wagner, Albert F.; Harding, Lawerence B.; Asher, Robert L.; Feller, David F. ); Dixon, David A. ); Peterson, Kirk A.; Song, Yang; Qian, Ximei; Ng, C Y.; Liu, Jianbo; Wenwu, Chen

    2001-12-01

    Several photoionization experiments utilizing the positive ion cycle to derive the O-H bond energy converge to a consensus value of AE0(OH+/H2O)= 146117? 24 cm-1 (18.1162? 0.0030 eV). With the most accurate currently available ZEKE value. IE(OH)= 104989? 2 cm-1, corroborated by a number of photoelectron measurements,Error! Bookmark not defined.,Error! Bookmark not defined.,Error! Bookmark not defined.,Error! Bookmark not defined. this leads to D0(H?OH)= 41128? 24 cm-1= 117.59? 0.07 kcal/mol. This corresponds to DHf 0(OH)= 8.85? 0.07 kcal/mol, and implies D0(OH)= 35593? 24 cm-1= 101.76? 0.07 kcal/mol. The most sophisticated theoretical calculations performed so far on the HxO system, CCSD(T)/aug-cc-pVnZ, n=Q, 5, 6, and 7, extrapolated to the CBS limit and including corrections for core-valence effects, scalar relativistic effects, incomplete correlation recovery, and diagonal Born-Oppenheimer corrections reproduce the experimental results to within 0.0 - 0.2 k cal/mol. The new values of the two successive bond dissociation energies of water supersede the previously accepted values,Error! Bookmark not defined.,Error! Bookmark not defined. which were based on spectroscopic determinationsError! Bookmark not defined.,Error! Bookmark not defined. of D0(OH) using a very short Birge-Sponer extrapolation on OH/OD A1S+. An exhaustive analysis of the latter approach, combined with the application of the same procedure on a calculated potential energy curve for the state in question, demonstrates that the Birge-Sponer extrapolation underestimates the bond dissociation energy, in spite of the fact that only the last vibrational level was not observed experimentally. The new values affect a large number of other thermochemical quantities which directly or indirectly rely on or refer to D0(H-OH), D0(OH), or DHf?(OH).

  20. Bond dissociation energies in alcohols: kinetics and photochemical evidence regarding ion thermochemistry

    SciTech Connect

    Moylan, C.R.; Brauman, J.I.

    1984-07-19

    Gas-phase proton transfer from benzyl alcohol to fluoride ion is encounter controlled, whereas transfer from neopentyl alcohol to fluoride ion is slow. These observations suggest that the equilibrium gas-phase acidity of HF lies between those of the two alcohols, in contrast to the tabulated order. A small adjustment in the gas-phase acidities of alcohols not only makes the kinetics consistent but also resolves a long-standing discrepancy between RO-H bond energies measured by kinetic techniques and those determined by acidity/electron affinity data. It also accounts for the observed branching ratio in the IR laser photolysis of the neopentyl alcohol-fluoride ion complex. 21 references, 1 table.

  1. Size-extensivity-corrected multireference configuration interaction schemes to accurately predict bond dissociation energies of oxygenated hydrocarbons

    SciTech Connect

    Oyeyemi, Victor B.; Krisiloff, David B.; Keith, John A.; Libisch, Florian; Pavone, Michele; Carter, Emily A.

    2014-01-28

    Oxygenated hydrocarbons play important roles in combustion science as renewable fuels and additives, but many details about their combustion chemistry remain poorly understood. Although many methods exist for computing accurate electronic energies of molecules at equilibrium geometries, a consistent description of entire combustion reaction potential energy surfaces (PESs) requires multireference correlated wavefunction theories. Here we use bond dissociation energies (BDEs) as a foundational metric to benchmark methods based on multireference configuration interaction (MRCI) for several classes of oxygenated compounds (alcohols, aldehydes, carboxylic acids, and methyl esters). We compare results from multireference singles and doubles configuration interaction to those utilizing a posteriori and a priori size-extensivity corrections, benchmarked against experiment and coupled cluster theory. We demonstrate that size-extensivity corrections are necessary for chemically accurate BDE predictions even in relatively small molecules and furnish examples of unphysical BDE predictions resulting from using too-small orbital active spaces. We also outline the specific challenges in using MRCI methods for carbonyl-containing compounds. The resulting complete basis set extrapolated, size-extensivity-corrected MRCI scheme produces BDEs generally accurate to within 1 kcal/mol, laying the foundation for this scheme's use on larger molecules and for more complex regions of combustion PESs.

  2. Size-extensivity-corrected multireference configuration interaction schemes to accurately predict bond dissociation energies of oxygenated hydrocarbons.

    PubMed

    Oyeyemi, Victor B; Krisiloff, David B; Keith, John A; Libisch, Florian; Pavone, Michele; Carter, Emily A

    2014-01-28

    Oxygenated hydrocarbons play important roles in combustion science as renewable fuels and additives, but many details about their combustion chemistry remain poorly understood. Although many methods exist for computing accurate electronic energies of molecules at equilibrium geometries, a consistent description of entire combustion reaction potential energy surfaces (PESs) requires multireference correlated wavefunction theories. Here we use bond dissociation energies (BDEs) as a foundational metric to benchmark methods based on multireference configuration interaction (MRCI) for several classes of oxygenated compounds (alcohols, aldehydes, carboxylic acids, and methyl esters). We compare results from multireference singles and doubles configuration interaction to those utilizing a posteriori and a priori size-extensivity corrections, benchmarked against experiment and coupled cluster theory. We demonstrate that size-extensivity corrections are necessary for chemically accurate BDE predictions even in relatively small molecules and furnish examples of unphysical BDE predictions resulting from using too-small orbital active spaces. We also outline the specific challenges in using MRCI methods for carbonyl-containing compounds. The resulting complete basis set extrapolated, size-extensivity-corrected MRCI scheme produces BDEs generally accurate to within 1 kcal/mol, laying the foundation for this scheme's use on larger molecules and for more complex regions of combustion PESs. PMID:25669533

  3. Size-extensivity-corrected multireference configuration interaction schemes to accurately predict bond dissociation energies of oxygenated hydrocarbons

    NASA Astrophysics Data System (ADS)

    Oyeyemi, Victor B.; Krisiloff, David B.; Keith, John A.; Libisch, Florian; Pavone, Michele; Carter, Emily A.

    2014-01-01

    Oxygenated hydrocarbons play important roles in combustion science as renewable fuels and additives, but many details about their combustion chemistry remain poorly understood. Although many methods exist for computing accurate electronic energies of molecules at equilibrium geometries, a consistent description of entire combustion reaction potential energy surfaces (PESs) requires multireference correlated wavefunction theories. Here we use bond dissociation energies (BDEs) as a foundational metric to benchmark methods based on multireference configuration interaction (MRCI) for several classes of oxygenated compounds (alcohols, aldehydes, carboxylic acids, and methyl esters). We compare results from multireference singles and doubles configuration interaction to those utilizing a posteriori and a priori size-extensivity corrections, benchmarked against experiment and coupled cluster theory. We demonstrate that size-extensivity corrections are necessary for chemically accurate BDE predictions even in relatively small molecules and furnish examples of unphysical BDE predictions resulting from using too-small orbital active spaces. We also outline the specific challenges in using MRCI methods for carbonyl-containing compounds. The resulting complete basis set extrapolated, size-extensivity-corrected MRCI scheme produces BDEs generally accurate to within 1 kcal/mol, laying the foundation for this scheme's use on larger molecules and for more complex regions of combustion PESs.

  4. A promising tool to achieve chemical accuracy for density functional theory calculations on Y-NO homolysis bond dissociation energies.

    PubMed

    Li, Hong Zhi; Hu, Li Hong; Tao, Wei; Gao, Ting; Li, Hui; Lu, Ying Hua; Su, Zhong Min

    2012-01-01

    A DFT-SOFM-RBFNN method is proposed to improve the accuracy of DFT calculations on Y-NO (Y = C, N, O, S) homolysis bond dissociation energies (BDE) by combining density functional theory (DFT) and artificial intelligence/machine learning methods, which consist of self-organizing feature mapping neural networks (SOFMNN) and radial basis function neural networks (RBFNN). A descriptor refinement step including SOFMNN clustering analysis and correlation analysis is implemented. The SOFMNN clustering analysis is applied to classify descriptors, and the representative descriptors in the groups are selected as neural network inputs according to their closeness to the experimental values through correlation analysis. Redundant descriptors and intuitively biased choices of descriptors can be avoided by this newly introduced step. Using RBFNN calculation with the selected descriptors, chemical accuracy (?1 kcal·mol(-1)) is achieved for all 92 calculated organic Y-NO homolysis BDE calculated by DFT-B3LYP, and the mean absolute deviations (MADs) of the B3LYP/6-31G(d) and B3LYP/STO-3G methods are reduced from 4.45 and 10.53 kcal·mol(-1) to 0.15 and 0.18 kcal·mol(-1), respectively. The improved results for the minimal basis set STO-3G reach the same accuracy as those of 6-31G(d), and thus B3LYP calculation with the minimal basis set is recommended to be used for minimizing the computational cost and to expand the applications to large molecular systems. Further extrapolation tests are performed with six molecules (two containing Si-NO bonds and two containing fluorine), and the accuracy of the tests was within 1 kcal·mol(-1). This study shows that DFT-SOFM-RBFNN is an efficient and highly accurate method for Y-NO homolysis BDE. The method may be used as a tool to design new NO carrier molecules. PMID:22942689

  5. The Dissociation Energies of He2, HeH, and ArH; A Bond Function Study

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Partridge, Harry; Arnold, James (Technical Monitor)

    1998-01-01

    The bond energies and bond lengths are determined for He2, HeH, and ArH at the CCSD(T) level using both atom-centered basis sets and those that include bond functions. The addition of bond functions dramatically improves the rate of convergence of the results with respect to the size of the atom-centered basis set; with bond functions, triple zeta atom-centered basis set, outperform quintuple zeta basis sets without bond functions. The addition of bond functions also reduces the number of diffuse functions that must be added to the atom-centered sets. Employing bond functions appear to offer a very cost effective method of computing the interaction between weakly bound systems, especially for He.

  6. Diffusion Monte Carlo Study of Bond Dissociation Energies for BH2, B(OH)2, BCl2, and BCl

    NASA Astrophysics Data System (ADS)

    Li, Hui-ran; Cheng, Xin-lu; Zhang, Hong

    2012-02-01

    On basis of bond dissociation energies (BDEs) for BH2, B(OH)2, BCl2, and BCl, the diffusion Monte Carlo (DMC) method is applied to explore the BDEs of HB-H, HOB-OH, ClB-Cl, and B-Cl. The effect of the choice of orbitals, as well as the backflow transformation, is studied. The Slater-Jastrow DMC algorithm gives BDEs of 359.1±0.12 kJ/mol for HB-H, 410.5±0.50 kJ/mol for HOB-OH, 357.8±1.46 kJ/mol for ClB-Cl, and 504.5±0.96 kJ/mol for B-Cl using B3PW91 orbitals and similar BDEs when B3LYP orbitals are used. DMC with backflow corrections (BF-DMC) gives a HB-H BDE of 369.9±0.12 kJ/mol which is close to one of the available experimental value (375.8 kJ/mol). In the case of HOB-OH BDE, the BF-DMC calculation is 446.0±1.84 kJ/mol that is closer to the experimental BDE. The BF-DMC BDE for ClB-Cl is 343.2±2.34 kJ/mol and the BF-DMC B-Cl BDE is 523.3±0.33 kJ/mol, which are close to the experimental BDEs, 341.9 and 530.0 kJ/mol, respectively.

  7. The antimony-group 11 chemical bond: Dissociation energies of the diatomic molecules CuSb, AgSb, and AuSb

    SciTech Connect

    Carta, V.; Ciccioli, A. E-mail: andrea.ciccioli@uniroma1.it; Gigli, G. E-mail: andrea.ciccioli@uniroma1.it

    2014-02-14

    The intermetallic molecules CuSb, AgSb, and AuSb were identified in the effusive molecular beam produced at high temperature under equilibrium conditions in a double-cell-like Knudsen source. Several gaseous equilibria involving these species were studied by mass spectrometry as a function of temperature in the overall range 1349–1822 K, and the strength of the chemical bond formed between antimony and the group 11 metals was for the first time measured deriving the following thermochemical dissociation energies (D{sub 0}{sup ?}, kJ/mol): 186.7 ± 5.1 (CuSb), 156.3 ± 4.9 (AgSb), 241.3 ± 5.8 (AuSb). The three species were also investigated computationally at the coupled cluster level with single, double, and noniterative quasiperturbative triple excitations (CCSD(T)). The spectroscopic parameters were calculated from the potential energy curves and the dissociation energies were evaluated at the Complete Basis Set limit, resulting in an overall good agreement with experimental values. An approximate evaluation of the spin-orbit effect was also performed. CCSD(T) calculations were further extended to the corresponding group 11 arsenide species which are here studied for the first time and the following dissociation energies (D{sub 0}{sup ?}, kJ/mol): 190 ± 10 (CuAs), 151 ± 10 (AgAs), 240 ± 15 (AuAs) are proposed. Taking advantage of the new experimental and computational information here presented, the bond energy trends along group 11 and 4th and 5th periods of the periodic table were analyzed and the bond energies of the diatomic species CuBi and AuBi, yet experimentally unobserved, were predicted on an empirical basis.

  8. Dispersion-correcting potentials can significantly improve the bond dissociation enthalpies and noncovalent binding energies predicted by density-functional theory

    SciTech Connect

    DiLabio, Gino A.; Koleini, Mohammad; Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4

    2014-05-14

    Dispersion-correcting potentials (DCPs) are atom-centered Gaussian functions that are applied in a manner that is similar to effective core potentials. Previous work on DCPs has focussed on their use as a simple means of improving the ability of conventional density-functional theory methods to predict the binding energies of noncovalently bonded molecular dimers. We show in this work that DCPs developed for use with the LC-?PBE functional along with 6-31+G(2d,2p) basis sets are capable of simultaneously improving predicted noncovalent binding energies of van der Waals dimer complexes and covalent bond dissociation enthalpies in molecules. Specifically, the DCPs developed herein for the C, H, N, and O atoms provide binding energies for a set of 66 noncovalently bonded molecular dimers (the “S66” set) with a mean absolute error (MAE) of 0.21 kcal/mol, which represents an improvement of more than a factor of 10 over unadorned LC-?PBE/6-31+G(2d,2p) and almost a factor of two improvement over LC-?PBE/6-31+G(2d,2p) used in conjunction with the “D3” pairwise dispersion energy corrections. In addition, the DCPs reduce the MAE of calculated X-H and X-Y (X,Y = C, H, N, O) bond dissociation enthalpies for a set of 40 species from 3.2 kcal/mol obtained with unadorned LC-?PBE/6-31+G(2d,2p) to 1.6 kcal/mol. Our findings demonstrate that broad improvements to the performance of DFT methods may be achievable through the use of DCPs.

  9. Dispersion-correcting potentials can significantly improve the bond dissociation enthalpies and noncovalent binding energies predicted by density-functional theory

    NASA Astrophysics Data System (ADS)

    DiLabio, Gino A.; Koleini, Mohammad

    2014-05-01

    Dispersion-correcting potentials (DCPs) are atom-centered Gaussian functions that are applied in a manner that is similar to effective core potentials. Previous work on DCPs has focussed on their use as a simple means of improving the ability of conventional density-functional theory methods to predict the binding energies of noncovalently bonded molecular dimers. We show in this work that DCPs developed for use with the LC-?PBE functional along with 6-31+G(2d,2p) basis sets are capable of simultaneously improving predicted noncovalent binding energies of van der Waals dimer complexes and covalent bond dissociation enthalpies in molecules. Specifically, the DCPs developed herein for the C, H, N, and O atoms provide binding energies for a set of 66 noncovalently bonded molecular dimers (the "S66" set) with a mean absolute error (MAE) of 0.21 kcal/mol, which represents an improvement of more than a factor of 10 over unadorned LC-?PBE/6-31+G(2d,2p) and almost a factor of two improvement over LC-?PBE/6-31+G(2d,2p) used in conjunction with the "D3" pairwise dispersion energy corrections. In addition, the DCPs reduce the MAE of calculated X-H and X-Y (X,Y = C, H, N, O) bond dissociation enthalpies for a set of 40 species from 3.2 kcal/mol obtained with unadorned LC-?PBE/6-31+G(2d,2p) to 1.6 kcal/mol. Our findings demonstrate that broad improvements to the performance of DFT methods may be achievable through the use of DCPs.

  10. Dissociation energy of molecules in dense gases

    NASA Technical Reports Server (NTRS)

    Kunc, J. A.

    1992-01-01

    A general approach is presented for calculating the reduction of the dissociation energy of diatomic molecules immersed in a dense (n = less than 10 exp 22/cu cm) gas of molecules and atoms. The dissociation energy of a molecule in a dense gas differs from that of the molecule in vacuum because the intermolecular forces change the intramolecular dynamics of the molecule, and, consequently, the energy of the molecular bond.

  11. S-OO bond dissociation energies and enthalpies of formation of the thiomethyl peroxyl radicals CH{sub 3}S(O){sub n}OO (n=0,1,2)

    SciTech Connect

    Salta, Zoi; Kosmas, Agnie Mylona; Lesar, Antonija

    2014-10-06

    Optimized geometries, S-OO bond dissociation energies and enthalpies of formation for a series of thiomethyl peroxyl radicals are investigated using high level ab initio and density functional theory methods. The results show that the S-OO bond dissociation energy is largest in the methylsulfonyl peroxyl radical, CH{sub 3}S(O){sub 2}OO, which contains two sulfonic type oxygen atoms followed by the methylthiyl peroxyl radical, CH{sub 3}SOO. The methylsulfinyl peroxyl radical, CH{sub 3}S(O)OO, which contains only one sulfonic type oxygen shows the least stability with regard to dissociation to CH{sub 3}S(O)+O{sub 2}. This stabilization trend is nicely reflected in the variations of the S-OO bond distance which is found to be shortest in CH{sub 3}S(O){sub 2}OO and longest in CH{sub 3}S(O)OO.

  12. Excitation energies with linear response density matrix functional theory along the dissociation coordinate of an electron-pair bond in N-electron systems.

    PubMed

    van Meer, R; Gritsenko, O V; Baerends, E J

    2014-01-14

    Time dependent density matrix functional theory in its adiabatic linear response formulation delivers exact excitation energies ?? and oscillator strengths f? for two-electron systems if extended to the so-called phase including natural orbital (PINO) theory. The Lo?wdin-Shull expression for the energy of two-electron systems in terms of the natural orbitals and their phases affords in this case an exact phase-including natural orbital functional (PILS), which is non-primitive (contains other than just J and K integrals). In this paper, the extension of the PILS functional to N-electron systems is investigated. With the example of an elementary primitive NO functional (BBC1) it is shown that current density matrix functional theory ground state functionals, which were designed to produce decent approximations to the total energy, fail to deliver a qualitatively correct structure of the (inverse) response function, due to essential deficiencies in the reconstruction of the two-body reduced density matrix (2RDM). We now deduce essential features of an N-electron functional from a wavefunction Ansatz: The extension of the two-electron Lo?wdin-Shull wavefunction to the N-electron case informs about the phase information. In this paper, applications of this extended Lo?wdin-Shull (ELS) functional are considered for the simplest case, ELS(1): one (dissociating) two-electron bond in the field of occupied (including core) orbitals. ELS(1) produces high quality ??(R) curves along the bond dissociation coordinate R for the molecules LiH, Li2, and BH with the two outer valence electrons correlated. All of these results indicate that response properties are much more sensitive to deficiencies in the reconstruction of the 2RDM than the ground state energy, since derivatives of the functional with respect to both the NOs and the occupation numbers need to be accurate. PMID:24437859

  13. Excitation energies with linear response density matrix functional theory along the dissociation coordinate of an electron-pair bond in N-electron systems

    NASA Astrophysics Data System (ADS)

    van Meer, R.; Gritsenko, O. V.; Baerends, E. J.

    2014-01-01

    Time dependent density matrix functional theory in its adiabatic linear response formulation delivers exact excitation energies ?? and oscillator strengths f? for two-electron systems if extended to the so-called phase including natural orbital (PINO) theory. The Löwdin-Shull expression for the energy of two-electron systems in terms of the natural orbitals and their phases affords in this case an exact phase-including natural orbital functional (PILS), which is non-primitive (contains other than just J and K integrals). In this paper, the extension of the PILS functional to N-electron systems is investigated. With the example of an elementary primitive NO functional (BBC1) it is shown that current density matrix functional theory ground state functionals, which were designed to produce decent approximations to the total energy, fail to deliver a qualitatively correct structure of the (inverse) response function, due to essential deficiencies in the reconstruction of the two-body reduced density matrix (2RDM). We now deduce essential features of an N-electron functional from a wavefunction Ansatz: The extension of the two-electron Löwdin-Shull wavefunction to the N-electron case informs about the phase information. In this paper, applications of this extended Löwdin-Shull (ELS) functional are considered for the simplest case, ELS(1): one (dissociating) two-electron bond in the field of occupied (including core) orbitals. ELS(1) produces high quality ??(R) curves along the bond dissociation coordinate R for the molecules LiH, Li2, and BH with the two outer valence electrons correlated. All of these results indicate that response properties are much more sensitive to deficiencies in the reconstruction of the 2RDM than the ground state energy, since derivatives of the functional with respect to both the NOs and the occupation numbers need to be accurate.

  14. Short H-bonds and spontaneous self-dissociation in ,,H2O...20 : Effects of H-bond topology

    E-print Network

    Ciobanu, Cristian

    Short H-bonds and spontaneous self-dissociation in ,,H2O...20 : Effects of H-bond topology Jer bond isomers in (H2O)20 , assumed to be similar in the past, differs by up to 70 kcal/mol. The isomers energy. This belief implicitly lies behind several calculations performed to date2­6 for the (H2O)20

  15. Metal cation dependence of interactions with amino acids: bond dissociation energies of Rb(+) and Cs(+) to the acidic amino acids and their amide derivatives.

    PubMed

    Armentrout, P B; Yang, Bo; Rodgers, M T

    2014-04-24

    Metal cation-amino acid interactions are key components controlling the secondary structure and biological function of proteins, enzymes, and macromolecular complexes comprising these species. Determination of pairwise interactions of alkali metal cations with amino acids provides a thermodynamic vocabulary that begins to quantify these fundamental processes. In the present work, we expand a systematic study of such interactions by examining rubidium and cesium cations binding with the acidic amino acids (AA), aspartic acid (Asp) and glutamic acid (Glu), and their amide derivatives, asparagine (Asn) and glutamine (Gln). These eight complexes are formed using electrospray ionization and their bond dissociation energies (BDEs) are determined experimentally using threshold collision-induced dissociation with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy-dependent cross sections include consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. Quantum chemical calculations are conducted at the B3LYP, MP2(full), and M06 levels of theory using def2-TZVPPD basis sets, with results showing reasonable agreement with experiment. At 0 and 298 K, most levels of theory predict that the ground-state conformers for M(+)(Asp) and M(+)(Asn) involve tridentate binding of the metal cation to the backbone carbonyl, amino, and side-chain carbonyl groups, although tridentate binding to the carboxylic acid group and side-chain carbonyl is competitive for M(+)(Asn). For the two longer side-chain amino acids, Glu and Gln, multiple structures are competitive. A comparison of these results to those for the smaller alkali cations, Na(+) and K(+), provides insight into the trends in binding energies associated with the molecular polarizability and dipole moment of the side chain. For all four metal cations, the BDEs are inversely correlated with the size of the metal cation and follow the order Asp < Glu < Asn < Gln. PMID:24528155

  16. Thermochemistry of C7H16 to C10H22 alkane isomers: primary, secondary, and tertiary C-H bond dissociation energies and effects of branching.

    PubMed

    Hudzik, Jason M; Bozzelli, Joseph W; Simmie, John M

    2014-10-01

    Standard enthalpies of formation (?H°f 298) of methyl, ethyl, primary and secondary propyl, and n-butyl radicals are evaluated and used in work reactions to determine internal consistency. They are then used to calculate the enthalpy of formation for the tert-butyl radical. Other thermochemical properties including standard entropies (S°(T)), heat capacities (Cp(T)), and carbon-hydrogen bond dissociation energies (C-H BDEs) are reported for n-pentane, n-heptane, 2-methylhexane, 2,3-dimethylpentane, and several branched higher carbon number alkanes and their radicals. ?H°f 298 and C-H BDEs are calculated using isodesmic work reactions at the B3LYP (6-31G(d,p) and 6-311G(2d,2p) basis sets), CBS-QB3, CBS-APNO, and G3MP2B3 levels of theory. Structures, moments of inertia, vibrational frequencies, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) level for contributions to entropy and heat capacities. Enthalpy calculations for these hydrocarbon radical species are shown to have consistency with the CBS-QB3 and CBS-APNO methods using all work reactions. Our recommended ideal gas phase ?H°f 298 values are from the average of all CBS-QB3, CBS-APNO, and for G3MP2B3, only where the reference and target radical are identical types, and are compared with literature values. Calculated values show agreement between the composite calculation methods and the different work reactions. Secondary and tertiary C-H bonds in the more highly branched alkanes are shown to have bond energies that are several kcal mol(-1) lower than the BDEs in corresponding smaller molecules often used as reference species. Entropies and heat capacities are calculated and compared to literature values (when available) when all internal rotors are considered. PMID:25180943

  17. C-C and C-Heteroatom Bond Dissociation Energies in CH3R?C(OH)2: Energetics for Photocatalytic Processes of Organic Diolates on TiO2 Surfaces

    SciTech Connect

    Wang, Tsang-Hsiu; Dixon, David A.; Henderson, Michael A.

    2010-08-26

    The bond energies of a range of gem-diols, CH3R?C(OH)2 (R? = H, F, Cl, Br, CN, NO2, CF3, CH3CH2, CH3CH2CH2, CH3CH2CH2CH2, ((CH3)2)CH, (CH3)3C, ((CH3)2CH)CH2, (CH3CH2)(CH3)CH, C6H5 (CH3CH2)(CH3)CH) which serve as models for binding to a surface have been studied with density functional theory (DFT) and the molecular orbital G3(MP2) methods to provide thermodynamic data for the analysis of the photochemistry of ketones on TiO2. The ultraviolet (UV) photon-induced photodecomposition of adsorbed acetone and 3,3-dimethylbutanone on the rutile TiO2 (110) surface have been investigated with photon stimulated desorption (PSD) and temperature programmed desorption (TPD). The C-CH3 and C-C(R?) bond dissociation energies in CH3R?C(OH)2 were predicted, and our calculated bond dissociation energies are in excellent agreement with the available experimental values. We used a series of isodemic reactions to provide small corrections to the various bond dissociation energies. The calculated bond dissociation energies are in agreement with the observed photodissociation processes except for R? = CF3, suggesting that these processes are under thermodynamic control. For R? = CF3, reaction dynamics also play a role in determining the photodissociation mechanism. The gas phase Brönsted acidities of the gem-diols were calculated. For three molecules, R? = Cl, Br, and NO2, loss of a proton leads to the formation of a complex of acetic acid with the anion Cl-, Br-, and NO2-. The acidities of these three species are very high with the former two having acidities comparable to CF3SO3H. The ketones (R?RC(=O)) are weak Lewis acids except where addition of OH- leads to the dissociation of the complex to form an anion bonded to acetic acid, R' = NO2, Cl, and Br. The X-C bond dissociation energies for a number of X-CO2- species were calculated and these should be useful in correlating with photochemical reactivity studies.

  18. (*/*) Conical Intersection Seam Experimentally Observed in the S-D Bond Dissociation Reaction of Thiophenold1

    E-print Network

    Kim, Sang Kyu

    , *) and continuum (S2, *) states has been observed in the ultrafast S-D bond dissociation reaction of thiophenol-d1(*/*) Conical Intersection Seam Experimentally Observed in the S-D Bond Dissociation Reaction

  19. Structure, energetics, and vibrational properties of Si-H bond dissociation in silicon

    SciTech Connect

    Tuttle, B.; Van de Walle, C.G.

    1999-05-01

    We investigate hydrogen dissociation from an isolated Si-H bond in bulk silicon, using {ital ab initio} density-functional total-energy calculations. From the bonding site, we find that hydrogen needs to overcome a barrier of less than 2.0 eV in order to reach the next lowest local minimum in the energy surface. This minimum occurs at the antibonding site and is 1.2 eV higher in energy than the ground state. In addition, we consider the role of lattice relaxations and free carriers during the dissociation process. We discuss the relevance of our results for Si-H dissociation in several systems, including the Si-SiO{sub 2} interface. {copyright} {ital 1999} {ital The American Physical Society}

  20. Electron Transfer Dissociation (ETD) of Peptides Containing Intrachain Disulfide Bonds

    NASA Astrophysics Data System (ADS)

    Cole, Scott R.; Ma, Xiaoxiao; Zhang, Xinrong; Xia, Yu

    2012-02-01

    The fragmentation chemistry of peptides containing intrachain disulfide bonds was investigated under electron transfer dissociation (ETD) conditions. Fragments within the cyclic region of the peptide backbone due to intrachain disulfide bond formation were observed, including: c (odd electron), z (even electron), c-33 Da, z + 33 Da, c + 32 Da, and z-32 Da types of ions. The presence of these ions indicated cleavages both at the disulfide bond and the N-C? backbone from a single electron transfer event. Mechanistic studies supported a mechanism whereby the N-C? bond was cleaved first, and radical-driven reactions caused cleavage at either an S-S bond or an S-C bond within cysteinyl residues. Direct ETD at the disulfide linkage was also observed, correlating with signature loss of 33 Da (SH) from the charge-reduced peptide ions. Initial ETD cleavage at the disulfide bond was found to be promoted amongst peptides ions of lower charge states, while backbone fragmentation was more abundant for higher charge states. The capability of inducing both backbone and disulfide bond cleavages from ETD could be particularly useful for sequencing peptides containing intact intrachain disulfide bonds. ETD of the 13 peptides studied herein all showed substantial sequence coverage, accounting for 75%-100% of possible backbone fragmentation.

  1. Three methods to measure RH bond energies

    SciTech Connect

    Berkowitz, J.; Ellison, G.B.; Gutman, D.

    1993-03-21

    In this paper the authors compare and contrast three powerful methods for experimentally measuring bond energies in polyatomic molecules. The methods are: radical kinetics; gas phase acidity cycles; and photoionization mass spectroscopy. The knowledge of the values of bond energies are a basic piece of information to a chemist. Chemical reactions involve the making and breaking of chemical bonds. It has been shown that comparable bonds in polyatomic molecules, compared to the same bonds in radicals, can be significantly different. These bond energies can be measured in terms of bond dissociation energies.

  2. Ferric-Thiolate Bond Dissociation Studied with Electronic Structure Calculations.

    PubMed

    Arantes, Guilherme Menegon; Field, Martin J

    2015-10-01

    The stability and reactivity of iron-sulfur clusters are fundamental properties for the biological function of these prosthetic groups. Here, we investigate the ferric-thiolate bond dissociation of model iron-sulfur tetrahedral complexes with high-level ab initio multiconfigurational electronic structure calculations. We find that the reaction mechanism is homolytic with a spin-crossing from the sextet state in the reactant to quartet state in the product. We also compare several density functionals and semiempirical configuration interaction with the high-level ab initio results to find an accurate but computationally more efficient method to describe the reaction. The functionals M06 and those based on the OPTX exchange functional show the best performance and may reasonably describe the various electron correlation effects involved in ferric-thiolate bond dissociation. PMID:26351881

  3. Competition between Covalent and Noncovalent Bond Cleavages in Dissociation of Phosphopeptide-Amine Complexes

    SciTech Connect

    Laskin, Julia; Yang, Zhibo; Woods, Amina S.

    2011-04-21

    Interactions between quaternary amino or guanidino groups with anions are ubiquitous in nature. Here, we present a first study focused on quantifying such interactions using complexes of phosphorylated A3pXA3-NH2 (X=S, T, Y) peptides with decamethonium (DCM) or diaguanidinodecane (DGD) ligands as model systems. Time- and collision energy-resolved surface-induced dissociation (SID) of the singly charged complexes was examined using a specially configured Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS). Dissociation thresholds and activation energies were obtained from RRKM modeling of the experimental data that has been described and carefully characterized in our previous studies. We demonstrate that covalent bond cleavages resulting in phosphate abstraction by the cationic ligand are characterized by low dissociation thresholds and relatively tight transition states. In contrast, high dissociation barriers and large positive activation entropies were obtained for cleavages of non-covalent bonds. Dissociation parameters obtained from the modeling of the experimental data are in excellent agreement with the results of density functional theory (DFT) calculations. Comparison between the experimental data and theoretical calculations indicate that phosphate abstraction by the ligand is rather localized and mainly affected by the identity of the phosphorylated side chain. The hydrogen bonding in the peptide and ligand properties play a minor role in determining the energetics and dynamics of the phosphate abstraction channel

  4. Characterization and Modeling of the Collision Induced Dissociation Patterns of Deprotonated Glycosphingolipids: Cleavage of the Glycosidic Bond

    NASA Astrophysics Data System (ADS)

    Rožman, Marko

    2015-08-01

    Glycosphingolipid fragmentation behavior was investigated by combining results from analysis of a series of negative ion tandem mass spectra and molecular modeling. Fragmentation patterns extracted from 75 tandem mass spectra of mainly acidic glycosphingolipid species (gangliosides) suggest prominent cleavage of the glycosidic bonds with retention of the glycosidic oxygen atom by the species formed from the reducing end (B and Y ion formation). Dominant product ions arise from dissociation of sialic acids glycosidic bonds whereas product ions resulting from cleavage of other glycosidic bonds are less abundant. Potential energy surfaces and unimolecular reaction rates of several low-energy fragmentation pathways leading to cleavage of glycosidic bonds were estimated in order to explain observed dissociation patterns. Glycosidic bond cleavage in both neutral (unsubstituted glycosyl group) and acidic glycosphingolipids was the outcome of the charge-directed intramolecular nucleophilic substitution (SN2) mechanism. According to the suggested mechanism, the nucleophile in a form of carboxylate or oxyanion attacks the carbon at position one of the sugar ring, simultaneously breaking the glycosidic bond and yielding an epoxide. For gangliosides, unimolecular reaction rates suggest that dominant product ions related to the cleavage of sialic acid glycosidic bonds are formed via direct dissociation channels. On the other hand, low abundant product ions related to the dissociation of other glycosidic bonds are more likely to be the result of sequential dissociation. Although results from this study mainly contribute to the understanding of glycosphingolipid fragmentation chemistry, some mechanistic findings regarding cleavage of the glycosidic bond may be applicable to other glycoconjugates.

  5. Formation and Dissociation of Intra-Intermolecular Hydrogen-Bonded Solute-Solvent Complexes: Chemical

    E-print Network

    Fayer, Michael D.

    and dissociation (chemical exchange) of this type of three-centered hydrogen bond complex were observed in real in the most basic and important chemical and biological phenomena.1-3 The strength of hydrogen bonds lies between van der Waals forces and covalent bonds. Although not a true chemical bond, a hydrogen bond

  6. On the dissociation energy of Mg2

    NASA Technical Reports Server (NTRS)

    Partridge, Harry; Bauschlicher, Charles W., Jr.; Pettersson, Lars G. M.; Mclean, A. D.; Liu, Bowen

    1990-01-01

    The bonding in the X 1Sigma(+)g state of Mg2 is investigated using near-complete valence one-particle Slater and Gaussian basis sets containing up to h functions. It is shown that the four-electron complete CI limit can be approached using a sequence of either second-order CI (SOCI) or interacting correlated fragment (ICF) calculations. At the valence level, the best estimate of the dissociation energy D(e) was 464/cm. This is a lower limit and is probably within 5/cm of the complete basis value.

  7. Peroxide Bond Driven Dissociation of Hydroperoxy-Cholesterol Esters Following Collision Induced Dissociation

    NASA Astrophysics Data System (ADS)

    Hutchins, Patrick M.; Murphy, Robert C.

    2011-05-01

    Oxidative modification of polyunsaturated fatty acids, which occurs through enzymatic and nonenzymatic processes, is typically initiated by the attachment of molecular oxygen to an unsaturated fatty acyl chain forming a lipid hydroperoxide (LOOH). Enzymatic pathways are critical for cellular homeostasis but aberrant lipid peroxidation has been implicated in important pathologies. Analysis of primary oxidation products such as hydroperoxides has proven to be challenging for a variety of reasons. While negative ion electrospray ionization has been used for the specific detection of some LOOH species, hydroperoxide dehydration in the ion source has been a significant drawback. Here we describe positive ion electrospray ionization of ammoniated 13-hydroperoxy-9Z, 11E-octadecadienoyl cholesterol and 9-hydroperoxy-10E, 12Z-octadecadienoyl cholesterol, [M + NH4]+, following normal phase high-pressure liquid-chromatography. Dehydration in the ion source was not prevalent and the ammoniated molecular ion was the major species observed. Collisionally induced dissociation of the two positional isomers yielded unique product ion spectra resulting from carbon-carbon cleavages along their acyl chains. Further investigation of this behavior revealed that complex collision induced dissociations were initiated by scission of the hydroperoxide bond that drove subsequent acyl chain cleavages. Interestingly, some of the product ions retained the ammonium nitrogen through the formation of covalent carbon-nitrogen or oxygen-nitrogen bonds. These studies were carried out using hydroperoxy-octadecadienoate cholesteryl esters as model compounds, however the observed mechanisms of [LOOH + NH4]+ ionization and dissociation are likely applicable to the analysis of other lipid hydroperoxides and may serve as the basis for selective LOOH detection as well as aid in the identification of unknown lipid hydroperoxides.

  8. Which Ab Initio Wave Function Methods Are Adequate for Quantitative Calculations of the Energies of Biradicals? The Performance of Coupled-Cluster and Multi-Reference Methods Along a Single-Bond Dissociation Coordinate

    SciTech Connect

    Yang, Ke; Jalan, Amrit; Green, William H.; Truhlar, Donald G.

    2013-01-08

    We examine the accuracy of single-reference and multireference correlated wave function methods for predicting accurate energies and potential energy curves of biradicals. The biradicals considered are intermediate species along the bond dissociation coordinates for breaking the F?F bond in F2, the O?O bond in H2O2, and the C?C bond in CH3CH3. We apply a host of single-reference and multireference approximations in a consistent way to the same cases to provide a better assessment of their relative accuracies than was previously possible. The most accurate method studied is coupled cluster theory with all connected excitations through quadruples, CCSDTQ. Without explicit quadruple excitations, the most accurate potential energy curves are obtained by the single-reference RCCSDt method, followed, in order of decreasing accuracy, by UCCSDT, RCCSDT, UCCSDt, seven multireference methods, including perturbation theory, configuration interaction, and coupled-cluster methods (with MRCI+Q being the best and Mk-MR-CCSD the least accurate), four CCSD(T) methods, and then CCSD.

  9. Characterization and Modeling of the Collision Induced Dissociation Patterns of Deprotonated Glycosphingolipids: Cleavage of the Glycosidic Bond.

    PubMed

    Rožman, Marko

    2016-01-01

    Glycosphingolipid fragmentation behavior was investigated by combining results from analysis of a series of negative ion tandem mass spectra and molecular modeling. Fragmentation patterns extracted from 75 tandem mass spectra of mainly acidic glycosphingolipid species (gangliosides) suggest prominent cleavage of the glycosidic bonds with retention of the glycosidic oxygen atom by the species formed from the reducing end (B and Y ion formation). Dominant product ions arise from dissociation of sialic acids glycosidic bonds whereas product ions resulting from cleavage of other glycosidic bonds are less abundant. Potential energy surfaces and unimolecular reaction rates of several low-energy fragmentation pathways leading to cleavage of glycosidic bonds were estimated in order to explain observed dissociation patterns. Glycosidic bond cleavage in both neutral (unsubstituted glycosyl group) and acidic glycosphingolipids was the outcome of the charge-directed intramolecular nucleophilic substitution (SN2) mechanism. According to the suggested mechanism, the nucleophile in a form of carboxylate or oxyanion attacks the carbon at position one of the sugar ring, simultaneously breaking the glycosidic bond and yielding an epoxide. For gangliosides, unimolecular reaction rates suggest that dominant product ions related to the cleavage of sialic acid glycosidic bonds are formed via direct dissociation channels. On the other hand, low abundant product ions related to the dissociation of other glycosidic bonds are more likely to be the result of sequential dissociation. Although results from this study mainly contribute to the understanding of glycosphingolipid fragmentation chemistry, some mechanistic findings regarding cleavage of the glycosidic bond may be applicable to other glycoconjugates. Graphical Abstract ?. PMID:26297186

  10. The dissociative chemisorption of water on Ni(111): Mode- and bond-selective chemistry on metal surfaces

    NASA Astrophysics Data System (ADS)

    Farjamnia, Azar; Jackson, Bret

    2015-06-01

    A fully quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore the dissociative chemisorption of H2O, HOD, and D2O on Ni(111). For this late barrier system, excitation of both the bending and stretching modes significantly enhances dissociative sticking. The vibrational efficacies vary somewhat from mode-to-mode but are all relatively close to one, in contrast to methane dissociation, where the behavior is less statistical. Similar to methane dissociation, the motion of lattice atoms near the dissociating molecule can significantly modify the height of the barrier to dissociation, leading to a strong variation in dissociative sticking with substrate temperature. Given a rescaling of the barrier height, our results are in reasonable agreement with measurements of the dissociative sticking of D2O on Ni(111), for both laser-excited molecules with one or two quanta of excitation in the antisymmetric stretch and in the absence of laser excitation. Even without laser excitation, the beam contains vibrationally excited molecules populated at the experimental source temperature, and these make significant contributions to the sticking probability. At high collision energies, above the adiabatic barrier heights, our results correlate with these barrier heights and mode softening effects. At lower energies, dissociative sticking occurs primarily via vibrationally nonadiabatic pathways. We find a preference for O-H over O-D bond cleavage for ground state HOD molecules at all but the highest collision energies, and excitation of the O-H stretch gives close to 100% O-H selectivity at lower energies. Excitation of the O-D stretch gives a lower O-D cleavage selectivity, as the interaction with the surface leads to energy transfer from the O-D stretch into the O-H bond, when mode softening makes these vibrations nearly degenerate.

  11. The dissociative chemisorption of water on Ni(111): Mode- and bond-selective chemistry on metal surfaces.

    PubMed

    Farjamnia, Azar; Jackson, Bret

    2015-06-21

    A fully quantum approach based on an expansion in vibrationally adiabatic eigenstates is used to explore the dissociative chemisorption of H2O, HOD, and D2O on Ni(111). For this late barrier system, excitation of both the bending and stretching modes significantly enhances dissociative sticking. The vibrational efficacies vary somewhat from mode-to-mode but are all relatively close to one, in contrast to methane dissociation, where the behavior is less statistical. Similar to methane dissociation, the motion of lattice atoms near the dissociating molecule can significantly modify the height of the barrier to dissociation, leading to a strong variation in dissociative sticking with substrate temperature. Given a rescaling of the barrier height, our results are in reasonable agreement with measurements of the dissociative sticking of D2O on Ni(111), for both laser-excited molecules with one or two quanta of excitation in the antisymmetric stretch and in the absence of laser excitation. Even without laser excitation, the beam contains vibrationally excited molecules populated at the experimental source temperature, and these make significant contributions to the sticking probability. At high collision energies, above the adiabatic barrier heights, our results correlate with these barrier heights and mode softening effects. At lower energies, dissociative sticking occurs primarily via vibrationally nonadiabatic pathways. We find a preference for O-H over O-D bond cleavage for ground state HOD molecules at all but the highest collision energies, and excitation of the O-H stretch gives close to 100% O-H selectivity at lower energies. Excitation of the O-D stretch gives a lower O-D cleavage selectivity, as the interaction with the surface leads to energy transfer from the O-D stretch into the O-H bond, when mode softening makes these vibrations nearly degenerate. PMID:26093571

  12. The Breathing Orbital Valence Bond Method in Diffusion Monte Carlo: C-H Bond Dissociation ofAcetylene

    SciTech Connect

    Domin, D.; Braida, Benoit; Lester Jr., William A.

    2008-05-30

    This study explores the use of breathing orbital valence bond (BOVB) trial wave functions for diffusion Monte Carlo (DMC). The approach is applied to the computation of the carbon-hydrogen (C-H) bond dissociation energy (BDE) of acetylene. DMC with BOVB trial wave functions yields a C-H BDE of 132.4 {+-} 0.9 kcal/mol, which is in excellent accord with the recommended experimental value of 132.8 {+-} 0.7 kcal/mol. These values are to be compared with DMC results obtained with single determinant trial wave functions, using Hartree-Fock orbitals (137.5 {+-} 0.5 kcal/mol) and local spin density (LDA) Kohn-Sham orbitals (135.6 {+-} 0.5 kcal/mol).

  13. Hydrogen Bond Dissociation and Reformation in Methanol Oligomers Following Hydroxyl Stretch Relaxation

    E-print Network

    Fayer, Michael D.

    Hydrogen Bond Dissociation and Reformation in Methanol Oligomers Following Hydroxyl Stretch, 2002 Vibrational relaxation and hydrogen bond dynamics in methanol-d dissolved in CCl4 have been-d molecules both accepting and donating hydrogen bonds at 2500 cm-1 . Following vibrational relaxation

  14. Ground State D, Dissociation Energy from the Near-dissociation Behaviorof Rotational Level Spacings1

    E-print Network

    Le Roy, Robert J.

    Ground State D, Dissociation Energy from the Near-dissociation Behaviorof Rotational Level Spacings the dissociation energy of a diatomic molecule from the rotational term value(s) of a single vibrational level lying near dissociation is derived and tested. It is based on expressions relating the characteristic

  15. The Dissociation Energies of CH4 and C2H2 Revisited

    NASA Technical Reports Server (NTRS)

    Partridge, Harry; Bauschlicher, Charles W., Jr.; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    The bond dissociation energies of CH4 and C2H2 and their fragments are investigated using basis set extrapolations and high levels of correlation. The computed bond dissociation energies (D(sub e)) are accurate to within 0.2 kcal/mol. The agreement with the experimental (D(sub 0)) values is excellent if we assume that the zero-point energy of C2H is 9.18 kcal/mol. The effect of core (1s) correlation on the bond dissociation energies of C-H bonds is shown to vary from 0.2 to 0.7 kcal/mol and that for C-C bonds varies from 0.4 to 2.2 kcal/mol.

  16. The C-H Dissociation Energy of C2H6

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Partridge, Harry; Langhoff, Stephen R. (Technical Monitor)

    1994-01-01

    The C-H bond energy in C2H6 is computed to be 99.76 +/- 0.35 kcal/mol, which is in excellent agreement with the most recent experimental values. The calculation of the C-H bond energy by direct dissociation and by an isodesmic reaction is discussed.

  17. Bond dissociation mechanism of ethanol during carbon nanotube synthesis via alcohol catalytic CVD technique: Ab initio molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Oguri, Tomoya; Shimamura, Kohei; Shibuta, Yasushi; Shimojo, Fuyuki; Yamaguchi, Shu

    2014-03-01

    Dissociation of ethanol on a nickel cluster is investigated by ab initio molecular dynamics simulation to reveal the bond dissociation mechanism of carbon source molecules during carbon nanotube synthesis. C-C bonds in only CHxCO fragments are dissociated on the nickel cluster, whereas there is no preferential structure among the fragments for C-O bond dissociation. The dissociation preference is uncorrelated with the bond dissociation energy of corresponding bonds in freestanding molecules but is correlated with the energy difference between fragment molecules before and after dissociation on the nickel surface. Moreover, carbon-chain formation occurs after C-C bond dissociation in a continuous simulation. What determines the chirality of CNTs? What happens at the dissociation stage of carbon source molecules? Regarding the former question, many researchers have pointed out the good epitaxial relationship between a graphite network and a close-packed facet (i.e., fcc(1 1 1) or hcp(0 0 0 1)) of transition metals [17-19]. Therefore, the correlation between the chirality of CNTs and the angle of the step edge on metal (or metal carbide) surfaces has been closely investigated [20-22]. In association with this geometric matching, the epitaxial growth of graphene on Cu(1 1 1) and Ni(1 1 1) surfaces has recently been achieved via CCVD technique [23-25], which is a promising technique for the synthesis of large-area and monolayer graphene.Regarding the latter question, it is empirically known that the yield and quality of CNT products strongly depend on the choice of carbon source molecules and additives. For example, it is well known that the use of ethanol as carbon source molecules yields a large amount of SWNTs without amorphous carbons (called the alcohol CCVD (ACCVD) technique) compared with the CCVD process using hydrocarbons [4]. Moreover, the addition of a small amount of water dramatically enhances the activity and lifetime of the catalytic metal (called the supergrowth CVD technique) [26]. Recently, several experimental studies have been carried out in an attempt to understand these complicated dissociation processes. For example, Tomie et al. [27] performed in situ mass spectroscopic analysis during CNT synthesis by the ACCVD technique and revealed that ethylene molecules are formed by the dissociation of ethanol, which means that C-O bonds in the ethanol molecules are dissociated during CNT synthesis. Moreover, Xiang et al. [28] employed isotopically labeled ethanol (i.e., 12CH3-13CH2-OH, 13CH3-12CH2-OH, and so forth) to trace the carbon atoms during CNT synthesis and revealed that the carbon further away from the hydroxyl group in the ethanol is preferentially incorporated into the SNWT structure, which was confirmed from the different G band peaks of the Raman spectra. This experimental finding shows that the C-C bonds in ethanol molecules are dissociated during CNT synthesis. Although many experimental studies [29-32] have revealed part of the dissociation process during CNT growth, it is not yet well understood how the initial dissociation of carbon source molecules affects the subsequent formation process of CNTs.In parallel with the many experimental studies, there has been numerous computational works focusing on the formation process of CNTs. However, most of these studies [9-16] did not take the dissociation of carbon source molecules into account and examined the cap formation process starting from isolated carbon atoms. This is mainly due to the fact that a low-impact interatomic potential appropriately describing the dissociation of carbon source molecules has not been established for classical molecular dynamics (MD) simulation. Meanwhile, several classical MD simulations using the ReaxFF potential [33], which describes chemical reactions with a reasonable degree of accuracy but has a high computational cost, have demonstrated the dissociation of hydrocarbons on a nickel cluster [34] and a flat metal surface [35]. However, it is still challenging to treat the dissociation process of carbon source molec

  18. Qualifying Energy Conservation Bonds 

    E-print Network

    Briggs, J.

    2013-01-01

    ) of the interest cost associated with the transaction • Typical effective interest rates anywhere from 0%-2% depending on credit strength • Bond issuance or private placement is acceptable 2 What are QECB’s ESL-KT-13-12-39 CATEE 2013: Clean Air Through Energy... Bonds (QECB’s) CATEE Conference December 18, 2013 ESL-KT-13-12-39 CATEE 2013: Clean Air Through Energy Efficiency Conference, San Antonio, Texas Dec. 16-18 • Originally authorized by the Energy Improvement & Extension Act of 2008 • American Recovery...

  19. Birge-Sponer Estimation of the C-H Bond Dissociation Energy in Chloroform Using Infrared, Near-Infrared, and Visible Absorption Spectroscopy: An Experiment in Physical Chemistry

    ERIC Educational Resources Information Center

    Myrick, M. L.; Greer, A. E.; Nieuwland, A. A.; Priore, R. J.; Scaffidi, J.; Andreatta, Danielle; Colavita, Paula

    2008-01-01

    The fundamental and overtone vibrational absorption spectroscopy of the C-H unit in CHCl[subscript 3] is measured for transitions from the v = 0 energy level to v = 1 through v = 5 energy levels. The energies of the transitions exhibit a linearly-decreasing spacing between adjacent vibrational levels as the vibrational quantum number increases.…

  20. Femtosecond dynamics of dative bonding: Concepts of reversible and dissociative electron transfer reactions

    PubMed Central

    Zhong, Dongping; Zewail, Ahmed H.

    1999-01-01

    With fs time, speed, and angular resolution of the elementary steps in electron transfer reactions, we report direct observation of reversible and dissociative processes for dative bonding involving covalent and ionic characters. For bimolecular reactions of various donors and acceptors we find strong correlation between the structure and the dynamics. The dynamics from the transition state to final products involve two elementary processes, with different reaction times, speed, and angular distributions. For example, for the R2S?I2 (R = C2H5) system, it is shown that after charge separation, the reversible electron transfer occurs in less than 150 fs (fastest trajectory) and is followed by the rupture of the I—I bond with the release of the first I-atom in 510 fs. However, the second process of the remaining and trapped I-atom takes 1.15 ps with its speed (500 m/s) being much smaller than the first one (1,030 m/s). The S—I—I average angle is 130°. These findings, on this and the other systems reported here, elucidate the mechanism and address some concepts of nonconcertedness, caging, and restricted energy redistribution. PMID:10077556

  1. Selectin receptor-ligand bonds: Formation limited by shear rate and dissociation governed by the Bell model

    NASA Astrophysics Data System (ADS)

    Chen, Shuqi; Springer, Timothy A.

    2001-01-01

    We have studied the principles that govern the formation and dissociation of an adhesive bond between a cell moving in shear flow and a substrate and tested different theories of how force affects bond dissociation. Viscosity relates the kinematics of fluid movement (shear rate, units of time1) to shear stress (units of force/area, the product of shear rate and viscosity). At different medium viscosities, the formation of receptor-ligand bonds between a cell in the flowstream and P-selectin on the vessel wall showed a similar efficiency as a function of shear rate but not of shear stress. Therefore, bondformation was a function of shear rate and hence of the kinematics of receptor and ligand movement. By contrast, the kinetics of bond dissociation was a function of shear stress and hence of force on the bond. The different requirements for bond formation and dissociation allowed dissociation kinetics to be measured at higher forces on the bond by increasing medium viscosity. Data over an extended range of forces on the bond therefore could be collected that enabled five different proposed equations, relating force to bond dissociation, to be compared for fit to experimental data. The relationship proposed by Bell [Bell, G. I. (1978) Science 200, 618-627] fit the data significantly the best and also predicted an off-rate in the absence of force that best matched an independent measurement [Mehta, P., Cummings, R. D. & McEver, R. P. (1998) J. Biol. Chem. 273, 32506-32513].

  2. Theoretical dissociation energies for ionic molecules

    NASA Technical Reports Server (NTRS)

    Langhoff, S. R.; Bauschlicher, C. W., Jr.; Partridge, H.

    1986-01-01

    Ab initio calculations at the self-consistent-field and singles plus doubles configuration-interaction level are used to determine accurate spectroscopic parameters for most of the alkali and alkaline-earth fluorides, chlorides, oxides, sulfides, hydroxides, and isocyanides. Numerical Hartree-Fock (NHF) calculations are performed on selected systems to ensure that the extended Slater basis sets employed for the diatomic systems are near the Hartree-Fock limit. Extended Gaussian basis sets of at least triple-zeta plus double polarization equality are employed for the triatomic system. With this model, correlation effects are relatively small, but invariably increase the theoretical dissociation energies. The importance of correlating the electrons on both the anion and the metal is discussed. The theoretical dissociation energies are critically compared with the literature to rule out disparate experimental values. Theoretical (sup 2)Pi - (sup 2)Sigma (sup +) energy separations are presented for the alkali oxides and sulfides.

  3. A Redetermination of the Dissociation Energy of MgO(+)

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Partridge, Harry

    1994-01-01

    In 1986, we reported a dissociation energy (D(sub 0) of 2.31 eV for the X(sup 2)Pi ground state of MgO(+). This value was determined by computing the dissociation energy to the Mg(2+) + O(-) limit and adjusting the value to the Mg(+) + O limit using the experimental Ionization Potential (IP) of Mg(+) and the Electron Affinity (EA) of O. The success of this method relies on the assumption that there is little covalent contribution to the bonding. The very small (0.04 eV) correlation contribution to the binding energy was taken as corroboration for the validity of this approach. Our earlier theoretical value was estimated to be accurate to at least 0.2 eV. It is in excellent agreement with the subsequent value of 2.30 +/- 0.13 eV determined by Freiser and co-workers from photodissociation experiments. It is also consistent with the upper (less than 3.1 eV) and lower (greater than 1.1 eV) bounds determined by Rowe obtained by studying the reactions of Mg(+) with 03 and NO2. However, it is inconsistent with an upper bound of 1.7 eV reported by Kappes and Staley based on their failure to observe MgO(+) in the reaction of Mg(+) with N2O. The picture became somewhat clouded, however, by the recent guided-ion beam mass spectrometric studies of Dalleska and Armentrout. Their initial analysis of the reaction data for Mg(+) + O2 lead to a bond dissociation energy of 2.92 +/- 0.25 eV, which is considerably larger than the value of 2.47 +/- 0.06 eV deduced from their studies of the Mg(+)+NO2 reaction.

  4. The dissociation energy of N2

    NASA Technical Reports Server (NTRS)

    Almlof, Jan; Deleeuw, Bradley J.; Taylor, Peter R.; Bauschlicher, Charles W., Jr.; Siegbahn, Per

    1989-01-01

    The requirements for very accurate ab initio quantum chemical prediction of dissociation energies are examined using a detailed investigation of the nitrogen molecule. Although agreement with experiment to within 1 kcal/mol is not achieved even with the most elaborate multireference CI (configuration interaction) wave functions and largest basis sets currently feasible, it is possible to obtain agreement to within about 2 kcal/mol, or 1 percent of the dissociation energy. At this level it is necessary to account for core-valence correlation effects and to include up to h-type functions in the basis. The effect of i-type functions, the use of different reference configuration spaces, and basis set superposition error were also investigated. After discussing these results, the remaining sources of error in our best calculations are examined.

  5. Hydrogen Bond and Ligand Dissociation Dynamics in Fluoride Sensing of Re(I)-Polypyridyl Complex.

    PubMed

    Verma, Sandeep; Aute, Sunil; Das, Amitava; Ghosh, Hirendra N

    2015-11-25

    Hydrogen bonding interaction plays an essential role in the early phases of molecular recognition and colorimetric sensing of various anions in aprotic media. In this work, the host-guest interaction between fac-[Re(CO)3Cl(L)] with L = 4-([2,2'-bipyridin]-4-yl)phenol and fluoride ions is investigated for the hydrogen bond dynamics and the changing local coordination environment. The stoichiometric studies using (1)H NMR and ESI-MS spectroscopies have shown that proton transfer in the H-bonded phenol-fluoride complex activates the dissociation of the CO ligand in the Re(I) center. The phenol-to-phenolate conversion during formation of HF2(-) ion induces nucleophilic lability of the CO ligand which is probed by intraligand charge transfer (ILCT) and ligand-to-metal charge transfer (LMCT) transitions in transient absorption spectroscopy. After photoexcitation, phenol-phenoxide conversion rapidly equilibrates in 280 fs time scale and the ensuing excited state [Re(II)(bpy•(-)-phenolate¯) (CO)3Cl]* undergoes CO dissociation in the ultrafast time scale of ?3 ps. A concerted mechanism of hydrogen cleavage and coordination change is established in anion sensing studies of the rhenium complex. PMID:26514688

  6. Photodissociation Dynamics of Thiophenol-d1: The Nature of Excited Electronic States along the S-D Bond Dissociation Coordinate

    E-print Network

    Kim, Sang Kyu

    , 2009 The S-D bond dissociation dynamics of thiophenol-d1 (C6H5SD) pumped at 266, 243, and 224 nm of thiophenol.7-9 The S-H bond dissociation resulting from the perpendicular transition is prompt and gives rise-D Bond Dissociation Coordinate Jeong Sik Lim, Heechol Choi, Ivan S. Lim, Seong Byung Park, Yoon Sup Lee

  7. Computational Study of Bond Dissociation Enthalpies for Substituted $\\beta$-O-4 Lignin Model Compounds

    SciTech Connect

    Younker, Jarod M; Beste, Ariana; Buchanan III, A C

    2011-01-01

    The biopolymer lignin is a potential source of valuable chemicals. Phenethyl phenyl ether (PPE) is representative of the dominant $\\beta$-O-4 ether linkage. Density functional theory (DFT) is used to calculate the Boltzmann-weighted carbon-oxygen and carbon-carbon bond dissociation enthalpies (BDEs) of substituted PPE. These values are important in order to understand lignin decomposition. Exclusion of all conformers that have distributions of less than 5\\% at 298 K impacts the BDE by less than 1 kcal mol$^{-1}$. We find that aliphatic hydroxyl/methylhydroxyl substituents introduce only small changes to the BDEs (0-3 kcal mol$^{-1}$). Substitution on the phenyl ring at the $ortho$ position substantially lowers the C-O BDE, except in combination with the hydroxyl/methylhydroxyl substituents, where the effect of methoxy substitution is reduced by hydrogen bonding. Hydrogen bonding between the aliphatic substituents and the ether oxygen in the PPE derivatives has a significant influence on the BDE. CCSD(T)-calculated BDEs and hydrogen bond strengths of $ortho$-substituted anisoles when compared with M06-2X values confirm that the latter method is sufficient to describe the molecules studied and provide an important benchmark for lignin model compounds.

  8. Molecular dissociation in the presence of catalysts: interpreting bond breaking as a quantum dynamical phase transition.

    PubMed

    Ruderman, A; Dente, A D; Santos, E; Pastawski, H M

    2015-08-12

    In this work we show that molecular chemical bond formation and dissociation in the presence of the d-band of a metal catalyst can be described as a quantum dynamical phase transition (QDPT). This agrees with DFT calculations that predict sudden jumps in some observables as the molecule breaks. According to our model this phenomenon emerges because the catalyst provides for a non-Hermitian Hamiltonian. We show that when the molecule approaches the surface, as occurs in the Heyrovsky reaction of H2, the bonding H2 orbital has a smooth crossover into a bonding molecular orbital built with the closest H orbital and the surface metal d-states. The same occurs for the antibonding state. Meanwhile, two resonances appear within the continuous spectrum of the d-band, which are associated with bonding and antibonding orbitals between the furthest H atom and the d-states at the second metallic layer. These move toward the band center, where they collapse into a pure metallic resonance and an almost isolated H orbital. This phenomenon constitutes a striking example of the non-trivial physics enabled when one deals with non-Hermitian Hamiltonian beyond the usual wide band approximation. PMID:26189372

  9. Molecular dissociation in presence of catalysts: Interpreting bond breaking as a quantum dynamical phase transition

    E-print Network

    A. Ruderman; A. D. Dente; E. Santos; H. M. Pastawski

    2015-02-20

    In this work we show that the molecular chemical bond formation and dissociation in presence of the d-band of a metal catalyst can be described as a Quantum Dynamical Phase Transition (QDPT). This agree with DFT calculations that predict sudden jumps in some observables as the molecule breaks. According to our model this phenomenon emerges because the catalyst provides for a non- Hermitian Hamiltonian. We show that when the molecule approaches the surface, as occurs in the Heyrovsky reaction of H 2, the bonding H 2 orbital has a smooth crossover into a bonding molecular orbital built with the closest H orbital and the surface metal d-states. The same occurs for the antibonding state. Meanwhile, two resonances appear within the continuous spectrum of the d- band which are associated with bonding and antibonding orbitals between the furthest H atom and the d-states at the second metallic layer. These move towards the band center where they collapse into a pure metallic resonance and an almost isolated H orbital. This phenomenon constitutes a striking example of the non-trivial physics enabled when one deals with non-Hermitian Hamiltonian beyond the usual wide band approximation.

  10. Photodissociation of o-C 6H 4I(CH 2Cl) in the near ultraviolet: a case of photoselective C-I bond dissociation

    NASA Astrophysics Data System (ADS)

    Senapati, Dulal; Das, Puspendu K.

    2005-02-01

    We report the photodissociation dynamics of ortho-iodobenzyl chloride ( o-C 6H 4I(CH 2Cl)) in the ultraviolet. The gas phase dissociation dynamics of o-iodobenzyl chloride at 222, 236, 266, 280, and ˜304 nm was monitored by probing the quantum yields of I* ( 2P 1/2) as well as Cl* ( 2P 1/2) production using suitable resonance enhanced multiphoton ionization detection schemes. We find that only iodine atoms in the ground (I ( 2P 3/2)) as well as excited (I*) states are produced in the dissociation. No Cl ( 2P 3/2) or Cl* atoms were detected. This accidental bond selective dissociation in o-iodobenzyl chloride is perhaps due to weak coupling among various chromophores present in the molecule and inefficient interchromophore energy transfer among them.

  11. On the dissociation energy of BH

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Taylor, Peter R.

    1990-01-01

    The dissociation energy D(0) of the X 1Sigma(+) state has been determined to be 81.5 + or - 0.5 kcal/mol. This value includes an estimate for basis set incompleteness and for core-core and core-valence correlation. The barrier in the A 1Pi state potential is estimated to be 1.9 + or - 0.2 kcal/mol. By analyzing the tunneling through the barrier, it is demonstrated that D(0) and the predissociation limit differ by about 0.8-0.9 kcal/mol. Thus the experimental predissociation limit of 82.5 + or - 0.4 kcal/mol is consistent with the values computed for D(0) and the barrier in this work.

  12. S H bond dissociation enthalpies: The importance of a complete basis set approach

    NASA Astrophysics Data System (ADS)

    Cabral do Couto, P.; Costa Cabral, Benedito J.; Martinho Simões, José A.

    2006-04-01

    The S-H homolytic bond dissociation enthalpies (BDEs) for several compounds of reference were estimated by different theoretical methods including CCSD(T), CBS-QB3, and the multi-coefficient extrapolated density functional theory multi-level approaches, MCG3-MPWB and MCG3-TS. Emphasis was placed on the importance of extrapolating theoretical BDEs to complete basis set. A very good agreement between S-H BDEs from CCSD(T) calculations and experiment is observed when a simple dual extrapolation scheme to complete basis set proposed by Truhlar is adopted. For thiophenol, our CCSD(T) estimate for the S-H BDE (347.2 kJ mol -1) supports a recent experimental value obtained from time-resolved photoacoustic calorimetry (349 ± 5 kJ mol -1).

  13. Effects of Carbonyl Bond and Metal Cluster Dissociation and Evaporation Rates on Predictions of Nanotube Production in HiPco

    NASA Technical Reports Server (NTRS)

    Scott, Carl D.; Smalley, Richard E.

    2002-01-01

    The high-pressure carbon monoxide (HiPco) process for producing single-wall carbon nanotubes (SWNT) uses iron pentacarbonyl as the source of iron for catalyzing the Boudouard reaction. Attempts using nickel tetracarbonyl led to no production of SWNTs. This paper discusses simulations at a constant condition of 1300 K and 30 atm in which the chemical rate equations are solved for different reaction schemes. A lumped cluster model is developed to limit the number of species in the models, yet it includes fairly large clusters. Reaction rate coefficients in these schemes are based on bond energies of iron and nickel species and on estimates of chemical rates for formation of SWNTs. SWNT growth is measured by the co-formation of CO2. It is shown that the production of CO2 is significantly greater for FeCO due to its lower bond energy as compared with that ofNiCO. It is also shown that the dissociation and evaporation rates of atoms from small metal clusters have a significant effect on CO2 production. A high rate of evaporation leads to a smaller number of metal clusters available to catalyze the Boudouard reaction. This suggests that if CO reacts with metal clusters and removes atoms from them by forming MeCO, this has the effect of enhancing the evaporation rate and reducing SWNT production. The study also investigates some other reactions in the model that have a less dramatic influence.

  14. The Kinetics of Dissociations of Aluminum - Oxygen Bonds in Aqueous Complexes - An NMR Study

    SciTech Connect

    Dr. William Casey

    2003-09-03

    OAK B262 The Kinetics of Dissociations of Aluminum--Oxygen Bonds in Aqueous Complexes--An NMR Study. In this project we determined rates and mechanisms of Al(III)-O bond rupture at mineral surfaces and in dissolved aluminum complexes. We then compared the experimental results to simulations in an attempt to predict rate coefficients. Most of the low-temperature reactions that are geochemically important involve a bonded atom or molecule that is replaced with another. We probe these reactions at the most fundamental level in order to establish a model to predict rates for the wide range of reactions that cannot be experimentally studied. The chemistry of small aluminum cluster (Figure) provides a window into the hydrolytic processes that control rates of mineral formation and the transformation of adsorbates into extended structures. The molecule shown below as an example exposes several types of oxygens to the bulk solution including seven structurally distinct sets of bridging hydroxyls. This molecule is a rich model for the aqueous interface of aluminum (hydr)oxide minerals, since it approaches colloidal dimensions in size, yet is a dissolved complex with +18 charge. We have conducted both {sup 17}O- {sup 27}Al- and {sup 19}F-NMR experiments to identify the reactive sites and to determine the rates of isotopic exchange between these sites and the bulk solution. The research was enormously successful and led to a series of papers that are being used as touchstones for assessing the accuracy of computer models of bond ruptures in water.

  15. Bond-Selective and Mode-Specific Dissociation of CH3D and CH2D2 on Pt(111).

    PubMed

    Hundt, P Morten; Ueta, Hirokazu; van Reijzen, Maarten E; Jiang, Bin; Guo, Hua; Beck, Rainer D

    2015-12-17

    Infrared laser excitation of partially deuterated methanes (CH3D and CH2D2) in a molecular beam is used to control their dissociative chemisorption on a Pt(111) single crystal and to determine the quantum state-resolved dissociation probabilities. The exclusive detection of C-H cleavage products adsorbed on the Pt(111) surface by infrared absorption reflection spectroscopy indicates strong bond selectivity for both methane isotopologues upon C-H stretch excitation. Furthermore, the dissociative chemisorption of both methane isotopologues is observed to be mode-specific. Excitation of symmetric C-H stretch modes produces a stronger reactivity increase than excitation of the antisymmetric C-H stretch modes, whereas bend overtone excitation has a weaker effect on reactivity. The observed mode specificity and bond selectivity are rationalized by the sudden vector projection model in terms of the overlap of the reactant's normal mode vectors with the reaction coordinate at the transition state. PMID:26414099

  16. Electron-induced dissociation (EID) for structure characterization of glycerophosphatidylcholine: determination of double-bond positions and localization of acyl chains.

    PubMed

    Jones, Jace W; Thompson, Christopher J; Carter, Claire L; Kane, Maureen A

    2015-12-01

    Glycerophospholipids are a highly abundant and diverse collection of biologically relevant lipids, and distinction between isomeric and isobaric species is a fundamental aspect for confident identification. The ability to confidently assign a unique structure to a glycerophospholipid of interest is dependent on determining the number and location of the points of unsaturation and assignment of acyl chain position. The use of high-energy electrons (>20?eV) to induce gas-phase dissociation of intact precursor ions results in diagnostic product ions for localizing double-bond positions and determining acyl chain assignment. We describe a high-resolution, tandem mass spectrometry method for structure characterization of glycerophospholipids using electron-induced dissociation (EID). Furthermore, the inclusion of nomenclature to systematically assign bond cleavage sites with acyl chain position and double-bond location enables a uniform platform for lipid identification. The EID methodology detailed here combines novel application of an electron-based dissociation technique with high-resolution mass spectrometry that facilitates a new experimental approach for lipid biomarker discovery and validation. Copyright © 2015 John Wiley & Sons, Ltd. PMID:26634966

  17. Mass spectrometric and theoretical studies on dissociation of the Ssbnd S bond in the allicin: Homolytic cleavage vs heterolytic cleavage

    NASA Astrophysics Data System (ADS)

    Zhang, Xiang

    2012-08-01

    On the basis of the tandem mass spectrometry (ESI-MS/MS) technique and DFT calculations, an experimental and theoretical investigation has been conducted into the gas-phase dissociation of the S1sbnd S1' bond in the allicin as well as that of the Ssbnd C (S1sbnd C2, S1'sbnd C2') bond. Meanwhile, the influence of protonation, alkali metal ion and electron transfer on the dissociation of the S1sbnd S1' bond has been taken into account. ESI-MS/MS experiments and DFT calculations show that in the neutral allicin, [allicin + Li]+ and [allicin + Na]+, the S1sbnd S1' bond favors homolytic cleavage, while in the allicin radical cation and protonated allicin, the S1sbnd S1' bond prefers heterolytic cleavage. In addition, alkali metal ions can strengthen the S1sbnd S1' bond in the allicin, while protonation or the loss of an electron will weaken the S1sbnd S1' bond.

  18. Photodissociation dynamics of thiophenol-d1: the nature of excited electronic states along the S-D bond dissociation coordinate.

    PubMed

    Lim, Jeong Sik; Choi, Heechol; Lim, Ivan S; Park, Seong Byung; Lee, Yoon Sup; Kim, Sang Kyu

    2009-10-01

    The S-D bond dissociation dynamics of thiophenol-d1 (C6H5SD) pumped at 266, 243, and 224 nm are examined using the velocity map ion imaging technique. At both 266 and 243 nm, distinct peaks associated with X and A states of the phenylthiyl radical (C6H5S*) are observed in the D+ image at high and low kinetic energy regions, respectively. The partitioning of the available energy into the vibrational energy of the phenylthiyl radical is found to be enhanced much more strongly at 266 nm compared to that at 243 nm. This indicates that the pipi* electronic excitation at 266 nm is accompanied by significant vibrational excitation. Given the relatively large anisotropy parameter of -0.6, the S-D dissociation at 266 nm is prompt and should involve the efficient coupling to the upper-lying n(pi)sigma* repulsive potential energy surface. The optical excitation of thiophenol at 224 nm is tentatively assigned to the pisigma* transition, which leads to the fast dissociation on the repulsive potential energy surface along the S-D coordinate. The nature of the electronic transitions associated with UV absorption bands is investigated with high-level ab initio calculations. Excitations to different electronic states of thiophenol result in unique branching ratios and vibrational excitations for the fragment of the phenylthiyl radical in the two lowest electronic states. PMID:19728695

  19. Photodissociation Dynamics of Thiophenol-d1: The Nature of Excited Electronic States along the S-D Bond Dissociation Coordinate

    NASA Astrophysics Data System (ADS)

    Lim, Jeong Sik; Choi, Heechol; Lim, Ivan S.; Park, Seong Byung; Lee, Yoon Sup; Kim, Sang Kyu

    2009-09-01

    The S-D bond dissociation dynamics of thiophenol-d1 (C6H5SD) pumped at 266, 243, and 224 nm are examined using the velocity map ion imaging technique. At both 266 and 243 nm, distinct peaks associated with X˜ and à states of the phenylthiyl radical (C6H5S·) are observed in the D+ image at high and low kinetic energy regions, respectively. The partitioning of the available energy into the vibrational energy of the phenylthiyl radical is found to be enhanced much more strongly at 266 nm compared to that at 243 nm. This indicates that the ??* electronic excitation at 266 nm is accompanied by significant vibrational excitation. Given the relatively large anisotropy parameter of -0.6, the S-D dissociation at 266 nm is prompt and should involve the efficient coupling to the upper-lying n??* repulsive potential energy surface. The optical excitation of thiophenol at 224 nm is tentatively assigned to the ??* transition, which leads to the fast dissociation on the repulsive potential energy surface along the S-D coordinate. The nature of the electronic transitions associated with UV absorption bands is investigated with high-level ab initio calculations. Excitations to different electronic states of thiophenol result in unique branching ratios and vibrational excitations for the fragment of the phenylthiyl radical in the two lowest electronic states.

  20. The thermodynamics and kinetics of phosphoester bond formation, use, and dissociation in biology, with the example of polyphosphate in platelet activation, trasience, and mineralization.

    NASA Astrophysics Data System (ADS)

    Omelon, S. J.

    2014-12-01

    Mitochondria condense orthophosphates (Pi), forming phosphoester bonds for ATP production that is important to life. This represents an exchange of energy from dissociated carbohydrate bonds to phosophoester bonds. These bonds are available to phosphorylate organic compounds or hydrolyze to Pi, driving many biochemical processes. The benthic bacteria T. namibiensis 1 and Beggiatoa 2 condense Pi into phosphate polymers in oxygenated environments. These polyphosphates (polyPs) are stored until the environment becomes anoxic, when these bacteria retrieve the energy from polyP dissociation into Pi3. Dissociated Pi is released outside of the bacteria, where it precipitates as apatite.The Gibbs free energy of polyP phosphoester bond hydrolysis is negative, however, the kinetics are slow4. Diatoms contain a polyP pool that is stable until after death, after which the polyPs hydrolyze and form apatite5. The roles of polyP in eukaryotic organism biochemistry continue to be discovered. PolyPs have a range of biochemical roles, such as bioavailable P-storage, stress adaptation, and blood clotting6. PolyP-containing granules are released from anuclear platelets to activate factor V7 and factor XII in the blood clotting process due to their polyanionic charge8. Platelets have a lifespan of approximately 8 days, after which they undergo apoptosis9. Data will be presented that demonstrate the bioactive, thermodynamically unstable polyP pool within older platelets in vitro can spontaneously hydrolyze and form phosphate minerals. This process is likely avoided by platelet digestion in the spleen and liver, possibly recycling platelet polyPs with their phosphoester bond energy for other biochemical roles. 1 Schulz HN et al. Science (2005) 307: 416-4182 Brüchert V et al. Geochim Cosmochim Acta (2003) 67: 4505-45183 Goldhammer T et al. Nat Geosci (2010) 3: 557-5614 de Jager H-J et al. J Phys Chem A (1988) 102: 2838-28415 Diaz, J et al. Science (2008) 320: 652-6556 Mason KD et al. Cell (2007) 128(6): 1173-11867 Smith SA. et al. PNAS (2006) 103(4): 903-908. 8 Müller F et al. Cell (2009) 139(6): 1143-11569 Ruiz FA et al. J Biol Chem (2004) 279(43): 44250-44257.

  1. The Se-H bond of benzeneselenols (ArSe-H): Relationship between bond dissociation enthalpy and spin density of radicals

    NASA Astrophysics Data System (ADS)

    Nam, Pham Cam; Nguyen, Minh Tho

    2013-03-01

    Bond dissociation enthalpies (BDE) of benzeneselenol (ArSe-H) and its para and meta-substituted derivatives are calculated using the (RO)B3LYP/6-311++G(2df,2p)//(U)B3LYP/6-311G(d,p) procedure. The computed BDE(Se-H) = 308 ± 8 kJ/mol for the parent PhSe-H is significantly smaller than the experimental value of 326.4 ± 16.7 kJ/mol [Kenttamaa and coworkers, J. Phys. Chem. 100 (1996) 6608] but larger than a previous value of 280.3 kJ/mol [Newcomb et al., J. Am. Chem. Soc. 113 (1991) 949]. The substituent effects on BDE's are analyzed in terms of a relationship between BDE(Se-H) and Mulliken atomic spin densities at the Se radical centers of ArSe (? radicals). Good correlations between Hammett's substituent constants with BDE(Se-H) are established. Proton affinity and ionization energy amount to PA(C6H5SeH) = 814 ± 4 kJ/mol and IE(C6H5SeH) = 8.0 ± 0.1 eV. IEs of the substituted benzeneselenols are also determined. Calculated results thus suggest that 4-amino-benzeneselenol derivatives emerge as efficient antioxidants.

  2. Accurate In Bond Energies

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Arnold, James O. (Technical Monitor)

    1999-01-01

    InXn atomization energies are computed for n = 1-3 and X = H, Cl, and CH3. The geometries and frequencies are determined using density functional theory. The atomization energies are computed at the coupled cluster level of theory. The complete basis set limit is obtained by extrapolation. The scalar relativistic effect is computed using the Douglas-Kroll approach. While the heats of formation for InH, InCl and InCl3 are in good agreement with experiment, the current results show that the experimental value for In(CH3)3 must be wrong.

  3. Dissociation energy of the ground state of NaH

    SciTech Connect

    Huang, Hsien-Yu; Lu, Tsai-Lien; Whang, Thou-Jen; Chang, Yung-Yung; Tsai, Chin-Chun

    2010-07-28

    The dissociation energy of the ground state of NaH was determined by analyzing the observed near dissociation rovibrational levels. These levels were reached by stimulated emission pumping and fluorescence depletion spectroscopy. A total of 114 rovibrational levels in the ranges 9{<=}v{sup ''}{<=}21 and 1{<=}J{sup ''}{<=}14 were assigned to the X {sup 1}{Sigma}{sup +} state of NaH. The highest vibrational level observed was only about 40 cm{sup -1} from the dissociation limit in the ground state. One quasibound state, above the dissociation limit and confined by the centrifugal barrier, was observed. Determining the vibrational quantum number at dissociation v{sub D} from the highest four vibrational levels yielded the dissociation energy D{sub e}=15 815{+-}5 cm{sup -1}. Based on new observations and available data, a set of Dunham coefficients and the rotationless Rydberg-Klein-Rees curve were constructed. The effective potential curve and the quasibound states were discussed.

  4. Effects of Charge State on Fragmentation Pathways, Dynamics, and Activation Energies of Ubiquitin Ions Measured by Blackbody Infrared Radiative Dissociation

    PubMed Central

    Jockusch, Rebecca A.; Schnier, Paul D.; Price, William D.; Strittmatter, Eric. F.; Demirev, Plamen A.; Williams*, Evan R.

    2005-01-01

    Blackbody infrared radiative dissociation spectra of the (M + 5H)5+ through (M + 11H)11+ ions of the protein ubiquitin (8.6 kDa) formed by electrospray ionization were measured in a Fourier-transform mass spectrometer. The 5+ ion dissociates exclusively by loss of water and/or ammonia, whereas the 11+ charge state dissociates only by formation of complementary y and b ions. These two processes are competitive for intermediate charge state ions, with the formation of y and b ions increasingly favored for the higher charge states. The y and b ions are formed by cleavage of the backbone amide bond on the C-terminal side of acidic residues exclusively, with cleavage adjacent to aspartic acid favored. Thermal unimolecular dissociation rate constants for the dissociation of each of these charge states were measured. From the temperature dependence of these rates, Arrhenius activation parameters in the rapid energy exchange limit are obtained. The activation energies (Ea) and preexponential factors (A) for the 5+, 8+, and 9+ ions are 1.2 eV and 1012 s?1, respectively. These values for the 6+ and 7+ ions are 0.9–1.0 eV and 109 s?1, and those for the 10+ and 11+ ions are 1.6 eV and 1016–1017 s?1. Thus, with the exception of the 5+ ion, the higher charge states of ubiquitin have larger dissociation activation energies than the lower charge states. The different A factors observed for production of y and b ions from different precursor charge states indicate that they are formed by different mechanisms, ranging from relatively complex rearrangements to direct bond cleavages. These results clearly demonstrate that the relative dissociation rates of large biomolecule ions by themselves are not necessarily a reliable indicator of their relative dissociation energies, even when similar fragment ions are formed. PMID:9075403

  5. Electron-induced dissociation (EID) for structure characterization of glycerophosphatidylcholine: determination of double-bond positions and localization of acyl chains.

    PubMed

    Jones, J W; Thompson, C J; Carter, C L; Kane, M A

    2015-12-01

    Mass spectrometry continues to drive the field of lipidomics across many areas of research because of its unique capability for characterizing lipids. With an accurate molecular weight, often in combination with ion mobility or liquid chromatography, MS can deconstruct a complex mixture of lipids into a table of lipid species annotated by class and isobar. Tandem MS, typically low energy CID, can further distinguish isobars by the different fatty acid fragments and in some cases reveal the fatty acid bonding position. In the Special Feature Kane and coworkers at University of Maryland apply a new electron-induced dissociation technique to singly-charged mono- and di-unsaturated phospholipids and show how the resulting fragmentation patterns indicate the fatty acid position as well as the double bond location. PMID:26634981

  6. Energy and Entropy Effects in Dissociation of Peptide Radical Anions

    SciTech Connect

    Laskin, Julia; Yang, Zhibo; Lam, Corey; Chu, Ivan K.

    2012-04-15

    Time- and collision energy-resolved surface-induced dissociation (SID) of peptide radical anions was studied for the first time using a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) configured for SID experiments. Peptide radical cations and anions were produced by gas-phase fragmentation of CoIII(salen)-peptide complexes. The effect of the charge, radical, and the presence of a basic residue on the energetics and dynamics of dissociation of peptide ions was examined using RVYIHPF (1) and HVYIHPF (2) as model systems. Comparison of the survival curves for of [M+H]{sup +}, [M-H]{sup -}, M{sup +{sm_bullet}}, and [M-2H]{sup -{sm_bullet}} ions of these precursors demonstrated that even-electron ions are more stable towards fragmentation than their odd-electron counterparts. RRKM modeling of the experimental data demonstrated that the lower stability of the positive radicals is mainly attributed to lower dissociation thresholds while entropy effects are responsible the relative instability of the negative radicals. Substitution of arginine with less basic histidine residue has a strong destabilizing effect on the [M+H]{sup +} ions and a measurable stabilizing effect on the odd-electron ions. Lower threshold energies for dissociation of both positive and negative radicals of 1 are attributed to the presence of lower-energy dissociation pathways that are most likely promoted by the presence of the basic residue.

  7. Dissociation of OCS by high energy highly charged ion impact

    NASA Astrophysics Data System (ADS)

    Rani Jana, Mridula; Ghosh, Pradip N.; Ray, Biswajit; Bapat, Bhas; Kushawaha, Rajesh Kumar; Saha, Koushik; Prajapati, Ishwar A.; Safvan, C. P.

    2014-09-01

    Various dissociation channels of OCSq+ (where q = 2 to 4), formed in the interaction of 5 MeV u-1 Si12+ ion beam with neutral OCS, have been studied using recoil-ion momentum spectroscopy. The concerted and/or sequential nature of dissociation is inferred from the shape and slope of the coincidence islands in the 2D coincidence map. It is observed that the C+ + S+ + O channel results from concerted as well as sequential decay of OCS2+. However the other channels originate purely from the concerted process in which the two terminal fragments (oxygen and sulphur) fly back to back and the central carbon fragment is left with negligible momentum. The kinetic energy release (KER) distributions for all the fragmentation channels arising from the dissociation of OCSq+ (where q = 2 to 4) have been measured and compared with the available data in the literature. It is observed that the KER values for complete Coulomb fragmentation channels are much smaller than those of incomplete Coulomb fragmentation cases and the KER increases with the increasing charge states of the parent molecular ions. From the momentum correlation map, we estimated the geometry of the precursor molecular ion undergoing three-body dissociation and inferred that bent dissociative states are involved in most of the fragmentation channels of OCSq+.

  8. Dissociation of OCS by high energy highly charged ion impact

    NASA Astrophysics Data System (ADS)

    Jana, Mridula Rani; Ghosh, Pradip N.; Ray, Biswajit; Bapat, Bhas; Kushawaha, Rajesh Kumar; Saha, Koushik; Prajapati, Ishwar A.; Safvan, C. P.

    2014-09-01

    Various dissociation channels of OCS q+ (where q = 2 to 4), formed in the interaction of 5 MeV u-1 Si12+ ion beam with neutral OCS, have been studied using recoil-ion momentum spectroscopy. The concerted and/or sequential nature of dissociation is inferred from the shape and slope of the coincidence islands in the 2D coincidence map. It is observed that the C+ + S+ + O channel results from concerted as well as sequential decay of OCS2+. However the other channels originate purely from the concerted process in which the two terminal fragments (oxygen and sulphur) fly back to back and the central carbon fragment is left with negligible momentum. The kinetic energy release (KER) distributions for all the fragmentation channels arising from the dissociation of OCS q+ (where q = 2 to 4) have been measured and compared with the available data in the literature. It is observed that the KER values for complete Coulomb fragmentation channels are much smaller than those of incomplete Coulomb fragmentation cases and the KER increases with the increasing charge states of the parent molecular ions. From the momentum correlation map, we estimated the geometry of the precursor molecular ion undergoing three-body dissociation and inferred that bent dissociative states are involved in most of the fragmentation channels of OCS q+.

  9. Theoretical determination of the alkali-metal superoxide bond energies

    NASA Technical Reports Server (NTRS)

    Partridge, Harry; Bauschlicher, Charles W., Jr.; Sodupe, Mariona; Langhoff, Stephen R.

    1992-01-01

    The bond dissociation energies for the alkali-metal superoxides have been computed using extensive Gaussian basis sets and treating electron correlation at the modified coupled-pair functional level. Our computed D0 values are 61.4, 37.2, 40.6, and 38.4 kcal/mol for LiO2, NaO2, KO2, and RbO2, respectively. These values, which are expected to be lower bounds and accurate to 2 kcal/mol, agree well with some of the older flame data, but rule out several recent experimental measurements.

  10. First-row hydrides: Dissociation and ground state energies using quantum Monte Carlo

    E-print Network

    Anderson, James B.

    First-row hydrides: Dissociation and ground state energies using quantum Monte Carlo Arne Lu. The dissociation energies De have been calculated with accuracies of 0.5 kcal mol 1 or better. For all hydrides, the dissociation energies are consistent with experimental values. The fixed-node quantum Monte Carlo method can

  11. Toward a General Mechanism of Electron Capture Dissociation

    E-print Network

    Simons, Jack

    Toward a General Mechanism of Electron Capture Dissociation Erik A. Syrstad and Frantisek Turecek calculations with the goal of elucidating the energetics of electron capture dissociation (ECD) of multiply, resulting in exothermic electron capture. The NOC bond dissociation and transition state energies in charge

  12. Dissociation energy and vibrational predissociation dynamics of the ammonia dimer

    NASA Astrophysics Data System (ADS)

    Case, Amanda S.; Heid, Cornelia G.; Kable, Scott H.; Crim, F. Fleming

    2011-08-01

    Experiments using infrared excitation of either the intramolecular symmetric N-H stretch (?NH,S) or the intramolecular antisymmetric N-H stretch (?NH,A) of the ammonia dimer ((NH3)2) in combination with velocity-map ion imaging provide new information on the dissociation energy of the dimer and on the energy disposal in its dissociation. Ion imaging using resonance enhanced multiphoton ionization to probe individual rovibrational states of one of the ammonia monomer fragments provides recoil speed distributions. Analyzing these distributions for different product states gives a dissociation energy of D0 = 660 ± 20 cm-1 for the dimer. Fitting the distributions shows that rotations are excited up to their energetic limit and determines the correlation of the fragment vibrations. The fragments NH3(v2 = 3+) and NH3(v2 = 2+) have a vibrational ground-state partner NH3(v = 0), but NH3(v2 = 1+) appears in partnership with another fragment in v2 = 1. This propensity is consistent with the idea of minimizing the momentum gap between the initial and final states by depositing a substantial fraction of the available energy into internal excitation.

  13. Mechanistic Examination of C?–C? Bond Cleavages of Tryptophan Residues during Dissociations of Molecular Peptide Radical Cations

    SciTech Connect

    Song, Tao; Ma, Ching-Yung; Chu, Ivan K.; Siu, Chi-Kit; Laskin, Julia

    2013-02-14

    In this study, we used collision-induced dissociation (CID) to examine the gas-phase fragmentations of [GnW]•+ (n = 2-4) and [GXW]•+ (X = C, S, L, F, Y, Q) species. The C?–C? bond cleavage of a C-terminal decarboxylated tryptophan residue ([M - CO2]•+) can generate [M - CO2 - 116]+, [M - CO2 - 117]•+, and [1H-indole]•+ (m/z 117) species as possible product ions. Competition between the formation of [M - CO2 - 116]+ and [1H-indole]•+ systems implies the existence of a proton-bound dimer formed between the indole ring and peptide backbone. Formation of such a proton-bound dimer is facile via a protonation of the tryptophan ?-carbon atom as suggested by density functional theory (DFT) calculations. DFT calculations also suggested the initially formed ion 2--the decarboxylated species that is active against C?–C? bond cleavage -can efficiently isomerize to form a more-stable -radical isomer (ion 9) as supported by Rice-Ramsperger-Kassel-Marcus (RRKM) modeling. The C?–C? bond cleavage of a tryptophan residue also can occur directly from peptide radical cations containing a basic residue. CID of [WGnR]•+ (n = 1-3) radical cations consistently resulted in predominant formation of [M-116]+ product ions. It appears that the basic arginine residue tightly sequesters the proton and allows the charge-remote C?–C? bond cleavage to prevail over the charge-directed one. DFT calculations predicted the barrier for the former is 6.2 kcal mol -1 lower than that of the latter. Furthermore, the pathway involving a salt-bridge intermediate also was accessible during such a bond cleavage event.

  14. The dissociation energy of He2(+)

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Partridge, Harry; Ceperley, David

    1989-01-01

    Ab initio potential energy curves for He2(+) are computed using full CI wavefunctions in conjuction with large Gaussian and Slater basis sets. The computed curves yield rotational-vibrational transitions with errors of less than 1/cm. They also yield quasi-bound levels with energies and lifetimes in reasonable agreement with translational spectroscopy measurements. The best D(e) is estimated to be 2.470 eV. Green's function Monte Carlo calculations yield a very similar value, 2.466 + or - 0.005.

  15. Direct dynamics study of N-protonated diglycine surface-induced dissociation. Influence of collision energy.

    PubMed

    Wang, Yanfei; Hase, William L; Song, Kihyung

    2003-12-01

    A quantum mechanical and molecular mechanical (QM + MM) direct dynamics classical trajectory simulation is used to study energy transfer and fragmentation in the surface-induced dissociation (SID) of N-protonated diglycine, (gly)2H+. The peptide ion collides with the hydrogenated diamond [111] surface. The Austin Model 1 (AM1) semiempirical electronic structure theory is used for the (gly)2H+ intramolecular potential and molecular mechanical functions are used for the diamond surface potential and peptide/surface intermolecular potential. The simulations are performed at collision energies Ei of 30, 50, 70, and 100 eV and collision angle of 0 degrees (perpendicular to the surface). The percent energy transfer to the peptide ion is nearly independent of Ei, while energy transfer to the surface increases with increase in Ei. A smaller percent of the energy remains in peptide translation as Ei is increased. These trends in energy transfer are consistent with previous trajectory simulations of SID. At each Ei the most likely initial pathway leading to fragmentation is rupture of the +H3NCH2-CONHCH2COOH bond. Fragmentation occurs by two general mechanisms. One is the traditional Rice-Ramsperger-Kassel-Marcus (RRKM) model in which the peptide ion is activated by its collision with the surface, "bounces off", and then dissociates after undergoing intramolecular vibrational energy redistribution (IVR). The other mechanism is shattering in which the ion fragments as it collides with the surface. Shattering is the origin of the large increase in number of product channels with increase in Ei, i.e., 6 at 30 eV, but 59 at 100 eV. Shattering becomes the dominant dissociation mechanism at high Ei. PMID:14652188

  16. Effect of pulse intensity distributions on fragment internal energy in the infrared multiphoton dissociation of vinyl

    E-print Network

    dissociation of vinyl cyanide John S. McKillop, Robert J. Gordon,a) and Richard N. Zare Department of the rovibra- tional energy distributions of fragmentsl formed in the infrared multiphoton dissociation (IRMPD rotational temperatures on the laser intensity and (2) a statistical distribution in dissociation lifetimes

  17. Effects of carbonyl bond, metal cluster dissociation, and evaporation rates on predictions of nanotube production in high-pressure carbon monoxide.

    PubMed

    Scott, Carl D; Smalley, Richard E

    2003-01-01

    The high-pressure carbon monoxide (HiPco) process for producing single-wall carbon nanotubes (SWNTs) uses iron pentacarbonyl as the source of iron for catalyzing the Boudouard reaction. Attempts using nickel tetracarbonyl led to no production of SWNTs. This paper discusses simulations at a constant condition of 1300 K and 30 atm in which the chemical rate equations are solved for different reaction schemes. A lumped cluster model is developed to limit the number of species in the models, yet it includes fairly large clusters. Reaction rate coefficients in these schemes are based on bond energies of iron and nickel species and on estimates of chemical rates for formation of SWNTs. SWNT growth is measured by the conformation of CO2. It is shown that the production of CO2 is significantly greater for FeCO because of its lower bond energy as compared with that of NiCO. It is also shown that the dissociation and evaporation rates of atoms from small metal clusters have a significant effect on CO2 production. A high rate of evaporation leads to a smaller number of metal clusters available to catalyze the Boudouard reaction. This suggests that if CO reacts with metal clusters and removes atoms from them by forming MeCO, this has the effect of enhancing the evaporation rate and reducing SWNT production. The study also investigates some other reactions in the model that have a less dramatic influence. PMID:12908232

  18. Effects of carbonyl bond, metal cluster dissociation, and evaporation rates on predictions of nanotube production in high-pressure carbon monoxide

    NASA Technical Reports Server (NTRS)

    Scott, Carl D.; Smalley, Richard E.

    2003-01-01

    The high-pressure carbon monoxide (HiPco) process for producing single-wall carbon nanotubes (SWNTs) uses iron pentacarbonyl as the source of iron for catalyzing the Boudouard reaction. Attempts using nickel tetracarbonyl led to no production of SWNTs. This paper discusses simulations at a constant condition of 1300 K and 30 atm in which the chemical rate equations are solved for different reaction schemes. A lumped cluster model is developed to limit the number of species in the models, yet it includes fairly large clusters. Reaction rate coefficients in these schemes are based on bond energies of iron and nickel species and on estimates of chemical rates for formation of SWNTs. SWNT growth is measured by the conformation of CO2. It is shown that the production of CO2 is significantly greater for FeCO because of its lower bond energy as compared with that of NiCO. It is also shown that the dissociation and evaporation rates of atoms from small metal clusters have a significant effect on CO2 production. A high rate of evaporation leads to a smaller number of metal clusters available to catalyze the Boudouard reaction. This suggests that if CO reacts with metal clusters and removes atoms from them by forming MeCO, this has the effect of enhancing the evaporation rate and reducing SWNT production. The study also investigates some other reactions in the model that have a less dramatic influence.

  19. Probing the potential energy landscape for dissociation of protonated indole via threshold collision-induced dissociation and theoretical studies

    NASA Astrophysics Data System (ADS)

    Yang, Zhibo; Ruan, Chunhai; Ahmed, H.; Rodgers, M. T.

    2007-09-01

    Collision-induced dissociation of protonated indole with Xe is studied as a function of kinetic energy using guided ion beam tandem mass spectrometry techniques. Activated dissociation resulting in endothermic loss of neutral HCN (or HNC) is the only pathway observed over the range of collision energies examined. The cross-section threshold for this activated dissociation pathway is interpreted to yield 0 and 298 K activation energies for this process after accounting for the effects of multiple ion-neutral collisions, the internal energy distribution of the protonated indole cations, and their lifetimes for dissociation. Density functional theory (DFT) calculations at the MPW1PW91/6-31G* level of theory are used to determine the structures of indole, the protonated indole tautomers, and the transition states, intermediates, and products involved in the activated dissociation of protonated indole. Four distinct pathways between the reactant ion and dissociation products are computed. In all cases, the ionic product formed is C6H5CH2+, while the neutral product is HCN in three of the pathways and HNC in the fourth. The vibrational frequencies and rotational constants of the ground state tautomer of protonated indole and the rate-determining transition state along each of the pathways computed are used for the thermodynamic analysis of the experimental data. The theoretical activation energies and potential energy landscapes for activated dissociation of protonated indole are determined from single point calculations at the MPW1PW91/6-311+G(2d,2p) and MP2(full)/6-311+G(2d,2p) levels of theory, using the MPW1PW91/6-31G* optimized geometries. Both theories produce similar potential energy landscapes for elimination of HCN (or HNC) from protonated indole. Theory suggests that elimination of HNC is favored over HCN. However, our threshold measurements probe the lowest-energy pathway available and are in much better agreement with the higher-energy HCN elimination pathways, suggesting that theory underestimates the activation energy for loss of HNC.

  20. Three methods to measure RH bond energies

    SciTech Connect

    Berkowitz, J. ); Ellison, G.B. ); Gutman, D. )

    1994-03-17

    We present a critical review of three different experimental methods used to measure bond energies: radical kinetics, gas-phase acidity cycles, and photoionization mass spectrometry. These experimental techniques are currently in use to measure the bond energies of a large number of molecules. We discuss the basic premises of each of these experiments and explicitly try to point out the strengths and weaknesses of each method. We directly compare each of these procedures using a set of about 30 important molecules. These three different techniques have only a few disagreements among them, the case of ethylene being the most serious. For the overwhelming number of studies, all measurements lead to bond energies within each other's error bars. We include tables of ionization potentials, electron affinities, and heats of formation for about 40 important organic and inorganic radicals. We also list bond energies for the parent molecules at 0 and 298 K. 273 refs., 10 figs., 5 tabs.

  1. Excitation and multiple dissociation of projectiles at intermediate energy

    SciTech Connect

    Pouliot, J.; Chan, Y.; Dacal, A.; DiGregorio, D.E.; Harmon, B.A.; Knop, R.; Ortiz, M.E.; Plagnol, E.; Stokstad, R.G.; Moisan, C.

    1989-04-01

    Cross sections for the multiple breakup of /sup 16/O, /sup 14/N and /sup 12/C projectiles scattered by a Au target were measured with an array of 34 phoswich detectors. The dissociation of the projectiles into as many as five charged particles has been observed. The yields of different exit channels correlate approximately with the threshold energy for separation of the projectile into the observed fragments. The excitation spectrum of the primary projectile-like nucleus was reconstructed from the measured positions and kinetic energies of the individual fragments. The energy sharing between projectile and target is consistent with a fast excitation mechanism in which differential increases in projectile excitation energy appear to be accompanied by comparable increases in target excitation. Calculations of the yields based on a sequence of binary decays are presented. The question of prompt or sequential decay is also considered by examining the directional correlations of the particles. 19 refs., 8 figs.

  2. Dissociation of internal energy-selected methyl bromide ion revealed from threshold photoelectron-photoion coincidence velocity imaging

    SciTech Connect

    Tang, Xiaofeng; National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029 ; Zhou, Xiaoguo E-mail: yanbing@jlu.edu.cn; Liu, Shilin; Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 ; Sun, Zhongfa; Liu, Fuyi; Sheng, Liusi; Yan, Bing E-mail: yanbing@jlu.edu.cn

    2014-01-28

    Dissociative photoionization of methyl bromide (CH{sub 3}Br) in an excitation energy range of 10.45–16.90 eV has been investigated by using threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging. The coincident time-of-flight mass spectra indicate that the ground state X{sup 2}E of CH{sub 3}Br{sup +} is stable, and both A{sup 2}A{sub 1} and B{sup 2}E ionic excited states are fully dissociative to produce the unique fragment ion of CH{sub 3}{sup +}. From TPEPICO 3D time-sliced velocity images of CH{sub 3}{sup +} dissociated from specific state-selected CH{sub 3}Br{sup +} ion, kinetic energy release distribution (KERD) and angular distribution of CH{sub 3}{sup +} fragment ion are directly obtained. Both spin-orbit states of Br({sup 2}P) atom can be clearly observed in fast dissociation of CH{sub 3}Br{sup +}(A{sup 2}A{sub 1}) ion along C–Br rupture, while a KERD of Maxwell-Boltzmann profile is obtained in dissociation of CH{sub 3}Br{sup +}(B{sup 2}E) ion. With the aid of the re-calculated potential energy curves of CH{sub 3}Br{sup +} including spin-orbit coupling, dissociation mechanisms of CH{sub 3}Br{sup +} ion in A{sup 2}A{sub 1} and B{sup 2}E states along C–Br rupture are revealed. For CH{sub 3}Br{sup +}(A{sup 2}A{sub 1}) ion, the CH{sub 3}{sup +} + Br({sup 2}P{sub 1/2}) channel is occurred via an adiabatic dissociation by vibration, while the Br({sup 2}P{sub 3/2}) formation is through vibronic coupling to the high vibrational level of X{sup 2}E state followed by rapid dissociation. C–Br bond breaking of CH{sub 3}Br{sup +}(B{sup 2}E) ion can occur via slow internal conversion to the excited vibrational level of the lower electronic states and then dissociation.

  3. Low-energy dissociative electron attachment to CF2

    NASA Astrophysics Data System (ADS)

    Chourou, S. T.; Larson, Ã.; Orel, A. E.

    2015-08-01

    We present the results of a theoretical study of dissociative electron attachment (DEA) of low-energy electrons to CF2. We carried out electron scattering calculations using the complex Kohn variational method at the static-exchange and relaxed self-consistent field (SCF) level at the equilibrium geometry and compare our differential cross sections to other results. We then repeated these calculations as a function of the three internal degrees of freedom to obtain the resonance energy surfaces and autoionization widths. We use this data as input to form the Hamiltonian relevant to the nuclear dynamics. The multidimensional wave equation is solved using the multiconfiguration time-dependent Hartree (MCTDH) approach within the local approximation.

  4. X-ray structure of the metcyano form of dehaloperoxidase from Amphitrite ornata: evidence for photoreductive dissociation of the iron-cyanide bond

    SciTech Connect

    de Serrano, V.S.; Davis, M.F.; Gaff, J.F.; Zhang, Q.; Chen, Z.; D'Antonio, E.L.; Bowden, E.F.; Rose, R.; Franzen, S.

    2010-11-09

    X-ray crystal structures of the metcyano form of dehaloperoxidase-hemoglobin (DHP A) from Amphitrite ornata (DHPCN) and the C73S mutant of DHP A (C73SCN) were determined using synchrotron radiation in order to further investigate the geometry of diatomic ligands coordinated to the heme iron. The DHPCN structure was also determined using a rotating-anode source. The structures show evidence of photoreduction of the iron accompanied by dissociation of bound cyanide ion (CN{sup -}) that depend on the intensity of the X-ray radiation and the exposure time. The electron density is consistent with diatomic molecules located in two sites in the distal pocket of DHPCN. However, the identities of the diatomic ligands at these two sites are not uniquely determined by the electron-density map. Consequently, density functional theory calculations were conducted in order to determine whether the bond lengths, angles and dissociation energies are consistent with bound CN{sup -} or O{sub 2} in the iron-bound site. In addition, molecular-dynamics simulations were carried out in order to determine whether the dynamics are consistent with trapped CN{sup -} or O{sub 2} in the second site of the distal pocket. Based on these calculations and comparison with a previously determined X-ray crystal structure of the C73S-O{sub 2} form of DHP [de Serrano et al. (2007), Acta Cryst. D63, 1094-1101], it is concluded that CN{sup -} is gradually replaced by O{sub 2} as crystalline DHP is photoreduced at 100 K. The ease of photoreduction of DHP A is consistent with the reduction potential, but suggests an alternative activation mechanism for DHP A compared with other peroxidases, which typically have reduction potentials that are 0.5 V more negative. The lability of CN{sup -} at 100 K suggests that the distal pocket of DHP A has greater flexibility than most other hemoglobins.

  5. A new quantum isotope effect: Extreme local mode selectivity in unimolecular dissociations imposed by antagonism between dynamic propensities of educts and zero point energies of products

    NASA Astrophysics Data System (ADS)

    Hartke, B.; Manz, J.

    1990-01-01

    We predict a new quantum isotope effect for unimolecular dissociations of molecules with two equivalent but isotopically substituted bonds l (light isotope) and h (heavy isotope), e.g., HOT where l=HO and h=OT. Consider two near-degenerate local vibrational excitations of bonds l or h, with energies between the gap of product zero point energies. Dynamically, these excitations should induce preferential fissions of bonds l or h, but energetically, these decay channels are open and closed, respectively. Therefore, local excitation of bond h must be followed by extremely slow internal vibrational energy redistribution to bond l before dissociation, whereas local excitation of bond l induces direct, rapid decay. The resulting decay rates differ by many orders of magnitudes. The effect is demonstrated by fast Fourier transform propagation of representative wavepackets for a model system, HOT?H+OT. Extended applications to more excited educts HOT also confirm an effect discovered previously for HOD, i.e., local mode selective control of competing bond fissions H+OT?HOT?HO+T.

  6. Theoretical investigation on the bond dissociation enthalpies of phenolic compounds extracted from Artocarpus altilis using ONIOM(ROB3LYP/6-311++G(2df,2p):PM6) method

    NASA Astrophysics Data System (ADS)

    Thong, Nguyen Minh; Duong, Tran; Pham, Linh Thuy; Nam, Pham Cam

    2014-10-01

    Theoretical calculations have been performed to predict the antioxidant property of phenolic compounds extracted from Artocarpus altilis. The Osbnd H bond dissociation enthalpy (BDE), ionization energy (IE), and proton dissociation enthalpy (PDE) of the phenolic compounds have been computed. The ONIOM(ROB3LYP/6-311++G(2df,2p):PM6) method is able to provide reliable evaluation for the BDE(Osbnd H) in phenolic compounds. An important property of antioxidants is determined via the BDE(Osbnd H) of those compounds extracted from A. altilis. Based on the BDE(Osbnd H), compound 12 is considered as a potential antioxidant with the estimated BDE value of 77.3 kcal/mol in the gas phase.

  7. Bond Energies in Models of the Schrock Metathesis Catalyst

    SciTech Connect

    Vasiliu, Monica; Li, Shenggang; Arduengo, Anthony J.; Dixon, David A.

    2011-06-02

    Heats of formation, adiabatic and diabatic bond dissociation energies (BDEs) of the model Schrock-type metal complexes M(NH)(CRR?)(OH)? (M = Cr, Mo, W; CRR? = CH?, CHF, CF?) and MO?(OH)? compounds, and Brønsted acidities and fluoride affinities for the M(NH)(CH?)(OH) ? transition metal complexes are predicted using high level CCSD(T) calculations. The metallacycle intermediates formed by reaction of C?H4 with M(NH)-(CH?)(OH)2 and MO?(OH)? are investigated at the same level of theory. Additional corrections were added to the complete basis set limit to obtain near chemical accuracy ((1 kcal/mol). A comparison between adiabatic and diabatic BDEs is made and provides an explanation of trends in the BDEs. Electronegative groups bonded on the carbenic carbon lead to less stable Schrock-type complexes as the adiabatic BDEs ofMdCF? andMdCHF bonds are much lower than theMdCH? bonds. The Cr compounds have smaller BDEs than theWorMo complexes and should be less stable. Different M(NH)(OH)?(C?H?) and MO(OH)?(OC?H4) metallacycle intermediates are investigated, and the lowest-energy metallacycles have a square pyramidal geometry. The results show that consideration of the singlet_triplet splitting in the carbene in the initial catalyst as well as in the metal product formed by the retro [2+2] cycloaddition is a critical component in the design of an effective olefin metathesis catalyst in terms of the parent catalyst and the groups being transferred.

  8. Adhesive bonding using variable frequency microwave energy

    DOEpatents

    Lauf, R.J.; McMillan, A.D.; Paulauskas, F.L.; Fathi, Z.; Wei, J.

    1998-09-08

    Methods of facilitating the adhesive bonding of various components with variable frequency microwave energy are disclosed. The time required to cure a polymeric adhesive is decreased by placing components to be bonded via the adhesive in a microwave heating apparatus having a multimode cavity and irradiated with microwaves of varying frequencies. Methods of uniformly heating various articles having conductive fibers disposed therein are provided. Microwave energy may be selectively oriented to enter an edge portion of an article having conductive fibers therein. An edge portion of an article having conductive fibers therein may be selectively shielded from microwave energy. 26 figs.

  9. Adhesive bonding using variable frequency microwave energy

    DOEpatents

    Lauf, R.J.; McMillan, A.D.; Paulauskas, F.L.; Fathi, Z.; Wei, J.

    1998-08-25

    Methods of facilitating the adhesive bonding of various components with variable frequency microwave energy are disclosed. The time required to cure a polymeric adhesive is decreased by placing components to be bonded via the adhesive in a microwave heating apparatus having a multimode cavity and irradiated with microwaves of varying frequencies. Methods of uniformly heating various articles having conductive fibers disposed therein are provided. Microwave energy may be selectively oriented to enter an edge portion of an article having conductive fibers therein. An edge portion of an article having conductive fibers therein may be selectively shielded from microwave energy. 26 figs.

  10. Adhesive bonding using variable frequency microwave energy

    DOEpatents

    Lauf, Robert J. (Oak Ridge, TN); McMillan, April D. (Knoxville, TN); Paulauskas, Felix L. (Oak Ridge, TN); Fathi, Zakaryae (Cary, NC); Wei, Jianghua (Raleigh, NC)

    1998-01-01

    Methods of facilitating the adhesive bonding of various components with variable frequency microwave energy are disclosed. The time required to cure a polymeric adhesive is decreased by placing components to be bonded via the adhesive in a microwave heating apparatus having a multimode cavity and irradiated with microwaves of varying frequencies. Methods of uniformly heating various articles having conductive fibers disposed therein are provided. Microwave energy may be selectively oriented to enter an edge portion of an article having conductive fibers therein. An edge portion of an article having conductive fibers therein may be selectively shielded from microwave energy.

  11. Heterobimetallic complexes of rhodium dibenzotetramethylaza[14]annulene [(tmtaa)Rh-M]: formation, structures, and bond dissociation energetics.

    PubMed

    Imler, Gregory H; Peters, Garvin M; Zdilla, Michael J; Wayland, Bradford B

    2015-01-01

    A rhodium(II) dibenzotetramethylaza[14]annulene dimer ([(tmtaa)Rh]2) undergoes metathesis reactions with [CpCr(CO)3]2, [CpMo(CO)3]2, [CpFe(CO)2]2, [Co(CO)4]2, and [Mn(CO)5]2 to form (tmtaa)Rh-M complexes (M = CrCp(CO)3, MoCp(CO)3, FeCp(CO)2, Co(CO)4, or Mn(CO)5). Molecular structures were determined for (tmtaa)Rh-FeCp(CO)2, (tmtaa)Rh-Co(?-CO)(CO)3, and (tmtaa)Rh-Mn(CO)5 by X-ray diffraction. Equilibrium constants measured for the metathesis reactions permit the estimation of several (tmtaa)Rh-M bond dissociation enthalpies (Rh-Cr = 19 kcal mol(-1), Rh-Mo = 25 kcal mol(-1), and Rh-Fe = 27 kcal mol(-1)). Reactivities of the bimetallic complexes with synthesis gas to form (tmtaa)Rh-C(O)H and M-H are surveyed. PMID:25529638

  12. Formation and reshuffling of disulfide bonds in bovine serum albumin demonstrated using tandem mass spectrometry with collision-induced and electron-transfer dissociation.

    PubMed

    Rombouts, Ine; Lagrain, Bert; Scherf, Katharina A; Koehler, Peter; Delcour, Jan A

    2015-01-01

    Thermolysin hydrolyzates of freshly isolated, extensively stored (6 years, 6?°C, dry) and heated (60 min, 90?°C, in excess water) bovine serum albumin (BSA) samples were analyzed with liquid chromatography (LC) electrospray ionization (ESI) tandem mass spectrometry (MS/MS) using alternating electron-transfer dissociation (ETD) and collision-induced dissociation (CID). The positions of disulfide bonds and free thiol groups in the different samples were compared to those deduced from the crystal structure of native BSA. Results revealed non-enzymatic posttranslational modifications of cysteine during isolation, extensive dry storage, and heating. Heat-induced extractability loss of BSA was linked to the impact of protein unfolding on the involvement of specific cysteine residues in intermolecular and intramolecular thiol-disulfide interchange and thiol oxidation reactions. The here developed approach holds promise for exploring disulfide bond formation and reshuffling in various proteins under conditions relevant for chemical, biochemical, pharmaceutical and food processing. PMID:26193081

  13. Formation and reshuffling of disulfide bonds in bovine serum albumin demonstrated using tandem mass spectrometry with collision-induced and electron-transfer dissociation

    PubMed Central

    Rombouts, Ine; Lagrain, Bert; Scherf, Katharina A.; Koehler, Peter; Delcour, Jan A.

    2015-01-01

    Thermolysin hydrolyzates of freshly isolated, extensively stored (6 years, 6?°C, dry) and heated (60?min, 90?°C, in excess water) bovine serum albumin (BSA) samples were analyzed with liquid chromatography (LC) electrospray ionization (ESI) tandem mass spectrometry (MS/MS) using alternating electron-transfer dissociation (ETD) and collision-induced dissociation (CID). The positions of disulfide bonds and free thiol groups in the different samples were compared to those deduced from the crystal structure of native BSA. Results revealed non-enzymatic posttranslational modifications of cysteine during isolation, extensive dry storage, and heating. Heat-induced extractability loss of BSA was linked to the impact of protein unfolding on the involvement of specific cysteine residues in intermolecular and intramolecular thiol-disulfide interchange and thiol oxidation reactions. The here developed approach holds promise for exploring disulfide bond formation and reshuffling in various proteins under conditions relevant for chemical, biochemical, pharmaceutical and food processing. PMID:26193081

  14. High-Efficiency Recognition and Identification of Disulfide Bonded Peptides in Rat Neuropeptidome Using Targeted Electron Transfer Dissociation Tandem Mass Spectrometry.

    PubMed

    Yu, Xi; Khani, Abbas; Ye, Xueting; Petruzziello, Filomena; Gao, Huiyuan; Zhang, Xiaozhe; Rainer, Gregor

    2015-12-01

    The main goal of the present study is to develop a method to recognize and identify endogenous intrachain disulfide bonded peptide, which are rarely sequenced in current peptidomics studies. In order to achieve highly efficient detection of these peptides in a neuropeptidome analysis, we alkylated the peptides, mined the raw mass spectrometry data, and then recognized the candidates of untreated disulfide bonded peptides from unalkylated peptide extracts. After removing more than 90% features, targeted electron transfer dissociation fragmentation was performed for detecting and fragmenting disulfide bonded peptides, and even most of them were present in low abundance in the original sample. Diverse endogenous disulfide bonded peptides were then detected and sequenced, opening up new perspectives for comprehensively understanding the response of a neuropeptidome. PMID:26531061

  15. Excitation Mechanism in the Collision-Induced Dissociation of Methane Molecular Ion at Kiloelectronvolt Translational Energy

    E-print Network

    Kim, Myung Soo

    ARTICLES Excitation Mechanism in the Collision-Induced Dissociation of Methane Molecular Ion component arising from vibrational excitation and a large KER component from electronic excitation. CH4 energy content. It has been found that the collision-induced dissociation (CID) via electronic excitation

  16. Bond-Energy and Surface-Energy Calculations in Metals

    ERIC Educational Resources Information Center

    Eberhart, James G.; Horner, Steve

    2010-01-01

    A simple technique appropriate for introductory materials science courses is outlined for the calculation of bond energies in metals from lattice energies. The approach is applied to body-centered cubic (bcc), face-centered cubic (fcc), and hexagonal-closest-packed (hcp) metals. The strength of these bonds is tabulated for a variety metals and is…

  17. Tubulin Bond Energies and Microtubule Biomechanics Determined from Nanoindentation in Silico

    PubMed Central

    2015-01-01

    Microtubules, the primary components of the chromosome segregation machinery, are stabilized by longitudinal and lateral noncovalent bonds between the tubulin subunits. However, the thermodynamics of these bonds and the microtubule physicochemical properties are poorly understood. Here, we explore the biomechanics of microtubule polymers using multiscale computational modeling and nanoindentations in silico of a contiguous microtubule fragment. A close match between the simulated and experimental force–deformation spectra enabled us to correlate the microtubule biomechanics with dynamic structural transitions at the nanoscale. Our mechanical testing revealed that the compressed MT behaves as a system of rigid elements interconnected through a network of lateral and longitudinal elastic bonds. The initial regime of continuous elastic deformation of the microtubule is followed by the transition regime, during which the microtubule lattice undergoes discrete structural changes, which include first the reversible dissociation of lateral bonds followed by irreversible dissociation of the longitudinal bonds. We have determined the free energies of dissociation of the lateral (6.9 ± 0.4 kcal/mol) and longitudinal (14.9 ± 1.5 kcal/mol) tubulin–tubulin bonds. These values in conjunction with the large flexural rigidity of tubulin protofilaments obtained (18,000–26,000 pN·nm2) support the idea that the disassembling microtubule is capable of generating a large mechanical force to move chromosomes during cell division. Our computational modeling offers a comprehensive quantitative platform to link molecular tubulin characteristics with the physiological behavior of microtubules. The developed in silico nanoindentation method provides a powerful tool for the exploration of biomechanical properties of other cytoskeletal and multiprotein assemblies. PMID:25389565

  18. Free energy perturbation study of water dimer dissociation kinetics

    NASA Astrophysics Data System (ADS)

    Ming, Yi; Lai, Geeling; Tong, Chinghang; Wood, Robert H.; Doren, Douglas J.

    2004-07-01

    An efficient approach is described for using accurate ab initio calculations to determine the rates of elementary condensation and evaporation processes that lead to nucleation of aqueous aerosols. The feasibility of the method is demonstrated in an application to evaporation rates of water dimer at 230 K. The method, known as ABC-FEP (ab initio/classical free energy perturbation), begins with a calculation of the potential of mean force for the dissociation (evaporation) of small water clusters using a molecular dynamics (MD) simulation with a model potential. The free energy perturbation is used to calculate how changing from the model potential to a potential calculated from ab initio methods would alter the potential of mean force. The difference in free energy is the Boltzmann-weighted average of the difference between the ab initio and classical potential energies, with the average taken over a sample of configurations from the MD simulation. In principle, the method does not require a highly accurate model potential, though more accurate potentials require fewer configurations to achieve a small sampling error in the free energy perturbation step. To test the feasibility of obtaining accurate potentials of mean force from ab initio calculations at a modest number of configurations, the free energy perturbation method has been used to correct the errors when some standard models for bulk water (SPC, TIP4P, and TIP4P?FQ) are applied to water dimer. To allow a thorough exploration of sampling issues, a highly accurate fit to results of accurate ab initio calculations, known as SAPT-5s, as been used a proxy for the ab initio calculations. It is shown that accurate values for a point on the potential of mean force can be obtained from any of the water models using ab initio calculations at only 50 configurations. Thus, this method allows accurate simulations of small clusters without the need to develop water models specifically for clusters.

  19. Free energy perturbation study of water dimer dissociation kinetics.

    PubMed

    Ming, Yi; Lai, Geeling; Tong, Chinghang; Wood, Robert H; Doren, Douglas J

    2004-07-01

    An efficient approach is described for using accurate ab initio calculations to determine the rates of elementary condensation and evaporation processes that lead to nucleation of aqueous aerosols. The feasibility of the method is demonstrated in an application to evaporation rates of water dimer at 230 K. The method, known as ABC-FEP (ab initio/classical free energy perturbation), begins with a calculation of the potential of mean force for the dissociation (evaporation) of small water clusters using a molecular dynamics (MD) simulation with a model potential. The free energy perturbation is used to calculate how changing from the model potential to a potential calculated from ab initio methods would alter the potential of mean force. The difference in free energy is the Boltzmann-weighted average of the difference between the ab initio and classical potential energies, with the average taken over a sample of configurations from the MD simulation. In principle, the method does not require a highly accurate model potential, though more accurate potentials require fewer configurations to achieve a small sampling error in the free energy perturbation step. To test the feasibility of obtaining accurate potentials of mean force from ab initio calculations at a modest number of configurations, the free energy perturbation method has been used to correct the errors when some standard models for bulk water (SPC, TIP4P, and TIP4PFQ) are applied to water dimer. To allow a thorough exploration of sampling issues, a highly accurate fit to results of accurate ab initio calculations, known as SAPT-5s, as been used a proxy for the ab initio calculations. It is shown that accurate values for a point on the potential of mean force can be obtained from any of the water models using ab initio calculations at only 50 configurations. Thus, this method allows accurate simulations of small clusters without the need to develop water models specifically for clusters. PMID:15260604

  20. Elementary Steps of Syngas Reactions on Mo2C(001): Adsorption Thermochemistry and Bond Dissociation

    SciTech Connect

    Medford, Andrew

    2012-02-16

    Density functional theory (DFT) and ab initio thermodynamics are applied in order to investigate the most stable surface and subsurface terminations of Mo{sub 2}C(001) as a function of chemical potential and in the presence of syngas. The Mo-terminated (001) surface is then used as a model surface to evaluate the thermochemistry and energetic barriers for key elementary steps in syngas reactions. Adsorption energy scaling relations and Broensted-Evans-Polanyi relationships are established and used to place Mo{sub 2}C into the context of transition metal surfaces. The results indicate that the surface termination is a complex function of reaction conditions and kinetics. It is predicted that the surface will be covered by either C{sub 2}H{sub 2} or O depending on conditions. Comparisons to transition metals indicate that the Mo-terminated Mo{sub 2}C(001) surface exhibits carbon reactivity similar to transition metals such as Ru and Ir, but is significantly more reactive towards oxygen.

  1. Rotational spectrum, dynamics and bond energy of 2,5-dihydrofuran-krypton van der Waals complex

    NASA Astrophysics Data System (ADS)

    Velino, Biagio; Melandri, Sonia; Maris, Assimo; Favero, Paolo G.; Caminati, Walther

    The equilibrium conformation, dynamics and dissociation energy of the weakly bonded 2,5-dihydrofuran-Kr complex have been deduced from its free jet millimetre-wave spectrum. The equilibrium distance of Kr with respect to the centre of mass of the molecule is 3.61 Å, with Kr tilted 12.8o from the perpendicular to the centre of mass of the ring towards the oxygen atom. The dissociation energy is estimated from the centrifugal distortion constant DJ to be about 3.5kJ mol-1.

  2. Complexes of neon with nonaromatic ring molecules: Rotational spectrum, dynamics, and bond energy of 2,5-dihydrofuran-neon

    NASA Astrophysics Data System (ADS)

    Maris, Assimo; Favero, Paolo G.; Dell'Erba, Adele; Caminati, Walther

    1999-05-01

    The equilibrium configuration, dynamics, and dissociation energy of the very weakly bonded 2,5-dihydrofuran⋯Ne complex have been deduced from its free jet millimeter wave spectrum. The equilibrium distance of Ne with respect to the center of mass of the molecule is 3.30 Å, with Ne tilted 7.3° from the perpendicular to the center of mass of the ring toward the oxygen atom. The dissociation energy is estimated, from the centrifugal distortion constant DJ, to be ca. 1.1 kJ/mol.

  3. Potential energy surface for C2H4I2+ dissociation including spin-orbit effects

    SciTech Connect

    Siebert, Matthew R.; Aquino, Adelia J.; De Jong, Wibe A.; Granucci, Giovanni; Hase, William L.

    2012-10-24

    Previous experiments [Baer, et al. J. Phys. Chem. A 116, 2833 (2012)] have studied the dissociation of 1,2-diiodoethane radical cation (C2H4I2+•) and found a one-dimensional distribution of translational energy; an odd finding considering most product relative translational energy distributions are two-dimensional. The goal of this study is to obtain an accurate understanding of the potential energy surface (PES) topology for the unimolecular decomposition reaction C2H4I2+• - C2H4I+ + I•. This is done through comparison of many single-reference electronic structure methods, coupled-cluster single point (energy) calculations, and multi-reference calculations used to quantify spin-orbit (SO) coupling effects. We find that the structure of the C2H4I2+• reactant has a substantial effect on the role of SO coupling on the reaction energy. Both the BHandH and MP2 theories with an ECP/6-31++G** basis set, and without SO coupling corrections, provide accurate models for the reaction energetics. MP2 theory gives an unsymmetric structure with different C-I bond lengths, resulting in a SO energy for C2H4I2+• similar to that for the product I-atom and a negligible SO correction to the reaction energy. In contrast, DFT gives a symmetric structure for C2H4I2+•, similar to that of the neutral C2H4I2 parent, resulting in a substantial SO correction and increasing the reaction energy by 6.0-6.5 kcal/mol. Also, we find that for this system single point energy calculations are inaccurate, since a small change in geometry can lead to a large change in energy.

  4. Interaction geometries and energies of hydrogen bonds to C[double bond]O and C[double bond]S acceptors: a comparative study.

    PubMed

    Wood, Peter A; Pidcock, Elna; Allen, Frank H

    2008-08-01

    The occurrence, geometries and energies of hydrogen bonds from N-H and O-H donors to the S acceptors of thiourea derivatives, thioamides and thiones are compared with data for their O analogues - ureas, amides and ketones. Geometrical data derived from the Cambridge Structural Database indicate that hydrogen bonds to the C[double bond]S acceptors are much weaker than those to their C[double bond]O counterparts: van der Waals normalized hydrogen bonds to O are shorter than those to S by approximately 0.25 A. Further, the directionality of the approach of the hydrogen bond with respect to S, defined by the C[double bond]S...H angle, is in the range 102-109 degrees , much lower than the analogous C[double bond]O...H angle which lies in the range 127-140 degrees . Ab initio calculations using intermolecular perturbation theory show good agreement with the experimental results: the differences in hydrogen-bond directionality are closely reproduced, and the interaction energies of hydrogen bonds to S are consistently weaker than those to O, by approximately 12 kJ mol(-1), for each of the three compound classes. There are no CSD examples of hydrogen bonds to aliphatic thiones, (Csp(3))(2)C=S, consistent with the near-equality of the electronegativities of C and S. Thioureas and thioamides have electron-rich N substituents replacing the Csp(3) atoms. Electron delocalization involving C[double bond]S and the N lone pairs then induces a significant >C(delta+)[double bond]S(delta-) dipole, which enables the formation of the medium-strength C[double bond]S...H bonds observed in thioureas and thioamides. PMID:18641451

  5. In situ and theoretical studies for the dissociation of water on an active Ni/CeO2 catalyst: importance of strong metal-support interactions for the cleavage of O-H bonds.

    PubMed

    Carrasco, Javier; López-Durán, David; Liu, Zongyuan; Ducho?, Tomáš; Evans, Jaime; Senanayake, Sanjaya D; Crumlin, Ethan J; Matolín, Vladimir; Rodríguez, José A; Ganduglia-Pirovano, M Verónica

    2015-03-23

    Water dissociation is crucial in many catalytic reactions on oxide-supported transition-metal catalysts. Supported by experimental and density-functional theory results, the effect of the support on O?H bond cleavage activity is elucidated for nickel/ceria systems. Ambient-pressure O?1s photoemission spectra at low Ni loadings on CeO2 (111) reveal a substantially larger amount of OH groups as compared to the bare support. Computed activation energy barriers for water dissociation show an enhanced reactivity of Ni adatoms on CeO2 (111) compared with pyramidal Ni4 particles with one Ni atom not in contact with the support, and extended Ni(111) surfaces. At the origin of this support effect is the ability of ceria to stabilize oxidized Ni(2+) species by accommodating electrons in localized f-states. The fast dissociation of water on Ni/CeO2 has a dramatic effect on the activity and stability of this system as a catalyst for the water-gas shift and ethanol steam reforming reactions. PMID:25651288

  6. In-situ and theoretical studies for the dissociation of water on an active Ni/CeO? catalyst: Importance of strong metal-support interactions for the cleavage of O-H bonds

    DOE PAGESBeta

    Carrasco, Javier; Rodriguez, Jose A.; Lopez-Duran, David; Liu, Zongyuan; Duchon, Tomas; Evans, Jaime; Senanayake, Sanjaya D.; Crumlin, Ethan J.; Matolin, Vladimir; Ganduglia-Pirovano, M. Veronica

    2015-03-23

    Water dissociation is crucial in many catalytic reactions on oxide-supported transition-metal catalysts. Here, supported by experimental and density-functional theory results, we elucidate the effect of the support on O-H bond cleavage activity for nickel/ceria systems. Ambient-pressure O1s photoemission spectra at low Ni loadings on CeO?(111) reveal a substantially larger amount of OH groups as compared to the bare support. Our computed activation energy barriers for water dissociation show an enhanced reactivity of Ni adatoms on CeO?(111) compared with pyramidal Ni? particles with one Ni atom not in contact with the support, and extended Ni(111) surfaces. At the origin of thismore »support effect is the ability of ceria to stabilize oxidized Ni²? species by accommodating electrons in localized f-states. The fast dissociation of water on Ni/CeO? has a dramatic effect on the activity and stability of this system as a catalyst for the water-gas shift and ethanol steam reforming reactions.« less

  7. In-situ and theoretical studies for the dissociation of water on an active Ni/CeO? catalyst: Importance of strong metal-support interactions for the cleavage of O-H bonds

    SciTech Connect

    Carrasco, Javier; Rodriguez, Jose A.; Lopez-Duran, David; Liu, Zongyuan; Duchon, Tomas; Evans, Jaime; Senanayake, Sanjaya D.; Crumlin, Ethan J.; Matolin, Vladimir; Ganduglia-Pirovano, M. Veronica

    2015-03-23

    Water dissociation is crucial in many catalytic reactions on oxide-supported transition-metal catalysts. Here, supported by experimental and density-functional theory results, we elucidate the effect of the support on O-H bond cleavage activity for nickel/ceria systems. Ambient-pressure O1s photoemission spectra at low Ni loadings on CeO?(111) reveal a substantially larger amount of OH groups as compared to the bare support. Our computed activation energy barriers for water dissociation show an enhanced reactivity of Ni adatoms on CeO?(111) compared with pyramidal Ni? particles with one Ni atom not in contact with the support, and extended Ni(111) surfaces. At the origin of this support effect is the ability of ceria to stabilize oxidized Ni²? species by accommodating electrons in localized f-states. The fast dissociation of water on Ni/CeO? has a dramatic effect on the activity and stability of this system as a catalyst for the water-gas shift and ethanol steam reforming reactions.

  8. Dual-Regge Approach to High-Energy, Low-Mass Diffraction Dissociation

    E-print Network

    L. L. Jenkovszky; O. E. Kuprash; J. W. Lamsa; V. K. Magas; R. Orava

    2011-03-01

    A dual-Regge model with a nonlinear proton Regge trajectory in the missing mass channel, describing the experimental data on low-mass single diffraction dissociation, is constructed. Predictions for the LHC energies are given.

  9. Velocity Dependence of Charmonium Dissociation Temperature in High-Energy Nuclear Collisions

    E-print Network

    Yunpeng Liu; Nu Xu; Pengfei Zhuang

    2013-05-30

    In high-energy nuclear collisions, heavy quark potential at finite temperature controls the quarkonium production. Including the relaxation of the medium induced by the relative velocity between quarkonia and the deconfined expanding matter, the Debye screening is reduced and the quarkonium dissociation takes place at a higher temperature. As a consequence of the velocity dependent dissociation temperature, the quarkonium suppression at high transverse momentum is significantly weakened in high energy nuclear collisions at RHIC and LHC.

  10. Comparative study of the dissociation energies of Ni2 and Ni2(+)

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Partridge, Harry; Langhoff, Stephen R.

    1992-01-01

    Computations at the internally contracted averaged coupled-pair-functional level of theory yield a dissociation energy (Do) for Ni2(+) that is 0.17 eV larger than that of Ni2. This finding is consistent with the collision-induced dissociation experiments of Lian, Su, and Armentrout, but rules out the results from the resonant two-photon dissociation experiments of Lessen and Brucat, which predict that the Do value of Ni2(+) is about 1 eV larger than that of Ni2.

  11. Direct molecular simulation of nitrogen dissociation based on an ab initio potential energy surface

    NASA Astrophysics Data System (ADS)

    Valentini, Paolo; Schwartzentruber, Thomas E.; Bender, Jason D.; Nompelis, Ioannis; Candler, Graham V.

    2015-08-01

    The direct molecular simulation (DMS) approach is used to predict the internal energy relaxation and dissociation dynamics of high-temperature nitrogen. An ab initio potential energy surface (PES) is used to calculate the dynamics of two interacting nitrogen molecules by providing forces between the four atoms. In the near-equilibrium limit, it is shown that DMS reproduces the results obtained from well-established quasiclassical trajectory (QCT) analysis, verifying the validity of the approach. DMS is used to predict the vibrational relaxation time constant for N2-N2 collisions and its temperature dependence, which are in close agreement with existing experiments and theory. Using both QCT and DMS with the same PES, we find that dissociation significantly depletes the upper vibrational energy levels. As a result, across a wide temperature range, the dissociation rate is found to be approximately 4-5 times lower compared to the rates computed using QCT with Boltzmann energy distributions. DMS calculations predict a quasi-steady-state distribution of rotational and vibrational energies in which the rate of depletion of high-energy states due to dissociation is balanced by their rate of repopulation due to collisional processes. The DMS approach simulates the evolution of internal energy distributions and their coupling to dissociation without the need to precompute rates or cross sections for all possible energy transitions. These benchmark results could be used to develop new computational fluid dynamics models for high-enthalpy flow applications.

  12. Methanol Oxidative Dehydrogenation on Oxide Catalysts: Molecular and Dissociative Routes and Hydrogen Addition Energies as Descriptors of Reactivity

    SciTech Connect

    Deshlahra, Prashant; Iglesia, Enrique

    2014-11-13

    The oxidative dehydrogenation (ODH) of alkanols on oxide catalysts is generally described as involving H-abstraction from alkoxy species formed via O–H dissociation. Kinetic and isotopic data cannot discern between such routes and those involving kinetically-relevant H-abstraction from undissociated alkanols. Here, we combine such experiments with theoretical estimates of activation energies and entropies to show that the latter molecular routes prevail over dissociative routes for methanol reactions on polyoxometalate (POM) clusters at all practical reaction temperatures. The stability of the late transition states that mediate H-abstraction depend predominantly on the stability of the O–H bond formed, making H-addition energies (HAE) accurate and single-valued descriptors of reactivity. Density functional theory-derived activation energies depend linearly on HAE values at each O-atom location on clusters with a range of composition (H3PMo12, H4SiMo12, H3PW12, H4PV1Mo11, and H4PV1W11); both barriers and HAE values reflect the lowest unoccupied molecular orbital energy of metal centers that accept the electron and the protonation energy of O-atoms that accept the proton involved in the H-atom transfer. Bridging O-atoms form O–H bonds that are stronger than those of terminal atoms and therefore exhibit more negative HAE values and higher ODH reactivity on all POM clusters. For each cluster composition, ODH turnover rates reflect the reactivity-averaged HAE of all accessible O-atoms, which can be evaluated for each cluster composition to provide a rigorous and accurate predictor of ODH reactivity for catalysts with known structure. These relations together with oxidation reactivity measurements can then be used to estimate HAE values and to infer plausible structures for catalysts with uncertain active site structures.

  13. Relativistic state-specific multireference perturbation theory incorporating improved virtual orbitals: Application to the ground state single-bond dissociation.

    PubMed

    Ghosh, Anirban; Chaudhuri, Rajat K; Chattopadhyay, Sudip; Mahapatra, Uttam Sinha

    2015-10-01

    Using four-component (4c) relativistic spinors, we present a computationally economical relativistic ab initio method for molecular systems employing our recently proposed second-order state-specific multireference perturbation theory (SSMRPT) incorporating the improved virtual orbital-complete active space configuration interaction (IVO-CASCI) reference wavefunction. The resulting method, 4c-IVO-SSMRPT [calculate one state at a time] is tested in pilot calculations on the homonuclear dimers including Li(2), Na(2), K(2), Rb(2), F(2), Cl(2), and Br(2) through the computations of the ground state potential energy curves (PECs). As SSMRPT curbs intruder effects, 4c-IVO-SSMRPT is numerically stable. To our knowledge, the SSMRPT in the 4c relativistic framework has not been explored in the past. Selective spectroscopic constants that are closely related to the correct shape and accuracy of the energy surfaces have been extracted from the computed PECs. For the halogen molecules, a relativistic destabilization of the bond has been found. Relativistic and electron correlation effects need to be incorporated to get reliable estimates. Our results are in good accordance with reference theoretical and experimental data which manifests the computational accuracy and efficiency of the new 4c-IVO-SSMRPT method. The method opens for an improved description of MR systems containing heavy elements. The inexpensiveness of IVO-CASCI makes 4c-IVO-SSMRPT method promising for studies on large systems of heavy elements. PMID:26272333

  14. Accuracy of DLPNO-CCSD(T) Method for Noncovalent Bond Dissociation Enthalpies from Coinage Metal Cation Complexes.

    PubMed

    Minenkov, Yury; Chermak, Edrisse; Cavallo, Luigi

    2015-10-13

    The performance of the domain based local pair-natural orbital coupled-cluster (DLPNO-CCSD(T)) method has been tested to reproduce the experimental gas phase ligand dissociation enthalpy in a series of Cu(+), Ag(+), and Au(+) complexes. For 33 Cu(+)-noncovalent ligand dissociation enthalpies, all-electron calculations with the same method result in MUE below 2.2 kcal/mol, although a MSE of 1.4 kcal/mol indicates systematic underestimation of the experimental values. Inclusion of scalar relativistic effects for Cu either via effective core potential (ECP) or Douglass-Kroll-Hess Hamiltonian, reduces the MUE below 1.7 kcal/mol and the MSE to -1.0 kcal/mol. For 24 Ag(+)-noncovalent ligand dissociation enthalpies, the DLPNO-CCSD(T) method results in a mean unsigned error (MUE) below 2.1 kcal/mol and vanishing mean signed error (MSE). For 15 Au(+)-noncovalent ligand dissociation enthalpies, the DLPNO-CCSD(T) methods provides larger MUE and MSE, equal to 3.2 and 1.7 kcal/mol, which might be related to poor precision of the experimental measurements. Overall, for the combined data set of 72 coinage metal ion complexes, DLPNO-CCSD(T) results in a MUE below 2.2 kcal/mol and an almost vanishing MSE. As for a comparison with computationally cheaper density functional theory (DFT) methods, the routinely used M06 functional results in MUE and MSE equal to 3.6 and -1.7 kcal/mol. Results converge already at CC-PVTZ quality basis set, making highly accurate DLPNO-CCSD(T) estimates affordable for routine calculations (single-point) on large transition metal complexes of >100 atoms. PMID:26574257

  15. Partition Function and Dissociation Energy for Sc 2X5? -u

    NASA Astrophysics Data System (ADS)

    Akeby, H.; Pettersson, L. G. M.

    1993-05-01

    An improved partition function for the Sc2 dimer including eight low-lying states has been computed at the multireference internally contracted ACPF level using large, generally contracted basis sets. The experimental third-law value for the dissociation energy is recomputed using the new dimer partition function giving an experimental dissociation energy of 1.05 eV, a reduction by 0.07 eV compared with the earlier experimental value. The computed spectrum is very strongly affected by dynamical correlation so that lower-level theoretical approaches such as CASSCF are shown to give unreliable results.

  16. Distinct dissociation kinetics between ion pairs: Solvent-coordinate free-energy landscape analysis.

    PubMed

    Yonetani, Yoshiteru

    2015-07-28

    Different ion pairs exhibit different dissociation kinetics; however, while the nature of this process is vital for understanding various molecular systems, the underlying mechanism remains unclear. In this study, to examine the origin of different kinetic rate constants for this process, molecular dynamics simulations were conducted for LiCl, NaCl, KCl, and CsCl in water. The results showed substantial differences in dissociation rate constant, following the trend kLiCl < kNaCl < kKCl < kCsCl. Analysis of the free-energy landscape with a solvent reaction coordinate and subsequent rate component analysis showed that the differences in these rate constants arose predominantly from the variation in solvent-state distribution between the ion pairs. The formation of a water-bridging configuration, in which the water molecule binds to an anion and a cation simultaneously, was identified as a key step in this process: water-bridge formation lowers the related dissociation free-energy barrier, thereby increasing the probability of ion-pair dissociation. Consequently, a higher probability of water-bridge formation leads to a higher ion-pair dissociation rate. PMID:26233144

  17. Distinct dissociation kinetics between ion pairs: Solvent-coordinate free-energy landscape analysis

    NASA Astrophysics Data System (ADS)

    Yonetani, Yoshiteru

    2015-07-01

    Different ion pairs exhibit different dissociation kinetics; however, while the nature of this process is vital for understanding various molecular systems, the underlying mechanism remains unclear. In this study, to examine the origin of different kinetic rate constants for this process, molecular dynamics simulations were conducted for LiCl, NaCl, KCl, and CsCl in water. The results showed substantial differences in dissociation rate constant, following the trend kLiCl < kNaCl < kKCl < kCsCl. Analysis of the free-energy landscape with a solvent reaction coordinate and subsequent rate component analysis showed that the differences in these rate constants arose predominantly from the variation in solvent-state distribution between the ion pairs. The formation of a water-bridging configuration, in which the water molecule binds to an anion and a cation simultaneously, was identified as a key step in this process: water-bridge formation lowers the related dissociation free-energy barrier, thereby increasing the probability of ion-pair dissociation. Consequently, a higher probability of water-bridge formation leads to a higher ion-pair dissociation rate.

  18. On the Dissociation of Methyl Orange: Spectrophotometric Investigation in Aqueous Solutions from 10 to 90ºC and Theoretical Evidence for Intramolecular Dihydrogen Bonding

    SciTech Connect

    Boily, Jean F.; Seward, Terry M.

    2005-12-01

    The dissociation of methyl orange was investigated by spectrophotometry in aqueous solutions from 10 to 90°C and by quantum chemical calculations. Combined chemometric and thermodynamic analyses of the spectrophotometric data were used to simultaneously extract the thermodynamic stabilities and the spectrophotometric attributes of the dominant methyl orange species in solutions containing less than 20.00 mmol kg-1 perchloric acid and submicromolal concentrations of methyl orange. The analyses revealed the presence of only one monomeric deprotonated and one monomeric protonated species. The spectra did not reveal any evidence for the presence of tautomeric equilibria between the protonated azo and ammonium species in the experimental range studied. Thermodynamic analyses of the temperature dependent dissociation constants showed the reactions to be endothermic and enthalpy driven reaction with increasing acidity and increasing temperature. All molar absorption coefficients in the 275-375 nm range can be adequately reproduced in the 10-90°C range with a set of Gauss-Lorentz parameters and used to predict the absorption spectra for any desired condition. The dominant features of the spectrophotometric attributes of the methyl orange species could also be retrieved in Time Dependent-Density Functional Theory (TD-DFT) calculations. Topological analyses of the electron density also revealed the formation of a dihydrogen bond between the azo proton and an adjacent phenyl ring hydridic hydrogen which increases the stability of the azo molecules relative to the ammonium molecule.

  19. Ultrafast dissociation in polyhalogenated ethane: alternative mechanisms

    NASA Astrophysics Data System (ADS)

    Travnikova, O.; Nicolas, C.; Kimberg, V.; Flammini, R.; Liu, X.-J.; Patanen, M.; Svensson, S.; Miron, C.

    2014-04-01

    Dissociation, a simple unimolecular reaction, can be obscure, especially in complex molecules with numerous degrees of freedom. Here we suggest an ultrafast dissociation mechanism involving multimode dynamics evolving on the barrierless potential energy surface. The mechanism is elaborated from the analysis of the nuclear dynamics in X-ray excited molecules. It implies that in large molecules dissociation may yield to heavy fragments on very short timescales owing to the internal motion of light linkages. In particular, the rotation of the C2H4-moiety in 1-bromo-2-chloroethane leads to the dissociation of C-Cl or C-Br bonds in Cl2p or Br3d core-excited states in ~ 7 fs.

  20. The Heterolytic Dissociation of Neutral and Protonated Nitrous Acid Hong Wu and Rainer Glaser*

    E-print Network

    Glaser, Rainer

    The Heterolytic Dissociation of Neutral and Protonated Nitrous Acid Hong Wu and Rainer Glaser+ and of their dissociation products NO+ , HO- , and water were studied with the DFT methods B3LYP and MPW1PW91J/mol. The experimental heterolytic bond dissociation energy of E0 ) 917.80 kJ/mol for HONO and of H298 ) 77.3 k

  1. Diffractive dissociation in high energy pp collisions in additive quark model

    NASA Astrophysics Data System (ADS)

    Shabelski, Yu. M.; Shuvaev, A. G.

    2015-09-01

    High energy (CERN SPS and LHC) pp (pbar{p}) scattering is treated in the framework of the Additive Quark Model together with Pomeron exchange theory. Reasonable agreement with experimental data is achieved both for the elastic scattering and for the diffractive dissociation with natural parameters for the strong matter distribution inside proton.

  2. Diffractive dissociation in high energy pp collisions in Additive Quark Model

    E-print Network

    Yu. M. Shabelski; A. G. Shuvaev

    2015-04-14

    High energy (CERN SPS and LHC) $pp$ ($p\\bar p$) scattering is treated in the framework of Additive Quark Model together with Pomeron exchange theory. The reasonable agreement with experimental data is achieved both for the elastic scattering and for the diffractive dissociation with natural parameters for the strong matter distribution inside proton.

  3. Dual-Regge approach to high-energy, low-mass diffraction dissociation

    SciTech Connect

    Jenkovszky, L. L.; Kuprash, O. E.; Laemsae, J. W.; Magas, V. K.; Orava, R.

    2011-03-01

    A dual-Regge model with a nonlinear proton Regge trajectory in the missing mass (M{sub X}{sup 2}) channel, describing the experimental data on low-mass single diffraction dissociation (SDD), is constructed. Predictions for the LHC energies are given.

  4. Communication: Towards the binding energy and vibrational red shift of the simplest organic hydrogen bond: Harmonic constraints for methanol dimer

    SciTech Connect

    Heger, Matthias; Suhm, Martin A.; Mata, Ricardo A.

    2014-09-14

    The discrepancy between experimental and harmonically predicted shifts of the OH stretching fundamental of methanol upon hydrogen bonding to a second methanol unit is too large to be blamed mostly on diagonal and off-diagonal anharmonicity corrections. It is shown that a decisive contribution comes from post-MP2 electron correlation effects, which appear not to be captured by any of the popular density functionals. We also identify that the major deficiency is in the description of the donor OH bond. Together with estimates for the electronic and harmonically zero-point corrected dimer binding energies, this work provides essential constraints for a quantitative description of this simple hydrogen bond. The spectroscopic dissociation energy is predicted to be larger than 18 kJ/mol and the harmonic OH-stretching fundamental shifts by about ?121 cm{sup ?1} upon dimerization, somewhat more than in the anharmonic experiment (?111 cm{sup ?1})

  5. Kinetic Energy Distribution of H(2p) Atoms from Dissociative Excitation of H2

    NASA Technical Reports Server (NTRS)

    Ajello, Joseph M.; Ahmed, Syed M.; Kanik, Isik; Multari, Rosalie

    1995-01-01

    The kinetic energy distribution of H(2p) atoms resulting from electron impact dissociation of H2 has been measured for the first time with uv spectroscopy. A high resolution uv spectrometer was used for the measurement of the H Lyman-alpha emission line profiles at 20 and 100 eV electron impact energies. Analysis of the deconvolved 100 eV line profile reveals the existence of a narrow line peak and a broad pedestal base. Slow H(2p) atoms with peak energy near 80 meV produce the peak profile, which is nearly independent of impact energy. The wings of H Lyman-alpha arise from dissociative excitation of a series of doubly excited Q(sub 1) and Q(sub 2) states, which define the core orbitals. The fast atom energy distribution peaks at 4 eV.

  6. Ion appearance energies at electron-impact dissociative ionization of sulfur hexafluoride molecule and its fragments

    NASA Astrophysics Data System (ADS)

    Demesh, Shandor Sh.; Remeta, Eugene Yu.

    2015-07-01

    Theoretical analysis of appearance energies for SF{/k +} ( k = 0- n) ion fragments of SF6 molecule as well as F+ and F{2/+} ions at electron-impact dissociative ionization of SF n ( n = 1-6) molecules is presented. Theoretical methods of GAMESS software package were used to calculate the total energies of neutral and charged molecular and atomic fragments. The dissociative ionization process is concluded to occur via repulsive highly-excited electronic states of the SF6 molecule and its fragments, due to which the observed appearance energies exceed the theoretical values. The electron binding energies on the molecular orbitals in the SF6 molecule are compared with the ion fragment appearance energies.

  7. Do Bond Functions Help for the Calculation of Accurate Bond Energies?

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Arnold, James (Technical Monitor)

    1998-01-01

    The bond energies of 8 chemically bound diatomics are computed using several basis sets with and without bond functions (BF). The bond energies obtained using the aug-pVnZ+BF basis sets (with a correction for basis set superposition error, BSSE) tend to be slightly smaller that the results obtained using the aug-pV(n+I)Z basis sets, but slightly larger than the BSSE corrected aug-pV(n+I)Z results. The aug-cc-pVDZ+BF and aug-cc-pVTZ+BF basis sets yield reasonable estimates of bond energies, but, in most cases, these results cannot be considered highly accurate. Extrapolation of the results obtained with basis sets including bond functions appears to be inferior to the results obtained by extrapolation using atom-centered basis sets. Therefore bond functions do not appear to offer a path for obtaining highly accurate results for chemically bound systems at a lower computational cost than atom centered basis sets.

  8. A Unified Kinetics and Equilibrium Experiment: Rate Law, Activation Energy, and Equilibrium Constant for the Dissociation of Ferroin

    ERIC Educational Resources Information Center

    Sattar, Simeen

    2011-01-01

    Tris(1,10-phenanthroline)iron(II) is the basis of a suite of four experiments spanning 5 weeks. Students determine the rate law, activation energy, and equilibrium constant for the dissociation of the complex ion in acid solution and base dissociation constant for phenanthroline. The focus on one chemical system simplifies a daunting set of…

  9. Fragment appearance energies in dissociative ionization of a sulfur hexafluoride molecule by electron impact

    NASA Astrophysics Data System (ADS)

    Demesh, Sh. Sh.; Zavilopulo, A. N.; Shpenik, O. B.; Remeta, E. Yu.

    2015-06-01

    Theoretical analysis of the fragment appearance energies corresponding to possible channels of formation of SF{/k +} fragments in dissociative ionization of the SF6 molecule by an electron impact is carried out. The total energies of neutral and ion molecular and atomic fragments are calculated using the theoretical methods of the GAMESS program complex. It is concluded that apart from dissociative ionization via autoionizing repulsive electronic states of the SF6 molecule, the excitation channels for SF{/k +} fragments and F2 molecules play a significant role, which leads to higher values of the observed fragment appearance energy as compared to theoretical values. The dependence of the energy corresponding to the formation of SF{/k +} c fragments on the number k of fluorine atoms is considered.

  10. Prediction of drug candidates' sensitivity toward autoxidation: computational estimation of C-H dissociation energies of carbon-centered radicals.

    PubMed

    Andersson, Thomas; Broo, Anders; Evertsson, Emma

    2014-07-01

    A method to predict a compound's sensitivity toward autoxidation using bond dissociation energies for hydrogen abstraction is described. The methodology is based on quantum mechanics and has been validated with a small molecule test set. Through this work, it has been observed that stabilization of an incipient radical by more than a single functional group is normally required to trigger autoxidation. The method has also been used to understand salt effects, wherein protonation of a basic amine stabilizes proximal C-H bonds to autoxidation. It can be used to support understanding of autoxidation processes and can form a predictive role for propensity to form potentially genotoxic and other degradation products. An automated protocol has been developed that allows the nonspecialist to perform quantum chemical calculations. The protocol is robust to enable general usage such that drug-like molecules can be handled by the tool and give an answer in hours (up to some days) depending on the size of the molecule. The efficiency of the tool makes it possible to perform risk assessment for autoxidation of small lists of molecules and could typically be used for shortlisted candidates before drug nomination, during drug formulation development, and during due diligence for in-licensing compounds. PMID:24823496

  11. Evaluation of the Rh(II)-Rh(II) bond dissociation enthalpy for [(TMTAA)Rh]2 by 1H NMR T2 measurements: application in determining the Rh-C(O)- BDE in [(TMTAA)Rh]2C?O.

    PubMed

    Imler, Gregory H; Zdilla, Michael J; Wayland, Bradford B

    2013-10-01

    Toluene solutions of the rhodium(II) dimer of dibenzotetramethylaza[14]annulene ([(TMTAA)Rh]2; (1)) manifest an increase in the line widths for the singlet methine and methyl (1)H NMR resonances with increasing temperature that result from the rate of dissociation of the diamagnetic Rh(II)-Rh(II) bonded dimer (1) dissociating into paramagnetic Rh(II) monomers (TMTAA) Rh (2). Temperature dependence of the rates of Rh(II)-Rh(II) dissociation give the activation parameters for bond homolysis ?H(‡)(app) = 24(1) kcal mol(-1) and ?S(‡)(app) = 10 (1) cal K(-1) mol(-1) and an estimate for the Rh(II)-Rh(II) bond dissociation enthalpy (BDE) of 22 kcal mol(-1). Thermodynamic values for reaction of 1 with CO to form (TMTAA)Rh-C(O)-Rh(TMTAA) (3) ?H1° = -14 (1) kcal mol(-1), ?S1°= -30(3) cal K(-1) mol(-1)) were used in deriving a (TMTAA)Rh-C(O)- BDE of 53 kcal mol(-1). PMID:24004457

  12. High-energy single diffractive dissociation of nucleons and the 3P-model applicability range

    E-print Network

    A. A. Godizov

    2015-11-30

    The adequacy of the triple-pomeron interaction approximation (the 3P-model) for description of the high-energy single diffractive dissociation of nucleons is analyzed via application to the available experimental data on nucleon-nucleon scattering, including the recent results produced by CMS Collaboration. It is argued that the total contribution of secondary reggeon exchanges is not negligible up to the Tevatron energy.

  13. The Calculation of Accurate Metal-Ligand Bond Energies

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W.; Partridge, Harry, III; Ricca, Alessandra; Arnold, James O. (Technical Monitor)

    1997-01-01

    The optimization of the geometry and calculation of zero-point energies are carried out at the B3LYP level of theory. The bond energies are determined at this level, as well as at the CCSD(T) level using very large basis sets. The successive OH bond energies to the first row transition metal cations are reported. For most systems there has been an experimental determination of the first OH. In general, the CCSD(T) values are in good agreement with experiment. The bonding changes from mostly covalent for the early metals to mostly electrostatic for the late transition metal systems.

  14. Experimental and theoretical investigations of energy transfer and hydrogen-bond breaking in small water and HCl clusters.

    PubMed

    Samanta, Amit K; Czakó, Gábor; Wang, Yimin; Mancini, John S; Bowman, Joel M; Reisler, Hanna

    2014-08-19

    Water is one of the most pervasive molecules on earth and other planetary bodies; it is the molecule that is searched for as the presumptive precursor to extraterrestrial life. It is also the paradigm substance illustrating ubiquitous hydrogen bonding (H-bonding) in the gas phase, liquids, crystals, and amorphous solids. Moreover, H-bonding with other molecules and between different molecules is of the utmost importance in chemistry and biology. It is no wonder, then, that for nearly a century theoreticians and experimentalists have tried to understand all aspects of H-bonding and its influence on reactivity. It is somewhat surprising, therefore, that several fundamental aspects of H-bonding that are particularly important for benchmarking theoretical models have remained unexplored experimentally. For example, even the binding strength between two gas-phase water molecules has never been determined with sufficient accuracy for comparison with high-level electronic structure calculations. Likewise, the effect of cooperativity (nonadditivity) in small H-bonded networks is not known with sufficient accuracy. An even greater challenge for both theory and experiment is the description of the dissociation dynamics of H-bonded small clusters upon acquiring vibrational excitation. This is because of the long lifetimes of many clusters, which requires running classical trajectories for many nanoseconds to achieve dissociation. In this Account, we describe recent progress and ongoing research that demonstrates how the combined and complementary efforts of theory and experiment are enlisted to determine bond dissociation energies (D0) of small dimers and cyclic trimers of water and HCl with unprecedented accuracy, describe dissociation dynamics, and assess the effects of cooperativity. The experimental techniques rely on IR excitation of H-bonded X-H stretch vibrations, measuring velocity distributions of fragments in specific rovibrational states, and determining product state distributions at the pair-correlation level. The theoretical methods are based on high-level ab initio potential energy surfaces used in quantum and classical dynamical calculations. We achieve excellent agreement on D0 between theory and experiments for all of the clusters that we have compared, as well as for cooperativity in ring trimers of water and HCl. We also show that both the long-range and the repulsive parts of the potential must be involved in bond breaking. We explain why H-bonds are so resilient and hard to break, and we propose that a common motif in the breaking of cyclic trimers is the opening of the ring following transfer of one quantum of stretch excitation to form open-chain structures that are weakly bound. However, it still takes many vibrational periods to release one monomer fragment from the open-chain structures. Our success with water and HCl dimers and trimers led us to embark on a more ambitious project: studies of mixed water and HCl small clusters. These clusters eventually lead to ionization of HCl and serve as prototypes of acid dissociation in water. Measurements and calculations of such ionizations are yet to be achieved, and we are now characterizing these systems by adding monomers one at a time. We describe our completed work on the HCl-H2O dimer and mention our recent theoretical results on larger mixed clusters. PMID:25072730

  15. Picosecond IR-UV pump-probe spectroscopic study of the dynamics of the vibrational relaxation of jet-cooled phenol. II. Intracluster vibrational energy redistribution of the OH stretching vibration of hydrogen-bonded clusters.

    PubMed

    Kayano, Masakazu; Ebata, Takayuki; Yamada, Yuji; Mikami, Naohiko

    2004-04-22

    A picosecond time-resolved IR-UV pump-probe spectroscopic study has been carried out for investigating the intracluster vibrational energy redistribution (IVR) and subsequent dissociation of hydrogen-bonded clusters of phenol (C6H5OH) and partially deuterated phenol (C6D5OH, phenol-d5) with various solvent molecules. The H-bonded OH stretching vibration was pumped by a picosecond IR pulse, and the transient S1-S0 UV spectra from the pumped level as well as the redistributed levels were observed with a picosecond UV laser. Two types of hydrogen-bonded clusters were investigated with respect to the effect of the H-bonding strength on the energy flow process: the first is of a strong "sigma-type H-bond" such as phenol-(dimethyl ether)(n=1) and phenol dimer, and the second is phenol-(ethylene)(n=1) having a weak "pi-type H-bond." It was found that the population of the IR-pumped OH level exhibits a single-exponential decay, whose rate increases with the H-bond strength. On the other hand, the transient UV spectrum due to the redistributed levels showed a different time evolutions at different monitoring UV frequency. From an analysis of the time profiles of the transient UV spectra, the following three-step scheme has been proposed for describing the energy flow starting from the IVR of the initially excited H-bonded OH stretching level to the dissociation of the H bond. (1) The intramolecular vibrational energy redistribution takes place within the phenolic site, preparing a hot phenol. (2) The energy flows from the hot phenol to the intermolecular vibrational modes of the cluster. (3) Finally, the hydrogen bond dissociates. Among the three steps, the rate constant of the first step was strongly dependent on the H-bond strength, while the rate constants of the other two steps were almost independent of the H-bond strength. For the dissociation of the hydrogen bond, the observed rate constants were compared with those calculated by the Rice, Ramsperger, Kassel, and Marcus model. The result suggests that dissociation of the hydrogen bond takes place much faster than complete energy randomization within the clusters. PMID:15267651

  16. Performance of an integrated approach for prediction of bond dissociation enthalpies of phenols extracted from ginger and tea

    NASA Astrophysics Data System (ADS)

    Nam, Pham Cam; Chandra, Asit K.; Nguyen, Minh Tho

    2013-01-01

    Integration of the (RO)B3LYP/6-311++G(2df,2p) with the PM6 method into a two-layer ONIOM is found to produce reasonably accurate BDE(O-H)s of phenolic compounds. The chosen ONIOM model contains only two atoms of the breaking bond as the core zone and is able to provide reliable evaluation for BDE(O-H) for phenols and tocopherol. Deviation of calculated values from experiment is ±(1-2) kcal/mol. BDE(O-H) of several curcuminoids and flavanoids extracted from ginger and tea are computed using the proposed model. The BDE(O-H) values of enol curcumin and epigallocatechin gallate are predicted to be 83.3 ± 2.0 and 76.0 ± 2.0 kcal/mol, respectively.

  17. Compact two-electron wave function for bond dissociation and Van der Waals interactions: A natural amplitude assessment

    SciTech Connect

    Giesbertz, Klaas J. H.; Leeuwen, Robert van

    2014-05-14

    Electron correlations in molecules can be divided in short range dynamical correlations, long range Van der Waals type interactions, and near degeneracy static correlations. In this work, we analyze for a one-dimensional model of a two-electron system how these three types of correlations can be incorporated in a simple wave function of restricted functional form consisting of an orbital product multiplied by a single correlation function f?(r{sub 12}) depending on the interelectronic distance r{sub 12}. Since the three types of correlations mentioned lead to different signatures in terms of the natural orbital (NO) amplitudes in two-electron systems, we make an analysis of the wave function in terms of the NO amplitudes for a model system of a diatomic molecule. In our numerical implementation, we fully optimize the orbitals and the correlation function on a spatial grid without restrictions on their functional form. Due to this particular form of the wave function, we can prove that none of the amplitudes vanishes and moreover that it displays a distinct sign pattern and a series of avoided crossings as a function of the bond distance in agreement with the exact solution. This shows that the wave function ansatz correctly incorporates the long range Van der Waals interactions. We further show that the approximate wave function gives an excellent binding curve and is able to describe static correlations. We show that in order to do this the correlation function f?(r{sub 12}) needs to diverge for large r{sub 12} at large internuclear distances while for shorter bond distances it increases as a function of r{sub 12} to a maximum value after which it decays exponentially. We further give a physical interpretation of this behavior.

  18. Various Carbon to Carbon Bond Lengths Inter-related via the Golden Ratio, and their Linear Dependence on Bond Energies

    E-print Network

    Raji Heyrovska

    2008-09-11

    This work presents the relations between the carbon to carbon bond lengths in the single, double and triple bonds and in graphite, butadiene and benzene. The Golden ratio, which was shown to divide the Bohr radius into two parts pertaining to the charged particles, the electron and proton, and to divide inter-atomic distances into their cationic and anionic radii, also plays a role in the carbon-carbon bonds and in the ionic/polar character of those in graphite, butadiene and benzene. Further, the bond energies of the various CC bonds are shown to vary linearly with the bond lengths.

  19. How resonance assists hydrogen bonding interactions: an energy decomposition analysis.

    PubMed

    Beck, John Frederick; Mo, Yirong

    2007-01-15

    Block-localized wave function (BLW) method, which is a variant of the ab initio valence bond (VB) theory, was employed to explore the nature of resonance-assisted hydrogen bonds (RAHBs) and to investigate the mechanism of synergistic interplay between pi delocalization and hydrogen-bonding interactions. We examined the dimers of formic acid, formamide, 4-pyrimidinone, 2-pyridinone, 2-hydroxpyridine, and 2-hydroxycyclopenta-2,4-dien-1-one. In addition, we studied the interactions in beta-diketone enols with a simplified model, namely the hydrogen bonds of 3-hydroxypropenal with both ethenol and formaldehyde. The intermolecular interaction energies, either with or without the involvement of pi resonance, were decomposed into the Hitler-London energy (DeltaEHL), polarization energy (DeltaEpol), charge transfer energy (DeltaECT), and electron correlation energy (DeltaEcor) terms. This allows for the examination of the character of hydrogen bonds and the impact of pi conjugation on hydrogen bonding interactions. Although it has been proposed that resonance-assisted hydrogen bonds are accompanied with an increasing of covalency character, our analyses showed that the enhanced interactions mostly originate from the classical dipole-dipole (i.e., electrostatic) attraction, as resonance redistributes the electron density and increases the dipole moments in monomers. The covalency of hydrogen bonds, however, changes very little. This disputes the belief that RAHB is primarily covalent in nature. Accordingly, we recommend the term "resonance-assisted binding (RAB)" instead of "resonance-assisted hydrogen bonding (RHAB)" to highlight the electrostatic, which is a long-range effect, rather than the electron transfer nature of the enhanced stabilization in RAHBs. PMID:17143867

  20. Kinetic energies of fragment ions produced by dissociative photoionization of NO

    NASA Technical Reports Server (NTRS)

    Samson, J. A. R.; Angel, G. C.; Rstgi, O. P.

    1985-01-01

    The kinetic energies of ions produced by dissociative photoionization of NO have been measured at the discrete resonance lines of He (584A) and Ne (736A), and with undispersed synchrotron radiation. O sup + ions were identified with energies from 0 to approximately 0.5 eV and two groups of N sup + ions one with energy of 0.36 eV and another with energies between 0.9 and 1.5 eV, apparently produced by predissociation of the C sup 3 P 1 and B'1 sigma states respectively.

  1. Methods for associating or dissociating guest materials with a metal organic framework, systems for associating or dissociating guest materials within a series of metal organic frameworks, thermal energy transfer assemblies, and methods for transferring thermal energy

    DOEpatents

    McGrail, B. Peter; Brown, Daryl R.; Thallapally, Praveen K.

    2014-08-05

    Methods for releasing associated guest materials from a metal organic framework are provided. Methods for associating guest materials with a metal organic framework are also provided. Methods are provided for selectively associating or dissociating guest materials with a metal organic framework. Systems for associating or dissociating guest materials within a series of metal organic frameworks are provided. Thermal energy transfer assemblies are provided. Methods for transferring thermal energy are also provided.

  2. Effects of density functionals and dispersion interactions on geometries, bond energies and harmonic frequencies of Etbnd UX3 (E = N, P, CH; X = H, F, Cl)

    NASA Astrophysics Data System (ADS)

    Pandey, Krishna Kumar; Patidar, Pankaj; Patidar, Sunil Kumar; Vishwakarma, Ravi

    2014-12-01

    Quantum-chemical calculations have been performed to evaluate the geometries, bonding nature and harmonic frequencies of the compounds [Etbnd UX3] at DFT, DFT-D3, DFT-D3(BJ) and DFT-dDSc levels using different density functionals BP86, BLYP, PBE, revPBE, PW91, TPSS and M06-L. The stretching frequency of Utbnd N bond in [Ntbnd UF3] calculated with DFT/BLYP closely resembles with the experimental value. The performance of different density functionals for accurate Utbnd N vibrational frequencies follows the order BLYP > revPBE > BP86 > PW91 > TPSS > PBE > M06-L. The BLYP functional gives accurate value of the Utbnd E bond distances. The uranium atom in the studied compounds [Etbnd UX3] is positively charged. Upon going from [Etbnd UF3] to [Etbnd UCl3], the partial Hirshfeld charge on uranium atom decreases because of the lower electronegativity of chlorine compared to flourine. The Gopinathan-Jug bond order for Utbnd E bonds ranges from 2.90 to 3.29. The Utbnd E bond dissociation energies vary with different density functionals as M06-L < TPSS < BLYP < revPBE < BP86 < PBE ? PW91. The orbital interactions ?Eorb, in all studied compounds [Etbnd UX3] are larger than the electrostatic interaction ?Eelstat, which means the Utbnd N bonds in these compound have greater degree of covalent character (in the range 63.8-77.2%). The Usbnd E ?-bonding interaction is the dominant bonding interaction in the nitride and methylidyne complexes while it is weaker in [Ptbnd UX3]. The dispersion energy contributions to the total bond dissociation energies are rather small. Compared to the Grimme's D3(BJ) corrections, the Corminboeuf's dispersion corrections are larger with metaGGA functionals (TPSS, M06-L) while smaller with GGA functionals.

  3. Effects of density functionals and dispersion interactions on geometries, bond energies and harmonic frequencies of EUX3 (E=N, P, CH; X=H, F, Cl).

    PubMed

    Pandey, Krishna Kumar; Patidar, Pankaj; Patidar, Sunil Kumar; Vishwakarma, Ravi

    2014-12-10

    Quantum-chemical calculations have been performed to evaluate the geometries, bonding nature and harmonic frequencies of the compounds [EUX3] at DFT, DFT-D3, DFT-D3(BJ) and DFT-dDSc levels using different density functionals BP86, BLYP, PBE, revPBE, PW91, TPSS and M06-L. The stretching frequency of UN bond in [NUF3] calculated with DFT/BLYP closely resembles with the experimental value. The performance of different density functionals for accurate UN vibrational frequencies follows the order BLYP>revPBE>BP86>PW91>TPSS>PBE>M06-L. The BLYP functional gives accurate value of the UE bond distances. The uranium atom in the studied compounds [EUX3] is positively charged. Upon going from [EUF3] to [EUCl3], the partial Hirshfeld charge on uranium atom decreases because of the lower electronegativity of chlorine compared to flourine. The Gopinathan-Jug bond order for UE bonds ranges from 2.90 to 3.29. The UE bond dissociation energies vary with different density functionals as M06-Lbonds in these compound have greater degree of covalent character (in the range 63.8-77.2%). The UE ?-bonding interaction is the dominant bonding interaction in the nitride and methylidyne complexes while it is weaker in [PUX3]. The dispersion energy contributions to the total bond dissociation energies are rather small. Compared to the Grimme's D3(BJ) corrections, the Corminboeuf's dispersion corrections are larger with metaGGA functionals (TPSS, M06-L) while smaller with GGA functionals. PMID:25014545

  4. Theoretical study of the dissociation energy and the red and violet band systems of CN

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Taylor, Peter R.

    1988-01-01

    The dissociation energy D0 is determined here for the CN ground-state and radiative lifetimes for the A 2Pi and B 2Sigma(+) states. D0 is found to be 7.65 + or - 0.06 eV, corresponding to Delta Hf (CN) = 105.3 + or - 1.5 kcal/mole. These results are compared with current experimental estimates and with previous theoretical calculations.

  5. Determination of the long-range potential and dissociation energy g state of Na2

    E-print Network

    Le Roy, Robert J.

    Determination of the long-range potential and dissociation energy of the 1 3 g state of Na2 Bing of Waterloo, Waterloo, Ontario, N2L 3G1 Canada Received 6 June 1995; accepted 26 July 1995 The 1 3 g state, 39, 50­55, 57, 58, and 62 of the 1 3 g state of Na2 have been experi- mentally observed by the high

  6. The role of cold carriers and the multiple-carrier process of Si-H bond dissociation for hot-carrier degradation in n- and p-channel LDMOS devices

    NASA Astrophysics Data System (ADS)

    Sharma, Prateek; Tyaginov, Stanislav; Jech, Markus; Wimmer, Yannick; Rudolf, Florian; Enichlmair, Hubert; Park, Jong-Mun; Ceric, Hajdin; Grasser, Tibor

    2016-01-01

    We apply our hot-carrier degradation (HCD) model, which uses the information about the carrier energy distribution, to represent HCD data measured in n- and p-channel LDMOS transistors. In the first version of our model we use the spherical harmonics expansion approach to solve the Boltzmann transport equation (BTE), while in the second version we employ the drift-diffusion scheme. In the latter case the carrier energy distribution function is approximated by an analytic expression with parameters found using the drift-diffusion scheme. The model, which has already been verified with nLDMOS transistors, is used to represent the carrier distribution functions, interface state density profiles, and changes of the drain currents vs. stress time in pLDMOS transistor. Particular attention is paid to study the role of the cold fraction of the carrier ensemble. We check the validity of the model by neglecting the effect of cold carriers in HCD modeling in the case of nLDMOS devices stressed at high voltages. In our model, cold carriers are represented by the corresponding term in the analytic formula for the carrier distribution function as well as by the multiple-carrier process of the Si-H bond dissociation. We show that even in high-voltage devices stressed at high drain voltages the thermalized carriers still have a substantial contribution to HCD.

  7. Strength of Chemical Bonds

    NASA Technical Reports Server (NTRS)

    Christian, Jerry D.

    1973-01-01

    Students are not generally made aware of the extraordinary magnitude of the strengths of chemical bonds in terms of the forces required to pull them apart. Molecular bonds are usually considered in terms of the energies required to break them, and we are not astonished at the values encountered. For example, the Cl2 bond energy, 57.00 kcal/mole, amounts to only 9.46 x 10(sup -20) cal/molecule, a very small amount of energy, indeed, and impossible to measure directly. However, the forces involved in realizing the energy when breaking the bond operate over a very small distance, only 2.94 A, and, thus, f(sub ave) approx. equals De/(r - r(sub e)) must be very large. The forces involved in dissociating the molecule are discussed in the following. In consideration of average forces, the molecule shall be assumed arbitrarily to be dissociated when the atoms are far enough separated so that the potential, relative to that of the infinitely separated atoms, is reduced by 99.5% from the potential of the molecule at the equilibrium bond length (r(sub e)) for Cl2 of 1.988 A this occurs at 4.928 A.

  8. Response to the Comment by J. Grunenberg on "The Nature of the Fourth Bond in the Ground State of C2 : The Quadruple Bond Conundrum''.

    PubMed

    Shaik, Sason; Danovich, David; Hiberty, Philippe C

    2015-11-16

    The quadruple bond structure in C2 emerges from solid quantum-chemical calculations and won't go away! There is no mystery in the rather small bond dissociation energy, and this cannot constitute the reason to reconsider the whole concept of quadruple bonding. PMID:26482677

  9. The Dissociation Energies of AlH2 and AlAr

    NASA Technical Reports Server (NTRS)

    Ricca, Alessandra; Partridge, Harry; Bauschlicher, Charles W., Jr.; Visscher, Luuk; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    The D(sub 0) values for AlH2 and AlAr are computed using the coupled cluster approach in conjunction with large basis sets. Basis set superposition and spin-orbit effects are accounted for as they are sizeable due to the small binding energy. The computed dissociation energy for AlAr is 101 /cm , which is 83% of the experimental value (122.4/ cm). Our best estimate for the H2 binding energy in AlH2 is 40 +/- 28 /cm.

  10. An improved potential energy surface and multi-temperature quasiclassical trajectory calculations of N2 + N2 dissociation reactions

    NASA Astrophysics Data System (ADS)

    Bender, Jason D.; Valentini, Paolo; Nompelis, Ioannis; Paukku, Yuliya; Varga, Zoltan; Truhlar, Donald G.; Schwartzentruber, Thomas; Candler, Graham V.

    2015-08-01

    Accurate modeling of high-temperature hypersonic flows in the atmosphere requires consideration of collision-induced dissociation of molecular species and energy transfer between the translational and internal modes of the gas molecules. Here, we describe a study of the N2 + N2?N2 + 2N and N2 + N2?4N nitrogen dissociation reactions using the quasiclassical trajectory (QCT) method. The simulations used a new potential energy surface for the N4 system; the surface is an improved version of one that was presented previously. In the QCT calculations, initial conditions were determined based on a two-temperature model that approximately separates the translational-rotational temperature from the vibrational temperature of the N2 diatoms. Five values from 8000 K to 30 000 K were considered for each of the two temperatures. Over 2.4 × 109 trajectories were calculated. We present results for ensemble-averaged dissociation rate constants as functions of the translational-rotational temperature T and the vibrational temperature Tv. The rate constant depends more strongly on T when Tv is low, and it depends more strongly on Tv when T is low. Quasibound reactant states contribute significantly to the rate constants, as do exchange processes at higher temperatures. We discuss two sets of runs in detail: an equilibrium test set in which T = Tv and a nonequilibrium test set in which Tv < T. In the equilibrium test set, high-v and moderately-low-j molecules contribute most significantly to the overall dissociation rate, and this state specificity becomes stronger as the temperature decreases. Dissociating trajectories tend to result in a major loss of vibrational energy and a minor loss of rotational energy. In the nonequilibrium test set, as Tv decreases while T is fixed, higher-j molecules contribute more significantly to the dissociation rate, dissociating trajectories tend to result in a greater rotational energy loss, and the dissociation probability's dependence on v weakens. In this way, as Tv decreases, rotational energy appears to compensate for the decline in average vibrational energy in promoting dissociation. In both the equilibrium and nonequilibrium test sets, in every case, the average total internal energy loss in the dissociating trajectories is between 10.2 and 11.0 eV, slightly larger than the equilibrium potential energy change of N2 dissociation.

  11. An improved potential energy surface and multi-temperature quasiclassical trajectory calculations of N2 + N2 dissociation reactions.

    PubMed

    Bender, Jason D; Valentini, Paolo; Nompelis, Ioannis; Paukku, Yuliya; Varga, Zoltan; Truhlar, Donald G; Schwartzentruber, Thomas; Candler, Graham V

    2015-08-01

    Accurate modeling of high-temperature hypersonic flows in the atmosphere requires consideration of collision-induced dissociation of molecular species and energy transfer between the translational and internal modes of the gas molecules. Here, we describe a study of the N2 + N2?N2 + 2N and N2 + N2?4N nitrogen dissociation reactions using the quasiclassical trajectory (QCT) method. The simulations used a new potential energy surface for the N4 system; the surface is an improved version of one that was presented previously. In the QCT calculations, initial conditions were determined based on a two-temperature model that approximately separates the translational-rotational temperature from the vibrational temperature of the N2 diatoms. Five values from 8000 K to 30,000 K were considered for each of the two temperatures. Over 2.4 × 10(9) trajectories were calculated. We present results for ensemble-averaged dissociation rate constants as functions of the translational-rotational temperature T and the vibrational temperature T(v). The rate constant depends more strongly on T when T(v) is low, and it depends more strongly on T(v) when T is low. Quasibound reactant states contribute significantly to the rate constants, as do exchange processes at higher temperatures. We discuss two sets of runs in detail: an equilibrium test set in which T = T(v) and a nonequilibrium test set in which T(v) < T. In the equilibrium test set, high-v and moderately-low-j molecules contribute most significantly to the overall dissociation rate, and this state specificity becomes stronger as the temperature decreases. Dissociating trajectories tend to result in a major loss of vibrational energy and a minor loss of rotational energy. In the nonequilibrium test set, as T(v) decreases while T is fixed, higher-j molecules contribute more significantly to the dissociation rate, dissociating trajectories tend to result in a greater rotational energy loss, and the dissociation probability's dependence on v weakens. In this way, as T(v) decreases, rotational energy appears to compensate for the decline in average vibrational energy in promoting dissociation. In both the equilibrium and nonequilibrium test sets, in every case, the average total internal energy loss in the dissociating trajectories is between 10.2 and 11.0 eV, slightly larger than the equilibrium potential energy change of N2 dissociation. PMID:26254650

  12. Photo-mechanical energy conversion using polymer brush dissociation

    E-print Network

    J. M. Deutsch

    2013-01-03

    A device is investigated that continuously and directly converts light into mechanical energy, using polymers and photodissociation. A polymer brush tethered to a surface, is brought into contact with a parallel plate a small distance above it that contains reaction sites where photodissociation of bound polymer and light can occur. Under the appropriate conditions, the collective effect of these polymers is to apply a force parallel to the plates, converting incoming light into mechanical work. Numerical work is carried out to understand this effect, a three dimensional Langevin simulation, solution to the Fokker Planck equation, and a one dimensional Monte Carlo simulation. Theoretical analysis of the Fokker Planck equation is used to study a model where equilibration of the unbound state occurs and equilibration to a metastable equilibrium is achieved in the bound state. It is shown that the work per cycle can be made much larger than the thermal energy but at the expense of requiring a greatly diminished photodissociation rate. Parameters are discussed in order optimize mechanical energy conversion.

  13. Bond order analysis based on the Laplacian of electron density in fuzzy overlap space.

    PubMed

    Lu, Tian; Chen, Feiwu

    2013-04-11

    Bond order is an important concept for understanding the nature of a chemical bond. In this work, we propose a novel definition of bond order, called the Laplacian bond order (LBO), which is defined as a scaled integral of negative parts of the Laplacian of electron density in fuzzy overlap space. Many remarkable features of LBO are exemplified by numerous structurally diverse molecules. It is shown that LBO has a direct correlation with the bond polarity, the bond dissociation energy, and the bond vibrational frequency. The dissociation behavior of LBO of the N-N bond in N2 has been studied. Effects of the basis sets, theoretic methods, and geometrical conformations on LBO have also been investigated. Through comparisons, we discussed in details similarities and discrepancies among LBO, Mayer bond order, natural localized molecular orbital bond order, fuzzy overlap population, and electron density at bond critical points. PMID:23514314

  14. How Well Can New-Generation Density Functionals Describe the Energetics of Bond-Dissociation Reactions Producing Radicals?

    SciTech Connect

    Zhao, Yan; Truhlar, Donald G.

    2008-02-14

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The performance of various density functionals has been tested for three sets of reaction energies involving radicals. It is shown that two recently designed functionals, M05-2X and M06-2X, provide the best performance. These functionals provide useful and affordable methods for future mechanistic studies involving organic radicals.

  15. Insights into the free-energy dependence of intramolecular dissociative electron transfers.

    PubMed

    Antonello, Sabrina; Crisma, Marco; Formaggio, Fernando; Moretto, Alessandro; Taddei, Ferdinando; Toniolo, Claudio; Maran, Flavio

    2002-09-25

    To study the relationship between rate and driving force of intramolecular dissociative electron transfers, a series of donor-spacer-acceptor (D-Sp-A) systems has been devised and synthesized. cis-1,4-Cyclohexanedyil and a perester functional group were kept constant as the spacer and acceptor, respectively. By changing the aryl substituents of the phthalimide moiety, which served as the donor, the driving force could be varied by 0.74 eV. X-ray diffraction crystallography and ab initio conformational calculations pointed to D-Sp-A molecules having the cis-(cyclohexane) equatorial(phthalimido)-axial(perester) conformation and the same D/A orientation. The intramolecular dissociative electron-transfer process was studied by electrochemical means in N,N-dimethylformamide, in comparison with thermodynamic and kinetic information obtained with models of the acceptor and the donor. The intramolecular process consists of the electron transfer from the electrochemically generated phthalimide-moiety radical anion to the peroxide functional group. The electrochemical analysis provided clear evidence of a concerted dissociative electron-transfer mechanism, leading to the cleavage of the O-O bond. Support for this mechanism was obtained by ab initio MO calculations, which provided information about the LUMO of the acceptor and the SOMO of the donor. The intramolecular rate constants were determined and compared with the corresponding intermolecular values, the latter data being obtained by using the model molecules. As long as the effective location of the centroid of the donor SOMO does not vary significantly by changing the aryl substituent(s), the intramolecular dissociative electron transfer obeys the same main rules already highlighted for the corresponding intermolecular process. On the other hand, introduction of a nitro group drags the SOMO away from the acceptor, and consequently, the intramolecular rate drops by as much as 1.6 orders of magnitude from the expected value. Therefore, a larger solvent reorganization than for intermolecular electron transfers and the effective D/A distance and thus electronic coupling must be taken into account for quantitative predictions of intramolecular rates. PMID:12236765

  16. Re-evaluation of the bond length-bond strength rule: The stronger bond is not always the shorter bond.

    PubMed

    Kraka, Elfi; Setiawan, Dani; Cremer, Dieter

    2016-01-01

    A set of 42 molecules with N-F, O-F, N-Cl, P-F, and As-F bonds has been investigated in the search for potential bond anomalies, which lead to reverse bond length-bond strength (BLBS) relationships. The intrinsic strength of each bond investigated has been determined by the local stretching force constant obtained at the CCSD(T)/aug-cc-pVTZ level of theory. N-F or O-F bond anomalies were found for fluoro amine radicals, fluoro amines, and fluoro oxides, respectively. A rationale for the deviation from the normal Badger-type inverse BLBS relation is given and it is shown that electron withdrawal accompanied by strong orbital contraction and bond shortening is one of the prerequisites for a bond anomaly. In the case of short electron-rich bonds such as N-F or O-F, anomeric delocalization of lone pair electrons in connection with lone pair repulsion are decisive whether a bond anomaly can be observed. This is quantitatively assessed with the help of the CCSD(T) local stretching force constants, CCSD(T) charge distributions, and G4 bond dissociation energies. Bond anomalies are not found for fluoro phosphines and fluoro arsines because the bond weakening effects are no longer decisive. © 2015 Wiley Periodicals, Inc. PMID:26515027

  17. Effective coordination number: A simple indicator of activation energies for NO dissociation on Rh(100) surfaces

    SciTech Connect

    Ghosh, Prasenjit; Pushpa, Raghani; Gironcoli, Stefano de

    2009-12-15

    We have used density-functional theory to compute the activation energy for the dissociation of NO on two physical and two hypothetical systems: unstrained and strained Rh(100) surfaces and monolayers of Rh atoms on strained and unstrained MgO(100) surfaces. We find that the activation energy, relative to the gas phase, is reduced when a monolayer of Rh is placed on MgO, due both to the chemical nature of the substrate and the strain imposed by the substrate. The former effect is the dominant one, though both effects are of the same order of magnitude. We find that both effects are encapsulated in a simple quantity which we term as the 'effective coordination number'(n{sub e}); the activation energy is found to vary linearly with n{sub e}. We have compared the performance of n{sub e} as a predictor of activation energy of NO dissociation on the above-mentioned Rh surfaces with the two well-established indicators, namely, the position of the d-band center and the coadsorption energy of N and O. We find that for the present systems n{sub e} performs as well as the other two indicators.

  18. Low energy electron induced cytosine base release in 2?-deoxycytidine-3?-monophosphate via glycosidic bond cleavage: A time-dependent wavepacket study

    SciTech Connect

    Bhaskaran, Renjith; Sarma, Manabendra

    2014-09-14

    Low energy electron (LEE) induced cytosine base release in a selected pyrimidine nucleotide, viz., 2?-deoxycytidine-3?-monophosphate is investigated using ab initio electronic structure methods and time dependent quantum mechanical calculations. It has been noted that the cytosine base scission is comparatively difficult process than the 3? C–O bond cleavage from the lowest ?{sup *} shape resonance in energy region <1 eV. This is mainly due to the high activation energy barrier associated with the electron transfer from the ?{sup *} orbital of the base to the ?{sup *} orbital of the glycosidic N–C bond. In addition, the metastable state formed after impinging LEE (0–1 eV) has very short lifetime (10 fs) which may decay in either of the two competing auto-detachment or dissociation process simultaneously. On the other hand, the selected N–C mode may cleave to form the cytosine base anion at higher energy regions (>2 eV) via tunneling of the glycosidic bond. Resonance states generated within this energy regime will exist for a duration of ?35–55 fs. Comparison of salient features of the two dissociation events, i.e., 3? C–O single strand break and glycosidic N–C bond cleavage in 3?-dCMPH molecule are also provided.

  19. Low energy electron induced cytosine base release in 2'-deoxycytidine-3'-monophosphate via glycosidic bond cleavage: A time-dependent wavepacket study

    NASA Astrophysics Data System (ADS)

    Bhaskaran, Renjith; Sarma, Manabendra

    2014-09-01

    Low energy electron (LEE) induced cytosine base release in a selected pyrimidine nucleotide, viz., 2'-deoxycytidine-3'-monophosphate is investigated using ab initio electronic structure methods and time dependent quantum mechanical calculations. It has been noted that the cytosine base scission is comparatively difficult process than the 3' C-O bond cleavage from the lowest ?* shape resonance in energy region <1 eV. This is mainly due to the high activation energy barrier associated with the electron transfer from the ?* orbital of the base to the ?* orbital of the glycosidic N-C bond. In addition, the metastable state formed after impinging LEE (0-1 eV) has very short lifetime (10 fs) which may decay in either of the two competing auto-detachment or dissociation process simultaneously. On the other hand, the selected N-C mode may cleave to form the cytosine base anion at higher energy regions (>2 eV) via tunneling of the glycosidic bond. Resonance states generated within this energy regime will exist for a duration of ˜35-55 fs. Comparison of salient features of the two dissociation events, i.e., 3' C-O single strand break and glycosidic N-C bond cleavage in 3'-dCMPH molecule are also provided.

  20. Photodissociation of CH2. I - Potential energy surfaces of the dissociation into CH and H

    NASA Technical Reports Server (NTRS)

    Bearda, Robert A.; Van Hemert, Marc C.; Van Dishoeck, Ewine F.

    1992-01-01

    The possible photodissociation pathways of the CH2 radical are studied using ab initio multireference configuration-interaction methods, and accurate photodissociation cross sections and branching ratios for the production of CH + H and C + H2 are obtained. Potential energy surfaces were calculated using the Wuppertal-Bonn self-consistent field plus a multireference single and double-excitation configuration interaction package of programs. Two-dimensional potential energy surfaces of the ten lowest triplet states correlating with the seven lowest states of CH were calculated as functions of bond angle and one C-H bond distance, keeping the other C-H bond distance fixed at the equilibrium CH2 value.

  1. DISSOCIATION CONNECTIONIST

    E-print Network

    Bullinaria, John

    DISSOCIATION IN CONNECTIONIST SYSTEMS John A. Bullinaria (School of Computer Science, only single dissociations were found. Each damage type results in the activation feeding into #12; each. We see this in Figure 1: clear dissociations with the regulars more robust than frequency matched

  2. Students' Interdisciplinary Reasoning about "High-Energy Bonds" and ATP

    E-print Network

    Dreyfus, Benjamin W; Sawtelle, Vashti; Svoboda, Julia; Turpen, Chandra; Redish, Edward F

    2012-01-01

    Students' sometimes contradictory ideas about ATP (adenosine triphosphate) and the nature of chemical bonds have been studied in the biology and chemistry education literatures, but these topics are rarely part of the introductory physics curriculum. We present qualitative data from an introductory physics course for undergraduate biology majors that seeks to build greater interdisciplinary coherence and therefore includes these topics. In these data, students grapple with the apparent contradiction between the energy released when the phosphate bond in ATP is broken and the idea that an energy input is required to break a bond. We see that students' perceptions of how each scientific discipline bounds the system of interest can influence how they justify their reasoning about a topic that crosses disciplines. This has consequences for a vision of interdisciplinary education that respects disciplinary perspectives while bringing them into interaction in ways that demonstrate consistency amongst the perspectiv...

  3. A Comparison of Energy-Resolved Vibrational Activation/Dissociation Characteristics of Protonated and Sodiated High Mannose N-Glycopeptides

    NASA Astrophysics Data System (ADS)

    Aboufazeli, Forouzan; Kolli, Venkata; Dodds, Eric D.

    2015-04-01

    Fragmentation of glycopeptides in tandem mass spectrometry (MS/MS) plays a pivotal role in site-specific protein glycosylation profiling by allowing specific oligosaccharide compositions and connectivities to be associated with specific loci on the corresponding protein. Although MS/MS analysis of glycopeptides has been successfully performed using a number of distinct ion dissociation methods, relatively little is known regarding the fragmentation characteristics of glycopeptide ions with various charge carriers. In this study, energy-resolved vibrational activation/dissociation was examined via collision-induced dissociation for a group of related high mannose tryptic glycopeptides as their doubly protonated, doubly sodiated, and hybrid protonated sodium adduct ions. The doubly protonated glycopeptide ions with various compositions were found to undergo fragmentation over a relatively low but wide range of collision energies compared with the doubly sodiated and hybrid charged ions, and were found to yield both glycan and peptide fragmentation depending on the applied collision energy. By contrast, the various doubly sodiated glycopeptides were found to dissociate over a significantly higher but narrow range of collision energies, and exhibited only glycan cleavages. Interestingly, the hybrid protonated sodium adduct ions were consistently the most stable of the precursor ions studied, and provided fragmentation information spanning both the glycan and the peptide moieties. Taken together, these findings illustrate the influence of charge carrier over the energy-resolved vibrational activation/dissociation characteristics of glycopeptides, and serve to suggest potential strategies that exploit the analytically useful features uniquely afforded by specific charge carriers or combinations thereof.

  4. Does Nitric Acid Dissociate at the Aqueous Solution Surface?

    SciTech Connect

    Lewis, Tanza; Winter, Berndt; Stern, Abraham C.; Baer, Marcel D.; Mundy, Christopher J.; Tobias, Douglas J.; Hemminger, J. C.

    2011-11-03

    Nitric acid is a prevalent component of atmospheric aerosols, and the extent of nitric acid dissociation at aqueous interfaces is relevant to its role in heterogeneous atmospheric chemistry. Several experimental and theoretical studies have suggested that the extent of dissociation of nitric acid near aqueous interfaces is less than in bulk solution. Here, dissociation of HNO3 at the surface of aqueous nitric acid is quantified using X-ray photoelectron spectroscopy of the nitrogen local electronic structure. The relative amounts of undissociated HNO3(aq) and dissociated NO3-(aq) are identified by the distinguishable N1s core-level photoelectron spectra of the two species, and we determine the degree of dissociation, ?int, in the interface (the first ~3 layers of solution) as a function of HNO3 concentration. Our measurements show that dissociation is decreased by approximately 20% near the solution interface compared with bulk, and furthermore that dissociation occurs even in the top-most solution layer. The experimental results are supported by first-principles MD simulations, which show that hydrogen-bonds between HNO3 and water molecules at the solution surface stabilize the molecular form at low concentration, in analogy to the stabilization of molecular HNO3 that occurs in bulk solution at high concentration. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.

  5. Storing Renewable Energy in Chemical Bonds

    SciTech Connect

    Helm, Monte; Bullock, Morris

    2013-03-27

    With nearly 7 billion people, the world's population is demanding more electricity every year. Improved technologies are bringing wind and solar power to our electrical grid. However, wind turbines and solar panels only work when the wind blows or the sun shines. PNNL scientists discuss catalysis approaches for storing and releasing energy on demand.

  6. Storing Renewable Energy in Chemical Bonds

    ScienceCinema

    Helm, Monte; Bullock, Morris

    2014-06-13

    With nearly 7 billion people, the world's population is demanding more electricity every year. Improved technologies are bringing wind and solar power to our electrical grid. However, wind turbines and solar panels only work when the wind blows or the sun shines. PNNL scientists discuss catalysis approaches for storing and releasing energy on demand.

  7. Homolytic S-S bond dissociation of 11 bis(thiocarbonyl)disulfides R-C(=S)-S-S-C(=S)R and prediction of a novel rubber vulcanization accelerator.

    PubMed

    Mak, Adrian Matthew; Steudel, Ralf; Wong, Ming Wah

    2008-06-01

    The structures and energetics of eight substituted bis(thiocarbonyl)disulfides (RCS(2))(2), their associated radicals RCS(2)(*), and their coordination compounds with a lithium cation have been studied at the G3X(MP2) level of theory for R = H, Me, F, Cl, OMe, SMe, NMe(2), and PMe(2). The effects of substituents on the dissociation of (RCS(2))(2) to RCS(2)(*) were analyzed using isodesmic stabilization reactions. Electron-donating groups with an unshared pair of electrons have a pronounced stabilization effect on both (RCS(2))(2) and RCS(2)(*). The S-S bond dissociation enthalpy of tetramethylthiuram disulfide (TMTD, R = NMe(2)) is the lowest in the above series (155 kJ mol(-1)), attributed to the particular stability of the formed Me(2)NCS(2)(*) radical. Both (RCS(2))(2) and the fragmented radicals RCS(2)(*) form stable chelate complexes with a Li(+) cation. The S-S homolytic bond cleavage in (RCS(2))(2) is facilitated by the reaction [Li(RCS(2))(2)](+)+Li(+)-->2 [Li(RCS(2))](*+). Three other substituted bis(thiocarbonyl) disulfides with the unconventional substituents R = OSF(5), Gu(1), and Gu(2) have been explored to find suitable alternative rubber vulcanization accelerators. Bis(thiocarbonyl)disulfide with a guanidine-type substituent, (Gu(1)CS(2))(2), is predicted to be an effective accelerator in sulfur vulcanization of rubber. Compared to TMTD, (Gu(1)CS(2))(2) is calculated to have a lower bond dissociation enthalpy and smaller associated barrier for the S-S homolysis. PMID:18418826

  8. Bond length and local energy density property connections for non-transition-metal oxide-bonded interactions.

    PubMed

    Gibbs, G V; Spackman, M A; Jayatilaka, D; Rosso, K M; Cox, D F

    2006-11-01

    For a variety of molecules and earth materials, the theoretical local kinetic energy density, G(r(c)), increases and the local potential energy density, V(r(c)), decreases as the M-O bond lengths (M = first- and second-row metal atoms bonded to O) decrease and the electron density, rho(r(c)), accumulates at the bond critical points, r(c). Despite the claim that the local kinetic energy density per electronic charge, G(r(c))/rho(r(c)), classifies bonded interactions as shared interactions when less than unity and closed-shell when greater, the ratio was found to increase from 0.5 to 2.5 au as the local electronic energy density, H(r(c)) = G(r(c)) + V(r(c)), decreases and becomes progressively more negative. The ratio appears to be a measure of the character of a given M-O bonded interaction, the greater the ratio, the larger the value of rho(r(c)), the smaller the coordination number of the M atom and the more shared the bonded interaction. H(r(c))/rho(r(c)) versus G(r(c))/rho(r(c)) scatter diagrams categorize the M-O bonded interactions into domains with the local electronic energy density per electron charge, H(r(c))/rho(r(c)), tending to decrease as the electronegativity differences for the bonded pairs of atoms decrease. The values of G(r(c)) and V(r(c)), estimated with a gradient-corrected electron gas theory expression and the local virial theorem, are in good agreement with theoretical values, particularly for the bonded interactions involving second-row M atoms. The agreement is poorer for shared C-O and N-O bonded interactions. PMID:17078623

  9. Model analysis of ground-state dissociation energies and equilibrium separations in alkali-metal diatomic compounds

    NASA Astrophysics Data System (ADS)

    Lombardi, Erminio; Jansen, Laurens

    1986-05-01

    Ground-state dissociation energies De and equilibrium distances Re for the series of homonuclear alkali-metal diatomic molecules Li2,Na2,..., as well as those for six heteronuclear alkali-metal diatomic compounds, are evaluated on the basis of a simple valence-bond model. Each alkali-metal atom in a diatomic molecule is characterized by two quantities: a Gaussian parameter ?e of the valence-electron function and a valence-to-core ``relative-size'' parameter ??(?c/?e)2, with ?c the Gaussian parameter for the core-electron charge distribution. For the homonuclear diatomic molecules, accurate results are obtained with a 2s Gaussian valence function (r2-a2)G orthogonalized to the core. For each homonuclear diatomic molecule there exists an optimal (?e,?) set yielding values of De and Re in practically quantitative agreement with experiment. The quantities ?e and ? exhibit the expected physical behavior over the series in that ?e decreases from Li2 to Cs2, and ? is highest for the lightest diatomic molecule Li2. The compounds K2, Rb2, and Cs2 are found to be ``Heitler-London'' molecules to within 5% of their binding energies. An approximate, similar, analysis of six heteronuclear diatomic compounds yields close agreement with experiment for LiNa and RbCs, whereas with the other four compounds (LiK, NaK, NaRb, and NaCs) the agreement with experimental De and Re is to within at most 5%. Also RbCs is a ``Heitler-London'' molecule to a very good approximation.

  10. Dissociated methanol test results

    SciTech Connect

    Finegold, J.G.; McKinnon, J.T.

    1982-04-01

    The design and testing of an automotive fuel system that provides hydrogen-rich gases to an internal combustion engine by catalytically cracking, or dissociating, methanol on board the vehicle is described. The vaporization and dissociation of methanol absorb heat from the engine exhaust and increase the lower heating value of the fuel by approximately 22%. In addition, raising the compression ratio and burning with excess air increase the engine thermal efficiency. Engine dynamometer test results with dissociated methanol demonstrated improvement in brake thermal efficiency compared to gasoline from 30% to 100% depending on engine speed and torque. Lower speeds and torques produce the largest improvements. Maps of exhaust temperature and exhaust heat content are presented. The exhaust temperature is almost always high enough for dissociation to occur, but at lower power outputs, there is only enough exhaust energy for partial dissociation of the methanol.

  11. Reactive collisions of very low-energy electrons with H_2+: rotational transitions and dissociative recombination

    NASA Astrophysics Data System (ADS)

    Epée Epée, M. D.; Mezei, J. Zs; Motapon, O.; Pop, N.; Schneider, I. F.

    2016-01-01

    A new series of computations has been performed to obtain cross-sections and rate coefficients for state-to-state rotational transitions in the H2+ ion, induced by collisions with very low-energy electrons. Following our recent work on the HD+ ion (Motapon et al. 2014), and using the same molecular structure data sets, excitations Ni+ rArr Ni++2 for Ni+=0 to 10, and de-excitations Ni+ ? Ni+-2, for Ni+=2 to 10, in the energy range 0.01 meV-0.3 eV, have been explored. The calculated cross-sections have been convolved in order to obtain Maxwell rate coefficients for electronic temperatures up to a few hundred of Kelvin. Moreover, Maxwell rate coefficients for dissociative recombination have been calculated for the same initial rotational levels.

  12. Dissociation of Benzene Dication [C6H6]2+: Exploring the Potential Energy Surface Smriti Anand and H. Bernhard Schlegel*

    E-print Network

    Schlegel, H. Bernhard

    Dissociation of Benzene Dication [C6H6]2+: Exploring the Potential Energy Surface Smriti Anand The singlet potential energy surface for the dissociation of benzene dication has been explored, and its three such as acetylene, cyclopropane, butadiene, cyclohexane, benzene, toluene, and naphthalene. The Coulomb explosion

  13. Organic Solar Cells with Graded Exciton-dissociation Interfaces.................................................................................................................EN.1 Luminescent Solar Concentrators for Energy-harvesting in Displays ........

    E-print Network

    Reif, Rafael

    Energy Organic Solar Cells with Graded Exciton-dissociation Interfaces.................................................................................................................EN.1 Luminescent Solar Concentrators for Energy-harvesting in Displays ...................................................................................EN.3 Nano-engineered Organic Solar-energy-harvesting System

  14. Dissociative amnesia.

    PubMed

    Staniloiu, Angelica; Markowitsch, Hans J

    2014-08-01

    Dissociative amnesia is one of the most enigmatic and controversial psychiatric disorders. In the past two decades, interest in the understanding of its pathophysiology has surged. In this report, we review new data about the epidemiology, neurobiology, and neuroimaging of dissociative amnesia and show how advances in memory research and neurobiology of dissociation inform proposed pathogenetic models of the disorder. Dissociative amnesia is characterised by functional impairment. Additionally, preliminary data suggest that affected people have an increased and possibly underestimated suicide risk. The prevalence of dissociative amnesia differs substantially across countries and populations. Symptoms and disease course also vary, indicating a possibly heterogeneous disorder. The accompanying clinical features differ across cultural groups. Most dissociative amnesias are retrograde, with memory impairments mainly involving the episodic-autobiographical memory domain. Anterograde dissociative amnesia occurring without significant retrograde memory impairments is rare. Functional neuroimaging studies of dissociative amnesia with prevailing retrograde memory impairments show changes in the network that subserves autobiographical memory. At present, no evidence-based treatments are available for dissociative amnesia and no broad framework exists for its rehabilitation. Further research is needed into its neurobiology, course, treatment options, and strategies to improve differential diagnoses. PMID:26360734

  15. Argon hydrochloride, Ar.HCl, bond energy by infrared spectroscopy

    NASA Technical Reports Server (NTRS)

    Miziolek, A. W.; Pimentel, G. C.

    1976-01-01

    The infrared absorption of argon (200 to 760 torr) and hydrogen chloride (2 to 6 torr) mixtures is reexamined in the missing Q branch region (spectral region between 2860 and 3010 wavelength/cm) at temperatures ranging from 195 to 298 K. The temperature dependence of two absorption features of the argon hydrogen chloride complex, at 2887 and 2879 wavelength/cm, leads to a bond energy estimate that depends on the assumptions made about the internal degrees of freedom of the complex. It is shown that agreement with experiment can be reached for well depths near 1.2 kcal/mole. This result is relatively insensitive to the choice of the vibrational frequencies and anharmonicities, but does depend on the extent to which the energy level manifolds are truncated to avoid molecular excitation in excess of the bond energy. The bond energy is found to deviate from the commonly accepted value of 0.4 kcal/mole. Possible causes for the discrepancy are considered.

  16. Energy-based analysis of biochemical cycles using bond graphs.

    PubMed

    Gawthrop, Peter J; Crampin, Edmund J

    2014-11-01

    Thermodynamic aspects of chemical reactions have a long history in the physical chemistry literature. In particular, biochemical cycles require a source of energy to function. However, although fundamental, the role of chemical potential and Gibb's free energy in the analysis of biochemical systems is often overlooked leading to models which are physically impossible. The bond graph approach was developed for modelling engineering systems, where energy generation, storage and transmission are fundamental. The method focuses on how power flows between components and how energy is stored, transmitted or dissipated within components. Based on the early ideas of network thermodynamics, we have applied this approach to biochemical systems to generate models which automatically obey the laws of thermodynamics. We illustrate the method with examples of biochemical cycles. We have found that thermodynamically compliant models of simple biochemical cycles can easily be developed using this approach. In particular, both stoichiometric information and simulation models can be developed directly from the bond graph. Furthermore, model reduction and approximation while retaining structural and thermodynamic properties is facilitated. Because the bond graph approach is also modular and scaleable, we believe that it provides a secure foundation for building thermodynamically compliant models of large biochemical networks. PMID:25383030

  17. Energy-based analysis of biochemical cycles using bond graphs

    PubMed Central

    Gawthrop, Peter J.; Crampin, Edmund J.

    2014-01-01

    Thermodynamic aspects of chemical reactions have a long history in the physical chemistry literature. In particular, biochemical cycles require a source of energy to function. However, although fundamental, the role of chemical potential and Gibb's free energy in the analysis of biochemical systems is often overlooked leading to models which are physically impossible. The bond graph approach was developed for modelling engineering systems, where energy generation, storage and transmission are fundamental. The method focuses on how power flows between components and how energy is stored, transmitted or dissipated within components. Based on the early ideas of network thermodynamics, we have applied this approach to biochemical systems to generate models which automatically obey the laws of thermodynamics. We illustrate the method with examples of biochemical cycles. We have found that thermodynamically compliant models of simple biochemical cycles can easily be developed using this approach. In particular, both stoichiometric information and simulation models can be developed directly from the bond graph. Furthermore, model reduction and approximation while retaining structural and thermodynamic properties is facilitated. Because the bond graph approach is also modular and scaleable, we believe that it provides a secure foundation for building thermodynamically compliant models of large biochemical networks. PMID:25383030

  18. Dissociation energies of Ag-RG (RG = Ar, Kr, Xe) and AgO molecules from velocity map imaging studies

    NASA Astrophysics Data System (ADS)

    Cooper, Graham A.; Kartouzian, Aras; Gentleman, Alexander S.; Iskra, Andreas; van Wijk, Robert; Mackenzie, Stuart R.

    2015-09-01

    The near ultraviolet photodissociation dynamics of silver atom—rare gas dimers have been studied by velocity map imaging. Ag-RG (RG = Ar, Kr, Xe) species generated by laser ablation are excited in the region of the C (2?+)?X (2?+) continuum leading to direct, near-threshold dissociation generating Ag* (2P3/2) + RG (1S0) products. Images recorded at excitation wavelengths throughout the C (2?+)?X (2?+) continuum, coupled with known atomic energy levels, permit determination of the ground X (2?+) state dissociation energies of 85.9 ± 23.4 cm-1 (Ag-Ar), 149.3 ± 22.4 cm-1 (Ag-Kr), and 256.3 ± 16.0 cm-1 (Ag-Xe). Three additional photolysis processes, each yielding Ag atom photoproducts, are observed in the same spectral region. Two of these are markedly enhanced in intensity upon seeding the molecular beam with nitrous oxide, and are assigned to photodissociation of AgO at the two-photon level. These features yield an improved ground state dissociation energy for AgO of 15 965 ± 81 cm-1, which is in good agreement with high level calculations. The third process results in Ag atom fragments whose kinetic energy shows anomalously weak photon energy dependence and is assigned tentatively to dissociative ionization of the silver dimer Ag2.

  19. IR Spectra and Bond Energies Computed Using DFT

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles; Andrews, Lester; Arnold, James (Technical Monitor)

    2000-01-01

    The combination of density functional theory (DFT) frequencies and infrared (IR) intensities and experimental spectra is a very powerful tool in the identification of molecules and ions. The computed and measured isotopic ratios make the identification much more secure than frequencies and intensities alone. This will be illustrated using several examples, such as Mn(CO)n and Mn(CO)n-. The accuracy of DFT metal-ligand bond energies will also be discussed.

  20. Adsorption of water on O(2x2)/Ru(0001): thermal stability and inhibition of dissociation by H2O-O bonding

    SciTech Connect

    Mugarza, Aitor; Shimizu, Tomoko; Cabrera-Sanfelix, Pepa; Sanchez-Portal, Daniel; Arnau, Andres; Salmeron, Miquel

    2008-08-01

    The effect of preadsorbed oxygen on the subsequent adsorption and reactions of water on Ru(0001) has been studied using low temperature scanning tunneling microscopy and DFT calculations. Experiments were carried out for O coverages close to 0.25 ML. It was found that no dissociation of water takes place up to the desorption temperature of {approx}180-230 K. DFT calculations show that intact water on O(2x2)/Ru(0001) is {approx} 0.49 eV more stable than the dissociation products, H and OH, at their preferred fcc and top adsorption sites.

  1. "Vibrational bonding": a new type of chemical bond is discovered.

    PubMed

    Rhodes, Christopher J; Macrae, Roderick M

    2015-01-01

    A long-sought but elusive new type of chemical bond, occurring on a minimum-free, purely repulsive potential energy surface, has recently been convincingly shown to be possible on the basis of high-level quantum-chemical calculations. This type of bond, termed a vibrational bond, forms because the total energy, including the dynamical energy of the nuclei, is lower than the total energy of the dissociated products, including their vibrational zero-point energy. For this to be the case, the ZPE of the product molecule must be very high, which is ensured by replacing a conventional hydrogen atom with its light isotope muonium (Mu, mass = 1/9 u) in the system Br-H-Br, a natural transition state in the reaction between Br and HBr. A paramagnetic species observed in the reaction Mu +Br2 has been proposed as a first experimental sighting of this species, but definitive identification remains challenging. PMID:25942773

  2. Analysis of liquid metal embrittlement from a bond energy viewpoint

    NASA Technical Reports Server (NTRS)

    Kelley, M. J.; Stoloff, N. S.

    1975-01-01

    Absorption induced embrittlement of solid metals by certain liquid metals is analyzed through an Engel-Brewer calculation of the solid-liquid interaction energy, and of the effect of the latter in reducing fracture surface energy. The reduction in fracture surface energy is estimated by comparison of the electronic contribution to the solid-liquid interaction energy with solid-solid bond energy for some 40 liquid-solid couples. Regular solution theory is used to estimate mutual solubility as the relative difference in parameter values. Embrittlement can be predicted by using reduction in fracture surface energy and solubility parameter difference as critical variables. The effect of solute additions to the liquid on the degree of embrittlement is interpreted via the same two variables; the principal effect of solutes is to modify solubility relationships at the solid-liquid interface.

  3. Effects of Exchange Energy and Spin-Orbit Coupling on Bond Energies

    ERIC Educational Resources Information Center

    Smith, Derek W.

    2004-01-01

    Since chemical reactions involve the breaking and making of bonds, understanding the relative strengths of bonds is of paramount importance in the study, teaching, and practice of chemistry. Further, it is showed that free atoms having p(super n) configuration with n = 2,3, or 4 are stabilized by exchange energy, and by spin-orbit coupling for n =…

  4. Superplastic deformation and energy dissipation mechanism in surface-bonded carbon nanofibers

    E-print Network

    Sansoz, Frederic

    Superplastic deformation and energy dissipation mechanism in surface-bonded carbon nanofibers 12 December 2014 Accepted 20 December 2014 Keywords: Carbon nanofibers Superplasticity Fracture mechanisms in cone-stacked carbon nanofibers. The sim- ulations predict that the surface bond density

  5. Controlling the bond scission sequence of oxygenates for energy applications

    NASA Astrophysics Data System (ADS)

    Stottlemyer, Alan L.

    The so called "Holy Grail" of heterogeneous catalysis is a fundamental understanding of catalyzed chemical transformations which span multidimensional scales of both length and time, enabling rational catalyst design. Such an undertaking is realizable only with an atomic level understanding of bond formation and destruction with respect to intrinsic properties of the metal catalyst. In this study, we investigate the bond scission sequence of small oxygenates (methanol, ethanol, ethylene glycol) on bimetallic transition metal catalysts and transition metal carbide catalysts. Oxygenates are of interest both as hydrogen carriers for reforming to H2 and CO and as fuels in direct alcohol fuel cells (DAFC). To address the so-called "materials gap" and "pressure gap" this work adopted three parallel research approaches: (1) ultra high vacuum (UHV) studies including temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS) on polycrystalline surfaces; (2) DFT studies including thermodynamic and kinetic calculations; (3) electrochemical studies including cyclic voltammetry (CV) and chronoamperometry (CA). Recent studies have suggested that tungsten monocarbide (WC) may behave similarly to Pt for the electrooxidation of oxygenates. TPD was used to quantify the activity and selectivity of oxygenate decomposition for WC and Pt-modifiedWC (Pt/WC) as compared to Pt. While decomposition activity was generally higher on WC than on Pt, scission of the C-O bond resulted in alkane/alkene formation on WC, an undesired product for DAFC. When Pt was added to WC by physical vapor deposition C-O bond scission was limited, suggesting that Pt synergistically modifies WC to improve the selectivity toward C-H bond scission to produce H2 and CO. Additionally, TPD confirmed WC and Pt/WC to be more CO tolerant than Pt. HREELS results verified that surface intermediates were different on Pt/WC as compared to Pt or WC and evidence of aldehyde intermediates was observed on the Pt and Pt/WC surfaces. For CH3OH decomposition, DFT calculations suggested that the bond scission sequence could be controlled using monolayer coverage of Pt on WC. The Ni/Pt bimetallic system was studied as an example for using oxygenates as a hydrogen source. There are two well characterized surface structures for the Ni/Pt system: the surface configuration, in which the Ni atoms reside primarily on the surface of the Pt bulk, and the subsurface configuration, in which the second atomic layer is enriched in Ni atoms and the surface is enriched in Pt atoms. These configurations are denoted NiPtPt and PtNiPt, respectively. DFT results revealed that trends established for the Ni/Pt(111) system extend to the Ni/Pt(100) analogue. TPD studies revealed that the NiPtPt surface was more active for oxygenate reforming than the Pt or PtNiPt surfaces. HREELS confirmed the presence of strongly bound reaction intermediates, including aldehyde-like species, and suggested that the first decomposition step was likely O-H bond scission. Thus, the binding energies of the deprotonated reaction intermediates are important parameters in controlling the decomposition pathways of oxygenates. These studies have demonstrated that the bond scission sequence of oxygenate decomposition can be controlled using bimetallic and transition metal carbide catalysts. While this study has focused on oxygenate decomposition for energy applications, the principles and methodology applied herein are universally applicable to the development of novel and marketable value-added products. The value in such a methodology is in the combination of both calculations to predict catalytic and chemical properties, and experiments to fine-tune theoretical predictions.

  6. Experiments with crystal deflectors for high energy ion beams: Electromagnetic dissociation probability for well channeled ions

    NASA Astrophysics Data System (ADS)

    Scandale, W.; Taratin, A. M.; Kovalenko, A. D.

    2013-01-01

    The paper presents the current status with the use of the crystal defectors for high energy ion beams. The channeling properties of multicharged ions are discussed. The results of the experiments on the deflection and extraction (collimation) of high energy ion beams with bent crystals performed in the accelerator centers are shortly considered. The analysis of the recent collimation experiment with a Pb nuclei of 270GeV/c per charge at the CERN Super Proton Synchrotron showed that the channeling efficiency was as large as about 90%. For Pb ions of the LHC energies a new mechanism, which can reduce the channeling efficiency, appears. The electromagnetic dissociation (ED) becomes possible for well channeled particles. However, the estimations performed in the paper show that the ED probability is small and should not visibly reduce the collimation efficiency. On the other hand, the aligned crystal gives the possibility to study the ED processes of heavy nuclei in the conditions when nuclear interactions are fully suppressed.

  7. Discovery and Mechanistic Studies of Facile N-Terminal C?–C Bond Cleavages in the Dissociation of Tyrosine-Containing Peptide Radical Cations

    SciTech Connect

    Mu, Xiaoyan; Song, Tao; Xu, Minjie; Lai, Cheuk-Kuen; Siu, Chi-Kit; Laskin, Julia; Chu, Ivan K.

    2014-03-28

    Gas phase fragmentations of protein and peptide (M) ions in a mass spectrometer—induced by, for example, electron-capture dissociation1-2 and electron-transfer dissociation3-422 —form the foundation for top-down amino acid sequencing approaches for the rapid identification of protein components in complex biological samples. During these processes, protonated protein and peptide radicals ([M + nH]•(n – 1)+)5–8 are generated; their fragmentations are governed largely by the properties of the unpaired electron. Because of their importance in modern bioanalytical chemistry, considerable attention has been drawn recently toward understanding the radical cation chemistry behind the fragmentations of these odd-electron biomolecular ions in the gas phase.

  8. The kinetic energy spectrum of protons produced by the dissociative ionization of H2 by electron impact

    NASA Technical Reports Server (NTRS)

    Khakoo, M. A.; Srivastava, S. K.

    1985-01-01

    The kinetic energy spectra of protons resulting from the dissociative ionization of H2 by electron impact have been measured for electron impact energies from threshold (approximately 17 eV) to 160 eV at 90 deg and 30 deg detection angles, using a crossed-beam experimental arrangement. To check reliability, two separate proton energy analysis methods have been employed, i.e., a time-of-flight proton energy analysis and an electrostatic hemispherical energy analyzer. The present results are compared with previous measurements.

  9. Dissociation dynamics of fluorinated ethene cations: from time bombs on a molecular level to double-regime dissociators.

    PubMed

    Harvey, Jonelle; Bodi, Andras; Tuckett, Richard P; Sztáray, Bálint

    2012-03-21

    The dissociative photoionization mechanism of internal energy selected C(2)H(3)F(+), 1,1-C(2)H(2)F(2)(+), C(2)HF(3)(+) and C(2)F(4)(+) cations has been studied in the 13-20 eV photon energy range using imaging photoelectron photoion coincidence spectroscopy. Five predominant channels have been found; HF loss, statistical and non-statistical F loss, cleavage of the C-C bond post H or F-atom migration, and cleavage of the C=C bond. By modelling the breakdown diagrams and ion time-of-flight distributions using statistical theory, experimental 0 K appearance energies, E(0), of the daughter ions have been determined. Both C(2)H(3)F(+) and 1,1-C(2)H(2)F(2)(+) are veritable time bombs with respect to dissociation via HF loss, where slow dissociation over a reverse barrier is followed by an explosion with large kinetic energy release. The first dissociative ionization pathway for C(2)HF(3) and C(2)F(4) involves an atom migration across the C=C bond, giving CF-CHF(2)(+) and CF-CF(3)(+), respectively, which then dissociate to form CHF(2)(+), CF(+) and CF(3)(+). The nature of the F-loss pathway has been found to be bimodal for C(2)H(3)F and 1,1-C(2)H(2)F(2), switching from statistical to non-statistical behaviour as the photon energy increases. The dissociative ionization of C(2)F(4) is found to be comprised of two regimes. At low internal energies, CF(+), CF(3)(+) and CF(2)(+) are formed in statistical processes. At high internal energies, a long-lived excited electronic state is formed, which loses an F atom in a non-statistical process and undergoes statistical redistribution of energy among the nuclear degrees of freedom. This is followed by a subsequent dissociation. In other words only the ground electronic state phase space stays inaccessible. The accurate E(0) of CF(3)(+) and CF(+) formation from C(2)F(4) together with the now well established ?(f)H(o) of C(2)F(4) yield self-consistent enthalpies of formation for the CF(3), CF, CF(3)(+) and CF(+) species. PMID:22322889

  10. Tubulin Bond Energies and Microtubule Biomechanics Determined from Nanoindentation in Silico

    E-print Network

    Barsegov, Valeri

    Tubulin Bond Energies and Microtubule Biomechanics Determined from Nanoindentation in Silico Olga, are stabilized by longitudinal and lateral noncovalent bonds between the tubulin subunits. However (14.9 ± 1.5 kcal/mol) tubulin-tubulin bonds. These values in conjunction with the large flexural

  11. Energy and temperature dependent dissociation of the Na(+)(benzene)1,2 clusters: importance of anharmonicity.

    PubMed

    Kolakkandy, Sujitha; Paul, Amit K; Pratihar, Subha; Kohale, Swapnil C; Barnes, George L; Wang, Hai; Hase, William L

    2015-01-28

    Chemical dynamics simulations were performed to study the unimolecular dissociation of randomly excited Na(+)(Bz) and Na(+)(Bz)2 clusters; Bz = benzene. The simulations were performed at constant energy, and temperatures in the range of 1200-2200 K relevant to combustion, using an analytic potential energy surface (PES) derived in part from MP2/6-311+G* calculations. The clusters decompose with exponential probabilities, consistent with RRKM unimolecular rate theory. Analyses show that intramolecular vibrational energy redistribution is sufficiently rapid within the clusters that their unimolecular dynamics is intrinsically RRKM. Arrhenius parameters, determined from the simulations of the clusters, are unusual in that Ea is ?10 kcal/mol lower the Na(+)(Bz) ? Na(+) + Bz dissociation energy and the A-factor is approximately two orders-of-magnitude too small. Analyses indicate that temperature dependent anharmonicity is important for the Na(+)(Bz) cluster's unimolecular rate constants k(T). This is consistent with the temperature dependent anharmonicity found for the Na(+)(Bz) cluster from a Monte Carlo calculation based on the analytic PES used for the simulations. Apparently temperature dependent anharmonicity is quite important for unimolecular dissociation of the Na(+)(Bz)1,2 clusters. PMID:25637986

  12. Energy and temperature dependent dissociation of the Na+(benzene)1,2 clusters: Importance of anharmonicity

    NASA Astrophysics Data System (ADS)

    Kolakkandy, Sujitha; Paul, Amit K.; Pratihar, Subha; Kohale, Swapnil C.; Barnes, George L.; Wang, Hai; Hase, William L.

    2015-01-01

    Chemical dynamics simulations were performed to study the unimolecular dissociation of randomly excited Na+(Bz) and Na+(Bz)2 clusters; Bz = benzene. The simulations were performed at constant energy, and temperatures in the range of 1200-2200 K relevant to combustion, using an analytic potential energy surface (PES) derived in part from MP2/6-311+G* calculations. The clusters decompose with exponential probabilities, consistent with RRKM unimolecular rate theory. Analyses show that intramolecular vibrational energy redistribution is sufficiently rapid within the clusters that their unimolecular dynamics is intrinsically RRKM. Arrhenius parameters, determined from the simulations of the clusters, are unusual in that Ea is ˜10 kcal/mol lower the Na+(Bz) ? Na+ + Bz dissociation energy and the A-factor is approximately two orders-of-magnitude too small. Analyses indicate that temperature dependent anharmonicity is important for the Na+(Bz) cluster's unimolecular rate constants k(T). This is consistent with the temperature dependent anharmonicity found for the Na+(Bz) cluster from a Monte Carlo calculation based on the analytic PES used for the simulations. Apparently temperature dependent anharmonicity is quite important for unimolecular dissociation of the Na+(Bz)1,2 clusters.

  13. Theoretical study of the dissociation energy and the red and violet band systems of CN

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Langhoff, Stephen R.; Taylor, Peter R.

    1987-01-01

    The dissociation energy (D sub O) of CN is determined to be 7.65 + or - 0.06 eV. This corresponds to delta H sub f (CN) = 105.3 + or - 1.5 kcal/mole, in excellent agreement with Engleman and Rouse (1975), but considerably larger than the recent value deduced from shock-tube studies by Colket (1984). The result is obtained not only from extensive ab initio MRCI calculations using a very large Gaussian basis set, but also from extrapolation of the directly computed value by comparison of computed and experimental results fo NO, C2, and N2. As an additional calibration of the methods, the D sub O value for CN was computed from the corresponding value for CN(-) using the experimental electron affinity data. The lifetime of the nu prime = 0 level of the violet (B 2 sigma + yields X 2 sigma +) system was computed to be 62.4 ns, in good agreement with both experiment and previous calculations. Lifetimes for the red (A 2 pi yields X 2 sigma +) system decrease with increasing nu prime, which is consistent both with the recent experiment and calculations. While the computed lifetimes are significantly longer that those obtained from the experiment, they are shorter than those deduced from an analysis of the solar spectrum. However the D sub O and f (sub OO) are consistent with Lambert's model for the solar spectrum.

  14. Resonant structure of low-energy H{sub 3}{sup +} dissociative recombination

    SciTech Connect

    Petrignani, Annemieke; Altevogt, Simon; Berg, Max H.; Bing, Dennis; Grieser, Manfred; Hoffmann, Jens; Jordon-Thaden, Brandon; Krantz, Claude; Mendes, Mario B.; Novotny, Oldrich; Novotny, Steffen; Buhr, Henrik; Kreckel, Holger; Kokoouline, Viatcheslav; Greene, Chris H.; Orlov, Dmitry A.; Repnow, Roland; Sorg, Tobias; Stuetzel, Julia; Wolf, Andreas

    2011-03-15

    High-resolution dissociative recombination rate coefficients of rotationally cool and hot H{sub 3}{sup +} in the vibrational ground state have been measured with a 22-pole trap setup and a Penning ion source, respectively, at the ion storage-ring TSR. The experimental results are compared with theoretical calculations to explore the dependence of the rate coefficient on ion temperature and to study the contributions of different symmetries to probe the rich predicted resonance spectrum. The kinetic energy release was investigated by fragment imaging to derive internal temperatures of the stored parent ions under differing experimental conditions. A systematic experimental assessment of heating effects is performed which, together with a survey of other recent storage-ring data, suggests that the present rotationally cool rate-coefficient measurement was performed at 380{sub -130}{sup +50} K and that this is the lowest rotational temperature so far realized in storage-ring rate-coefficient measurements on H{sub 3}{sup +}. This partially supports the theoretical suggestion that temperatures higher than assumed in earlier experiments are the main cause for the large gap between the experimental and the theoretical rate coefficients. For the rotationally hot rate-coefficient measurement a temperature of below 3250 K is derived. From these higher-temperature results it is found that increasing the rotational ion temperature in the calculations cannot fully close the gap between the theoretical and the experimental rate coefficients.

  15. Kinetic-energy, femtosecond resolved reaction dynamics. Modes of dissociation (in iodobenzene) from time-velocity correlations

    NASA Astrophysics Data System (ADS)

    Cheng, P. Y.; Zhong, D.; Zewail, Ahmed H.

    1995-05-01

    We report on the use of '2D' time-velocity correlations to study in real time the dynamics of reactions with multiple channels. By resolving the kinetic energy on the femtosecond time scale we are able to directly identify the direct-mode and complex-mode dissociation pathways of iodobenzene. The coherent wave packet dynamics and the nature of IVR in the benzen ring are discussed and related to the experimental observations.

  16. Classification of metal-oxide bonded interactions based on local potential- and kinetic-energy densities

    SciTech Connect

    Gibbs, Gerald V.; Cox, David; Crawford, T Daniel; Rosso, Kevin M.; Ross, Nancy; Downs, R. T.

    2006-02-28

    A classification of the HF bonded interactions comprising a large number of molecules has been proposed by Espinosa et al. [J. Chem. Phys. 117, 5529 (2002)] based on the ratio |V(rc)|/G(rc) where |V(rc)| is the magnitude of the local potential energy density and G(rc) is the local kinetic density evaluated at the bond critical points, rc. A calculation of the ratio for the MO bonded interactions comprising a relatively large number of molecules and earth materials, together with the constraints imposed by the values of Ñ2?(rc) and the local electronic energy density H(rc) = G(rc) + V(rc) in the HF study, yielded the same classification for the oxides as found for the fluorides. This is true despite the different trends of the bond critical point and local energy properties with the bond length displayed by the HF and MO bonded interactions. LiO, NaO and MgO bonded interactions classify as closed shell ionic bonds, BeO, AlO, SiO, BO and PO bonded interactions classify as bonds of intermediate character and NO bonded interactions classify as shared covalent bonds. CO and SO bonded interactions classify as both intermediate and covalent bonded interactions. The CO triple bonded interaction classifies as a bond of intermediate character and the CO single bonded interaction classifies as a covalent bond whereas their H(rc) value indicates that they are both covalent bonds. The |V(rc)|/G(rc) ratios for the BeO, AlO and SiO bonded interactions indicate that they have a substantial component of ionic character despite their classification as bonds of intermediate character. The trend between |V(rc)|/G(rc) and the character of the bonded interaction is consistent with trends expected from electronegativity considerations. The connection between the net charges and the experimental SiO bond length evaluated for the Si and O atoms comprising two orthosilicates are examined in terms of the |V(rc)|/G(rc) values.

  17. The Trouble with Chemical Energy: Why Understanding Bond Energies Requires an Interdisciplinary Systems Approach

    ERIC Educational Resources Information Center

    Cooper, Melanie M.; Klymkowsky, Michael W.

    2013-01-01

    Helping students understand "chemical energy" is notoriously difficult. Many hold inconsistent ideas about what energy is, how and why it changes during the course of a chemical reaction, and how these changes are related to bond energies and reaction dynamics. There are (at least) three major sources for this problem: 1) the way biologists talk…

  18. On the photostability of peptides after selective photoexcitation of the backbone: prompt versus slow dissociation.

    PubMed

    Byskov, Camilla Skinnerup; Jensen, Frank; Jørgensen, Thomas J D; Nielsen, Steen Brøndsted

    2014-08-14

    Vulnerability of biomolecules to ultraviolet radiation is intimately linked to deexcitation pathways: photostability requires fast internal conversion to the electronic ground state, but also intramolecular vibrational redistribution and cooling on a time scale faster than dissociation. Here we present a protocol to disentangle slow and non-hazardous statistical dissociation from prompt cleavage of peptide bonds by 210 nm light based on experiments on protonated peptides isolated in vacuo and tagged by 18-crown-6 ether (CE). The weakest link in the system is between the charged site and CE, which is remote from the initial site of excitation. Hence loss of CE serves as direct proof that energy has reached the charge-site end, leaving the backbone intact. Our work demonstrates that excitation of tertiary amide moieties (proline linkages) results in both prompt dissociation and statistical dissociation after energy randomisation over all vibrational degrees of freedom. PMID:24945849

  19. Calculation of activation energies for hydrogen-atom abstractions by radicals containing carbon triple bonds

    NASA Technical Reports Server (NTRS)

    Brown, R. L.; Laufer, A. H.

    1981-01-01

    Activation energies are calculated by the bond-energy-bond-order (BEBO) and the bond-strength-bond-length (BSBL) methods for the reactions of C2H radicals with H2, CH4, and C2H6 and for the reactions of CN radicals with H2 and CH4. The BSBL technique accurately predicts the activation energies for these reactions while the BEBO method yields energies averaging 9 kcal higher than those observed. A possible reason for the disagreement is considered.

  20. Dissociation energies of AgRG (RG = Ar, Kr, Xe) and AgO molecules from velocity map imaging studies

    E-print Network

    Cooper, Graham A; Gentleman, Alexander S; Iskra, Andreas; van Wijk, Robert; Mackenzie, Stuart R

    2015-01-01

    The near ultraviolet photodissociation dynamics of silver atom rare gas dimers have been studied by velocity map imaging. AgRG (RG = Ar, Kr, Xe) species generated by laser ablation are excited in the region of the C dissociation generating Ag* (2P3/2) + RG (1S0) products. Images recorded at excitation wavelengths throughout the C dissociation energies of 85.9 +/- 23.4 cm-1 (AgAr), 149.3 +/- 22.4 cm-1 (AgKr) and 256.3 +/- 16.0 cm-1 (AgXe). Three additional photolysis processes, each yielding Ag atom photoproducts, are observed in the same spectral region. Two of these are markedly enhanced in intensity upon seeding the molecular beam with nitrous oxide, and are assigned to photodissociation of AgO at the two photon level. These features yield an improved ground state dissociation energy for AgO of 15965 +/- 81 cm-1, which is in good agreement with ...

  1. Energetics of the ruthenium-halide bond in olefin metathesis (pre)catalysts.

    PubMed

    Falivene, Laura; Poater, Albert; Cazin, Catherine S J; Slugovc, Christian; Cavallo, Luigi

    2013-05-28

    A DFT analysis of the strength of the Ru-halide bond in a series of typical olefin metathesis (pre)catalysts is presented. The calculated Ru-halide bond energies span the rather broad window of 25-43 kcal mol(-1). This indicates that in many systems dissociation of the Ru-halide bond is possible and is actually competitive with dissociation of the labile ligand generating the 14e active species. Consequently, formation of cationic Ru species in solution should be considered as a possible event. PMID:23235534

  2. A revised set of values of single-bond radii derived from the observed interatomic distances in metals by correction for bond number and resonance energy

    PubMed Central

    Pauling, Linus; Kamb, Barclay

    1986-01-01

    An earlier discussion [Pauling, L. (1947) J. Am. Chem. Soc. 69, 542] of observed bond lengths in elemental metals with correction for bond number and resonance energy led to a set of single-bond metallic radii with values usually somewhat less than the corresponding values obtained from molecules and complex ions. A theory of resonating covalent bonds has now been developed that permits calculation of the number of resonance structures per atom and of the effective resonance energy per bond. With this refined method of correcting the observed bond lengths for the effect of resonance energy, a new set of single-bond covalent radii, in better agreement with values from molecules and complex ions, has been constructed. PMID:16593698

  3. Dissociation of a product of a surface reaction in the gas phase: XeF2 reaction with Si.

    PubMed

    Hefty, R C; Holt, J R; Tate, M R; Gosalvez, D B; Bertino, M F; Ceyer, S T

    2004-05-01

    Xenon difluoride interacts with Si(100)2 x 1 by atom abstraction, whereby a dangling bond abstracts a F atom from XeF2, scattering the complementary XeF. Partitioning of the reaction exothermicity produces sufficient XeF rovibrational excitation for dissociation to occur. The resulting F and Xe atoms are shown to arise from dissociation of XeF in the gas phase by demonstrating that the angle-resolved velocity distributions of F, Xe, and XeF conserve momentum, energy, and mass. This experiment documents the first observation of dissociation of a surface reaction product in the gas phase. PMID:15169537

  4. Metallic bond effects on mean excitation energies for stopping powers

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Xu, Y. J.

    1982-01-01

    Mean excitation energies for first row metals are evaluated by means of the local plasma approximation. Particle corrections based on Pines' (1953) procedure and the Wigner Seitz (1934) model of the metallic state are included. The agreement with experimental values is remarkably good. In contrast to previous work, the calculations given here estimate shifts in the plasma frequency according to the theory for plane wave states in an extended plasma as calculated by Pines. It is demonstrated that the effects of the metallic bond in lithium and beryllium are quite large and that they appear mainly as a result of collective oscillations in the 'free' electron gas formed from the valence electrons. The usefulness of the plasma frequency shift derived for a degenerate electron gas in predicting the plasma frequency shift within the ion core is considered surprising.

  5. Cleavage of thymine N3H bonds by low-energy electrons attached Magali Theodore 1

    E-print Network

    Simons, Jack

    Cleavage of thymine N3­H bonds by low-energy electrons attached to base p* orbitals Magali The. In earlier studies, we considered SSBs induced by low-energy electrons that attach to DNA bases' p* orbitals or to phosphate P@O p* orbitals to cleave sugar­phosphate C­O bonds or base­sugar N1­C bonds. We also studied

  6. Adsorption and dissociation of hydrogen molecules on bare and functionalized carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Dag, S.; Ozturk, Y.; Ciraci, S.; Yildirim, T.

    2005-10-01

    Interaction between hydrogen molecules and bare as well as functionalized single-wall carbon nanotubes (SWNT) is investigated using first-principles plane wave method. It is found that the binding energy of the H2 physisorbed on the outer surface of the bare SWNT is very weak, and cannot be enhanced significantly either by increasing the curvature of the surface through radial deformation, or by the coadsorption of a Li atom that makes the semiconducting tube metallic. Although the bonding is strengthened upon adsorption directly to the Li atom, its nature continues to be physisorption. However, the character of the bonding changes dramatically when SWNT is functionalized by the adsorption of a Pt atom. A single H2 is chemisorbed to the Pt atom on the SWNT either dissociatively or molecularly. The dissociative adsorption is favorable energetically and is followed by the weakening of the Pt-SWNT bond. Out of two adsorbed H2 , the first one can be adsorbed dissociatively and the second one is chemisorbed molecularly. The nature of bonding is a very weak physisorption for the third adsorbed H2 . Palladium also promotes the chemisorption of H2 with relatively smaller binding energy. Present results reveal the important effect of transition metal atom adsorbed on SWNT and these results advance our understanding of the molecular and dissociative adsorption of hydrogen for efficient hydrogen storage.

  7. Dissociation of diatomic gases

    NASA Technical Reports Server (NTRS)

    Hansen, C. F.

    1991-01-01

    The Landau-Zener theory of reactive cross sections has been applied to diatomic molecules dissociating from a ladder of rotational and vibrational states. Although the preexponential factor of the Arrhenius rate expression is shown to be a complex function of the dimensionless activation energy, the average over all states in the ladder is well represented by a single factor that varies about as T exp (-n), where the coefficient n is the order of unity. This relation agrees very well with experimental data for dissociation of O2 and N2, for example. The results validate previous empirical assignment of a single preexponential factor in the Arrhenius expression and justify the extrapolation of the expression well beyond the range of data. The theory is then used to calculate the effect of vibrational nonequilibrium on dissociation rate. For Morse oscillators the results are about the same as for harmonic oscillators, and the dissociation from a ladder of equilibrium rotational and nonequilibrium vibrational states is close to an analytic approximation provided by Hammerling, Kivel, and Teare for harmonic oscillators all dissociating from the ground rotational state.

  8. Calculation of the Gibbs free energy of solvation and dissociation of HCl in water via Monte Carlo simulations and continuum solvation models.

    PubMed

    McGrath, Matthew J; Kuo, I-F Will; Ngouana W, Brice F; Ghogomu, Julius N; Mundy, Christopher J; Marenich, Aleksandr V; Cramer, Christopher J; Truhlar, Donald G; Siepmann, J Ilja

    2013-08-28

    The Gibbs free energy of solvation and dissociation of hydrogen chloride in water is calculated through a combined molecular simulation/quantum chemical approach at four temperatures between T = 300 and 450 K. The Gibbs free energy is first decomposed into the sum of two components: the Gibbs free energy of transfer of molecular HCl from the vapor to the aqueous liquid phase and the standard-state Gibbs free energy of acid dissociation of HCl in aqueous solution. The former quantity is calculated using Gibbs ensemble Monte Carlo simulations using either Kohn-Sham density functional theory or a molecular mechanics force field to determine the system's potential energy. The latter Gibbs free energy contribution is computed using a continuum solvation model utilizing either experimental reference data or micro-solvated clusters. The predicted combined solvation and dissociation Gibbs free energies agree very well with available experimental data. PMID:23831584

  9. Abstract. We present a general approach for describing chemical processes (bond breaking and bond formation)

    E-print Network

    Goddard III, William A.

    Abstract. We present a general approach for describing chemical processes (bond breaking and bond the dissoci- ation and formation of chemical bonds. Although high- quality quantum mechanical (QM®c bond orders into speci®c bonds and do not allow bond breaking [1, 2]. In contrast, a chemical reaction

  10. Trajectory Study of Energy Transfer and Unimolecular Dissociation of Highly Excited Allyl with Argon

    E-print Network

    Houston, Paul L.

    with Argon Riccardo Conte,*, Paul L. Houston,*,,§ and Joel M. Bowman*, Department of Chemistry and Cherry L of allyl with argon and on allyl dissociation is investigated. About 90 000 classical scattering potential and an interaction one, and it has already been used in a previous work on allyl-argon scattering

  11. Photofragment translational spectroscopy of three body dissociations and free radicals

    SciTech Connect

    North, S.W.

    1995-04-01

    This dissertation describes several three-body dissociations and the photodissociation of methyl radicals studied using photofragment translational spectroscopy. The first chapter provides an introduction to three body dissociation, examines current experimental methodology, and includes a discussion on the treatment of photofragment translational spectroscopy data arising from three-body fragmentation. The ultraviolet photodissociation of azomethane into two methyl radicals and nitrogen is discussed in chapter 2. Chapter 3 describes the photodissociation of acetone at 248 nm and 193 nm. At 248 nm the translational energy release from the initial C-C bond cleavage matches the exit barrier height and a comparison with results at 266 nm suggests that is invariant to the available energy. A fraction of the nascent CH{sub 3}CO radicals spontaneously dissociate following rotational averaging. The for the second C-C bond cleavage also matches the exit barrier height. At 193 nm the experimental data can be successfully fit assuming that the dynamics are analogous to those at 248 nm. A simplified model of energy partitioning which adequately describes the experimental results is discussed. Experiments on acetyl halides provide additional evidence to support the proposed acetone dissociation mechanism. A value of 17.0{+-}1.0 kcal/mole for the barrier height, CH{sub 3}CO decomposition has been determined. The photodissociation of methyl radical at 193 nm and 212.8 nm is discussed in the chapter 5. The formation of CH{sub 2} ({sup 1}A{sub l}) and H ({sup 2}S) was the only single photon dissociation pathway observed at both wavelengths.

  12. The adsorption and dissociation of CO on Fe(111)

    NASA Astrophysics Data System (ADS)

    Booyens, Sharon; Bowker, Michael; Willock, David J.

    2014-07-01

    We present DFT calculations relating to fundamental aspects of the adsorption, molecular diffusion and dissociation pathways available for CO on the Fe(111) surface. On the clean surface CO dissociates most easily from di-bridge (DB) sites with both carbon and oxygen atoms interacting with the surface via a tilted configuration. This adsorption site is 0.52 eV higher in energy than the lowest energy at the shallow hollow site and so CO bond cleavage takes place following molecular migration. The lowest calculated barriers are also found when the molecule re-orientates during the dissociation process to maintain a surface co-ordination for the O atom of at least two. When carbon is pre-adsorbed on the surface we find a small stabilisation of the molecularly adsorbed state when the CO⋯C separation is ~ 3 Å, but repulsive interactions reduce the binding energy at shorter distances. The molecularly adsorbed states are affected by the presence of surface carbon with some structures that are transition states for molecular diffusion becoming minima with co-adsorbed carbon. This also leads to lower energy pathways for Cdbnd O bond cleavage so that our results indicate that surface carbide formation is auto-catalytic at low C coverage.

  13. Collision-induced dissociation products of the protonated dipeptide carnosine: structural elucidation, fragmentation pathways and potential energy surface analysis.

    PubMed

    Moustafa, Eslam M; Ritacco, Ida; Sicilia, Emilia; Russo, Nino; Shoeib, Tamer

    2015-05-21

    Collision-induced dissociation (CID) experiments on protonated carnosine, [carnosine + H](+), with several collision energies were shown to yield eleven different fragment ions with the generation of product ions [carnosine-H2O + H](+) and [carnosine-NH3 + H](+) being the lowest energy processes. Energy-resolved CID showed that at slightly higher collision energies the ions [histidine + H](+) and [histidine-H2O-CO + H](+) are formed. At even higher energies four other product ions were observed, however, attained relatively lower abundances. Quantum chemistry calculations, carried out at different levels of theory, were employed to probe fragmentation mechanisms that account for all the experimental data. All the adopted computational protocols give similar energetic trends, and the range of the calculated free energy barrier values for the generation of all the observed product ions is in agreement with the fragmentation mechanisms offered here. PMID:25903223

  14. Vibrational and Electronic Energy Transfer and Dissociation of Diatomic Molecules by Electron Collisions

    NASA Technical Reports Server (NTRS)

    Huo, Winifred M.; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    At high altitudes and velocities equal to or greater than the geosynchronous return velocity (10 kilometers per second), the shock layer of a hypersonic flight will be in thermochemical nonequilibrium and partially ionized. The amount of ionization is determined by the velocity. For a trans atmospheric flight of 10 kilometers per second and at an altitude of 80 kilometers, a maximum of 1% ionization is expected. At a velocity of 12 - 17 kilometer per second, such as a Mars return mission, up to 30% of the atoms and molecules in the flow field will be ionized. Under those circumstances, electrons play an important role in determining the internal states of atoms and molecules in the flow field and hence the amount of radiative heat load and the distance it takes for the flow field to re-establish equilibrium. Electron collisions provide an effective means of transferring energy even when the electron number density is as low as 1%. Because the mass of an electron is 12,760 times smaller than the reduced mass of N2, its average speed, and hence its average collision frequency, is more than 100 times larger. Even in the slightly ionized regime with only 1% electrons, the frequency of electron-molecule collisions is equal to or larger than that of molecule-molecule collisions, an important consideration in the low density part of the atmosphere. Three electron-molecule collision processes relevant to hypersonic flows will be considered: (1) vibrational excitation/de-excitation of a diatomic molecule by electron impact, (2) electronic excitation/de-excitation, and (3) dissociative recombination in electron-diatomic ion collisions. A review of available data, both theory and experiment, will be given. Particular attention will be paid to tailoring the molecular physics to the condition of hypersonic flows. For example, the high rotational temperatures in a hypersonic flow field means that most experimental data carried out under room temperatures are not applicable. Also, the average electron temperature is expected to be between 10,000 and 20,000 K. Thus only data for low energy electrons are relevant to the model.

  15. Using beryllium bonds to change halogen bonds from traditional to chlorine-shared to ion-pair bonds.

    PubMed

    Alkorta, Ibon; Elguero, José; Mó, Otilia; Yáñez, Manuel; Del Bene, Janet E

    2015-01-21

    Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to investigate the structures, binding energies, and bonding characteristics of binary complexes HFBe:FCl, R2Be:FCl, and FCl:N-base, and of ternary complexes HFBe:FCl:N-base and R2Be:FCl:N-base for R = H, F, Cl; N-base = NH3, NHCH2, NCH. Dramatic synergistic cooperative effects have been found between the Be···F beryllium bonds and the Cl···N halogen bonds in ternary complexes. The Cl···N traditional halogen bonds and the Be···F beryllium bonds in binary complexes become significantly stronger in ternary complexes, while the F-Cl bond weakens. Charge-transfer from F to the empty p(?) orbital of Be leads to a bending of the XYBe molecule and a change in the hybridization of Be, which in the limit becomes sp(2). As a function of the intrinsic basicity of the nitrogen base and the intrinsic acidity of the Be derivative, the halogen-bond type evolves from traditional to chlorine-shared to ion-pair bonds. The mechanism by which an ion-pair complex is formed is similar to that involved in the dissociative proton attachment process. EOM-CCSD spin-spin coupling constants (1X)J(Cl-N) across the halogen bond in these complexes also provide evidence of the same evolution of the halogen-bond type. PMID:25486548

  16. Interstellar Isomers: The Importance of Bonding Energy Differences

    NASA Technical Reports Server (NTRS)

    Remijan, Anthony J.; Hollis, J. M.; Lovas, F. J.; Plusquellic, D. F.; Jewell, P. R.

    2005-01-01

    We present strong detections of methyl cyanide (CH3CN), vinyl cyanide (CH2CHCN), ethyl cyanide (CH3CH2CN) and cyanodiacetylene (HC4CN) molecules with the Green Bank Telescope (GBT) toward the Sgr B2(N) molecular cloud. Attempts to detect the corresponding isocyanide isomers were only successful in the case of methyl isocyanide (CH3NC) for its J(sub K) = 1(sub 0) - 0(sub 0) transition, which is the first interstellar report of this line. To determine the spatial distribution of CH3NC, we used archival Berkeley-Illinois-Maryland Association (BIMA) array data for the J(sub K) = 1(sub 0) - 0(sub 0) transitions but no emission was detected. From ab initio calculations, the bonding energy difference between the cyanide and isocyanide molecules is greater than 8500 per centimeter (greater than 12,000 K). Thus, cyanides are the more stable isomers and would likely be formed more preferentially over their isocyanide counterparts. That we detect CH3NC emission with a single antenna (Gaussian beamsize(omega(sub B))=1723 arcsec(sup 2)) but not with an interferometer (omega(sub b)=192 arcsec(sup 2)), strongly suggests that CH3NC has a widespread spatial distribution toward the Sgr B2(N) region. Other investigators have shown that CH3CN is present both in the LMH hot core of Sgr B2(N) and in the surrounding medium, while we have shown that CH3NC appears to be deficient in the LMH hot core. Thus, largescale, non-thermal processes in the surrounding medium may account for the conversion of CH3CN to CH3NC while the LMH hot core, which is dominated by thermal processes, does not produce a significant amount of CH3NC. Ice analog experiments by other investigators have shown that radiation bombardment of CH3CN can produce CH3NC, thus supporting our observations. We conclude that isomers separated by such large bonding energy differences are distributed in different interstellar environments, making the evaluation of column density ratios between such isomers irrelevant unless it can be independently shown that these species are co-spatial.

  17. Free Energy Landscapes for S-H Bonds in (Cp2Mo2S4)-Mo-star Complexes

    SciTech Connect

    Appel, Aaron M.; Lee, Suh-Jane; Franz, James A.; DuBois, Daniel L.; Rakowski DuBois, Mary

    2009-03-23

    Extensive thermochemical data have been determined for a series of complexes derived from Cp*Mo(? S)2(? SMe)(? SH)MoCp* and Cp*Mo(? S)2(? SH)2MoCp*. These data include electrochemical potentials, pKa values, homolytic solution bond dissociation free energies (SBDFEs), and hydride donor abilities in acetonitrile. Thermochemical data ranged from +0.6 to -2.0 V vs FeCp2+/o for electrochemical potentials, 5 to 31 for pKa values, 43 to 68 kcal/mol for homolytic SBDFEs, and 44 to 84 kcal/mol for hydride donor abilities. The observed values for these thermodynamic parameters are comparable to those of many transition metal hydrides, which is consistent with the many parallels in the chemistry of these two classes of compounds. The wealth of thermochemical data are presented in free energy landscapes as a useful approach to visualizing and understanding the relative stabilities of all of the species under specified conditions. This work was supported by the U.S. Department of Energy's (DOE) Office of Basic Energy Sciences, Chemical Sciences program. The Pacific Northwest National Laboratory is operated by Battelle for DOE.

  18. Dissociative electron attachment studies on acetone

    SciTech Connect

    Prabhudesai, Vaibhav S. Tadsare, Vishvesh; Ghosh, Sanat; Gope, Krishnendu; Davis, Daly; Krishnakumar, E.

    2014-10-28

    Dissociative electron attachment (DEA) to acetone is studied in terms of the absolute cross section for various fragment channels in the electron energy range of 0–20 eV. H{sup ?} is found to be the most dominant fragment followed by O{sup ?} and OH{sup ?} with only one resonance peak between 8 and 9 eV. The DEA dynamics is studied by measuring the angular distribution and kinetic energy distribution of fragment anions using Velocity Slice Imaging technique. The kinetic energy and angular distribution of H{sup ?} and O{sup ?} fragments suggest a many body break-up for the lone resonance observed. The ab initio calculations show that electron is captured in the multi-centered anti-bonding molecular orbital which would lead to a many body break-up of the resonance.

  19. Theoretical Electric Dipole Moments and Dissociation Energies for the Ground States of GaH-BrH

    NASA Technical Reports Server (NTRS)

    Pettersson, Lars G. M.; Langhoff, Stephen R.

    1986-01-01

    Reliable experimental diople moments are available for the ground states of SeH and BrH whereas no values have been reported for GaH and AsH a recently reported experimental dipole moment for GeH of 1.24 + or -0.01 D has been seriously questioned, and a much lower value of, 0.1 + or - 0.05 D, suggested. In this work, we report accurate theoretical dipole moments, dipole derivatives, dissociation energies, and spectroscopic constants (tau(sub e), omega(sub e)) for the ground states of GaH through BrH.

  20. Dissociation Energies and Potential Energy Functions for the Ground X 1

    E-print Network

    Le Roy, Robert J.

    -Crossing' A 1 + States of NaH Sadru-Dean Walji, Katherine M. Sentjens and Robert J. Le Roy Department determination of centrifugal (non-adiabatic) and potential-energy (adiabatic) Born-Oppenheimer breakdown potential energy function and Born-Oppenheimer breakdown (BOB) correction functions that explain all

  1. Size-dependent stability toward dissociation and ligand binding energies of phosphine-ligated gold cluster ions

    SciTech Connect

    Johnson, Grant E.; Priest, Thomas A.; Laskin, Julia

    2014-01-01

    The stability of sub-nanometer size gold clusters ligated with organic molecules is of paramount importance to the scalable synthesis of monodisperse size-selected metal clusters with highly tunable chemical and physical properties. For the first time, a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR-MS) equipped with surface induced dissociation (SID) has been employed to investigate the time and collision energy resolved fragmentation behavior of cationic doubly charged gold clusters containing 7-9 gold atoms and 6-7 triphenylphosphine (TPP) ligands prepared by reduction synthesis in solution. The TPP ligated gold clusters are demonstrated to fragment through three primary dissociation pathways: (1) Loss of a neutral TPP ligand from the precursor gold cluster, (2) asymmetric fission and (3) symmetric fission and charge separation of the gold core resulting in formation of complementary pairs of singly charged fragment ions. Threshold energies and activation entropies of these fragmentation pathways have been determined employing Rice-Ramsperger-Kassel-Marcus (RRKM) modeling of the experimental SID data. It is demonstrated that the doubly charged cluster ion containing eight gold atoms and six TPP ligands, (8,6)2+, exhibits exceptional stability compared to the other cationic gold clusters examined in this study due to its large ligand binding energy of 1.76 eV. Our findings demonstrate the dramatic effect of the size and extent of ligation on the gas-phase stability and preferred fragmentation pathways of small TPP-ligated gold clusters.

  2. Seniority number description of potential energy surfaces: Symmetric dissociation of water, N2, C2, and Be2

    NASA Astrophysics Data System (ADS)

    Bytautas, Laimutis; Scuseria, Gustavo E.; Ruedenberg, Klaus

    2015-09-01

    The present study further explores the concept of the seniority number (?) by examining different configuration interaction (CI) truncation strategies in generating compact wave functions in a systematic way. While the role of ? in addressing static (strong) correlation problem has been addressed in numerous previous studies, the usefulness of seniority number in describing weak (dynamic) correlation has not been investigated in a systematic way. Thus, the overall objective in the present work is to investigate the role of ? in addressing also dynamic electron correlation in addition to the static correlation. Two systematic CI truncation strategies are compared beyond minimal basis sets and full valence active spaces. One approach is based on the seniority number (defined as the total number of singly occupied orbitals in a determinant) and another is based on an excitation-level limitation. In addition, molecular orbitals are energy-optimized using multiconfigurational-self-consistent-field procedure for all these wave functions. The test cases include the symmetric dissociation of water (6-31G), N2 (6-31G), C2 (6-31G), and Be2 (cc-pVTZ). We find that the potential energy profile for H2O dissociation can be reasonably well described using only the ? = 0 sector of the CI wave function. For the Be2 case, we show that the full CI potential energy curve (cc-pVTZ) is almost exactly reproduced using either ?-based (including configurations having up to ? = 2 in the virtual-orbital-space) or excitation-based (up to single-plus-double-substitutions) selection methods, both out of a full-valence-reference function. Finally, in dissociation cases of N2 and C2, we shall also consider novel hybrid wave functions obtained by a union of a set of CI configurations representing the full valence space and a set of CI configurations where seniority-number restriction is imposed for a complete set (full-valence-space and virtual) of correlated molecular orbitals, simultaneously. We discuss the usefulness of the seniority number concept in addressing both static and dynamic electron correlation problems along dissociation paths.

  3. Characterization of a beta-Asp33 isoform of recombinant hirudin sequence variant 1 by low-energy collision-induced dissociation.

    PubMed

    Schindler, P; Müller, D; Märki, W; Grossenbacher, H; Richter, W J

    1996-09-01

    A new low-concentration congener (Ib) of recombinant hirudin sequence variation 1 was structurally characterized as a beta-Asp33 isoform of the parent protein (Ia). alpha-beta Isomerization at the 33-position was expected in view of the previous isolation of a potential precursor (Asp33-Gly34-anhydro-hirudin (Ic)), i.e., a succinimide-type dehydration product liable to undergo facile hydrolysis with ring opening, yielding beta- (along with alpha-) aspartates. In order to identify and locate the modified site in Ib, a sufficiently small peptide ([28-35]-octapeptide IIIb) was prepared by disulfide bond reduction, S-alkylation (pyridylethylation) and twofold enzymatic degradation (Glu-C protease followed by trypsin). When [M + H] + ions of IIIb were analyzed by electrospray ionization tandem mass spectrometry (ESIMS/MS) and low-energy collision-induced dissociation (CID), a singular [bn + H2O]+ ion indicative of beta-Asp in the neighboring 'n + 1' position was observed for n = 5. This located the beta-Asp residue unambiguously in the 6-position of IIIb and thus, as expected, in the 33-position of Ib. The formation of this highly diagnostic [bn + H2O]+ ion, for which precedents had only been reported for CID under high-energy conditions, requires net OH migration from one to another amino acid position. Confirmatory results from 18O-labeling of the suspected migratory oxygen atom (beta-Asp33-CO18OH) together with the low-energy genesis suggest a specific charge-triggered rather than charge-remote mechanism for the formation of the ion. The analogy of this process to the ejection of the C-terminal amino acid similarly involving net OH rearrangement is discussed. PMID:8831150

  4. Bond Energy Sums in Benzene, Cyclohexatriene and Cyclohexane Prove Resonance Unnecessary

    E-print Network

    Raji Heyrovska

    2008-07-27

    The recent new structure of benzene shows that it consists of three C atoms of radii as in graphite alternating with three C atoms with double bond radii. This is different from the hypothetical cyclohexatriene (Kekule structure) involving alternate double and single bonds. It was shown that the difference in the bond energy sum of the atomic structure of benzene from that of the Kekule structure is the energy (erroneously) assumed to be due to resonance. Here it is shown that the present structure of benzene also explains the energy of hydrogenation into cyclohexane and its difference from that of cyclohexatriene.

  5. Dissociative ionization of H2+ : Few-cycle effect in the joint electron-ion energy spectrum

    NASA Astrophysics Data System (ADS)

    Mosert, V.; Bauer, D.

    2015-10-01

    Joint electron-ion energy spectra for the dissociative ionization of a model H2+ in few-cycle, infrared laser pulses are calculated via the numerical ab initio solution of the time-dependent Schrödinger equation. A strong, pulse-dependent modulation of the ionization probability for certain values of the protons' kinetic energy (but almost independent of the electron's energy) is observed. With the help of models with frozen ions, this feature, which mistakenly might be attributed to vibrational excitations, is traced back to the transient population of electronically excited states, followed by ionization. This assertion is further corroborated employing a two-level model incorporating strong-field ionization from the excited state.

  6. Protein sequence and structural studies employing matrix-assisted laser desorption ionization-high energy collision-induced dissociation

    NASA Astrophysics Data System (ADS)

    Medzihradszky, K. F.; Maltby, D. A.; Qiu, Y.; Yu, Z.; Hall, S. C.; Chen, Y.; Burlingame, A. L.

    1997-01-01

    Matrix-assisted laser desorption ionization (MALDI) is one of the most sensitive ionization methods currently available for the mass spectrometric investigation of a wide range of structural problems involving macromolecules of biomedical significance. This laboratory has recently reported the use of MALDI with tandem mass spectrometry and high energy collision induced dissociation for the unambiguous de novo sequence analysis of peptides from an unknown P450 protein [K.F. Medzihradszky, G.W. Adams, R.H. Bateman, M.R. Green and A.L. Burlingame, J. Am. Soc. Mass Spectrom., 7 (1996) 1]. This report describes the characteristics and the advantages now available using high energy collisional activation of MALDI-generated pseudomolecular ions for sequence and structural characterization of proteins and covalently modified proteins that are not accessible under low energy conditions for many types of structures.

  7. Dissociative recombination of CH4(+).

    PubMed

    Thomas, Richard D; Kashperka, Iryna; Vigren, E; Geppert, Wolf D; Hamberg, Mathias; Larsson, Mats; af Ugglas, Magnus; Zhaunerchyk, Vitali

    2013-10-01

    CH4(+) is an important molecular ion in the astrochemistry of diffuse clouds, dense clouds, cometary comae, and planetary ionospheres. However, the rate of one of the common destruction mechanisms for molecular ions in these regions, dissociative recombination (DR), is somewhat uncertain. Here, we present absolute measurements for the DR of CH4(+) made using the heavy ion storage ring CRYRING in Stockholm, Sweden. From our collision-energy dependent cross-sections, we infer a thermal rate constant of k(Te) = 1.71(±0.02) × 10(–6)(Te/300)(?0.66(±0.02)) cm3 s(–1) over the region of electron temperatures 10 ? Te ? 1000 K. At low collision energies, we have measured the branching fractions of the DR products to be CH4 (0.00 ± 0.00); CH3 + H (0.18 ± 0.03); CH2 + 2H (0.51 ± 0.03); CH2 + H2 (0.06 ± 0.01); CH + H2 + H (0.23 ± 0.01); and CH + 2H2 (0.02 ± 0.01), indicating that two or more C–H bonds are broken in 80% of all collisions. PMID:23651407

  8. Low energy collision-induced dissociation and photodissociation studies of the (N2O,H2O) + cluster ion

    NASA Astrophysics Data System (ADS)

    Bastian, Michael J.; Dressler, Rainer A.; Levandier, Dale J.; Murad, Edmond; Muntean, Felician; Armentrout, P. B.

    1997-06-01

    Low energy collision-induced dissociation (CID) and photodissociation measurements of monohydrated nitrous oxide cluster ions are presented. The CID measurements have been conducted with ions produced in both thermal and supersonic jet sources, and with both Ne and Ar as collision gases. In all experiments, H2O+, N2O+, and N2OH+ fragments are observed, for which CID thresholds (0 K) of 1.04±0.06, 1.43±0.12 and 1.32±0.10 eV are determined, respectively. The thermal source experimental thresholds are consistent with all fragment ions originating from a single isomeric precursor ion, [N2O?H2O]+. Whereas both N2O+ and N2OH+ CID curves are comparable in the thermal source and supersonic jet source experiments, considerable differences are observed in the H2O+ CID measurements. The differences are attributed to loosely bound cluster-ion isomeric forms produced in the jet source experiment. In the photodissociation experiments, branching ratios measured with the present jet source are very similar to those observed in previously reported thermal experiments [S. T. Graul, H-S. Kim, and M. T. Bowers, Int. J. Mass Spectrom. Ion Proc. 117, 507 (1992)]. All of the fragment ions can be accounted for by invoking an optical transition from ground state [N2O?H2O]+ to an excited state associated with the N2O+H2O+ (Ã) dissociation limit. The H2O+ and N2O+ branching ratios are primarily governed by predissociation of the upper state followed by charge-transfer dynamics along a repulsive dissociation coordinate. Formation of N2OH+ is postulated to be controlled by a competing internal conversion process that leads to a longer-lived complex that decays to proton transfer products.

  9. Atomistic spectrometrics of local bond-electron-energy pertaining to Na and K clusters

    NASA Astrophysics Data System (ADS)

    Bo, Maolin; Wang, Yan; Huang, Yongli; Liu, Yonghui; Li, Can; Sun, Chang Q.

    2015-01-01

    Consistency between density functional theory calculations and photoelectron spectroscopy measurements confirmed our predications on the undercoordination-induced local bond relaxation and core level shift of Na and K clusters. It is clarified that the shorter and stronger bonds between under-coordinated atoms cause local densification and local potential well depression and shift the electron binding-energy accordingly. Numerical consistency turns out the energy levels for an isolated Na (E2p = 31.167 eV) and K (E3p = 18.034 eV) atoms and their respective bulk shifts of 2.401 eV and 2.754 eV, which is beyond the scope of conventional approaches. This strategy has also resulted in quantification of the local bond length, bond energy, binding energy density, and atomic cohesive energy associated with the undercoordinated atoms.

  10. CH3(+) Formation in the Dissociation of Energy-Selected CH3F(+) Studied by Double Imaging Electron/Ion Coincidences.

    PubMed

    Tang, Xiaofeng; Garcia, Gustavo A; Nahon, Laurent

    2015-06-11

    The dissociation of energy-selected methyl fluoride ion CH3F(+) along the CH3(+) and F formation channel has been investigated in detail in the 12.2-19.8 eV energy range. Three low-lying electronic states of the CH3F(+) ion, X(2)E, A(2)A1, and B(2)E, were prepared and analyzed by the method of double imaging photoelectron photoion coincidence (i(2)PEPICO). Three types of CH3(+) fragment ions corresponding to the dissociation of X(2)E, A(2)A1, and B(2)E electronic states have been observed and identified through their kinetic energy release distribution (KERD) curves, showing that the dissociation of the CH3F(+) ion in the different electronic states along the CH3(+) formation channel is state-specific, even outside of the Franck-Condon region. Highly excited vibrational levels of the X(2)E ground state can be populated through a resonant or near-resonant autoionization process and undergo vibrational predissociation into CH3(+) fragment ions. The A(2)A1 first excited state is repulsive along the F-loss coordinate, and its dissociation is direct and fast. The CH3F(+) ions in the B(2)E excited state first undergo an internal conversion toward the hot cation ground state X(2)E and then statistically dissociate into CH3(+) and F fragments. PMID:25534716

  11. Free Energy Diagram for the Heterogeneous Enzymatic Hydrolysis of Glycosidic Bonds in Cellulose.

    PubMed

    Sørensen, Trine Holst; Cruys-Bagger, Nicolaj; Borch, Kim; Westh, Peter

    2015-09-01

    Kinetic and thermodynamic data have been analyzed according to transition state theory and a simplified reaction scheme for the enzymatic hydrolysis of insoluble cellulose. For the cellobiohydrolase Cel7A from Hypocrea jecorina (Trichoderma reesei), we were able to measure or collect relevant values for all stable and activated complexes defined by the reaction scheme and hence propose a free energy diagram for the full heterogeneous process. For other Cel7A enzymes, including variants with and without carbohydrate binding module (CBM), we obtained activation parameters for the association and dissociation of the enzyme-substrate complex. The results showed that the kinetics of enzyme-substrate association (i.e. formation of the Michaelis complex) was almost entirely entropy-controlled and that the activation entropy corresponded approximately to the loss of translational and rotational degrees of freedom of the dissolved enzyme. This implied that the transition state occurred early in the path where the enzyme has lost these degrees of freedom but not yet established extensive contact interactions in the binding tunnel. For dissociation, a similar analysis suggested that the transition state was late in the path where most enzyme-substrate contacts were broken. Activation enthalpies revealed that the rate of dissociation was far more temperature-sensitive than the rates of both association and the inner catalytic cycle. Comparisons of one- and two-domain variants showed that the CBM had no influence on the transition state for association but increased the free energy barrier for dissociation. Hence, the CBM appeared to promote the stability of the complex by delaying dissociation rather than accelerating association. PMID:26183776

  12. Hypovalency--a kinetic-energy density description of a 4c-2e bond.

    PubMed

    Jacobsen, Heiko

    2009-06-01

    A bond descriptor based on the kinetic energy density, the localized-orbital locator (LOL), is used to characterize the nature of the chemical bond in electron deficient multi-center bonds. The boranes B(2)H(6), B(4)H(4), B(4)H(10), [B(6)H(6)](2-), and [B(6)H(7)](-) serve as prototypical examples of hypovalent 3c-2e and 4c-2e bonding. The kinetic energy density is derived from a set of Kohn-Sham orbitals obtained from pure density functional calculations (PBE/TZVP), and the topology of LOL is analyzed in terms of (3,-3) attractors (Gamma). The B-B-B and B-H-B 3c-2e, and the B-B-H-B 4c-2e bonding situations are defined by their own characteristic LOL profiles. The presence of one attractor in relation to the three or four atoms that are engaged in electron deficient bonding provides sufficient indication of the type of 3c-2e or 4c-2e bond present. For the 4c-2e bond in [B(6)H(7)](-) the LOL analysis is compared to results from an experimental QTAIM study. PMID:19452076

  13. Theoretical insights into the structures and mechanical properties of HMX/NQ cocrystal explosives and their complexes, and the influence of molecular ratios on their bonding energies.

    PubMed

    Li, Yong-Xiang; Chen, Shu-Sen; Ren, Fu-de

    2015-09-01

    Molecular dynamics (MD) methods were employed to study the binding energies and mechanical properties of selected crystal planes of 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane (HMX)/nitroguanidine (NQ) cocrystals at different molecular molar ratios. The densities and detonation velocities of the cocrystals at different molar ratios were estimated. The intermolecular interaction and bond dissociation energy (BDE) of the N-NO2 bond in the HMX:NQ (1:1) complex were calculated using the B3LYP, MP2(full) and M06-2X methods with the 6-311++G(d,p) and 6-311++G(2df,2p) basis sets. The results indicated that the HMX/NQ cocrystal prefers cocrystalizing in a 1:1 molar ratio, and the cocrystallization is dominated by the (0 2 0) and (1 0 0) facets. The K, G, and E values of the ratio of 1:1 are smaller than those of the other ratios, and the 1:1 cocrystal has the best ductility. The N-NO2 bond becomes stronger upon the formation of the intermolecular H-bonding interaction and the sensitivity of HMX decreases in the cocrystal. This sensitivity change in the HMX/NQ cocrystal originates not only from the formation of the intermolecular interaction but also from the increment of the BDE of N-NO2 bond in comparison with isolated HMX. The HMX/NQ (1:1) cocrystal exhibits good detonation performance. Reduced density gradient (RDG) reveals the nature of cocrystallization. Analysis of the surface electrostatic potential further confirmed that the sensitivity decreases in complex (or cocrystal) in comparison with that in isolated HMX. PMID:26318201

  14. Comparison of the proton-transfer paths in hydrogen bonds from theoretical potential-energy surfaces and the concept of conservation of bond order III. O-H-O hydrogen bonds.

    PubMed

    Majerz, Irena; Olovsson, Ivar

    2010-01-01

    The quantum-mechanically derived reaction coordinates (QMRC) for the proton transfer in O-H-O hydrogen bonds have been derived from ab initio calculations of potential-energy surfaces. A comparison is made between the QMRC and the corresponding bond-order reaction coordinates (BORC) derived by applying the Pauling bond order concept together with the principle of conservation of bond order. In agreement with earlier results for N-H-N(+) hydrogen bonds there is virtually perfect agreement between the QMRC and BORC curves for intermolecular O-H-O hydrogen bonds. For intramolecular O-H-O hydrogen bonds, the donor and acceptor parts of the molecule impose strong constraints on the O···O distance and the QMRC does not follow the BORC relation in the whole range. The neutron-determined proton positions are located close to the theoretically calculated potential-energy minima, and where the QMRC and the BORC curves coincide with each other. The results confirm the universal character of intermolecular hydrogen bonds: BORC is identical with QMRC and the proton can be moved from donor to acceptor keeping its valency equal to 1. The shape of PES for intramolecular hydrogen bonds is more complex as it is sensitive to the geometry of the molecule as well as of the hydrogen bridge. PMID:20379578

  15. Cascade Dissociations of Peptide Cation-Radicals. Part2. Infrared Multiphoton Dissociation and Mechanistic Studies of z-Ions from Pentapeptides

    PubMed Central

    Ledvina, Aaron R.; Chung, Thomas W.; Hui, Renjie; Coon, Joshua J.

    2013-01-01

    Dissociations of z4 ions from pentapeptides AAXAR, where X = H, Y, F, W, and V, produce dominant z2 ions that account for >50% of the fragment ion intensity. The dissociation has been studied in detail by experiment and theory and found to involve several isomerization and bond-breaking steps. Isomerizations in z4 ions proceed by amide transcis rotations followed by radical-induced transfer of a ?-hydrogen atom from the side chain, forming stable C? radical intermediates. These undergo rate-determining cleavage of the C?—CO bond at the X residue followed by loss of the neutral AX fragment, forming x2 intermediates. The latter were detected by energy-resolved resonant excitation collision-activated dissociation (CAD) and infrared multiphoton dissociation (IRMPD) experiments. The x2 intermediates undergo facile loss of HNCO to form z2 fragment ions, as also confirmed by energy-resolved CAD and IRMPD MS4 experiments. The loss of HNCO from the x2 ion from AAHWR is kinetically hampered by the Trp residue that traps the OCNH radical group in a cyclic intermediate. PMID:22669762

  16. Rhodium-Carbon Bond Energies in TpRh(CNneopentyl)(CH2X)H: Quantifying Stabilization Effects in M-C Bonds

    E-print Network

    Jones, William D.

    Rhodium-Carbon Bond Energies in TpRh(CNneopentyl)(CH2X)H: Quantifying Stabilization Effects in M carbonyl shows preferential formation of linear over branched aldehydes (4:1), and use of a bulkier rhodium

  17. Low-Energy Collision-Induced Dissociation Fragmentation Analysis of Cysteinyl-Modified Peptides

    SciTech Connect

    Borisov, Oleg V.; Goshe, Michael B.); Conrads, Thomas P.); Rakov, Vsevolod S.); Veenstra, Timothy D.); Smith, Richard D.)

    2002-05-15

    The development of methods to chemically modify and isolate cysteinyl-residue containing peptides (Cys-peptides) for LC-MS/MS analysis has generated considerable interest in the field of proteomics. Methods using isotope-coded affinity tags (ICAT) and (+)-biotinyl-iodoacetamidyl-3,6-dioxaoctanediamine (iodoacetyl-PEO-biotin) employ similar Cys-modifying reagents that contain a thiolate-specific biotin group to modify and isolate Cys-containing peptides in conjunction with immobilized avidin. For these strategies to be effective on a proteome-wide level, the presence of the ICAT or acetyl-PEO-biotin tag should not interfere with the efficiency of induced dissociation in MS/MS experiments or with the identification of the modified Cys-peptides by automated database searching algorithms. We have compared the collision-induced dissociation (CID) fragmentation patterns of peptides labeled with iodoacetyl-PEO-biotin and the ICAT reagent to those of the unmodified peptides. CID of Cys-peptides modified with either reagent resulted in the formation of ions attributed to the modified Cys-peptides as well as those unique to the labeling reagent. As demonstrated by analyzing acetyl-PEO-biotin labeled peptides from ribonuclease A and the ICAT-labeled proteome of D. radiodurans, the presence of these labeled-specific product ions provides a useful identifier to discern whether a peptide has been modified with the Cys-specific reagent, especially when a number of peptides analyzed using these methods do not contain a modified Cys-residue, and to differentiate identical Cys-peptides labeled with either ICAT-D0 or ICAT-D8.

  18. Hydrogen bond cooperativity in water hexamers: atomic energy perspective of local stabilities.

    PubMed

    Albrecht, Laura; Chowdhury, Saptarshi; Boyd, Russell J

    2013-10-17

    Atomic energies are used to describe local stability in eight low-lying water hexamers: prism, cage, boat 1, boat 2, bag, chair, book 1, and book 2. The energies are evaluated using the quantum theory of atoms in molecules (QTAIM) at MP2/aug-cc-pVTZ geometries. It is found that the simple, stabilizing cooperativity observed in linear hydrogen-bonded water systems is diminished as clusters move from nearly planar to three-dimensional structures. The prism, cage, and bag clusters can have local water stabilities differing up to 5 kcal mol(-1) as a result of mixed cooperative and anticooperative interactions. At the atomic level, in many cases a water may have a largely stabilized oxygen atom but the net water stability will be diminished due to strong destabilization of the water's hydrogen atoms. Analysis of bond critical point (BCP) electron densities shows that the reduced cooperativity results in a decrease in hydrogen bond strength and an increase in covalent bond strength, most evident in the prism. The chair, with the greatest cooperativity, has the largest average electron density at the BCP per hydrogen bond, whereas the cage has the largest total value for BCP density at all hydrogen bonds. The cage also has the second largest value (after the prism) for covalent bond critical point densities and an oxygen-oxygen BCP which may factor into the experimentally observed stability of the structure. PMID:24067198

  19. Protein unfolding from free-energy calculations: Integration of the Gaussian network model with bond binding energies

    NASA Astrophysics Data System (ADS)

    Srivastava, Amit; Granek, Rony

    2015-02-01

    Motivated by single molecule experiments, we study thermal unfolding pathways of four proteins, chymotrypsin inhibitor, barnase, ubiquitin, and adenylate kinase, using bond network models that combine bond energies and elasticity. The protein elasticity is described by the Gaussian network model (GNM), to which we add prescribed bond binding energies that are assigned to all (nonbackbone) connecting bonds in the GNM of native state and assumed identical for simplicity. Using exact calculation of the Helmholtz free energy for this model, we consider bond rupture single events. The bond designated for rupture is chosen by minimizing the free-energy difference for the process, over all (nonbackbone) bonds in the network. Plotting the free-energy profile along this pathway at different temperatures, we observe a few major partial unfolding, metastable or stable, states, that are separated by free-energy barriers and change role as the temperature is raised. In particular, for adenylate kinase we find three major partial unfolding states, which is consistent with single molecule FRET experiments [Pirchi et al., Nat. Commun. 2, 493 (2011), 10.1038/ncomms1504] for which hidden Markov analysis reveals between three and five such states. Such states can play a major role in enzymatic activity.

  20. Calculation of the Gibbs Free Energy of Solvation and Dissociation of HCl in Water via Monte Carlo Simulations and Continuum Solvation Models

    SciTech Connect

    McGrath, Matthew; Kuo, I-F W.; Ngouana, Brice F.; Ghogomu, Julius N.; Mundy, Christopher J.; Marenich, Aleksandr; Cramer, Christopher J.; Truhlar, Donald G.; Siepmann, Joern I.

    2013-08-28

    The free energy of solvation and dissociation of hydrogen chloride in water is calculated through a combined molecular simulation quantum chemical approach at four temperatures between T = 300 and 450 K. The free energy is first decomposed into the sum of two components: the Gibbs free energy of transfer of molecular HCl from the vapor to the aqueous liquid phase and the standard-state free energy of acid dissociation of HCl in aqueous solution. The former quantity is calculated using Gibbs ensemble Monte Carlo simulations using either Kohn-Sham density functional theory or a molecular mechanics force field to determine the system’s potential energy. The latter free energy contribution is computed using a continuum solvation model utilizing either experimental reference data or micro-solvated clusters. The predicted combined solvation and dissociation free energies agree very well with available experimental data. CJM was supported by the US Department of Energy,Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  1. Regulating energy transfer of excited carriers and the case for excitation-induced hydrogen dissociation on hydrogenated graphene

    PubMed Central

    Bang, Junhyeok; Meng, Sheng; Sun, Yi-Yang; West, Damien; Wang, Zhiguo; Gao, Fei; Zhang, S. B.

    2013-01-01

    Understanding and controlling of excited carrier dynamics is of fundamental and practical importance, particularly in photochemistry and solar energy applications. However, theory of energy relaxation of excited carriers is still in its early stage. Here, using ab initio molecular dynamics (MD) coupled with time-dependent density functional theory, we show a coverage-dependent energy transfer of photoexcited carriers in hydrogenated graphene, giving rise to distinctively different ion dynamics. Graphene with sparsely populated H is difficult to dissociate due to inefficient transfer of the excitation energy into kinetic energy of the H. In contrast, H can easily desorb from fully hydrogenated graphane. The key is to bring down the H antibonding state to the conduction band minimum as the band gap increases. These results can be contrasted to those of standard ground-state MD that predict H in the sparse case should be much less stable than that in fully hydrogenated graphane. Our findings thus signify the importance of carrying out explicit electronic dynamics in excited-state simulations. PMID:23277576

  2. Effects of Electron Kinetic Energy and Ion-Electron Inelastic Collisions in Electron Capture Dissociation Measured using Ion Nanocalorimetry

    PubMed Central

    O’Brien, Jeremy T.; Prell, James S.; Holm, Anne I. S.; Williams, Evan R.

    2008-01-01

    Ion nanocalorimetry is used to measure the effects of electron kinetic energy in electron capture dissociation (ECD). With ion nanocalorimetry, the internal energy deposited into a hydrated cluster upon activation can be determined from the number of water molecules that evaporate. Varying the heated cathode potential from ?1.3 to ?2.0 V during ECD has no effect on the average number of water molecules lost from the reduced clusters of either [Ca(H2O)15]2+ or [Ca(H2O)32]2+ even when these data are extrapolated to a cathode potential of zero volts. These results indicate that the initial electron kinetic energy does not go into internal energy in these ions upon ECD. No effects of ion heating from inelastic ion-electron collisions are observed for electron irradiation times up to 200 ms, although some heating occurs for [Ca(H2O)17]2+ at longer irradiation times. In contrast, this effect is negligible for [Ca(H2O)32]2+, a cluster size typically used in nanocalorimetry experiments, indicating that energy transfer from inelastic ion-electron collisions is negligible compared to effects of radiative absorption and emission for these larger clusters. These results have significance towards establishing the accuracy with which electrochemical red-ox potentials, measured on an absolute basis in the gas phase using ion nanocalorimetry, can be related to relative potentials measured in solution. PMID:18372190

  3. Bond Graph Modeling and Validation of an Energy Regenerative System for Emulsion Pump Tests

    PubMed Central

    Li, Yilei; Zhu, Zhencai; Chen, Guoan

    2014-01-01

    The test system for emulsion pump is facing serious challenges due to its huge energy consumption and waste nowadays. To settle this energy issue, a novel energy regenerative system (ERS) for emulsion pump tests is briefly introduced at first. Modeling such an ERS of multienergy domains needs a unified and systematic approach. Bond graph modeling is well suited for this task. The bond graph model of this ERS is developed by first considering the separate components before assembling them together and so is the state-space equation. Both numerical simulation and experiments are carried out to validate the bond graph model of this ERS. Moreover the simulation and experiments results show that this ERS not only satisfies the test requirements, but also could save at least 25% of energy consumption as compared to the original test system, demonstrating that it is a promising method of energy regeneration for emulsion pump tests. PMID:24967428

  4. Bond graph modeling and validation of an energy regenerative system for emulsion pump tests.

    PubMed

    Li, Yilei; Zhu, Zhencai; Chen, Guoan

    2014-01-01

    The test system for emulsion pump is facing serious challenges due to its huge energy consumption and waste nowadays. To settle this energy issue, a novel energy regenerative system (ERS) for emulsion pump tests is briefly introduced at first. Modeling such an ERS of multienergy domains needs a unified and systematic approach. Bond graph modeling is well suited for this task. The bond graph model of this ERS is developed by first considering the separate components before assembling them together and so is the state-space equation. Both numerical simulation and experiments are carried out to validate the bond graph model of this ERS. Moreover the simulation and experiments results show that this ERS not only satisfies the test requirements, but also could save at least 25% of energy consumption as compared to the original test system, demonstrating that it is a promising method of energy regeneration for emulsion pump tests. PMID:24967428

  5. Dissociative Recombination without a Curve Crossing

    NASA Technical Reports Server (NTRS)

    Guberman, Steven L.

    1994-01-01

    Ab initio calculations show that a curve crossing is not always needed for a high dissociative- recombination cross section. For HeH(+), in which no neutral states cross the ion potential curve, dissociative recombination is driven by the nuclear kinetic-energy operator on adiabatic potential curves. The kinetic-energy derivative operator allows for capture into repulsive curves that are outside of the classical turning points for the nuclear motion. The dominant dissociative route is the C (2)Sigma(+) state leading to H(n = 2) atoms. An analogous mechanism is proposed for the dissociative recombination of H3(+).

  6. Molecular resonant dissociation of surface-adsorbed molecules by plasmonic nanoscissors

    NASA Astrophysics Data System (ADS)

    Zhang, Zhenglong; Sheng, Shaoxiang; Zheng, Hairong; Xu, Hongxing; Sun, Mengtao

    2014-04-01

    The ability to break individual bonds or specific modes in chemical reactions is an ardently sought goal by chemists and physicists. While photochemistry based methodologies are very successful in controlling e.g. photocatalysis, photosynthesis and the degradation of plastic, it is hard to break individual molecular bonds for those molecules adsorbed on the surface because of the weak light-absorption in molecules and the redistribution of the resulting vibrational energy both inside the molecule and to its surrounding environment. Here we show how to overcome these obstacles with a plasmonic hot-electron mediated process and demonstrate a new method that allows the sensitive control of resonant dissociation of surface-adsorbed molecules by `plasmonic' scissors. To that end, we used a high-vacuum tip-enhanced Raman spectroscopy (HV-TERS) setup to dissociate resonantly excited NC2H6 fragments from Malachite green. The surface plasmons (SPs) excited at the sharp metal tip not only enhance the local electric field to harvest the light incident from the laser, but crucially supply `hot electrons' whose energy can be transferred to individual bonds. These processes are resonant Raman, which result in some active chemical bonds and then weaken these bonds, followed by dumping in lots of indiscriminant energy and breaking the weakest bond. The method allows for sensitive control of both the rate and probability of dissociation through their dependence on the density of hot electrons, which can be manipulated by tuning the laser intensity or tunneling current/bias voltage in the HV-TERS setup, respectively. The concepts of plasmonic scissors open up new versatile avenues for the deep understanding of in situ surface-catalyzed chemistry.The ability to break individual bonds or specific modes in chemical reactions is an ardently sought goal by chemists and physicists. While photochemistry based methodologies are very successful in controlling e.g. photocatalysis, photosynthesis and the degradation of plastic, it is hard to break individual molecular bonds for those molecules adsorbed on the surface because of the weak light-absorption in molecules and the redistribution of the resulting vibrational energy both inside the molecule and to its surrounding environment. Here we show how to overcome these obstacles with a plasmonic hot-electron mediated process and demonstrate a new method that allows the sensitive control of resonant dissociation of surface-adsorbed molecules by `plasmonic' scissors. To that end, we used a high-vacuum tip-enhanced Raman spectroscopy (HV-TERS) setup to dissociate resonantly excited NC2H6 fragments from Malachite green. The surface plasmons (SPs) excited at the sharp metal tip not only enhance the local electric field to harvest the light incident from the laser, but crucially supply `hot electrons' whose energy can be transferred to individual bonds. These processes are resonant Raman, which result in some active chemical bonds and then weaken these bonds, followed by dumping in lots of indiscriminant energy and breaking the weakest bond. The method allows for sensitive control of both the rate and probability of dissociation through their dependence on the density of hot electrons, which can be manipulated by tuning the laser intensity or tunneling current/bias voltage in the HV-TERS setup, respectively. The concepts of plasmonic scissors open up new versatile avenues for the deep understanding of in situ surface-catalyzed chemistry. Electronic supplementary information (ESI) available: Further experimental spectra and theoretical calculations. See DOI: 10.1039/c3nr06799h

  7. Low-Energy (0.1 eV) Electron Attachment SS Bond Cleavage

    E-print Network

    Simons, Jack

    Low-Energy (0.1 eV) Electron Attachment S­S Bond Cleavage Assisted by Coulomb Stabilization the Rydberg radical H3C­S­S­CH2­CH2­NH3) or into the S­S antibonding * orbital is shown to be able to produce the same S­S bond fragmentation products H3C­S and HS­CH2­CH2­NH2, albeit by very different pathways

  8. Statistical Characterization of the Charge State and Residue Dependence of Low-Energy CID Peptide Dissociation Patterns

    SciTech Connect

    Huang, Yingying; Triscari, Joseph M.; Tseng, George C.; Pasa-Tolic, Ljiljana; Lipton, Mary S.; Smith, Richard D.; Wysocki, Vicki H.

    2005-09-01

    Data mining was performed on 28 330 unique peptide tandem mass spectra for which sequences were assigned with high confidence. By dividing the spectra into different sets based on structural features and charge states of the corresponding peptides, chemical interactions involved in promoting specific cleavage patterns in gas-phase peptides were characterized. Pairwise fragmentation maps describing cleavages at all Xxx-Zzz residue combinations for b and y ions reveal that the difference in basicity between Arg and Lys results in different dissociation patterns for singly charged Arg- and Lys-ending tryptic peptides. While one dominant protonation form (proton localized) exists for Arg-ending peptides, a heterogeneous population of different protonated forms or more facile interconversion of protonated forms (proton partially mobile) exists for Lys-ending peptides. Cleavage C-terminal to acidic residues dominates spectra from peptides that have a localized proton and cleavage N-terminal to Pro dominates those that have a mobile or partially mobile proton. When Pro is absent from peptides that have a mobile or partially mobile proton, cleavage at each peptide bond becomes much more prominent. Whether the above patterns can be found in b ions, y ions, or both depends on the location of the proton holder(s). Enhanced cleavages C-terminal to branched aliphatic residues (Ile, Val, Leu) are observed in both b and y ions from peptides that have a mobile proton, as well as in y ions from peptides that have a partially mobile proton; enhanced cleavages N-terminal to these residues are observed in b ions from peptides that have a partially mobile proton. Statistical tools have been designed to visualize the fragmentation maps and measure the similarity between them. The pairwise cleavage patterns observed expand our knowledge of peptide gas-phase fragmentation behaviors and should be useful in algorithm development that employs improved models to predict fragment ion intensities.

  9. Chemical Bonds II

    ERIC Educational Resources Information Center

    Sanderson, R. T.

    1972-01-01

    The continuation of a paper discussing chemical bonding from a bond energy viewpoint, with a number of examples of single and multiple bonds. (Part I appeared in volume 1 number 3, pages 16-23, February 1972.) (AL)

  10. Vibrationally resolved structure in O{sub 2}{sup +} dissociation induced by intense ultrashort laser pulses

    SciTech Connect

    Zohrabi, M.; McKenna, J.; Gaire, B.; Johnson, Nora G.; Carnes, K. D.; De, S.; Bocharova, I. A.; Magrakvelidze, M.; Ray, D.; Litvinyuk, I. V.; Cocke, C. L.; Ben-Itzhak, I.

    2011-05-15

    Laser-induced dissociation of O{sub 2}{sup +} is studied in the strong-field limit using two independent methods, namely a crossed laser-ion-beam coincidence 3D momentum imaging method and a supersonic gas jet velocity map imaging technique (790 and 395 nm, 8-40 fs, {approx}10{sup 15} W/cm{sup 2}). The measured kinetic energy release spectra from dissociation of O{sub 2}{sup +} and dissociative ionization of O{sub 2} reveal vibrational structure which persists over a wide range of laser intensities. The vibrational structure is similar for O{sub 2}{sup +} produced incoherently in an ion source and coherently by laser pulses. By evaluation of the potential energy curves, we assign the spectral energy peaks to dissociation of the v=10-15 vibrational states of the metastable a {sup 4}{Pi}{sub u} state via the dissociation pathway |a {sup 4}{Pi}{sub u}>{yields}|f {sup 4}{Pi}{sub g}-1{omega}>--a mechanism equivalent to bond softening in H{sub 2}{sup +}.

  11. Quantum enhancement of vibrational predissociation near the dissociation threshold

    NASA Astrophysics Data System (ADS)

    Côté, R.; Dashevskaya, E. I.; Nikitin, E. E.; Troe, J.

    2004-01-01

    We discuss quantum enhancement of the quasiclassical vibrational predissociation (VP) rate of an atom (A)-diatom (BC) van der Waals (vdW) complex A-BC from a state lying close to the dissociation threshold. The enhancement is due to the accumulation of a noticeable fraction of the state population near the outer turning point of the A-BC bond. For potentials behaving as power-laws at large separations, the enhancement manifests itself in the variation of the energy dependence of the VP frequency factor from the classical frequency to its quantum counterpart. We show that it is related to the complex scattering length associated with the vibrational relaxation of BC in collisions with A. We also discuss the corrected quasiclassical quantization condition for energy levels of a diatom lying very close to the dissociation threshold. Our results generalize those of J. Trost, C. Eltshka, and H. Friedrich [J. Phys. B 31, 361 (1998)] and C. Boisseau et al. [Eur. Phys. J. D 12, 199 (2000)] for the calculation of complex energy levels of an anharmonic oscillator that dissociates from highly excited states under the action of a weak high-frequency perturbation.

  12. Identification of General Linear Relationships between Activation Energies and Enthalpy Changes for Dissociation Reactions at Surfaces

    E-print Network

    Alavi, Ali

    Identification of General Linear Relationships between Activation Energies and Enthalpy Changes is the activation energy. Thanks to recent computational and methodological advances, it is now possible to determine activation energies and reaction pathways for elementary catalytic reactions from first principles

  13. Analysis of a compressed thin film bonded to a compliant substrate: the energy scaling law

    E-print Network

    patterns, determining for each the associated scaling law. The one with the best law was a periodic "MiuraAnalysis of a compressed thin film bonded to a compliant substrate: the energy scaling law Robert V law of the minimum energy with respect to the physical parameters of the problem, and we prove

  14. The dissociation of low energy 1,2-propanediol ions: an intriguing mechanism revisited

    NASA Astrophysics Data System (ADS)

    Burgers, Peter C.; Fell, Lorne M.; Milliet, Arielle; Rempp, Muriel; Ruttink, Paul J. A.; Terlouw, Johan K.

    1997-11-01

    The fascinating unimolecular chemistry of ionized 1,2-propanediol, CH3C(H)OHCH2OH[middle dot]+, 1, has been re-examined using computational chemistry (ab initio MO and density functional theories) in conjunction with modern tandem mass spectrometric and 13C labelling experiments. The calculations allow a considerable simplification of a previously proposed complex mechanism (Org. Mass Spectrom., 23 (1988) 355). Again, the central intermediates are proposed to be stable hydrogen bridged ion--dipole complexes, but our present calculations indicate that the key transformation now is the rearrangement CH3C(H)OH+[middle dot][middle dot][middle dot]O(H)-CH2. --> CH3C(H)OH+[middle dot][middle dot][middle dot].OCH3, which can best be viewed as the cation-catalyzed 1,2-hydrogen shift .CH2OH --> CH3O., a rearrangement which does not occur so easily in the unassisted system. Another important process is the electron transfer CH3C(H)=O[middle dot][middle dot][middle dot]CH3OH[middle dot]+ --> O=CH(CH3)[middle dot]+[middle dot][middle dot][middle dot]O(H)CH3 which allows proton transfer to generate CH3OH2+ + CH3C=O.. Other dissociation processes (loss of CH3., H2O, H2O + CH3., H2O + CH4) are interpreted in terms of Bohme's `methyl cation shuttle' (J. Am. Chem. Soc., 118 (1996) 4500) taking place in ion-dipole complexes. The most stable intermediate is the hydrogen bridged ion-dipole complex CH2=CHOH.+[middle dot][middle dot][middle dot]O(H)CH3, which is the reacting configuration for loss of methanol.

  15. PREDICTION OF BOND DISSOCIATION ENERGIES AND TRANSITION STATE BARRIERS BY A MODIFIED COMPLETE BASIS SET MODEL CHEMISTRY. (R824970)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  16. Phonon-energy-coupling enhancement: Strengthening the chemical bonds of the SiO2/Si system

    E-print Network

    Chen, Zhi

    Phonon-energy-coupling enhancement: Strengthening the chemical bonds of the SiO2/Si system Zhi and Engineering, University of Kentucky, Lexington, Kentucky 40506 Fuqian Yang Department of Chemical-energy-coupling enhancement. The vibrational modes of the Si­Si and Si­O bonds exhibit enhanced energy coupling when the rapid

  17. High-Energy Collision-Induced Dissociation by MALDI TOF/TOF Causes Charge-Remote Fragmentation of Steroid Sulfates

    NASA Astrophysics Data System (ADS)

    Yan, Yuetian; Ubukata, Masaaki; Cody, Robert B.; Holy, Timothy E.; Gross, Michael L.

    2014-08-01

    A method for structural elucidation of biomolecules dating to the 1980s utilized high-energy collisions (~10 keV, laboratory frame) that induced charge-remote fragmentations (CRF), a class of fragmentations particularly informative for lipids, steroids, surfactants, and peptides. Unfortunately, the capability for high-energy activation has largely disappeared with the demise of magnetic sector instruments. With the latest designs of tandem time-of-flight mass spectrometers (TOF/TOF), however, this capability is now being restored to coincide with the renewed interest in metabolites and lipids, including steroid-sulfates and other steroid metabolites. For these metabolites, structure determinations are required at concentration levels below that appropriate for NMR. To meet this need, we explored CRF with TOF/TOF mass spectrometry for two groups of steroid sulfates, 3-sulfates and 21-sulfates. We demonstrated that the current generation of MALDI TOF/TOF instruments can generate charge-remote fragmentations for these materials. The resulting collision-induced dissociation (CID) spectra are useful for positional isomer differentiation and very often allow the complete structure determination of the steroid. We also propose a new nomenclature that directly indicates the cleavage sites on the steroid ring with carbon numbers.

  18. Low-mass ions produced from peptides by high-energy collision-induced dissociation in tandem mass spectrometry.

    PubMed

    Falick, A M; Hines, W M; Medzihradszky, K F; Baldwin, M A; Gibson, B W

    1993-11-01

    High-energy collision-induced dissociation (CID) mass spectrometry provides a rapid and sensitive means for determining the primary sequence of peptides. The low-mass region (below mass 300) of a large number of tandem CID spectra of peptides has been analyzed. This mass region contains several types of informative fragment ions, including dipeptide ions, immonium ions, and other related ions. Useful low-mass ions are also present in negative-ion CID spectra. Immonium ions (general structure [H2N=CH-R](+), where R is the amino acid side chain) and related ions characteristic of specific amino acid residues give information as to the presence or absence of these residues in the peptide being analyzed. Tables of observed immonium and reiated ions for the 20 standard amino acids and for a number of modified amino acids are presented. A database consisting of 228 high-energy CID spectra of peptides has been established, and the frequency of occurrence of various ions indicative of specific ammo acid residues has been determined. Two model computer-aided schemes for analysis of the ammo-acid content of unknown peptides have been developed and tested against the database. PMID:24227532

  19. Comparison of the proton-transfer path in hydrogen bonds from theoretical potential-energy surfaces and the concept of conservation of bond order. II. (N-H...N)(+) hydrogen bonds.

    PubMed

    Majerz, Irena; Olovsson, Ivar

    2007-08-01

    The quantum-mechanically derived reaction coordinates (QMRC) for the proton transfer in (N-H-N)(+) hydrogen bonds have been derived from ab initio calculations of potential-energy surfaces. A comparison is made between the QMRC and the corresponding bond-order reaction coordinates (BORC) derived by applying the Pauling bond-order concept together with the principle of conservation of bond order. We find virtually perfect agreement between the QMRC and the BORC for intermolecular (N-H-N)(+) hydrogen bonds. In contrast, for intramolecular (N-H-N)(+) hydrogen bonds, the donor and acceptor parts of the molecule impose strong constraints on the N-N distance and the QMRC does not follow the BORC relation in the whole range. The X-ray determined hydrogen positions are not located exactly at the theoretically calculated potential-energy minima, but instead at the point where the QMRC and the BORC coincide with each other. On the other hand, the optimized hydrogen positions, with other atoms in the cation fixed as in the crystal structure, are closer to these energy minima. Inclusion of the closest neighbours in the theoretical calculations has a rather small effect on the optimized hydrogen positions. [Part I: Olovsson (2006). Z. Phys. Chem. 220, 797-810.]. PMID:17641436

  20. Average bond energies between boron and elements of the fourth, fifth, sixth, and seventh groups of the periodic table

    NASA Technical Reports Server (NTRS)

    Altshuller, Aubrey P

    1955-01-01

    The average bond energies D(gm)(B-Z) for boron-containing molecules have been calculated by the Pauling geometric-mean equation. These calculated bond energies are compared with the average bond energies D(exp)(B-Z) obtained from experimental data. The higher values of D(exp)(B-Z) in comparison with D(gm)(B-Z) when Z is an element in the fifth, sixth, or seventh periodic group may be attributed to resonance stabilization or double-bond character.

  1. Dissociation and dissociative phase transition in dense hydrogen

    SciTech Connect

    Khomkin, A. L. Shumikhin, A. S.

    2012-01-15

    A simple physical model is proposed for dissociating dense fluid hydrogen. We propose that free dissociated atoms interact via quantum electron-electron exchange analogously to the interaction in the liquid-metal phase of alkali metals. The density dependence of a hydrogen atom's binding energy in such a quasi-liquid is calculated. It is shown that the transition from the molecular fluid to liquid hydrogen is a first-order phase transition. The critical parameters of the transition are determined: P{sub c} = 72 GPa, T{sub c} = 10500 K, and {rho}{sub c} = 0.5 g/cm{sup 3}. The possibility of the metastable existence of atomic liquid hydrogen in a dissociated molecular fluid under decreased pressure is established.

  2. Chemical bond as a test of density-gradient expansions for kinetic and exchange energies

    SciTech Connect

    Perdew, J.P.; Levy, M.; Painter, G.S.; Wei, S.; Lagowski, J.B.

    1988-01-15

    Errors in kinetic and exchange contributions to the molecular bonding energy are assessed for approximate density functionals by reference to near-exact Hartree-Fock values. From the molecular calculations of Allan et al. and of Lee and Ghosh, it is demonstrated that the density-gradient expansion does not accurately describe the noninteracting kinetic contribution to the bonding energy, even when this expansion is carried to fourth order and applied in its spin-density-functional form to accurate Hartree-Fock densities. In a related study, it is demonstrated that the overbinding of molecules such as N/sub 2/ and F/sub 2/, which occurs in the local-spin-density (LSD) approximation for the exchange-correlation energy, is not attributable to errors in the self-consistent LSD densities. Contrary to expectations based upon the Gunnarsson-Jones nodality argument, it is found that the LSD approximation for the exchange energy can seriously overbind a molecule even when bonding does not create additional nodes in the occupied valence orbitals. LSD and exact values for the exchange contribution to the bonding energy are displayed and discussed for several molecules.

  3. Strain effect on the adsorption, diffusion, and molecular dissociation of hydrogen on Mg (0001) surface

    SciTech Connect

    Lei, Huaping; Wang, Caizhuang; Yao, Yongxin; Hupalo, Myron; Wang, Yangang; Supercomputing Center of Computer Network Information Center, CAS, Beijing 100190 ; McDougall, Dan; Tringides, Michael; Ho, Kaiming; Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011

    2013-12-14

    The adsorption, diffusion, and molecular dissociation of hydrogen on the biaxially strained Mg (0001) surface have been systematically investigated by the first principle calculations based on density functional theory. When the strain changes from the compressive to tensile state, the adsorption energy of H atom linearly increases while its diffusion barrier linearly decreases oppositely. The dissociation barrier of H{sub 2} molecule linearly reduces in the tensile strain region. Through the chemical bonding analysis including the charge density difference, the projected density of states and the Mulliken population, the mechanism of the strain effect on the adsorption of H atom and the dissociation of H{sub 2} molecule has been elucidated by an s-p charge transfer model. With the reduction of the orbital overlap between the surface Mg atoms upon the lattice expansion, the charge transfers from p to s states of Mg atoms, which enhances the hybridization of H s and Mg s orbitals. Therefore, the bonding interaction of H with Mg surface is strengthened and then the atomic diffusion and molecular dissociation barriers of hydrogen decrease accordingly. Our works will be helpful to understand and to estimate the influence of the lattice deformation on the performance of Mg-containing hydrogen storage materials.

  4. A periodic energy decomposition analysis method for the investigation of chemical bonding in extended systems

    SciTech Connect

    Raupach, Marc; Tonner, Ralf

    2015-05-21

    The development and first applications of a new periodic energy decomposition analysis (pEDA) scheme for extended systems based on the Kohn-Sham approach to density functional theory are described. The pEDA decomposes the bonding energy between two fragments (e.g., the adsorption energy of a molecule on a surface) into several well-defined terms: preparation, electrostatic, Pauli repulsion, and orbital relaxation energies. This is complemented by consideration of dispersion interactions via a pairwise scheme. One major extension toward a previous implementation [Philipsen and Baerends, J. Phys. Chem. B 110, 12470 (2006)] lies in the separate discussion of electrostatic and Pauli and the addition of a dispersion term. The pEDA presented here for an implementation based on atomic orbitals can handle restricted and unrestricted fragments for 0D to 3D systems considering periodic boundary conditions with and without the determination of fragment occupations. For the latter case, reciprocal space sampling is enabled. The new method gives comparable results to established schemes for molecular systems and shows good convergence with respect to the basis set (TZ2P), the integration accuracy, and k-space sampling. Four typical bonding scenarios for surface-adsorbate complexes were chosen to highlight the performance of the method representing insulating (CO on MgO(001)), metallic (H{sub 2} on M(001), M = Pd, Cu), and semiconducting (CO and C{sub 2}H{sub 2} on Si(001)) substrates. These examples cover diverse substrates as well as bonding scenarios ranging from weakly interacting to covalent (shared electron and donor acceptor) bonding. The results presented lend confidence that the pEDA will be a powerful tool for the analysis of surface-adsorbate bonding in the future, enabling the transfer of concepts like ionic and covalent bonding, donor-acceptor interaction, steric repulsion, and others to extended systems.

  5. A nearly exact MCSCF+CI calculation of the dissociation energy of OH. [Multiconfiguration, Self-Consistent Field plus Configuration Interaction

    NASA Technical Reports Server (NTRS)

    Arnold, J. O.; Whiting, E. E.; Sharbaugh, L. F.

    1976-01-01

    The dissociation energy and dipole moment of the ground state of OH have been obtained with a newly developed multiconfiguration, self-consistent field plus configuration interaction CDC 7600 computer program. The computed value of the dissociation energy is 4.62 eV, which is within the uncertainty limits for the experimental value of 4.63 plus or minus 0.01 eV. The computed value of the dipole moment is 1.645 D, which is very close to the experimental result of 1.66 plus or minus 0.01 D. The present results are also compared to the data obtained from similar calculations with the BISON-MC computer program developed by Das and Wahl.

  6. Asymmetric hydrogen bonds in a centrosymmetric environment. III. Quantum mechanical calculations of the potential-energy surfaces for the very short hydrogen bonds in potassium hydrogen dichloromaleate.

    PubMed

    Majerz, I; Olovsson, I

    2007-10-01

    In the crystal structure of potassium hydrogen dichloromaleate there are two short hydrogen bonds of 2.44 A. The 'heavy-atom' structure is centrosymmetric (space group P1) with centers of symmetry in the middle of the O-O bonds, suggesting centered hydrogen bonds. However, earlier unconventional types of refinements of the extensive neutron data taken at 30, 90, 135, 170 and 295 K demonstrated that the H atoms are actually non-centered in the hydrogen bonds, although the environment is centrosymmetric. Traditionally it has been assumed that the hydrogen distribution adopts the same symmetry as the environment. Reviewing these unusual results it was considered of great interest to verify that the non-centered locations of the H atoms are reasonable from an energy point of view. Quantum mechanical calculations have now been carried out for the potential-energy surfaces (PES) for both the centered and non-centered locations of the H atoms. In all cases the non-centered positions are closer to the energy minima in the PES than the centered positions, and this result confirms that the structure is best described with non-centered H atoms. There is virtually perfect agreement between the quantum-mechanically derived reaction coordinates (QMRC) and the bond-order reaction coordinates (BORC) derived using Pauling's bond-order concept together with the principle of conservation of bond order. [Part I: Olovsson et al. (2001). Acta Cryst. B57, 311-316; Part II: Olovsson et al. (2002). Acta Cryst. B58, 627-631.]. PMID:17873444

  7. Diffraction dissociation at the LHC

    SciTech Connect

    Jenkovszky, Laszlo; Orava, Risto; Salii, Andrii

    2013-04-15

    We report on recent calculations of low missing mass single (SD) and double (DD) diffractive dissociation at LHC energies. The calculations are based on a dual-Regge model, dominated by a single Pomeron exchange. The diffractively excited states lie on the nucleon trajectory N*, appended by the isolated Roper resonance. Detailed predictions for the squared momentum transfer and missing mass dependence of the differential and integrated single-and double diffraction dissociation in the kinematical range of present and future LHC measurements are given.

  8. A second-generation reactive empirical bond order (REBO) potential energy expression for hydrocarbons

    E-print Network

    Zhigilei, Leonid V.

    for hydrocarbons This article has been downloaded from IOPscience. Please scroll down to see the full text article-generation reactive empirical bond order (REBO) potential energy expression for hydrocarbons Donald W Brenner1 , Olga, lengths, and force constants for hydrocarbon molecules, as well as elastic properties, interstitial defect

  9. Condensed Lecture Notes, Part 2 Bond energy of NaCl

    E-print Network

    6 Condensed Lecture Notes, Part 2 Bond energy of NaCl If NaCl were diatomic molecule of the type Na that satisfy the octet (duplet) rule. If multiple structures are ok, then the rule of thumb is that the lowest, not OFF. 7. If there are multiple equivalent structures which satisfy the octet rule, then we say

  10. Contributions of mass and bond energy difference and interface defects on thermal boundary conductance

    NASA Astrophysics Data System (ADS)

    Choi, ChangJin; Roberts, Nicholas

    2015-09-01

    The impact of mass and bond energy difference and interface defects on thermal boundary conductance (TBC) is investigated using non-equilibrium molecular dynamics (NEMD) with the Lennard-Jones (L-J) interatomic potential. Results show that the maximum TBC is achieved when the mass and bond energy of two dissimilar materials are matched, although the effective thermal conductivity is not necessarily a maximum due to the contributions of the thermal conductivity of the constituent materials. Mass and bond energy differences result in a mismatch between phonon dispersions, limiting high frequency phonon transport at the interface. This frequency mismatch is defined by a frequency ratio, which is a ratio of the characteristic frequencies of the two materials, presented in the discussion section, and is a reference of the level of phonon dispersion mismatch. Inelastic scattering may result at higher temperatures, especially when there exists a bond energy difference, resulting in strain in the lattice, which would allow phonons outside the allowable frequency range to contribute to transport. TBC decreases abruptly with small mass differences, but at which point larger differences in mass have no impact. In addition, interdiffusion across the interface further reduces the TBC between the frequency ratios of 0.79 and 1.26 while vacancies have negligible impact.

  11. Ionic bond effects on the mean excitation energy for stopping power

    NASA Technical Reports Server (NTRS)

    Wilson, J. W.; Chang, C. K.; Kamaratos, E.; Xu, Y. J.

    1982-01-01

    Molecular mean excitation energies for ionic bonded molecules calculated according to the local plasma approximation are compared to the Bragg rule. Adjustments of 15% are calculated for LiF in agreement with experiments while 6% adjustments are predicted for HF and 3% for LiH.

  12. Bonding Motifs of Noble-Gas Compounds As Described by the Local Electron Energy Density.

    PubMed

    Borocci, Stefano; Giordani, Maria; Grandinetti, Felice

    2015-06-18

    The bonding situation of some exemplary noble-gas (Ng) compounds, including HNg(+), HNgF, FNgO(-), Ng-HF, and NgBeO (Ng = He-Xe) was assayed by examining their local electron energy density H(r). In general, this function partitions the space of atomic species (neutral and ionic) into inner regions of negative values and outer regions of positive values. In the formation of chemical bonds, these atomic regions combine so to form a molecular H(r), Hmol(r), whose plotted form naturally shows the "covalent" and "noncovalent" regions of the molecular species and allows also the recognition of different types of noncovalent interactions such van der Waals, hydrogen, and ionic or partially ionic bonds. The qualitative assignment of the various bonding motifs is corroborated by the topological analysis of Hmol(r), which typically includes several critical points of rank 3 and variable signature. These points are, in particular, characterized here in terms of their bond degree (BD). From a previous definition (Espinosa J. Chem. Phys. 2002, 117, 5529-5542), this quantity is taken as the ratio between the energy density calculated at the critical point of H(r), H(rc), and the corresponding electron density ?(rc): BD = -H(rc)/?(rc). Thus, the BD is positive for covalent interactions (H(rc) < 0) and negative for noncovalent interactions (H(rc) > 0). For structurally related species, the BD result, in general, positively correlated with the binding energies and is, therefore, a semiquantitative index of stability. The present study suggests the general validity of the Hmol(r) to effectively assay the bonding motifs of noble-gas compounds. PMID:25988571

  13. Agostic interactions and dissociation in the first layer of water on Pt(111).

    PubMed

    Jacob, Timo; Goddard, William A

    2004-08-01

    Recent quantum mechanical (QM) calculations for a monolayer of H(2)O on Ru(0001) suggested a novel stable structure with half the waters dissociated. However, different studies on Pt(111) suggested an undissociated bilayer structure in which the outer half of the water has the OH bonds toward the surface rather than the O lone pair. Since water layers on Pt are important in many catalytic processes (e.g., the fuel cell cathode), we calculated the energetics and structure of the first monolayer of water on the Pt(111) surface using QM [periodic slab using density functional calculations (DFT) with the PBE-flavor of exchange-correlation functional]. We find that the fully saturated surface ((2)/(3) ML) has half the water almost parallel to the surface (forming a Pt-O Lewis acid-base bond), whereas the other half are perpendicular to the surface, but with the H down toward the surface (forming a Pt-HO agostic bond). This leads to a net bond energy of 0.60 eV/water = 13.8 kcal/mol (the standard ice model with the H up configuration of the water molecules perpendicular to the surface is less stable by 0.092 eV/water = 2.1 kcal/mol). We examined whether the partial dissociation of water proposed for Ru(0001) could occur on Pt(111). For the saturated water layer ((2)/(3) ML) we find a stable structure with half the H(2)O dissociated (forming Pt-OH and Pt-H covalent bonds), which is less favorable by only 0.066 eV/water = 1.51 kcal/mol. These results confirm the interpretation of combined experimental (XAS, XES, XPS) and theoretical (DFT cluster and periodic including spectrum calculations) studies, which find only the H down undissociated case. We find that the undissociated structure leads to a vertical displacement between the two layers of oxygens of approximately 0.42 A (for both H down and H up). In contrast, the partially dissociated system leads to a flat structure with a separation of the oxygen layers of 0.08 A. Among the partially dissociated systems, we find that all subsurface positions for the dissociated hydrogen are less favorable than adsorbing on top of the free Pt surface atom. Our results suggest that for less than (1)/(3) ML, clustering would be observed rather than ordered monolayer structures. PMID:15281827

  14. Oxygen-oxygen bonds : catalytic redox pathways in energy storage

    E-print Network

    Fried, Stephen D. (Stephen David), 1987-

    2009-01-01

    Introduction: The present understanding of energy - its many forms, and its governing role in the time evolution of physical systems - underlies many of the most fundamental and unifying principles furnished by scientific ...

  15. Quantum entanglement and the dissociation process of diatomic molecules

    NASA Astrophysics Data System (ADS)

    Esquivel, Rodolfo O.; Flores-Gallegos, Nelson; Molina-Espíritu, Moyocoyani; Plastino, A. R.; Angulo, Juan Carlos; Antolín, Juan; Dehesa, Jesús S.

    2011-09-01

    In this work, we investigate quantum entanglement-related aspects of the dissociation process of some selected, representative homo- and heteronuclear diatomic molecules. This study is based upon high-quality ab initio calculations of the (correlated) molecular wavefunctions involved in the dissociation processes. The values of the electronic entanglement characterizing the system in the limit cases corresponding to (i) the united-atom representation and (ii) the asymptotic region when atoms dissociate are discussed in detail. It is also shown that the behaviour of the electronic entanglement as a function of the reaction coordinate R exhibits remarkable correspondences with the phenomenological description of the physically meaningful regimes comprising the processes under study. In particular, the extrema of the total energies and the electronic entanglement are shown to be associated with the main physical changes experienced by the molecular spatial electronic density, such as charge depletion and accumulation or bond cleavage regions. These structural changes are characterized by several selected descriptors of the density, such as the Laplacian of the electronic molecular distributions (LAP), the molecular electrostatic potential (MEP) and the atomic electric potentials fitted to the MEP.

  16. Reconciling Coulomb Dissociation and Radiative Capture Measurements H. Esbensen,1

    E-print Network

    Bertsch George F.

    Reconciling Coulomb Dissociation and Radiative Capture Measurements H. Esbensen,1 G. F. Bertsch,2) We calculate the energy spectrum for 8B dissociation on a Pb target to all orders in the Coulomb and nuclear fields, and show that the slope of S17E obtained in previous analyses of Coulomb dissociation data

  17. Vibrational analysis of HOCl up to 98{percent} of the dissociation energy with a Fermi resonance Hamiltonian

    SciTech Connect

    Jost, R.; Joyeux, M.; Skokov, S.; Bowman, J.

    1999-10-01

    We have analyzed the vibrational energies and wave functions of HOCl obtained from previous {ital ab initio} calculations [J. Chem. Phys. {bold 109}, 2662 (1998); {bold 109}, 10273 (1998)]. Up to approximately 13&hthinsp;000 cm{sup {minus}1}, the normal modes are nearly decoupled, so that the analysis is straightforward with a Dunham model. In contrast, above 13&hthinsp;000 cm{sup {minus}1} the Dunham model is no longer valid for the levels with no quanta in the OH stretch (v{sub 1}=0). In addition to v{sub 1}, these levels can only be assigned a so-called polyad quantum number P=2v{sub 2}+v{sub 3}, where 2 and 3 denote, respectively, the bending and OCl stretching normal modes. In contrast, the levels with v{sub 1}{ge}2 remain assignable with three v{sub i} quantum numbers up to the dissociation (D{sub 0}=19&hthinsp;290&hthinsp;cm{sup {minus}1}). The interaction between the bending and the OCl stretch ({omega}{sub 2}{congruent}2{omega}{sub 3}) is well described with a simple, fitted Fermi resonance Hamiltonian. The energies and wave functions of this model Hamiltonian are compared with those obtained from {ital ab initio} calculations, which in turn enables the assignment of many additional {ital ab initio} vibrational levels. Globally, among the 809 bound levels calculated below dissociation, 790 have been assigned, the lowest unassigned level, No. 736, being located at 18&hthinsp;885 cm{sup {minus}1} above the (0,0,0) ground level, that is, at about 98{percent} of D{sub 0}. In addition, 84 {open_quotes}resonances{close_quotes} located above D{sub 0} have also been assigned. Our best Fermi resonance Hamiltonian has 29 parameters fitted with 725 {ital ab initio} levels, the rms deviation being of 5.3 cm{sup {minus}1}. This set of 725 fitted levels includes the full set of levels up to No. 702 at 18&hthinsp;650 cm{sup {minus}1}. The {ital ab initio} levels, which are assigned but not included in the fit, are reasonably predicted by the model Hamiltonian, but with a typical error of the order of 20 cm{sup {minus}1}. The classical analysis of the periodic orbits of this Hamiltonian shows that two bifurcations occur at 13&hthinsp;135 and 14&hthinsp;059 cm{sup {minus}1} for levels with v{sub 1}=0. Above each of these bifurcations two new families of periodic orbits are created. The quantum counterpart of periodic orbits are wave functions with {open_quotes}pearls{close_quotes} aligned along the classical periodic orbits. The complicated sequence of {ital ab initio} wave functions observed within each polyad is nicely reproduced by the wave functions of the Fermi resonance Hamiltonian and by the corresponding shapes of periodic orbits. We also present a comparison between calculated and measured energies and rotational constants for 25 levels, leading to a secure vibrational assignment for these levels. The largest difference between experimental and calculated energies reaches 22 cm{sup {minus}1} close to D{sub 0}. {copyright} {ital 1999 American Institute of Physics.}

  18. The Scalar Relativistic Contribution to Ga-Halide Bond Energies

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Arnold, James O. (Technical Monitor)

    1998-01-01

    The one-electron Douglas Kroll (DK) and perturbation theory (+R) approaches are used to compute the scalar relativistic contribution to the atomization energies of GaFn. These results are compared with the previous GaCln results. While the +R and DK results agree well for the GaCln atom nation energies, they differ for GaFn. The present work suggests that the DK approach is more accurate than the +R approach. In addition, the DK approach is less sensitive to the choice of basis set. The computed atomization energies of GaF2 and GaF3 are smaller than the somewhat uncertain experiments. It is suggested that additional calibration calculations for the scalar relativistic effects in GaF2 and GaF3 would be valuable.

  19. Serum lipidomics profiling using LC-MS and high-energy collisional dissociation fragmentation: focus on triglyceride detection and characterization.

    PubMed

    Bird, Susan S; Marur, Vasant R; Sniatynski, Matthew J; Greenberg, Heather K; Kristal, Bruce S

    2011-09-01

    There is a growing need both clinically and experimentally to improve the characterization of blood lipids. A liquid chromatography-mass spectrometry (LC-MS) method, developed for the qualitative and semiquantitative detection of lipids in biological samples and previously validated in mitochondrial samples, was now evaluated for the profiling of serum lipids. Data were acquired using high-resolution, full scan MS and high-energy, collisional dissociation (HCD), all ion fragmentation. The method was designed for efficient separation and detection in both positive and negative ionization mode and evaluated using standards spanning seven lipid classes. Platform performance, related to the identification and characterization of serum triglycerides (TGs), was assessed using extracted ion chromatograms with mass tolerance windows of 5 ppm or less from full scan exact mass measurements determined using SIEVE nondifferential LC-MS analysis software. The platform showed retention time coefficients of variation (CV) of <0.3%, mass accuracy values of <2 ppm error, and peak area CV of <13%, with the majority of that error coming from sample preparation and extraction rather than the LC-MS analysis, and linearity was shown to be over 4 orders of magnitude (r(2) = 0.999) for the standard TG (15:0)(3) spiked into serum. Instrument mass accuracy and precision were critical to the identification of unknown TG species, in part because these parameters enabled us to reduce false positives. In addition to detection and relative quantitation of TGs in serum, TG structures were characterized through the use of alternating HCD scans at different energies to produce diagnostic fragmentations on all ions in the analysis. The lipidomics method was applied to serum samples from 192 rats maintained on diets differing in macronutrient composition. The analysis identified 86 TG species with 81 unique masses that varied over 3.5 orders of magnitude and showed diet-dependency, consistent with TGs linking diet and disease risk. PMID:21774539

  20. Detection and Characterization of Low Abundance Glycopeptides Via Higher-Energy C-Trap Dissociation and Orbitrap Mass Analysis

    NASA Astrophysics Data System (ADS)

    Hart-Smith, Gene; Raftery, Mark J.

    2012-01-01

    Broad-scale mass spectrometric analyses of glycopeptides are constrained by the considerable complexity inherent to glycoproteomics, and techniques are still being actively developed to address the associated analytical difficulties. Here we apply Orbitrap mass analysis and higher-energy C-trap dissociation (HCD) to facilitate detailed insights into the compositions and heterogeneity of complex mixtures of low abundance glycopeptides. By generating diagnostic oxonium product ions at mass measurement errors of <5 ppm, highly selective glycopeptide precursor ion detections are made at sub-fmol limits of detection: analyses of proteolytic digests of a hen egg glycoprotein mixture detect 88 previously uncharacterized glycopeptides from 666 precursor ions selected for MS/MS, with only one false positive due to co-fragmentation of a non-glycosylated peptide with a glycopeptide. We also demonstrate that by (1) identifying multiple series of glycoforms using high mass accuracy single stage MS spectra, and (2) performing product ion scans at optimized HCD collision energies, the identification of peptide + N-acetylhexosamine (HexNAc) ions (Y1 ions) can be readily achieved at <5 ppm mass measurement errors. These data allow base peptide sequences and glycan compositional information to be attained with high confidence, even for glycopeptides that produce weak precursor ion signals and/or low quality MS/MS spectra. The glycopeptides characterized from low fmol abundances using these methods allow two previously unreported glycosylation sites on the Gallus gallus protein ovoglycoprotein (amino acids 82 and 90) to be confirmed; considerable glycan heterogeneities at amino acid 90 of ovoglycoprotein, and amino acids 34 and 77 of Gallus gallus ovomucoid are also revealed.

  1. Detection and characterization of low abundance glycopeptides via higher-energy C-trap dissociation and orbitrap mass analysis.

    PubMed

    Hart-Smith, Gene; Raftery, Mark J

    2012-01-01

    Broad-scale mass spectrometric analyses of glycopeptides are constrained by the considerable complexity inherent to glycoproteomics, and techniques are still being actively developed to address the associated analytical difficulties. Here we apply Orbitrap mass analysis and higher-energy C-trap dissociation (HCD) to facilitate detailed insights into the compositions and heterogeneity of complex mixtures of low abundance glycopeptides. By generating diagnostic oxonium product ions at mass measurement errors of <5 ppm, highly selective glycopeptide precursor ion detections are made at sub-fmol limits of detection: analyses of proteolytic digests of a hen egg glycoprotein mixture detect 88 previously uncharacterized glycopeptides from 666 precursor ions selected for MS/MS, with only one false positive due to co-fragmentation of a non-glycosylated peptide with a glycopeptide. We also demonstrate that by (1) identifying multiple series of glycoforms using high mass accuracy single stage MS spectra, and (2) performing product ion scans at optimized HCD collision energies, the identification of peptide + N-acetylhexosamine (HexNAc) ions (Y1 ions) can be readily achieved at <5 ppm mass measurement errors. These data allow base peptide sequences and glycan compositional information to be attained with high confidence, even for glycopeptides that produce weak precursor ion signals and/or low quality MS/MS spectra. The glycopeptides characterized from low fmol abundances using these methods allow two previously unreported glycosylation sites on the Gallus gallus protein ovoglycoprotein (amino acids 82 and 90) to be confirmed; considerable glycan heterogeneities at amino acid 90 of ovoglycoprotein, and amino acids 34 and 77 of Gallus gallus ovomucoid are also revealed. PMID:22083589

  2. The bond energy of Rh2 Jon D. Langenberg and Michael D. Morse

    E-print Network

    Morse, Michael D.

    The bond energy of Rh2 Jon D. Langenberg and Michael D. Morse Department of Chemistry, University In a spectroscopic investigation of jet-cooled Rh2 by the resonant two-photon ionization method, an abrupt energy of Rh2 is assigned as D0 Rh2 19 405 4 cm 1 2.4059 0.0005 eV. This value is compared to the results

  3. Dissociation and Decay of Ultracold Sodium Molecules We have studied the dissociation and decay of ultracold molecules. Sodium molecules

    E-print Network

    Dissociation and Decay of Ultracold Sodium Molecules We have studied the dissociation and decay of ultracold molecules. Sodium molecules were formed in a highly excited vibrational state by recombining two cooling. Dissociation energy of sodium molecules as a function of magnetic field ramp rate. The dashed

  4. Dissociative Electron Attachment to Hydrocarbons. A Laboratory Study

    NASA Astrophysics Data System (ADS)

    Szymanska, E.; Mason, N. J.

    2011-05-01

    Laboratory studies of PAHs continue to be essential if we are to interpret the wealth and variety of processes contributing to star formation. In the realm of gas-phase kinetics reactions involving negative ions are being studied to help modellers understand the role of these species in interstellar chemistry. Observations have shown that PAHs molecules are abundant and ubiquitous in the interstellar medium of galaxies, play an important role in its physical and chemical characteristics and form a key link between small hydrocarbon species and large carbonaceous grains. There is therefore considerable interest in the mechanisms by which these molecules and their anions may form. One method is electron induced chemistry within the icy mantles on the surface of dust grains. In particular it has been recently shown that functional group dependence exists in electron attachment processes giving rise to site selective fragmentation of molecules at the C-H, O-H and N-H bonds at energies well beyond the threshold for the breaking of any of these bonds allowing novel forms of chemistry that have little or no activation barriers, such as are necessary in the ISM. In this poster we present the results of recent studies on dissociative electron attachment (DEA) to PAHs using an improved version of a Velocity Map Imaging (VMI) spectrometer comprised of a magnetically collimated and low energy pulsed electron gun, a Faraday cup, an effusive molecular beam, a pulsed field ion extraction, a time of flight analyzer and a two-dimensional position sensitive detector consisting of microchannel plate and a phosphor screen. The VMI spectrometer measures the kinetic energy and angular distribution of the fragment anions produced in the dissociative electron attachment process. Kinetic energy measurements provide information on the internal energies of the fragment anions and determine the dissociation limits of the parent negative ion resonant states responsible for the dissociative electron attachment process. Angular distribution measurements provide information about the symmetry of these negative ion resonant states. We shall present the details, results and conclusions of these measurements during the conference for some illustrative hydrocarbons.

  5. Six-dimensional quantum dynamics of dissociative chemisorption of H2 on Co(0001) on an accurate global potential energy surface.

    PubMed

    Jiang, Bin; Hu, Xixi; Lin, Sen; Xie, Daiqian; Guo, Hua

    2015-09-28

    Cobalt is a widely used catalyst for many heterogeneous reactions, including the Fischer-Tropsch (FT) process, which converts syngas (H2 and CO) to higher hydrocarbons. As a result, a better understanding of the key chemical steps on the Co surface, such as the dissociative chemisorption of H2 as an initial step of the FT process, is of fundamental importance. Here, we report an accurate full-dimensional global potential energy surface for the dissociative chemisorption of H2 on the rigid Co(0001) surface constructed from more than 3000 density functional theory points. The high-fidelity potential energy surface was obtained using the permutation invariant polynomial-neural network method, which preserves both the permutation symmetry of H2 and translational symmetry of the Co(0001) surface. The reaction path features a very low barrier on the top site. Full-dimensional quantum dynamical calculations provide insights into the dissociation dynamics and influence of the initial vibrational, rotational, and orientational degrees of freedom. PMID:26286861

  6. Dissociation of C-10 Nuclei in a Track Nuclear Emulsion at an Energy of 1.2 GeV per Nucleon

    E-print Network

    K. Z. Mamatkulov; R. R. Kattabekov; S. S. Alikulov; D. A. Artemenkov; R. N. Bekmirzaev; V. Bradnova; P. I. Zarubin; I. G. Zarubina; N. V. Kondratieva; D. O. Krivenkov; A. I. Malakhov; K. Olimov; N. G. Peresadko; N. G. Polukhina; V. V. Rusakova; R. Stanoeva; S. P. Kharlamov

    2015-07-30

    The charge topology in the fragmentation of $^{10}$C nuclei in a track nuclear emulsion at an energy of 1.2 GeV per nucleon is studied. In the coherent dissociation of $^{10}$C nuclei, about 82% of events are associated with the channel $^{10}$C $\\rightarrow$ 2$\\alpha +$ 2\\emph{p}. The angular distributions and correlations of product fragments are presented for this channel. It is found that among $^{10}$C $\\rightarrow$ 2$\\alpha +$ 2\\emph{p} events, about 30% are associated with the process in which dissociation through the ground state of the unstable $^9$Be$_{g.s.}$ nucleus is followed by $^8$Be$_{g.s.} +$ \\emph{p} decays.

  7. Dissociation of {sup 10}C nuclei in a track nuclear emulsion at an energy of 1.2 GeV per nucleon

    SciTech Connect

    Mamatkulov, K. Z.; Kattabekov, R. R.; Alikulov, S. S.; Artemenkov, D. A.; Bekmirzaev, R. N.; Bradnova, V.; Zarubin, P. I. Zarubina, I. G.; Kondratieva, N. V.; Kornegrutsa, N. K.; Krivenkov, D. O.; Malakhov, A. I.; Olimov, K.; Peresadko, N. G.; Polukhina, N. G.; Rukoyatkin, P. A.; Rusakova, V. V.; Stanoeva, R.; Kharlamov, S. P.

    2013-10-15

    The charge topology in the fragmentation of {sup 10}C nuclei in a track nuclear emulsion at an energy of 1.2 GeV per nucleon is studied. In the coherent dissociation of {sup 10}C nuclei, about 82% of events are associated with the channel {sup 10}C {yields} 2{alpha}+ 2p. The angular distributions and correlations of product fragments are presented for this channel. It is found that among {sup 10}C {yields} 2{alpha}+ 2p events, about 30% are associated with the process in which dissociation through the ground state of the unstable {sup 9}Be{sub g.s.} nucleus is followed by {sup 8}Be{sub g.s.} + p decays.

  8. Electronic structure, molecular bonding and potential energy surfaces

    SciTech Connect

    Ruedenberg, K.

    1993-12-01

    By virtue of the universal validity of the generalized Born-Oppenheimer separation, potential energy surfaces (PES`) represent the central conceptual as well as quantitative entities of chemical physics and provide the basis for the understanding of most physicochemical phenomena in many diverse fields. The research in this group deals with the elucidation of general properties of PES` as well as with the quantitative determination of PES` for concrete systems, in particular pertaining to reactions involving carbon, oxygen, nitrogen and hydrogen molecules.

  9. An experimental study of SO3 dissociation as a mechanism for converting and transporting solar energy

    NASA Technical Reports Server (NTRS)

    Mccrary, J. H.; Mccrary, G. E.; Chubb, T. A.; Won, Y. S.

    1981-01-01

    The high temperature catalytic dissocation of SO3 is an important chemical process being considered in the development and application of solar-thermal energy conversion, transport, and storage systems. A facility for evaluating chemical converter-heat exchangers at temperatures to 1000 C with high flow rates of gaseous SO3 feedstock has been assembled and operated on the NMSU campus. Several quartz and metal reactors containing different catalyst configurations have been tested. Descriptions of the test facility and of the reactors are given along with a presentation and discussion of experimental results.

  10. Methane dissociation on Ni(111): A fifteen-dimensional potential energy surface using neural network method

    NASA Astrophysics Data System (ADS)

    Shen, Xiangjian; Chen, Jun; Zhang, Zhaojun; Shao, Kejie; Zhang, Dong H.

    2015-10-01

    In the present work, we develop a highly accurate, fifteen-dimensional potential energy surface (PES) of CH4 interacting on a rigid flat Ni(111) surface with the methodology of neural network (NN) fit to a database consisted of about 194 208 ab initio density functional theory (DFT) energy points. Some careful tests of the accuracy of the fitting PES are given through the descriptions of the fitting quality, vibrational spectrum of CH4 in vacuum, transition state (TS) geometries as well as the activation barriers. Using a 25-60-60-1 NN structure, we obtain one of the best PESs with the least root mean square errors: 10.11 meV for the entrance region and 17.00 meV for the interaction and product regions. Our PES can reproduce the DFT results very well in particular for the important TS structures. Furthermore, we present the sticking probability S0 of ground state CH4 at the experimental surface temperature using some sudden approximations by Jackson's group. An in-depth explanation is given for the underestimated sticking probability.

  11. Bond-Weakening Catalysis: Conjugate Aminations Enabled by the Soft Homolysis of Strong N–H Bonds

    PubMed Central

    Tarantino, Kyle T.; Miller, David C.; Callon, Ted A.

    2015-01-01

    The ability of redox-active metal centers to weaken the bonds in associated ligands is well precedented, but has rarely been utilized as a mechanism of substrate activation in catalysis. Here we describe a catalytic bond-weakening protocol for conjugate amination wherein the strong N–H bonds in N-aryl amides (N–H bond dissociation free energies ~100 kcal/mol) are destabilized by ~33 kcal/mol upon by coordination to a reducing titanocene complex, enabling their abstraction by the weak H-atom acceptor TEMPO through a proton-coupled electron transfer process. Significantly, this soft homolysis mechanism provides a method to generate closed-shell, metalated nucleophiles under neutral conditions in the absence of a Brønsted base. PMID:25945955

  12. Wavepacket theory of collisional dissociation in molecules

    SciTech Connect

    Kulander, K.

    1980-01-01

    An explicit integration scheme is used to solve the time dependent Schroedinger equation for wavepackets which model collisions in the collinear H + H/sub 2/ system. A realistic LEPS-type potential energy surface is used. Collision energies considered are above the dissociation threshold and probabilities for collision induced dissociation are reported. Also quantum mechanical state-to-state transition probabilities are generated. These results are compared to extensive classical trajectory calculations performed on this same system. The time evolution of the wavepacket densities is studied to understand the dynamics of the collinear collisional dissociation process.

  13. Quantum dynamics study of fulvene double bond photoisomerization: The role of intramolecular vibrational energy redistribution and excitation energy

    SciTech Connect

    Blancafort, Lluis; Gatti, Fabien; Meyer, Hans-Dieter

    2011-10-07

    The double bond photoisomerization of fulvene has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method. Fulvene is a test case to develop optical control strategies based on the knowledge of the excited state decay mechanism. The decay takes place on a time scale of several hundred femtoseconds, and the potential energy surface is centered around a conical intersection seam between the ground and excited state. The competition between unreactive decay and photoisomerization depends on the region of the seam accessed during the decay. The dynamics are carried out on a four-dimensional model surface, parametrized from complete active space self-consistent field calculations, that captures the main features of the seam (energy and locus of the seam and associated branching space vectors). Wave packet propagations initiated by single laser pulses of 5-25 fs duration and 1.85-4 eV excitation energy show the principal characteristics of the first 150 fs of the photodynamics. Initially, the excitation energy is transferred to a bond stretching mode that leads the wave packet to the seam, inducing the regeneration of the reactant. The photoisomerization starts after the vibrational energy has flowed from the bond stretching to the torsional mode. In our propagations, intramolecular energy redistribution (IVR) is accelerated for higher excess energies along the bond stretch mode. Thus, the competition between unreactive decay and isomerization depends on the rate of IVR between the bond stretch and torsion coordinates, which in turn depends on the excitation energy. These results set the ground for the development of future optical control strategies.

  14. Bond ionicity, lattice energy, bond energy and microwave dielectric properties of ZnZr(Nb1-xAx)2O8 (A = Ta, Sb) ceramics.

    PubMed

    Zhang, Ping; Zhao, Yonggui; Haitao, Wu

    2015-10-14

    The dependence of microwave dielectric properties on the structural characteristics of ZnZr(Nb1-xAx)2O8 (A = Ta, Sb) (0 ?x? 0.10) ceramics is investigated. All the compounds were prepared by a conventional solid-state reaction method and analyzed via multiphase structure refinement. The diffraction patterns of ZnZr(Nb1-xAx)2O8 (A = Ta, Sb) show the monoclinic wolframite structure of ZrZrNb2O8 which consists of an oxygen octahedron, with the Nb ion in the center of the oxygen octahedron. For the ZnZr(Nb1-xAx)2O8 (A = Ta, Sb) ceramics, the dielectric constant (?r) decreased with the decrease in Nb-site bond ionicity. The quality factor (Q×f) of ZnZr(Nb1-xSbx)2O8 ceramics was found to be the highest (89?400 GHz), which is explained in terms of the average of the Nb-site lattice energy. With the decrease in the bond energy of the Nb-site, the temperature coefficient of resonant frequency (|?f|) value increased. The substitution of A(5+) (A = Ta, Sb) for Nb(5+) effectively influences the microstructure and microwave dielectric properties of ZrZrNb2O8 ceramics. PMID:26348992

  15. Effect of ZnO on the interfacial bonding between Na 2O-B 2O 3-SiO 2 vitrified bond and diamond

    NASA Astrophysics Data System (ADS)

    Wang, P. F.; Li, Zh. H.; Li, J.; Zhu, Y. M.

    2009-08-01

    Diamond composites were prepared by sintering diamond grains with low melting Na 2O-B 2O 3-SiO 2 vitrified bonds in air. The influence of ZnO on the wettability and flowing ability of Na 2O-B 2O 3-SiO 2 vitrified bonds was characterized by wetting angle, the interfacial bonding states between diamond grains and the vitrified bonds were observed by scanning electron microscope (SEM), and the micro-scale bonding mechanism in the interfaces was investigated by means of energy-dispersive spectrometer (EDS), Fourier transform infrared (FTIR) spectrometer and X-ray photoelectron spectroscopy (XPS). The experimental results showed that ZnO facilitated the dissociation of boron/silicon-oxygen polyhedra and the formation of larger amount of non-bridging oxygen in the glass network, which resulted in the increase of the vitrified bonds' wettability and the formation of -C dbnd O, -O-H and -C-H bonds on the surface of diamond grains. B and Si diffused from the vitrified bonds to the interface, and C-C, C-O, C dbnd O and C-B bond formed on the surface of sintered diamond grains during sintering process, by which the interfacial bonding between diamond grains and the vitrified bonds was strengthened.

  16. Full Empirical Potential Curves and Improved Dissociation Energies for the X ^1?^+ and a ^1? States of CH^+

    NASA Astrophysics Data System (ADS)

    Cho, Young-Sang; Le Roy, Robert

    2014-06-01

    CH^+ has been a species of interest since the dawn of molecular astrophysics,and it is an important intermediate in combustion processes. In the domain of `conventional' spectroscopy there have been a number of studies of low v' and v" portions of the A ^1?-X ^1?^+ band system of various isotopologues, and Amano recently reported microwave measurements of the ground-state R(0) lines of 12CH^+, 13CH^+ and 12CD^+. used photodissociation spectroscopy to observe transitions to very high-J' tunneling-predissociation levels (shape resonances) involving v(A)=0-10, for many of which they also measured the photo-fragment kinetic energy release. More recently Hechtfischer et al. used photodissociation spectroscopy of `Feschbach resonance' levels at very high v'(A) and low J' to obtain the first direct measurement of the 12CH^+ dissociation energy with near-spectroscopic accuracy (± 1.1 cm-1). However, to date, all analyses of the data for this system had been performed using traditional band-constant or Dunham-expansion fits to data for the lowest vibrational levels, and there have been no attempts to combine the `conventional' low-v data with the high-J' and high-v' photodissociation data in a single treatment. The present work has addressed this problem by performing a Direct-Potential-Fit (DPF) analysis that obtains full analytic potential energy functions for the X ^1?^+ and A ^1? states of CH^+ that are able to account for all of the available data (on average) within their uncertainties. A.E. Douglas and G. Herzberg, Astrophys. J. 94, 381 (1941). T. Amano, Astrophys. J. Lett. {716}, L1 (2010) H. Helm, P.C. Crosby, M.M. Graff and J.T. Mosley, Phys. Rev. A 25, 304 (1982) U. Hechtfischer and C. J. Williams, M. Lange, J. Linkemann, D. Schwalm, R. Wester, A. Wolf and D. Zajfman, J.Chem.Phys. 117, 8754 (2002). H.S.P. Müller, Astron. Astrophys. 514, L7 (2010)

  17. Complete-active-space second-order perturbation theory (CASPT2//CASSCF) study of the dissociative electron attachment in canonical DNA nucleobases caused by low-energy electrons (0-3 eV).

    PubMed

    Francés-Monerris, Antonio; Segarra-Martí, Javier; Merchán, Manuela; Roca-Sanjuán, Daniel

    2015-12-01

    Low-energy (0-3 eV) ballistic electrons originated during the irradiation of biological material can interact with DNA/RNA nucleobases yielding transient-anion species which undergo decompositions. Since the discovery that these reactions can eventually lead to strand breaking of the DNA chains, great efforts have been dedicated to their study. The main fragmentation at the 0-3 eV energy range is the ejection of a hydrogen atom from the specific nitrogen positions. In the present study, the methodological approach introduced in a previous work on uracil [I. González-Ramírez et al., J. Chem. Theory Comput. 8, 2769-2776 (2012)] is employed to study the DNA canonical nucleobases fragmentations of N-H bonds induced by low-energy electrons. The approach is based on minimum energy path and linear interpolation of internal coordinates computations along the N-H dissociation channels carried out at the complete-active-space self-consistent field//complete-active-space second-order perturbation theory level. On the basis of the calculated theoretical quantities, new assignations for the adenine and cytosine anion yield curves are provided. In addition, the ?1 (-) and ?2 (-) states of the pyrimidine nucleobases are expected to produce the temporary anions at electron energies close to 1 and 2 eV, respectively. Finally, the present theoretical results do not allow to discard neither the dipole-bound nor the valence-bound mechanisms in the range of energies explored, suggesting that both possibilities may coexist in the experiments carried out with the isolated nucleobases. PMID:26646889

  18. High-energy collision-activated and electron-transfer dissociation of gas-phase complexes of tryptophan with Na+, K+, and Ca2+

    NASA Astrophysics Data System (ADS)

    Fujihara, Akimasa; Sha, Yuki; Matsuo, Sou; Toyoda, Michisato; Hayakawa, Shigeo

    2014-10-01

    The structure and reactivity of gas-phase complexes of tryptophan (Trp) with Na+, K+, and Ca2+ were examined by high-energy collision-activated dissociation (CAD) and electron transfer dissociation (ETD) using alkali metal targets. In the CAD spectra of M+Trp (M = Na and K), neutral Trp loss was the primary dissociation pathway, and the product ion of collision-induced intracomplex electron transfer from the indole ? ring of Trp to the alkali metal ion was observed, indicating a charge-solvated structure in which Trp is non-zwitterionic. The NH3 loss observed in the CAD spectrum of Ca2+Trp2 is ascribed to a CZ (mixed charge-solvated/zwitterionic)-type structure, in which one Trp is non-zwitterionic and the other Trp adopts a zwitterionic structure with an NH3+ moiety. The H atom and NH3 losses observed in the ETD spectrum of Ca2+Trp2 indicate the formation of a hypervalent radical in the complex, R-NH3, via electron transfer from the alkali metal target to the NH3+ group of the CZ-type structure. Ca2+ attachment to Trp cluster induces the zwitterionic structure of Trp in the gas phase, and an electron transfer to the zwitterionic Trp forms the hypervalent radical as a reaction intermediate.

  19. 2590 J. Am. Chem. SOC.1995,117, 2590-2599 The C-H Bond Energy of Benzene

    E-print Network

    Ellison, Barney

    2590 J. Am. Chem. SOC.1995,117, 2590-2599 The C-H Bond Energy of Benzene Gustavo E. Davico ion with benzene and phenide ion with ammonia: c&6 +NH2- C6H5- +NH3. The ratio of these rate constants for derived. The enthalpy of deprotonationof benzene, the C-H bond dissociationenergy, and the electron

  20. Electronic structure, stacking energy, partial charge, and hydrogen bonding in four periodic B-DNA models

    NASA Astrophysics Data System (ADS)

    Poudel, Lokendra; Rulis, Paul; Liang, Lei; Ching, W. Y.

    2014-08-01

    We present a theoretical study of the electronic structure of four periodic B-DNA models labeled (AT)10,(GC)10, (AT)5(GC)5, and (AT-GC)5 where A denotes adenine, T denotes thymine, G denotes guanine, and C denotes cytosine. Each model has ten base pairs with Na counterions to neutralize the negative phosphate group in the backbone. The (AT)5(GC)5 and (AT-GC)5 models contain two and five AT-GC bilayers, respectively. When compared against the average of the two pure models, we estimate the AT-GC bilayer interaction energy to be 19.015 Kcal/mol, which is comparable to the hydrogen bonding energy between base pairs obtained from the literature. Our investigation shows that the stacking of base pairs plays a vital role in the electronic structure, relative stability, bonding, and distribution of partial charges in the DNA models. All four models show a highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) gap ranging from 2.14 to 3.12 eV with HOMO states residing on the PO4 + Na functional group and LUMO states originating from the bases. Our calculation implies that the electrical conductance of a DNA molecule should increase with increased base-pair mixing. Interatomic bonding effects in these models are investigated in detail by analyzing the distributions of the calculated bond order values for every pair of atoms in the four models including hydrogen bonding. The counterions significantly affect the gap width, the conductivity, and the distribution of partial charge on the DNA backbone. We also evaluate quantitatively the surface partial charge density on each functional group of the DNA models.

  1. Using Qualified Energy Conservation Bonds for Public Building Upgrades. Reducing Energy Bills in the City of Philadelphia

    SciTech Connect

    Zimring, Mark

    2012-07-18

    Qualified Energy Conservation Bonds (QECBs) are federally-subsidized bonds that enable state, tribal, and local government issuers to borrow money to fund a range of energy conservation projects, including public building upgrades that reduce energy use by at least 20 percent, at very attractive borrowing rates and long terms. As part of the American Recovery and Reinvestment Act (ARRA), the City of Philadelphia received a $15 million QECB award from the U.S. Department of the Treasury (Treasury). The city leveraged $6.25 million of its QECB allocation to finance half of a $12.6 million initiative to upgrade the energy efficiency of City buildings. The upgrades to four city facilities are expected to deliver over $10 million of net savings, and are a major step towards achieving the city’s goal of reducing government energy consumption by 30 percent by 2015.

  2. The vibrational dynamics of 3D HOCl above dissociation

    SciTech Connect

    Lin, Yi-Der; Reichl, L. E.; Jung, Christof

    2015-03-28

    We explore the classical vibrational dynamics of the HOCl molecule for energies above the dissociation energy of the molecule. Above dissociation, we find that the classical dynamics is dominated by an invariant manifold which appears to stabilize two periodic orbits at energies significantly above the dissociation energy. These stable periodic orbits can hold a large number of quantum states and likely can support a significant quasibound state of the molecule, well above the dissociation energy. The classical dynamics and the lifetime of quantum states on the invariant manifold are determined.

  3. Density function theory study of the adsorption and dissociation of carbon monoxide on tungsten nanoparticles.

    PubMed

    Weng, Meng-Hsiung; Ju, Shin-Pon; Chen, Hsin-Tsung; Chen, Hui-Lung; Lu, Jian-Ming; Lin, Ken-Huang; Lin, Jenn-Sen; Hsieh, Jin-Yuan; Yang, Hsi-Wen

    2013-02-01

    The adsorption and dissociation properties of carbon monoxide (CO) molecule on tungsten W(n) (n = 10-15) nanoparticles have been investigated by density-functional theory (DFT) calculations. The lowest-energy structures for W(n) (n = 10-15) nanoparticles are found by the basin-hopping method and big-bang method with the modified tight-binding many-body potential. We calculated the corresponding adsorption energies, C-O bond lengths and dissociation barriers for adsorption of CO on nanoparticles. The electronic properties of CO on nanoparticles are studied by the analysis of density of state and charge density. The characteristic of CO on W(n) nanoparticles are also compared with that of W bulk. PMID:23646573

  4. Early Mechanistic Events in Biotin Dissociation from Streptavidin

    SciTech Connect

    Hyre, D. E.

    2002-01-01

    The streptavidin-biotin system has provided a unique opportunity to investigate the molecular details of ligand dissociation pathways. An underlying mechanistic question is whether ligand dissociation proceeds with a relatively ordered process of bond breaking and ligand escape. Here we report a joint computational and crystallographic study of the earliest events in biotin dissociation. In molecular dynamics potential of mean force simulations, a water molecule from a defined access channel intercalated into the hydrogen bond between Asp 128 and biotin, bridging them and stabilizing an intermediate state. In forced biotin dissociation simulations, this event led to subsequent bond breaking steps and ligand escape. In equilibrium simulations, the water molecule was sometimes observed to move back to the access channel with re-formation of the biotin hydrogen bond. Analysis of streptavidin crystal structures revealed a close overlap of crystallographically defined and simulated waters in the water access channel. These results suggest that biotin dissociation is initiated by stochastic coupling of water entry with lengthening of a specific biotin hydrogen-bonding interaction.

  5. Shock-induced initiation and energy release behavior of polymer bonded explosive materials

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Cai, Xuanming; Hypervelocity Impact Research Center Team

    2015-06-01

    In this paper, an initially sealed vented test chamber and a test projectile with a recessed hole were designed to complete the experiments. As the initiation takes place on the interior, great amounts of thermo-chemical energy gases were vented through a hole formed by the penetration process. The gas pressure inside the chamber was used to evaluate the energy release behavior of polymer bonded explosive materials. The impact pressure of the projectile was measured by the PVDF sensors. Based on the earlier work that the constitutive equation of polymer bonded explosive materials was established, the impact pressure of the projectile was obtained through the numerical simulation. The experimental results reveal that the impact pressure is significant to the energy release behavior, and in some extent the gas pressure improves with the velocity of the projectile. The impact pressure obtained by the experiments is comparing with which obtained through the numerical simulation, and the results of the comparing is that the value of them are closely relative. The experimental results also indicate that the constitutive equation of polymer bonded explosive materials used in the numerical simulation can correctly describe the mechanical behavior of PBX materials.

  6. Isomerization and dissociation dynamics of HCN in a picosecond infrared laser field: A full-dimensional classical study

    SciTech Connect

    Gong Jiangbin; Ma Ao; Rice, Stuart A.

    2005-04-08

    We report a full-dimensional study of the classical dynamics of HCN{yields}HNC isomerization and of HCN rovibrational dissociation driven by a strong but nonionizing picosecond infrared laser field. The dynamics of the isolated molecule and of the molecule in liquid Ar have both been studied. Our theoretical and numerical results show that when all degrees of freedom are accounted for the field induced molecular dynamics can be totally different from what was found in previous studies, where the HCN molecule is restricted to a plane containing the external field. It is shown that as HCN is driven by an infrared laser field, the rotation of the H atom around the C-N bond provides an important and highly efficient energy absorption mechanism. In the presence of a monochromatic picosecond infrared laser field with an intensity of 10{sup 13} W/cm{sup 2}, this energy absorption mechanism generates considerable HCN{yields}HNC isomerization yield or high rovibrational dissociation yield without molecular preorientation or prealignment. Our study of the field induced isomerization and dissociation dynamics of the same system in liquid Ar shows that the picosecond isomerization dynamics is insignificantly affected by the surrounding atomic liquid whereas the dissociation yield may be greatly suppressed in a high density liquid. The implications of this study for full-dimensional quantum dynamics of multiphoton rovibrational excitation and dissociation of triatomics are briefly discussed.

  7. Dissociation Dynamics and Stability of Cyclic Alkoxy Radicals and Alkoxide Anions

    E-print Network

    Continetti, Robert E.

    Dissociation Dynamics and Stability of Cyclic Alkoxy Radicals and Alkoxide Anions Leah S. Alconcel, California 92093-0314 ReceiVed December 14, 2000 Abstract: Photodetachment and dissociative photodetachment energy, dissociation into HCO + C2H4 is observed. The A(2A) state completely dissociates into HCO + C2H4

  8. Products of Dissociative Recombination in the Ionosphere

    NASA Technical Reports Server (NTRS)

    Cosby, Philip

    1996-01-01

    SRI International undertook a novel experimental measurement of the product states formed by dissociative ro-combination (DR) of C2(+), NO(+), and N2(+) as a function of both electron energy and reactant ion vibrational level. For these measurements we used a recently developed experimental technique for measuring dissociation product distributions that allows both the branching ratios to be accurately determined and the electronic and ro-vibrational state composition of the reactant ions to be specified. DR is the dominant electron loss mechanism in all regions of the ionosphere. In this process, electron attachment to the molecular ion produces an unstable neutral molecule that rapidly dissociates.

  9. TiCl, TiH and TiH+ Bond Energies, a Test of a Correlation Consistent Ti Basis Set

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Arnold, James O. (Technical Monitor)

    1999-01-01

    Correlation consistent basis sets are developed for Ti atom. The polarization functions are optimized for the average of the 3F and 5F states. One series of correlation consistent basis sets is for 3d and 4s correlation, while the second series includes 3s and 3p correlation as well as 3d and 4s correlation. These basis sets are tested using the Ti 3F-5F separation and the dissociation energies of TiCl X4Phi, TiH X4Phi, and TiH(+) X3Phi. The CCSD(T) complete basis set limit values are determined by extrapolation. The Douglas Kroll approach is used to compute the scalar relativistic effect. Spin-orbit effects are taken from experiment and/or computed at the CASSCF level. The Ti 3F-5F separation is in excellent agreement with experiment, while the TiCl, TiH, and TiH(+) bond energies are in good agreement with experiment. Extrapolation with the valence basis set is consistent with other atoms, while including 3s and 3p correlation appears to make extrapolation.

  10. Chemical Dynamics Simulations of Benzene Dimer Dissociation.

    PubMed

    Ma, Xinyou; Paul, Amit K; Hase, William L

    2015-06-25

    Classical chemical dynamics simulations were performed to study the intramolecular and unimolecular dissociation dynamics of the benzene dimer, Bz2 ? 2 Bz. The dissociation of microcanonical ensembles of Bz2 vibrational states, at energies E corresponding to temperatures T of 700-1500 K, were simulated. For the large Bz2 energies and large number of Bz2 vibrational degrees of freedom, s, the classical microcanonical (RRKM) and canonical (TST) rate constant expressions become identical. The dissociation rate constant for each T is determined from the initial rate dN(t)/dt of Bz2 dissociation, and the k(T) are well-represented by the Arrhenius eq k(T) = A exp(-E(a)/RT). The E(a) of 2.02 kcal/mol agrees well with the Bz2 dissociation energy of 2.32 kcal/mol, and the A-factor of 2.43 × 10(12) s(-1) is of the expected order-of-magnitude. The form of N(t) is nonexponential, resulting from weak coupling between the Bz2 intramolecular and intermolecular modes. With this weak coupling, large Bz2 vibrational excitation, and low Bz2 dissociation energy, most of the trajectories dissociate directly. Simulations, with only the Bz2 intramolecular modes excited at 1000 K, were also performed to study intramolecular vibrational energy redistribution (IVR) between the intramolecular and intermolecular modes. Because of restricted IVR, the initial dissociation is quite slow, but N(t) ultimately becomes exponential, suggesting an IVR time of 20.7 ps. PMID:26024045

  11. A shock-tube determination of the CN ground state dissociation energy and electronic transition moments for the CN violet and red band systems

    NASA Technical Reports Server (NTRS)

    Arnold, J. O.; Nicholls, R. W.

    1973-01-01

    The CN ground state dissociation energy and the sum of squares of the electronic transition moments of the CN violet bands have been simultaneously determined from spectral emission measurements behind incident shock waves. The unshocked test gases were composed of various CO2-CO-N2-Ar mixtures, and the temperatures behind the incident shocks ranged from 3500 to 8000 K. The variation of the electronic transition moment with internuclear separation was found to be small for both the CN violet and red band systems.

  12. Dissociative adsorption of CH3X (X = Br and Cl) on a silicon(100) surface revisited by density functional theory

    NASA Astrophysics Data System (ADS)

    Wang, Chen-Guang; Huang, Kai; Ji, Wei

    2014-11-01

    During the dissociative adsorption on a solid surface, the substrate usually participates in a passive manner to accommodate fragments produced upon the cleavage of the internal bond(s) of a (transient) molecular adsorbate. This simple picture, however, neglects the flexibility of surface atoms. Here, we report a Density Functional Theory study to revisit our early studies of the dissociative adsorption of CH3X (X = Br and Cl) on Si(100). We have identified a new reaction pathway, which involves a flip of a silicon dimer; this new pathway agrees better with experiments. For our main exemplar of CH3Br, insights have been gained using a simple model that involves a three-atom reactive center, Br-C-Si. When the silicon dimer flips, the interaction between C and Si in the Br-C-Si center is enhanced, evident in the increased energy-split of the frontier orbitals. We also examine how the dissociation dynamics of CH3Br is altered on a heterodimer (Si-Al, Si-P, and Si-Ge) in a Si(100) surface. In each case, we conclude, on the basis of computed reaction pathways, that no heterodimer flipping is involved before the system transverses the transition state to dissociative adsorption.

  13. Dissociative adsorption of CH?X (X = Br and Cl) on a silicon(100) surface revisited by density functional theory.

    PubMed

    Wang, Chen-Guang; Huang, Kai; Ji, Wei

    2014-11-01

    During the dissociative adsorption on a solid surface, the substrate usually participates in a passive manner to accommodate fragments produced upon the cleavage of the internal bond(s) of a (transient) molecular adsorbate. This simple picture, however, neglects the flexibility of surface atoms. Here, we report a Density Functional Theory study to revisit our early studies of the dissociative adsorption of CH3X (X = Br and Cl) on Si(100). We have identified a new reaction pathway, which involves a flip of a silicon dimer; this new pathway agrees better with experiments. For our main exemplar of CH3Br, insights have been gained using a simple model that involves a three-atom reactive center, Br-C-Si. When the silicon dimer flips, the interaction between C and Si in the Br-C-Si center is enhanced, evident in the increased energy-split of the frontier orbitals. We also examine how the dissociation dynamics of CH3Br is altered on a heterodimer (Si-Al, Si-P, and Si-Ge) in a Si(100) surface. In each case, we conclude, on the basis of computed reaction pathways, that no heterodimer flipping is involved before the system transverses the transition state to dissociative adsorption. PMID:25381532

  14. Absolute cross sections for the dissociation of hydrogen cluster ions in high-energy collisions with helium atoms

    SciTech Connect

    Eden, S.; Tabet, J.; Samraoui, K.; Louc, S.; Farizon, B.; Farizon, M.; Ouaskit, S.; Maerk, T. D.

    2006-02-15

    Absolute dissociation cross sections are reported for H{sub n}{sup +} clusters of varied mass (n=3,5,...,35) following collisions with He atoms at 60 keV/amu. Initial results have been published previously for a smaller range of cluster sizes [Ouaskit et al., Phys. Rev. A 49, 1484 (1994)]. The present extended study includes further experimental results, reducing the statistical errors associated with the absolute cross sections. The previously suggested quasilinear dependence of the H{sub n}{sup +} dissociation cross sections upon n is developed with reference to expected series of geometrical shells of H{sub 2} molecules surrounding a H{sub 3}{sup +} core. Recent calculations identify n=9 as corresponding to the first closed H{sub 2} shell [e.g., Stich et al., J. Chem. Phys. 107, 9482 (1997)]. Recurrence of the distinct characteristics observed in the dissociation-cross-section dependence upon cluster size around n=9 provides the basis for the presently proposed subsequent closed shells at n=15, 21, 27, and 33, in agreement with the calculations of Nagashima et al. [J. Phys. Chem. 96, 4294 (1992)].

  15. The dissociation energies of NF(X{sup 3}{Sigma}{sup {minus}}) and NCl(X{sup 3}{Sigma}{sup {minus}})

    SciTech Connect

    Xantheas, S.S.; Dunning, T.H. Jr.; Mavridis, A.

    1997-02-01

    We have computed potential energy functions for the ground states (X{sup 3}{Sigma}{sup {minus}}) of NF and NCl using a series of correlation consistent basis sets ranging from double to sextuple zeta quality and including core-valence correlation effects in conjunction with coupled-cluster single and double excitations with perturbative treatment of triple excitations [CCSD(T)] and large internally contracted multireference configuration interaction (icMRCI) wave functions. The best estimates for the dissociation energies (D{sub e}{close_quote}s) are 76.6{plus_minus}1.3 kcal/mol for NF and 64.6{plus_minus}1.3 kcal/mol for NCl, respectively. Our results suggest that previous experimental {ital estimates} for the dissociation energy of NCl are in error by as much as 15 kcal/mol. The calculated spectroscopic constants for NF and NCl are in good agreement with the measured constants. {copyright} {ital 1997 American Institute of Physics.}

  16. Gas-Phase Dissociation Pathways of Multiply Charged Peptide Clusters

    PubMed Central

    Jurchen, John C.; Garcia, David E.; Williams, Evan R.

    2005-01-01

    Numerous studies of cluster formation and dissociation have been conducted to determine properties of matter in the transition from the condensed phase to the gas phase using materials as diverse as atomic nuclei, noble gasses, metal clusters, and amino acids. Here, electrospray ionization is used to extend the study of cluster dissociation to peptides including leucine enkephalin with 7–19 monomer units and 2–5 protons, and somatostatin with 5 monomer units and 4 protons under conditions where its intramolecular disulfide bond is either oxidized or reduced. Evaporation of neutral monomers and charge separation by cluster fission are the competing dissociation pathways of both peptides. The dominant fission product for all leucine enkephalin clusters studied is a proton-bound dimer, presumably due to the high gas-phase stability of this species. The branching ratio of the fission and evaporation processes for leucine enkephalin clusters appears to be determined by the value of z2/n for the cluster where z is the charge and n the number of monomer units in the cluster. Clusters with low and high values of z2/n dissociate primarily by evaporation and cluster fission respectively, with a sharp transition between dissociation primarily by evaporation and primarily by fission measured at a z2/n value of ~0.5. The dependence of the dissociation pathway of a cluster on z2/n is similar to the dissociation of atomic nuclei and multiply charged metal clusters indicating that leucine enkephalin peptide clusters exist in a state that is more disordered, and possibly fluid, rather than highly structured in the dissociative transition state. The branching ratio, but not the dissociation pathway of [somatostatin5 + 4H]4+ is altered by the reduction of its internal disulfide bond indicating that monomer conformational flexibility plays a role in peptide cluster dissociation. PMID:14652186

  17. The Effect of Carbon Monoxide Co-Adsorption on Ni-Catalysed Water Dissociation

    PubMed Central

    Mohsenzadeh, Abas; Borjesson, Anders; Wang, Jeng-Han; Richards, Tobias; Bolton, Kim

    2013-01-01

    The effect of carbon monoxide (CO) co-adsorption on the dissociation of water on the Ni(111) surface has been studied using density functional theory. The structures of the adsorbed water molecule and of the transition state are changed by the presence of the CO molecule. The water O–H bond that is closest to the CO is lengthened compared to the structure in the absence of the CO, and the breaking O–H bond in the transition state structure has a larger imaginary frequency in the presence of CO. In addition, the distances between the Ni surface and H2O reactant and OH and H products decrease in the presence of the CO. The changes in structures and vibrational frequencies lead to a reaction energy that is 0.17 eV less exothermic in the presence of the CO, and an activation barrier that is 0.12 eV larger in the presence of the CO. At 463 K the water dissociation rate constant is an order of magnitude smaller in the presence of the CO. This reveals that far fewer water molecules will dissociate in the presence of CO under reaction conditions that are typical for the water-gas-shift reaction. PMID:24287907

  18. THE JOURNAL OF CHEMICAL PHYSICS 142, 044305 (2015) Dissociation energies and potential energy functions for the ground X 1

    E-print Network

    Le Roy, Robert J.

    2015-01-01

    . Sentjens, and Robert J. Le Roy Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1 of centrifugal (non-adiabatic) and potential-energy (adiabatic) Born-Oppenheimer breakdown correction functions quantum-mechanically accurate analytic potential energy function and Born-Oppenheimer breakdown (BOB

  19. Monte Carlo configuration interaction with perturbation corrections for dissociation energies of first row diatomic molecules: C{sub 2}, N{sub 2}, O{sub 2}, CO, and NO

    SciTech Connect

    Kelly, Thomas P.; Greer, James C.; Perera, Ajith; Bartlett, Rodney J.

    2014-02-28

    Dissociation energies for the diatomic molecules C{sub 2}, N{sub 2}, O{sub 2}, CO, and NO are estimated using the Monte Carlo configuration interaction (MCCI) and augmented by a second order perturbation theory correction. The calculations are performed using the correlation consistent polarized valence “triple zeta” atomic orbital basis and resulting dissociation energies are compared to coupled cluster calculations including up to triple excitations (CCSDT) and Full Configuration Interaction Quantum Monte Carlo (FCIQMC) estimates. It is found that the MCCI method readily describes the correct behavior for dissociation for the diatomics even when capturing only a relatively small fraction (?80%) of the correlation energy. At this level only a small number of configurations, typically O(10{sup 3}) from a FCI space of dimension O(10{sup 14}), are required to describe dissociation. Including the perturbation correction to the MCCI estimates, the difference in dissociation energies with respect to CCSDT ranges between 1.2 and 3.1 kcal/mol, and the difference when comparing to FCIQMC estimates narrows to between 0.5 and 1.9 kcal/mol. Discussions on MCCI's ability to recover static and dynamic correlations and on the form of correlations in the electronic configuration space are presented.

  20. Further Theoretical Evidence for Hydrogen-Assisted CO Dissociation on Ru(0001)

    SciTech Connect

    Alfonso, Dominic R.

    2013-10-10

    Extensive calculations based on spin-polarized density functional theory were carried out to examine how CH{sub x} are formed from the dissociation of CO on Ru(0001) in the presence of hydrogen. Common pathways, such as the direct CO dissociation and H-assisted route leading to HCO or COH, including alternative routes that involve the formation of HCOH and CH{sub 2}O, were examined. The reaction energy and barrier for each elementary step were calculated. The calculations show that the carbide mechanism is not the main reaction pathway for the conversion of CO on Ru(0001). Complementary microkinetic simulations utilizing results from first-principles quantum mechanical calculations indicate that a branch starting from the hydrogenation of CO to HCOH (via COH intermediate) and subsequent C–O bond cleavage is more plausible.

  1. Dissociative recombination in aeronomy

    NASA Technical Reports Server (NTRS)

    Fox, J. L.

    1989-01-01

    The importance of dissociative recombination in planetary aeronomy is summarized, and two examples are discussed. The first is the role of dissociative recombination of N2(+) in the escape of nitrogen from Mars. A previous model is updated to reflect new experimental data on the electronic states of N produced in this process. Second, the intensity of the atomic oxygen green line on the nightside of Venus is modeled. Use is made of theoretical rate coefficients for production of O (1S) in dissociative recombination from different vibrational levels of O2(+).

  2. Identification of a previously unobserved dissociative ionization pathway in time-resolved photospectroscopy of the deuterium molecule.

    PubMed

    Cao, Wei; Laurent, Guillaume; Ben-Itzhak, Itzik; Cocke, C Lewis

    2015-03-20

    A femtosecond vacuum ultraviolet (VUV) pulse with high spectral resolution (<200??meV) is selected from the laser-driven high order harmonics. This ultrafast VUV pulse is synchronized with an infrared (IR) laser pulse to study dissociative ionization in deuterium molecules. At a VUV photon energy of 16.95 eV, a previously unobserved bond-breaking pathway is found in which the dissociation direction does not follow the IR polarization. We interpret it as corresponding to molecules predissociating into two separated atoms, one of which is photoionized by the following IR pulse. A time resolved study allows us to determine the lifetime of the intermediate predissociation process to be about 1 ps. Additionally, the dissociative ionization pathways show high sensitivity to the VUV photon energy. As the VUV photon energy is blueshifted to 17.45 eV, the more familiar bond-softening channel is opened to compete with the newly discovered pathway. The interpretation of different pathways is supported by the energy sharing between the electron and nuclei. PMID:25839264

  3. Identification of a Previously Unobserved Dissociative Ionization Pathway in Time-Resolved Photospectroscopy of the Deuterium Molecule

    NASA Astrophysics Data System (ADS)

    Cao, Wei; Laurent, Guillaume; Ben-Itzhak, Itzik; Cocke, C. Lewis

    2015-03-01

    A femtosecond vacuum ultraviolet (VUV) pulse with high spectral resolution (<200 meV ) is selected from the laser-driven high order harmonics. This ultrafast VUV pulse is synchronized with an infrared (IR) laser pulse to study dissociative ionization in deuterium molecules. At a VUV photon energy of 16.95 eV, a previously unobserved bond-breaking pathway is found in which the dissociation direction does not follow the IR polarization. We interpret it as corresponding to molecules predissociating into two separated atoms, one of which is photoionized by the following IR pulse. A time resolved study allows us to determine the lifetime of the intermediate predissociation process to be about 1 ps. Additionally, the dissociative ionization pathways show high sensitivity to the VUV photon energy. As the VUV photon energy is blueshifted to 17.45 eV, the more familiar bond-softening channel is opened to compete with the newly discovered pathway. The interpretation of different pathways is supported by the energy sharing between the electron and nuclei.

  4. Dissociative electron attachment in nonplanar chlorocarbons with ??/??-coupled molecular orbitals

    NASA Astrophysics Data System (ADS)

    Aflatooni, K.; Gallup, G. A.; Burrow, P. D.

    2010-03-01

    Total absolute cross sections for the dissociative electron attachment (DEA) process are reported for a series of nonplanar ethylenic and phenylic compounds monosubstituted with (CH2)nCl groups, where n=1-4. Coupling between the local ?? molecular orbitals provided by the unsaturated moieties and the ?? (C-Cl) orbital is thus examined as a function of the separation of these groups. In particular, the coupling is viewed from the perspective of the interacting temporary negative ions formed by short lived occupation of these orbitals and their decay into the DEA channel. A theoretical treatment of "remote" bond breaking, presented elsewhere, satisfactorily accounts for DEA in the chloroethylenic compounds presented here and emphasizes not only the delocalization of the coupled anionic wave functions but the importance of their relative phases. The dependence of the cross sections on the vertical attachment energies, measured by electron transmission spectroscopy, is also explored and compared to that found previously in chlorinated alkanes.

  5. Hallucinogens and Dissociative Drugs

    MedlinePLUS

    ... in bizarre or dangerous behavior. Hallucinogens such as LSD, psilocybin, peyote, DMT, and ayahuasca cause emotions to ... Take Hallucinogenic or Dissociative Drugs? How Do Hallucinogens (LSD, Psilocybin, Peyote, DMT, and Ayahuasca) Affect the Brain ...

  6. Comparison of DFT with Traditional Methods for the Calculation of Vibrational Frequencies and Bond Energies

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W.; Arnold, James O. (Technical Monitor)

    1997-01-01

    The vibrational frequencies of MO2 are computed at many levels of theory, including HF, B3LYP, BP86, CASSCF, MP2, and CCSD(T). The computed results are compared with the available experimental results. Most of the methods fail for at least one state of the systems considered. The accuracy of the results and the origin of the observed failures are discussed. The B3LYP bond energies are compared with traditional methods for a variety of systems, ranging from FeCOn+ to SiCln and its positive ions. The cases where B3LYP differs from the traditional methods are discussed.

  7. Electronic structure, charge transfer and bonding in intermetallics using EELS and density functional theory[Electron Energy Loss Spectroscopy

    SciTech Connect

    Humphreys, C.J.; Botton, G.A.; Pankhurst, D.A.; Keast, V.J.; Temmerman, W.M.

    1999-07-01

    Electron energy loss spectroscopy and density functional theory have been used to show that there is a covalent component to the bonding in NiAl, CoAl and FeAl, between the transition metal atom and Al. There is no charge transfer and no ionic component to the bonding in NiAl and probably not in CoAl and FeAl. The bonding is non-stoichiometric NiAl is studied. Preliminary results are given for a {Sigma}{sub 3} boundary in NiAl.

  8. Combining ab initio quantum mechanics with a dipole-field model to describe acid dissociation reactions in water: first-principles free energy and entropy calculations.

    PubMed

    Maurer, Patrick; Iftimie, Radu

    2010-02-21

    We introduce a novel approach to compute dissociation free energy and entropy values in simulations that employ a density functional theory description of the acidic moiety and of the solvent. The approach consists of utilizing an alchemical transformation of a weak acid A-COOH into the strong acid B-COOH, which makes it practical to employ alchemical free energy perturbation methods in the context of ab initio molecular dynamics simulations. The present alchemical transformation circumvents the need to tackle changes in the total number of electrons and atoms by replacing the chemical residue responsible for the change in acidity with an easily tunable external effective potential. Our investigation demonstrates that (1) a simple but effective class of external potentials that control acidity changes in the acetic/trifluoroacetic acid series can be achieved by replacing the methyl and trifluoromethyl substituents by screened dipoles. Using this dipole-field/quantum-mechanics (DF/QM) approach one can predict gas-phase geometries, proton dissociation energies, total dipole moments, and water binding energies in good agreement with full-QM values. (2) The resulting alchemical perturbation calculations are stable and well converged and allow one to compute absolute pK(a) values whose accuracy is limited primarily by the exchange-correlation functional employed: H-COOH=2.5+/-0.6 (full-QM calculation), 3.7 (exp); F(3)C-COOH=0.4+/-0.6 (DF/QM calculation), 0.5 (exp); H(3)C-COOH=3.1+/-0.7 (DF/QM calculation), 4.7 (exp); 3) Our DF/QM model predicts that the difference in acidity between H-COOH and H(3)C-COOH is dominated by solvent entropy effects, in excellent agreement with experimental observations. The calculated difference between the dissociation energies of these acids is DeltaDelta(d)U=0.0+/-0.26 kcal/mol while the experimental value is 0.0+/-0.1 kcal/mol. PMID:20170220

  9. Combining ab initio quantum mechanics with a dipole-field model to describe acid dissociation reactions in water: First-principles free energy and entropy calculations

    NASA Astrophysics Data System (ADS)

    Maurer, Patrick; Iftimie, Radu

    2010-02-01

    We introduce a novel approach to compute dissociation free energy and entropy values in simulations that employ a density functional theory description of the acidic moiety and of the solvent. The approach consists of utilizing an alchemical transformation of a weak acid A-COOH into the strong acid B-COOH, which makes it practical to employ alchemical free energy perturbation methods in the context of ab initio molecular dynamics simulations. The present alchemical transformation circumvents the need to tackle changes in the total number of electrons and atoms by replacing the chemical residue responsible for the change in acidity with an easily tunable external effective potential. Our investigation demonstrates that (1) a simple but effective class of external potentials that control acidity changes in the acetic/trifluoroacetic acid series can be achieved by replacing the methyl and trifluoromethyl substituents by screened dipoles. Using this dipole-field/quantum-mechanics (DF/QM) approach one can predict gas-phase geometries, proton dissociation energies, total dipole moments, and water binding energies in good agreement with full-QM values. (2) The resulting alchemical perturbation calculations are stable and well converged and allow one to compute absolute pKa values whose accuracy is limited primarily by the exchange-correlation functional employed: H-COOH=2.5±0.6 (full-QM calculation), 3.7 (exp); F3C-COOH=0.4±0.6 (DF/QM calculation), 0.5 (exp); H3C-COOH=3.1±0.7 (DF/QM calculation), 4.7 (exp); 3) Our DF/QM model predicts that the difference in acidity between H-COOH and H3C-COOH is dominated by solvent entropy effects, in excellent agreement with experimental observations. The calculated difference between the dissociation energies of these acids is ??dU =0.0±0.26 kcal/mol while the experimental value is 0.0±0.1 kcal/mol.

  10. Nano-Bonding of Silicon Oxides-based surfaces at Low Temperature: Bonding Interphase Modeling via Molecular Dynamics and Characterization of Bonding Surfaces Topography, Hydro-affinity and Free Energy

    NASA Astrophysics Data System (ADS)

    Whaley, Shawn D.

    In this work, a new method, "Nanobonding(TM)" [1,2] is conceived and researched to bond Si-based surfaces, via nucleation and growth of a 2 D silicon oxide SiOxHx interphase connecting the surfaces at the nanoscale across macroscopic domains. Nanobonding cross-bridges two smooth surfaces put into mechanical contact in an O2/H 2O mixed ambient below T ?200 °C via arrays of SiOxH x molecules connecting into a continuous macroscopic bonding interphase. Nano-scale surface planarization via wet chemical processing and new spin technology are compared via Tapping Mode Atomic Force Microscopy (TMAFM) , before and after nano-bonding. Nanobonding uses precursor phases, 2D nano-films of beta-cristobalite (beta-c) SiO2, nucleated on Si(100) via the Herbots-Atluri (H-A) method [1]. beta-c SiO2 on Si(100) is ordered and flat with atomic terraces over 20 nm wide, well above 2 nm found in native oxides. When contacted with SiO2 this ultra-smooth nanophase can nucleate and grow domains with cross-bridging molecular strands of hydroxylated SiOx, instead of point contacts. The high density of molecular bonds across extended terraces forms a strong bond between Si-based substrates, nano- bonding [2] the Si and silica. A new model of beta-cristobalite SiO2 with its <110> axis aligned along Si[100] direction is simulated via ab-initio methods in a nano-bonded stack with beta-c SiO2 in contact with amorphous SiO2 (a-SiO2), modelling cross-bridging molecular bonds between beta-c SiO2 on Si(100) and a-SiO2 as during nanobonding. Computed total energies are compared with those found for Si(100) and a-SiO2 and show that the presence of two lattice cells of !-c SiO2 on Si(100) and a-SiO2 lowers energy when compared to Si(100)/ a-SiO 2 Shadow cone calculations on three models of beta-c SiO2 on Si(100) are compared with Ion Beam Analysis of H-A processed Si(100). Total surface energy measurements via 3 liquid contact angle analysis of Si(100) after H-A method processing are also compared. By combining nanobonding experiments, TMAFM results, surface energy data, and ab-initio calculations, an atomistic model is derived and nanobonding is optimized. [1] US Patent 6,613,677 (9/2/03), 7,851,365 (12/14/10), [2] Patent Filed: 4/30/09, 10/1/2011

  11. Bent Bonds and Multiple Bonds.

    ERIC Educational Resources Information Center

    Robinson, Edward A.; Gillespie, Ronald J.

    1980-01-01

    Considers carbon-carbon multiple bonds in terms of Pauling's bent bond model, which allows direct calculation of double and triple bonds from the length of a CC single bond. Lengths of these multiple bonds are estimated from direct measurements on "bent-bond" models constructed of plastic tubing and standard kits. (CS)

  12. Simple non-empirical procedure for spin-component-scaled MP2 methods applied to the calculation of dissociation energy curve of noncovalently-interacting systems

    E-print Network

    Grabowski, I; Della Sala, F

    2013-01-01

    We present a simple and non-empirical method to determine optimal scaling coefficients, within the (spin-component)-scaled MP2 approach, for calculating intermolecular potential energies of noncovalently-interacting systems. The method is based on an observed proportionality between (spin-component) MP2 and CCSD(T) energies for a wide range of intermolecular distances and allows to compute with high accuracy a large portion of the dissociation curve at the cost of a single CCSD(T) calculation. The accuracy of the present procedure is assessed for a series of noncovalently-interacting test systems: the obtained results reproduce CCSD(T) quality in all cases and definitely outperform conventional MP2, CCSD and SCS-MP2 results. The difficult case of the Beryllium dimer is also considered.

  13. Direct high-energy neutral-channel dissociative recombination of cold H[sub 3][sup +] in an ion storage ring

    SciTech Connect

    Larsson, M.; Danared, H.; Mowat, J.R.; Sigray, P.; Sundstroem, G.; Brostroem, L.; Filevich, A.; Kaellberg, A.; Mannervik, S.; Rensfelt, K.G.; Datz, S. Manne Siegbahn Institute of Physics, S-10405 Stockholm Department of Physics, North Carolina State University, Raleigh, North Carolina 27695-8202 Department of Physics, Comision Nacional de Energia Atomica TANDAR, Av. Libertador 8250, 1429 Buenos Aires Physics Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831 )

    1993-01-25

    The cross section for neutral-channel dissociative recombination of vibrationally cooled H[sub 3][sup +] at energies between 0.0025 and 30 eV has been measured by utilizing the electron cooler at the storage ring CRYRING. The molecular ions were stored at an energy of 32.6 MeV and phase-space cooled by the electron cooler for about 8 s prior to data taking. A peak in the cross section at 9.4 eV is interpreted as a direct adiabatic neutral-channel recombination through the [sup 2][ital A][sub 1] resonant state. The cross section below 1 eV is in rather good agreement with single-pass data.

  14. Dissociative Ionization of Benzene by Electron Impact

    NASA Technical Reports Server (NTRS)

    Huo, Winifred; Dateo, Christopher; Kwak, Dochan (Technical Monitor)

    2002-01-01

    We report a theoretical study of the dissociative ionization (DI) of benzene from the low-lying ionization channels. Our approach makes use of the fact that electron motion is much faster than nuclear motion and DI is treated as a two-step process. The first step is electron-impact ionization resulting in an ion with the same nuclear geometry as the neutral molecule. In the second step the nuclei relax from the initial geometry and undergo unimolecular dissociation. For the ionization process we use the improved binary-encounter dipole (iBED) model. For the unimolecular dissociation step, we study the steepest descent reaction path to the minimum of the ion potential energy surface. The path is used to analyze the probability of unimolecular dissociation and to determine the product distributions. Our analysis of the dissociation products and the thresholds of the productions are compared with the result dissociative photoionization measurements of Feng et al. The partial oscillator strengths from Feng et al. are then used in the iBED cross section calculations.

  15. Imaging the molecular dynamics of dissociative electron attachment to water

    SciTech Connect

    Adaniya, Hidihito; Rudek, B.; Osipov, Timur; Haxton, Dan; Weber, Thorsten; Rescigno, Thomas N.; McCurdy, C.W.; Belkacem, Ali

    2009-10-19

    Momentum imaging experiments on dissociative electron attachment to the water molecule are combined with ab initio theoretical calculations of the angular dependence of the quantum mechanical amplitude for electron attachment to provide a detailed picture of the molecular dynamics of dissociation attachment via the two lowest energy Feshbach resonances. The combination of momentum imaging experiments and theory can reveal dissociation dynamics for which the axial recoil approximation breaks down and thus provides a powerful reaction microscope for DEA to polyatomics.

  16. Exploring the nature of silicon-noble gas bonds in H3SiNgNSi and HSiNgNSi compounds (Ng = Xe, Rn).

    PubMed

    Pan, Sudip; Saha, Ranajit; Chattaraj, Pratim K

    2015-01-01

    Ab initio and density functional theory-based computations are performed to investigate the structure and stability of H3SiNgNSi and HSiNgNSi compounds (Ng = Xe, Rn). They are thermochemically unstable with respect to the dissociation channel producing Ng and H3SiNSi or HSiNSi. However, they are kinetically stable with respect to this dissociation channel having activation free energy barriers of 19.3 and 23.3 kcal/mol for H3SiXeNSi and H3SiRnNSi, respectively, and 9.2 and 12.8 kcal/mol for HSiXeNSi and HSiRnNSi, respectively. The rest of the possible dissociation channels are endergonic in nature at room temperature for Rn analogues. However, one three-body dissociation channel for H3SiXeNSi and one two-body and one three-body dissociation channels for HSiXeNSi are slightly exergonic in nature at room temperature. They become endergonic at slightly lower temperature. The nature of bonding between Ng and Si/N is analyzed by natural bond order, electron density and energy decomposition analyses. Natural population analysis indicates that they could be best represented as (H3SiNg)+(NSi)- and (HSiNg)+(NSi)-. Energy decomposition analysis further reveals that the contribution from the orbital term (?Eorb) is dominant (ca. 67%-75%) towards the total attraction energy associated with the Si-Ng bond, whereas the electrostatic term (?Eelstat) contributes the maximum (ca. 66%-68%) for the same in the Ng-N bond, implying the covalent nature of the former bond and the ionic nature of the latter. PMID:25809612

  17. Exploring the Nature of Silicon-Noble Gas Bonds in H3SiNgNSi and HSiNgNSi Compounds (Ng = Xe, Rn)

    PubMed Central

    Pan, Sudip; Saha, Ranajit; Chattaraj, Pratim K.

    2015-01-01

    Ab initio and density functional theory-based computations are performed to investigate the structure and stability of H3SiNgNSi and HSiNgNSi compounds (Ng = Xe, Rn). They are thermochemically unstable with respect to the dissociation channel producing Ng and H3SiNSi or HSiNSi. However, they are kinetically stable with respect to this dissociation channel having activation free energy barriers of 19.3 and 23.3 kcal/mol for H3SiXeNSi and H3SiRnNSi, respectively, and 9.2 and 12.8 kcal/mol for HSiXeNSi and HSiRnNSi, respectively. The rest of the possible dissociation channels are endergonic in nature at room temperature for Rn analogues. However, one three-body dissociation channel for H3SiXeNSi and one two-body and one three-body dissociation channels for HSiXeNSi are slightly exergonic in nature at room temperature. They become endergonic at slightly lower temperature. The nature of bonding between Ng and Si/N is analyzed by natural bond order, electron density and energy decomposition analyses. Natural population analysis indicates that they could be best represented as (H3SiNg)+(NSi)? and (HSiNg)+(NSi)?. Energy decomposition analysis further reveals that the contribution from the orbital term (?Eorb) is dominant (ca. 67%–75%) towards the total attraction energy associated with the Si-Ng bond, whereas the electrostatic term (?Eelstat) contributes the maximum (ca. 66%–68%) for the same in the Ng–N bond, implying the covalent nature of the former bond and the ionic nature of the latter. PMID:25809612

  18. Intriguing Role of a Quaternary Ammonium Cation in the Dissociation Chemistry of Keggin Polyoxometalate Anions

    NASA Astrophysics Data System (ADS)

    Cao, Jie; Li, Chenchen; Zhang, Zhengxiang; Xu, Chong; Yan, Jie; Cui, Fengyun; Hu, Changwen

    2012-02-01

    The gas-phase fragmentations of a series of Keggin polyoxometalate anions with molecular formula of TBAn[XM12O40] (X = P, Si; M = Mo, W) were studied by electrospray ionization tandem mass spectrometry. The bare polyoxoanions [XM12O40]n- as well as the non-covalent complexes {TBA[XM12O40]}(n-1)- and {TBAm[XM12O40]2}3- displayed characteristic dissociation pathways. Fragmentation of [XM12O40]n- led to pairs of complementary product anions whose total stoichiometry and charge matched those of the precursor anion, consistent with the previous study by Ma et al. The nature of the non-covalent interaction between [XM12O40]n- and TBA+ was addressed in detail via the example of {TBA[XM12O40]}(n-1)-. The non-covalent interaction [1] primarily dominated by the Coulombic attraction of the opposite charges completely changed the dissociation chemistry of [XM12O40]n-. The non-covalent complexes {TBA[XM12O40]}(n-1)- and {TBAm[XM12O40]2}3-, formed by the charge reduction during the electrospray process, underwent distinct dissociation routes: {TBA[XM12O40]}(n-1)- fragmented to give rise to its product ion {(C4H9)[XM12O40]}(n-1)- by cleaving the N-C covalent bond inside the TBA+ cation whereas {TBAm[XM12O40]2}3- dissociated into a pair of product ions, {TBAi[XM12O40]}2- and {TBAm-i[XM12O40]}-, by breaking the non-covalent bond between [XM12O40]n- and TBA+. In addition, energy-variable CID was used to map the relative stabilities of the ion clusters in the gas phase, which was in excellent agreement with the relative orders of thermal stability in the condensed phase.

  19. The key role of dislocation dissociation in the plastic behaviour of single crystal nickel-based superalloy with low stacking fault energy: Three-dimensional discrete dislocation dynamics modelling

    NASA Astrophysics Data System (ADS)

    Huang, Minsheng; Li, Zhenhuan

    2013-12-01

    To model the deformation of single crystal nickel based superalloys (SCNBS) with low stacking fault energy (SFE), three-dimensional discrete dislocation dynamics (3D-DDD) is extended by incorporating dislocation dissociation mechanism. The present 3D-DDD simulations show that, consistent with the existing TEM observation, the leading partial can enter the matrix channel efficiently while the trailing partial can hardly glide into it when the dislocation dissociation is taken into account. To determine whether the dislocation dissociation can occur or not, a critical percolation stress (CPS) based criterion is suggested. According to this CPS criterion, for SCNBS there exists a critical matrix channel width. When the channel width is lower than this critical value, the dislocation tends to dissociate into an extended configuration and vice versa. To clarify the influence of dislocation dissociation on CPS, the classical Orowan formula is improved by incorporating the SFE. Moreover, the present 3D-DDD simulations also show that the yielding stress of SCNBSs with low SFE may be overestimated up to 30% if the dislocation dissociation is ignored. With dislocation dissociation being considered, the size effect due to the width of ? matrix channel and the length of ?? precipitates on the stress-strain responses of SCNBS can be enhanced remarkably. In addition, due to the strong constraint effect by the two-phase microstructure in SCNBS, the configuration of formed junctions is quite different from that in single phase crystals such as Cu. The present results not only provide clear understanding of the two-phase microstructure levelled microplastic mechanisms in SCNBSs with low SFE, but also help to develop new continuum-levelled constitutive laws for SCNBSs.

  20. Bridging the momentum distribution and the potential energy surface of protons in hydrogen bonds

    NASA Astrophysics Data System (ADS)

    Morrone, Joseph; Lin, Lin; Car, Roberto; Parrinello, Michele

    2010-03-01

    Open path integral Car-Parrinello molecular dynamics studies have uncovered the proton momentum distribution in various phases of ice [1,2]. These systems exhibit a wide range of behavior, including symmetric hydrogen bonds and quantum tunneling. In this work, we provide an in-depth statistical analysis of the simulation results. This analysis reveals a direct relation between the open path formalism of quantum particles and their underlying potential energy surface. Application of this analysis to ice systems provides quantitative information about the principle axes of the potential energy surface that the proton experiences, and indicates that the oxygen-oxygen distance is a proper reaction coordinate for such systems. Our analysis also facilitates a direct observation of anharmonic effects along the principle axes. [1] J. A. Morrone and R. Car, Phys. Rev. Lett. 101, 17801, 2008. [2] J. A. Morrone, L. Lin and R. Car, J. Chem. Phys. 130, 204511, 2009.

  1. Tripartite efflux pumps: energy is required for dissociation, but not assembly or opening of the outer membrane channel of the pump

    PubMed Central

    Janganan, Thamarai K; Bavro, Vassiliy N; Zhang, Li; Borges-Walmsley, Maria Inês; Walmsley, Adrian R

    2013-01-01

    The MtrCDE multidrug pump, from Neisseria gonorrhoeae, is assembled from the inner and outer membrane proteins MtrD and MtrE, which are connected by the periplasmic membrane fusion protein MtrC. Although it is clear that MtrD delivers drugs to the channel of MtrE, it remains unclear how drug delivery and channel opening are connected. We used a vancomycin sensitivity assay to test for opening of the MtrE channel. Cells expressing MtrE or MtrE-E434K were insensitive to vancomycin; but became moderately and highly sensitive to vancomycin respectively, when coexpressed with MtrC, suggesting that the MtrE channel opening requires MtrC binding and is energy-independent. Cells expressing wild-type MtrD, in an MtrCE background, were vancomycin-insensitive, but moderately sensitive in an MtrCE-E434K background. The mutation of residues involved in proton translocation inactivated MtrD and abolished drug efflux, rendered both MtrE and MtrE-E434K vancomycin-insensitive; imply that the pump–component interactions are preserved, and that the complex is stable in the absence of proton flux, thus sealing the open end of MtrE. Following the energy-dependent dissociation of the tripartite complex, the MtrE channel is able to reseal, while MtrE-E434K is unable to do so, resulting in the vancomycin-sensitive phenotype. Thus, our findings suggest that opening of the OMP via interaction with the MFP is energy-independent, while both drug export and complex dissociation require active proton flux. PMID:23565750

  2. Chemical activation of molecules by metals: Experimental studies of electron distributions and bonding

    NASA Astrophysics Data System (ADS)

    Lichtenberger, D. L.

    1991-10-01

    The formal relationship between measured molecular ionization energies and thermodynamic bond dissociation energies has been developed into a single equation which unifies the treatment of covalent bonds, ionic bonds, and partially ionic bonds. This relationship has been used to clarify the fundamental thermodynamic information relating to metal-hydrogen, metal-alkyl, and metal-metal bond energies. We have been able to obtain a direct observation and measurement of the stabilization energy provided by the agostic interaction of the C-H bond with the metal. The ionization energies have also been used to correlate the rates of carbonyl substitution reactions of (eta sup 5-C5H4)Rh(CO)2 complexes, and to reveal the electronic factors that control the stability of the transition state. The extent that the electronic features of these bonding interactions transfer to other chemical systems is being investigated in terms of the principle of additivity of ligand electronic effects. Specific examples under study include metal- phosphines, metal-halides, and metallocenes. Especially interesting has been the recent application of these techniques to the characterization of the soccer-ball shaped C60 molecule, buckminsterfullerene, and its interaction with a metal surface. The high resolution valence ionizations in the gas phase reveal the high symmetry of the molecule, and studies of thin films of C60 reveal weak intermolecular interactions. Scanning tunneling and atomic force microscopy reveal the arrangement of spherical molecules on gold substrates, with significant delocalization of charge from the metal surface.

  3. Evaluating interaction energies of weakly bonded systems using the Buckingham-Hirshfeld method

    SciTech Connect

    Krishtal, A.; Van Alsenoy, C.; Geerlings, P.

    2014-05-14

    We present the finalized Buckingham-Hirshfeld method (BHD-DFT) for the evaluation of interaction energies of non-bonded dimers with Density Functional Theory (DFT). In the method, dispersion energies are evaluated from static multipole polarizabilities, obtained on-the-fly from Coupled Perturbed Kohn-Sham calculations and partitioned into diatomic contributions using the iterative Hirshfeld partitioning method. The dispersion energy expression is distributed over four atoms and has therefore a higher delocalized character compared to the standard pairwise expressions. Additionally, full multipolar polarizability tensors are used as opposed to effective polarizabilities, allowing to retain the anisotropic character at no additional computational cost. A density dependent damping function for the BLYP, PBE, BP86, B3LYP, and PBE0 functionals has been implemented, containing two global parameters which were fitted to interaction energies and geometries of a selected number of dimers using a bi-variate RMS fit. The method is benchmarked against the S22 and S66 data sets for equilibrium geometries and the S22x5 and S66x8 data sets for interaction energies around the equilibrium geometry. Best results are achieved using the B3LYP functional with mean average deviation values of 0.30 and 0.24 kcal/mol for the S22 and S66 data sets, respectively. This situates the BHD-DFT method among the best performing dispersion inclusive DFT methods. Effect of counterpoise correction on DFT energies is discussed.

  4. Structure and bonding of [(SIPr)AgX] (X = Cl, Br, I and OTf).

    PubMed

    Wong, Valerie H L; White, Andrew J P; Hor, T S Andy; Hii, King Kuok Mimi

    2015-12-01

    A series of iso-structural complexes [(SIPr)AgX] (X = Cl, Br, I, OTf; SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolidene) were synthesised, including the first example of a N-heterocyclic carbene silver(i) complex containing an O-bound triflate. Bond Energy Dissociation and Natural Orbitals for Chemical Valence bond analyses (BEDA & ETS-NOCV) revealing a significant NHC ? M ?-back-donation, which influences the stability and sigma-donicity of these complexes. PMID:26489888

  5. Q: a molecular dynamics program for free energy calculations and empirical valence bond simulations in biomolecular systems.

    PubMed

    Marelius, J; Kolmodin, K; Feierberg, I; Aqvist, J

    1998-01-01

    A new molecular dynamics program for free energy calculations in biomolecular systems is presented. It is principally designed for free energy perturbation simulations, empirical valence bond calculations, and binding affinity estimation by linear interaction energy methods. Evaluation of ligand-binding selectivity and free energy profiles for nucleophile activation in two protein tyrosine phosphatases as well as absolute binding affinity estimation for a lysine-binding protein are given as examples. PMID:10522241

  6. Hydrogen Bond Lifetimes and Energetics for Solute/Solvent Complexes Studied with 2D-IR Vibrational Echo Spectroscopy

    E-print Network

    Fayer, Michael D.

    Hydrogen Bond Lifetimes and Energetics for Solute/Solvent Complexes Studied with 2D-IR Vibrational@stanford.edu Abstract: Weak hydrogen-bonded solute/solvent complexes are studied with ultrafast two the dissociation and formation rates of the hydrogen-bonded complexes. The dissociation rates of the weak hydrogen

  7. A theoretical study of H2 dissociation on (?3 ×?3 )R30°CO/Ru(0001)

    NASA Astrophysics Data System (ADS)

    Groot, I. M. N.; Juanes-Marcos, J. C.; Olsen, R. A.; Kroes, G. J.

    2010-04-01

    We have studied the influence of preadsorbed CO on the dissociative adsorption of H2 on Ru(0001) with density functional theory calculations. For a coverage of 1/3 ML CO, we investigated different possible reaction paths for hydrogen dissociation using nudged elastic band and adaptive nudged elastic band calculations. One reaction path was studied in detail through an energy decomposition and molecular orbital type of analysis. The minimum barrier for H2 dissociation is found to be 0.29 eV. At the barrier the H-H bond is hardly stretched. Behind this barrier a molecular chemisorption minimum is present. Next, the molecule overcomes a second barrier, with a second local chemisorption minimum behind it. To finally dissociate to chemisorbed atoms, the molecule has to overcome a third barrier. To move along the reaction path from reactants to products, the hydrogen molecule needs to rotate, and to significantly change its center-of-mass position. The procedure of mapping out reaction paths for H2 reacting on low-index surfaces of bare metals (computing two-dimensional elbow plots for fixed impact high-symmetry sites and H2 orientations parallel to the surface) does not work for H2+CO/Ru. The first barrier in the path is recovered, but the features of the subsequent stretch to the dissociative chemisorption minimum are not captured, because the molecule is not allowed to change its center-of-mass position or to rotate. The dissociative chemisorption of H2 on CO/Ru(0001) is endoergic, in contrast to the case of H2 on bare Ru(0001). The zero-point energy corrected energies of molecularly and dissociatively chemisorbed H2 are very close, suggesting that it may be possible to detect molecularly chemisorbed H2 on (?3 ×?3 )R30°CO/Ru(0001). The presence of CO on the surface increases the barrier height to dissociation compared with bare Ru(0001). Based on an energy decomposition and molecular orbital analysis we attribute the increase in the barrier height mainly to an occupied-occupied interaction between the bonding H2 ?g orbital and the (surface-hybridized) CO 1? orbitals, i.e., to site blocking. There is a small repulsive contribution to the barrier from the interaction between the H2 molecule and the Ru part of the CO covered Ru surface, but it is smaller than one might expect based on the calculations of H2 interacting with a clean Ru surface, and on calculations of H2 interacting with the CO overlayer only. Actually, the analysis suggests that the Ru surface as a subsystem is (slightly) more reactive for the reaction path studied with CO preadsorbed on it than without it. Thus, the results indicate that the influence of CO on H2 dissociation on Ru is not only a simple site-blocking effect, the electronic structure of the underlying Ru is changed.

  8. Atom abstraction and gas phase dissociation in the interaction of XeF2 with Si(100)

    NASA Astrophysics Data System (ADS)

    Hefty, R. C.; Holt, J. R.; Tate, M. R.; Ceyer, S. T.

    2008-12-01

    Xenon difluoride reacts with Si(100)2×1 by single atom abstraction whereby a dangling bond abstracts a F atom from XeF2, scattering the complementary XeF product molecule into the gas phase, as observed in a molecular beam surface scattering experiment. Partitioning of the available reaction energy produces sufficient rovibrational excitation in XeF for dissociation of most of the XeF to occur. The resulting F and Xe atoms are shown to arise from the dissociation of gas phase XeF by demonstrating that the angle-resolved velocity distributions of F, Xe, and XeF conserve momentum, energy, and mass. Dissociation occurs within 2 Å of the surface and within a vibrational period of the excited XeF molecule. Approximately an equal amount of the incident XeF2 is observed to react by two atom abstraction, resulting in adsorption of a second F atom and scattering of a gas phase Xe atom. Two atom abstraction occurs for those XeF product molecules whose bond axes at the transition state are oriented within ±60° of the normal and with the F end pointed toward the surface.

  9. Identification of c-Type Heme-Containing Peptides Using Non-Activated Immobilized Metal Affinity Cchromatography Resin Enrichment and Higher-Energy Collisional Dissociation

    SciTech Connect

    Zhang, Haizhen; Yang, Feng; Qian, Weijun; Brown, Roslyn N.; Wang, Yuexi; Merkley, Eric D.; Park, Jea H.; Monroe, Matthew E.; Purvine, Samuel O.; Moore, Ronald J.; Shi, Liang; Fredrickson, Jim K.; Pasa-Tolic, Ljiljana; Smith, Richard D.; Lipton, Mary S.

    2011-10-01

    c-type cytochromes play essential roles in many biological activities of both prokaryotic and eukaryotic cells, including electron transfer, enzyme catalysis and induction of apoptosis. We report a novel enrichment strategy for identifying c-type heme-containing peptides that uses non-activated IMAC resin. The strategy demonstrated at least seven-fold enrichment for heme-containing peptides digested from a cytochrome c protein standard, and quantitative linear performance was also assessed for heme-containing peptide enrichment. Heme-containing peptides extracted from the periplasmic fraction of Shewanella oneidensis MR-1 were further identified using higher-energy collisional dissociation tandem mass spectrometry. The results demonstrated the applicability of this enrichment strategy to identify c-type heme-containing peptides from a highly complex biological sample, and at the same time, confirmed the periplasmic localization of heme-containing proteins during suboxic respiration activities of S. oneidensis MR-1.

  10. Strain-Induced Water Dissociation on Supported Ultrathin Oxide Films

    E-print Network

    Song, Zhenjun; Xu, Hu

    2015-01-01

    Controlling the dissociation of single water molecule on an insulating surface plays a crucial role in many catalytic reactions. In this Letter, we have identified the enhanced chemical reactivity of ultrathin MgO(100) films deposited on Mo(100) substrate that causes water dissociation. We reveal that the ability to split water on insulating surface closely depends on the lattice mismatch between ultrathin films and the underlying substrate, and substrate-induced in-plane tensile strain dramatically results in water dissociation on MgO(100). Three dissociative adsorption configurations of water with lower energy are predicted, and the structural transition going from molecular form to dissociative form is almost barrierless. Our results provide an effective avenue to achieve water dissociation at the single-molecule level and shed light on how to tune the chemical reactions of insulating surfaces by choosing the suitable substrates.

  11. Homolytic molecular dissociation in natural orbital functional theory.

    PubMed

    Matxain, J M; Piris, M; Ruipérez, F; Lopez, X; Ugalde, J M

    2011-12-01

    The dissociation of diatomic molecules of the 14-electron isoelectronic series N(2), O(2)(2+), CO, CN(-) and NO(+) is examined using the Piris natural orbital functional. It is found that the method describes correctly the dissociation limit yielding an integer number of electrons on the dissociated atoms, in contrast to the fractional charges obtained when using the variational two-particle reduced density matrix method under the D, Q and G positivity necessary N-representability conditions. The chemistry of the considered systems is discussed in terms of their dipole moments, natural orbital occupations and bond orders as well as atomic Mulliken populations at the dissociation limit. The values obtained agree well with accurate multiconfigurational wave function based CASSCF results and the available experimental data. PMID:21904734

  12. NASA LAW, October 25-28, 2010, Gatlinburg Dissociative Recombination in an Ion Storage Ring

    E-print Network

    Savin, Daniel Wolf

    in binding the free electron. This excess energy is stabilized by dissociation into neutral, often excited device provides a beam of electrons with only 1 meV energy spread. At matching beam velocities, elastic+ and D3O+ can dissoci- ate upon capture of a free electron, a process known as dissociative recombination

  13. Excited state dynamics of liquid water: Insight from the dissociation reaction following two-photon excitation

    E-print Network

    Elles, Christopher G.; Shkrob, Ilya A.; Crowell, Robert A.; Bradforth, Stephen E.

    2007-04-25

    The authors use transient absorption spectroscopy to monitor the ionization and dissociation products following two-photon excitation of pure liquid water. The primary decay mechanism changes from dissociation at an excitation energy of 8.3e...

  14. Novel C?-C? Bond Cleavages of Tryptophan-Containing Peptide Radical Cations

    NASA Astrophysics Data System (ADS)

    Song, Tao; Hao, Qiang; Law, Chun-Hin; Siu, Chi-Kit; Chu, Ivan K.

    2012-02-01

    In this study, we observed unprecedented cleavages of the C?-C? bonds of tryptophan residue side chains in a series of hydrogen-deficient tryptophan-containing peptide radical cations (M•+) during low-energy collision-induced dissociation (CID). We used CID experiments and theoretical density functional theory (DFT) calculations to study the mechanism of this bond cleavage, which forms [M - 116]+ ions. The formation of an ?-carbon radical intermediate at the tryptophan residue for the subsequent C?-C? bond cleavage is analogous to that occurring at leucine residues, producing the same product ions; this hypothesis was supported by the identical product ion spectra of [LGGGH - 43]+ and [WGGGH - 116]+, obtained from the CID of [LGGGH]•+ and [WGGGH]•+, respectively. Elimination of the neutral 116-Da radical requires inevitable dehydrogenation of the indole nitrogen atom, leaving the radical centered formally on the indole nitrogen atom ([Ind]•-2), in agreement with the CID data for [WGGGH]•+ and [W1-CH3GGGH]•+; replacing the tryptophan residue with a 1-methyltryptophan residue results in a change of the base peak from that arising from a neutral radical loss (116 Da) to that arising from a molecule loss (131 Da), both originating from C?-C? bond cleavage. Hydrogen atom transfer or proton transfer to the ?-carbon atom of the tryptophan residue weakens the C?-C? bond and, therefore, decreases the dissociation energy barrier dramatically.

  15. Molecular and Dissociative Adsorption of Water on (TiO2)n Clusters, n = 1-4.

    PubMed

    Chen, Mingyang; Straatsma, Tjerk P; Dixon, David A

    2015-11-19

    The low energy structures of the (TiO2)n(H2O)m (n ? 4, m ? 2n) and (TiO2)8(H2O)m (m = 3, 7, 8) clusters were predicted using a global geometry optimization approach, with a number of new lowest energy isomers being found. Water can molecularly or dissociatively adsorb on pure and hydrated TiO2 clusters. Dissociative adsorption is the dominant reaction for the first two H2O adsorption reactions for n = 1, 2, and 4, for the first three H2O adsorption reactions for n = 3, and for the first four H2O adsorption reactions for n = 8. As more H2O's are added to the hydrated (TiO2)n cluster, dissociative adsorption becomes less exothermic as all the Ti centers become 4-coordinate. Two types of bonds can be formed between the molecularly adsorbed water and TiO2 clusters: a Lewis acid-base Ti-O(H2) bond or an O···H hydrogen bond. The coupled cluster CCSD(T) results show that at 0 K the H2O adsorption energy at a 4-coordinate Ti center is ?15 kcal/mol for the Lewis acid-base molecular adsorption and ?7 kcal/mol for the H-bond molecular adsorption, in comparison to that of 8-10 kcal/mol for the dissociative adsorption. The cluster size and geometry independent dehydration reaction energy, ED, for the general reaction 2(-TiOH) ? -TiOTi- + H2O at 4-coordinate Ti centers was estimated from the aggregation reaction of nTi(OH)4 to form the monocyclic ring cluster (TiO3H2)n + nH2O. ED is estimated to be -8 kcal/mol, showing that intramolecular and intermolecular dehydration reactions are intrinsically thermodynamically allowed for the hydrated (TiO2)n clusters with all of the Ti centers 4-coordinate, which can be hindered by cluster geometry changes caused by such processes. Bending force constants for the TiOTi and OTiO bonds are determined to be 7.4 and 56.0 kcal/(mol·rad(2)). Infrared vibrational spectra were calculated using density functional theory, and the new bands appearing upon water adsorption were assigned. PMID:26485060

  16. Pathological Dissociation as Measured by the Child Dissociative Checklist

    ERIC Educational Resources Information Center

    Wherry, Jeffrey N.; Neil, Debra A.; Taylor, Tamara N.

    2009-01-01

    The component structure of the Child Dissociative Checklist was examined among abused children. A factor described as pathological dissociation emerged that was predicted by participants being male. There also were differences in pathological dissociation between groups of sexually abused and physically abused children. Replication of this factor…

  17. Dissociation and psychosis in dissociative identity disorder and schizophrenia.

    PubMed

    Laddis, Andreas; Dell, Paul F

    2012-01-01

    Dissociative symptoms, first-rank symptoms of schizophrenia, and delusions were assessed in 40 schizophrenia patients and 40 dissociative identity disorder (DID) patients with the Multidimensional Inventory of Dissociation (MID). Schizophrenia patients were diagnosed with the Structured Clinical Interview for the DSM-IV Axis I Disorders; DID patients were diagnosed with the Structured Clinical Interview for DSM-IV Dissociative Disorders-Revised. DID patients obtained significantly (a) higher dissociation scores; (b) higher passive-influence scores (first-rank symptoms); and (c) higher scores on scales that measure child voices, angry voices, persecutory voices, voices arguing, and voices commenting. Schizophrenia patients obtained significantly higher delusion scores than did DID patients. What is odd is that the dissociation scores of schizophrenia patients were unrelated to their reports of childhood maltreatment. Multiple regression analyses indicated that 81% of the variance in DID patients' dissociation scores was predicted by the MID's Ego-Alien Experiences Scale, whereas 92% of the variance in schizophrenia patients' dissociation scores was predicted by the MID's Voices Scale. We propose that schizophrenia patients' responses to the MID do not index the same pathology as do the responses of DID patients. We argue that neither phenomenological definitions of dissociation nor the current generation of dissociation instruments (which are uniformly phenomenological in nature) can distinguish between the dissociative phenomena of DID and what we suspect are just the dissociation-like phenomena of schizophrenia. PMID:22651674

  18. Electronic structures and chemical bonding in transition metal monosilicides MSi (M = 3d, 4d, 5d elements).

    PubMed

    Wu, Z J; Su, Z M

    2006-05-14

    Bond distances, vibrational frequencies, electron affinities, ionization potentials, dissociation energies, and dipole moments of the title molecules in neutral, positively, and negatively charged ions were studied using the density functional method. Ground state was assigned for each species. The bonding patterns were analyzed and compared with both the available data and across the series. It was found that besides an ionic component, covalent bonds are formed between the metal s,d orbitals and the silicon 3p orbital. The covalent character increases from ScSi (YSi) to NiSi (PdSi) for 3d (4d) metal monosilicides, then decreases. For 5d metal monosilicides, the covalent character increases from LaSi to OsSi, then decreases. For the dissociation of cations, the dissociation channel depends on the magnitude of the ionization potential between metal and silicon. If the ionization potential of the metal is smaller than that of silicon, channel MSi+ --> M+ + Si is favored. Otherwise, MSi+ --> M + Si+ will be favored. A similar behavior was observed for anions, in which the dissociation channel depends on the magnitude of electron affinity. PMID:16709105

  19. Electronic structures and chemical bonding in transition metal monosilicides MSi (M =3d, 4d, 5d elements)

    NASA Astrophysics Data System (ADS)

    Wu, Z. J.; Su, Z. M.

    2006-05-01

    Bond distances, vibrational frequencies, electron affinities, ionization potentials, dissociation energies, and dipole moments of the title molecules in neutral, positively, and negatively charged ions were studied using the density functional method. Ground state was assigned for each species. The bonding patterns were analyzed and compared with both the available data and across the series. It was found that besides an ionic component, covalent bonds are formed between the metal s,d orbitals and the silicon 3p orbital. The covalent character increases from ScSi (YSi) to NiSi (PdSi) for 3d (4d) metal monosilicides, then decreases. For 5d metal monosilicides, the covalent character increases from LaSi to OsSi, then decreases. For the dissociation of cations, the dissociation channel depends on the magnitude of the ionization potential between metal and silicon. If the ionization potential of the metal is smaller than that of silicon, channel MSi+?M++Si is favored. Otherwise, MSi+?M+Si+ will be favored. A similar behavior was observed for anions, in which the dissociation channel depends on the magnitude of electron affinity.

  20. Transport pathways for mobile ions in disordered solids from the analysis of energy-scaled bond-valence mismatch landscapes.

    PubMed

    Adams, Stefan; Rao, R Prasada

    2009-05-01

    Structure-property relationships provide valuable guidelines for a systematic development of functional materials. Here an augmented bond-valence approach is worked out that is linked directly to the energy scale. This energy-scaled bond-valence approach is then used to identify ion-conduction pathways and to establish structure-property relationships in complex disordered solids using lithium silicate glasses as model systems. Representative local structure models of glassy solid electrolytes as a basis for the pathway analysis are derived from molecular dynamics simulations. Predictions of the bond-valence model from a static structure model are compared to a complete trajectory analysis, showing a high degree of agreement. The method yields consistent results when changing the simulation force field and is applicable to a wide range of glasses. PMID:19370216

  1. Dissociative Reactions to Incest.

    ERIC Educational Resources Information Center

    Hall, J. Mark

    In contrast to Freud's later and revised view of the etiology of hysterical, or dissociative, symptoms, it is now known that real, and not fantasized, sexual experiences in childhood are experienced in disociative symptomatology. It is useful to understand that incest involves both traumatic events, that is, incidents of sexual violation per se,…

  2. Dissociation by acceleration

    E-print Network

    Kasper Peeters; Marija Zamaklar

    2007-11-21

    We show that mesons, described using rotating relativistic strings in a holographic setup, undergo dissociation when their acceleration 'a' exceeds a value which scales with the angular momentum 'J' as a_max ~ \\sqrt{T_s/J}, where 'T_s' is the string tension.

  3. Dissociative Identity Disorder

    ERIC Educational Resources Information Center

    Schmidt, Tom

    2007-01-01

    Few psychological disorders in the Diagnostic Statistical Manual have generated as much controversy as Dissociative Identity Disorder (DID). For the past 35 years diagnoses of DID, previously referred to as Multiple Personality Disorder (MPD), have increased exponentially, causing various psychological researchers and clinicians to question the…

  4. Introduction to dissociative recombination

    NASA Technical Reports Server (NTRS)

    Guberman, Steven L.; Mitchell, J. Brian A.

    1989-01-01

    Dissociative recombination (DR) of molecular ions with electrons has important consequences in many areas of physical science. Ab-initio calculations coupled with resonant scattering theory and multichannel quantum defect studies have produced detailed results illuminating the role of ion vibrational excitation, the quantum yields of the DR products, and the role of Rydberg states. The theoretical and experimental results are discussed.

  5. A Comparative Ab Initio Study of the Primary Hydration and Proton Dissociation of Various Imide and Sulfonic Acid Ionomers

    SciTech Connect

    Clark II, Jeffrey K.; Paddison, Stephen J.; Eikerling, Michael; Dupuis, Michel; Zawodzinski, Jr., Thomas A.

    2012-03-29

    We compare the role of neighboring group substitutions on proton dissociation of hydrated acidic moieties suitable for proton exchange membranes through electronic structure calculations. Three pairs of ionomers containing similar electron withdrawing groups within the pair were chosen for the study: two fully fluorinated sulfonyl imides (CF3SO2NHSO2CF3 and CF3CF2SO2NHSO2CF3), two partially fluorinated sulfonyl imides (CH3SO2NHSO2CF3 and C6H5SO2NHSO2CF2CF3), and two aromatic sulfonic acid based material s (CH3C6H4SO3H and CH3 OC6 - H3OCH3C6H4SO3H). Fully optimized counterpoise (CP) corrected geometries were obtained for each ionomer fragment with the inclusion of water molecules at the B3LYP/6-311G** level of density functional theory. Spontaneous proton dissociation was observed upon addition of three water molecules in each system, and the transition to a solvent-separated ion pair occurred when four water molecules were introduced. No considerable quantitative or qualitative differences in proton dissociation, hydrogen bond networks formed, or water binding energies were found between systems containing similar electron withdrawing groups. Each of the sulfonyl imide ionomers exhibited qualitatively similar results regarding proton dissociation and separation. The fully fluorinated sulfonyl imides, however, showed a greater propensity to exist in dissociated and ion-pair separated states at low degrees of hydration than the partially fluorinated sulfonyl imides. This effect is due to the additional electron withdrawing groups providing charge stabilization as the dissociated proton migrates away from the imide anion.

  6. Bond- and Site-Selective Loss of H{sup -} from Pyrimidine Bases

    SciTech Connect

    Ptasinska, Sylwia; Denifl, Stephan; Grill, Verena; Maerk, Tilmann D.; Illenberger, Eugen; Scheier, Paul

    2005-08-26

    Electron attachment to gas phase thymine and uracil leads to H{sup -} loss within a broad and structured feature in the energy range between about 5 and 12 eV consisting of 4 overlapping resonances. By using thymine and uracil methylated at the N1 and N3 positions, respectively, and taking into account recent results from partly deuterated thymine, we find that by tuning the electron energy, H{sup -} loss turns out to be not only bond selective, i.e., (C-H) versus (N-H) bonds, but also site selective (N1 versus N3 site). Such a bond and site selectivity by energy has not been observed before in dissociative electron attachment. Implications for the mechanism of strand breaks observed in plasmid DNA are considered.

  7. Dissociation of equimolar mixtures of aqueous carboxylic acids in ionic liquids: role of specific interactions.

    PubMed

    Shukla, Shashi Kant; Kumar, Anil

    2015-04-30

    Hammett acidity function observes the effect of protonation/deprotonation on the optical density/absorbance of spectrophotometric indicator. In this work, the Hammett acidity, H0, of equimolar mixtures of aqueous HCOOH, CH3COOH, and CH3CH2COOH was measured in 1-methylimidazolium-, 1-methylpyrrolidinium-, and 1-methylpiperidinium-based protic ionic liquids (PILs) and 1-butyl-3-methylimidazolium-based aprotic ionic liquid (AIL) with formate (HCOO(-)) anion. Higher H0 values were observed for the equimolar mixtures of aqueous carboxylic acids in protic ionic liquids compared with those of the aprotic ionic liquid because of the involvement of the stronger specific interactions between the conjugate acid of ionic liquid and conjugate base of carboxylic acids as suggested by the hard-soft acid base (HSAB) theory. The different H0 values for the equimolar mixtures of aqueous carboxylic acids in protic and aprotic ionic liquids were noted to depend on the activation energy of proton transfer (Ea,H(+)). The higher activation energy of proton transfer was obtained in AIL, indicating lower ability to form specific interactions with solute than that of PILs. Thermodynamic parameters determined by the "indicator overlapping method" further confirmed the involvement of the secondary interactions in the dissociation of carboxylic acids. On the basis of the thermodynamic parameter values, the potential of different ionic liquids in the dissociation of carboxylic acids was observed to depend on the hydrogen bond donor acidity (?) and hydrogen bond acceptor basicity (?), characteristics of specific interactions. PMID:25839210

  8. Dissociative adsorption of CH{sub 3}X (X = Br and Cl) on a silicon(100) surface revisited by density functional theory

    SciTech Connect

    Wang, Chen-Guang; Huang, Kai E-mail: wji@ruc.edu.cn; Ji, Wei E-mail: wji@ruc.edu.cn

    2014-11-07

    During the dissociative adsorption on a solid surface, the substrate usually participates in a passive manner to accommodate fragments produced upon the cleavage of the internal bond(s) of a (transient) molecular adsorbate. This simple picture, however, neglects the flexibility of surface atoms. Here, we report a Density Functional Theory study to revisit our early studies of the dissociative adsorption of CH{sub 3}X (X = Br and Cl) on Si(100). We have identified a new reaction pathway, which involves a flip of a silicon dimer; this new pathway agrees better with experiments. For our main exemplar of CH{sub 3}Br, insights have been gained using a simple model that involves a three-atom reactive center, Br-C-Si. When the silicon dimer flips, the interaction between C and Si in the Br-C-Si center is enhanced, evident in the increased energy-split of the frontier orbitals. We also examine how the dissociation dynamics of CH{sub 3}Br is altered on a heterodimer (Si-Al, Si-P, and Si-Ge) in a Si(100) surface. In each case, we conclude, on the basis of computed reaction pathways, that no heterodimer flipping is involved before the system transverses the transition state to dissociative adsorption.

  9. Nucleosomes accelerate transcription factor dissociation

    E-print Network

    Poirier, Michael

    Nucleosomes accelerate transcription factor dissociation Yi Luo1 , Justin A. North2 , Sean D. Rose2 on the order of seconds. The factors that regulate TF dynamics in vivo and increase dissociation rates by orders of magnitude are not known. We investigated TF binding and dissociation dynamics

  10. Three dimensions of dissociative amnesia.

    PubMed

    Dell, Paul F

    2013-01-01

    Principal axis factor analysis with promax rotation extracted 3 factors from the 42 memory and amnesia items of the Multidimensional Inventory of Dissociation (MID) database (N = 2,569): Discovering Dissociated Actions, Lapses of Recent Memory and Skills, and Gaps in Remote Memory. The 3 factors' shared variance ranged from 36% to 64%. Construed as scales, the 3 factor scales had Cronbach's alpha coefficients of .96, .94, and .93, respectively. The scales correlated strongly with mean Dissociative Experiences Scale scores, mean MID scores, and total scores on the Structured Clinical Interview for DSM-IV Dissociative Disorders-Revised (SCID-D-R). What is interesting is that the 3 amnesia factors exhibited a range of correlations with SCID-D-R Amnesia scores (.52, .63, and .70, respectively), suggesting that the SCID-D-R Amnesia score emphasizes gaps in remote memory over amnesias related to dissociative identity disorder. The 3 amnesia factor scales exhibited a clinically meaningful pattern of significant differences among dissociative identity disorder, dissociative disorder not otherwise specified-1, dissociative amnesia, depersonalization disorder, and nonclinical participants. The 3 amnesia factors may have greater clinical utility for frontline clinicians than (a) amnesia as discussed in the context of the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, nosology of the dissociative disorders or (b) P. Janet's (1893/1977 ) 4-fold classification of dissociative amnesia. The author recommends systematic study of the phenomenological differences within specific dissociative symptoms and their differential relationship to specific dissociative disorders. PMID:23282045

  11. Quantum Monte Carlo activation barrier for hydrogen dissociation on copper to unprecedented accuracy

    E-print Network

    Hoggan, Philip E

    2015-01-01

    Many chemical reactions involve bond-dissociation. This is also true for reactions at solid surfaces, in which the dissociation step is often limiting but facilitated in comparison to gas phase reaction channels. This work considers hydrogen dissociation. Reliable molecular beam results are available for this reaction at some copper surfaces. Heterogeneous catalysis by copper is simulated. It was investigated in our previous work since it is in many ways a prototype metal presenting a close-packed surface here. These hydrogen molecules are adsorbed at Cu(111) and fixed geometries on the dissociation reaction pathway for stretched and distant equilibrium H$_2$ are given by using Density Functional Theory (DFT) calculations in a plane wave basis. The PBE wave-functions at these bond-lengths serve as trial input for Quantum Monte Carlo (QMC) simulations of the ground states to obtain highly accurate correlated results for the associated activation barriers indicating the catalytic effect on this dissociation. Th...

  12. Isotope dependent, temperature regulated, energy repartitioning in a low-barrier, short-strong hydrogen bonded cluster

    E-print Network

    Iyengar, Srinivasan S.

    Isotope dependent, temperature regulated, energy repartitioning in a low-barrier, short/deuterium isotope effects, in a fundamental organic hydrogen bonded system using multiple experimental infrared the isotopically labeled systems arises from an analysis of the simulated cluster spectroscopy and leads

  13. Microsolvation of methylmercury: structures, energies, bonding and NMR constants ((199)Hg, (13)C and (17)O).

    PubMed

    Flórez, Edison; Maldonado, Alejandro F; Aucar, Gustavo A; David, Jorge; Restrepo, Albeiro

    2016-01-21

    Hartree-Fock (HF) and second order perturbation theory (MP2) calculations within the scalar and full relativistic frames were carried out in order to determine the equilibrium geometries and interaction energies between cationic methylmercury (CH3Hg(+)) and up to three water molecules. A total of nine structures were obtained. Bonding properties were analyzed using the Quantum Theory of Atoms In Molecules (QTAIM). The analyses of the topology of electron densities reveal that all structures exhibit a partially covalent HgO interaction between methylmercury and one water molecule. Consideration of additional water molecules suggests that they solvate the (CH3HgOH2)(+) unit. Nuclear magnetic shielding constants ?((199)Hg), ?((13)C) and ?((17)O), as well as indirect spin-spin coupling constants J((199)Hg-(13)C), J((199)Hg-(17)O) and J((13)C-(17)O), were calculated for each one of the geometries. Thermodynamic stability and the values of NMR constants correlate with the ability of the system to directly coordinate oxygen atoms of water molecules to the mercury atom in methylmercury and with the formation of hydrogen bonds among solvating water molecules. Relativistic effects account for 11% on ?((13)C) and 14% on ?((17)O), which is due to the presence of Hg (heavy atom on light atom, HALA effect), while the relativistic effects on ?((199)Hg) are close to 50% (heavy atom on heavy atom itself, HAHA effect). J-coupling constants are highly influenced by relativity when mercury is involved as in J((199)Hg-(13)C) and J((199)Hg-(17)O). On the other hand, our results show that the values of NMR constants for carbon and oxygen, atoms which are connected through mercury (C-HgO), are highly correlated and are greatly influenced by the presence of water molecules. Water molecules introduce additional electronic effects to the relativistic effects due to the mercury atom. PMID:26670708

  14. Effect of ultrasonic energy on nanoscale interfacial structure in copper wire bonding on aluminium pads

    NASA Astrophysics Data System (ADS)

    Xu, H.; Liu, C.; Silberschmidt, V. V.; Chen, Z.; Acoff, V. L.

    2011-04-01

    The effect of ultrasonic vibration on nanoscale interfacial structure of thermosonic copper wire bonding on aluminium pads was investigated. It was found that bonding strength was determined by the extent of fragmentation of a native aluminium oxide overlayer (5-10 nm thick) on aluminium pads, forming paths for formation of intermetallic compound CuAl2 in areas of direct contact of bonded metal surfaces. The degree of fracture of the oxide layer was strongly affected by a level of ultrasonic power.

  15. Ionization and dissociation dynamics of vinyl bromide probed by femtosecond extreme ultraviolet transient absorption spectroscopy

    SciTech Connect

    Lin, Ming-Fu; Neumark, Daniel M.; Department of Chemistry, University of California, Berkeley, California 94720 ; Gessner, Oliver; Leone, Stephen R.; Department of Chemistry, University of California, Berkeley, California 94720; Department of Physics, University of California, Berkeley, California 94720

    2014-02-14

    Strong-field induced ionization and dissociation dynamics of vinyl bromide, CH{sub 2}=CHBr, are probed using femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy. Strong-field ionization is initiated with an intense femtosecond, near infrared (NIR, 775 nm) laser field. Femtosecond XUV pulses covering the photon energy range of 50-72 eV probe the subsequent dynamics by measuring the time-dependent spectroscopic features associated with transitions of the Br (3d) inner-shell electrons to vacancies in molecular and atomic valence orbitals. Spectral signatures are observed for the depletion of neutral C{sub 2}H{sub 3}Br, the formation of C{sub 2}H{sub 3}Br{sup +} ions in their ground (X{sup ~}) and first excited (A{sup ~}) states, the production of C{sub 2}H{sub 3}Br{sup ++} ions, and the appearance of neutral Br ({sup 2}P{sub 3/2}) atoms by dissociative ionization. The formation of free Br ({sup 2}P{sub 3/2}) atoms occurs on a timescale of 330 ± 150 fs. The ionic A{sup ~} state exhibits a time-dependent XUV absorption energy shift of ?0.4 eV within the time window of the atomic Br formation. The yield of Br atoms correlates with the yield of parent ions in the A{sup ~} state as a function of NIR peak intensity. The observations suggest that a fraction of vibrationally excited C{sub 2}H{sub 3}Br{sup +} (A{sup ~}) ions undergoes intramolecular vibrational energy redistribution followed by the C–Br bond dissociation. The C{sub 2}H{sub 3}Br{sup +} (X{sup ~}) products and the majority of the C{sub 2}H{sub 3}Br{sup ++} ions are relatively stable due to a deeper potential well and a high dissociation barrier, respectively. The results offer powerful new insights about orbital-specific electronic processes in high field ionization, coupled vibrational relaxation and dissociation dynamics, and the correlation of valence hole-state location and dissociation in polyatomic molecules, all probed simultaneously by ultrafast table-top XUV spectroscopy.

  16. Reactive molecular dynamic simulations of hydrocarbon dissociations on Ni(111) surfaces

    NASA Astrophysics Data System (ADS)

    Liu, Bin; Lusk, Mark T.; Ely, James F.

    2012-03-01

    Empirical potential parameters for H, C and Ni elements have been developed for the ReaxFF force field in order to study the decomposition of small hydrocarbon molecules on nickel using molecular dynamics simulations. These parameters were optimized using the geometrical and energetic information obtained from density functional (DFT) calculations on a subset of hydrogen and methane reactions with nickel (111) surfaces. The resulting force field was then used to obtain a molecular perspective of the dynamics of the methane dissociative adsorption on Ni(111) as well as two other small alkane molecules, ethane and n-butane. NVT simulations of dissociative adsorption of methane over a range of temperatures enabled the estimation of the sticking coefficient for the adsorption as well as the activation energy of the first C-H bond breaking. The rate constants of each elementary step (both forward and reverse) of CHx dissociation on Ni(111) were obtained by monitoring the surface species and a microkinetic model was constructed as a result. Qualitative analyses of the simulations of ethane and n-butane decompositions on Ni(111) demonstrate that such reactive MD technique can also be used to obtain useful information on complex reaction networks.

  17. Dissociation Channels of the 1-Propenyl Radical and Its Photolytic Precursor cis-1-Bromopropene

    E-print Network

    Butler, Laurie J.

    Dissociation Channels of the 1-Propenyl Radical and Its Photolytic Precursor cis-1-Bromopropene photodissociation dynamics of cis-1-bromopropene upon excitation at 193 nm and the unimolecular dissociation. The lowest-energy dissociation barrier of the 1-propenyl radical is experimentally determined for the first

  18. Orientational anisotropy in oxygen dissociation on Rh,,110... Saw Wai Hla

    E-print Network

    Hla, Saw-Wai

    Orientational anisotropy in oxygen dissociation on Rh,,110... Saw Wai Hla ICTP, Strada Costiera 11 Scanning tunneling microscopy study of O2 dissociation on Rh 110 at 170 K shows a low-energy disso- ciation-9 Dissociative adsorption of O2 on Rh 110 occurs at tem- peratures above 100 K and leads to a variety of ordered

  19. Coordination-resolved local bond contraction and electron binding-energy entrapment of Si atomic clusters and solid skins

    SciTech Connect

    Bo, Maolin; Huang, Yongli; Zhang, Ting; Wang, Yan E-mail: ecqsun@ntu.edu.sg; Zhang, Xi; Li, Can; Sun, Chang Q. E-mail: ecqsun@ntu.edu.sg

    2014-04-14

    Consistency between x-ray photoelectron spectroscopy measurements and density-function theory calculations confirms our bond order-length-strength notation-incorporated tight-binding theory predictions on the quantum entrapment of Si solid skin and atomic clusters. It has been revealed that bond-order deficiency shortens and strengthens the Si-Si bond, which results in the local densification and quantum entrapment of the core and valence electrons. Unifying Si clusters and Si(001) and (111) skins, this mechanism has led to quantification of the 2p binding energy of 96.089?eV for an isolated Si atom, and their bulk shifts of 2.461?eV. Findings evidence the significance of atomic undercoordination that is of great importance to device performance.

  20. Estimation of individual binding energies in some dimers involving multiple hydrogen bonds using topological properties of electron charge density

    NASA Astrophysics Data System (ADS)

    Ebrahimi, A.; Habibi Khorassani, S. M.; Delarami, H.

    2009-11-01

    Individual hydrogen bond (HB) energies have been estimated in several systems involving multiple HBs such as adenine-thymine and guanine-cytosine using electron charge densities calculated at X⋯H hydrogen bond critical points (HBCPs) by atoms in molecules (AIM) method at B3LYP/6-311++G ?? and MP2/6-311++G ?? levels. A symmetrical system with two identical H bonds has been selected to search for simple relations between ?HBCP and individual EHB. Correlation coefficient between EHB and ?HBCP in the base of linear, quadratic, and exponential equations are acceptable and equal to 0.95. The estimated individual binding energies EHB are in good agreement with the results of atom-replacement approach and natural bond orbital analysis (NBO). The EHB values estimated from ? values at H⋯X BCP are in satisfactory agreement with the main geometrical parameter H⋯X. With respect to the obtained individual binding energies, the strength of a HB depends on the substituent and the cooperative effects of other HBs.

  1. Electron-impact-induced dissociation of small argon clusters

    NASA Astrophysics Data System (ADS)

    Pflüger, Thomas; Ren, Xueguang; Dorn, Alexander

    2015-05-01

    We study electron-impact-induced dissociation of small van der Waals-bound argon complexes at a projectile energy of 120 eV. Kinetic-energy-release (KER) spectra of the Ar2 and Ar3 parent species for the final charge states 2 Ar+, Ar++Ar2+, and Ar2+ Ar+ and electron energies have been measured together with angular distributions of fragment ions. They are used to identify dissociation mechanisms such as interatomic Coulombic decay (ICD).

  2. Oxidative addition of the C-I bond on aluminum nanoclusters

    NASA Astrophysics Data System (ADS)

    Sengupta, Turbasu; Das, Susanta; Pal, Sourav

    2015-07-01

    Energetics and the in-depth reaction mechanism of the oxidative addition step of the cross-coupling reaction are studied in the framework of density functional theory (DFT) on aluminum nanoclusters. Aluminum metal in its bulk state is totally inactive towards carbon-halogen bond dissociation but selected Al nanoclusters (size ranging from 3 to 20 atoms) have shown a significantly lower activation barrier towards the oxidative addition reaction. The calculated energy barriers are lower than the gold clusters and within a comparable range with the conventional and most versatile Pd catalyst. Further investigations reveal that the activation energies and other reaction parameters are highly sensitive to the geometrical shapes and electronic structures of the clusters rather than their size, imposing the fact that comprehensive studies on aluminum clusters can be beneficial for nanoscience and nanotechnology. To understand the possible reaction mechanism in detail, the reaction pathway is investigated with the ab initio Born Oppenheimer Molecular Dynamics (BOMD) simulation and the Natural Bond Orbital (NBO) analysis. In short, our theoretical study highlights the thermodynamic and kinetic details of C-I bond dissociation on aluminum clusters for future endeavors in cluster chemistry.Energetics and the in-depth reaction mechanism of the oxidative addition step of the cross-coupling reaction are studied in the framework of density functional theory (DFT) on aluminum nanoclusters. Aluminum metal in its bulk state is totally inactive towards carbon-halogen bond dissociation but selected Al nanoclusters (size ranging from 3 to 20 atoms) have shown a significantly lower activation barrier towards the oxidative addition reaction. The calculated energy barriers are lower than the gold clusters and within a comparable range with the conventional and most versatile Pd catalyst. Further investigations reveal that the activation energies and other reaction parameters are highly sensitive to the geometrical shapes and electronic structures of the clusters rather than their size, imposing the fact that comprehensive studies on aluminum clusters can be beneficial for nanoscience and nanotechnology. To understand the possible reaction mechanism in detail, the reaction pathway is investigated with the ab initio Born Oppenheimer Molecular Dynamics (BOMD) simulation and the Natural Bond Orbital (NBO) analysis. In short, our theoretical study highlights the thermodynamic and kinetic details of C-I bond dissociation on aluminum clusters for future endeavors in cluster chemistry. Electronic supplementary information (ESI) available: Cartesian coordinates for the optimized structures and harmonic frequencies, sample IRC data and plot, grid data for three dimensional potential energy surface and contour plot and data for BOMD simulation. See DOI: 10.1039/c5nr02278a

  3. Photodissociation of aniline N-H bonds in clusters of different nature.

    PubMed

    Poterya, Viktoriya; Nachtigallová, Dana; Lengyel, Jozef; Fárník, Michal

    2015-10-14

    We investigated the solvent effects on the N-H bond photodisociation dynamics of aniline (PhNH2) in clusters using velocity map imaging (VMI). The VMI experiment was accompanied by a time-of-flight mass spectrometry after electron ionization to reveal the cluster nature. The H-fragment images were recorded at 243 nm in various expansion regimes corresponding to different species: isolated molecules; small (PhNH2)N, N ? 3, clusters; larger (PhNH2)N, N ? 10; small mixed PhNH2·(H2O)N, N ? 10, clusters; and individual PhNH2 molecules deposited on large (H2O)N, N? = 430. The H-fragment kinetic energy distributions exhibit fast fragments around 0.8 eV (A) assigned previously to a direct dissociation along a repulsive ??* state potential, and slow statistical fragments peaking near 0.2 eV (B). In the aniline clusters the contribution of fast fragments (A) decreases relatively to (B) with increasing cluster size. A similar effect is observed when aniline is solvated with water molecules. The experimental data are interpreted with ab initio calculations. Cluster structures were calculated with both N-H bonds of an aniline molecule participating in hydrogen bonding, as well as the ones with free N-H bonds. The latter ones yield preferentially the fast fragments as the isolated molecule. For N-H engaged in hydrogen bonding a barrier increased along the N-H coordinate on the dissociative ??* state potential surface, and also the energy of ??*/S0 conical intersection increased. Thus the fast dissociation channel was closed stabilizing the molecule in clusters. The population could be funnelled through other conical intersections into the hot ground state which decayed statistically, yielding the slow H-fragments. PMID:26346396

  4. Accounting for the differences in the structures and relative energies of the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I4 2+, the Se-I pi-bonded Se2I4 2+, and their higher-energy isomers by AIM, MO, NBO, and VB methodologies.

    PubMed

    Brownridge, Scott; Crawford, Margaret-Jane; Du, Hongbin; Harcourt, Richard D; Knapp, Carsten; Laitinen, Risto S; Passmore, Jack; Rautiainen, J Mikko; Suontamo, Reijo J; Valkonen, Jussi

    2007-02-01

    The bonding in the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I42+ (three sigma + two pi bonds), the Se-I pi-bonded Se2I42+ (four sigma + one pi bonds), and their higher-energy isomers have been studied using modern DFT and ab initio calculations and theoretical analysis methods: atoms in molecules (AIM), molecular orbital (MO), natural bond orbital (NBO), and valence bond (VB) analyses, giving their relative energies, theoretical bond orders, and atomic charges. The aim of this work was to seek theory-based answers to four main questions: (1) Are the previously proposed simple pi*-pi* bonding models valid for S2I42+ and Se2I42+? (2) What accounts for the difference in the structures of S2I42+ and Se2I42+? (3) Why are the classically bonded isolobal P2I4 and As2I4 structures not adopted? (4) Is the high experimentally observed S-S bond order supported by theoretical bond orders, and how does it relate to high bond orders between other heavier main group elements? The AIM analysis confirmed the high bond orders and established that the weak bonds observed in S2I42+ and Se2I42+ are real and the bonding in these cations is covalent in nature. The full MO analysis confirmed that S2I42+ contains three sigma and two pi bonds, that the positive charge is essentially equally distributed over all atoms, that the bonding between S2 and two I2+ units in S2I42+ is best described by two mutually perpendicular 4c2e pi*-pi* bonds, and that in Se2I42+, two SeI2+ moieties are joined by a 6c2e pi*-pi* bond, both in agreement with previously suggested models. The VB treatment provided a complementary approach to MO analysis and provided insight how the formation of the weak bonds affects the other bonds. The NBO analysis and the calculated AIM charges showed that the minimization of the electrostatic repulsion between EI2+ units (E = S, Se) and the delocalization of the positive charge are the main factors that explain why the nonclassical structures are favored for S2I42+ and Se2I42+. The difference in the structures of S2I42+ and Se2I42+ is related to the high strength of the S-S pi bond compared to the weak S-I sigma bond and the additional stabilization from increased delocalization of positive charge in the structure of S2I42+ compared to the structure of Se2I42+. The investigation of the E2X42+ series (E = S, Se, Te; X = Cl, Br, I) revealed that only S2I42+ adopts the highly np pi-np pi (n > or = 3)-bonded structure, while all other dications favor the pi-bonded Se2I42+ structure. Theoretical bond order calculations for S2I42+ confirm the previously presented experimentally based bond orders for S-S (2.1-2.3) and I-I (1.3-1.5) bonds. The S-S bond is determined to have the highest reported S-S bond order in an isolated compound and has a bond order that is either similar to or slightly less than the Si-Si bond order in the proposed triply bonded [(Me3Si)2CH]2(iPr)SiSi triple bond SiSi(iPr)[CH(SiMe3)2]2 depending on the definition of bond orders used. PMID:17257010

  5. Dissociation of strong acid revisited: X-ray photoelectron spectroscopy and molecular dynamics simulations of HNO3 in water

    SciTech Connect

    Lewis, Tanza; Winter, Berndt; Stern, Abraham C.; Baer, Marcel D.; Mundy, Christopher J.; Tobias, Douglas J.; Hemminger, J. C.

    2011-08-04

    Molecular-level insight into the dissociation of nitric acid in water is obtained from photoelectron X-ray spectroscopy and first-principles molecular dynamics (MD) simulations. Our combined studies reveal surprisingly abrupt changes in solvation configurations of undissociated nitric acid at approximately 4 M concentration. Experimentally, this is inferred from N1s binding energy shifts of HNO3(aq) as a function of concentration, and is associated with variations in the local electronic structure of the nitrogen atom. It also shows up as a discontinuity in the degree of dissociation as a function of concentration, determined here from the N1s photoelectron signal intensity, which can be separately quantified for undissociated HNO3(aq) and dissociated NO3-(aq). Intermolecular interactions within the nitric acid solution are discussed on the basis of MD simulations, which reveal that molecular HNO3 interacts remarkably weakly with solvating water molecules at low concentration; around 4 M there is a turnover to a more structured solvation shell, accompanied by an increase in hydrogen bonding between HNO3 and water. We suggest that the driving force behind the more structured solvent configuration of HNO3 is the overlap of nitric acid solvent shells that sets in around 4 M concentration. This work was supported by the US Department of Energy Basic Energy Sciences' Chemical Sciences, Geosciences & Biosciences Division. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

  6. A first principle study for the adsorption and absorption of carbon atom and the CO dissociation on Ir(100) surface

    SciTech Connect

    Erikat, I. A.; Hamad, B. A.

    2013-11-07

    We employ density functional theory to examine the adsorption and absorption of carbon atom as well as the dissociation of carbon monoxide on Ir(100) surface. We find that carbon atoms bind strongly with Ir(100) surface and prefer the high coordination hollow site for all coverages. In the case of 0.75?ML coverage of carbon, we obtain a bridging metal structure due to the balance between Ir–C and Ir–Ir interactions. In the subsurface region, the carbon atom prefers the octahedral site of Ir(100) surface. We find large diffusion barrier for carbon atom into Ir(100) surface (2.70 eV) due to the strong bonding between carbon atom and Ir(100) surface, whereas we find a very small segregation barrier (0.22 eV) from subsurface to the surface. The minimum energy path and energy barrier for the dissociation of CO on Ir(100) surface are obtained by using climbing image nudge elastic band. The energy barrier of CO dissociation on Ir(100) surface is found to be 3.01 eV, which is appreciably larger than the association energy (1.61 eV) of this molecule.

  7. Rapid bond rearrangement in molecules after core-electron excitation

    NASA Astrophysics Data System (ADS)

    Sorensen, S. L.; Gisselbrecht, M.; Laksman, J.; Månsson, E. P.; Céolin, D.; Sankari, A.; Afaneh, F.

    2014-04-01

    Experimental studies of core-excited molecules using three-dimensional multi particle momentum imaging are presented where bond rearrangement processes in dication species are analysed. The aim of the study is to understand the relation between the geometric changes associated with core-excited states and the kinetic energy released in particular molecular dissociation processes. The kinematics of individual fragmentation channels are studied by fully three-dimensional momentum imaging of fragments in coincidence. Examples are presented where the high efficiency of the instrument and the fully three-dimensional momentum capabilities are exploited to understand nuclear motion leading to bond rearrangement in core-excited states. We identify bond-rearrangement processes in water, carbonyl sulphide and acetylene which are initiated in the core-excited state. In water this is evidenced by the H+2/O+ ion pair, and in carbonyl sulphide the OS++C+ pair is the fingerprint of this reaction. In acetylene the H+2 + C+2 ion pair indicates a molecular geometry that changes from linear to strongly bent. We measure the angular distribution of all fragments and fragment pairs and for the bond rearrangement processes in water and in core-excited acetylene the angular distribution of fragments suggests that the bond rearrangement is very rapid.

  8. Lipidomics profiling by high-resolution LC-MS and high-energy collisional dissociation fragmentation: focus on characterization of mitochondrial cardiolipins and monolysocardiolipins.

    PubMed

    Bird, Susan S; Marur, Vasant R; Sniatynski, Matthew J; Greenberg, Heather K; Kristal, Bruce S

    2011-02-01

    A liquid chromatography-mass spectrometry (LC-MS) method was used for separation of lipid classes as well as both qualitative and semiquantitative detection of individual lipids in biological samples. Data were acquired using high-resolution full-scan MS and high-energy collisional dissociation (HCD) all ion fragmentation. The method was evaluated for efficient separation and detection in both positive and negative ionization mode using standards spanning six lipid classes. Platform linearity and robustness, related to the mitochondrial lipid cardiolipin (CL), were assessed using extracted ion chromatograms with mass tolerance windows of 5 ppm or less from full scan exact mass measurements. The platform CL limit of detection was determined to be 5 pmol (0.9 ?M) on the column, with mass accuracy <1.5 ppm, retention time coefficients of variation (CV) < 0.5%, and area CV < 13%. This mass accuracy was critical to the identification of unknown CL species in mitochondria samples, through the elimination of false positives. In addition to detection and relative quantitation of CL species in mitochondria, CL structures were characterized through the use of alternating HCD scans at different energies to produce diagnostic fragmentations on all ions in the analysis. The developed lipid profiling method was applied to mitochondrial samples from an animal study related to the linkages between diet, mitochondrial function, and disease. The analysis identified 28 unique CL species and two monolysocardiolipin species that are often associated with mitochondrial stress and dysfunction. PMID:21192696

  9. Bond Energies and Thermochemical Properties of Ring-Opened Diradicals and Carbenes of exo-Tricyclo[5.2.1.0(2,6)]decane.

    PubMed

    Hudzik, Jason M; Castillo, Álvaro; Bozzelli, Joseph W

    2015-09-24

    Exo-tricyclo[5.2.1.0(2,6)]decane (TCD) or exo-tetrahydrodicyclopentadiene is an interesting strained ring compound and the single-component high-energy density hydrocarbon fuel known as JP-10. Important initial reactions of TCD at high temperatures could cleave a strained carbon-carbon (C-C) bond in the ring system creating diradicals also constrained by the remaining ring system. This study determines the thermochemical properties of these diradicals (TCD-H2 mJ-nJ where m and n correspond to the cleaved carbons sites) including the carbon-carbon bond dissociation energy (C-C BDE) corresponding to the cleaved TCD site. Thermochemical properties including enthalpies (?H°f298), entropies (S(T)), heat capacities (Cp(T)), and C-H and C-C BDEs for the parent (TCD-H2 m-n), radical (TCD-H2 mJ-n and m-nJ), diradical (TCD-H2 mJ-nJ), and carbene (TCD-H2 mJJ-n and m-nJJ) species are determined. Structures, vibrational frequencies, moments of inertia, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) level of theory. Standard enthalpies of formation in the gas phase for the TCD-H2 m-n parent and radical species are determined using the B3LYP density functional theory and the higher level G3MP2B3 and CBS-QB3 composite methods. For singlet and triplet TCD diradicals and carbenes, M06-2X, ?B97X-D, and CCSD(T) methods are included in the analysis to determine ?H°f298 values. The C-C BDEs are further calculated using CASMP2(2,2)/aug-cc-pvtz//CASSCF(2,2)/cc-pvtz and with the CASMP2 energies extrapolated to the complete basis set limit. The bond energies calculated with these methods are shown to be comparable to the other calculation methods. Isodesmic work reactions are used for enthalpy analysis of these compounds for effective cancelation of systematic errors arising from ring strain. C-C BDEs range from 77.4 to 84.6 kcal mol(-1) for TCD diradical singlet species. C-H BDEs for the parent TCD-H2 m-n carbon sites range from 93 to 101 kcal mol(-1) with a similar range seen for loss of the second hydrogen to generate the diradical singlet species. A wider range for C-C BDEs is seen for the carbenes from about 77 to 100 kcal mol(-1) as compared to the diradicals. Results from the DFT methods for the parents, radicals, diradicals, and carbenes are in good agreement with results from the composite methods using our sets of work reactions. PMID:26295335

  10. Structure and bonding of isoleptic coinage metal (Cu, Ag, Au) dimethylaminonitrenes in the gas phase.

    PubMed

    Fedorov, Alexey; Couzijn, Erik P A; Nagornova, Natalia S; Boyarkin, Oleg V; Rizzo, Thomas R; Chen, Peter

    2010-10-01

    Dimethylaminonitrene complexes of IMesM(+) (IMes =1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; M = Cu, Ag, Au) were prepared in the gas phase and structurally characterized by high-resolution infrared spectroscopy of the cold species, ion-molecule reactions, and DFT computations. We measured the binding energies of the nitrene fragment to the IMesM(+) moiety by energy-resolved collision-induced dissociation experiments in the gas phase, affording a trend in bond strength of M = Cu ? Au > Ag. This trend is explained in terms of a detailed metal-nitrogen bonding analysis, from which relativistic effects on the bonding were assessed. Various density functionals were evaluated for reproducing the observed thermochemical data and Truhlar's M06 functional was found to give the best agreement. PMID:20843043

  11. High-energy, stable and recycled molecular solar thermal storage materials using AZO/graphene hybrids by optimizing hydrogen bonds

    NASA Astrophysics Data System (ADS)

    Luo, Wen; Feng, Yiyu; Qin, Chengqun; Li, Man; Li, Shipei; Cao, Chen; Long, Peng; Liu, Enzuo; Hu, Wenping; Yoshino, Katsumi; Feng, Wei

    2015-10-01

    An important method for establishing a high-energy, stable and recycled molecular solar heat system is by designing and preparing novel photo-isomerizable molecules with a high enthalpy and a long thermal life by controlling molecular interactions. A meta- and ortho-bis-substituted azobenzene chromophore (AZO) is covalently grafted onto reduced graphene oxide (RGO) for solar thermal storage materials. High grafting degree and close-packed molecules enable intermolecular hydrogen bonds (H-bonds) for both trans-(E) and cis-(Z) isomers of AZO on the surface of nanosheets, resulting in a dramatic increase in enthalpy and lifetime. The metastable Z-form of AZO on RGO is thermally stabilized with a half-life of 52 days by steric hindrance and intermolecular H-bonds calculated using density functional theory (DFT). The AZO-RGO fuel shows a high storage capacity of 138 Wh kg-1 by optimizing intermolecular H-bonds with a good cycling stability for 50 cycles induced by visible light at 520 nm. Our work opens up a new method for making advanced molecular solar thermal storage materials by tuning molecular interactions on a nano-template.An important method for establishing a high-energy, stable and recycled molecular solar heat system is by designing and preparing novel photo-isomerizable molecules with a high enthalpy and a long thermal life by controlling molecular interactions. A meta- and ortho-bis-substituted azobenzene chromophore (AZO) is covalently grafted onto reduced graphene oxide (RGO) for solar thermal storage materials. High grafting degree and close-packed molecules enable intermolecular hydrogen bonds (H-bonds) for both trans-(E) and cis-(Z) isomers of AZO on the surface of nanosheets, resulting in a dramatic increase in enthalpy and lifetime. The metastable Z-form of AZO on RGO is thermally stabilized with a half-life of 52 days by steric hindrance and intermolecular H-bonds calculated using density functional theory (DFT). The AZO-RGO fuel shows a high storage capacity of 138 Wh kg-1 by optimizing intermolecular H-bonds with a good cycling stability for 50 cycles induced by visible light at 520 nm. Our work opens up a new method for making advanced molecular solar thermal storage materials by tuning molecular interactions on a nano-template. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03558a

  12. Chemical Bonds I

    ERIC Educational Resources Information Center

    Sanderson, R. T.

    1972-01-01

    Chemical bonding is discussed from a bond energy, rather than a wave mechanics, viewpoint. This approach is considered to be more suitable for the average student. (The second part of the article will appear in a later issue of the journal.) (AL)

  13. Low energy (0-4 eV) electron impact to N{sub 2}O clusters: Dissociative electron attachment, ion-molecule reactions, and vibrational Feshbach resonances

    SciTech Connect

    Vizcaino, Violaine; Denifl, Stephan; Maerk, Tilmann D.; Scheier, Paul; Illenberger, Eugen

    2010-10-21

    Electron attachment to clusters of N{sub 2}O in the energy range of 0-4 eV yields the ionic complexes [(N{sub 2}O){sub n}O]{sup -}, [(N{sub 2}O){sub n}NO]{sup -}, and (N{sub 2}O){sub n}{sup -} . The shape of the ion yields of the three homologous series differs substantially reflecting the different formation mechanisms. While the generation of [(N{sub 2}O){sub n}O]{sup -} can be assigned to dissociative electron attachment (DEA) of an individual N{sub 2}O molecule in the target cluster, the formation of [(N{sub 2}O){sub n}NO]{sup -} is interpreted via a sequence of ion molecule reactions involving the formation of O{sup -} via DEA in the first step. The nondecomposed complexes (N{sub 2}O){sub n}{sup -} are preferentially formed at very low energies (below 0.5 eV) as a result of intramolecular stabilization of a diffuse molecular anion at low energy. The ion yields of [(N{sub 2}O){sub n}O]{sup -} and (N{sub 2}O){sub n}{sup -} versus electron energy show sharp peaks at the threshold region, which can be assigned to vibrational Feshbach resonances mediated by the diffuse anion state as already observed in an ultrahigh resolution electron attachment study of N{sub 2}O clusters [E. Leber, S. Barsotti, J. Boemmels, J. M. Weber, I. I. Fabrikant, M.-W. Ruf, and H. Hotop, Chem. Phys. Lett. 325, 345 (2000)].

  14. Modeling the dissociation and ionization of a sputtered organic molecule

    NASA Astrophysics Data System (ADS)

    Solomko, V.; Verstraete, M.; Delcorte, A.; Garrison, B. J.; Gonze, X.; Bertrand, P.

    2006-07-01

    The evolution of an organic molecule after sputtering from a gold surface has been analyzed by classical molecular dynamics and ab initio calculations to gain insight into the ionization and fragmentation processes occurring in SIMS. The calculated ionization potential (6.2 eV) of the tetraphenylnaphthalene (TPN) molecule has been found to be close to the unimolecular dissociation energy (5.4 eV) of the most favorable reaction channel involving the loss of a phenyl ring. On the other hand, our calculations show that the internal energies of sputtered TPN molecules can be significantly larger than 5-6 eV. Therefore, it appears energetically possible to relax such excited molecules via both fragmentation and ionization. We propose to virtually decompose the TPN molecule into its basic fragments. The rationale is that, if the molecule is very excited, then separate parts (e.g. pendant phenyl rings) can interact with each other almost independently. The analysis of the molecular motion after emission shows that the oscillations along the phenyl-naphthalene bond direction, expected to induce the molecule fragmentation by the loss of a phenyl ring, are relatively small (they store only about 0.2 eV). On the other hand, the relative energy stored in the inter-phenyl interactions, modulated by their bending and responsible for ionization according to our hypothesis, oscillates over a range of 6-7 eV and favors ionization.

  15. Unraveling the interplay between hydrogen bonding and rotational energy barrier to fine-tune the properties of triazine molecular glasses.

    PubMed

    Laventure, Audrey; De Grandpré, Guillaume; Soldera, Armand; Lebel, Olivier; Pellerin, Christian

    2016-01-21

    Mexylaminotriazine derivatives form molecular glasses with outstanding glass-forming ability (GFA), high resistance to crystallization (glass kinetic stability, GS), and a glass transition temperature (Tg) above room temperature that can be conveniently modulated by selection of the headgroup and ancillary groups. A common feature of all these compounds is their secondary amino linkers, suggesting that they play a critical role in their GFA and GS for reasons that remain unclear because they can simultaneously form hydrogen (H) bonds and lead to a high interconversion energy barrier between different rotamers. To investigate independently and better control the influence of H bonding capability and rotational energy barrier on Tg, GFA and GS, a library of twelve analogous molecules was synthesized with different combinations of NH, NMe and O linkers. Differential scanning calorimetry (DSC) revealed that these compounds form, with a single exception, kinetically stable glasses with Tg values spanning a very broad range from -25 to 94 °C. While variable temperature infrared spectroscopy combined to chemometrics reveals that, on average, around 60% of the NH groups are still H-bonded as high as 40 °C above Tg, critical cooling rates obtained by DSC clearly show that molecules without H-bond donating linkers also present an outstanding GFA, meaning that H bonding plays a dominant role in controlling Tg but is not required to prevent crystallization. It is a high interconversion energy barrier, provoking a distribution of rotamers, that most efficiently promotes both GFA and resistance to crystallization. These new insights pave the way to more efficient glass engineering by extending the possible range of accessible Tg, allowing in particular the preparation of homologous glass-formers with high GS at ambient temperature in either the viscous or vitreous state. PMID:26675473

  16. Collision-induced dissociation of protonated guanine

    NASA Astrophysics Data System (ADS)

    Gregson, John M.; McCloskey, James A.

    1997-11-01

    Guanine and its naturally or xenobiotically modified derivatives occur widely in nucleic acids and other natural products, yet the potential applications of tandem mass spectrometry in structural studies is limited by the complexity of dissociation pathways of the guanine nucleus. The low energy-collision induced dissociation (CID) of protonated guanine has been studied using analogs independently labeled with 15N at each of the five nitrogen atoms and by 18O at position 6. Following activation under multi-collision conditions, protonated guanine dissociates along two major pathways starting with expulsion of either NH3 or cyanamide. The reactions are rationalized in terms of initial opening of the pyrimidine ring, which results in loss of identity of ring atom N-1 and exocyclic N2. The equivalence of N-1 and N6 is retained under low energy (single collision) conditions, and upon methyl substitution at either nitrogen atom. Other reactions show the pyrimidine ring rather than the imidazole moiety to be the principal site of reactivity, analogous to the dissociation chemistry of protonated adenine.

  17. Mediatorless solar energy conversion by covalently bonded thylakoid monolayer on the glassy carbon electrode.

    PubMed

    Lee, Jinhwan; Im, Jaekyun; Kim, Sunghyun

    2016-04-01

    Light reactions of photosynthesis that take place in thylakoid membranes found in plants or cyanobacteria are among the most effective ways of utilizing light. Unlike most researches that use photosystem I or photosystem II as conversion units for converting light to electricity, we have developed a simple method in which the thylakoid monolayer was covalently immobilized on the glassy carbon electrode surface. The activity of isolated thylakoid membrane was confirmed by measuring evolving oxygen under illumination. Glassy carbon surfaces were first modified with partial or full monolayers of carboxyphenyl groups by reductive C-C coupling using 4-aminobenzoic acid and aniline and then thylakoid membrane was bioconjugated through the peptide bond between amine residues of thylakoid and carboxyl groups on the surface. Surface properties of modified surfaces were characterized by cyclic voltammetry, contact angle measurements, and electrochemical impedance spectroscopy. Photocurrent of 230nAcm(-2) was observed when the thylakoid monolayer was formed on the mixed monolayer of 4-carboxylpheny and benzene at applied potential of 0.4V vs. Ag/AgCl. A small photocurrent resulted when the 4-carboxyphenyl full monolayer was used. This work shows the possibility of solar energy conversion by directly employing the whole thylakoid membrane through simple surface modification. PMID:26625272

  18. Sticker Bonding.

    ERIC Educational Resources Information Center

    Frazier, Laura Corbin

    2000-01-01

    Introduces a science activity on the bonding of chemical compounds. Assigns students the role of either a cation or anion and asks them to write the ions they may bond with. Assesses students' understanding of charge, bonding, and other concepts. (YDS)

  19. Bond Issues.

    ERIC Educational Resources Information Center

    Pollack, Rachel H.

    2000-01-01

    Notes trends toward increased borrowing by colleges and universities and offers guidelines for institutions that are considering issuing bonds to raise money for capital projects. Discussion covers advantages of using bond financing, how use of bonds impacts on traditional fund raising, other cautions and concerns, and some troubling aspects of…

  20. THE DISSOCIATIVE TURN IN PSYCHOANALYSIS.

    PubMed

    Itzkowitz, Sheldon

    2015-06-01

    In his response to the Roundtable Discussions on what is effective in psychoanalytic psychotherapy, the author focuses on the renewed interest in the concept of dissociation that began to emerge toward the end of the 20th century. A contemporary psychoanalytic position informed by the impact of developmental trauma has led to an understanding of and interest in the dissociative mind. The actuality of trauma during infancy and early childhood is recognized as a key factor leading to the emergence of dissociative processes, the potential dissociative structuring of the mind, and mind being characterized by multiple, discontinuous, centers of consciousness. The therapeutic goal in the psychoanalytic work with fragmented patients is to establish communication and understanding between the dissociated self-states. The author offers two brief clinical examples of working with dissociated self-states. PMID:26177756

  1. Adhesive-Bonded Composite Joint Analysis with Delaminated Surface Ply Using Strain-Energy Release Rate

    NASA Technical Reports Server (NTRS)

    Chadegani, Alireza; Yang, Chihdar; Smeltzer, Stanley S. III

    2012-01-01

    This paper presents an analytical model to determine the strain energy release rate due to an interlaminar crack of the surface ply in adhesively bonded composite joints subjected to axial tension. Single-lap shear-joint standard test specimen geometry with thick bondline is followed for model development. The field equations are formulated by using the first-order shear-deformation theory in laminated plates together with kinematics relations and force equilibrium conditions. The stress distributions for the adherends and adhesive are determined after the appropriate boundary and loading conditions are applied and the equations for the field displacements are solved. The system of second-order differential equations is solved to using the symbolic computation tool Maple 9.52 to provide displacements fields. The equivalent forces at the tip of the prescribed interlaminar crack are obtained based on interlaminar stress distributions. The strain energy release rate of the crack is then determined by using the crack closure method. Finite element analyses using the J integral as well as the crack closure method are performed to verify the developed analytical model. It has been shown that the results using the analytical method correlate well with the results from the finite element analyses. An attempt is made to predict the failure loads of the joints based on limited test data from the literature. The effectiveness of the inclusion of bondline thickness is justified when compared with the results obtained from the previous model in which a thin bondline and uniform adhesive stresses through the bondline thickness are assumed.

  2. The Dissociative Recombination of OH(+)

    NASA Technical Reports Server (NTRS)

    Guberman, Steven L.

    1995-01-01

    Theoretical quantum chemical calculations of the cross sections and rates for the dissociative recombination of the upsilon = 0 level of the ground state of OH(+) show that recombination occurs primarily along the 2 (2)Pi diabatic route. The products are 0((1)D) and a hot H atom with 6.1 eV kinetic energy. The coupling to the resonances is very small and the indirect recombination mechanism plays only a minor role. The recommended value for the rate coefficient is (6.3 +/- 0.7) x 10(exp -9)x (T(e)/1300)(exp -0.48) cu.cm/s for 10 less than T(e) less than 1000 K.

  3. Chemical bonding in view of electron charge density and kinetic energy density descriptors.

    PubMed

    Jacobsen, Heiko

    2009-05-01

    Stalke's dilemma, stating that different chemical interpretations are obtained when one and the same density is interpreted either by means of natural bond orbital (NBO) and subsequent natural resonance theory (NRT) application or by the quantum theory of atoms in molecules (QTAIM), is reinvestigated. It is shown that within the framework of QTAIM, the question as to whether for a given molecule two atoms are bonded or not is only meaningful in the context of a well-defined reference geometry. The localized-orbital-locator (LOL) is applied to map out patterns in covalent bonding interaction, and produces results that are consistent for a variety of reference geometries. Furthermore, LOL interpretations are in accord with NBO/NRT, and assist in an interpretation in terms of covalent bonding. PMID:19090572

  4. Recurrent dissociative fugue.

    PubMed

    Mamarde, Abhishek; Navkhare, Praveen; Singam, Amrita; Kanoje, Akash

    2013-10-01

    Dissociative fugue is a rarely reported diagnostic entity. It is one of the least understood and yet clinically one of the most fascinating disorders in mental health. Here, we describe a case of fugue in a 32-year-old man who was brought to mental hospital with complete loss of memory for events pertaining to identity of self. This case illustrates the nature of presentation in hospital setting like mental hospital and effort taken to reintegrate his identity and reunite with his family. PMID:24379504

  5. Effects of molecular dissociation on the hydrogen equation of state

    NASA Astrophysics Data System (ADS)

    Bonev, Stanimir; Schwegler, Eric; Galli, Giulia; Gygi, Francois

    2002-03-01

    It has been suggested recently(François Gygi and G. Galli, submitted to Phys. Rev. Lett.) that the physical mechanism behind the larger compressibility of liquid deuterium observed in laser shock experiments as compared to ab initio simulations may be related to shock-induced electronic excitations. A possible result of such non-adiabatic processes is hindering of the molecular dissociation. This has motivated us to study the importance of molecular dissociation on the hydrogen equation of state. To this end, we have carried out ab initio molecular dynamics simulations of liquid deuterium where intramolecular dissociation is prevented by the use of bond length contraints. Simulations at both fixed thermodynamic conditions and dynamical simulations of shocked deuterium will be discussed.

  6. DFT study of sulfur derivatives of cumulenes and their protonated forms of interstellar interest and calculations of dissociation energies of protonated forms (SC(CH)C(n-2)S)(+) (n?=?3-8).

    PubMed

    Benmensour, Mohamed Ali; Djennane-Bousmaha, Sema; Boucekkine, Abdou

    2014-07-01

    A theoretical study of the sulfur cumulenes SCnS (n?=?3-8), CnS ( n?=?1-8) and of their protonated forms (SCnS)H(+) and (CnS)H(+) that might exist in the interstellar environment, has been carried out by means of the standard B3LYP/6-311G** method. The geometries and relative energies of singlet and triplet states according to the number of carbons have been computed. Like neutral species, we have found that the ground state of the most stable protonated forms (SC(CH)Cn-2S)(+) and ((HC)Cn-1S)(+), alternates between a triplet state for the even series and a singlet state for the odd series. We provided the data needed to simulate infrared and microwave spectra (vibration frequencies, dipole moments, and rotational constants) for each protonated species (SCnS)H(+) and (CnS)H(+) and for each neutral CnS species. The computing of dissociation energies of the most stable protonated forms (SC(CH)Cn-2S)(+) (n?=?3-8) has shown that the lowest values are obtained for the dissociation of compounds with an even number of carbons, in their triplet state, which produce the observed fragments CS and C3S. The dissociation of even protonated forms requires less energy than for the odd protonated forms. PMID:24935110

  7. Electron Attachment Step in Electron Capture Dissociation (ECD) and Electron Transfer Dissociation (ETD)

    E-print Network

    Simons, Jack

    Electron Attachment Step in Electron Capture Dissociation (ECD) and Electron Transfer Dissociation initio electronic structure calculations to estimate the cross sections with which electrons are attached (in electron capture dissociation (ECD)) or transferred (in electron transfer dissociation (ETD

  8. High-energy, stable and recycled molecular solar thermal storage materials using AZO/graphene hybrids by optimizing hydrogen bonds.

    PubMed

    Luo, Wen; Feng, Yiyu; Qin, Chengqun; Li, Man; Li, Shipei; Cao, Chen; Long, Peng; Liu, Enzuo; Hu, Wenping; Yoshino, Katsumi; Feng, Wei

    2015-10-01

    An important method for establishing a high-energy, stable and recycled molecular solar heat system is by designing and preparing novel photo-isomerizable molecules with a high enthalpy and a long thermal life by controlling molecular interactions. A meta- and ortho-bis-substituted azobenzene chromophore (AZO) is covalently grafted onto reduced graphene oxide (RGO) for solar thermal storage materials. High grafting degree and close-packed molecules enable intermolecular hydrogen bonds (H-bonds) for both trans-(E) and cis-(Z) isomers of AZO on the surface of nanosheets, resulting in a dramatic increase in enthalpy and lifetime. The metastable Z-form of AZO on RGO is thermally stabilized with a half-life of 52 days by steric hindrance and intermolecular H-bonds calculated using density functional theory (DFT). The AZO-RGO fuel shows a high storage capacity of 138 Wh kg(-1) by optimizing intermolecular H-bonds with a good cycling stability for 50 cycles induced by visible light at 520 nm. Our work opens up a new method for making advanced molecular solar thermal storage materials by tuning molecular interactions on a nano-template. PMID:26289389

  9. The influence of large-amplitude librational motion on the hydrogen bond energy for alcohol-water complexes.

    PubMed

    Andersen, J; Heimdal, J; Wugt Larsen, R

    2015-10-01

    The far-infrared absorption spectra have been recorded for hydrogen-bonded complexes of water with methanol and t-butanol embedded in cryogenic neon matrices at 2.8 K. The partial isotopic substitution of individual subunits enabled by a dual inlet deposition procedure provides for the first time unambiguous assignments of the intermolecular high-frequency out-of-plane and low-frequency in-plane donor OH librational modes for mixed alcohol-water complexes. The vibrational assignments confirm directly that water acts as the hydrogen bond donor in the most stable mixed complexes and the tertiary alcohol is a superior hydrogen bond acceptor. The class of large-amplitude donor OH librational motion is shown to account for up to 5.1 kJ mol(-1) of the destabilizing change of vibrational zero-point energy upon intermolecular OHO hydrogen bond formation. The experimental findings are supported by complementary electronic structure calculations at the CCSD(T)-F12/aug-cc-pVTZ level of theory. PMID:26304774

  10. Vibrational dynamics up to the dissociation threshold: A case study of two-dimensional HOCl

    NASA Astrophysics Data System (ADS)

    Joyeux, Marc; Sugny, Dominique; Lombardi, Maurice; Jost, Remy; Schinke, Reinhard; Skokov, Sergei; Bowman, Joël

    2000-12-01

    This work is aimed at extending recent studies dealing with the highly excited vibrational dynamics of HOCl [J. Chem. Phys. 111, 6807 (1999); J. Chem. Phys. 112, 77 (2000)], by taking advantage of the fact that the OH-stretch remains largely decoupled from the two other degrees of freedom up to and above the dissociation threshold. The molecule is thus reduced to a two-dimensional (2D) system by freezing the OH bond length to its equilibrium value. All of the calculated bound states of the 2D system, as well as the first 40 resonances, can be assigned with a Fermi polyad quantum number. The bifurcation diagram of the principal families of periodic orbits (POs) is extended to higher energies compared to 3D studies. In particular, the birth of "inversion" states (states exploring two equivalent wells connected through the linear HOCl configuration) is related to a period-doubling bifurcation of the families of bending POs, while "dissociation" states (states for which the energy flows back and forth along the dissociation pathway) are shown to lie on top of three successive families of POs born at saddle-node bifurcations. Based on the derivation of a classical analogue of the quantum Fermi polyad number, the energies of particular quantum states and classical POs are plotted on the same diagram for the 2D ab initio surface and are shown to agree perfectly. In contrast, comparison of classical Poincaré surfaces of section and quantum Husimi distributions suggests that the classical dynamics of 2D HOCl is much more chaotic than the quantum dynamics. This observation is discussed in terms of the quantum/classical correspondence, and particularly of the vague tori introduced by Reinhardt. It is nevertheless shown that quantum and classical mechanics agree in predicting a slow intramolecular vibrational energy redistribution (IVR) between the OCl stretch and the bend degrees of freedom.

  11. Hyperglycemia associated dissociative fugue (organic dissociative disorder) in an elderly

    PubMed Central

    Ram, Dushad; Ashoka, H. G; Gowdappa, Basavnna

    2015-01-01

    Inadequate glycemic control in patients with diabetes is known to be associated with psychiatric disorders such as depression, anxiety disorder, and cognitive impairment. However, dissociative syndrome has not been reported so far. Here we are reporting a case of repeated dissociative fugue associated with hyperglycemia, in an elderly with type II diabetes. Possible neurobiological mechanism has been discussed. PMID:26286620

  12. Dynamics of the Dissociation of Hydrogen on Stepped Platinum Surfaces Using the ReaxFF Reactive Force Field

    E-print Network

    van Duin, Adri

    Dynamics of the Dissociation of Hydrogen on Stepped Platinum Surfaces Using the ReaxFF Reactive, Pasadena, California 91125 ReceiVed: October 24, 2005; In Final Form: January 7, 2006 The dissociation scaling with incident energy and angular dependence at collision energies where a direct dissociation

  13. Covalent bonds are created by the drive of electron waves to lower their kinetic energy through expansion

    SciTech Connect

    Schmidt, Michael W.; Ruedenberg, Klaus; Ivanic, Joseph

    2014-05-28

    An analysis based on the variation principle shows that in the molecules H{sub 2}{sup +}, H{sub 2}, B{sub 2}, C{sub 2}, N{sub 2}, O{sub 2}, F{sub 2}, covalent bonding is driven by the attenuation of the kinetic energy that results from the delocalization of the electronic wave function. For molecular geometries around the equilibrium distance, two features of the wave function contribute to this delocalization: (i) Superposition of atomic orbitals extends the electronic wave function from one atom to two or more atoms; (ii) intra-atomic contraction of the atomic orbitals further increases the inter-atomic delocalization. The inter-atomic kinetic energy lowering that (perhaps counter-intuitively) is a consequence of the intra-atomic contractions drives these contractions (which per se would increase the energy). Since the contractions necessarily encompass both, the intra-atomic kinetic and potential energy changes (which add to a positive total), the fact that the intra-atomic potential energy change renders the total potential binding energy negative does not alter the fact that it is the kinetic delocalization energy that drives the bond formation.

  14. Covalent bonds are created by the drive of electron waves to lower their kinetic energy through expansion

    SciTech Connect

    Schmidt, Michael W; Ivanic, Joseph; Ruedenberg, Klaus

    2014-05-28

    An analysis based on the variation principle shows that in the molecules H2 +, H2, B2, C2, N2, O2, F2, covalent bonding is driven by the attenuation of the kinetic energy that results from the delocalization of the electronic wave function. For molecular geometries around the equilibrium distance, two features of the wave function contribute to this delocalization: (i) Superposition of atomic orbitals extends the electronic wave function from one atom to two or more atoms; (ii) intra-atomic contraction of the atomic orbitals further increases the inter-atomic delocalization. The inter-atomic kinetic energy lowering that (perhaps counter-intuitively) is a consequence of the intra-atomic contractions drives these contractions (which per se would increase the energy). Since the contractions necessarily encompass both, the intra-atomic kinetic and potential energy changes (which add to a positive total), the fact that the intra-atomic potential energy change renders the total potential binding energy negative does not alter the fact that it is the kinetic delocalization energy that drives the bond formation.

  15. Covalent bonds are created by the drive of electron waves to lower their kinetic energy through expansion

    PubMed Central

    Schmidt, Michael W.; Ivanic, Joseph; Ruedenberg, Klaus

    2014-01-01

    An analysis based on the variation principle shows that in the molecules H2+, H2, B2, C2, N2, O2, F2, covalent bonding is driven by the attenuation of the kinetic energy that results from the delocalization of the electronic wave function. For molecular geometries around the equilibrium distance, two features of the wave function contribute to this delocalization: (i) Superposition of atomic orbitals extends the electronic wave function from one atom to two or more atoms; (ii) intra-atomic contraction of the atomic orbitals further increases the inter-atomic delocalization. The inter-atomic kinetic energy lowering that (perhaps counter-intuitively) is a consequence of the intra-atomic contractions drives these contractions (which per se would increase the energy). Since the contractions necessarily encompass both, the intra-atomic kinetic and potential energy changes (which add to a positive total), the fact that the intra-atomic potential energy change renders the total potential binding energy negative does not alter the fact that it is the kinetic delocalization energy that drives the bond formation. PMID:24880263

  16. Is the decrease of the total electron energy density a covalence indicator in hydrogen and halogen bonds?

    PubMed

    Angelina, Emilio L; Duarte, Darío J R; Peruchena, Nélida M

    2013-05-01

    In this work, halogen bonding (XB) and hydrogen bonding (HB) complexes were studied with the aim of analyzing the variation of the total electronic energy density H(r b ) with the interaction strengthening. The calculations were performed at the MP2/6-311++G(2d,2p) level of approximation. To explain the nature of such interactions, the atoms in molecules theory (AIM) in conjunction with reduced variational space self-consistent field (RVS) energy decomposition analysis were carried out. Based on the local virial theorem, an equation to decompose the total electronic energy density H(r b ) in two energy densities, (-G(r b )) and 1/4?(2)?(r b ), was derived. These energy densities were linked with the RVS interaction energy components. Through the connection between both decomposition schemes, it was possible to conclude that the decrease in H(r b ) with the interaction strengthening observed in the HB as well as the XB complexes, is mainly due to the increase in the attractive electrostatic part of the interaction energy and in lesser extent to the increase in its covalent character, as is commonly considered. PMID:23187685

  17. Bond selective chemistry beyond the adiabatic approximation

    SciTech Connect

    Butler, L.J.

    1993-12-01

    One of the most important challenges in chemistry is to develop predictive ability for the branching between energetically allowed chemical reaction pathways. Such predictive capability, coupled with a fundamental understanding of the important molecular interactions, is essential to the development and utilization of new fuels and the design of efficient combustion processes. Existing transition state and exact quantum theories successfully predict the branching between available product channels for systems in which each reaction coordinate can be adequately described by different paths along a single adiabatic potential energy surface. In particular, unimolecular dissociation following thermal, infrared multiphoton, or overtone excitation in the ground state yields a branching between energetically allowed product channels which can be successfully predicted by the application of statistical theories, i.e. the weakest bond breaks. (The predictions are particularly good for competing reactions in which when there is no saddle point along the reaction coordinates, as in simple bond fission reactions.) The predicted lack of bond selectivity results from the assumption of rapid internal vibrational energy redistribution and the implicit use of a single adiabatic Born-Oppenheimer potential energy surface for the reaction. However, the adiabatic approximation is not valid for the reaction of a wide variety of energetic materials and organic fuels; coupling between the electronic states of the reacting species play a a key role in determining the selectivity of the chemical reactions induced. The work described below investigated the central role played by coupling between electronic states in polyatomic molecules in determining the selective branching between energetically allowed fragmentation pathways in two key systems.

  18. Ionization of dimethyluracil dimers leads to facile proton transfer in the absence of hydrogen bonds.

    PubMed

    Golan, Amir; Bravaya, Ksenia B; Kudirka, Romas; Kostko, Oleg; Leone, Stephen R; Krylov, Anna I; Ahmed, Musahid

    2012-04-01

    Proton transfer is ubiquitous in chemistry and biology, occurring, for example, in proteins, enzyme reactions and across proton channels and pumps. However, it has always been described in the context of hydrogen-bonding networks ('proton wires') acting as proton conduits. Here, we report efficient intramolecular ionization-induced proton transfer across a 1,3-dimethyluracil dimer, a model ?-stacked system with no hydrogen bonds. Upon photoionization by tunable vacuum ultraviolet synchrotron radiation, the dimethyluracil dimer undergoes proton transfer and dissociates to produce a protonated monomer. Deuterated dimethyluracil experiments confirm that proton transfer occurs from the methyl groups and not from the aromatic C-H sites. Calculations reveal qualitative differences between the proton transfer reaction coordinate in the ?-stacked and hydrogen-bonded base pairs, and that proton transfer in methylated dimers involves significant rearrangements of the two fragments, facilitating a relatively low potential energy barrier of only 0.6 eV in the ionized dimer. PMID:22437719

  19. Pathways and kinetics of methane and ethane C-H bond cleavage on PdO(101)

    NASA Astrophysics Data System (ADS)

    Antony, Abbin; Asthagiri, Aravind; Weaver, Jason F.

    2013-09-01

    We used conventional density functional theory (DFT) and dispersion-corrected DFT (DFT-D3) calculations to investigate C-H bond activation pathways for methane and ethane ?-complexes adsorbed on the PdO(101) surface. The DFT-D3 calculations predict lower and more physically realistic values of the apparent C-H bond cleavage barriers, which are defined relative to the gas-phase energy level, while giving nearly the same energy differences between stationary states as predicted by conventional DFT for a given reaction pathway. For the stable CH4 ?2 complex on PdO(101), DFT-D3 predicts that the C-H bond cleavage barriers are 55.2 and 16.1 kJ/mol relative to the initial molecularly adsorbed and gaseous states, respectively. We also predict that dehydrogenation of the resulting CH3 groups and conversion to CH3O species are significantly more energetically demanding than the initial C-H bond activation of CH4 on PdO(101). Using DFT-D3, we find that an ?2 and an ?1 ethane complex can undergo C-H bond cleavage on PdO(101) with intrinsic energy barriers that are similar to that of the methane complex, but with apparent barriers that are close to zero. We also investigated the dissociation kinetics of methane and ethane on PdO(101) using microkinetic models, with parameters derived from the DFT-D3 relaxed structures. We find that a so-called 3N - 2 model, in which two frustrated adsorbate motions are treated as free motions, predicts desorption pre-factors and alkane dissociation probabilities that agree well with estimates obtained from the literature. The microkinetic simulations demonstrate the importance of accurately describing entropic contributions in kinetic simulations of alkane dissociative chemisorption.

  20. Homolytic dissociation of the vulcanization accelerator tetramethylthiuram disulfide (TMTD) and structures and stabilities of the related radicals Me2NCSn* (n = 1-4).

    PubMed

    Steudel, Ralf; Steudel, Yana; Mak, Adrian Matthew; Wong, Ming Wah

    2006-12-01

    The homolytic dissociation of the important vulcanization accelerator tetramethylthiuram disulfide (TMTD) has been studied by ab initio calculations according to the G3X(MP2) and G3X(MP2)-RAD theories. Homolytic cleavage of the SS bond requires a low enthalpy of 150.0 kJ mol-1, whereas 268.0 kJ mol-1 is needed for the dissociation of one of the C-S single bonds. To cleave one of the SS bonds of the corresponding trisulfide (TMTT) requires 191.1 kJ mol-1. Me2NCS2* is a particularly stable sulfur radical as reflected in the low S-H bond dissociation enthalpy of the corresponding acid Me2NC(=S)SH (301.7 kJ mol-1). Me2NCS2* (2B2) is a sigma radical characterized by the unpaired spin density shared equally between the two sulfur atoms and by a 4-center (NCS2) delocalized pi system. The ESR g-tensors of the radicals Me2NCSn* (n = 1-3) have been calculated. Both TMTD and the mentioned radicals form stable chelate complexes with a Li+ cation, which here serves as a model for the zinc ions used in accelerated rubber vulcanization. Although the binding energy of the complex [Li(TMTD)]+ is larger than that of the isomeric species [Li(S2CNMe2)2]+ (12), the dissociation enthalpy of TMTD as a ligand is smaller (125.5 kJ mol-1) than that of free TMTD. In other words, the homolytic dissociation of the SS bonds of TMTD is facilitated by the presence of Li+ ions. The sulfurization of TMTD in the presence of Li+ to give the paramagnetic complex [Li(S3CNMe2)2]+ is strongly exothermic. These results suggest that TMTD reacts with naked zinc ions as well as with the surface atoms of solid zinc oxide particles in an analogous manner producing highly reactive complexes, which probably initiate the crosslinking process during vulcanization reactions of natural or synthetic rubber accelerated by TMTD/ZnO. PMID:17137356

  1. Dissociation, absorption and ionization of some important sulfur oxoanions (S2On2- n = 2, 3, 4, 6, 7 and 8)

    NASA Astrophysics Data System (ADS)

    Abedi, M.; Farrokhpour, H.; Farnia, S.; Chermahini, A. Najafi

    2015-08-01

    In this work, a systematic theoretical study was performed on the dissociation, absorption and ionization of several important sulfur oxoanions (S2On2- (n = 2, 3, 4, 6, 7 and 8)). ?Eelec (thermal corrected energy), ?H° and ?G° of the dissociation reactions of the oxoanions to their radical monoanions were calculated using combined computational levels of theories such as Gaussian-3 (G3) and a new version of complete basis set method (CBS-4M) in different environments including gas phase, microhydrated in gas phase and different solvents. Calculations showed S2O72- is the most stable anion against the dissociation to its radical monoanions (SO4-rad + SO3-rad). It was also found that S2O42- has more tendency to dissociate to its radical anions (SO2-rad + SO2-rad) compared to the other anions. The absorption spectra of the anions were also calculated using the time-dependent density functional theory (TD-DFT) employing M062X functional. The effect of microhydration and electrostatic field of solvent on the different aspects (intensity, energy shift and assignment) of the absorption spectra of these anions were also discussed. It was observed that both hydrogen bonding and electrostatic effect of water increases the intensity of the absorption spectrum compared to the gas phase. Effect of microhydration in shifting the spectra to the shorter wavelength is considerably higher than the effect of electrostatic field of water. Finally, several gas phase ionization energies of the anions were calculated using the symmetry-adapted cluster-configuration interaction methodology (SAC-CI) and found that the first electron detachment energies of S2O22-, S2O32- and S2O42- are negative. Natural bonding orbital (NBO) calculations were also performed to assign the electron detachment bands of the anions.

  2. Collisionless dissociation of SF6 using two resonant frequency CO2 laser fields

    NASA Technical Reports Server (NTRS)

    Gower, M. C.; Gustafson, T. K.

    1977-01-01

    The collisionless dissociation of SF6 has been studied using simultaneous irradiation by two frequencies from a CO2 laser which are both nearly resonant with the SF6nu3 absorption band. It was found that the dissociation was enhanced, and occurred over a wider frequency range, than for single frequency dissociation. No threshold effect was observed for a weak resonant and a much higher energy field pumping slightly off-resonance. For such two frequency irradiation, the peak in the dissociation curve was found to be shifted to lower frequencies with respect to that for single frequency dissociation.

  3. Financing Public Sector Projects with Clean Renewable Energy Bonds; Fact Sheet Series on Financing Renewable Energy Projects, National Renewable Energy Laboratory (NREL)

    SciTech Connect

    Kreycik, C.; Couglin, J.

    2009-12-01

    Clean renewable energy bonds (CREBs) present a low-cost opportunity for public entities to issue bonds to finance renewable energy projects. The federal government lowers the cost of debt by providing a tax credit to the bondholder in lieu of interest payments from the issuer. Because CREBs are theoretically interest free, they may be more attractive than traditional tax-exempt municipal bonds. In February 2009, Congress appropriated a total of $2.4 billion for the "New CREBs" program. No more than one-third of the budget may be allocated to each of the eligible entities: governmental bodies, electric cooperatives, and public power providers. Applications for this round of "New CREBs" were due to the Internal Revenue Service (IRS) on August 4, 2009. There is no indication Congress will extend the CREBs program; thus going forward, only projects that are approved under the 2009 round will be able to issue CREBs. This factsheet explains the CREBs mechanism and provides guidance on procedures related to issuing CREBs.

  4. Effects of oxygen dissociation on hypervelocity combustion experiments

    NASA Technical Reports Server (NTRS)

    Bakos, R. J.; Morgan, R. G.; Tamagno, J.

    1992-01-01

    Results are presented of a comparative experimental study conducted to measure the effects of the test gas oxygen dissociation produced in reflected shock tunnels on hypervelocity combustion. An identical combustor model was tested in a reflected shock tunnel with test gas containing about 50 pct by mass of oxygen in dissociated form, as either nitric oxide or atomic oxygen, and in an expansion tube with test gas having negligible dissociated oxygen. Comparisons are made at two test conditions that are energy equivalent to flight conditions at Mach 13.5 and 17.

  5. General features of the dissociative recombination of polyatomic molecules

    DOE PAGESBeta

    Pratt, S. T.; Jungen, Ch.; Schneider, I. F.; Dulieu, O.; Robert, J.

    2015-01-29

    We discuss some aspects of a simple expression for the low-energy dissociative recombination cross section that applies when the recombination process is dominated by the indirect mechanism. In most previous applications, this expression has been applied to capture into vibrationally excited Rydberg states with the assumption that capture is always followed by prompt dissociation. Here we consider the dissociative recombination of larger polyatomic ions and electrons. More specifically, we consider capture into electronically core-excited Rydberg states, and begin to assess its potential importance for larger systems.

  6. Doorway mechanism for Dissociative Electron attachment

    E-print Network

    Simons, Jack

    Doorway mechanism for Dissociative Electron attachment Thomas Sommerfeld Southeastern Louisiana University Hammond, LA Hammond, LA #12;Doorway mechanism for Dissociative Electron attachment Outline Dissociative Electron attachment Doorway mechanism for electron capture Electroninduced Waterloss from

  7. Dissociative States and Neural Complexity

    ERIC Educational Resources Information Center

    Bob, Petr; Svetlak, Miroslav

    2011-01-01

    Recent findings indicate that neural mechanisms of consciousness are related to integration of distributed neural assemblies. This neural integration is particularly vulnerable to past stressful experiences that can lead to disintegration and dissociation of consciousness. These findings suggest that dissociation could be described as a level of…

  8. Dissociative Excitation of Thymine by Electron Impact

    NASA Astrophysics Data System (ADS)

    McConkey, William; Tiessen, Collin; Hein, Jeffrey; Trocchi, Joshuah; Kedzierski, Wladek

    2014-05-01

    A crossed electron-gas beam system coupled to a VUV spectrometer has been used to investigate the dissociation of thymine (C5H6N2O2) into excited atomic fragments in the electron-impact energy range from threshold to 375 eV. A special stainless steel oven is used to vaporize the thymine and form it into a beam where it is intersected by a magnetically collimated electron beam, typical current 50 ?A. The main features in the spectrum are the H Lyman series lines. The probability of extracting excited C or N atoms from the ring is shown to be very small. In addition to spectral data, excitation probability curves as a function of electron energy will be presented for the main emission features. Possible dissociation channels and excitation mechanisms in the parent molecule will be discussed. The authors thank NSERC (Canada) for financial support.

  9. Autocatalytic dissociation of water at stepped transition metal surfaces

    NASA Astrophysics Data System (ADS)

    Pekoez, Rengin; Woerner, Swenja; Ghiringhelli, Luca M.; Donadio, Davide

    2014-03-01

    By means of density functional theory calculations, we investigate the adsorption and dissociation of water clusters on flat and stepped surfaces of several transition metals: Rh, Ir, Pd, Pt, and Ru. We find that water binds preferentially to the edge of the steps than to terrace sites, so that isolated clusters or one-dimensional water wires can be isolated by differential desorption. The enhanced reactivity of metal atoms at the step edge and the cooperative effect of hydrogen bonding enhance the chances of partial dissociation of water clusters on stepped surfaces. For example, water dissociation on Pt and Ir surface turns from endothermic at terraces to exothermic at steps. The interpretation of water dissociation is achieved by analyzing changes in the electronic structure of both water and metals, especially focusing on the interaction between the lone-pair electrons of water and the d-band of the metals. The shift in the energetics of water dissociation at steps is expected to play a prominent role in catalysis and fuel cells reactions, as the density of steps at surfaces could be an additional parameter to design more efficient anode materials or catalytic substrates.

  10. Tubulin bond energies and microtubule biomechanics determined from nanoindentation in silico

    E-print Network

    Kononova, Olga; Theisen, Kelly E; Marx, Kenneth A; Dima, Ruxandra I; Ataullakhanov, Fazly I; Grishchuk, Ekaterina L; Barsegov, Valeri

    2015-01-01

    Microtubules, the primary components of the chromosome segregation machinery, are stabilized by longitudinal and lateral non-covalent bonds between the tubulin subunits. However, the thermodynamics of these bonds and the microtubule physico-chemical properties are poorly understood. Here, we explore the biomechanics of microtubule polymers using multiscale computational modeling and nanoindentations in silico of a contiguous microtubule fragment. A close match between the simulated and experimental force-deformation spectra enabled us to correlate the microtubule biomechanics with dynamic structural transitions at the nanoscale. Our mechanical testing revealed that the compressed MT behaves as a system of rigid elements interconnected through a network of lateral and longitudinal elastic bonds. The initial regime of continuous elastic deformation of the microtubule is followed by the transition regime, during which the microtubule lattice undergoes discrete structural changes, which include first the reversib...

  11. Experimental determination of the HO-Br bond energy and its relevance to the stratospheric and tropospheric ozone cycles

    SciTech Connect

    Ruscic, B.; Berkowitz, J.

    1996-02-01

    The HO-Br bond energy (and consequently the heat of formation of HOBr) has been determined experimentally for the first time. HOBr can be photolyzed in the stratosphere to form Br and OH, both of which can react with ozone, and destroy it. Previous calculations modeling stratospheric reactions have assumed a lower stability than that found in the current research. The stability of HOBr was determined by measuring the threshold for formation of Br{sup +} from this molecule, using photoionization mass spectrometry. Their work was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences.

  12. Ultrasonically bonded value assembly

    NASA Technical Reports Server (NTRS)

    Salvinski, R. J. (inventor)

    1975-01-01

    A valve apparatus capable of maintaining a fluid-tight seal over a relatively long period of time by releasably bonding a valve member to its seat is described. The valve member is bonded or welded to the seat and then released by the application of the same energy to the bond joint. The valve member is held in place during the bonding by a clamping device. An appropriate force device can activate the opening and closing of the valve member. Various combinations of material for the valve member and valve seat can be utilized to provide an adequate sealing bond. Aluminum oxide, stainless steel, inconel, tungsten carbide as hard materials and copper, aluminum, titanium, silver, and gold as soft materials are suggested.

  13. Differential Cross Sections for Electromagnetic Dissociation

    E-print Network

    John W. Norbury; Anne Adamczyk

    2006-12-19

    Differential cross sections for electromagnetic dissociation in nucleus-nucleus collisions are calculated. The kinetic energy distribution is parameterized with a Boltzmann distribution and the angular distribution is assumed isotropic in the projectile frame. In order to be useful for three-dimensional transport codes, these cross sections are available in both the projectile and lab frames. Comparison between theory and experiment is good. The formalism applies to single and multiple nucleon removal, alpha particle removal, and fission in electromagnetic reactions of nuclei.

  14. Structural characterization of multiple pyoverdines secreted by two Pseudomonas strains using liquid chromatography-high resolution tandem mass spectrometry with varying dissociation energies.

    PubMed

    Wei, Hua; Aristilde, Ludmilla

    2015-06-01

    High-affinity iron (Fe)-scavenging molecules, or siderophores, are secreted by microorganisms to acquire and compete for Fe. Pyoverdine (PVD), the primary siderophore produced by Pseudomonas, consists of a dihydroxyquinoline-type chromophore, a peptide chain of variable length and conformation, and a side chain composed of a dicarboxylic acid or its monoamide derivative. Elucidation of the PVD structures secreted by different Pseudomonas strains is an important step toward understanding their Fe-transport strategies. In this study, we characterized multiple PVDs secreted by Pseudomonas putida KT2440 and Pseudomonas fluorescens RA12 using ultra-high performance liquid chromatography coupled with high-resolution quadrupole-orbitrap tandem mass spectrometry. To avoid purification steps prior to characterizing the bacterial supernatants, PVD candidates were identified by extracting fragments of the dihydroxyquinoline component from the chromatographic peaks. Varying collisional dissociation energies were subsequently applied to achieve, with high mass accuracy, a broad coverage of fragments of the entire PVD. Our approach allowed us to discriminate between three different PVD structures in the secretion of each strain. The three PVDs of P. putida possess the same peptide chain of seven amino acids, Asp-Orn-OHAsp-Dab-Gly-Ser-cOHOrn, with a cyclicized portion present in two of the PVDs. For P. fluorescens, two of the PVDs had the same peptide chain of 13 amino acids, Ala-Lys-Gly-Gly-Ala-OHAsp-Gly-Ser-Ala-Ala-Ala-Ala-cOHOrn, whereas a third PVD had a Ser substituting for the first Ala. The side chain of the PVDs was either succinic acid or succinamide. The present approach can be employed for simultaneous structural characterization of several peptidic siderophores and related molecules in bacterial secretions. Graphical abstract Characterizing mutiple pyoverdine (PVD) structures in bacterial secretions without prepurification step. PMID:25895945

  15. ADSORPTION AND DISSOCIATION OF O2 ON Ti3Al (0001) STUDIED BY FIRST-PRINCIPLES

    NASA Astrophysics Data System (ADS)

    Wei, Li-Jing; Guo, Jian-Xin; Dai, Xiu-Hong; Wang, Ying-Long; Liu, Bao-Ting

    2015-05-01

    The adsorption and dissociation of oxygen molecule on Ti3Al (0001) surface have been investigated by density functional theory (DFT) with the generalized gradient approximation (GGA). All possible adsorption sites including nine vertical and fifteen parallel sites of O2 are considered on Ti3Al (0001) surface. It is found that all oxygen molecules dissociate except for three vertical adsorption sites after structure optimization. This indicates that oxygen molecules prefer to dissociate on the junction site between Ti and Al atoms. Oxygen atoms coming from dissociation of oxygen molecule tend to occupy the most stable adsorption sites of the Ti3Al (0001) surface. The distance of O-O is related to the surface dissociation distance of Ti3Al (0001) surface. The valence electron localization function (ELF) and projected density of states (DOS) show that the bonds of O-O are breakaway at parallel adsorption end structures.

  16. Quarkonium dissociation by anisotropy

    E-print Network

    Mariano Chernicoff; Daniel Fernandez; David Mateos; Diego Trancanelli

    2013-01-25

    We compute the screening length for quarkonium mesons moving through an anisotropic, strongly coupled N=4 super Yang-Mills plasma by means of its gravity dual. We present the results for arbitrary velocities and orientations of the mesons, as well as for arbitrary values of the anisotropy. The anisotropic screening length can be larger or smaller than the isotropic one, and this depends on whether the comparison is made at equal temperatures or at equal entropy densities. For generic motion we find that: (i) mesons dissociate above a certain critical value of the anisotropy, even at zero temperature; (ii) there is a limiting velocity for mesons in the plasma, even at zero temperature; (iii) in the ultra-relativistic limit the screening length scales as $(1-v^2)^\\epsilon$ with \\epsilon =1/2, in contrast with the isotropic result \\epsilon =1/4.

  17. Investigation of intense femto-second laser ionization and dissociation of methane with time-dependent density-functional approach

    NASA Astrophysics Data System (ADS)

    Irani, E.; Sadighi-Bonabi, R.; Anvari, A.

    2014-06-01

    Three dimensional calculations of electronic dynamics of CH4 in a strong laser field are presented with time-dependent density-functional theory. Time evolution of dipole moment and electron localization function is presented. The dependence of dissociation rate on the laser characters is shown and optimal effective parameters are evaluated. The optimum field leads to 76% dissociation probability for GAUSSIAN envelope and 40 fs (FWHM) at 1016 W cm-2. The dissociation probability is calculated by optimum convolution of dual short pulses. By combining of field assisted dissociation process and Ehrenfest molecular dynamics, time variation of bond length, velocity and orientation effect are investigated.

  18. Ab initio Investigation of Effect of Vacancy on Dissociation of Water Molecule on Cu(111) Surface

    E-print Network

    Kaware, Vaibhav

    2015-01-01

    Water dissociation is a rate limiting step in many industrially important chemical reactions. In this investigation, climbing image nudged elastic band (CINEB) method, within the framework of density functional theory, is used to report the activation energies (E a ) of water dissociation on Cu(111) surface with a vacancy. Introduction of vacancy results in a reduced coordination of the dissociated products, which facilitates their availability for reactions that involve water dissociation as an intermediate step. Activation energy for dissociation of water reduces by nearly 0.2 eV on Cu(111) surface with vacancy, in comparison with that of pristine Cu(111) surface. We also find that surface modification of the Cu upper surface is one of the possible pathways to dissociate water when the vacancy is introduced. Activation energy, and the minimum energy path (MEP) leading to the transition state remain same for various product configurations. CINEB corresponding to hydrogen gas evolution is also performed which...

  19. Structure Effects on Coulomb Dissociation of $^8$B

    E-print Network

    F. M. Nunes; R. Shyam; I. J. Thompson

    1998-05-23

    Coulomb Dissociation provides an alternative method for determining the radiative capture cross sections at astrophysically relevant low relative energies. For the breakup of $^8$B on $^{58}$Ni, we calculate the total Coulomb Dissociation cross section and the angular distribution for E1, E2 and M1. Our calculations are performed first within the standard first order semiclassical theory of Coulomb Excitation, including the correct three body kinematics, and later including the projectile-target nuclear interactions.

  20. Deuterium enrichment by selective photo-induced dissociation of an organic carbonyl compound

    DOEpatents

    Marling, John B. (Livermore, CA)

    1981-01-01

    A method for producing a deuterium enriched material by photoinduced dissociation which uses as the working material a gas phase photolytically dissociable organic carbonyl compound containing at least one hydrogen atom bonded to an atom which is adjacent to a carbonyl group and consisting of molecules wherein said hydrogen atom is present as deuterium and molecules wherein said hydrogen atom is present as another isotope of hydrogen. The organic carbonyl compound is subjected to intense infrared radiation at a preselected wavelength to selectively excite and thereby induce dissociation of the deuterium containing species to yield a deuterium enriched stable molecular product. Undissociated carbonyl compound, depleted in deuterium, is preferably redeuterated for reuse.

  1. Performance and Reliability of Bonded Interfaces for High-Temperature Packaging; NREL (National Renewable Energy Laboratory)

    SciTech Connect

    DeVoto, Douglas

    2015-06-10

    This is a technical review of the DOE VTO EDT project EDT063, Performance and Reliability of Bonded Interfaces for High-Temperature Packaging. A procedure for analyzing the reliability of sintered-silver through experimental thermal cycling and crack propagation modeling has been outlined and results have been presented.

  2. Aircraft surface coatings study: Energy efficient transport program. [sprayed and adhesive bonded coatings for drag reduction

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Surface coating materials for application on transport type aircraft to reduce drag, were investigated. The investigation included two basic types of materials: spray on coatings and adhesively bonded films. A cost/benefits analysis was performed, and recommendations were made for future work toward the application of this technology.

  3. Thermal Dissociation and Roaming Isomerization of Nitromethane: Experiment and Theory.

    PubMed

    Annesley, Christopher J; Randazzo, John B; Klippenstein, Stephen J; Harding, Lawrence B; Jasper, Ahren W; Georgievskii, Yuri; Ruscic, Branko; Tranter, Robert S

    2015-07-16

    The thermal decomposition of nitromethane provides a classic example of the competition between roaming mediated isomerization and simple bond fission. A recent theoretical analysis suggests that as the pressure is increased from 2 to 200 Torr the product distribution undergoes a sharp transition from roaming dominated to bond-fission dominated. Laser schlieren densitometry is used to explore the variation in the effect of roaming on the density gradients for CH3NO2 decomposition in a shock tube for pressures of 30, 60, and 120 Torr at temperatures ranging from 1200 to 1860 K. A complementary theoretical analysis provides a novel exploration of the effects of roaming on the thermal decomposition kinetics. The analysis focuses on the roaming dynamics in a reduced dimensional space consisting of the rigid-body motions of the CH3 and NO2 radicals. A high-level reduced-dimensionality potential energy surface is developed from fits to large-scale multireference ab initio calculations. Rigid body trajectory simulations coupled with master equation kinetics calculations provide high-level a priori predictions for the thermal branching between roaming and dissociation. A statistical model provides a qualitative/semiquantitative interpretation of the results. Modeling efforts explore the relation between the predicted roaming branching and the observed gradients. Overall, the experiments are found to be fairly consistent with the theoretically proposed branching ratio, but they are also consistent with a no-roaming scenario and the underlying reasons are discussed. The theoretical predictions are also compared with prior theoretical predictions, with a related statistical model, and with the extant experimental data for the decomposition of CH3NO2, and for the reaction of CH3 with NO2. PMID:25886024

  4. Electron-induced dissociation of CO2 on TiO2(110).

    PubMed

    Lee, Junseok; Sorescu, Dan C; Deng, Xingyi

    2011-07-01

    The electron-induced dissociation of CO(2) adsorbed at the oxygen vacancy defect on the TiO(2)(110) surface has been investigated at the single-molecular level using scanning tunneling microscopy (STM). Electron injection from the STM tip into the adsorbed CO(2) induces the dissociation of CO(2). The oxygen vacancy defect is found to be healed by the oxygen atom released during the dissociation process. Statistical analysis shows that the dissociation of CO(2) is one-electron process. The bias-dependent dissociation yield reveals that the threshold energy for electron-induced dissociation of CO(2) is 1.4 eV above the conduction-band minimum of TiO(2). The formation of a transient negative ion by the injected electron is considered to be the key process in CO(2) dissociation. PMID:21648466

  5. Diffusion bonding

    NASA Astrophysics Data System (ADS)

    Brown, L. E.

    1993-03-01

    A temperature between 400 and 500 and a pressure between 40 MPa and 160 MPa were indicated by a two-factor, three-level factorial experiment for diffusion bonding of molybdenum sheet substrates. These substrates were sputter ion plated with palladium (0.5 microns) and silver (10 microns) films on the mating surfaces, with the silver used as a bonding interlayer. The palladium acted as an adhesive layer between the silver film and molybdenum substrate. The silver diffusion bonds that resulted were qualitatively characterized at the interfacial regions, and bonds with no visible interface were obtained at 7500X magnification. Correlations were obtained for voids found optically at the silver/silver bonding interface and colored image maps, illustrating bond quality, produced by nondestructive ultrasonic imaging. Above 160 MPa, the bonding process produces samples with a nonuniform load distribution. These samples contained regions with gaps and well-bonded regions at the silver/silver interface, and all had macroscopic deformation of the silver films.

  6. Collisionless dissociation and isotopic enrichment of SF6 using high-powered CO2 laser radiation

    NASA Technical Reports Server (NTRS)

    Gower, M. C.; Billman, K. W.

    1977-01-01

    Dissociation of S-32F6 and the resultant isotopic enrichment of S-34F6 using high-powered CO2 laser radiation has been studied with higher experimental sensitivity than previously reported. Enrichment factors have been measured as a function of laser pulse number, wavelength, energy and time duration. A geometry independent dissociation cross section is introduced and measured values are presented. Threshold energy densities, below which no dissociation was observed, were also determined.

  7. Electrophilic, Ambiphilic, and Nucleophilic C-H bond Activation. Understanding the electronic continuum of C-H bond activation through transition-state and reaction pathway interaction energy decompositions

    SciTech Connect

    Ess, Daniel H.; Goddard, William A.; Periana, Roy A.

    2010-10-29

    The potential energy and interaction energy profiles for metal- and metal-ligand-mediated alkane C-H bond activation were explored using B3LYP density functional theory (DFT) and the absolutely localized molecular orbital energy decomposition analysis (ALMO-EDA). The set of complexes explored range from late transition metal group 10 (Pt and Pd) and group 11 (Au) metal centers to group 7-9 (Ir, Rh, Ru, and W) metal centers as well as a group 3 Sc complex. The coordination geometries, electron metal count (d8, d6, d4, and d0), and ligands (N-heterocycles, O-donor, phosphine, and Cp*) are also diverse. Quantitative analysis using ALMO-EDA of both directions of charge-transfer stabilization (occupied to unoccupied orbital stabilization) energies between the metal-ligand fragment and the coordinated C-H bond in the transition state for cleavage of the C-H bond allows classification of C-H activation reactions as electrophilic, ambiphilic, or nucleophilic on the basis of the net direction of charge-transfer energy stabilization. This bonding pattern transcends any specific mechanistic or bonding paradigm, such as oxidative addition, ?-bond metathesis, or substitution. Late transition metals such as Au(III), Pt(II), Pd(II), and Rh(III) metal centers with N-heterocycle, halide, or O-donor ligands show electrophilically dominated reaction profiles with forward charge-transfer from the C-H bond to the metal, leading to more stabilization than reverse charge transfer from the metal to the C-H bond. Transition states and reaction profiles for d6 Ru(II) and Ir(III) metals with Tp and acac ligands were found to have nearly equal forward and reverse charge-transfer energy stabilization. This ambiphilic region also includes the classically labeled electrophilic cationic species Cp*(PMe3)Ir(Me). Nucleophilic character, where the metal to C-H bond charge-transfer interaction is most stabilizing, was found in metathesis reactions with W(II) and Sc(III) metal center complexes in reactions as well as late transition metal Ir(I) and Rh(I) pincer complexes that undergo C-H bond insertion. Comparison of pincer ligands shows that the PCP ligand imparts more nucleophilic character to an Ir metal center than a deprotonated PNP ligand. The PCP and POCOP ligands do not show a substantial difference in the electronics of C-H activation. It was also found that Rh(I) is substantially more nucleophilic than Ir(I). Lastly, as a qualitative approximation, investigation of transition-state fragment orbital energies showed that relative frontier orbital energy gaps correctly reflect electrophilic, ambiphilic, or nucleophilic charge-transfer stabilization patterns.

  8. CCl bond fission dynamics and angular momentum recoupling in the 235 nm photodissociation of allyl chloride

    E-print Network

    Butler, Laurie J.

    C­Cl bond fission dynamics and angular momentum recoupling in the 235 nm photodissociation of allyl/2) products by 2 1 resonance enhanced multiphoton ionization shows that primary C­Cl bond fission of allyl(2 P3/2) of 0.097/0.903. The minor dissociation channel for C­Cl bond fission, producing low kinetic

  9. State-resolved imaging of CO from propenal photodissociation: Signatures of concerted three-body dissociation

    SciTech Connect

    Dey, Arghya; Fernando, Ravin; Suits, Arthur G.

    2014-04-21

    State-selected DC sliced images of propenal photodissociation show clear signatures of a novel synchronous concerted three-body dissociation of propenal recently proposed by Lee and co-workers to give C{sub 2}H{sub 2} + H{sub 2} + CO [S. H. Lee, C. H. Chin, C. Chaudhuri, ChemPhysChem 12, 753 (2011)]. Unlike any prior example of a concerted 3-body dissociation event, this mechanism involves breaking three distinct bonds and yields 3 distinct molecules. DC sliced images of CO fragments were recorded for a range of rotational levels for both v = 0 and v = 1. The results show formation of two distinct CO product channels having dissimilar translational energy distributions with characteristic rovibrational state distributions. The images for CO (v = 0) show a large contribution of slower CO fragments at lower rotational levels (J = 5–25). This slow component is completely absent from the v = 1 CO images. The images for the higher rotational levels of the v = 0 and v = 1 CO are nearly identical, and this provides a basis for decomposing the two channels for v = 0. The quantum state and translational energy distributions for the slow channel are readily assigned to the 3-body dissociation based on the properties of the transition state. The faster CO fragments dominating the higher rotational levels in both v = 0 and v = 1 are attributed to formation of CH{sub 3}CH + CO, also in agreement with the inferences based on previous non-state-resolved measurements with supporting theoretical calculations.

  10. Fluid hydrogen at high density - Pressure dissociation

    NASA Technical Reports Server (NTRS)

    Saumon, Didier; Chabrier, Gilles

    1991-01-01

    A model for the Helmholtz free energy of fluid hydrogen at high density and high temperature is developed. This model aims at describing both pressure and temperature dissociation and ionization and bears directly on equations of state of partially ionized plasmas, as encountered in astrophysical situations and high-pressure experiments. This paper focuses on a mixture of hydrogen atoms and molecules and is devoted to the study of the phenomenon of pressure dissociation at finite temperatures. In the present model, the strong interactions are described with realistic potentials and are computed with a modified Weeks-Chandler-Andersen fluid perturbation theory that reproduces Monte Carlo simulations to better than 3 percent. Theoretical Hugoniot curves derived from the model are in excellent agreement with experimental data.

  11. Using Qualified Energy Conservation Bonds (QECBs) to Fund a Residential Energy Efficiency Loan Program: Case Study on Saint Louis County, MO

    SciTech Connect

    Zimring, Mark

    2011-06-23

    Qualified Energy Conservation Bonds (QECBs) are federally-subsidized debt instruments that enable state, tribal, and local government issuers to borrow money to fund a range of qualified energy conservation projects. QECBs offer issuers very attractive borrowing rates and long terms, and can fund low-interest energy efficiency loans for home and commercial property owners. Saint Louis County, MO recently issued over $10 million of QECBs to finance the Saint Louis County SAVES residential energy efficiency loan program. The county's experience negotiating QECB regulations and restrictions can inform future issuers.

  12. Alkali Metal-Glucose Interaction Probed with Infrared Pre-Dissociation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Kregel, Steven J.; Marsh, Brett; Zhou, Jia; Garand, Etienne

    2015-06-01

    The efficient extraction of cellulose from biomass and its subsequent conversion to glucose derivatives is an attractive goal in the field of energy science. However, current industrial methods require high ionic strength and harsh conditions. Ionic liquids (IL's) are a class of "green" compounds that have been shown to dissolve cellulose in concentrations of up to 25 wt%. In order to understand IL's extraordinary cellulose dissolving power, a molecular level understanding of the IL-cellulose interaction is needed. Toward that end, we have acquired infrared pre-dissociation spectra of M+-glucose, where M+=Li+, Na+, or K+. Through comparisons with density functional theory calculations, we have determined the relative abundances of various M+-glucose binding motifs in both the thermodynamic and kinetic limits. These results provide insight on the hydrogen bonding dynamics of glucose and are a step towards a fuller understanding of cellulose interactions with ionic liquids.

  13. Kinetic, Spectroscopic, and Theoretical Assessment of Associative and Dissociative Methanol Dehydration Routes in Zeolites

    SciTech Connect

    Jones, Andrew J.; Iglesia, Enrique

    2014-11-03

    Mechanistic interpretations of rates and in situ IR spectra combined with density functionals that account for van der Waals interactions of intermediates and transition states within confining voids show that associative routes mediate the formation of dimethyl ether from methanol on zeolitic acids at the temperatures and pressures of practical dehydration catalysis. Methoxy-mediated dissociative routes become prevalent at higher temperatures and lower pressures, because they involve smaller transition states with higher enthalpy, but also higher entropy, than those in associative routes. These enthalpy–entropy trade-offs merely reflect the intervening role of temperature in activation free energies and the prevalence of more complex transition states at low temperatures and high pressures. This work provides a foundation for further inquiry into the contributions of H-bonded methanol and methoxy species in homologation and hydrocarbon synthesis reactions from methanol.

  14. Rotational distributions following van der Waals molecule dissociation: Comparison between experiment and theory for benzene-Ar

    NASA Astrophysics Data System (ADS)

    Sampson, Rebecca K.; Bellm, Susan M.; McCaffery, Anthony J.; Lawrance, Warren D.

    2005-02-01

    The translational energy release distribution for dissociation of benzene-Ar has been measured and, in combination with the 610 rotational contour of the benzene product observed in emission, used to determine the rotational J,K distribution of 00 benzene products formed during dissociation from 61¯. Significant angular momentum is transferred to benzene on dissociation. The 00 rotational distribution peaks at J=31 and is skewed to low K:Javerage=27, ?K?average=10.3. The average angle between the total angular momentum vector and the unique rotational axis is determined to be 68°. This indicates that benzene is formed tumbling about in-plane axes rather than in a frisbeelike motion, consistent with Ar "pushing off" benzene from an off-center position above or below the plane. The J distribution is very well reproduced by angular momentum model calculations based on an equivalent rotor approach [A. J. McCaffery, M. A. Osborne, R. J. Marsh, W. D. Lawrance, and E. R. Waclawik, J. Chem. Phys. 121, 1694 (2004)], indicating that angular momentum constraints control the partitioning of energy between translation and rotation. Calculations for p-difluorobenzene-Ar suggest that the equivalent rotor model can provide a reasonable prediction of both J and K distributions in prolate (or near prolate) tops when dissociation leads to excitation about the unique, in-plane axis. Calculations for s-tetrazine-Ar require a small maximum impact parameter to reproduce the comparatively low J values seen for the s-tetrazine product. The three sets of calculations show that the maximum impact parameter is not necessarily equal to the bond length of the equivalent rotor and must be treated as a variable parameter. The success of the equivalent rotor calculations argues that angular momentum constraints control the partitioning between rotation and translation of the products.

  15. Dissociative absorption: An empirically unique, clinically relevant, dissociative factor.

    PubMed

    Soffer-Dudek, Nirit; Lassri, Dana; Soffer-Dudek, Nir; Shahar, Golan

    2015-11-01

    Research of dissociative absorption has raised two questions: (a) Is absorption a unique dissociative factor within a three-factor structure, or a part of one general dissociative factor? Even when three factors are found, the specificity of the absorption factor is questionable. (b) Is absorption implicated in psychopathology? Although commonly viewed as "non-clinical" dissociation, absorption was recently hypothesized to be specifically associated with obsessive-compulsive symptoms. To address these questions, we conducted exploratory and confirmatory factor analyses on 679 undergraduates. Analyses supported the three-factor model, and a "purified" absorption scale was extracted from the original inclusive absorption factor. The purified scale predicted several psychopathology scales. As hypothesized, absorption was a stronger predictor of obsessive-compulsive symptoms than of general psychopathology. In addition, absorption was the only dissociative scale that longitudinally predicted obsessive-compulsive symptoms. We conclude that absorption is a unique and clinically relevant dissociative tendency that is particularly meaningful to obsessive-compulsive symptoms. PMID:26241024

  16. dissociation in a strong laser field: An ab initio classical trajectory study Suk Kyoung Lee, Wen Li, H. Bernhard Schlegel

    E-print Network

    Schlegel, H. Bernhard

    HCO+ dissociation in a strong laser field: An ab initio classical trajectory study Suk Kyoung Lee dissociation times, mainly due to the reori- entation of HCO+ relative to the field direction prior to dissociation. The kinetic energy distribution at this intensity agrees with Wardlaw's wagging tail model

  17. Dissociation of acetone radical cation (CH3COCH3 d): An ab initio direct classical trajectory studyw

    E-print Network

    Schlegel, H. Bernhard

    Dissociation of acetone radical cation (CH3COCH3 1d - CH3CO1 þCH3 d): An ab initio direct classical 2004 First published as an Advance Article on the web 7th September 2004 The dissociation of acetone sampling was constructed by distributing 10 kcal molÀ1 of excess energy above the barrier. The dissociation

  18. Charge-transfer dissociation of vibrationally cold HeH : Evidence for and lifetime of the a 3

    E-print Network

    Zajfman, Daniel

    Charge-transfer dissociation of vibrationally cold HeH¿ : Evidence for and lifetime of the a 3 beams, the kinetic-energy release after dissociative charge transfer of vibrationally cold He of controversy in previous dissociative recombination experiments. PACS number s : 34.50. s, 33.15. e, 34.70. e

  19. Electron-impact dissociation of ozone cations to O+ fragments

    NASA Astrophysics Data System (ADS)

    Belic, D. S.; Urbain, X.; Defrance, P.

    2015-01-01

    Absolute cross sections for electron-impact dissociation of O3+ ions yielding an O+ fragment are measured. The animated electron-ion crossed-beam method is applied in the energy range from 1 eV to 2.5 keV. The maximum total cross section for O+ fragment production is found to be (3.6 ±0.3 ) ×10-16 cm2 at 75 eV and such a large value of the cross section extends down to low energies. The threshold energy is found to be below 2 eV. Contributions of dissociative excitation and dissociative ionization to O+ fragment production are determined separately. The total kinetic energy release distributions are determined at select electron energies. Present data are discussed and compared with recent results [S. H. M. Deng et al., Phys. Rev. A 82, 062715 (2010), 10.1103/PhysRevA.82.062715].

  20. Coinage metals binding as main group elements: structure and bonding of the carbene complexes [TM(cAAC)2] and [TM(cAAC)2](+) (TM = Cu, Ag, Au).

    PubMed

    Jerabek, Paul; Roesky, Herbert W; Bertrand, Guy; Frenking, Gernot

    2014-12-10

    Quantum chemical calculations using density functional theory have been carried out for the cyclic (alkyl)(amino)carbene (cAAC) complexes of the group 11 atoms [TM(cAAC)2] (TM = Cu, Ag, Au) and their cations [TM(cAAC)2](+). The nature of the metal-ligand bonding was investigated with the charge and energy decomposition analysis EDA-NOCV. The calculations show that the TM-C bonds in the charged adducts [TM(cAAC)2](+) are significantly longer than in the neutral complexes [TM(cAAC)2], but the cations have much higher bond dissociation energies than the neutral molecules. The intrinsic interaction energies ?Eint in [TM(cAAC)2](+) take place between TM(+) in the (1)S electronic ground state and (cAAC)2. In contrast, the metal-ligand interactions in [TM(cAAC)2] involve the TM atoms in the excited (1)P state yielding strong TM p(?) ? (cAAC)2 ? backdonation, which is absent in the cations. The calculations suggest that the cAAC ligands in [TM(cAAC)2] are stronger ? acceptors than ? donors. The trends of the intrinsic interaction energies and the bond dissociation energies of the metal-ligand bonds in [TM(cAAC)2] and [TM(cAAC)2](+) give the order Au > Cu > Ag. Calculations at the nonrelativistic level give weaker TM-C bonds, particularly for the gold complexes. The trend for the bond strength in the neutral and charged adducts without relativistic effects becomes Cu > Ag > Au. The EDA-NOCV calculations suggest that the weaker bonds at the nonrelativistic level are mainly due to stronger Pauli repulsion and weaker orbital interactions. The NBO picture of the C-TM-C bonding situation does not correctly represent the nature of the metal-ligand interactions in [TM(cAAC)2]. PMID:25394669

  1. Chemical activation of molecules by metals: Experimental studies of electron distributions and bonding

    SciTech Connect

    Lichtenberger, D.L.

    1991-10-01

    The formal relationship between measured molecular ionization energies and thermodynamic bond dissociation energies has been developed into a single equation which unifies the treatment of covalent bonds, ionic bonds, and partially ionic bonds. This relationship has been used to clarify the fundamental thermodynamic information relating to metal-hydrogen, metal-alkyl, and metal-metal bond energies. We have been able to obtain a direct observation and measurement of the stabilization energy provided by the agostic interaction of the C-H bond with the metal. The ionization energies have also been used to correlate the rates of carbonyl substitution reactions of ({eta}{sup 5}-C{sub 5}H{sub 4}X)Rh(CO){sub 2} complexes, and to reveal the electronic factors that control the stability of the transition state. The extent that the electronic features of these bonding interactions transfer to other chemical systems is being investigated in terms of the principle of additivity of ligand electronic effects. Specific examples under study include metal- phosphines, metal-halides, and metallocenes. Especially interesting has been the recent application of these techniques to the characterization of the soccer-ball shaped C{sub 60} molecule, buckminsterfullerene, and its interaction with a metal surface. The high-resolution valence ionizations in the gas phase reveal the high symmetry of the molecule, and studies of thin films of C{sub 60} reveal weak intermolecular interactions. Scanning tunneling and atomic force microscopy reveal the arrangement of spherical molecules on gold substrates, with significant delocalization of charge from the metal surface. 21 refs.

  2. Global functioning and disability in dissociative disorders.

    PubMed

    Mueller-Pfeiffer, Christoph; Rufibach, Kaspar; Perron, Noelle; Wyss, Daniela; Kuenzler, Cornelia; Prezewowsky, Cornelia; Pitman, Roger K; Rufer, Michael

    2012-12-30

    Dissociative disorders are frequent comorbid conditions of other mental disorders. Yet, there is controversy about their clinical relevance, and little systematic research has been done on how they influence global functioning. Outpatients and day care patients (N=160) of several psychiatric units in Switzerland were assessed with the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders (DSM)-IV Axis I Disorders, Structured Clinical Interview for DSM-IV Dissociative Disorders, Global Assessment of Functioning Scale, and World Health Organization Disability Assessment Schedule-II. The association between subjects with a dissociative disorder (N=30) and functional impairment after accounting for non-dissociative axis I disorders was evaluated by linear regression models. We found a proportion of 18.8% dissociative disorders (dissociative amnesia=0%, dissociative fugue=0.6%, depersonalization disorder=4.4%, dissociative identity disorder=7.5%, dissociative disorder-not-otherwise-specified=6.3%) across treatment settings. Adjusted for other axis I disorders, subjects with a comorbid dissociative identity disorder or dissociative disorder-not-otherwise-specified had a median global assessment of functioning score that was 0.86 and 0.88 times, respectively, the score of subjects without a comorbid dissociative disorder. These findings support the hypothesis that complex dissociative disorders, i.e., dissociative identity disorder and dissociative disorder-not-otherwise-specified, contribute to functional impairment above and beyond the impact of co-existing non-dissociative axis I disorders, and that they qualify as "serious mental illness". PMID:22578820

  3. Diffraction dissociation at the LHC

    E-print Network

    László Jenkovszky; Andrii Salii

    2013-10-22

    Predictions for the squared momentum transfer and missing mass dependence of the differential and integrated single- and double low missing-mass diffraction dissociation in the kinematical range of present and future LHC measurements are summarized.

  4. Energetics from Slow Infrared Multiphoton Dissociation of Biomolecules

    PubMed Central

    Jockusch, Rebecca A.; Paech, Kolja

    2005-01-01

    Photodissociation kinetics of the protonated pentapeptide leucine enkephalin measured using a cw CO2 laser and a Fourier-transform mass spectrometer are reported. A short induction period, corresponding to the time required to raise the internal energy of the ion population to a (dissociating) steady state, is observed. After this induction period, the dissociation data are accurately fit by first-order kinetics. A plot of the log of the unimolecular dissociation rate constant, kuni, as a function of the log of laser power is linear at low laser powers (<9 W, kuni <0.05 s?1), but tapers off at high laser power (9–33 W, kuni = 0.05–7 s?1). The entire measured dissociation curve can be accurately fit by an exponential function plus a constant. The experiment is simulated using a master equation formalism. In the model, the laser radiation is described as an energetically flat-topped distribution which is spatially uniform. This description is consistent with experimental results which indicate that ion motion within the cell averages out spatial inhomogeneities in the laser light. The model has several adjustable parameters. The effect of varying these parameters on the calculated kinetics and power dependence curves is discussed. A procedure for determining a limited range of threshold dissociation energy, Eo, which fits both the measured induction period and power dependence curves, is presented. Using this procedure, Eo of leucine enkephalin is determined to be 1.12–1.46 eV. This result is consistent with, although less precise than, values measured previously using blackbody infrared radiative dissociation. Although the blackbody dissociation results were used as a starting point to search for fits of the master equation model to experiment, these results demonstrate that it is, in principle, possible to determine a limited range of Eo from slow infrared multiphoton dissociation data alone. PMID:16467893

  5. Multi-reference weak pairs local configuration interaction: efficient calculations of bond breaking

    NASA Astrophysics Data System (ADS)

    Walter, Derek; Carter, Emily A.

    2001-09-01

    We present a new local multi-reference singles and doubles configuration interaction (MRSDCI) algorithm. The method presented here eliminates configurations if they involve simultaneous excitations out of widely separated internal orbitals and is therefore based on the weak pairs approximation of Saebø and Pulay. Although the resulting truncated CI expansions have only about 50% as many CSFs as the non-local MRSDCI, we show that they can recover over 99% of the correlation energy. Additionally, we show for the first time that they can accurately describe bond dissociation.

  6. Wave packet dynamics of H2(v1=8-14)+H2(v2=0-2): The role of the potential energy surface on different reactive and dissociative processes

    NASA Astrophysics Data System (ADS)

    Bartolomei, Massimiliano; Hernández, Marta I.; Campos-Martínez, José

    2005-02-01

    A time-dependent wave packet method has been used to study different competing products of H2+H2 collisions: four center reaction, collision induced dissociation, reactive dissociation, and three-body complex formation. A three-degree-of-freedom reduced dimensionality model has been used for five different geometries of the colliding complex (parallel H, crossed X, collinear L, and two T-shaped geometries TI and TII), with reactants in selected vibrational states with one diatom vibrationally "hot" and the other one vibrationally "cold." Product probabilities have been calculated using two potential energy surfaces [J. Chem. Phys. 101, 4004 (1994); J. Chem. Phys. 116, 666 (2002)] in order to compare their performance in the dynamics. The regions of the potential energy surfaces responsible of the threshold behavior of the probabilities have been identified. Overall, we have found that the most recent potential energy surface is less anisotropic, provides a smaller propensity for insertion-type processes, and gives lower energy thresholds.

  7. Accurate energies of hydrogen bonded nucleic acid base pairs and triplets in tRNA tertiary interactions

    PubMed Central

    2006-01-01

    Tertiary interactions are crucial in maintaining the tRNA structure and functionality. We used a combined sequence analysis and quantum mechanics approach to calculate accurate energies of the most frequent tRNA tertiary base pairing interactions. Our analysis indicates that six out of the nine classical tertiary interactions are held in place mainly by H-bonds between the bases. In the remaining three cases other effects have to be considered. Tertiary base pairing interaction energies range from ?8 to ?38 kcal/mol in yeast tRNAPhe and are estimated to contribute roughly 25% of the overall tRNA base pairing interaction energy. Six analyzed posttranslational chemical modifications were shown to have minor effect on the geometry of the tertiary interactions. Modifications that introduce a positive charge strongly stabilize the corresponding tertiary interactions. Non-additive effects contribute to the stability of base triplets. PMID:16461956

  8. High level ab initio calculations for ClF(n)+ (n = 1-6) ions: refining the recoupled pair bonding model.

    PubMed

    Chen, Lina; Woon, David E; Dunning, Thom H

    2013-05-23

    Based on detailed, high level ab initio calculations on a number of halogenated compounds of second row, late p-block elements, the SF(n), ClF(n), PFn, SCl(n), and SF(n)Cl families, we found that a new type of bond--the recoupled pair bond--accounts for the ability of these elements to form hypervalent, or hypercoordinated, compounds. Hypervalent molecules are formed when it is energetically favorable for the electrons in a lone pair orbital to be recoupled, allowing each of the electrons to form chemical bonds with ligands. In this paper, we characterize the structures and energies of the ground and low-lying excited states of the ClF(n)(+) (n = 1-6) ions, using high level ab initio methods [MRCI, CCSD(T)/RCCSD(T)] with large correlation consistent basis sets. We computed a number of quantities, including ClF(n)(+) structures, bond dissociation energies, and ClF(n) ionization energies and compared our results with the available experimental data. Both the bond dissociation energies and the ionization energies oscillate, variations that are readily explained using the recoupled pair bonding model. Comparisons are drawn between the ClF(n)(+) cations and their counterparts in the isoelectronic SF(n) series, which possess many similarities. We found two significant differences between the ClF(n)(+) and the SF(n) series: (i) the bond dissociation energies of ClF(n)(+) are much weaker than those of the corresponding SF(n) species, and (ii) there is no stable (3)A2 state in ClF2(+) corresponding to the stable state found in SF2. An examination of the Mulliken populations at the HF/AVTZ level for ClF(n)(+) and SF(n) species predicts that the F atom in the axial (recoupled pair bonding) position is more highly charged than the F atom in the equatorial (covalent bonding) position; there is also less charge transfer to the F atoms in ClF(n)(+) than in SF(n). The positive charge on Cl(+) makes it more difficult for an F atom to attract electrons from Cl(+) than from S and correspondingly less favorable to recouple the electrons in the lone pair orbitals in the ClF(n)(+) species. PMID:23590689

  9. Dissociative disorders in DSM-5.

    PubMed

    Spiegel, David; Lewis-Fernández, Roberto; Lanius, Ruth; Vermetten, Eric; Simeon, Daphne; Friedman, Matthew

    2013-01-01

    The rationale, research literature, and proposed changes to the dissociative disorders and conversion disorder in the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) are presented. Dissociative identity disorder will include reference to possession as well as identity fragmentation, to make the disorder more applicable to culturally diverse situations. Dissociative amnesia will include dissociative fugue as a subtype, since fugue is a rare disorder that always involves amnesia but does not always include confused wandering or loss of personality identity. Depersonalization disorder will include derealization as well, since the two often co-occur. A dissociative subtype of posttraumatic stress disorder (PTSD), defined by the presence of depersonalization or derealization in addition to other PTSD symptoms, is being recommended, based upon new epidemiological and neuroimaging evidence linking it to an early life history of adversity and a combination of frontal activation and limbic inhibition. Conversion disorder (functional neurological symptom disorder) will likely remain with the somatic symptom disorders, despite considerable dissociative comorbidity. PMID:23394228

  10. Electron-Impact Dissociation of Hydrocarbon Molecular Ions

    SciTech Connect

    Bannister, Mark E; Schultz, David Robert

    2014-01-01

    Absolute cross sections for electron-impact dissociation of CH_x^+ (x=1,2,3) producing CH_y^+ (y=0,1,2) fragment ions were measured in the 3-100 eV range using a crossed electron-ion beams technique with total uncertainties of about 11% near the cross section peaks. For CH^+ dissociation, although the measured energy dependence agrees well with two sets of storage ring measurements, the magnitude of the present results lies about 15% to 25% below the other results at the cross section peak near 40 eV. For dissociation of CH_2^+, the cross sections are nearly identical for energies above 15 eV, but they are dramatically different at lower energies. The CH^+ channel exhibits a strong peak rising from an observed threshold of about 6 eV; the C^+ channel is relatively flat down to the lowest measured energy. For dissociation of CH_3^+ and CD_3^+, good agreement is found with other results reported for the CH^+ fragment, but some differences are found for the CD_2^+ and C^+ fragments. A pilot study has also been undertaken to assess the feasibility of applying a molecular dynamics approach to treat the full range of electron-hydrocarbon dissociation processes, especially for energies above a few eV, in order to provide an overarching theoretical model that can be readily applied. Comparison with the experimental data for CH^+ shows favorable agreement.

  11. CO2 Dissociation using the Versatile Atmospheric Dielectric Barrier Discharge Experiment (VADER)

    NASA Astrophysics Data System (ADS)

    Lindon, Michael; Scime, Earl

    2014-09-01

    Dissociation of CO2 is investigated in an atmospheric pressure dielectric barrier discharge (DBD) with a simple, zero dimensional (0-D) chemical model and through experiment. The model predicts that the primary CO2 dissociation pathway within a DBD is electron impact dissociation and electron-vibrational excitation. The relaxation kinetics following dissociation are dominated by atomic oxygen chemistry. The experiments included investigating the energy efficiencies and dissociation rates of CO2 within a planar DBD, while the gas flow rate, voltage, gas composition, driving frequency, catalyst, and pulse modes were varied. Some of the VADER results include a maximum CO2 dissociation energy efficiency of 2.5 +/- 0.5%, a maximum CO_2 dissociation rate of 4 +/- 0.4*10^-6 mol CO2/s (5 +/- 0.5% percent dissociation), discovering that a resonant driving frequency of 30 kHz, dependent on both applied voltage and breakdown voltage, is best for efficient CO2 dissociation and that TiO2, a photocatalyst, improved dissociation efficiencies by an average of 18% at driving frequencies above 5 kHz.

  12. Selective Bond Cleavage in Potassium Collisions with Pyrimidine Bases of DNA

    NASA Astrophysics Data System (ADS)

    Almeida, Diogo; Ferreira da Silva, Filipe; García, Gustavo; Limão-Vieira, Paulo

    2013-01-01

    Electron transfer in alkali-molecule collisions to gas phase thymine and uracil yielding H- formation is selectively controlled in the energy range between 5.3 and 66.1 eV. By tuning the collision energy, electron transfer from the alkali to partly deuterated thymine, methylated thymine at the N1 and methylated uracil at the N3 positions, H- loss proceeds not only through the breaking of the (C-H) against (N-H) bonds but also through N1 against N3 sites. Such selectivity, as far as bond and site are concerned, is here reported for the first time by electron transfer induced dissociation experiments in alkali-molecule collisions.

  13. Collision-Induced Dissociation Fragmentation Inside Disulfide C-Terminal Loops of Natural Non-Tryptic Peptides

    NASA Astrophysics Data System (ADS)

    Samgina, Tatiana Y.; Vorontsov, Egor A.; Gorshkov, Vladimir A.; Artemenko, Konstantin A.; Zubarev, Roman A.; Ytterberg, Jimmy A.; Lebedev, Albert T.

    2013-07-01

    Collision-induced dissociation (CID) spectra of long non-tryptic peptides are usually quite complicated and rather difficult to interpret. Disulfide bond formed by two cysteine residues at C-terminus of frog skin peptides precludes one to determine sequence inside the forming loop. Thereby, chemical modification of S-S bonds is often used in "bottom up" sequencing approach. However, low-energy CID spectra of natural non-tryptic peptides with C-terminal disulfide cycle demonstrate an unusual fragmentation route, which may be used to elucidate the "hidden" C-terminal sequence. Low charge state protonated molecules experience peptide bond cleavage at the N-terminus of C-terminal cysteine. The forming isomeric acyclic ions serve as precursors for a series of b-type ions revealing sequence inside former disulfide cycle. The reaction is preferable for peptides with basic lysine residues inside the cycle. It may also be activated by acidic protons of Asp and Glu residues neighboring the loop. The observed cleavages may be quite competitive, revealing the sequence inside disulfide cycle, although S-S bond rupture does not occur in this case.

  14. Photodissociation of protonated tryptophan and alteration of dissociation pathways by complexation with crown ether

    SciTech Connect

    Kadhane, Umesh; Andersen, Jens Ulrik; Ehlerding, Anneli; Hvelplund, Preben; Kirketerp, Maj-Britt S.; Lykkegaard, Morten Koecks; Nielsen, Steen Broendsted; Panja, Subhasis; Wyer, Jean Ann; Zettergren, Henning

    2008-11-14

    The behavior of protonated tryptophan (TrpH{sup +}) and its complex with 18-crown-6-ether (CE) after photoexcitation has been explored based on measurements of dissociation lifetimes, fragmentation channels, and absorption spectra using an electrostatic ion storage ring. A recent implementation of pulsed power supplies for the ring elements with microsecond response times allows us to identify the daughter ion fragment masses and to disentangle fragmentation that occurs from excited states immediately after photoexcitation from that occurring on a longer time scale of several microseconds to milliseconds. We find that attachment of crown ether significantly alters the dissociation channels since it renders the {pi}{sigma}*(NH{sub 3}) state inaccessible and hence prevents the N-H bond breakage which is an important fragmentation channel of TrpH{sup +}. As a result, on a long time scale (>10 {mu}s), photoexcited TrpH{sup +}(CE) decays exponentially whereas TrpH{sup +} displays a power-law decay. The only ions remaining in the latter case are Trp{sup +{center_dot}} radical cations with a broad internal energy distribution caused by the departing hydrogen. Large changes in the fragment branching ratios as functions of excitation wavelength between 210 and 290 nm were found for both TrpH{sup +} and TrpH{sup +}(CE)

  15. Selective breaking of bonds in water with intense, 2-cycle, infrared laser pulses.

    PubMed

    Mathur, D; Dota, K; Dey, D; Tiwari, A K; Dharmadhikari, J A; Dharmadhikari, A K; De, S; Vasa, P

    2015-12-28

    One of the holy grails of contemporary science has been to establish the possibility of preferentially breaking one of several bonds in a molecule. For instance, the two O-H bonds in water are equivalent: given sufficient energy, either one of them is equally likely to break. We report bond-selective molecular fragmentation upon application of intense, 2-cycle pulses of 800 nm laser light: we demonstrate up to three-fold enhancement for preferential bond breaking in isotopically substituted water (HOD). Our experimental observations are rationalized by means of ab initio computations of the potential energy surfaces of HOD, HOD(+), and HOD(2+) and explorations of the dissociation limits resulting from either O-H or O-D bond rupture. The observations we report present a formidable theoretical challenge that need to be taken up in order to gain insights into molecular dynamics, strong field physics, chemical physics, non-adiabatic processes, mass spectrometry, and time-dependent quantum chemistry. PMID:26723674

  16. Influence of Ti nanocrystallization on microstructure, interface bonding, surface energy and blood compatibility of surface TiO 2 films

    NASA Astrophysics Data System (ADS)

    Shao, Honghong; Yu, Chunhang; Xu, Xiaojing; Wang, Ji; Zhai, Rui; Wang, Xiaojing

    2010-12-01

    Recent progress in ultrafine-grained/nano-grained (UFG/NG) titanium permits a consideration for TiO 2 films deposited on nano-grained titanium for antithrombogenic application such as artificial valves and stents. For this paper, the microstructure, interface bonding, surface energy, and blood compatibility features of TiO 2 films deposited by direct current magnetron reactive sputtering technology on NG titanium and coarse-grained (CG) titanium were investigated. The results show that the nanocrystallization of titanium substrate has a significant influence on TiO 2 films. At the same deposition parameters, the content of rutile phase of TiO 2 film was increased from 47% (on the CG titanium substrate) to 72% (on the NG titanium substrate); the adhesion of TiO 2 film was improved from 5.8 N to 17 N; the surface energy was reduced from 6.37 dyn/cm to 3.01 dyn/cm; the clotting time was improved from 18 min to 28 min; the platelets accumulation and pseudopodium of adherent platelets on TiO 2 film on NG titanium were considerably reduced compared to that on CG titanium. The present results demonstrate the possibility of improving the blood compatibility of TiO 2 film through the approach of substrate nanocrystallization. Also it may provide an attractive idea to prepare stents with biological coatings of more outstanding blood compatibility and interface bonding.

  17. Intense 2-cycle laser pulses induce time-dependent bond-hardening in a polyatomic molecule

    E-print Network

    K. Dota; M. Garg; A. K. Tiwari; J. A. Dharmadhikari; A. K. Dharmadhikari; D. Mathur

    2012-01-12

    A time-dependent bond-hardening process is discovered in a polyatomic molecule (tetramethyl silane, TMS) using few-cycle pulses of intense 800 nm light. In conventional mass spectrometry, symmetrical molecules like TMS do not exhibit a prominent molecular ion (TMS$^+$) as unimolecular dissociation into [Si(CH$_3$)$_3]^+$ proceeds very fast. Under strong field and few-cycle conditions, this dissociation channel is defeated by time-dependent bond-hardening: a field-induced potential well is created in the TMS$^+$ potential energy curve that effectively traps a wavepacket. The time-dependence of this bond hardening process is verified using longer-duration ($\\geq$ 100 fs) pulses; the relatively "slower" fall-off of optical field in such pulses allows the initially trapped wavepacket to leak out, thereby rendering TMS$^+$ unstable once again. Our results are significant as they demonstrate (i) optical generation of polyatomic ions that are normally inaccessible and (ii) optical control of dynamics in strong fields, with distinct advantages over weak-field control scenarios that demand a narrow bandwidth appropriate for a specified transition.

  18. Double Dissociation between Emotion Generation and Emotion Regulation 1 DOUBLE DISSOCIATION: CIRCADIAN OFF-PEAK TIMES

    E-print Network

    Double Dissociation between Emotion Generation and Emotion Regulation 1 DOUBLE DISSOCIATION: CIRCADIAN OFF-PEAK TIMES INCREASE EMOTIONAL REACTIVITY; AGING IMPAIRS EMOTION REGULATION VIA REAPPRAISAL Running Head: Double Dissociation between

  19. Scaling of the critical free length for progressive unfolding of self-bonded graphene

    SciTech Connect

    Kwan, Kenny; Cranford, Steven W.

    2014-05-19

    Like filled pasta, rolled or folded graphene can form a large nanocapsule surrounding a hollow interior. Use as a molecular carrier, however, requires understanding of the opening of such vessels. Here, we investigate a monolayer sheet of graphene as a theoretical trial platform for such a nanocapsule. The graphene is bonded to itself via aligned disulfide (S-S) bonds. Through theoretical analysis and atomistic modeling, we probe the critical nonbonded length (free length, L{sub crit}) that induces fracture-like progressive unfolding as a function of folding radius (R{sub i}). We show a clear linear scaling relationship between the length and radius, which can be used to determine the necessary bond density to predict mechanical opening/closing. However, stochastic dissipated energy limits any exact elastic formulation, and the required energy far exceeds the dissociation energy of the S-S bond. We account for the necessary dissipated kinetic energy through a simple scaling factor (?), which agrees well with computational results.

  20. Hydrogen bonding and reactivity of water to azines in their S1 (n,?*) electronic excited states in the gas phase and in solution.

    PubMed

    Reimers, Jeffrey R; Cai, Zheng-Li

    2012-07-01

    A unified picture is presented of water interacting with pyridine, pyridazine, pyrimidine, and pyrazine on the S(1) manifold in both gas-phase dimers and in aqueous solution. As (n,?*) excitation to the S(1) state removes electrons from the ground-state hydrogen bond, this analysis provides fundamental understanding of excited-state hydrogen bonding. Traditional interpretations view the excitation as simply breaking hydrogen bonds to form dissociated molecular products, but reactive processes such as photohydrolysis and excited-state proton coupled electron transfer (PCET) are also possible. Here we review studies performed using equations-of-motion coupled-cluster theory (EOM-CCSD), multireference perturbation theory (CASPT2), time-dependent density-functional theory (TD-DFT), and excited-state Monte Carlo liquid simulations, adding new results from symmetry-adapted-cluster configuration interaction (SAC-CI) and TD-DFT calculations. Invariably, gas-phase molecular dimers are identified as stable local minima on the S(1) surface with energies less than those for dissociated molecular products. Lower-energy biradical PCET minima are also identified that could lead to ground-state recombination and hence molecular dissociation, dissociation into radicals or ions, or hydration reactions leading to ring cleavage. For pyridine.water, the calculated barriers to PCET are low, suggesting that this mechanism is responsible for fluorescence quenching of pyridine.water at low energies rather than accepted higher-energy Dewar-benzene based "channel three" process. Owing to (n,?*) excitation localization, much higher reaction barriers are predicted for the diazines, facilitating fluorescence in aqueous solution and predicting that the as yet unobserved fluorescence from pyridazine.water and pyrimidine.water should be observable. Liquid simulations based on the assumption that the solvent equilibrates on the fluorescence timescale quantitatively reproduce the observed spectral properties, with the degree of (n,?*) delocalization providing a critical controlling factor. PMID:22532059