Sample records for bond dissociation energy

  1. 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.

  2. 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.

  3. A Reassessment of the Bond Dissociation Energies of Peroxides. An ab Initio Study

    E-print Network

    Schlegel, H. Bernhard

    dissociation enthalpies of 38 kcal/mol for diacetyl peroxide, 49 kcal/mol for trifluoroperoxyacetic acid, 23A Reassessment of the Bond Dissociation Energies of Peroxides. An ab Initio Study Robert D. Bach of 34 kcal/mol has been ascribed to a generic O-O bond dissociation energy. The present, high-level ab

  4. On the C?H bond dissociation energy of acetylene

    NASA Astrophysics Data System (ADS)

    Petersson, J. A. Montgomery G. A., Jr.

    1990-04-01

    Ab initio calculations, including extrapolation to the complete basis set limit, are reported for the C?H bond dissociation energy of acetylene. These calculations, which have a rms error of 0.51 kcal/mol per bond for the atomization energies of 13 well-known molecules, give D0(H-CCH) = 131.54 kcal/mol, in good agreement with previous results, but about 5 kcal/mol above the recent measurement of Green, Kinsey and Field ( D0 ? 126.647 0.002 kcal/mol), and that of Segall, Lavi, Wen and Wittig ( D0 = 127 1.5 kcal/mol). The electron affinity of CCH is calculated to be within 0.18 kcal/mol of the recent measurement of Ervin et al. (2.969 0.010 eV)

  5. The C?NO 2 bond dissociation energies of some nitroaromatic compounds: DFT study

    Microsoft Academic Search

    Juxiang Shao; Xinlu Cheng; Xiangdong Yang

    2006-01-01

    The C?NO2 bond dissociation energies in nitrobenzene; 3-amino-nitrobenze; 4-amino-nitrobenze; 1,3-dinitrobenzene; 1,4-dinitrobenzene;\\u000a 2-methyl-nitrobenzene; 4-methyl-nitrobenzene; and 1,3,5-trinitrobenzene nitroaromatic molecules, are computed using B3LYP,\\u000a B3PW91, B3P86 three-parameter hybrid Density Functional Theory (DFT) methods in conjunction with 6-31G** basis set. By comparing the computed energies and experimental ones, it is found that B3P86\\/6-31G** is not capable of predicting the satisfactory bond dissociation energy (BDE).

  6. 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.

  7. 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.

  8. 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.

  9. 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}.

  10. Bond Dissociation Free Energies (BDFEs) of the Acidic H-A Bonds in HA(*)(-) Radical Anions by Three Different Pathways.

    PubMed

    Zhao, Yongyu; Bordwell, Frederick G.

    1996-09-20

    Cleavage of radical anions, HA(*)(-), have been considered to give either H(*) + A(-) (path a) or H(-) + A(*) (path b), and factors determining the preferred mode of cleavage have been discussed. It is conceivable that cleavage to give a proton and a radical dianion, HA(*)(-) right harpoon over left harpoon H(+) + A(*)(2)(-) (path c), might also be feasible. A method, based on a thermodynamic cycle, to estimate the bond dissociation free energy (BDFE) by path c has been devised. Comparison of the BDFEs for cleavage of the radical anions derived from 24 nitroaromatic OH, SH, NH, and CH acids by paths a, b, c has shown that path c is favored thermodynamically. PMID:11667531

  11. Equilibrium Acidities and Homolytic Bond Dissociation Energies of Acidic C H Bonds in Alpha-Arylacetophenones and Related Compounds

    SciTech Connect

    Alnajjar, Mikhail S.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB); Zhang, Xian-Man (Pacific Northwest National Laboratory) [Pacific Northwest National Laboratory; Gleicher, Gerald J.(VISITORS) [VISITORS; Truksa, Scott V.(VISITORS) [VISITORS; Franz, James A.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB)

    2002-12-13

    The equilibrium acidities (pKAHs) and the oxidation potentials of the conjugate anions (Eox(A?{approx})s) were determined in dimethyl sulfoxide (DMSO) for eight ketones of the structure GCOCH3 and twenty of the structure RCOCH2G, (where R= alkyl, phenyl and G= alkyl, aryl). The homolytic bond dissociation energies (BDEs) for the acidic C H bonds of the ketones were estimated using the equation, BDEAH= 1.37pKAH+ 23.1Eox(A?{approx})+ 73.3. While the equilibrium acidities of GCOCH3 were found to be dependent on the remote substituent G, the BDE values for the C H bonds remained essentially invariant (93.5+ 0.5 kcal/mol). A linear correlation between pKAH values and (Eox(A?{approx})s) was found for the ketones. For RCOCH2G ketones, both pKAH and BDE values for the adjacent C-H bonds are sensitive to the nature of the substituent G. However, the steric bulk of the aryl group tends to exert a leveling effect on BDE's. The BDE of?p-9-anthracenylacetophenone is higher than that of??-2-anthracenylacetophenone by 3 kcal/mole, reflecting significant steric inhibition of resonance in the 9-substituted system. A range of 80.7 - 84.4 kcal/mole is observed for RCOCH2G ketones. The results are discussed in terms of solvation, steric, and resonance effects. Ab initio density functional theory (DFT) calculations are employed to illustrate the effect of steric interactions on radical and anion geometries. The DFT results parallel the trends in the experimental BDEs of??-arylacetophenones.

  12. A theory for calculating the surface-adsorbate bond dissociation energy from collision-induced desorption threshold measurements

    NASA Astrophysics Data System (ADS)

    Szulczewski, Gregory; Levis, Robert J.

    1993-04-01

    A model is presented for determining the bond dissociation energy, D0, of a surface-adsorbate complex from collision-induced desorption measurements. D0 is calculated from the minimum collision energy required for desorption by correcting for two energy transfer events using a model based on classical mechanics. The model is tested with measurements made for the CH4/Ni{111} system [Beckerle et al., J. Chem. Phys. 93, 4047 (1990)] and a D0 of 118 meV is found.

  13. 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.

  14. Thermal chemiluminescence from ?-irradiated polytetrafluoroethylene and its emission mechanism: Kinetic analysis and bond dissociation energy of fluoroperoxide group

    NASA Astrophysics Data System (ADS)

    Yamada, Emi; Noguchi, Tsuyoshi; Akai, Nobuyuki; Ishii, Hiroshi; Satoh, Chikahiro; Hironiwa, Takayuki; Millington, Keith R.; Nakata, Munetaka

    2014-11-01

    Temperature dependence of the time evolution of chemiluminescence intensity from ?-irradiated polytetrafluoroethylene was examined by heating isothermally in the range of 150 and 200 C. Kinetic analysis was carried out to estimate the rate constants, from which the dissociation energy of the Osbnd O bond in the fluoroperoxide group was determined to be 97 4 kJ mol-1, being consistent with the corresponding value for small fluorocarbon model systems obtained by quantum chemical calculations. This strongly supports the emission mechanism [sbnd CF(OOF)sbnd CF2sbnd ? sbnd COsbnd CF2sbnd + OF2 + h?] proposed in our previous paper to explain chemiluminescence from the ?-irradiated polytetrafluoroethylene.

  15. Gas-Phase and Solution-Phase Homolytic Bond Dissociation Energies of H-N(+) Bonds in the Conjugate Acids of Nitrogen Bases.

    PubMed

    Liu, Wei-Zhong; Bordwell, Frederick G.

    1996-07-12

    The oxidation potentials of 19 nitrogen bases (abbreviated as B: six primary amines, five secondary amines, two tertiary amines, three anilines, pyridine, quinuclidine, and 1,4-diazabicyclo[2,2,2]octane), i.e., E(ox)(B) values in dimethyl sulfoxide (DMSO) and/or acetonitrile (AN), have been measured. Combination of these E(ox)(B) values with the acidity values of the corresponding acids (pK(HB)(+)) in DMSO and/or AN using the equation: BDE(HB)(+) = 1.37pK(HB)(+) + 23.1 E(ox)(B) + C (C equals 59.5 kcal/mol in AN and 73.3 kcal/mol in DMSO) gave estimates of solution phase homolytic bond dissociation energies of H-B(+) bonds. Gas-phase BDE values of H-B(+) bonds were estimated from updated proton affinities (PA) and adiabatic ionization potentials (aIP) using the equation, BDE(HB(+))(g) = PA + aIP - 314 kcal/mol. The BDE(HB)(+) values estimated in AN were found to be 5-11 kcal/mol higher than the corresponding gas phase BDE(HB(+))(g) values. These bond-strengthening effects in solution are interpreted as being due to the greater solvation energy of the HB(+) cation than that of the B(+*) radical cation. PMID:11667411

  16. 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.

  17. 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

  18. Homolytic bond dissociation energies for C-H bonds adjacent to sulfur and aromatic moieties: The effects of substituents of C-H bond strengths of the benzylic positions in coal model compounds

    SciTech Connect

    Alnajjar, M.S.; Franz, J.A. [Pacific Northwest Lab., Richland, WA (United States); Gleicher, G.J.; Truksa, S. [Oregon State Univ., Corvallis, OR (United States). Dept. of Chemistry; Bordwell, F.; Zhang, Xian-Man [Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry

    1993-09-01

    Sulfur-containing compounds are precursors for thiyl radicals at coal liquefaction temperatures due to the weakness of The and S-S bonds. Thiyl radicals play important roles in hydrogen atom shuttling between benzylic positions and catalyze the cleavage and the formation of strong C-C bonds. Although many reactions of thiyl and other sulfur-containing radicals are qualitatively understood, the homolytic bond dissociation energies (EDE`s) and the thermochemistry associated with many key high molecular weight hydrocarbon and sulfur-containing organic structures important to coal is lacking because they are inappropriate for gas-phase techniques. The measurement of BDE`s has been proven to be difficult even in the simplest of molecules.

  19. 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.

  20. Study of the kinetics of the gas-phase, iodine catalyzed elimination of HBr from isobutylbromide: the tertiary C-H bond dissociation energy in isobutylbromide.

    E-print Network

    Jirustithipong, Pongsiri

    1975-01-01

    STUDY OF THE KINETICS OF THE GAS-PHASE, IODINE CATALYZED ELIMINATION OF HBr FROM ISOBUTYLBROMIDE THE TERTIARY C H BOND DISSOCIATION ENERGY IN ISOBUTYLBROMIDE. A Thesis by PONGSIRI JIRUSTITHIPONG Submitted to the Graduate College of Texas A...&M University in partial fulfillment of the -equi rement for the degree of MASTER OF SCIENCE August 1975 Major Subject: Chemi-. try STUDY OF THE KINETICS OF THE GAS-PHASE, IODINE CATALYZED ELIMINATION OF HBr FROiM ISOBUTYLBROMIDE; THE TERTIARY C-H BOND...

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

    NASA Astrophysics Data System (ADS)

    Carta, V.; Ciccioli, A.; Gigli, G.

    2014-02-01

    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_0, 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_0, 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.

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

    SciTech Connect

    DiLabio, Gino A., E-mail: Gino.DiLabio@nrc.ca [National Institute for Nanotechnology, National Research Council of Canada, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9 (Canada); Department of Chemistry, University of British Columbia, Okanagan, 3333 University Way, Kelowna, British Columbia V1V 1V7 (Canada); Koleini, Mohammad [National Institute for Nanotechnology, National Research Council of Canada, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9 (Canada) [National Institute for Nanotechnology, National Research Council of Canada, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9 (Canada); Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4 (Canada)

    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.

  3. 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.

  4. Mechanical switching and coupling between two dissociation pathways in a P-selectin adhesion bond

    E-print Network

    Peterson, Ellengene

    Mechanical switching and coupling between two dissociation pathways in a P-selectin adhesion bond energy barrier. Using a sensitive force probe to test the leukocyte adhesion bond P-selectin glycoprotein bonds exhibit a mechanical strength that increases in proportion to the logarithm of the rate of force

  5. 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 [Department of Chemistry, University of Ioannina, Ioannina 45110 (Greece); Lesar, Antonija [Department of Physical and Organic Chemistry, Joef Stefan Institute, Jamova 39, SI-1000, Ljubljana (Slovenia)

    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.

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

    SciTech Connect

    Meer, R. van; Gritsenko, O. V. [Faculty of Exact Sciences, Theoretical Chemistry, VU University, Amsterdam (Netherlands) [Faculty of Exact Sciences, Theoretical Chemistry, VU University, Amsterdam (Netherlands); WCU Program, Dep. of Chemistry, Pohang Univ. of Science and Techn., Pohang (Korea, Republic of); Baerends, E. J. [Faculty of Exact Sciences, Theoretical Chemistry, VU University, Amsterdam (Netherlands) [Faculty of Exact Sciences, Theoretical Chemistry, VU University, Amsterdam (Netherlands); WCU Program, Dep. of Chemistry, Pohang Univ. of Science and Techn., Pohang (Korea, Republic of); Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia)

    2014-01-14

    Time dependent density matrix functional theory in its adiabatic linear response formulation delivers exact excitation energies ?{sub ?} and oscillator strengths f{sub ?} for two-electron systems if extended to the so-called phase including natural orbital (PINO) theory. The Lwdin-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 Lwdin-Shull wavefunction to the N-electron case informs about the phase information. In this paper, applications of this extended Lwdin-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 ?{sub ?}(R) curves along the bond dissociation coordinate R for the molecules LiH, Li{sub 2}, 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.

  7. Highly Selective Dissociation of a Peptide Bond Following Excitation of Core Electrons.

    PubMed

    Lin, Yi-Shiue; Tsai, Cheng-Cheng; Lin, Huei-Ru; Hsieh, Tsung-Lin; Chen, Jien-Lian; Hu, Wei-Ping; Ni, Chi-Kung; Liu, Chen-Lin

    2015-06-18

    The controlled breaking of a specific chemical bond with photons in complex molecules remains a major challenge in chemistry. In principle, using the K-edge absorption of a particular atomic element, one might excite selectively a specific atomic entity in a molecule. We report here highly selective dissociation of the peptide bonds in N-methylformamide and N-methylacetamide on tuning the X-ray wavelength to the K-edge absorption of the atoms connected to (or near) the peptide bond. The high selectivity (56-71%) of this cleavage arises from the large energy shift of X-ray absorption, a large overlap of the 1s orbital and the valence ?* orbital that is highly localized on a peptide bond with antibonding character, and the relatively low bond energy of the peptide bonds. These characteristics indicate that the high selectivity on bond dissociation following core excitation could be a general feature for molecules containing peptide bonds. PMID:25988354

  8. Strong-field dissociative ionization of a linear triatomic molecule: Relationship between Coulomb-explosion energies and bond angle

    SciTech Connect

    Zhao, K.; Zhang, G.; Hill, W.T. III [Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742 (United States)

    2003-12-01

    Correlation images of the symmetric six-electron Coulomb-explosion channel of CO{sub 2} were used to isolate specific geometries (linear and bent) for angular-resolved analysis of the Coulomb-explosion energy in the framework of both the critical radius R{sub c} and dynamic screening models. We show that it is possible to connect the R{sub c} and screening pictures through a single parameter, a charge defect {sigma}, which depends on the charge state and the ratio between R{sub c} and the equilibrium bond length. Our data show that R{sub c} and hence {sigma} are slow varying functions of bond angle between 145 deg. and 180 deg. with R{sub c}{approx}4 a.u. and {sigma}{approx}0.5 for the symmetric six-electron channel of CO{sub 2}. In the R{sub c} picture, the experimental value for R{sub c} is consistent with a theoretical value associated with CO{sub 2}{sup 3+}, which is considerably smaller than that associated with CO{sub 2}{sup +}({approx}6 a.u.)

  9. 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

  10. Measuring Bond Energy of an Ionic Compound

    NSDL National Science Digital Library

    2007-08-09

    In this media-rich lesson, students investigate bond energy and the law of conservation of energy. They examine the chemistry behind instant cold packs by using a calorimeter to study the endothermic dissociation of ammonium chloride in water.

  11. 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 Brnsted 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.

  12. Three methods to measure RH bond energies

    SciTech Connect

    Berkowitz, J. [Argonne National Lab., IL (United States); Ellison, G.B. [Univ. of Colorado, Boulder, CO (United States). Dept. of Chemistry and Biochemistry; Gutman, D. [Catholic Univ. of America, Washington, DC (United States). Dept. of Chemistry

    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.

  13. Thermochemical properties and bond dissociation energies of C3-C5 cycloalkyl hydroperoxides and peroxy radicals: cycloalkyl radical + (3)O2 reaction thermochemistry.

    PubMed

    Auzmendi-Murua, Itsaso; Bozzelli, Joseph W

    2012-07-19

    Cyclic aliphatic hydrocarbons are major components in modern fuels; they can be present in the reactants, and they can be formed during the gas-phase oxidation processes. In combustion and thermal oxidation processes, these cyclics will form radicals that react with (3)O(2) to form peroxy radicals. In this study, density functional theory and higher level ab initio calculations are used to calculate thermochemical properties and bond dissociation energies of 3-5-membered cycloalkanes, corresponding hydroperoxides, hydroperoxycycloalkyl radicals, and cycloalkyl radicals that occur in these reaction systems. Geometries, vibration frequencies, and thermochemical properties, ?H(f 298), are calculated with the B3LYP/6-31 g(d,p), B3LYP/6-31 g(2d,2p), composite CBS-QB3, and G3MP2B3 methods. Standard enthalpies of formation at 298 K are evaluated using isodesmic reaction schemes with several work reactions for each species. Group additivity contributions are developed, and application of group additivity with comparison to calculated values is illustrated. Entropy and heat capacities, S(T) and C(p)(T) (5 K ? T ? 5000), are determined using geometric parameters and frequencies from the B3LYP/6-31 g(d,p) calculations. PMID:22779400

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

    SciTech Connect

    Tuttle, B. [Department of Physics, University of Illinois, Urbana, Illinois 61801 (United States)] [Department of Physics, University of Illinois, Urbana, Illinois 61801 (United States); Van de Walle, C.G. [Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, California 94304 (United States)] [Xerox Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, California 94304 (United States)

    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}

  15. 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.

  16. 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

  17. Active Thermochemical Tables: Sequential Bond Dissociation Enthalpies of Methane, Ethane, and Methanol and the Related Thermochemistry.

    PubMed

    Ruscic, Branko

    2015-07-16

    Active Thermochemical Tables (ATcT) thermochemistry for the sequential bond dissociations of methane, ethane, and methanol systems were obtained by analyzing and solving a very large thermochemical network (TN). Values for all possible C-H, C-C, C-O, and O-H bond dissociation enthalpies at 298.15 K (BDE298) and bond dissociation energies at 0 K (D0) are presented. The corresponding ATcT standard gas-phase enthalpies of formation of the resulting CHn, n = 4-0 species (methane, methyl, methylene, methylidyne, and carbon atom), C2Hn, n = 6-0 species (ethane, ethyl, ethylene, ethylidene, vinyl, ethylidyne, acetylene, vinylidene, ethynyl, and ethynylene), and COHn, n = 4-0 species (methanol, hydroxymethyl, methoxy, formaldehyde, hydroxymethylene, formyl, isoformyl, and carbon monoxide) are also presented. The ATcT thermochemistry of carbon dioxide, water, hydroxyl, and carbon, oxygen, and hydrogen atoms is also included, together with the sequential BDEs of CO2 and H2O. The provenances of the ATcT enthalpies of formation, which are quite distributed and involve a large number of relevant determinations, are analyzed by variance decomposition and discussed in terms of principal contributions. The underlying reasons for periodic appearances of remarkably low and/or unusually high BDEs, alternating along the dissociation sequences, are analyzed and quantitatively rationalized. The present ATcT results are the most accurate thermochemical values currently available for these species. PMID:25760799

  18. Combustion pathways of the alkylated heteroaromatics: bond dissociation enthalpies and alkyl group fragmentations

    SciTech Connect

    Hayes, C.J.; Hadad, C.M. [Ohio State University, Columbus, OH (United States). Dept. of Chemistry

    2009-11-15

    The bond dissociation enthalpies (BDEs) of the alkyl groups of the alkyl-substituted heterocycles have been studied and compiled using DFT methodology, with the intent of modeling the larger heterocyclic functionalities found in coal. DFT results were calibrated against CBS-QB3 calculations, and qualitative trends were reproduced between these methods. Loss of hydrogen at the benzylic position provided the most favorable route to radical formation, for both the azabenzenes and five-membered heterocycles. The ethyl derivatives had lower BDE values than the methyl derivatives due to increased stabilization of the corresponding radicals. Calculated spin densities correlated well with bond dissociation enthalpies for these compounds, while geometric effects were minimal with respect to the heterocycles themselves. Temperature effects on the bond dissociation enthalpies were minor, ranging by about 5 kcal/mol from 298 to 2000 K; the free energies of reaction dropped significantly over the same range due to entropic effects. Monocyclic heteroaromatic rings were seen to replicate the chemistry of multicyclic heteroaromatic systems.

  19. Time-resolved EPR and laser photolysis investigations of photoinduced ?-bond dissociation in an aromatic carbonyl compound having triplet ?,?* character

    NASA Astrophysics Data System (ADS)

    Yamaji, Minoru; Inomata, Susumu; Nakajima, Satoru; Akiyama, Kimio; Tero-Kubota, Shozo; Tobita, Seiji; Marciniak, Bronislaw

    2006-01-01

    Photochemical properties of photoinduced ?-bond dissociation in p-phenylbenzoylbenzyl phenyl sulfide (PPS) having the lowest triplet state (T 1) of ?,?* character in solution were investigated by time-resolved EPR and laser flash photolysis techniques. PPS was found to undergo photoinduced ?-bond cleavage in the excited lowest singlet state (S 1(n,?*)) with a quantum yield ( ?rad) of 0.15 for the radical formation, which was independent of excitation wavelengths. Based on the facts of the observation of the absorption spectrum of triplet PPS upon triplet sensitization of xanthone, and absence of CIDEP signal, ?-cleavage was shown to be absent in the T 1(?,?*) state of PPS. Considering the electronic character of the excited and dissociative states of PPS, a schematic energy diagram for the ?-bond dissociation of PPS was shown.

  20. 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.

  1. 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

  2. Energy pulse bonding

    NASA Technical Reports Server (NTRS)

    Smith, G. C.

    1972-01-01

    To eliminate many of the present termination problems a technique called energy pulse bonding (EPB) was developed. The process demonstrated the capability of: (1) joining conductors without prior removal of insulations, (2) joining conductors without danger of brittle intermetallics, (3) increased joint temperature capability, (4) simultaneous formation of several bonds, (5) capability of higher joint density, and (6) a production oriented process. The following metals were successfully bonded in the solid state: copper, beryllium copper, phosphor bronze, aluminum, brass, and Kovar.

  3. 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

  4. Bond-Selective Dissociation of Polyatomic Cations in Mid-Infrared Strong Fields

    E-print Network

    Schlegel, H. Bernhard

    Bond-Selective Dissociation of Polyatomic Cations in Mid-Infrared Strong Fields Suk Kyoung Lee, H, Michigan 48202, United States ABSTRACT: Strong field-induced dissociation by intense mid-infrared pulses of cations by intense mid-infrared laser fields. 1. INTRODUCTION Unimolecular reactions are essential

  5. O-H bond dissociation enthalpies in oximes: order restored.

    PubMed

    Pratt, Derek A; Blake, Jessie A; Mulder, Peter; Walton, John C; Korth, Hans-Gert; Ingold, Keith U

    2004-09-01

    The O-H bond dissociation enthalpies (BDEs) of 13 oximes, RR'C=NOH, having R and/or R' = H, alkyl, and aryl are reported. Experimental anchor points used to validate the results of theoretical calculations include (1) the O-H BDEs of (t-Bu)2C=NOH, t-Bu(i-Pr)C=NOH, and t-Bu(1-Ad)C=NOH determined earlier from the heat released in the reaction of (t-Bu)2C=NO* with (PhNH)2 in benzene and EPR spectroscopy (Mahoney, L. R.; Mendenhall, G. D.; Ingold, K. U. J. Am. Chem. Soc. 1973, 95, 8610), all of which were decreased by 1.7 kcal/mol to reflect a revision to the heat of formation of (E)-azobenzene (which has significant ramifications for other BDEs) and to correct for the heat of hydrogen bonding of (t-Bu)2C=NOH (alphaH2 = 0.43 measured in this work) to benzene, and (2) the measured rates of thermal decomposition of six RR'C=NOCH2Ph at 423 or 443 K, which were used to derive O-H BDEs for the corresponding RR'C=NOH. Claims (Bordwell, F. G.; Ji, G. Z. J. Org. Chem. 1992, 57, 3019; Bordwell, F. G.; Zhang, S. J. Am. Chem. Soc. 1995, 117, 4858; and Bordwell, F. G.; Liu, W.-Z. J. Am. Chem. Soc. 1996, 118, 10819) that the O-H BDEs in mono- and diaryloximes are significantly lower than those for alkyloximes due to delocalization of the unpaired electron into the aromatic ring have always been inconsistent with the known structures of iminoxyl radicals as are the purported perpendicular structures, i.e., phi(Calpha-C=N-O*) = 90 degrees, for sterically hindered dialkyl iminoxyl radicals. The present results confirm the 1973 conclusion that simple steric effects, not electron delocalization or dramatic geometric changes, are responsible for the rather small differences in oxime O-H BDEs. PMID:15327325

  6. Computational Study of Bond Dissociation Enthalpies for Lignin Model Compounds. Substituent Effects in Phenethyl Phenyl Ethers

    SciTech Connect

    Beste, Ariana [ORNL; Buchanan III, A C [ORNL

    2009-01-01

    Lignin is an abundant natural resource that is a potential source of valuable chemicals. Improved understanding of the pyrolysis of lignin occurs through the study of model compounds for which phenethyl phenyl ether (PhCH2CH2OPh, PPE) is the simplest example representing the dominant -O-4 ether linkage. The initial step in the thermal decomposition of PPE is the homolytic cleavage of the oxygen-carbon bond. The rate of this key step will depend on the bond dissociation enthalpy, which in turn will depend on the nature and location of relevant substituents. We used modern density functional methods to calculate the oxygen-carbon bond dissociation enthalpies for PPE and several oxygen substituted derivatives. Since carbon-carbon bond cleavage in PPE could be a competitive initial reaction under high temperature pyrolysis conditions, we also calculated substituent effects on these bond dissociation enthalpies. We found that the oxygen-carbon bond dissociation enthalpy is substantially lowered by oxygen substituents situated at the phenyl ring adjacent to the ether oxygen. On the other hand, the carbon-carbon bond dissociation enthalpy shows little variation with different substitution patterns on either phenyl ring.

  7. 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.

  8. Electronic Spectrum and Dissociation Energy of Fluorine

    Microsoft Academic Search

    A. L. G. Rees

    1957-01-01

    The continuous absorption spectrum of molecular fluorine and the Raman displacement for the 0?1 vibrational transition have been used to compute the potential energy curve for the repulsive 1&Pgr;u state dissociating to two normal fluorine atoms. This curve is consistent with a value of 37.10.85 kcal mole1 for the dissociation energy of the ground state. A weak absorption, attributed, on

  9. Substituent effects on Ni-S bond dissociation energies and kinetic stability of nickel arylthiolate complexes supported by a bis(phosphinite)-based pincer ligand.

    PubMed

    Zhang, Jie; Adhikary, Anubendu; King, Krista M; Krause, Jeanette A; Guan, Hairong

    2012-07-14

    Pincer complexes of the type [2,6-(R(2)PO)(2)C(6)H(3)]NiSC(6)H(4)Z (R = Ph and i-Pr; Z = p-OCH(3), p-CH(3), H, p-Cl, and p-CF(3)) have been synthesized from [2,6-(R(2)PO)(2)C(6)H(3)]NiCl and sodium arylthiolate. X-ray structure determinations of these thiolate complexes have shown a somewhat constant Ni-S bond length (approx. 2.20 ) but an almost unpredictable orientation of the thiolate ligand. Equilibrium constants for various thiolate exchange (between a nickel thiolate complex and a free thiol, or between two different nickel thiolate complexes) reactions have been measured. Evidently, the thiolate ligand with an electron-withdrawing substituent prefers to bond with "[2,6-(Ph(2)PO)(2)C(6)H(3)]Ni" rather than "[2,6-(i-Pr(2)PO)(2)C(6)H(3)]Ni", and bonds least favourably with hydrogen. The reactions of the thiolate complexes with halogenated compounds such as PhCH(2)Br, CH(3)I, CCl(4), and Ph(3)CCl have been examined and several mechanistic pathways have been explored. PMID:22552578

  10. Photodissociation Dynamics of Thiophenol-d1: The Nature of Excited Electronic States along the SD Bond Dissociation Coordinate

    Microsoft Academic Search

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

    2009-01-01

    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 states of the phenylthiyl radical (C6H5S) are observed in the D+ image at high and low kinetic energy regions, respectively. The partitioning of

  11. 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

  12. Correct description of the bond dissociation limit without breaking spin symmetry by a random-phase-approximation correlation functional.

    PubMed

    Hesselmann, Andreas; Grling, Andreas

    2011-03-01

    A correlation functional that is termed exact-exchange random phase approximation (EXX-RPA) functional and is obtained with the exact frequency-dependent exchange kernel via the fluctuation-dissipation theorem is shown to correctly describe electron pair bonds in the dissociation limit without the need to resort to symmetry breaking in spin space. Because the functional also yields more accurate electronic energies for molecules in their equilibrium geometry than standard correlation functionals, it combines accuracy at equilibrium bond distances and in dissociation processes with a correct description of spin, something all commonly employed correlation functionals fail to do. The reason why the EXX-RPA correlation functional yields distinctively and qualitatively better results than RPA approaches based on Hartree-Fock and time-dependent Hartree-Fock is explained. PMID:21405619

  13. Origin of the correlation of the rate constant of substrate hydroxylation by nonheme iron(IV)-oxo complexes with the bond-dissociation energy of the C-H bond of the substrate.

    PubMed

    Latifi, Reza; Bagherzadeh, Mojtaba; de Visser, Sam P

    2009-07-01

    Mononuclear nonheme iron containing systems are versatile and vital oxidants of substrate hydroxylation reactions in many biosystems, whereby the rate constant of hydroxylation correlates with the strength of the C-H bond that is broken in the process. The thermodynamic reason behind these correlations, however, has never been established. In this work results of a series of density functional theory calculations of substrate hydroxylation by a mononuclear nonheme iron(IV)-oxo oxidant with a 2 His/1 Asp structural motif analogous to alpha-ketoglutarate dependent dioxygenases are presented. The calculations show that these oxidants are very efficient and able to hydroxylate strong C-H bonds, whereby the hydrogen abstraction barriers correlate linearly with the strength of the C-H bond of the substrate that is broken. These trends have been rationalized using a valence bond (VB) curve-crossing diagram, which explains the correlation using electron transfer mechanisms in the hydrogen abstraction processes. We also rationalized the subsequent reaction step for radical rebound and show that the barrier is proportional to the electron affinity of the iron(III)-hydroxo intermediate complex. It is shown that nonheme iron(IV)-hydroxo complexes have a larger electron affinity than heme iron(IV)-hydroxo complexes and therefore also experience larger radical rebound barriers, which may have implications for product distributions and rearrangement reactions. Thus, detailed comparisons between heme and nonheme iron(IV)-oxo oxidants reveal the fundamental differences in monoxygenation capabilities of these important classes of oxidants in biosystems and synthetic analogues for the first time and enable us to make predictions of experimental processes. PMID:19472231

  14. 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].

  15. The beryllium pentamer: trailing an uneven sequence of dissociation energies.

    PubMed

    Ascik, Peter N; Rugango, Ren; Simmonett, Andrew C; Compaan, Katherine R; Schaefer, Henry F

    2012-04-10

    Recent high-resolution spectroscopic studies by Merritt, Bondybey, and Heaven (Science 2009, 324, 1548) have heightened the anticipation that small beryllium clusters will soon be observed in the laboratory. Beryllium clusters are important discrete models for the theoretical study of metals. The trigonal bipyramidal Be(5) molecule is studied using high-level coupled cluster methods. We obtain the optimized geometry, atomization and dissociation energies, and vibrational frequencies. The c~CCSDT(Q) method is employed to compute the atomization and dissociation energies. In this approach, complete basis set (CBS) extrapolations at the CCSD(T) level of theory are combined with an additive correction for the effect of iterative triple and perturbative quadruple excitations. Harmonic vibrational frequencies are obtained using analytic gradients computed at the CCSD(T) level of theory. We report an atomization energy of 129.6 kcal mol(-1) at the trigonal bipyramid global minimum geometry. The Be(5)?Be(4)+Be dissociation energy is predicted to be 39.5 kcal mol(-1). The analogous dissociation energies for the smaller beryllium clusters are 64.0 kcal mol(-1) (Be(4)?Be(3)+Be), 24.2 kcal mol(-1) (Be(3)?Be(2)+Be), and 2.7 kcal mol(-1) (Be(2)?Be+Be). The trigonal bipyramidal Be(5) structure has an equatorial-equatorial bond length of 2.000 and an axial-equatorial distance of 2.060 . Harmonic frequencies of 730, 611, 456, 583, 488, and 338 cm(-1) are obtained at the CCSD(T)/cc-pCVQZ level of theory. Quadruple excitations are found to make noticeable contributions to the energetics of the pentamer, which exhibits a significant level of static correlation. PMID:22392888

  16. 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.

  17. Amide-I relaxation-induced hydrogen bond distortion: An intermediate in electron capture dissociation mass spectrometry of ?-helical peptides?

    NASA Astrophysics Data System (ADS)

    Pouthier, Vincent; Tsybin, Yury O.

    2008-09-01

    Electron capture dissociation (ECD) of peptides and proteins in the gas phase is a powerful tool in tandem mass spectrometry whose current description is not sufficient to explain many experimental observations. Here, we attempt to bridge the current understanding of the vibrational dynamics in ?-helices with the recent experimental results on ECD of ?-helical peptides through consideration of amide-I relaxation-induced hydrogen bond distortion. Based on a single spine of H-bonded peptide units, we assume that charge neutralization upon electron capture by a charged ?-helix excites a nearby amide-I mode, which relaxes over a few picoseconds due to Fermi resonances with intramolecular normal modes. The amide-I population plays the role of an external force, which drives the displacements of each peptide unit. It induces a large immobile contraction of the H bonds surrounding the excited site whose lifetime is about the amide-I lifetime. In addition, it creates two lattice deformations describing H bond stretchings, which propagate from the excited region toward both termini of the ?-helix, get reflected at the termini and yield H bond contractions which move back to the excited region. Consequently, we show that H bonds experience rather large contractions whose amplitude depends on general features such as the position of the amide-I mode, the peptide length and the H bond force constants. When an H bond contraction is sufficiently large, it may promote a hydrogen atom transfer between two neighboring peptide units leading to the formation of a radical at charge site remote carbonyl carbon which is known to be a precursor to the rupture of the corresponding N-C? bond. The introduced here way of excitation energy generation and transfer may significantly advance ECD understanding and complement existing ECD mechanisms.

  18. FRONTIERS ARTICLE Imaging bond breaking and vibrational energy transfer in small water

    E-print Network

    Reisler, Hanna

    FRONTIERS ARTICLE Imaging bond breaking and vibrational energy transfer in small water containing it is possible to generate accurate potential energy surfaces (PESs) for small clusters, such as those of water (REMPI) are used to determine accurate bond dissociation energies (D0) of (H2O)2, (H2O)3, HClH2O and NH3

  19. Dissociation energies of some high temperature molecules containing aluminum

    NASA Technical Reports Server (NTRS)

    Stearns, C. A.; Kohl, F. J.

    1972-01-01

    The Knudsen cell mass spectrometric method has been used to investigate the gaseous molecules Al2, AlSi,AlSiO, AlC2, Al2C2, and AlAuC2. Special attention was given to the experimental considerations and techniques needed to identify and to measure ion intensities for very low abundance molecular species. Second- and third-law procedures were used to obtain reaction enthalpies for pressure calibration independent and isomolecular exchange reactions. Dissociation energies for the molecules were derived from the measured ion intensities, free-energy functions obtained from estimated molecular constants, and auxiliary thermodynamic data. The bonding and stability of these aluminum containing molecules are compared with other similar species.

  20. Thermochemical properties and bond dissociation enthalpies of 3- to 5-member ring cyclic ether hydroperoxides, alcohols, and peroxy radicals: cyclic ether radical + (3)O(2) reaction thermochemistry.

    PubMed

    Auzmendi-Murua, Itsaso; Bozzelli, Joseph W

    2014-05-01

    The formation of cyclic ethers is a major product in the oxidation of hydrocarbons, and the oxidation of biomass derived alcohols. Cyclic ethers are formed in the initial reactions of alkyl radicals with dioxygen in combustion and precombustion processes that occur at moderate temperatures. They represent a significant part of the oxygenated pollutants found in the exhaust gases of engines. Cyclic ethers can also be formed from atmospheric reactions of olefins. Additionally, cyclic ethers have been linked to the formation of the secondary organic aerosol (SOA) in the atmosphere. In combustion and thermal oxidation processes these cyclic ethers will form radicals that react with (3)O2 to form peroxy radicals. Density functional theory and higher level ab initio calculations are used to calculate thermochemical properties and bond dissociation enthalpies of 3 to 5 member ring cyclic ethers (oxirane, yC2O, oxetane, yC3O, and oxolane, yC4O), corresponding hydroperoxides, alcohols, hydroperoxy alkyl, and alkyl radicals which are formed in these oxidation reaction systems. Trends in carbon-hydrogen bond dissociation energies for the ring and hydroperoxide group relative to ring size and to distance from the ether group are determined. Bond dissociation energies are calculated for use in understanding effects of the ether oxygen in the cyclic ethers, their stability, and kinetic properties. Geometries, vibration frequencies, and enthalpies of formation, ?Hf,298, are calculated at the B3LYP/6-31G(d,p), B3LYP/6-31G(2d,2p), the composite CBS-QB3, and G3MP2B3 methods. Entropy and heat capacities, S(T) and Cp(T) (5 K ? T ? 5000), are determined using geometric parameters and frequencies from the B3LYP/6-31G(d,p) calculations. The strong effects of ring strain on the bond dissociation energies in these peroxy systems are also of fundamental interest. Oxetane and oxolane exhibit a significant stabilization, 10 kcal mol(-1), lower ?fH298 when an oxygen group is on the ether carbon relative to the isomer with the oxygen group on a secondary carbon. Relative to alkane systems the ether oxygen decreases bond dissociation energies (BDEs) on carbon sites adjacent to the ether by ?5 kcal mol(-1), and increases BDEs on nonether carbons ?1 kcal mol(-1). The cyclic structures have significant effects on the C-H, CO-OH, COO-H, and CO-H bond dissociation enthalpies. These values can be used to help calibrate calculations of larger more complex bicyclic and tricyclic hydrocarbon and ether species. PMID:24660891

  1. A Initio Study of Cluster Molecules Relevant to Materials Science and Astrophysics: Development of Combined Bond-Polarization Basis Sets for the Accurate AB Initio Calculation of Dissociation Energies

    Microsoft Academic Search

    Jan M. L. Martin

    1991-01-01

    The current state (December 1990) of ab initio theory is reviewed, with special emphasis on electron correlation methods. A new family of Gaussian basis sets, the 'combined bond-polarization' basis sets, is introduced. Relative to common large basis sets, binding energies can be computed either with comparable accuracy (+\\/-2 kcal\\/mol) at much reduced computational cost, or with much greater accuracy (+\\/-0.12

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

    SciTech Connect

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

    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.

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

    E-print Network

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

    2015-01-01

    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...

  4. 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.

  5. 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

  6. H-atom high-n Rydberg time-of-flight spectroscopy of CH bond fission in acrolein dissociated at 193 nm

    Microsoft Academic Search

    B. F. Parsons; D. E. Szpunar; L. J. Butler

    2002-01-01

    The experiments presented in this work use H-atom high-n Rydberg time-of-flight spectroscopy to measure the H-atom velocity distribution from one- and multiple-photon dissociation processes in acrolein following excitation at 193 nm. The one-photon H-atom signal is dominated by primary CH bond fission in acrolein. We compare some of the qualitative features of the recoil translational energy distribution for the observed

  7. H-atom high-n Rydberg time-of-flight spectroscopy of CH bond fission in acrolein dissociated at 193 nm

    Microsoft Academic Search

    B. F. Parsons; D. E. Szpunar; L. J. Butler

    2002-01-01

    The experiments presented in this work use H-atom high-n Rydberg time-of-flight spectroscopy to measure the H-atom velocity distribution from one- and multiple-photon dissociation processes in acrolein following excitation at 193 nm. The one-photon H-atom signal is dominated by primary C-H bond fission in acrolein. We compare some of the qualitative features of the recoil translational energy distribution for the observed

  8. 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.

  9. H-atom high-n Rydberg time-of-flight spectroscopy of CH bond fission in acrolein dissociated at 193 nm

    E-print Network

    Butler, Laurie J.

    H-atom high-n Rydberg time-of-flight spectroscopy of CH bond fission in acrolein dissociated-atom velocity distribution from one- and multiple-photon dissociation processes in acrolein following excitation at 193 nm. The one-photon H-atom signal is dominated by primary CH bond fission in acrolein. We compare

  10. 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.

  11. Accurate bond dissociation enthalpies of popular antioxidants predicted by the ONIOM-G3B3 method

    Microsoft Academic Search

    Min-Jie Li; Lei Liu; Yao Fu; Qing-Xiang Guo

    2007-01-01

    Radical-scavenging antioxidants play vital roles in the prevention of oxidative damage caused by free radicals, which is involved in many important chemical and biological processes. Using the ONIOM-G3B3 method, the bond dissociation enthalpies (BDEs) of coenzyme Q, flavonoids, olives, curcumins, indolinonic hydroxylamines, phenothiazines, edaravones and antioxidants used as food additives are predicted in the present study. On the basis of

  12. Combined use of ion mobility and collision-induced dissociation to investigate the opening of disulfide bridges by electron-transfer dissociation in peptides bearing two disulfide bonds.

    PubMed

    Massonnet, Philippe; Upert, Gregory; Smargiasso, Nicolas; Gilles, Nicolas; Quinton, Loc; De Pauw, Edwin

    2015-05-19

    Disulfide bonds are post-translational modifications (PTMs) often found in peptides and proteins. They increase their stability toward enzymatic degradations and provide the structure and (consequently) the activity of such folded proteins. The characterization of disulfide patterns, i.e., the cysteine connectivity, is crucial to achieve a global picture of the active conformation of the protein of interest. Electron-transfer dissociation (ETD) constitutes a valuable tool to cleave the disulfide bonds in the gas phase, avoiding chemical reduction/alkylation in solution. To characterize the cysteine pairing, the present work proposes (i) to reduce by ETD one of the two disulfide bridges of model peptides, resulting in the opening of the cyclic structures, (ii) to separate the generated species by ion mobility, and (iii) to characterize the species using collision-induced dissociation (CID). Results of this strategy applied to several peptides show different behaviors depending on the connectivity. The loss of SH radical species, observed for all the peptides, confirms the cleavage of the disulfides during the ETD process. PMID:25915795

  13. 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.

  14. Electron Transfer Dissociation Reveals Changes in the Cleavage Frequencies of Backbone Bonds Distant to Amide-to-Ester Substitutions in Polypeptides

    NASA Astrophysics Data System (ADS)

    Hansen, Thomas A.; Jung, Hye R.; Kjeldsen, Frank

    2011-11-01

    Interrogation of electron transfer dissociation (ETD) mass spectra of peptide amide-to-ester backbone bond substituted analogues (depsipeptides) reveals substantial differences in the entire backbone cleavage frequencies. It is suggested that the point permutation of backbone bonds leads to changes in the predominant ion structures by removal/weakening of specific hydrogen bonding. ETD responds to these changes by redistributing the cleavage frequencies of the peptide backbone bonds. In comparison, no distinction between depsi-/peptide was observed using collision-activated dissociation, which is consistent with a general unfolding and elimination of structural information of these ions. These results should encourage further exploration of depsipeptides for gas-phase structural characterization.

  15. Ensemble density functional theory method correctly describes bond dissociation, excited state electron transfer, and double excitations.

    PubMed

    Filatov, Michael; Huix-Rotllant, Miquel; Burghardt, Irene

    2015-05-14

    State-averaged (SA) variants of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, SA-REKS and state-interaction (SI)-SA-REKS, implement ensemble density functional theory for variationally obtaining excitation energies of molecular systems. In this work, the currently existing version of the SA-REKS method, which included only one excited state into the ensemble averaging, is extended by adding more excited states to the averaged energy functional. A general strategy for extension of the REKS-type methods to larger ensembles of ground and excited states is outlined and implemented in extended versions of the SA-REKS and SI-SA-REKS methods. The newly developed methods are tested in the calculation of several excited states of ground-state multi-reference systems, such as dissociating hydrogen molecule, and excited states of donor-acceptor molecular systems. For hydrogen molecule, the new method correctly reproduces the distance dependence of the lowest excited state energies and describes an avoided crossing between the doubly excited and singly excited states. For bithiophene-perylenediimide stacked complex, the SI-SA-REKS method correctly describes crossing between the locally excited state and the charge transfer excited state and yields vertical excitation energies in good agreement with the ab initio wavefunction methods. PMID:25978880

  16. Ensemble density functional theory method correctly describes bond dissociation, excited state electron transfer, and double excitations

    NASA Astrophysics Data System (ADS)

    Filatov, Michael; Huix-Rotllant, Miquel; Burghardt, Irene

    2015-05-01

    State-averaged (SA) variants of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, SA-REKS and state-interaction (SI)-SA-REKS, implement ensemble density functional theory for variationally obtaining excitation energies of molecular systems. In this work, the currently existing version of the SA-REKS method, which included only one excited state into the ensemble averaging, is extended by adding more excited states to the averaged energy functional. A general strategy for extension of the REKS-type methods to larger ensembles of ground and excited states is outlined and implemented in extended versions of the SA-REKS and SI-SA-REKS methods. The newly developed methods are tested in the calculation of several excited states of ground-state multi-reference systems, such as dissociating hydrogen molecule, and excited states of donor-acceptor molecular systems. For hydrogen molecule, the new method correctly reproduces the distance dependence of the lowest excited state energies and describes an avoided crossing between the doubly excited and singly excited states. For bithiophene-perylenediimide stacked complex, the SI-SA-REKS method correctly describes crossing between the locally excited state and the charge transfer excited state and yields vertical excitation energies in good agreement with the ab initio wavefunction methods.

  17. Accurate Calculation of the Dissociation Energy of the Highly Anharmonic System ClHCl(.).

    PubMed

    Stein, Christopher; Oswald, Rainer; Botschwina, Peter; Peterson, Kirk A

    2015-05-28

    Accurate bond dissociation energies (D0) are reported for different isotopologues of the highly anharmonic system ClHCl(-). The mass-independent equilibrium dissociation energy De was obtained by a composite method with frozen-core (fc) CCSD(T) as the basic contribution. Basis sets as large as aug-cc-pV8(+d)Z were employed, and extrapolation to the complete basis set (CBS) limit was carried out. Explicitly correlated calculations with the CCSD(T)-F12b method were also performed to support the conventionally calculated values. Core-core and core-valence correlation, scalar relativity, and higher-order correlation were considered as well. Two mass-dependent contributions, namely, the diagonal Born-Oppenheimer correction and the difference in zero-point energies between the complex and the HCl fragment, were then added in order to arrive at precise D0 values. Results for (35)ClH(35)Cl(-) and (35)ClD(35)Cl(-) are 23.81 and 23.63 kcal/mol, respectively, with estimated uncertainties of 0.05 kcal/mol. In contrast to FHF(-) ( Stein , C. ; Oswald , R. ; Sebald , P. ; Botschwina , P. ; Stoll , H. , Peterson , K. A. Mol. Phys. 2013 , 111 , 2647 - 2652 ), the D0 values of the bichloride species are larger than their De counterparts, which is an unusual situation in hydrogen-bonded systems. PMID:25405989

  18. Evidence for ion irradiation induced dissociation and reconstruction of Si-H bonds in hydrogen-implanted silicon

    SciTech Connect

    Di, Z. F.; Wang, Y. Q.; Nastasi, M. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Shao, L. [Department of Nuclear Engineering, Texas A and M University, 3133 TAMU, College Station, Texas 77843 (United States); Lee, J. K. [Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania 15261 (United States); Theodore, N. D. [Analog and Mixed-Signal Technologies, Freescale Semiconductor Inc., Tempe, Arizona 85284 (United States)

    2008-09-08

    We observe that H-related chemical bonds formed in H-implanted Si will evolve under subsequent ion irradiation. During ion irradiation hydrogen is inclined to dissociate from simple H-related defect complexes (i.e., VH{sub x} and IH{sub x}), diffuse, and attach to vacancy-type defects resulting in new platelet formation, which facilitate surface blistering after annealing, a process completely inhibited in the absence of ion irradiation. The understanding of our results provides insight into the structure and stability of hydrogen-related defects in silicon.

  19. 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.

  20. Distinction among isomeric unsaturated fatty acids as lithiated adducts by electrospray ionization mass spectrometry using low energy collisionally activated dissociation on a triple stage quadrupole instrument

    Microsoft Academic Search

    Fong-Fu Hsu; John Turk

    1999-01-01

    Features of tandem mass spectra of dilithiated adduct ions of unsaturated fatty acids obtained by electrospray ionization\\u000a mass spectrometry with low-energy collisionally activated dissociation (CAD) on a triple stage quadrupole instrument are described.\\u000a These spectra distinguish among isomeric unsaturated fatty acids and permit assignment of double-bond location. Informative\\u000a fragment ions reflect cleavage of bonds remote from the charge site on

  1. Combining liquid chromatography with ozone-induced dissociation for the separation and identification of phosphatidylcholine double bond isomers.

    PubMed

    Kozlowski, Rachel L; Campbell, J Larry; Mitchell, Todd W; Blanksby, Stephen J

    2015-07-01

    Revealing the inherent molecular diversity of lipid biology requires advanced analytical technologies. Distinguishing phospholipids that differ in the position(s) of carbon-carbon double bonds within their acyl chains presents a particular challenge because of their similar chromatographic and mass spectral behaviours. Here-for the first time-we combine reversed-phase liquid chromatography for separation of isomeric phospholipids with on-line mass spectral analysis by ozone-induced dissociation (OzID) for unambiguous double bond position assignment. The customised tandem linear ion-trap mass spectrometer used in our study is capable of acquiring OzID scans on a chromatographic timescale. Resolving the contributions of isomeric lipids that are indistinguishable based on conventional mass spectral analysis is achieved using the combination of liquid chromatography and OzID. Application of this method to the analysis of simple (egg yolk) and more complex (sheep brain) extracts reveals significant populations of the phosphatidylcholine PC 16:0_18:1(n-7) alongside the expected PC 16:0_18:1(n-9) isomer. Graphical Abstract Separation and identification double bond positional isomers of phosphatidylcholines using LC-OzID. PMID:25740545

  2. 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.

  3. 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.

  4. 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.

  5. Equilibrium Acidities and Homolytic Bond Dissociation Enthalpies of the Acidic C-H Bonds in P-(Para-substituted benzyl)triphenylphosphonium Cations and Related Cations.

    PubMed

    Zhang, Xian-Man; Fry, Albert J.; Bordwell, Frederick G.

    1996-06-14

    Equilibrium acidities (pK(HA)) of six P-(para-substituted benzyl)triphenylphosphonium (p-GC(6)H(4)CH(2)PPh(3)(+)) cations, P-allyltriphenylphosphonium cation, P-cinnamyltriphenylphosphonium cation, and As-(p-cyanobenzyl)triphenylarsonium cation, together with the oxidation potentials [E(ox)(A(-))] of their conjugate anions (ylides) have been measured in dimethyl sulfoxide (DMSO) solution. The acidifying effects of the alpha-triphenylphosphonium groups on the acidic C-H bonds in toluene and propene were found to be ca 25 pK(HA) units (34 kcal/mol). Introduction of an electron-withdrawing group such as 4-NO(2), 4-CN, or 4-Br into the para position of the benzyl ring in p-GC(6)H(4)CH(2)PPh(3)(+) cations resulted in an additional acidity increase, but introduction of the 4-OEt electron-donating group decreases the acidity. The equilibrium acidities of p-GC(6)H(4)CH(2)PPh(3)(+) cations were nicely linearly correlated with the Hammett sigma(-) constants of the substituents (G) with a slope of 4.78 pK(HA) units (R(2) = 0.992) (Figure 1). Reversible oxidation potentials of the P-(para-substituted benzyl)triphenylphosphonium ylides were obtained by fast scan cyclic voltammetry. The homolytic bond dissociation enthalpies (BDEs) of the acidic C-H bonds in these cations, estimated by combining their equilibrium acidities with the oxidation potentials of their corresponding conjugate anions, showed that the alpha-Ph(3)P(+) groups have negligible stabilizing or destabilizing effects on the adjacent radicals. The equilibrium acidity of As-(p-cyanobenzyl)triphenylarsonium cation is 4 pK(HA) units weaker than that of P-(p-cyanobenzyl)triphenylphosphonium cation, but the BDE of the acidic C-H bond in As-(p-cyanobenzyl)triphenylarsonium cation is ca 2 kcal/mol higher than that in P-(p-cyanobenzyl)triphenylphosphonium cation. PMID:11667288

  6. Dissociation energy of ekaplutonium fluoride E126F: the first diatomic with molecular spinors consisting of g atomic spinors.

    PubMed

    Malli, Gulzari L

    2006-02-21

    Our ab initio all-electron fully relativistic Dirac-Fock (DF) and nonrelativistic (NR) Hartree-Fock (HF) self-consistent field (SCF) calculations predict the superheavy diatomic ekaplutonium fluoride E126F to be bound with the calculated dissociation energy of 7.44 and 10.46 eV at the predicted E126-F bond lengths of 2.03 and 2.18 Angstroms, respectively. The antibinding effects of relativity to the dissociation energy of E126F are approximately 3 eV. The predicted dissociation energy with both our NR HF and relativistic DF SCF wave functions is fairly large and is comparable to that for very stable diatomics. This is the first case, where in a diatomic, an atom has g orbital (l = 4) occupied in its ground state electronic configuration and such superheavy diatomics would have occupied molecular spinors (orbitals) consisting of g atomic spinors (orbitals). This opens up a whole new field of chemistry where g atomic spinors (orbitals) may be involved in electronic structure and chemical bonding of systems of superheavy elements with Z> or =122. PMID:16497023

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

    SciTech Connect

    Tang, Xiaofeng [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China) [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China); National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029 (China); Zhou, Xiaoguo, E-mail: xzhou@ustc.edu.cn, E-mail: yanbing@jlu.edu.cn; Liu, Shilin [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China) [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China); Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China); Sun, Zhongfa [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China)] [Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China); Liu, Fuyi; Sheng, Liusi [National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029 (China)] [National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029 (China); Yan, Bing, E-mail: xzhou@ustc.edu.cn, E-mail: yanbing@jlu.edu.cn [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China)] [Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012 (China)

    2014-01-28

    Dissociative photoionization of methyl bromide (CH{sub 3}Br) in an excitation energy range of 10.4516.90 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 CBr 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 CBr 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. CBr 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.

  8. Mass spectrometric and theoretical studies on dissociation of the Csbnd S bond in the benzenesulfonic acid and benzenesulfinic acid anion series: Homolytic cleavage vs heterolytic cleavage

    NASA Astrophysics Data System (ADS)

    Zhang, Xiang

    2012-11-01

    The dissociation of the Csbnd S bond in a variety of para-substituted benzenesulfonic acid and benzenesulfinic acid anions has been investigated through the tandem mass spectrometry and density functional theory (DFT). For the Csbnd S bond in the para-substituted benzenesulfonic acid anions, only the homolytic cleavage occurs. DFT calculations indicate that the homolytic cleavage is 14.1 kcal/mol at least less than the heterolytic cleavage in the dissociation enthalpy. On the other hand, for the Csbnd S bond in the para-substituted benzenesulfinic acid anions, both homolytic cleavage and heterolytic cleavage take place. Calculations show that the enthalpy difference between these two cleavage modes is 9.5 kcal/mol at most. It is obvious that DFT calculations are well consistent with the MS/MS experiments.

  9. Autocatalytic cathodic dehalogenation triggered by dissociative electron transfer through a C-HO hydrogen bond.

    PubMed

    Roma?czyk, Piotr P; Rado?, Mariusz; Noga, Klemens; Kurek, Stefan S

    2013-10-28

    A combined action of the C-HOalkoxide hydrogen bonding and Cl?pyrazolyl dispersive interactions facilitates intramolecular electron transfer (ET) in the transient {Mo(I)(NO)(Tp(Me2))(Oalkoxide)}?(-)HCCl3 adduct ([Tp(Me2)](-) = ?(3)-hydrotris(3,5-dimethylpyrazol-1-yl)borate), setting off a radical autocatalytic process, eventually leading to chloroform degradation. In the voltammetric curve, this astonishingly fast process is seen as an almost vertical drop-down. The potential at which it occurs is favorably shifted by ca. 1 V in comparison with uncatalyzed reduction. As predicted by DFT calculations, crucial in the initial step is a close and prolonged contact between the electron donor (Mo(I) 4d-based SOMO) and acceptor (?(*)(C-Cl)-based LUMO). This occurs owing to the exceptionally short (dHO = 1.82 ) and nearly linear C-HOalkoxide bonding, which is reflected by a large ??C-H red-shift of 380 cm(-1) and a noticeable reorganization of electronic density along the H-bond axis. The advantageous noncovalent interactions inside the cavity formed by two pyrazolyl (pz) rings are strengthened during the C-Cl bond elongation coupled with the ET, giving rise to possible transition state stabilization. After the initial period, the reaction proceeds as a series of consecutive alternating direct or Mo(II/I)-mediated electron and proton transfers. Alcohols inhibit the electrocatalysis by binding with the {Mo(I)-Oalkoxide}?(-) active site, and olefins by trapping transient radicals. The proximity and stabilization effects, and competitive inhibition in the studied system may be viewed as analogous to those operating in enzymatic catalysis. PMID:24030591

  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 to or better than the best previous ab initio results can be obtained using the fixed-node quantum Monte Carlo, the dissociation energies are consistent with experimental values. The fixed-node quantum Monte Carlo method can

  11. 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. (NCSU)

    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.

  12. 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.

  13. Theoretical enthalpies of formation and C H bond dissociation enthalpies of n-bromopropane and its free radicals

    NASA Astrophysics Data System (ADS)

    Espinosa-Garca, J.

    2003-08-01

    The enthalpies of formation of n-bromopropane (CH 3CH 2CH 2Br) and its free radicals (CH 2CH 2CH 2Br, CH 3CHCH 2Br and CH 3CH 2CHBr) were estimated by molecular orbital integrated methods using several working chemical reactions with four variants of theoretical approaches (levels) and four extended basis sets. The recommended standard enthalpies of formation are: CH 3CH 2CH 2Br, -19.5 0.6 kcal mol -1, in excellent agreement with the only experimental datum available; CH 2CH 2CH 2Br, 28.7 0.3; CH 3CHCH 2Br, 23.1 1.4; and CH 3CH 2CHBr, 25.7 0.6 kcal mol -1. These enthalpies of formation correspond to bond dissociation enthalpies of D H0298(H- CH 2CH 2CH 2Br)=101.6 1.0; D H0298(CH 3CH-HCH 2Br)=96.0 2.1; and D H0298(CH 3CH 2CHBr-H)=98.6 1.2 kcal mol -1.

  14. Dynamics of N-OH bond dissociation in cyclopentanone and cyclohexanone oxime at 193 nm: laser-induced fluorescence detection of nascent OH (v'', J'').

    PubMed

    Kawade, Monali N; Saha, Ankur; Upadhyaya, Hari P; Kumar, Awadhesh; Naik, Prakash D

    2010-12-01

    Cyclohexanone oxime (CHO) and cyclopentanone oxime (CPO) in the vapor phase undergo N-OH bond scission upon excitation at 193 nm to produce OH, which was detected state selectively employing laser-induced fluorescence. The measured energy distribution between fragments for both oximes suggests that in CHO the OH produced is mostly vibrationally cold, with moderate rotational excitation, whereas in CPO the OH fragment is also formed in v'' = 1 (~2%). The rotational population of OH (v'' = 0, J'') from CHO is characterized by a rotational temperature of 1440 80 K, whereas the rotational populations of OH (v'' = 0, J'') and OH (v'' = 1, J'') from CPO are characterized by temperatures of 1360 90 K and 930 170 K, respectively. A high fraction of the available energy is partitioned to the relative translation of the fragments with f(T) values of 0.25 and 0.22 for CHO and CPO, respectively. In the case of CHO, the ?-doublet states of the nascent OH radical are populated almost equally in lower rotational quantum levels N'', with a preference for ?(+) (A') states for higher N''. However, there is no preference for either of the two spin orbit states ?(3/2) and ?(1/2) of OH. The nascent OH product in CPO is equally distributed in both ?-doublet states of ?(+) (A') and ?(-) (A'') for all N'', but has a preference for the ?(3/2) spin orbit state. Experimental work in combination with theoretical calculations suggests that both CHO and CPO molecules at 193 nm are excited to the S(2) state, which undergoes nonradiative relaxation to the T(2) state. Subsequently, molecules undergo the N-OH bond dissociation from the T(2) state with an exit barrier to produce OH (v'', J''). PMID:21058634

  15. 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

  16. Iridium porphyrins in CD3OD: reduction of Ir(III), CD3-OD bond cleavage, Ir-D acid dissociation and alkene reactions.

    PubMed

    Bhagan, Salome; Imler, Gregory H; Wayland, Bradford B

    2013-04-15

    Methanol solutions of iridium(III) tetra(p-sulfonatophenyl)porphyrin [(TSPP)Ir(III)] form an equilibrium distribution of methanol and methoxide complexes ([(TSPP)Ir(III)(CD3OD)(2-n)(OCD3)n]((3+n)-)). Reaction of [(TSPP)Ir(III) with dihydrogen (D2) in methanol produces an iridium hydride [(TSPP)Ir(III)-D(CD3OD)](4-) in equilibrium with an iridium(I) complex ([(TSPP)Ir(I)(CD3OD)](5-)). The acid dissociation constant of the iridium hydride (Ir-D) in methanol at 298 K is 3.5 10(-12). The iridium(I) complex ([(TSPP)Ir(I)(CD3OD)](5-)) catalyzes reaction of [(TSPP)Ir(III)-D(CD3OD)](4-) with CD3-OD to produce an iridium methyl complex [(TSPP)Ir(III)-CD3(CD3OD)](4-) and D2O. Reactions of the iridium hydride with ethene and propene produce iridium alkyl complexes, but the Ir-D complex fails to give observable addition with acetaldehyde and carbon monoxide in methanol. Reaction of the iridium hydride with propene forms both the isopropyl and propyl complexes with free energy changes (?G 298 K) of -1.3 and -0.4 kcal mol(-1) respectively. Equilibrium thermodynamics and reactivity studies are used in discussing relative Ir-D, Ir-OCD3 and Ir-CD2- bond energetics in methanol. PMID:23540797

  17. 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.

  18. Energy threshold effects in the collisionless dissociation of polyatomic molecules by ir laser radiation

    NASA Technical Reports Server (NTRS)

    Gower, M. C.; Billman, K. W.

    1977-01-01

    The threshold for collisionless dissociation of SF6, SiF4, and CF2Cl2 by focused CO2 laser radiation has been measured. This threshold is a laser pulse energy effect and, within experimental error, is found to be the same for all three gases. Provided collisions cannot occur during the laser pulse, the degree of dissociation produced depends only on the energy in the pulse, which is consistent with simple adiabatic vibrational heating of the molecules by the laser.

  19. July 18, 2012 Using Qualified Energy Conservation Bonds for Public

    E-print Network

    July 18, 2012 Using Qualified Energy Conservation Bonds for Public Building Upgrades: Reducing Energy Bills in the City of Philadelphia Qualified Energy Conservation Bonds (QECBs) are federally conservation projects, including public building upgrades that reduce energy use by at least 20 percent

  20. Ground state potential energy curve and dissociation energy of MgH.

    PubMed

    Shayesteh, Alireza; Henderson, Robert D E; Le Roy, Robert J; Bernath, Peter F

    2007-12-13

    New high-resolution visible emission spectra of the MgH molecule have been recorded with high signal-to-noise ratios using a Fourier transform spectrometer. Many bands of the A 2Pi-->X 2Sigma+ and B' 2Sigma+-->X 2Sigma+ electronic transitions of 24MgH were analyzed; the new data span the v' = 0-3 levels of the A 2Pi and B'2Sigma+ excited states and the v''=0-11 levels of the X 2Sigma+ ground electronic state. The vibration-rotation energy levels of the perturbed A 2Pi and B' 2Sigma+ states were fitted as individual term values, while those of the X 2Sigma+ ground state were fitted using the direct-potential-fit approach. A new analytic potential energy function that imposes the theoretically correct attractive potential at long-range, and a radial Hamiltonian that includes the spin-rotation interaction were employed, and a significantly improved value for the ground state dissociation energy of MgH was obtained. The v''=11 level of the X 2Sigma+ ground electronic state was found to be the highest bound vibrational level of 24MgH, lying only about 13 cm(-1) below the dissociation asymptote. The equilibrium dissociation energy for the X 2Sigma+ ground state of 24MgH has been determined to be De=11104.7+/-0.5 cm(-1) (1.37681+/-0.00006 eV), whereas the zero-point energy (v''=0) is 739.11+/-0.01 cm(-1). The zero-point dissociation energy is therefore D0=10365.6+/-0.5 cm(-1) (1.28517+/-0.00006 eV). The uncertainty in the new experimental dissociation energy of MgH is more than 2 orders of magnitude smaller than that for the best value available in the literature. MgH is now the only hydride molecule other than H2 itself for which all bound vibrational levels of the ground electronic state are observed experimentally and for which the dissociation energy is determined with subwavenumber accuracy. PMID:18020428

  1. Thermochemistry, bond energies, and internal rotor potentials of dimethyl tetraoxide.

    PubMed

    da Silva, Gabriel; Bozzelli, Joseph W

    2007-11-29

    Thermochemical properties of dimethyl tetraoxide (CH(3)OOOOCH(3)), the dimer of the methylperoxy radical, are studied using ab initio and density functional theory methods. Methylperoxy radicals are known to be important intermediates in the tropospheric ozone cycle, and the self-reaction of methylperoxy radicals, which is thought to proceed via dimethyl tetraoxide, leads to significant chain radical termination in this process. Dimethyl tetraoxide has five internal rotors, three of them unique; the potential energy profiles are calculated for these rotors, as well as for those in the CH(3)OO, CH(3)OOO, and CH(3)OOOO radicals. The dimethyl tetraoxide internal rotor profiles show barriers to rotation of 2-8 kcal mol(-1). Using B3LYP/6-31(d) geometries, frequencies, internal rotor potentials, and moments of inertia, we determine entropy and heat capacity values for dimethyl tetraoxide and its radicals. Isodesmic work reactions with the G3B3 and CBS-APNO methods are used; we calculate this enthalpy as -9.8 kcal mol(-1). Bond dissociation energies (BDEs) are calculated for all C-O and O-O bonds in dimethyl tetraoxide, again with the G3B3 and CBS-APNO theoretical methods, and we suggest the following BDEs: 46.0 kcal mol(-1) for CH(3)-OOOOCH(3), 20.0 kcal mol(-1) for CH(3)O-OOOCH(3), and 13.9 kcal mol(-1) for CH(3)OO-OOCH(3). From the BDE calculations and the isodesmic enthalpy of formation for dimethyl tetraoxide, we suggest enthalpies of 2.1, 5.8, and 1.4 kcal mol(-1) for the CH(3)OO, CH(3)OOO, and CH(3)OOOO radicals, respectively. We evaluate the suitability of 10 different density functional theory (DFT) methods for calculating thermochemical properties of dimethyl tetraoxide and its radicals with the 6-31G(d) and 6-311++G(3df,3pd) basis sets, using a variety of work reaction schemes. Overall, the best-performed DFT methods of those tested were TPSSh, BMK, and B1B95. Significant improvements in accuracy were made by moving from atomization to isodesmic work reactions, with most DFT methods yielding errors of less than 2 kcal mol(-1) with the 6-311++G(3df,3pd) basis set for isodesmic calculations on the dimethyl tetraoxide enthalpy. These isodesmic calculations were basis set consistent, with a considerable reduction in error found by using the 6-311++G(3df,3pd) basis set over the 6-31G(d) basis set. This was not the case, however, for atomization and bond dissociation work reactions, where the two basis sets returned similar results. Improved group additivity terms for the O-O-O moiety (O/O2 central atom group) are also determined. PMID:17983209

  2. 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; Lpez-Durn, David; Liu, Zongyuan; Ducho?, Tom; Evans, Jaime; Senanayake, Sanjaya D; Crumlin, Ethan J; Matoln, Vladimir; Rodrguez, Jos A; Ganduglia-Pirovano, M Vernica

    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

  3. 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 [Inst. de Catalisis y Petroleoquimica, CSIC, Madrid (Spain); CIC Energigune, Minana, Alava (Spain); Rodriguez, Jose A. [Brookhaven National Lab. (BNL), Upton, NY (United States); Stony Brook Univ., NY (United States); Lopez-Duran, David [Inst. de Catalisis y Petroleoquimica, CSIC, Madrid (Spain); CIC Energigune, Minana, Alava (Spain); Liu, Zongyuan [Brookhaven National Lab. (BNL), Upton, NY (United States); Stony Brook Univ., NY (United States); Duchon, Tomas [Charles Univ., Praha (Czech Republic); Evans, Jaime [Univ. Central de Venezuela, Caracas (Venezuela); Senanayake, Sanjaya D. [Brookhaven National Lab. (BNL), Upton, NY (United States); Crumlin, Ethan J. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Matolin, Vladimir [Charles Univ., Praha (Czech Republic); Ganduglia-Pirovano, M. Veronica [Inst. de Catalisis y Petroleoquimica, CSIC, Madrid (Spain)

    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 Ni? 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.

  4. 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 thismoresupport effect is the ability of ceria to stabilize oxidized Ni? 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

  5. Electron-nuclear energy sharing in above-threshold multiphoton dissociative ionization of H2.

    PubMed

    Wu, J; Kunitski, M; Pitzer, M; Trinter, F; Schmidt, L Ph H; Jahnke, T; Magrakvelidze, M; Madsen, C B; Madsen, L B; Thumm, U; Drner, R

    2013-07-12

    We report experimental observation of the energy sharing between electron and nuclei in above-threshold multiphoton dissociative ionization of H2 by strong laser fields. The absorbed photon energy is shared between the ejected electron and nuclei in a correlated fashion, resulting in multiple diagonal lines in their joint energy spectrum governed by the energy conservation of all fragment particles. PMID:23889391

  6. Breaking the carbon dimer: the challenges of multiple bond dissociation with full configuration interaction quantum Monte Carlo methods.

    PubMed

    Booth, George H; Cleland, Deidre; Thom, Alex J W; Alavi, Ali

    2011-08-28

    The full configuration interaction quantum Monte Carlo (FCIQMC) method, as well as its "initiator" extension (i-FCIQMC), is used to tackle the complex electronic structure of the carbon dimer across the entire dissociation reaction coordinate, as a prototypical example of a strongly correlated molecular system. Various basis sets of increasing size up to the large cc-pVQZ are used, spanning a fully accessible N-electron basis of over 10(12) Slater determinants, and the accuracy of the method is demonstrated in each basis set. Convergence to the FCI limit is achieved in the largest basis with only O[10(7)] walkers within random errorbars of a few tenths of a millihartree across the binding curve, and extensive comparisons to FCI, CCSD(T), MRCI, and CEEIS results are made where possible. A detailed exposition of the convergence properties of the FCIQMC methods is provided, considering convergence with elapsed imaginary time, number of walkers and size of the basis. Various symmetries which can be incorporated into the stochastic dynamic, beyond the standard abelian point group symmetry and spin polarisation are also described. These can have significant benefit to the computational effort of the calculations, as well as the ability to converge to various excited states. The results presented demonstrate a new benchmark accuracy in basis-set energies for systems of this size, significantly improving on previous state of the art estimates. PMID:21895156

  7. Bonding

    MedlinePLUS

    ... is a procedure that uses a tooth-colored composite resin (plastic) to repair a tooth. Bonding can ... cleaned regularly by a dental hygienist. Risks The composite resin used in bonding isn't nearly as ...

  8. Electron-Nuclear Energy Sharing in Above-Threshold Multiphoton Dissociative Ionization of H2

    E-print Network

    Thumm, Uwe

    Electron-Nuclear Energy Sharing in Above-Threshold Multiphoton Dissociative Ionization of H2 J. Wu4], where the photon energy is shared by the freed electrons and the nuclear fragments. For the molecular ionization [1015], and the imaging of inter- nuclear distance using nuclear kinetic energy release spec- tra

  9. Dissociation energies of six NO2 isotopologues by laser induced fluorescence spectroscopy and zero point energy of some triatomic molecules

    Microsoft Academic Search

    G. Michalski; R. Jost; D. Sugny; M. Joyeux; M. Thiemens

    2004-01-01

    We have measured the rotationless photodissociation threshold of six isotopologues of NO2 containing 14N, 15N, 16O, and 18O isotopes using laser induced fluorescence detection and jet cooled NO2 (to avoid rotational congestion). For each isotopologue, the spectrum is very dense below the dissociation energy while fluorescence disappears abruptly above it. The six dissociation energies ranged from 25 128.56 cm-1 for

  10. Probing the Conformational and Functional Consequences of Disulfide Bond Engineering in Growth Hormone by Hydrogen-Deuterium Exchange Mass Spectrometry Coupled to Electron Transfer Dissociation.

    PubMed

    Seger, Signe T; Breinholt, Jens; Faber, Johan H; Andersen, Mette D; Wiberg, Charlotte; Schjdt, Christine B; Rand, Kasper D

    2015-06-16

    Human growth hormone (hGH), and its receptor interaction, is essential for cell growth. To stabilize a flexible loop between helices 3 and 4, while retaining affinity for the hGH receptor, we have engineered a new hGH variant (Q84C/Y143C). Here, we employ hydrogen-deuterium exchange mass spectrometry (HDX-MS) to map the impact of the new disulfide bond on the conformational dynamics of this new hGH variant. Compared to wild type hGH, the variant exhibits reduced loop dynamics, indicating a stabilizing effect of the introduced disulfide bond. Furthermore, the disulfide bond exhibits longer ranging effects, stabilizing a short ?-helix quite distant from the mutation sites, but also rendering a part of the ?-helical hGH core slightly more dynamic. In the regions where the hGH variant exhibits a different deuterium uptake than the wild type protein, electron transfer dissociation (ETD) fragmentation has been used to pinpoint the residues responsible for the observed differences (HDX-ETD). Finally, by use of surface plasmon resonance (SPR) measurements, we show that the new disulfide bond does not compromise receptor affinity. Our work highlight the analytical potential of HDX-ETD combined with functional assays to guide protein engineering. PMID:25978680

  11. 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.

  12. Hyperthermal Energy Collisions of CF3 + Ions with Modified Surfaces: Surface-Induced Dissociation

    SciTech Connect

    Rezayat, T.; Shukla, A.

    2004-01-01

    Collisions of low-energy ions, especially polyatomic ions, with surfaces have become an active area of research due to their numerous applications in chemistry, physics and material sciences. An interesting aspect of such collisions is the dissociation of ions which has been successfully exploited for the characterization of colliding ions, especially high mass ions from biological molecules. However, detailed studies of the energy transfer and dissociation have been performed only for a few simple systems and hence the mechanism(s) of ions excitation and dissociation are not as well understood even for small ions. We have therefore undertaken a study of the dissociation of a small polyatomic ion, CF3+, at several collision energies between 28.8 eV and 159 eV in collision with fluorinated alkyl thiol on gold 111 crystal and a LiF surface. These experiments were performed using a custom built tandem mass spectrometer where the energy and intensity distributions of the scattered fragment ions were measured as a function of the fragment ion mass and scattering angle. In contrast with the previous studies of the dissociation of ethanol and acetone cations where the inelastically scattered primary ions dominated the collision process (up to ~50 eV maximum energy used in those experiments), we did not observe a measurable abundance of inelastically scattered undissociated CF3+ ions at all energies studied here. We observed all fragment ions, CF2+, CF+, F+ and C+ at all energies studied with the relative intensity of the highest energy pathway, C+, increasing with collision energy. Also, the dissociation efficiency decreased significantly as the collision energy was increased from to 159 eV. The energy distributions of nearly all the fragment ions showed two distinct components, one corresponding to the loss of nearly all of the kinetic energy and scattered over a broad angular range while the other corresponding to smaller kinetic energy losses and scattered closer to the surface parallel. The latter process is due to delayed dissociation of excited ions after they have passed the collision region.

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

    PubMed

    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(-1) upon dimerization, somewhat more than in the anharmonic experiment (-111 cm(-1)). PMID:25217897

  15. 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., E-mail: rmata@gwdg.de [Georg-August-Universitt Gttingen, Institut fr Physikalische Chemie, Tammannstr. 6, 37077 Gttingen (Germany)

    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})

  16. Trajectory study of energy transfer and unimolecular dissociation of highly excited allyl with argon.

    PubMed

    Conte, Riccardo; Houston, Paul L; Bowman, Joel M

    2014-09-11

    The influence of rotational excitation on energy transfer in single collisions of allyl with argon and on allyl dissociation is investigated. About 90,000 classical scattering simulations are performed in order to determine collision-induced changes in internal energy and in allyl rotational angular momentum. Dissociation is studied by means of about 50,000 additional trajectories evolved for the isolated allyl under three different conditions: allyl with no angular momentum (J = 0); allyl with the same microcanonically sampled initial conditions used for the collisions (J*); allyl evolving from the corresponding exit conditions after the collision. The potential energy surface is the sum of an intramolecular potential and an interaction one, and it has already been used in a previous work on allyl-argon scattering (Conte, R.; Houston, P. L.; Bowman, J. M. J. Phys. Chem. A 2013, 117, 14028-14041). Energy transfer data show that increased initial rotation favors, on average, increased relaxation of the excited molecule. The availability of a high-level intramolecular potential energy surface permits us to study the dependence of energy transfer on the type of starting allyl isomer. A turning point analysis is presented, and highly efficient collisions are detected. Collision-induced variations in the allyl rotational angular momentum may be quite large and are found to be distributed according to three regimes. The roles of rotational angular momentum, collision, and type of isomer on allyl unimolecular dissociation are considered by looking at dissociations times, kinetic energies of the fragments, and branching ratios. Generally, rotational angular momentum has a strong influence on the dissociation dynamics, while the single collision and the type of starting isomer are less influential. PMID:25116695

  17. Imaging of the dissociation dynamics of polyatomic molecules following low-energy electron resonant attachment

    NASA Astrophysics Data System (ADS)

    Belkacem, Ali

    2014-05-01

    There is a very large body of experimental work on dissociative electron attachment to molecules but the majority of that work is focused on the measurement of absolute total cross sections or energetic positions of the resonances. There is scarce information on the dynamics of electron attachment and the subsequent dissociation that often involves highly non-Born-Oppenheimer dynamics, funneling through conical intersections or intricate nuclear motion during the dissociation process. Through COLTRIMS detection techniques we investigate the electron attachment in a fixed-in-frame manner that yields direct information on the symmetries of the neutral and negatively charged resonant states. We will present a study that combines experimental data along with theoretical analysis of dissociative electron attachment to carbon dioxide, methanol and uracil. In these studies we demonstrated that an understanding of anion dissociation dynamics beyond simple one-dimensional models is crucial in interpreting the measured angular distributions. This work is supported by the Chemical Sciences Biosciences and Geosciences Division, Basic Energy Sciences, DOE.

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

    SciTech Connect

    Jenkovszky, L. L. [Bogolyubov Institute for Theoretical Physics (BITP), Ukrainian National Academy of Sciences, 14-b, Metrolohichna str., Kiev, 03680 (Ukraine); Kuprash, O. E. [Taras Shevchenko National University, Kiev (Ukraine); Laemsae, J. W. [Physics Department, Iowa State University, Ames, 50011 Iowa (United States); Magas, V. K. [Departament d'Estructura i Constituents de la Materia, Universitat de Barcelona, Diagonal 647, 08028 Barcelona (Spain); Orava, R. [Helsinki Institute of Physics, Division of Elementary Particle Physics, P.O. Box 64 (Gustaf Haellstroeminkatu 2a), FI-00014 University of Helsinki (Finland); CERN, CH-1211 Geneva 23 (Switzerland)

    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.

  19. Vibrational analysis of HOCl up to 98% of the dissociation energy with a Fermi resonance Hamiltonian

    E-print Network

    Vibrational analysis of HOCl up to 98% of the dissociation energy with a Fermi resonance and wave functions of HOCl obtained from previous ab initio calculations J. Chem. Phys. 109, 2662 1998 I. INTRODUCTION The HOCl molecule plays an important role in the chem- istry of the upper atmosphere

  20. 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

  1. On the Dissociation of Methyl Orange: Spectrophotometric Investigation in Aqueous Solutions from 10 to 90C 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 90C 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 10-90C 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.

  2. Dissociation of multiply ionized isocyanic acid through electron impact

    NASA Astrophysics Data System (ADS)

    Wang, Pengqian; Vidal, C. R.; Geith, Janna; Klaptke, Thomas M.; Fu, Werner

    2004-01-01

    The dissociation of singly to triply ionized isocyanic acid (HNCO) has been investigated by two- and three-dimensional covariance mapping techniques through electron impact ionization at an electron energy of 200 eV. The absolute cross sections for the various dissociation channels of up to triply ionized HNCO have been measured. The HNCO dications dissociate mostly into ion pairs, while the HNCO trications dissociate mostly into ion triples, both through all the possible bond cleavages and charge allocations. Some major ion-pair dissociation channels of HNCO2+ are supposed to be sequential dissociation through initial charge separation. The metastable decay traces caused by HNCO2+?H++NCO+ and HNCO+?HCO++N have been observed on the covariance map.

  3. 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.

  4. 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

  5. Boltzmann rovibrational collisional coarse-grained model for internal energy excitation and dissociation in hypersonic flows.

    PubMed

    Munaf, A; Panesi, M; Magin, T E

    2014-02-01

    A Boltzmann rovibrational collisional coarse-grained model is proposed to reduce a detailed kinetic mechanism database developed at NASA Ames Research Center for internal energy transfer and dissociation in N(2)-N interactions. The coarse-grained model is constructed by lumping the rovibrational energy levels of the N(2) molecule into energy bins. The population of the levels within each bin is assumed to follow a Boltzmann distribution at the local translational temperature. Excitation and dissociation rate coefficients for the energy bins are obtained by averaging the elementary rate coefficients. The energy bins are treated as separate species, thus allowing for non-Boltzmann distributions of their populations. The proposed coarse-grained model is applied to the study of nonequilibrium flows behind normal shock waves and within converging-diverging nozzles. In both cases, the flow is assumed inviscid and steady. Computational results are compared with those obtained by direct solution of the master equation for the rovibrational collisional model and a more conventional multitemperature model. It is found that the proposed coarse-grained model is able to accurately resolve the nonequilibrium dynamics of internal energy excitation and dissociation-recombination processes with only 20 energy bins. Furthermore, the proposed coarse-grained model provides a superior description of the nonequilibrium phenomena occurring in shock heated and nozzle flows when compared with the conventional multitemperature models. PMID:25353565

  6. Kinetic-energy distributions of O- produced by dissociative electron attachment to physisorbed O2

    Microsoft Academic Search

    M. A. Huels; L. Parenteau; M. Michaud; L. Sanche

    1995-01-01

    We report measurements of the kinetic energy (Ek) distributions of O- produced by low-energy electron impact (5.5-19.5 eV) on disordered multilayers of O2 physisorbed on a polycrystalline Pt substrate. The results confirm that dissociative electron attachment (DEA) proceeds via the formation of the 2Piu, 2Sigma+g(I), and 2Sigma+x(II) (x=g and\\/or u) states of O-*2. We also find evidence for an additional

  7. Dissociation pressure measurements on salts proposed for thermochemical energy storage

    Microsoft Academic Search

    R. W. Carling

    1979-01-01

    Chemical heat pumps employ salt hydrates, ammoniates, or methanolates for energy storage. The efficient operation of a chemical heat pump depends strongly upon the reaction energies and pressure\\/temperature relationships of these salts. An apparatus was assembled to measure pressure\\/temperature relationships and derive reaction energies. A sensitive cantilever balance used to prepare salt samples in situ so that the stoichiometry of

  8. 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.

  9. Natural bond orbital study on the strain energy in cyclotrisilane

    Microsoft Academic Search

    Ming-Chiu Ou; San-Yan Chu

    1995-01-01

    A comparative study between cyclotrisilane and cyclopropane by ab initio calculation and natural bond orbital analysis was carried out. A higher strain energy in the former can be attributed to a weaker rehybridization capbility of silicon relative to carbon in response to the angle strain such that SiH bond strengthening is less effective. Strained XH4 and X2H6 (X = C,

  10. Energetics and Dynamics of the Fragmentation Reactions of Protonated Peptides Containing Methionine Sulfoxide or Aspartic Acid via Energy- and Time-Resolved Surface Induced Dissociation

    SciTech Connect

    Lioe, Hadi; Laskin, Julia; Reid, Gavin E.; O'Hair, Richard Aj

    2007-10-25

    The surface-induced dissociation (SID) of six model peptides containing either methionine sulfoxide or aspartic acid (GAILM(O)GAILR, GAILM(O)GAILK, GAILM(O)GAILA, GAILDGAILR, GAILDGAILK, and GAILDGAILA) have been studied using a specially configured Fourier transform ion-cyclotron resonance mass spectrometer (FT-ICR MS). In particular, we have investigated the energetics and dynamics associated with (i) preferential cleavage of the methionine sulfoxide side chain via the loss of CH3SOH (64Da), and (ii) preferential cleavage of the amide bond C-terminal to aspartic acid. The role of proton mobility on these selective bond cleavage reactions was examined by changing the C-terminal residue of the peptide from arginine (non-mobile proton conditions) to lysine (partially-mobile proton conditions) to alanine (mobile proton conditions). Time- and energy-resolved fragmentation efficiency curves (TFEC) reveals that selective cleavages due to the methionine sulfoxide and aspartic acid residues are characterized by slow fragmentation kinetics. RRKM modeling of the experimental data suggests that the slow kinetics is associated with large negative entropy effects and these may be due to the presence of rearrangements prior to fragmentation. It was found that the Arrhenius pre-exponential factor (A) for peptide fragmentations occurring via selective bond cleavages are 12 orders of magnitude lower than non-selective peptide fragmentation reactions, while the dissociation threshold (E0) is relatively invariant. This means that selective bond cleavage is kinetically disfavored compared to non-selective amide bond cleavage. It was also found that the energetics and dynamics for the preferential loss of CH3SOH from peptide ions containing methionine sulfoxide are very similar to selective C-terminal amide bond cleavage at the aspartic acid residue. These results suggest that while preferential cleavage can compete with amide bond cleavage energetically, dynamically, these processes are much slower compared to amide bond cleavage, explaining why these selective bond cleavages are not observed if fragmentation is performed under mobile proton conditions. This study further affirms that fragmentation of peptide ions in the gas phase are predominantly governed by entropic effects.

  11. Tandem mass spectrometric characterization of bile acids and steroid conjugates based on low-energy collision-induced dissociation.

    PubMed

    Maekawa, Masamitsu; Shimada, Miki; Iida, Takashi; Goto, Junichi; Mano, Nariyasu

    2014-02-01

    We examined the characteristics of several bile acids and some steroid conjugates under low-energy-collision-induced dissociation conditions using a triple quadrupole tandem mass spectrometer. According to conjugation types, we observed characteristic product ions and/or neutral losses in the product ion spectra. Amino acid conjugates afforded specific product ions. For example, glycine-conjugated metabolites routinely produced a product ion at m/z 74, and taurine-conjugated metabolites produced product ions at m/z 124, 107, and 80. When a strong peak appeared at m/z 97, the molecule contained a sulfate group. In contrast to amino acid conjugates, carbohydrate conjugates required a combination of product ions and neutral losses for identification. We could discriminate a glucoside from an acyl galactoside according to the presence or absence of a product ion at m/z 161 and a neutral loss of 180 Da. Discrimination among esters, aliphatic ethers, and phenolic ether types of glucuronides was based upon differences in the intensities of a product ion at m/z 175 and a neutral loss of 176 Da. Furthermore, N-acetylglucosamine conjugates showed a characteristic product ion at m/z 202 and a neutral loss of 203 Da, and the appearance of a product ion at m/z 202 revealed the existence of N-acetylglucosamine conjugated to an aliphatic hydroxyl group without a double bond in the immediate vicinity. Together, the data presented here will help to enable the identification of unknown conjugated cholesterol metabolites by using low-energy collision-induced dissociation. PMID:24296272

  12. 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.

  13. The kinetic energy change on covalent bond formation

    PubMed Central

    March, Norman H.; Parr, Robert G.; Mucci, Joe F.

    1981-01-01

    Stimulated by an analysis of the classical molecular orbital and valence bond descriptions of the two-electron normal covalent bond (both faulty), the argument is made that there exist good representations of the kinetic energy change ?T, on nonpolar covalent bond formation in a diatomic molecule, of the form ?T(R) = ?F(R - r?)S(r?)dr?. Here F is a nonlinear response function which itself involves the overlap S. The kinetic change is known to satisfy the sum rule ?0??T(R)dR = Z?Z? exactly; it is shown how this can be built into the treatment by the use of Fourier transform methods. Also considered is ?0??T(R)R2dR, which is an important additional property of the kinetic energy change. Representation of ?T(R) as a Morse function, already known to be highly accurate, is shown to exactly conform to the proposed form. PMID:16593098

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

    SciTech Connect

    Giesbertz, Klaas J. H. [Theoretical Chemistry, Faculty of Exact Sciences, VU University, De Boelelaan 1083, 1081 HV Amsterdam (Netherlands)] [Theoretical Chemistry, Faculty of Exact Sciences, VU University, De Boelelaan 1083, 1081 HV Amsterdam (Netherlands); Leeuwen, Robert van [Department of Physics, Nanoscience Center, University of Jyvskyl, P.O. Box 35, 40014 Jyvskyl, Survontie 9, Jyvskyl (Finland)] [Department of Physics, Nanoscience Center, University of Jyvskyl, P.O. Box 35, 40014 Jyvskyl, Survontie 9, Jyvskyl (Finland)

    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.

  15. Binding affinities and non-bonded interaction energies

    Microsoft Academic Search

    Ronald M. A. Knegtel; Peter D. J. Grootenhuis

    1998-01-01

    The association of two molecules to form a stable complex involves a delicate interplay of electrostatic interactions, such as hydrogen bonds and ionic contacts, the matching of hydrophobic surfaces and entropic effects [1]. A schematic representation of the factors that play a role in molecular association is given in Fig. 1. These factors determine the change in free energy (DG)

  16. Metalcarbon bond energies for adsorbed hydrocarbons from calorimetric data

    E-print Network

    Campbell, Charles T.

    September 2004 Abstract Single crystal adsorption calorimetry (SCAC) is a powerful new method for measuring is available from either experiment or theory on well- defined surfaces, this method can provide crucially of how this bond energy should differ when the C atoms ligands are different. 2004 Elsevier B.V. All

  17. Ab initio calculation of the potential energy surface for the dissociation of H2 on the sulfur-covered Pd,,100... surface

    E-print Network

    Ab initio calculation of the potential energy surface for the dissociation of H2 on the sulfur March 1998 The presence of sulfur atoms on the Pd 100 surface is known to hinder the dissociative on the sulfur covered Pd 100 surface. The PES is changed significantly compared to the dissociation on the clean

  18. 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.

  19. Photodissociation of water in the first absorption band: A prototype for dissociation on a repulsive potential energy surface

    Microsoft Academic Search

    V. Engel; V. Staemmler; R. L. Vander Wal; F. F. Crim; R. J. Sension; B. Hudson; P. Andresen; S. Hennig; K. Weide; R. Schinke

    1992-01-01

    The photodissociation of water in the first absorption band, HO(X) + HO(A¹B) H(²S) + OH(²II), is a prototype of fast and direct bond rupture in an excited electronic state. It has been investigated from several perspectives-absorption spectrum, final state distributions of the products, dissociation of vibrationally excited states, isotope effects, and emission spectroscopy. The availability of a

  20. Relationship between bond energy and total work of fracture for asphalt binder-aggregate systems

    Microsoft Academic Search

    Jonathan Howson; Eyad Masad; Dallas Little; Emad Kassem

    2012-01-01

    Surface free energy is a thermodynamic material property representing the work required to create new surfaces of unit area in a vacuum. Surface free energy has been used to quantify and screen both the cohesive bond energy of asphalt binders and the adhesive bond energy of asphalt binderaggregate interfaces in wet and dry conditions. The bond energy is computed based

  1. 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, E-mail: msarma@iitg.ernet.in [Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781 039 (India)

    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? CO 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 NC bond. In addition, the metastable state formed after impinging LEE (01 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 NC 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 ?3555 fs. Comparison of salient features of the two dissociation events, i.e., 3? CO single strand break and glycosidic NC bond cleavage in 3?-dCMPH molecule are also provided.

  2. Relaxation of backbone bond geometry improves protein energy landscape modeling.

    PubMed

    Conway, Patrick; Tyka, Michael D; DiMaio, Frank; Konerding, David E; Baker, David

    2014-01-01

    A key issue in macromolecular structure modeling is the granularity of the molecular representation. A fine-grained representation can approximate the actual structure more accurately, but may require many more degrees of freedom than a coarse-grained representation and hence make conformational search more challenging. We investigate this tradeoff between the accuracy and the size of protein conformational search space for two frequently used representations: one with fixed bond angles and lengths and one that has full flexibility. We performed large-scale explorations of the energy landscapes of 82 protein domains under each model, and find that the introduction of bond angle flexibility significantly increases the average energy gap between native and non-native structures. We also find that incorporating bonded geometry flexibility improves low resolution X-ray crystallographic refinement. These results suggest that backbone bond angle relaxation makes an important contribution to native structure energetics, that current energy functions are sufficiently accurate to capture the energetic gain associated with subtle deformations from chain ideality, and more speculatively, that backbone geometry distortions occur late in protein folding to optimize packing in the native state. PMID:24265211

  3. Dissociation and desorption of ferrocene on graphite by low energy electron impact

    NASA Astrophysics Data System (ADS)

    Svensson, K.; Bedson, T. R.; Palmer, R. E.

    2000-04-01

    Ferrocene is an iron-containing organometallic molecule with the potential to be used for fabrication of metallic structures on the nanometre scale. We have used high resolution electron energy loss spectroscopy and scanning tunnelling microscopy to study the influence of low energy electron impact on ferrocene physisorbed on graphite. At electron energies below 10 eV we find that the ferrocene molecules are readily desorbed, leaving a clean graphite surface behind. For energies of 20-100 eV we find evidence of partial fragmentation of the ferrocene. At higher energies, exceeding 200 eV, there is complete disintegration of the molecules, leaving iron-containing nanoclusters in a stable film on the surface. Comparisons are drawn with photon-, thermal- and very high electron-energy induced dissociation and desorption.

  4. Effects of bonding force on contact pressure and frictional energy in wire bonding

    Microsoft Academic Search

    Yong Ding; Jang-kyo Kim; Pin Tong

    2006-01-01

    A numerical study is made of the elasto-plastic deformation taking place in ultrasonic wire bonding based on the finite element method. A special focus has been placed on how the important wire bonding parameters, such as bond force and power, affect the contact pressure along the wirebond pad interface. It is shown that the contact interface had a long elliptical

  5. Coulomb-Assisted Dissociative Electron Attachment: Application to a Model Peptide

    Microsoft Academic Search

    Monika Sobczyk; Iwona Anusiewicz; Joanna Berdys-Kochanska; Agnieszka Sawicka; Piotr Skurski; Jack Simons

    2005-01-01

    The fragmentation of positively charged gas-phase samples of peptides is used to infer the primary structure of such molecules. In electron capture dissociation (ECD) experiments, very low-energy electrons attach to the sample and rupture bonds to effect the fragmentation. It turns out that ECD fragmentation tends to produce cleavage of very specific types of bonds. In earlier works by this

  6. Heats of Formation and Bond Energies in Group III Compounds

    NASA Technical Reports Server (NTRS)

    Bauschlicher, Charles W., Jr.; Allendorf, Mark D.; Melius, Carl F.; Arnold, James O. (Technical Monitor)

    1999-01-01

    We present heats of formation and bond energies for Group-III compounds obtained from calculations of molecular ground-state I electronic energies. Data for compounds of the form MXn are presented, where M = B, Al, Ga, and In, X = He H, Cl, and CH3, and n = 1-3. Energies for the B, Al, and Ga compounds are obtained from G2 predictions, while those for the In compounds are obtained from CCSD(T)/CBS calculations; these are the most accurate calculations for indium-containing compounds published to date. In most cases, the calculated thermochemistry is in good agreement with published values derived from experiments for those species that have well-established heats of formation. Bond energies obtained from the heats of formation follow the expected trend (Cl much greater than CH3 approx. H). However, the CH3M-(CH3)2 bond energies obtained for trimethylgallium and trimethylindium are considerably stronger (greater than 15 kcal/mol) than currently accepted values.

  7. A simple model of the HNCO (1A') excited state potential energy surface and a classical trajectory analysis of the vibrationally directed bond-selected photodissociation

    NASA Astrophysics Data System (ADS)

    Brown, Steven S.; Cheatum, Christopher M.; Fitzwater, David A.; Crim, F. Fleming

    1996-12-01

    Recent state-selected photodissociation experiments on isocyanic acid, HNCO, have provided a wealth of data on its photochemistry and dissociation dynamics. The excited state potential energy surface on which the dissociation occurs is central to these observations but is relatively uncharacterized. We construct a two-dimensional analytical model for the excited state potential that is consistent with experimental observations, including the ultraviolet absorption spectrum and the dynamics of the C-N and N-H bond dissociations. We then test this surface by running classical trajectories on it, using Morse oscillator vibrational wave functions from the ground electronic state to determine the probability distributions of initial conditions. The trajectory calculation reproduces the experimentally observed variation in the photochemical branching with photolysis wavelength. It also reproduces the bond selectivity in the photodissociation of HNCO molecules containing three quanta of N-H stretching excitation (3?1) that we observed experimentally. Although the model for the surface is very simple and includes only two degrees of freedom, it captures the essential features that determine the photochemical branching in a direct dissociation.

  8. 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.

  9. 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

  10. Tailoring Bond Cleavage in Gas-Phase Biomolecules by Low Energy Electrons

    NASA Astrophysics Data System (ADS)

    Ptasinska, Sylwia

    2014-10-01

    The high energy quanta of impinging radiation can generate a large number (about 5x104) of secondary electrons per 1 MeV of energy deposited. When ejected in condensed phase water, the kinetic energy distribution of these free or quasi-free electrons is peaked below 10 eV. Low energy electrons also dominate in the secondary emission from biomolecular targets exposed to different energies of primary radiation. Due to the complexity of the radiation-induced processes in the condensed-phase environment, mechanisms of secondary electrons induced damage in biomolecules (BM) still need to be investigated. However, based on results from theory and different experiments accumulated within the last decade, it is now possible to determine the fundamental mechanisms that are involved in many chemical reactions induced in isolated gas-phase biomolecules by low energy electrons. The central finding of earlier research was the discovery of the bond- and site- selectivity in the dissociative electron attachment (DEA) process to biomolecules. It has been demonstrated that by tuning the energy of the incoming electron we can gain control over the location of the bond cleavage. These studies showed the selectivity in single bond cleavage reactions leading to the formation of the dehydrogenated closed shell anion (BM-H)- or the complementary reaction leading to H-. The loss of a hydrogen atom or an anion is fast compared with ring cleavage and the excision of heavier fragments and, hence, this reaction can compete efficiently with autodetachment. Moreover, site selectivity has been also observed in the metastable anion formation via the DEA process. Such delayed fragmentation was studied recently for the dehydrogenated closed-shell anion conversion into NCO- upon DEA proceeded a few ? sec after electron attachment, indicating a rather slow unimolecular decomposition. Interestingly, site selectivity was observed in the prompt as well as the metastable NCO- formation in DEA. The research described herein was supported by the Division of Chemical Sciences, Geosciences and Biosciences, Basic Energy Sciences, Office of Science, United States Department of Energy through Grant Number DE-FC02-04ER15533.

  11. Internal Energy Dependence of the H + Allene/H + Propyne Product Branching from the Unimolecular Dissociation of 2-Propenyl Radicals

    E-print Network

    Butler, Laurie J.

    Internal Energy Dependence of the H + Allene/H + Propyne Product Branching from the Unimolecular product channels as a function of internal energy in the dissociating radical isomer. The data resolve with internal energy to the two isomeric product channels: Based on energetic considerations alone, one expects

  12. The unimolecular dissociation of H2CO on the lowest triplet potential-energy surface

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Yukio; Wesolowski, Steven S.; Van Huis, Timothy J.; Schaefer, Henry F.

    1998-04-01

    The unimolecular dissociation reaction of H2CO on the triplet potential-energy surface has been studied via ab initio electronic structure theory. The stationary point geometries for the equilibrium and transition state are determined employing the configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory with large basis sets up to the correlation consistent (cc)-pVQZ basis. With the best method, cc-pVQZ CCSD(T), the first excited triplet ( 3A?) state lies 72.2 kcal/mol (25 260 cm-1) above the ground (X 1A1) state of H2CO, which is in excellent agreement with the experimental observation of 72.03 kcal/mol (25 194 cm-1). The dissociation limit (H?+HCO?) is located at 86.3 kcal/mol (30 170 cm-1) above the ground state of H2CO, which is again in good agreement with the two experimentally determined values of 86.57 kcal/mol (30 280 cm-1) and 86.71 kcal/mol (30 328.5 cm-1). With the same method the triplet dissociation transition state lies 92.4 kcal/mol (32 300 cm-1) above the ground state. Consequently, the activation energy for the dissociation reaction of H2CO on the triplet surface is determined ab initio to be 18.9-20.1 kcal/mol (6620-7040 cm-1) (including an estimated error bar of 1.2 kcal/mol or 420 cm-1). The zero-point vibrationally corrected exit barrier height is predicted to be 4.9-6.1 kcal/mol (1710-2130 cm-1). These newly predicted energies are consistent with the recent experimental observations by the Moore group at University of California-Berkeley (1987) and by the Wittig group at University of Southern California (1997).

  13. 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.

  14. 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.

  15. Ab initio calculations on accurate dissociation energy, equilibrium geometry, and analytic potential energy function for the b3? state of 7LiH molecule

    Microsoft Academic Search

    Deheng Shi; Yufang Liu; Jinfeng Sun; Zunlue Zhu; Xiangdong Yang

    2005-01-01

    The accurate dissociation energy and equilibrium geometry of the b3? state of 7LiH molecule is calculated using a symmetry-adapted-cluster configuration-interaction method in full active space. And the calculated results are 0.2580 eV and 0.1958 nm for the dissociation energy and equilibrium geometry, respectively. The whole potential energy curve for the b3? state is also calculated over the internuclear separation range

  16. Blackbody Infrared Radiative Dissociation of Protonated Oligosaccharides

    NASA Astrophysics Data System (ADS)

    Fentabil, Messele A.; Daneshfar, Rambod; Kitova, Elena N.; Klassen, John S.

    2011-12-01

    The dissociation pathways, kinetics, and energetics of protonated oligosaccharides in the gas phase were investigated using blackbody infrared radiative dissociation (BIRD). Time-resolved BIRD measurements were performed on singly protonated ions of cellohexaose (Cel6), which is composed of ?-(1 ? 4)-linked glucopyranose rings, and five malto-oligosaccharides (Malx, where x = 4-8), which are composed of ?-(1 ? 4)-linked glucopyranose units. At the temperatures investigated (85-160 C), the oligosaccharides dissociate at the glycosidic linkages or by the loss of a water molecule to produce B- or Y-type ions. The Y ions dissociate to smaller Y or B ions, while the B ions yield exclusively smaller B ions. The sequential loss of water molecules from the smallest B ions (B1 and B2) also occurs. Rate constants for dissociation of the protonated oligosaccharides and the corresponding Arrhenius activation parameters (Ea and A) were determined. The Ea and A-factors measured for protonated Malx (x > 4) are indistinguishable within error (~19 kcal mol-1, 1010 s-1), which is consistent with the ions being in the rapid energy exchange limit. In contrast, the Arrhenius parameters for protonated Cel6 (24 kcal mol-1, 1012 s-1) are significantly larger. These results indicate that both the energy and entropy changes associated with the glycosidic bond cleavage are sensitive to the anomeric configuration. Based on the results of this study, it is proposed that formation of B and Y ions occurs through a common dissociation mechanism, with the position of the proton establishing whether a B or Y ion is formed upon glycosidic bond cleavage.

  17. Near threshold dynamics and dissociation energy of the reaction H 2CO ? HCO + H

    NASA Astrophysics Data System (ADS)

    Terentis, Andrew C.; Kable, Scott H.

    1996-08-01

    The state-to-state dynamics of the gas phase reaction H 2CO ( v, J, Ka, Kc) + hv ? H + HCO( v, N, S, Ka, Kc) have been explored in a supersonic free jet. Seven rotational states within the 2 14 3 vibrational level of H 2CO were excited and the population distribution of the HCO ( v = 0, N, S, Ka, Kc) product states measured. The distributions are constrained severely by the available energy in the reaction with the lowest H 2CO state producing HCO in only three rotational states. Careful matching of the H 2CO and HCO energy levels leads to an estimate of the dissociation energy of the above reaction of 30328.5 0.5 cm -, which lead us to an estimate of the standard heat of formation of the formyl radical of ?Hf0 = 42.5 0.5 kJ mol -1.

  18. 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 =

  19. EPR Equilibration Measurement of the CH Bond Enthalpy in the Methylene Groups of 1,3,5Trimethyl2,4,6-tris(3,5-di- tert -butyl-4-hydroxybenzyl)benzene (Irganox)

    Microsoft Academic Search

    Sara Noem Mendiara; Marta E. J. Coronel

    2010-01-01

    On the basis of previous and current studies, it has been possible to evaluate and compare the bond dissociation energies\\u000a of the phenol (OH) bond and of the methylene and methyl (CH) bonds in Irganox (trade name) by means of electron paramagnetic\\u000a resonance records of galvinoxylirganoxyl hydrogen transfer reaction equilibria. The bond dissociation enthalpy of the CH\\u000a methylene and methyl

  20. Presolvated Low Energy Electron Attachment to Peptide Methyl esters in Aqueous Solution: C-O Bond Cleavage at 77K

    PubMed Central

    Kheir, Jeanette; Chomicz, Lidia; Engle, Alyson; Rak, Janusz; Sevilla, Michael D.

    2013-01-01

    In this study, the reactions of presolvated electrons with glycine methyl ester and N-acetylalanylalanine methyl ester (N-aAAMe) are investigated by electron spin resonance (ESR) spectroscopy and DFT calculations. Electrons were produced by gamma irradiation in neutral 7.5 M LiCl-D2O aqueous glasses at low temperatures. For glycine methyl ester electron addition at 77K results in both N-terminal deamination to form a glycyl radical and C-O ester bond cleavage to form methyl radicals. For samples of N-acetylalanylalanine methyl ester electrons are found to add to the peptide bonds at 77K and cleave the carboxyl ester groups to produce methyl radicals. On annealing to 160K electron adducts at the peptide links undergo chain scission to produce alanyl radicals and further annealing to 170K ?-carbon peptide backbone radicals are produced by hydrogen abstraction. DFT calculations for electron addition to the methyl ester portion of N-aAAMe show the cleavage reaction is highly favorable (free energy equals to ?30.7 kcal/mol) with the kinetic barrier of only 9.9 kcal/mol. A substantial electron affinity of the ester link (38.0 kcal/mol) provides more than sufficient energy to overcome this small barrier. Protonated peptide bond electron adducts, also show favorable N-C chain cleavage reactions of ?12.7 to ?15.5 kcal/mol with a barrier from 7.4 to 10.0 kcal/mol. The substantial adiabatic electron affinity (AEA) of the peptide bond and ester groups provides sufficient energy for the bond dissociation. PMID:23406302

  1. Theoretical Electron Density Distributions for Fe- and Cu-Sulfide Earth Materials: A Connection between Bond Length, Bond Critical Point Properties, Local Energy Densities, and Bonded Interactions

    SciTech Connect

    Gibbs, Gerald V.; Cox, David F.; Rosso, Kevin M.; Ross, Nancy L.; Downs, R. T.; Spackman, M. A.

    2007-03-01

    Bond critical point and local energy density properties together with net atomic charges were calculated for theoretical electron density distributions, F(r), generated for a variety of Fe and Cu metal-sulfide materials with high- and low-spin Fe atoms in octahedral coordination and high-spin Fe atoms in tetrahedral coordination. The electron density, F(rc), the Laplacian, 32F(rc), the local kinetic energy, G(rc), and the oxidation state of Fe increase as the local potential energy density, V(rc), the Fe-S bond lengths, and the coordination numbers of the Fe atoms decrease. The properties of the bonded interactions for the octahedrally coordinated low-spin Fe atoms for pyrite and marcasite are distinct from those for high-spin Fe atoms for troilite, smythite, and greigite. The Fe-S bond lengths are shorter and the values of F(rc) and 32F(rc) are larger for pyrite and marcasite, indicating that the accumulation and local concentration of F(r) in the internuclear region are greater than those involving the longer, high-spin Fe-S bonded interactions. The net atomic charges and the bonded radii calculated for the Fe and S atoms in pyrite and marcasite are also smaller than those for sulfides with high-spin octahedrally coordinated Fe atoms. Collectively, the Fe-S interactions are indicated to be intermediate in character with the low-spin Fe-S interactions having greater shared character than the highspin interactions. The bond lengths observed for chalcopyrite together with the calculated bond critical point properties are consistent with the formula Cu+Fe3+S2. The bond length is shorter and the F(rc) value is larger for the FeS4 tetrahedron displayed by metastable greigite than those displayed by chalcopyrite and cubanite, consistent with a proposal that the Fe atom in greigite is tetravalent. S-S bond paths exist between each of the surface S atoms of adjacent slabs of FeS6 octahedra comprising the layer sulfide smythite, suggesting that the neutral Fe3S4 slabs are linked together and stabilized by the pathways of electron density comprising S-S bonded interactions. Such interactions not only exist between the S atoms for adjacent S8 rings in native sulfur, but their bond critical point properties are similar to those displayed by the metal sulfides.

  2. Prediction of the bond lengths, vibrational frequencies, and bond dissociation energy of octahedral seaborgium hexacarbonyl, Sg(CO)

    Microsoft Academic Search

    Clinton S. Nash; Bruce E. Bursten

    1999-01-01

    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

  3. Dissociation of super-dislocations and the stacking fault energy in TiAl based alloys with Nb-doping

    NASA Astrophysics Data System (ADS)

    Yuan, Y.; Liu, H. W.; Zhao, X. N.; Meng, X. K.; Liu, Z. G.; Boll, Torben; Al-Kassab, Talaat

    2006-10-01

    Dissociations of super-dislocations in ?-TiAl in Nb-doped Ti-48 at.% Al-1 at.% Nb and Ti-48 at.% Al-10 at.% Nb have been studied by high resolution transmission electron microscopy (HRTEM) and weak beam transmission electron microscopy (TEM). The SISF energy was calculated to be 63 mJ/m2 in Ti-48 at.% Al-1 at.% Nb and 34 mJ/m2 in Ti-48 at.% Al-10 at.% Nb according to the dissociation width, respectively. Consequently, it is concluded that Nb-addition can decrease the SF energy significantly, which contribute obviously to the strengthening effect induced by Nb-doping.

  4. Dissociation dynamics of B 1s core-excited BF 3 probed by energy-selected electron energy-selected ion coincidence and angle-resolved ion spectroscopy

    Microsoft Academic Search

    Kiyoshi Ueda; K Ohmori; M. Okunishi; H. Chiba; Y. Shimizu; Y. Sato; T. Hayaishi; E. Shigemasa; A. Yagishita

    1996-01-01

    A coincidence study between energy-selected electrons and mass- and energy-selected ions shows that dissociation from the spectator-Auger-final states both above and below the double ionization threshold produces energetic B+ whereas dissociation following B 1s ionization produces energetic F+. An angle-resolved photoion study reveals that the B+ is ejected from the spectator-Auger-final states of the deformed C3v pyramidal molecule, after the

  5. Exchange-correlation energy and potential as approximate functionals of occupied and virtual Kohn-Sham orbitals: Application to dissociating H2

    NASA Astrophysics Data System (ADS)

    Grning, M.; Gritsenko, O. V.; Baerends, E. J.

    2003-04-01

    The standard local density approximation and generalized gradient approximations fail to properly describe the dissociation of an electron pair bond, yielding large errors (on the order of 50 kcal/mol) at long bond distances. To remedy this failure, a self-consistent Kohn-Sham (KS) method is proposed with the exchange-correlation (xc) energy and potential depending on both occupied and virtual KS orbitals. The xc energy functional of Buijse and Baerends [Mol. Phys. 100, 401 (2002); Phys. Rev. Lett. 87, 133004 (2001)] is employed, which, based on an ansatz for the xc-hole amplitude, is able to reproduce the important dynamical and nondynamical effects of Coulomb correlation through the efficient use of virtual orbitals. Self-consistent calculations require the corresponding xc potential to be obtained, to which end the optimized effective potential (OEP) method is used within the common energy denominator approximation for the static orbital Green's function. The problem of the asymptotic divergence of the xc potential of the OEP when a finite number of virtual orbitals is used is addressed. The self-consistent calculations reproduce very well the entire H2 potential curve, describing correctly the gradual buildup of strong left-right correlation in stretched H2.

  6. Characterization of the Rydberg Bonding in (NH4)2 Robyn Barrios, Piotr Skurski, and Jack Simons*

    E-print Network

    Simons, Jack

    Characterization of the Rydberg Bonding in (NH4)2 - Robyn Barrios, Piotr Skurski, and Jack Simons City, Utah 84112 ReceiVed: April 6, 2000; In Final Form: August 28, 2000 The Rydberg bonding in (NH4 performed for comparison with the Rydberg bonding cases. The dissociation energy De for (NH4)2 - f NH4 + NH4

  7. Modeling energy transport in ?-conjugated dendrimers containing triple bonds

    NASA Astrophysics Data System (ADS)

    Kau Lim, Pak; Shin, Yongwoo; Lin, Xi

    2012-02-01

    An accurate, transferrable, and computational efficient adapted Su-Schrieffer-Heeger model Hamiltonian is developed to describe triple bonds in linear and fractal-dimensional ?-conjugated systems. Chemical accuracy in the computed optical gaps is found for the cases of poly-(thiophene-ethynylene) and ploy-phenylacetylene of arbitrary lengths, with all errors less than 3% as compared to existing UV-visible adsorption spectra. The computed exciton migration processes in the phenylacetylene dendrimers indicates that such conjugated Bethe tree structures are efficient energy transduction funnels.

  8. 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.

  9. THE JOURNAL OF CHEMICAL PHYSICS 134, 064302 (2011) The CH bond dissociation energy of furan: Photoelectron

    E-print Network

    Lineberger, W. Carl

    2011-01-01

    of three of the most active vibrational modes upon ~X2 A ~X1 A photodetachment: 855(25), 1064 of furanide anion photodetachment, where the excess electron is strongly local- ized on the -carbon atom of coal;4,5 consequently, knowl- edge of its reactivity has the potential to improve current technology

  10. Dislocation Dissociation Strongly Influences on FrankRead Source Nucleation and Microplasticy of Materials with Low Stacking Fault Energy

    NASA Astrophysics Data System (ADS)

    Huang, Min-Sheng; Zhu, Ya-Xin; Li, Zhen-Huan

    2014-04-01

    The influence of dislocation dissociation on the evolution of FrankRead (F-R) sources is studied using a three-dimensional discrete dislocation dynamics simulation (3D-DDD). The classical Orowan nucleation stress and recently proposed Benzerga nucleation time models for F-R sources are improved. This work shows that it is necessary to introduce the dislocation dissociation scheme into 3D-DDD simulation, especially for simulations on micro-plasticity of small sized materials with low stacking fault energy.

  11. Experimental and Theoretical Investigations of the Dissociation Energy (D0) and Dynamics of the Water Trimer, (H2O)3

    E-print Network

    Reisler, Hanna

    Experimental and Theoretical Investigations of the Dissociation Energy (D0) and Dynamics of the Water Trimer, (H2O)3 Lee C. Ch'ng, Amit K. Samanta, Yimin Wang, Joel M. Bowman,*, and Hanna Reisler experimental-theoretical study of the predissociation dynamics of the water trimer following excitation

  12. Laser fluorescence study of AIO formed in the reaction AI + O2: Product state distribution, dissociation energy, and radiative

    E-print Network

    Zare, Richard N.

    Laser fluorescence study of AIO formed in the reaction AI + O2: Product state distribution, dissociation energy, and radiative lifetime P. J. Dagdigian*, H. W. Cruset, and R. N. Zare Department of Chemistry, Columbia University, New York, New York 10027 (Received 21 October 1974) The reaction Al + 0, --j

  13. Theoretical aspects of the biological catch bond.

    PubMed

    Prezhdo, Oleg V; Pereverzev, Yuriy V

    2009-06-16

    The biological catch bond is fascinating and counterintuitive. When an external force is applied to a catch bond, either in vivo or in vitro, the bond resists breaking and becomes stronger instead. In contrast, ordinary slip bonds, which represent the vast majority of biological and chemical bonds, dissociate faster when subjected to a force. Catch-bond behavior was first predicted theoretically 20 years ago and has recently been experimentally observed in a number of protein receptor-ligand complexes. In this Account, we review the simplest physical-chemical models that lead to analytic expressions for bond lifetime, the concise universal representations of experimental data, and the explicit requirements for catch binding. The phenomenon has many manifestations: increased lifetime with growing constant force is its defining characteristic. If force increases with time, as in jump-ramp experiments, catch binding creates an additional maximum in the probability density of bond rupture force. The new maximum occurs at smaller forces than the slip-binding maximum, merging with the latter at a certain ramp rate in a process resembling a phase transition. If force is applied periodically, as in blood flows, catch-bond properties strongly depend on force frequency. Catch binding results from a complex landscape of receptor-ligand interactions. Bond lifetime can increase if force (i) prevents dissociation through the native pathway and drives the system over a higher energy barrier or (ii) alters protein conformations in a way that strengthens receptor-ligand binding. The bond deformations can be associated with allostery; force-induced conformational changes at one end of the protein propagate to the binding site at the other end. Surrounding water creates further exciting effects. Protein-water tension provides an additional barrier that can be responsible for significant drops in bond lifetimes observed at low forces relative to zero force. This strong dependence of bond properties on weak protein-water interactions may provide universal activation mechanisms in many biological systems and create new types of catch binding. Molecular dynamics simulations provide atomistic insights: the molecular view of bond dissociation gives a foundation for theoretical models and differentiates between alternative interpretations of experimental data. The number of known catch bonds is growing; analogs are found in enzyme catalysis, peptide translocation through nanopores, DNA unwinding, photoinduced dissociation of chemical bonds, and negative thermal expansion of bulk materials, for example. Finer force resolution will likely provide many more. Understanding the properties of catch bonds offers insight into the behavior of biological systems subjected to external perturbations in general. PMID:19331389

  14. Direct evaluation of individual hydrogen bond energy in situ in intra- and intermolecular multiple hydrogen bonds system.

    PubMed

    Liu, Cui; Zhao, Dong-Xia; Yang, Zhong-Zhi

    2012-02-01

    The results of evaluating the individual hydrogen bond (H-bond) strength are expected to be helpful for the rational design of new strategies for molecular recognition or supramolecular assemblies. Unfortunately, there is few obvious and unambiguous means of evaluating the energy of a single H-bond within a multiple H-bonds system. We present a local analytic model, ABEEM?? H-bond energy (HBE) model based on ab initio calculations (MP2) as benchmark, to directly and rapidly evaluate the individual HBE in situ in inter- and intramolecular multiple H-bonds system. This model describes the HBE as the sum of electrostatic and van der Waals (vdW) interactions which all depend upon the geometry and environment, and the ambient environment of H-bond in the model is accounted fairly. Thus, it can fairly consider the cooperative effect and secondary effect. The application range of ABEEM?? HBE model is rather wide. This work has discussed the individual H-bond in DNA base pair and protein peptide dimers. The results indicate that the interactions among donor H atom, acceptor atom as well as those atoms connected to them with 1,2 or 1,3 relationships are all important for evaluating the HBE, although the interaction between the donor H atom and the acceptor atom is large. Furthermore, our model quantitatively indicates the polarization ability of N, O, and S in a new style, and gives the percentage of the polarization effect in HBE, which can not be given by fixed partial charge force field. PMID:22170234

  15. Bond Energies of Molecular Fragments to Metal Surfaces Track Their Bond Energies to H Atoms

    E-print Network

    Campbell, Charles T.

    , methanol, and formic acid), with a slope of 1.00. This parallels the known trend for organometallic efficiency and less pollution, and in developing better fuel cells and batteries. Thus, one would like for the production of clean fuels, the combustion of fuels, and the production of chemicals with improved energy

  16. "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

  17. High resolution studies of dissociative electron attachment to molecules: dependence on electron and vibrational energy

    NASA Astrophysics Data System (ADS)

    Ruf, M.-W.; Braun, M.; Marienfeld, S.; Fabrikant, I. I.; Hotop, H.

    2007-11-01

    For several molecules which are important for plasma processing and gaseous dielectrics (CF3I, CF3Br, CH3Br, and SF6), we have studied the dependence of dissociative electron attachment (DEA) on both the electron energy and on the initial vibrational energy. With reference to electron swarm data, we determine highly-resolved absolute DEA cross sections over a broad energy range, using the Laser Photoelectron Attachment (LPA) method (E = 0-0.2 eV, ?E ? 1-3 meV) and the EXtended Laser Photoelectron Attachment (EXLPA) method (0-2 eV, ?E ? 15-30 meV). The experimental data are compared with the results of R-matrix calculations, involving ab initioinformation on the potential energy curves and semiempirical autodetachment widths. For CF3I and CF3Br, previous DEA cross sections are found to be substantially too high. For CH3Br, the measurements confirm a predicted vibrational Feshbach resonance, associated with the v3 = 4 vibrational threshold, and the value of the activation energy (due to an intermediate barrier) for this exothermic DEA process. For SF6, we report absolute cross sections for SF6- as well as SF5- formation for vibrational temperatures ranging from 200 to 500 K. Moreover, the first absoluteDEA cross sections (SF5- formation) for CO2-laser excited SF6 molecules have been obtained at different initial vibrational temperatures. The results indicate that the effect of the mode-selective energy input into the v3-mode (predominantly v3 = 1) on the enhancement of SF5- formation is very similar to that of a corresponding rise of the average vibrational energy by thermal heating; at E = 2 meV electron energy, the results indicate an activation energy of about 0.38 eV.

  18. Relative Proton Affinities from Kinetic Energy Release Distributions for Dissociation of Proton-Bound Dimers

    SciTech Connect

    Hache, John J.(OFFICE OF FELLOWSHIP PROG) [OFFICE OF FELLOWSHIP PROG; Laskin, Julia (BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB); Futrell, Jean H.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB)

    2002-12-19

    Kinetic energy release distributions (KERDs) upon dissociation of proton-bound dimers are utilized along with Finite Heat Bath theory analysis to obtain relative proton affinities of monomeric species composing the dimer. The proposed approach allows accurate measurement of relative proton affinities based on KERD measurements for the compound with unknown thermochemical properties versus a single reference base. It also allows distinguishing the cases when dissociation of proton-bound dimers is associated with reverse activation barrier, for which both our approach and the kinetic method become inapplicable. Results are reported for the n-butanol-n-propanol dimer, for which there is no significant difference in entropy effects for two reactions and for the pyrrolidine-1,2-ethylenediamine dimer, which is characterized by a significant difference in entropy effects for the two competing reactions. Relative protonation affinities of -1.0?0.3 kcal/mol for the n-butanol-n-propanol pair and 0.27?0.10 kcal/mol for the pyrrolidine-1,2-ethylenediamine pair are in good agreement with literature values. Relative reaction entropies were extracted from the branching ratio and KERD measurements. Good correspondence was found between the relative reaction entropies for the n-butanol-n-propanol dimer (D(DS?)=-0.3?1.5 cal/mol K) and the relative protonation entropy for the two monomers (D(DSp)=0). However, the relative reaction entropy for the pyrrolidine-1,2-ethylenediamine dimer is higher than the difference in protonation entropies (D(DS?)=8.2?0.5 cal/mol K vs. D(DSp)=5 cal/mol K).

  19. 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.

  20. Dissociative disorders.

    PubMed

    Kihlstrom, John F

    2005-01-01

    The dissociative disorders, including "psychogenic" or "functional" amnesia, fugue, dissociative identity disorder (DID, also known as multiple personality disorder), and depersonalization disorder, were once classified, along with conversion disorder, as forms of hysteria. The 1970s witnessed an "epidemic" of dissociative disorder, particularly DID, which may have reflected enthusiasm for the diagnosis more than its actual prevalence. Traditionally, the dissociative disorders have been attributed to trauma and other psychological stress, but the existing evidence favoring this hypothesis is plagued by poor methodology. Prospective studies of traumatized individuals reveal no convincing cases of amnesia not attributable to brain insult, injury, or disease. Treatment generally involves recovering and working through ostensibly repressed or dissociated memories of trauma; at present, there are few quantitative or controlled outcome studies. Experimental studies are few in number and have focused largely on state-dependent and implicit memory. Depersonalization disorder may be in line for the next "epidemic" of dissociation. PMID:17716088

  1. Effects of electron kinetic energy and ion-electron inelastic collisions in electron capture dissociation measured using ion nanocalorimetry

    Microsoft Academic Search

    Jeremy T. OBrien; James S. Prell; Anne I. S. Holm; Evan R. Williams

    2008-01-01

    Ion nanocalorimetry is used to measure the effects of electron kinetic energy in electron capture dissociation (ECD). With\\u000a ion nanocalorimetry, the internal energy deposited into a hydrated cluster upon activation can be determined from the number\\u000a of water molecules that evaporate. Varying the heated cathode potential from ?1.3 to ?2.0 V during ECD has no effect on the\\u000a average number

  2. Making and Breaking Bonds

    NSDL National Science Digital Library

    The Concord Consortium

    2011-12-11

    Atoms collide and, under certain circumstances, react to form bonds with one another. The process of association is the bonding of atoms into a molecule while dissociation is the process by which a molecule breaks apart into simpler groups of atoms, individual atoms, or ions. Students interact with a molecular dynamics model to explore the making and breaking of bonds.

  3. Dissociative attachment and vibrational excitation in low-energy electron-CF3I collisions

    NASA Astrophysics Data System (ADS)

    Fabrikant, I.; Marienfeld, S.

    2005-05-01

    Trifluoroiodomethane (CF3I) is a plasma etching gas that provides CF3 radicals and I^- anions through an efficient dissociative electron attachment (DEA) process at near zero electron energies.^1 We have carried out a combined experimental and theoretical study of DEA to CF3I at electron energies below 1 eV. Measurements, performed at high resolution with two variants of the laser photoelectron attachment method,^2 yielded a joint DEA cross section over the range 1-500 meV, normalized in absolute size to the thermal DEA rate coefficient from swarm data.^1 At the onsets for excitation of one and two quanta for the C-I stretching mode ?3, clear downward cusps are detected. Calculations were performed by using the resonance R-matrix theory and the result for the thermal DEA rate coefficient.^1 The calculated DEA cross section shows good overall agreement with the experimental result in both shape and absolute size. In addition, we present theoretical cross sections for vibrational excitation of the ?3 mode which exhibit strong threshold peaks. ^1 L. G. Christophorou, J. K. Olthoff, J. Phys. Chem. Ref. Data 29, 553 (2000). ^2 H. Hotop, M.-W. Ruf, M. Allan, I. I. Fabrikant, Adv. At. Mol. Opt. Phys. 49, 85 (2003).

  4. Full-dimensional diabatic potential energy surfaces including dissociation: The 2E? state of NO3

    NASA Astrophysics Data System (ADS)

    Eisfeld, Wolfgang; Vieuxmaire, Olivier; Viel, Alexandra

    2014-06-01

    A scheme to produce accurate full-dimensional coupled diabatic potential energy surfaces including dissociative regions and suitable for dynamical calculations is proposed. The scheme is successfully applied to model the two-sheeted surface of the 2E? state of the NO3 radical. An accurate potential energy surface for the NO_3^- anion ground state is developed as well. Both surfaces are based on high-level ab initio calculations. The model consists of a diabatic potential matrix, which is expanded to higher order in terms of symmetry polynomials of symmetry coordinates. The choice of coordinates is key for the accuracy of the obtained potential energy surfaces and is discussed in detail. A second central aspect is the generation of reference data to fit the expansion coefficients of the model for which a stochastic approach is proposed. A third ingredient is a new and simple scheme to handle problematic regions of the potential energy surfaces, resulting from the massive undersampling by the reference data unavoidable for high-dimensional problems. The final analytical diabatic surfaces are used to compute the lowest vibrational levels of NO_3^- and the photo-electron detachment spectrum of NO_3^- leading to the neutral radical in the 2E? state by full dimensional multi-surface wave-packet propagation for NO3 performed using the Multi-Configuration Time Dependent Hartree method. The achieved agreement of the simulations with available experimental data demonstrates the power of the proposed scheme and the high quality of the obtained potential energy surfaces.

  5. Full-dimensional diabatic potential energy surfaces including dissociation: the E? state of NO?.

    PubMed

    Eisfeld, Wolfgang; Vieuxmaire, Olivier; Viel, Alexandra

    2014-06-14

    A scheme to produce accurate full-dimensional coupled diabatic potential energy surfaces including dissociative regions and suitable for dynamical calculations is proposed. The scheme is successfully applied to model the two-sheeted surface of the (2)E? state of the NO3 radical. An accurate potential energy surface for the NO?? anion ground state is developed as well. Both surfaces are based on high-level ab initio calculations. The model consists of a diabatic potential matrix, which is expanded to higher order in terms of symmetry polynomials of symmetry coordinates. The choice of coordinates is key for the accuracy of the obtained potential energy surfaces and is discussed in detail. A second central aspect is the generation of reference data to fit the expansion coefficients of the model for which a stochastic approach is proposed. A third ingredient is a new and simple scheme to handle problematic regions of the potential energy surfaces, resulting from the massive undersampling by the reference data unavoidable for high-dimensional problems. The final analytical diabatic surfaces are used to compute the lowest vibrational levels of NO?? and the photo-electron detachment spectrum of NO?? leading to the neutral radical in the (2)E? state by full dimensional multi-surface wave-packet propagation for NO3 performed using the Multi-Configuration Time Dependent Hartree method. The achieved agreement of the simulations with available experimental data demonstrates the power of the proposed scheme and the high quality of the obtained potential energy surfaces. PMID:24929376

  6. DISSOCIATIVE RECOMBINATION OF N 2 H + : EVIDENCE FOR FRACTURE OF THE N#N BOND W. D. Geppert, 1,2

    E-print Network

    Millar, Tom

    Branching ratios and absolute cross sections have been measured for the dissociative recombination of N 2 H # ! NH + N, consequently amounts to 64%. The cross section of the reaction could be fitted. The implications of these measurements for the chemistry of interstellar clouds are discussed. A standard model

  7. Block-Localized Density Functional Theory (BLDFT), Diabatic Coupling, and Their Use in Valence Bond Theory for Representing Reactive Potential Energy Surfaces

    PubMed Central

    Cembran, Alessandro; Song, Lingchun; Mo, Yirong; Gao, Jiali

    2010-01-01

    A multistate density functional theory in the framework of the valence bond model is described. The method is based on a block-localized density functional theory (BLDFT) for the construction of valence-bond-like diabatic electronic states and is suitable for the study of electron transfer reactions and for the representation of reactive potential energy surfaces. The method is equivalent to a valence bond theory with the treatment of the localized configurations by using density functional theory (VBDFT). In VBDFT, the electron densities and energies of the valence bond states are determined by BLDFT. A functional estimate of the off-diagonal matrix elements of the VB Hamiltonian is proposed, making use of the overlap integral between KohnSham determinants and the exchange-correlation functional for the ground state substituted with the transition (exchange) density. In addition, we describe an approximate approach, in which the off-diagonal matrix element is computed by wave function theory using block-localized KohnSham orbitals. The key feature is that the electron density of the adiabatic ground state is not directly computed nor used to obtain the ground-state energy; the energy is determined by diagonalization of the multistate valence bond Hamiltonian. This represents a departure from the standard single-determinant KohnSham density functional theory. The multistate VBDFT method is illustrated by the bond dissociation of H2+ and a set of three nucleophilic substitution reactions in the DBH24 database. In the dissociation of H2+, the VBDFT method yields the correct asymptotic behavior as the two protons stretch to infinity, whereas approximate functionals fail badly. For the SN2 nucleophilic substitution reactions, the hybrid functional B3LYP severely underestimates the barrier heights, while the approximate two-state VBDFT method overcomes the self-interaction error, and overestimates the barrier heights. Inclusion of the ionic state in a three-state model, VBDFT(3), significantly improves the computed barrier heights, which are found to be in accord with accurate results. The BLDFT method is a versatile theory that can be used to analyze conventional DFT results to gain insight into chemical bonding properties, and it is illustrated by examining the intricate energy contributions to the iondipole complex stabilization. PMID:20228960

  8. Block-Localized Density Functional Theory (BLDFT), Diabatic Coupling, and Their Use in Valence Bond Theory for Representing Reactive Potential Energy Surfaces.

    PubMed

    Cembran, Alessandro; Song, Lingchun; Mo, Yirong; Gao, Jiali

    2009-10-13

    A multistate density functional theory in the framework of the valence bond model is described. The method is based on a block-localized density functional theory (BLDFT) for the construction of valence-bond-like diabatic electronic states and is suitable for the study of electron transfer reactions and for the representation of reactive potential energy surfaces. The method is equivalent to a valence bond theory with the treatment of the localized configurations by using density functional theory (VBDFT). In VBDFT, the electron densities and energies of the valence bond states are determined by BLDFT. A functional estimate of the off-diagonal matrix elements of the VB Hamiltonian is proposed, making use of the overlap integral between Kohn-Sham determinants and the exchange-correlation functional for the ground state substituted with the transition (exchange) density. In addition, we describe an approximate approach, in which the off-diagonal matrix element is computed by wave function theory using block-localized Kohn-Sham orbitals. The key feature is that the electron density of the adiabatic ground state is not directly computed nor used to obtain the ground-state energy; the energy is determined by diagonalization of the multistate valence bond Hamiltonian. This represents a departure from the standard single-determinant Kohn-Sham density functional theory. The multistate VBDFT method is illustrated by the bond dissociation of H2+ and a set of three nucleophilic substitution reactions in the DBH24 database. In the dissociation of H2+, the VBDFT method yields the correct asymptotic behavior as the two protons stretch to infinity, whereas approximate functionals fail badly. For the S(N)2 nucleophilic substitution reactions, the hybrid functional B3LYP severely underestimates the barrier heights, while the approximate two-state VBDFT method overcomes the self-interaction error, and overestimates the barrier heights. Inclusion of the ionic state in a three-state model, VBDFT(3), significantly improves the computed barrier heights, which are found to be in accord with accurate results. The BLDFT method is a versatile theory that can be used to analyze conventional DFT results to gain insight into chemical bonding properties, and it is illustrated by examining the intricate energy contributions to the ion-dipole complex stabilization. PMID:20228960

  9. Electronic structures and chemical bonding in 4d- and 5d-transition metal mononitrides

    Microsoft Academic Search

    B. Hong; L. Cheng; M. Y. Wang; Z. J. Wu

    2010-01-01

    Bond distances, vibrational frequencies, dipole moments, dissociation energies, electron affinities and ionisation potentials of 4d- and 5d- transition metal mononitrides molecules in neutral, positively and negatively charged ions were studied using density functional method B3LYP. The bonding patterns are complex for these systems, which involves covalent, ionic and dative components. The calculated results are compared with the available data and

  10. 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 [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Buhr, Henrik [Department of Particle Physics, Weizmann Institute of Science, 76100 Rehovot (Israel); Kreckel, Holger [Columbia University, 550 West 120th Street, New York, New York 10027 (United States); Kokoouline, Viatcheslav [Department of Physics, University of Central Florida, Orlando, Florida 32816, USA, and Laboratoire Aime Cotton, CNRS, Universite Paris-Sud XI, F-91405 Orsay (France); Greene, Chris H. [Department of Physics and JILA, University of Colorado, Boulder, Colorado 80309-0440 (United States); 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.

  11. 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.

  12. Surface oxygen bond energy of Period IV transition metal oxides in the oxidation of carbon monoxide

    Microsoft Academic Search

    V. I. Marshneva; G. K. Boreskov

    1974-01-01

    The bond energies of oxygen have been determined by thermodesorption from Period IV transition metal oxides, both after treatment with oxygen and under steady state conditions of the catalytic oxidation of CO. With the exception of V2O5, there are several (23) forms of adsorbed oxygen with different bond energies on the surface of the oxide treated with oxygen.

  13. Dissociation of superdislocations and the stacking fault energy in TiAl based alloys with Nb-doping

    Microsoft Academic Search

    Y. Yuan; H. W. Liu; X. N. Zhao; X. K. Meng; Z. G. Liu; Torben Boll; Talaat Al-Kassab

    2006-01-01

    Dissociations of super-dislocations in ?-TiAl in Nb-doped Ti-48 at.% Al-1 at.% Nb and Ti-48 at.% Al-10 at.% Nb have been studied by high resolution transmission electron microscopy (HRTEM) and weak beam transmission electron microscopy (TEM). The SISF energy was calculated to be 63 mJ\\/m2 in Ti-48 at.% Al-1 at.% Nb and 34 mJ\\/m2 in Ti-48 at.% Al-10 at.% Nb according

  14. Structural characterization of fatty acids cationized with copper by electrospray ionization mass spectrometry under low-energy collision-induced dissociation.

    PubMed

    Afonso, Carlos; Riu, Anne; Xu, Ying; Fournier, Franoise; Tabet, Jean-Claude

    2005-03-01

    Fatty acids have for many years been characterized by mass spectrometry using electron ionization after chemical derivatization. When fatty acids are ionized using desorption/ionization methods such as electrospray ionization or fast atom bombardment, structural information is usually obtained through high-energy collision-induced dissociation (CID) using sector instruments. It has been shown that copper displays very interesting properties in the gas phase during CID. In this study, the reactivity of saturated and unsaturated fatty acid-copper [M-H+Cu(II)]+ complex and the role of the copper ion in promoting fragmentations were investigated under low-energy collisional activation conditions. The decomposition of these species in an ion trap instrument led to diagnostic ion series that reflect C--C bond cleavage, which involves Cu(II) reduction followed by the release of an alkyl radical. It was demonstrated that in this way the localization of one or two homoconjugated double bonds is possible using low-energy CID. Moreover, the distinction of cis and trans isomers is possible through characteristic product ions related to a specific loss of CO2. When these experiments are repeated using a triple-quadrupole instrument with argon as collision gas, a different behavior is observed as in this case, in addition to the product ion distributions observed in the ion trap, other distributions are observed that reflect the influence of the different kinetic shifts and the occurrence of consecutive decompositions. Different examples are presented with various saturated and unsaturated fatty acid chains. Mechanisms are proposed in order to rationalize the experimental observations. PMID:15674862

  15. Theoretical Aspects of the Biological Catch Bond

    Microsoft Academic Search

    Oleg V. Prezhdo; Yuriy V. Pereverzev

    2009-01-01

    he biological catch bond is fascinating and counterintuitive. When an external force is applied to a catch bond, either in vivo or in vitro, the bond resists breaking and becomes stronger instead. In contrast, ordinary slip bonds, which represent the vast majority of biological and chemical bonds, dissociate faster when subjected to a force. Catch-bond behavior was first predicted theoretically

  16. Characterization of intact N- and O-linked glycopeptides using higher energy collisional dissociation.

    PubMed

    Cao, Li; Toli?, Nikola; Qu, Yi; Meng, Da; Zhao, Rui; Zhang, Qibin; Moore, Ronald J; Zink, Erika M; Lipton, Mary S; Paa-Toli?, Ljiljana; Wu, Si

    2014-05-01

    Simultaneous elucidation of the glycan structure and the glycosylation site are needed to reveal the biological function of protein glycosylation. In this study, we employed a recent type of fragmentation termed higher energy collisional dissociation (HCD) to examine fragmentation patterns of intact glycopeptides generated from a mixture of standard glycosylated proteins. The normalized collisional energy (NCE) value for HCD was varied from 30 to 60% to evaluate the optimal conditions for the fragmentation of peptide backbones and glycoconjugates. Our results indicated that HCD with lower NCE values preferentially fragmented the sugar chains attached to the peptides to generate a ladder of neutral loss of monosaccharides, thereby enabling the putative glycan structure characterization. In addition, detection of the oxonium ions enabled unambiguous differentiation of glycopeptides from non-glycopeptides. In contrast, HCD with higher NCE values preferentially fragmented the peptide backbone and, thus, provided information needed for confident peptide identification. We evaluated the HCD approach with alternating NCE parameters for confident characterization of intact N- and O-linked glycopeptides in a single liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. In addition, we applied a novel data analysis pipeline, so-called GlycoFinder, to form a basis for automated data analysis. Overall, 38 unique intact glycopeptides corresponding to eight glycosylation sites (six N-linked and two O-linked sites) were confidently identified from a standard protein mixture. This approach provided concurrent characterization of both the peptide and the glycan, thereby enabling comprehensive structural characterization of glycoproteins in a single LC-MS/MS analysis. PMID:24440233

  17. Characterization of intact N- and O-linked glycopeptides using higher energy collisional dissociation

    SciTech Connect

    Cao, Li; Tolic, Nikola; Qu, Yi; Meng, Da; Zhao, Rui; Zhang, Qibin; Moore, Ronald J.; Zink, Erika M.; Lipton, Mary S.; Pasa-Tolic, Ljiljana; Wu, Si

    2014-01-15

    Simultaneous elucidation of the glycan structure and the glycosylation site are needed to reveal the biological function of protein glycosylation. In this study, we employed a recent type of fragmentation termed higher energy collisional dissociation (HCD) to examine fragmentation patterns of intact glycopeptides generated from a mixture of standard glycosylated proteins. The normalized collisional energy (NCE) value for HCD was varied from 30% to 60% to evaluate the optimal conditions for the fragmentation of peptide backbones and glycoconjugates. Our results indicated that HCD with lower NCE valuespreferentially fragmented the sugar chains attached to the peptides to generate a ladder of neutral loss of monosaccharides, thus enabling the putative glycan structure characterization. Also, detection of the oxonium ions enabled unambiguous differentiation of glycopeptides from non-glycopeptides. On the contrary, HCD with higher NCE values preferentially fragmented the peptide backbone and thus provided information needed for confident peptide identification. We evaluated the HCD approach with alternating NCE parameters for confident characterization of intact N-linked and O-linked glycopeptides in a single liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. In addition, we applied a novel data analysis pipeline, so-called GlycoFinder, to form a basis for automated data analysis. Overall, 38 unique intact glycopeptides corresponding to eight glycosylation sites (including six N-linked and two O-linked sites) were confidently identified from a standard protein mixture. This approach provided concurrent characterization of both, the peptide and the glycan, thus enabling comprehensive structural characterization of glycoproteins in a single LC-MS/MS analysis.

  18. Electron-induced ionization and dissociative ionization of iron pentacarbonyl molecules

    NASA Astrophysics Data System (ADS)

    Lacko, Michal; Papp, Peter; Wnorowski, Karol; Matej?k, tefan

    2015-03-01

    Electron ionization (EI) and dissociative ionization (DI) of Iron pentacarbonyl molecule (Fe(CO)5) was studied using a crossed molecular and electron beam mass spectrometry technique. Positive ions FeO(CO)+, FeC(CO)2+ and CO+ of Fe(CO)5 were detected for the first time. We have determined the experimental appearance energies of positive ions, the thresholds for dissociative reactions, the experimental bond dissociation energies for (CO)nFe+-CO bond breaks (for n = 4,..., 0) and their average value for Fe-C bond energy 1.25 eV in Fe(CO)5+. We have performed extensive density functional theory (DFT) studies of the ground states of neutral molecule and fragments 1 A1' Fe(CO)5, 3B1 Fe(CO)4, 3A1Fe(CO)3, 3?g Fe(CO)2, 3 ?FeCO as well as positive ions 2A1 Fe(CO)5+, 4A1 Fe(CO)4+, 4A1 Fe(CO)3+, 4?g Fe(CO)2+ and 4 ? FeCO+. The structures and energies of the states have beendetermined and the calculated bond dissociation energies (BDEs) were compared with present experiments as well as with previous works. Contribution to the Topical Issue "Elementary Processes with Atoms and Molecules in Isolated and Aggregated States", edited by Friedrich Aumayr, Bratislav Marinkovic, Stefan Matejick, John Tanis and Kurt H. Becker.

  19. Six-dimensional quantum dynamics for dissociative chemisorption of H2 and D2 on Ag(111) on a permutation invariant potential energy surface.

    PubMed

    Jiang, Bin; Guo, Hua

    2014-12-01

    A six-dimensional potential energy surface (PES) for H2 dissociation on rigid Ag(111) is developed by fitting ?4000 plane-wave density functional theory points using the recently proposed permutation invariant polynomial-neural network (PIP-NN) method, which enforces both the surface periodicity and molecular permutation symmetry. Quantum reactive scattering calculations on the PIP-NN PES yielded dissociative sticking probabilities for both H2 and D2. Good agreement with experiment was achieved at high collision energies, but the agreement is less satisfactory at low collision energies, due apparently to the neglect of surface temperature in our model. The dissociation is activated by both vibrational and translational excitations, with roughly equal efficacies. Rotational and alignment effects were examined and found to be quite similar to hydrogen dissociation on Ag(100) and Cu(111). PMID:25315820

  20. 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; Sztray, Blint

    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

  1. Origin of a Theory or Where did "near-dissociation theory" & the "Le Roy Radius"

    E-print Network

    Le Roy, Robert J.

    paper. This work used a conventional technique for determining the molecular dissociation energy from a plot of the vibrational level spacings Gv+1/2 vs. the vibrational quantum number v . It turned out, and sometimes also joined by hydrogen bonding; e.g., plastics 3. Metals: a "sea" of electrons loosely

  2. Kinetic energy distribution for the ionization and dissociation process of C2H4 by electron impact

    NASA Astrophysics Data System (ADS)

    Wang, X.; Chen, Z.; Wei, B.; Hutton, R.; Zou, Y.

    2015-01-01

    The dissociative ionization of ethylene molecules following impact by electrons in the energy range of 20 to 200 eV has been studied with a cold target recoil-ion momentum spectrometer (COLTRIMS). The relative partial cross sections for the ionic fragments C2Hn+ (n=0~3) with respect to C2H4+ were plotted as a function of the incident energy. By measuring the time of flight and position of the fragment ions, the kinetic energy distribution has been deduced. Taking advantage of the supersonic jet expansion, the thermal motion contributing to the kinetic energy distribution of the recoil-ions was reduced. The average kinetic energy of the recoil ions as a function of the incident electron energy has also been plotted. Furthermore, the average kinetic energy release for the dissociation to C2H3+ and C2H2+ were estimated as 0.76 eV and 0.73 eV respectively.

  3. 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.

  4. Identification of the strongest bonds in chemistry.

    PubMed

    Kalescky, Robert; Kraka, Elfi; Cremer, Dieter

    2013-09-12

    Increasing the effective electronegativity of two atoms forming a triple bond can increase the strength of the latter. The strongest bonds found in chemistry involve protonated species of hydrogen cyanide, carbon monoxide, and dinitrogen. CCSD(T)/CBS (complete basis set) and G4 calculations reveal that bond dissociation energies are misleading strength descriptors. The strength of the bond is assessed via the local stretching force constants, which suggest relative bond strength orders (RBSO) between 2.9 and 3.4 for heavy atom bonding (relative to the CO bond strength in methanol (RBSO = 1) and formaldehyde (RBSO = 2)) in [HCNH](+)((1)?(+)), [HCO](+)((1)?(+)), [HNN](+)((1)?(+)), and [HNNH](2+)((1)?g(+)). The increase in strength is caused by protonation, which increases the electronegativity of the heavy atom and thereby decreases the energy of the bonding AB orbitals (A, B: C, N, O). A similar effect can be achieved by ionization of a nonbonding or antibonding electron in CO or NO. The strongest bond with a RBSO value of 3.38 is found for [HNNH](2+) using scaled CCSD(T)/CBS frequencies determined for CCSD(T)/CBS geometries. Less strong is the NN bond in [FNNH](2+) and [FNNF](2+). PMID:23927609

  5. Experimental and Theoretical Investigations of Energy Transfer and Hydrogen-Bond Breaking in the Water Dimer

    E-print Network

    Reisler, Hanna

    Experimental and Theoretical Investigations of Energy Transfer and Hydrogen-Bond Breaking in the Water Dimer Lee C. Ch'ng, Amit K. Samanta, Gabor Czako,, Joel M. Bowman,*, and Hanna Reisler bonding in water is dominated by pairwise dimer interactions, and the predissociation of the water dimer

  6. Anionic copper complex fragmentations from enkephalins under low-energy collision-induced dissociation in an ion trap mass spectrometer.

    PubMed

    Bosse, Anne; Afonso, Carlos; Fournier, Franoise; Tasseau, Olivier; Pepe, Claude; Bellier, Bruno; Tabet, Jean-Claude

    2004-08-01

    Peptide metallation with Cu2+ was explored in the negative ESI mode using an ion trap mass spectrometer. Under these conditions, the [(M-3H) + CuII]- species formed were investigated under low-energy collision-induced dissociation conditions. MS2 experiments indicate a very different behavior of CuII metallated complexes compared with [M-H]- species. CuII induces an easy loss of CO2 and specific side-chain cleavages (by radical losses) at the C-terminal residue, as observed previously by prompt 'in source' dissociation experiments. The loss of CO2 yields an unstable carbylide that leads to further dissociations involving the migration of a proton or a hydrogen radical (through the reduction of CuII). Multistage MS3 experiments were carried out to rationalize this behavior. Fragmentation pathways are proposed in order to explain the product ions observed. The side-chain radical loss at the C-terminus was demonstrated to be a consecutive process. Finally, evidence is provided that the specific side-chain cleavages can be used for the differentiation of Leu/Ile and Gln/Lys residues when they are located at the C-terminus. The existence of a zwitterionic form in the case of the anionic YGGFK-CuII complex is proposed. PMID:15329842

  7. Energy and Atomic Configuration of Complete and Dissociated Dislocations. I. Edge Dislocation in an fcc Metal

    Microsoft Academic Search

    R. M. Cotterill; M. Doyama

    1966-01-01

    The arrangement of atoms around an edge dislocation in copper has been calculated by a variational method using a central-force approximation. The pairwise interaction between discrete atoms was represented by a Morse potential function. In the calculation of the complete dislocation, the atoms were not permitted to relax in a direction parallel to the dislocation line. This prevented dissociation. Linear-elasticity

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

    E-print Network

    Alavi, Ali

    for Dissociation Reactions at Surfaces Angelos Michaelides, Z.-P. Liu, C. J. Zhang, Ali Alavi, David A. King reactions at catalytic surfaces.1 The key parameter that controls the rate of each elementary reaction step of reactions on a variety of late transition metal surfaces. A complete list of the more than 50 elementary

  9. Dissociative recombination cross section and branching ratios of protonated dimethyl disulfide and N-methylacetamide.

    PubMed

    al-Khalili, A; Thomas, R; Ehlerding, A; Hellberg, F; Geppert, W D; Zhaunerchyk, V; af Ugglas, M; Larsson, M; Uggerud, E; Vedde, J; Adlhart, C; Semaniak, J; Kami?ska, M; Zubarev, R A; Kjeldsen, F; Andersson, P U; Osterdahl, F; Bednarska, V A; Pal, A

    2004-09-22

    Dimethyl disulfide (DMDS) and N-methylacetamide are two first choice model systems that represent the disulfide bridge bonding and the peptide bonding in proteins. These molecules are therefore suitable for investigation of the mechanisms involved when proteins fragment under electron capture dissociation (ECD). The dissociative recombination cross sections for both protonated DMDS and protonated N-methylacetamide were determined at electron energies ranging from 0.001 to 0.3 eV. Also, the branching ratios at 0 eV center-of-mass collision energy were determined. The present results give support for the indirect mechanism of ECD, where free hydrogen atoms produced in the initial fragmentation step induce further decomposition. We suggest that both indirect and direct dissociations play a role in ECD. PMID:15366993

  10. Molecular dynamics of gas phase hydrogen-bonded complexes

    E-print Network

    Wofford, Billy Alan

    1987-01-01

    and the thermo- dynamic functions for dimer formation for hydrogen-bonded systems using high resolution Fourier transform infrared spectroscopy. High resolution spectroscopy provides a powerful approach for the investi- gation of the molecular dynamics... CHAPTER III. DETERMINATION OF HYDROGEN-BONDED DISSOCIATION ENERGIES AND THERMODYNAMIC FUNCTIONS OF DIMER FORMATION USING HIGH RESOLUTION FTIR SPECTROSCOPY. . . . . . . . . . . , 30 Introduction. 30 Experimental Method. Results. 32 37 CHAPTER IV...

  11. Kinetics of CH4 and CO2 hydrate dissociation and gas bubble evolution via MD simulation.

    PubMed

    Uddin, M; Coombe, D

    2014-03-20

    Molecular dynamics simulations of gas hydrate dissociation comparing the behavior of CH4 and CO2 hydrates are presented. These simulations were based on a structurally correct theoretical gas hydrate crystal, coexisting with water. The MD system was first initialized and stabilized via a thorough energy minimization, constant volume-temperature ensemble and constant volume-energy ensemble simulations before proceeding to constant pressure-temperature simulations for targeted dissociation pressure and temperature responses. Gas bubble evolution mechanisms are demonstrated as well as key investigative properties such as system volume, density, energy, mean square displacements of the guest molecules, radial distribution functions, H2O order parameter, and statistics of hydrogen bonds. These simulations have established the essential similarities between CH4 and CO2 hydrate dissociation. The limiting behaviors at lower temperature (no dissociation) and higher temperature (complete melting and formation of a gas bubble) have been illustrated for both hydrates. Due to the shift in the known hydrate stability curves between guest molecules caused by the choice of water model as noted by other authors, the intermediate behavior (e.g., 260 K) showed distinct differences however. Also, because of the more hydrogen-bonding capability of CO2 in water, as reflected in its molecular parameters, higher solubility of dissociated CO2 in water was observed with a consequence of a smaller size of gas bubble formation. Additionally, a novel method for analyzing hydrate dissociation based on H-bond breakage has been proposed and used to quantify the dissociation behaviors of both CH4 and CO2 hydrates. Activation energies Ea values from our MD studies were obtained and evaluated against several other published laboratory and MD values. Intrinsic rate constants were estimated and upscaled. A kinetic reaction model consistent with macroscale fitted kinetic models has been proposed to indicate the macroscopic consequences of this analysis. PMID:24571292

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

    PubMed

    Gibbs, G V; Cox, D F; Crawford, T D; Rosso, K M; Ross, N L; Downs, R T

    2006-02-28

    A classification of the hydrogen fluoride H-F-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 /Vr(c)/ / Gr(c) where /Vr(c)/ is the magnitude of the local potential-energy density and Gr(c) is the local kinetic-energy density, each evaluated at a bond critical point r(c). A calculation of the ratio for the M-O bonded interactions comprising a relatively large number of oxide molecules and earth materials, together with the constraints imposed by the values of inverted Delta2rho r(c) and the local electronic energy density, Hr(c) = Gr(c) + Vr(c), in the H-F study, yielded practically the same classification for the oxides. This is true despite the different trends that hold between the bond critical point and local energy density properties with the bond lengths displayed by the H-F and M-O bonded interactions. On the basis of the ratio, Li-O, Na-O, and Mg-O bonded interactions classify as closed-shell ionic bonds, Be-O, Al-O, Si-O, B-O, and P-O interactions classify as bonds of intermediate character with the covalent character increasing from Be-O to P-O. N-O interactions classify as shared covalent bonds. C-O and S-O bonded interactions classify as both intermediate and covalent bonded interactions. The C-O double- and triple-bonded interactions classify as intermediate-bonded interactions, each with a substantial component of covalent character and the C-O single-bonded interaction classifies as a covalent bond whereas their local electronic energy density values indicate that they are each covalent bonded interactions. The ratios for the Be-O, Al-O, and Si-O bonded interactions indicate that they have a substantial component of ionic character despite their classification as bonds of intermediate character. The trend between the ratio and the character of the bonded interactions is consistent with trends expected from electronegativity considerations. The ratio increases as the net charges and the coordination numbers for the atoms for several Ni-sulfides decrease. On the contrary, the ratio for the Si-O bonded interactions for the orthosilicate, forsterite, Mg2SiO4, and the high-pressure silica polymorph, stishovite, decreases as the observed net atomic charges and the coordination numbers of Si and O increase in value. The ratio for the Ni-Ni bonded interactions for the Ni-sulfides and bulk Ni metal indicate that the interactions are intermediate in character with a substantial component of ionic character. PMID:16512733

  13. Toward a General Mechanism of Electron Capture Dissociation

    E-print Network

    Simons, Jack

    a sterically proximate amino acid residue to form a labile aminoketyl radical that dissociates by NOC bondToward 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

  14. Energy-sensitive imaging detector applied to the dissociative recombination of D{sub 2}H{sup +}

    SciTech Connect

    Buhr, H.; Schwalm, D. [Faculty of Physics, Weizmann Institute of Science, IL-76100 Rehovot (Israel); Max-Planck-Institut fuer Kernphysik, D-69121 Heidelberg (Germany); Mendes, M. B.; Novotny, O.; Berg, M. H.; Bing, D.; Krantz, C.; Orlov, D. A.; Sorg, T.; Stuetzel, J.; Varju, J.; Wolf, A. [Max-Planck-Institut fuer Kernphysik, D-69121 Heidelberg (Germany); Heber, O.; Rappaport, M. L.; Zajfman, D. [Faculty of Physics, Weizmann Institute of Science, IL-76100 Rehovot (Israel)

    2010-06-15

    We report on an energy-sensitive imaging detector for studying the fragmentation of polyatomic molecules in the dissociative recombination of fast molecular ions with electrons. The system is based on a large area (10x10 cm{sup 2}) position-sensitive, double-sided Si-strip detector with 128 horizontal and 128 vertical strips, whose pulse height information is read out individually. The setup allows us to uniquely identify fragment masses and is thus capable of measuring branching ratios between different fragmentation channels, kinetic energy releases, and breakup geometries as a function of the relative ion-electron energy. The properties of the detection system, which has been installed at the Test Storage Ring (TSR) facility of the Max-Planck Institute for Nuclear Physics in Heidelberg, is illustrated by an investigation of the dissociative recombination of the deuterated triatomic hydrogen cation D{sub 2}H{sup +}. A huge isotope effect is observed when comparing the relative branching ratio between the D{sub 2} + H and the HD + D channel; the ratio 2B(D{sub 2} + H)/B(HD + D), which is measured to be 1.27{+-}0.05 at relative electron-ion energies around 0 eV, is found to increase to 3.7{+-}0.5 at {approx}5 eV.

  15. Spondylopelvic dissociation.

    PubMed

    Sullivan, Matthew P; Smith, Harvey E; Schuster, James M; Donegan, Derek; Mehta, Samir; Ahn, Jaimo

    2014-01-01

    Spondylopelvic dissociation is a complex injury pattern resulting in multiplanar instability of the lumbopelvis. These injuries have traditionally been known as "suicide jumper's fractures" and have recently increased in prevalence as a result of under-vehicle explosions seen in the past decade of military conflicts in the Middle East. The hallmarks of spondylopelvic dissociation are bilateral vertical sacral fractures with a horizontal component, resulting in lumbosacral instability in the sagittal and axial planes. Surgical treatment has evolved greatly and both percutaneous and open options are available, with triangular osteosynthesis being the most relied on method of fixation. PMID:24267208

  16. 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

  17. 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.

  18. N+ charge transfer and N+2 dissociation in N2 at swarm energies

    Microsoft Academic Search

    E. Basurto; J. de Urquijo; C. Cisneros; I. Alvarez

    2001-01-01

    This paper reports a drift-tube-mass-spectrometer measurement of the relative abundances of N+ and N+2 in pure nitrogen, over a ratio of electric field to gas density, E\\/N, from 800 to 7200 Td [1 townsend (Td)=10-17 V cm2]. A proposed charge transfer dissociation scheme between the above two ions and N2 allowed us to obtain spatial rate coefficients for charge transfer

  19. 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.

  20. Bond-energy force-constant relationship for bent XY2, pyramidal XY3 and tetrahedral XY4 molecules

    Microsoft Academic Search

    G. Thyagarajan; C. R. Sarma; M. K. Subhedar

    1969-01-01

    A relation between the force constants and bond energies of polyatomic molecules of bent XY2, pyramidal XY3, and tetrahedral XY4 types has been deduced by employing an approximately separable potential function for the molecules and using specific functional forms for the bonded and nonbonded interactions. To test the validity of the relation deduced, bond energies were calculated from the available

  1. The unimolecular dissociation of H{sub 2}CO on the lowest triplet potential-energy surface

    SciTech Connect

    Yamaguchi, Y.; Wesolowski, S.S.; Van Huis, T.J.; Schaefer, H.F. III [Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia30602 (United States)] [Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia30602 (United States)

    1998-04-01

    The unimolecular dissociation reaction of H{sub 2}CO on the triplet potential-energy surface has been studied via {ital ab initio} electronic structure theory. The stationary point geometries for the equilibrium and transition state are determined employing the configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory with large basis sets up to the correlation consistent (cc)-pVQZ basis. With the best method, cc-pVQZ CCSD(T), the first excited triplet ({tilde a}{sup 3}A{sup {double_prime}}) state lies 72.2kcal/mol (25260cm{sup {minus}1}) above the ground ({tilde X}{sup 1}A{sub 1}) state of H{sub 2}CO, which is in excellent agreement with the experimental observation of 72.03kcal/mol (25194cm{sup {minus}1}). The dissociation limit (H{center_dot}+HCO{center_dot}) is located at 86.3kcal/mol (30170cm{sup {minus}1}) above the ground state of H{sub 2}CO, which is again in good agreement with the two experimentally determined values of 86.57kcal/mol (30280cm{sup {minus}1}) and 86.71kcal/mol (30328.5cm{sup {minus}1}). With the same method the triplet dissociation transition state lies 92.4kcal/mol (32300cm{sup {minus}1}) above the ground state. Consequently, the activation energy for the dissociation reaction of H{sub 2}CO on the triplet surface is determined {ital ab initio} to be 18.9{endash}20.1kcal/mol (6620{endash}7040cm{sup {minus}1}) (including an estimated error bar of 1.2kcal/mol or 420cm{sup {minus}1}). The zero-point vibrationally corrected exit barrier height is predicted to be 4.9{endash}6.1kcal/mol (1710{endash}2130cm{sup {minus}1}). These newly predicted energies are consistent with the recent experimental observations by the Moore group at University of California-Berkeley (1987) and by the Wittig group at University of Southern California (1997). {copyright} {ital 1998 American Institute of Physics.}

  2. 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.

  3. 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.

  4. Evidence of the existence of dissociated water molecules in water clusters

    NASA Astrophysics Data System (ADS)

    Lee, Chengteh; Sosa, Carlos; Novoa, Juan J.

    1995-09-01

    The dissociation of water molecules in the water cluster was investigated using ab initio methods and density functional theory. A stable minimum energy configuration of a cluster containing H3O+ and OH- ions was located for a water cluster with five water molecules, (H2O)5. There are six hydrogen bonds in the dissociated water cluster to form the minimum energy structure. A similar structure with H3O+ and OH- ions was also found for a (H2O)8 cluster.

  5. 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

  6. Zero Kinetic Energy Photofragment Spectroscopy: The Threshold Dissociation of NO2 J. A. Mueller, S. A. Rogers, and Paul L. Houston*

    E-print Network

    Houston, Paul L.

    Zero Kinetic Energy Photofragment Spectroscopy: The Threshold Dissociation of NO2 J. A. Mueller, S been developed and applied to the photodissociation of NO2. Photofragments with zero recoil kinetic. Called zero kinetic energy (ZKE) photofragment spectroscopy, the technique is most useful

  7. Ab initio and natural bond orbital (NBO) study on the strain energy of chlorocyclotrisilane and chlorocyclopropane

    Microsoft Academic Search

    M. S. Sadjadi; N. Farhadyar; K. Zare

    2007-01-01

    A comparative study between hexachlorocyclotrisilane (1) and hexachlorocyclopropane (2) by ab initio method and natural bond orbital (NBO) analysis was carried out using 6-31G?? basis set, implemented in GAUSSIAN 03 program. The s and p character of SiCl and SiSi bonds obtained for the compounds were then used to examine the rehybridization effect from the strain energy. A higher strain

  8. 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

  9. Characterization of ground and excited electronic state deprotonation energies of systems containing double bonds using natural bond orbital analysis

    Microsoft Academic Search

    Jay K. Badenhoop; Steve Scheiner

    1996-01-01

    Natural bond orbital analysis is applied to the ground and excited states of a set of neutral, cationic, and anionic doubly bonded species HnC=XHn (X=C, N, O) isoelectronic with ethylene. The character of the excitation is correlated with calculated charge shifts and geometry changes upon relaxation. For these planar molecules, depopulation of the ? bond or population of the ?*

  10. Nature of the chemical bond and origin of the inverted dipole moment in boron fluoride: a generalized valence bond approach.

    PubMed

    Fantuzzi, Felipe; Cardozo, Thiago Messias; Nascimento, Marco Antonio Chaer

    2015-05-28

    The generalized product function energy partitioning (GPF-EP) method has been applied to investigate the nature of the chemical bond and the origin of the inverted dipole moment of the BF molecule. The calculations were carried out with GPF wave functions treating all of the core electrons as a single Hartree-Fock group and the valence electrons at the generalized valence bond perfect-pairing (GVB-PP) or full GVB levels, with the cc-pVTZ basis set. The results show that the chemical structure of both X (1)?(+) and a (3)? states is composed of a single bond. The lower dissociation energy of the excited state is attributed to a stabilizing intraatomic singlet coupling involving the B 2sp-like lobe orbitals after bond dissociation. An increase of electron density on the B atom caused by the reorientation of the boron 2sp-like lobe orbitals is identified as the main responsible effect for the electric dipole inversion in the ground state of BF. Finally, it is shown that ? back-bonding from fluorine to boron plays a minor role in the electron density displacement to the bonding region in both states. Moreover, this effect is associated with changes in the quasi-classical component of the electron density only and does not contribute to covalency in either of the states. Therefore, at least for the case of the BF molecule, the term back-bonding is misleading, since it does not contribute to the bond formation. PMID:25531385

  11. Metal carbonyl bond strengths in Fe(CO){sub n} and Ni(CO){sub n}

    SciTech Connect

    Sunderlin, L.S.; Wang, D.; Squires, R.R. [Purdue Univ., West Lafayette, IN (United States)

    1992-04-01

    Energy-resolved collision-induced dissociation of Fe(CO){sub n} (n= 1-4) and Ni(CO){sub n} (n= 2,3) is used to determine the metal-carbonyl bond energies (kcal/mol). These values are within error limits of values reported previously.

  12. Looking for high energy density compounds among polynitraminepurines.

    PubMed

    Yan, Ting; Sun, Guangdong; Chi, Weijie; Li, Butong; Wu, Haishun

    2013-09-01

    A series of purine derivatives with nitramine groups are calculated by using density functional theory (DFT). The molecular theory density, heats of formation, bond dissociation energies and detonation performance are investigated at DFT-B3LYP/6-311G** level. The isodesmic reaction method is employed to calculate the HOFs of the energies obtained from electronic structure calculations. Results show that the position of nitramine groups can influence the values of HOFs. The bond dissociation energies and the impact sensitivity are analyzed to investigate the thermal stability of the purine derivatives. The calculated bond dissociation energies of ring-NHNO2 and NH-NO2 bond show that the NH-NO2 bond should be the trigger bond in pyrolysis processes. The H50 of most compounds are larger than that of CL-20 and RDX. PMID:23708652

  13. NeH+ dissociative recombination

    NASA Astrophysics Data System (ADS)

    Florescu, A. I.; Orel, A. E.

    2005-01-01

    The rate coefficient for the NeH+ dissociative recombination (DR) with electrons was recently measured at the ASTRID storage ring in Denmark. The rate coefficient, as a function of the electron energy, is non-negligible at near-zero energy and displays two broad peaks between 10 and 30 eV. Both peaks are due to DR via Rydberg states converging to different dissociation limits of the NeH+ ion. The first one is due to the capture of the incoming electron by doubly excited Rydberg states dissociating in Ne (1s22s22p53s) + H(n >= 2 s, p). This series of Rydberg states converges to the core-excited ion state dissociating to Ne (3s) + H+. The second peak is due to the electron capture by Rydberg states dissociating to Ne (1s22s22p5 n <= 3 s, p) + H(1s). This series converges to the second ionization limit limit Ne+ + H(1s). We will report resonances found in the 10-30 eV energy range by electron scattering calculations using the Complex Kohn Variational method. The resonances, electronic couplings between resonances and the autoionization widths will be used in the time-dependent wave packet calculation describing the dissociation dynamics. The calculated cross sections and dissociation rates will be compared to the experimental ones measured by Mitchell et al.

  14. State-to-state dissociation dynamics in CF3NO

    NASA Astrophysics Data System (ADS)

    Bower, R. D.; Jones, R. W.; Houston, P. L.

    1983-09-01

    The state-to-state dissociation dynamics of CF3NO have been investigated by exciting the parent compound in a supersonic jet expansion with one tunable laser and monitoring the state distribution of the NO fragment by one- or two-photon laser-induced fluorescence using a second tunable laser. At the lowest levels of excitation, CF3NO dissociates to give an NO distribution which is consistent with a statistical distribution of energy in the products. As more highly excited vibronic states of S1 are selected, the product distribution begins to show signs of nonstatistical behavior, although the deviations are small. The appearance time of the NO decreases nearly monotonically with increasing energy above the S1 origin and is equal to the fluorescence lifetime of the CF3NO* to within experimental error. It is likely that both the appearance time of the NO and the fluorescence lifetime of the CF3NO* measure the rate of internal conversion from S1 to highly excited vibrational levels of S0, which then dissociate in a nearly statistical fashion on the S0 surface. The barrier to dissociation of the CF3-NO bond is 39.610.23 kcal/mol.

  15. Towards simple orbital-dependent density functionals for molecular dissociation

    NASA Astrophysics Data System (ADS)

    Zhang, Igor Ying; Richter, Patrick; Scheffler, Matthias

    2015-03-01

    Density functional theory (DFT) is one of the leading first-principles electronic-structure theories. However, molecular dissociation remains a challenge, because it requires a well-balanced description of the drastically different electronic structure at different bond lengths. One typical and well-documented case is the dissociation of both H2+ and H2, for which all popular DFT functionals fail. We start from the Bethe-Goldstone equation to propose a simple orbital-dependent correlation functional which generalizes the linear adiabatic connection approach. The resulting scheme is based on second-order perturbation theory (PT2), but includes the self-consistent coupling of electron-hole pairs, which ensures the correct H2 dissociation limit and gives a finite correlation energy for systems with a (near)-degenerate energy gap. This coupling PT2-like (CPT2) approximation delivers a significant improvement over all existing functionals for both H2 and H2+ dissociation. We will demonstrate the reason for this improvement analytically for H2 in a minimal basis.

  16. A quasiclassical trajectory study of collisional energy transfer and dissociation in He + H2(v,j) using a new potential energy surface.

    PubMed

    Mandy, M E; McNamara, G J

    2006-01-19

    Quasiclassical trajectories for He + H2 were carried out using the recent ab initio potential of Boothroyd, Martin, and Peterson (J. Chem. Phys. 2003, 119, 3187) and results for the 348 (v, j) states of H2 are compared to those of earlier calculations that used the potential of Wilson, Kapral, and Burns (Chem. Phys. Lett. 1974, 24, 4884). Examined are the cross sections for energy transfer and dissociation, the extent of threshold elevation, and the interconversion of vibrational and rotational energy. Implications for modeling the interstellar medium are discussed. PMID:16405313

  17. DFT and ab initio potential energy scan and hydrogen bond analysis of N ?-substituted hydrazino acetamides: Characterization of the hydrazinoturn hydrogen bonding pattern

    Microsoft Academic Search

    Hossein A. Dabbagh; Elham Rasti; Alexandre Hocquet; Philippe Le Grel

    2009-01-01

    We studied a series of model primary amides in gas phase at the DFT (B3LYP) and HF at 6-31+G\\/6-31+G?? levels of theory in order to shed light on their conformation, structure, and intramolecular hydrogen bonding network. A potential energy scan was performed by rotating around the appropriate bond for each molecule studied in this paper. In this manner, it was

  18. Dissociation energy and electronic and vibrational spectroscopy of Co(+)(H2O) and its isotopomers.

    PubMed

    Kocak, Abdulkadir; Austein-Miller, Geoff; Pearson, Wright L; Altinay, Gokhan; Metz, Ricardo B

    2013-02-14

    The electronic spectra of Co(+)(H(2)O), Co(+)(HOD), and Co(+)(D(2)O) have been measured from 13,500 to 18,400 cm(-1) using photodissociation spectroscopy. Transitions to four excited electronic states with vibrational and partially resolved rotational structure are observed. Each electronic transition has an extended progression in the metal-ligand stretch, v(3), and the absolute vibrational quantum numbering is assigned by comparing isotopic shifts between Co(+)(H(2)(16)O) and Co(+)(H(2)(18)O). For the low-lying excited electronic states, the first observed transition is to v(3)' = 1. This allows the Co(+)-(H(2)O) binding energy to be determined as D(0)(0 K)(Co(+)-H(2)O) = 13730 90 cm(-1) (164.2 1.1 kJ/mol). The photodissociation spectrum shows a well-resolved K(a) band structure due to rotation about the Co-O axis. This permits determination of the spin rotation constants ?(aa)" = -6 cm(-1) and ?(aa)' = 4 cm(-1). However, the K(a) rotational structure depends on v(3)'. These perturbations in the spectrum make the rotational constants unreliable. From the nuclear spin statistics of the rotational structure, the ground state is assigned as (3)B(1). The electronic transitions observed are from the Co(+)(H(2)O) ground state, which correlates to the cobalt ion's (3)F, 3d(8) ground state, to excited states which correlate to the (3)F, 3d(7)4s and (3)P, 3d(8) excited states of Co(+). These excited states of Co(+) interact less strongly with water than the ground state. As a result, the excited states are less tightly bound and have longer metal-ligand bonds. Calculations at the CCSD(T)/aug-cc-pVTZ level also predict that binding to Co(+) increases the H-O-H angle in water from 104.1 to 106.8, as the metal removes electron density from the oxygen lone pairs. The O-H stretching frequencies of the ground electronic state of Co(+)(H(2)O) and Co(+)(HOD) have been measured by combining IR excitation with visible photodissociation in a double resonance experiment. In Co(+)(H(2)O) the O-H symmetric stretch is ?(1)" = 3609.7 1 cm(-1). The antisymmetric stretch is ?(5)" = 3679.5 2 cm(-1). These values are 47 and 76 cm(-1), respectively, lower than those in bare H(2)O. In Co(+)(HOD) the O-H stretch is observed at 3650 cm(-1), a red shift of 57 cm(-1) relative to bare HOD. PMID:22835001

  19. Calorimetric and computational study of thiacyclohexane 1-oxide and thiacyclohexane 1,1-dioxide (thiane sulfoxide and thiane sulfone). Enthalpies of formation and the energy of the S=O bond.

    PubMed

    Roux, Mara Victoria; Temprado, Manuel; Jimnez, Pilar; Dvalos, Juan Zenn; Notario, Rafael; Guzmn-Meja, Ramn; Juaristi, Eusebio

    2003-03-01

    A rotating-bomb combustion calorimeter specifically designed for the study of sulfur-containing compounds [J. Chem. Thermodyn. 1999, 31, 635] has been used for the determination of the enthalpy of formation of thiane sulfone, 4, Delta(f)H(o) m(g) = -394.8 +/- 1.5 kJ x mol(-1). This value stands in stark contrast with the enthalpy of formation reported for thiane itself, Delta(f)H(o) m(g) = -63.5 +/- 1.0 kJ x mol(-1), and gives evidence of the increased electronegativity of the sulfur atom in the sulfonyl group, which leads to significantly stronger C-SO2 bonds. Given the known enthalpy of formation of atomic oxygen in the gas phase, Delta(f)H(o) m(O,g) = +249.18 kJ x mol(-1), and the reported bond dissociation energy for the S=O bond in alkyl sulfones, BDE(S=O) = +470.0 kJ x mol(-1), it was possible to estimate the enthalpy of formation of thiane sulfoxide, 5, a hygroscopic compound not easy to use in experimental calorimetric measurements, Delta(f)H(o) m(5) = -174.0 kJ x mol(-1). The experimental enthalpy of formation of both 4 and 5 were closely reproduced by theoretical calculations at the G2(MP2)+ level, Delta(f)H(o) m(4) = -395.0 kJ x mol(-1) and Delta(f)H(o) m(5) = -178.0 kJ x mol(-1). Finally, calculated G2(MP2)+ values for the bond dissociation energy of the S=O bond in cyclic sulfoxide 5 and sulfone 4 are +363.7 and +466.2 kJ x mol(-1), respectively. PMID:12608789

  20. Validity of the site-averaging approximation for modeling the dissociative chemisorption of H2 on Cu(111) surface: a quantum dynamics study on two potential energy surfaces.

    PubMed

    Liu, Tianhui; Fu, Bina; Zhang, Dong H

    2014-11-21

    A new finding of the site-averaging approximation was recently reported on the dissociative chemisorption of the HCl/DCl+Au(111) surface reaction [T. Liu, B. Fu, and D. H. Zhang, J. Chem. Phys. 139, 184705 (2013); T. Liu, B. Fu, and D. H. Zhang, J. Chem. Phys. 140, 144701 (2014)]. Here, in order to investigate the dependence of new site-averaging approximation on the initial vibrational state of H2 as well as the PES for the dissociative chemisorption of H2 on Cu(111) surface at normal incidence, we carried out six-dimensional quantum dynamics calculations using the initial state-selected time-dependent wave packet approach, with H2 initially in its ground vibrational state and the first vibrational excited state. The corresponding four-dimensional site-specific dissociation probabilities are also calculated with H2 fixed at bridge, center, and top sites. These calculations are all performed based on two different potential energy surfaces (PESs). It is found that the site-averaging dissociation probability over 15 fixed sites obtained from four-dimensional quantum dynamics calculations can accurately reproduce the six-dimensional dissociation probability for H2 (v = 0) and (v = 1) on the two PESs. PMID:25416886

  1. Bond breaking in a Morse chain under tension: fragmentation patterns, higher index saddles, and bond healing.

    PubMed

    Mauguire, F A L; Collins, P; Ezra, G S; Wiggins, S

    2013-04-01

    We investigate the fragmentation dynamics of an atomic chain under tensile stress. We have classified the location, stability type (indices), and energy of all equilibria for the general n-particle chain, and have highlighted the importance of saddle points with index >1. We show that for an n = 2-particle chain under tensile stress the index 2 saddle plays a central role in organizing the dynamics. We apply normal form theory to analyze phase space structure and dynamics in a neighborhood of the index 2 saddle. We define a phase dividing surface (DS) that enables us to classify trajectories passing through a neighborhood of the saddle point using the values of the integrals associated with the normal form. We also generalize our definition of the dividing surface and define an extended dividing surface (EDS), which is used to sample and classify all trajectories that pass through a phase space neighborhood of the index 2 saddle at total energies less than that of the saddle. Classical trajectory simulations are used to study fragmentation patterns for the n = 2 chain under tension. That is, we investigate the relative probability for breaking one bond versus concerted fission of several (two, in this case) bonds. Initial conditions for trajectories are obtained by sampling the EDS at constant energy. We sample trajectories at fixed energies both above and below the energy of the saddle. The fate of trajectories (single versus multiple bond breakage) is explored as a function of the location of the initial condition on the EDS, and a connection made to the work of Chesnavich on collision-induced dissociation. A significant finding is that we can readily identify trajectories that exhibit bond healing. Such trajectories pass outside the nominal (index 1) transition state for single bond dissociation, but return to the potential well region, possibly several times, before ultimately dissociating. PMID:23574219

  2. Long time fluctuation of liquid water: l/f spectrum of energy fluctuation in hydrogen bond network rearrangement dynamics

    E-print Network

    Ramaswamy, Ram

    Long time fluctuation of liquid water: l/f spectrum of energy fluctuation in hydrogen bond network of the potential energy fluctuation of liquid water is examined and found to yield so-called l/f frequency bond network. `,* This rearrangement dynamics involves collective motion of water molecules and energy

  3. 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

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

    SciTech Connect

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

    2013-01-15

    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 which predicts 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.

  5. Primary and Secondary Dissociation from Allyl Iodide Excited at 193 nm: Centrifugal Effects in the Unimolecular Dissociation of the Allyl Radical

    E-print Network

    Butler, Laurie J.

    in the Unimolecular Dissociation of the Allyl Radical D. E. Szpunar, M. L. Morton, and L. J. Butler* The James Franck radicals as a function of their internal energy. Two C-I bond fission channels were found to produce the allyl radical, one channel forming I(2 P3/2 ) and the other forming I(2 P1/2). The nascent allyl

  6. 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 systems 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.

  7. 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.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

    Raupach, Marc; Tonner, Ralf

    2015-05-01

    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 (H2 on M(001), M = Pd, Cu), and semiconducting (CO and C2H2 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.

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

    PubMed

    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 (H2 on M(001), M = Pd, Cu), and semiconducting (CO and C2H2 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. PMID:26001445

  11. Dissociation mechanisms of excited CH3X (X = Cl, Br, and I) formed via high-energy electron transfer using alkali metal targets

    NASA Astrophysics Data System (ADS)

    Hayakawa, Shigeo; Tsujinaka, Taiga; Fujihara, Akimasa

    2012-11-01

    High-energy electron transfer dissociation (HE-ETD) on collisions with alkali metal targets (Cs, K, and Na) was investigated for CH3X+ (X = Cl, Br, and I) ions by a charge inversion mass spectrometry. Relative peak intensities of the negative ions formed via HE-ETD strongly depend on the precursor ions and the target alkali metals. The dependency is explained by the exothermicities of the respective dissociation processes. Peak shapes of the negative ions, especially of the X- ions, which comprise a triangle and a trapezoid, also strongly depend on the precursor ions and the target alkali metals. The trapezoidal part of the I- peak observed with the Na target is more dominant and much broader than that with the Cs target. This dependence on the targets shows an inverse relation between the peak width and the available energy, which corresponds to the exothermicity assuming formation of fragment pair in their ground internal states. From a comparison of the kinetic energy release value calculated from the trapezoidal shape of I- with the available energy of the near-resonant level on the CH3I potential energy curve reported by ab initio calculations, the trapezoidal part is attributed to the dissociation to CH3 + I(2P3/2) via the repulsive 3Q1 state of CH3I, which is not dominant in the photo-dissociation of CH3I. The observation of trapezoid shape of the CH2I- peak with the Cs target indicates spontaneous dissociation via repulsive potential from the 3R2 Rydberg state, although the correlation between the 3R2 Rydberg state and relevant repulsive states has not been reported by any theoretical calculation.

  12. Electron induced dissociation of trimethyl (methylcyclopentadienyl) platinum (IV): Total cross section as a function of incident electron energy

    NASA Astrophysics Data System (ADS)

    van Dorp, W. F.; Wnuk, J. D.; Gorham, J. M.; Fairbrother, D. H.; Madey, T. E.; Hagen, C. W.

    2009-10-01

    The total cross section has been measured for the electron induced dissociation of trimethyl (methylcyclopentadienyl) platinum (IV) [MeCpPt(IV)Me3], a Pt precursor often used in focused electron beam induced processing (FEBIP), for incident electron energies ranging between 3-3 keV. Measurements were performed for the precursor in the adsorbed state under ultrahigh vacuum conditions. The techniques used in this study were temperature programmed desorption, x-ray photoelectron spectroscopy and mass spectrometry. Two surfaces were used in these experiments, amorphous carbon overlayers containing embedded Pt atoms (a:C-Pt), formed by the electron decomposition of the Pt precursor, and atomically clean Au. The results from these three experiments revealed a comparatively low total cross section at 8 eV (4.20.310-17 cm2 on the a:C-Pt and 1.40.110-17 cm2 on the Au) that increases with increasing incident electron energy, reaching a maximum at around 150 eV (4.10.510-16 cm2 on the a:C-Pt and 2.30.210-16 cm2 on the clean Au), before decreasing at higher incident electron energies, up to 3000 eV. Differences in the measured cross sections between Au and a:C-Pt surfaces demonstrate that the substrate can influence the reaction cross section of adsorbed species. Temperature programmed desorption was also used to measure the adsorption energy of MeCpPt(IV)Me3, which was found to depend on both the substrate and the adsorbate coverage. The work in this paper demonstrates that surface science techniques can be used to quantitatively determine the total cross section of adsorbed FEBIP precursors for electron induced dissociation as a function of incident electron energy. These total cross section values are necessary to obtain quantitatively accurate information from FEBIP models and to compare the reaction efficiencies of different precursors on a quantitative basis.

  13. 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)

  14. Gas phase hydrogen-bonded complexes of aromatic molecules

    NASA Astrophysics Data System (ADS)

    Mons, Michel; Dimicoli, Iliana; Piuzzi, Franois

    The present review discusses the possibility of measuring the dissociation energy of gas phase complexes from their dissociative photoionization. A compilation of recent results on hydrogen-bonded complexes of aromatic molecules, with a polar solvent molecule (water, alcohol, NH 3 , HCl, etc.), playing the role of either proton donor or proton acceptor is presented. We show that laser experiments begin to provide a consistent set of energetic data that can be considered as benchmarks to assess quantum calculations as well as to parametrize the force field models used in biochemistry.

  15. An energetic scale for equilibrium H/D fractionation factors illuminates hydrogen bond free energies in proteins.

    PubMed

    Cao, Zheng; Bowie, James U

    2014-05-01

    Equilibrium H/D fractionation factors have been extensively employed to qualitatively assess hydrogen bond strengths in protein structure, enzyme active sites, and DNA. It remains unclear how fractionation factors correlate with hydrogen bond free energies, however. Here we develop an empirical relationship between fractionation factors and free energy, allowing for the simple and quantitative measurement of hydrogen bond free energies. Applying our empirical relationship to prior fractionation factor studies in proteins, we find: [1] Within the folded state, backbone hydrogen bonds are only marginally stronger on average in ?-helices compared to ?-sheets by ?0.2 kcal/mol. [2] Charge-stabilized hydrogen bonds are stronger than neutral hydrogen bonds by ?2 kcal/mol on average, and can be as strong as -7 kcal/mol. [3] Changes in a few hydrogen bonds during an enzyme catalytic cycle can stabilize an intermediate state by -4.2 kcal/mol. [4] Backbone hydrogen bonds can make a large overall contribution to the energetics of conformational changes, possibly playing an important role in directing conformational changes. [5] Backbone hydrogen bonding becomes more uniform overall upon ligand binding, which may facilitate participation of the entire protein structure in events at the active site. Our energetic scale provides a simple method for further exploration of hydrogen bond free energies. PMID:24501090

  16. 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.

  17. Charge Transfer and Bonding in Endohedral Fullerenes from High-Energy Spectroscopy

    Microsoft Academic Search

    Mark S. Golden; Thomas Pichler; Petra Rudolf

    2004-01-01

    This contribution deals with the investigation of charge transfer and bonding in endohedral fullerenes in the solid state using high-energy spectroscopies such as photoemission and x-ray absorption. An overview is given of the detailed and direct information that can be won as regards the valence state of the encapsulated species, the degree of hybridisation between the electronic states of the

  18. Bond Functions and Core Correlation Energy Contributions To HeBe Potential

    NASA Astrophysics Data System (ADS)

    Shalabi, A. S.; Nour, E. M.; Abdel Halim, W. S.

    An empirical scheme for implementation of bond functions in heteronuclear diatomics is suggested and applied to HeBe using universal even-tempered functions. The effects of bond functions and core-correlation energy on the interaction potential of HeBe calculated at the uncorrelated (SCF) and correlated (MBPT and CC) levels are examined. The results confirm that an accuracy of sub ? Hartree level can be obtained using even-tempered functions with s-, p-, and d- symmetry and that bond functions of size {4s2p} for He and {6s3p} for Be recovers 100% of energy lowering obtained from the addition of 10d atom-centered functions to He and 13d atom centred functions to Be. The various treatments of the electron correlation, conclude that the system is interacting weakly with a well depth from 14.5-24.7 ?Eh at a separation near 9.1a0 compared with 20.7-25.5 ?Eh previously reported with a rather limited basis set. The most reliable well depth corrected for BSSE (19.0 ?Eh) was obtained at the CC-SD(T)level at separation of 8.71a0 taking into account the effects of bond functions and core correlation energy. Potential energy curves at the CC-SD(T) valence and CC-SD(T) valence + core correlation levels are analyzed in analytical forms in terms of exchange repulsion, induction and dispersion components.

  19. Correlation energy estimates in periodic extended systems using the localized natural bond orbital coupled cluster approach

    Microsoft Academic Search

    N. Flocke; R. J. Bartlett

    2003-01-01

    A new approach for the determination of correlation energies in periodic extended systems is proposed using the high transferability of amplitudes and integrals from natural bond orbital coupled cluster (NBO CC) calculations performed for small subunits. It is shown that the NBO CC calculations can in fact deliver detailed correlated wave function information for extended periodic systems. As an example

  20. 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.

  1. 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

  2. Bridging the gap between molecular and elemental mass spectrometry: higher energy collisional dissociation (HCD) revealing elemental information.

    PubMed

    Esteban-Fernndez, Diego; El-Khatib, Ahmed H; Moraleja, Irene; Gmez-Gmez, M Milagros; Linscheid, Michael W

    2015-02-01

    Molecular mass spectrometry has been applied to simultaneously obtain molecular and elemental information from metal-containing species. Energy tuning of the higher-energy collision dissociation (HCD) fragmentation cell allows the controlled production of typical peptide fragments or elemental reporter ions informing about the metallic content of the analyzed species. Different instrumental configurations and fragmentation techniques have been tested, and the efficiency extracting the elemental information has been compared. HCD fragmentation operating at very high energy led to the best results. Platinum, lanthanides, and iodine reporter ions from peptides interacting with cisplatin, peptides labeled with lanthanides-MeCAT-IA, and iodinated peptides, respectively, were obtained. The possibility to produce abundant molecular and elemental ions in the same analysis simplifies the correlation between both signals and open pathways in metallomics studies enabling the specific tracking of metal-containing species. The proposed approach has been successfully applied to in solution standards and complex samples. Moreover, interesting preliminary MALDI-imaging experiments have been performed showing similar metal distribution compared to laser ablation (LA)-ICPMS. PMID:25528895

  3. Trans-reflection thermal driven deformable mirror with flexible bonding in high energy laser system

    NASA Astrophysics Data System (ADS)

    Ma, Xingkun; Huang, Lei; Gong, Mali; Xue, Qiao

    2014-09-01

    Deformable mirrors used in high energy laser system suffer from problems like the stress from adhesive solidification or the relatively expensive unit price of piezoceramic actuator. The thermal driven deformable mirror (TDDM) investigated here provided a promising prospect to solve these problems. Four scenarios of TDDM were studied and compared. Results showed that the trans-reflection TDDM with flexible bonding best met the requirement in practical use. The flexible bonding excluded the stress problem in the solidification of adhesives, trans-reflection brought about enough correction range, and the choice of thermo-electric cooler as actuator could greatly bring down the cost of adaptive optics apparatus as well.

  4. The Effect of Lepton Mass on the Energy and Bond Length of the Hydrogen Molecule Ion Frank Rioux

    E-print Network

    Rioux, Frank

    The Effect of Lepton Mass on the Energy and Bond Length of the Hydrogen Molecule Ion Frank Rioux geometry (bond length) and energy of the hydrogen molecule ion. The electron has several heavy weight). The molecular orbital for the hydrogen molecule ion is formed as a linear combination of scaled hydrogenic 1s

  5. Ab initio molecular dynamics of high-temperature unimolecular dissociation of gas-phase RDX and its dissociation products.

    PubMed

    Schweigert, Igor V

    2015-03-26

    Unimolecular dynamics of gas-phase hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and its dissociation products were simulated using density functional theory (DFT) at the M06-L level. The simulations of RDX at 2000 K showed that dissociation proceeds from multiple conformers, mostly via homolytic fission of an N-N bond with a minor contribution from elimination of HONO, in agreement with previous transition state theory calculations. However, the simulations of the fission and elimination products revealed that secondary N-N fission is facile and, at the simulated temperature of 1750 K, dominant over other mechanisms. The simulations of the resulting intermediates revealed a number of new unimolecular pathways that have not been previously considered. The transition structures and minimal energy paths were calculated for all reactions to confirm these observations. Based on these findings, a revised set of the unimolecular reactions contributing to gas-phase RDX decomposition is proposed. PMID:25738393

  6. Dissociative ionization of biomolecules

    NASA Astrophysics Data System (ADS)

    Huo, Winifred

    2004-09-01

    Dissociative ionization (DI) by electron impact plays a role in many different applications, including low-temperature plasma processing, the study of space and astrophysical plasmas, and the study of biological damages by high-energy radiation. In the present study, our goal is to understand the health hazard to humans from exposure to radiation during an extended space flight. DI by secondary electrons can damage the DNA, either directly by causing a DNA lesion, or indirectly by producing radicals and cations that attack the DNA. The theoretical model employed makes use of the fact that electronic motion is much faster than nuclear motion, allowing DI to be treated as a two-step process. The first step is electron-impact ionization resulting in a dissociative state of the molecular ion with the same geometry as the neutral molecule. In the second step the ion relaxes from the initial geometry and undergoes unimolecular dissociation. Thus the DI cross section is given by the product of the ionization cross section and the dissociation probability. For the ionization process we use the improved binary-encounter dipole (iBED) model. For unimolecular dissociation, we use the multiconfigurational self-consistent field (MCSCF) method to determine the minimum energy pathways to possible product channels. This model has been applied to study the DI of H_2O, NH_3, and CH_4, and the results are in good agreement with experiment. The DI from the low-lying channels of benzene has also been studied and the dissociation products are compared with photoionization measurements. The DI of the DNA bases guanine and cytosine are then discussed. Of the four DNA bases, guanine has the largest ionization cross section and cytosine has the smallest. The guanine radical cation is considered to be one of the precursors to the primary, direct-type lesions formed in DNA when it is irradiated. Comparison of DI products of guanine and cytosine will be made to understand the differences in their behavior upon irradiation.

  7. Bonding energy in (Li 2 OH) complex ions

    Microsoft Academic Search

    A. V. Nemukhin; N. F. Stepanov

    1987-01-01

    |UDC 539.19 On the basis of results from ab initio quantum-mechanical calculations, it is concluded that the energies of interaction of the Li + cation and the Li- anion with the LiOH molecule are quite similar (1.55 and 1.37 eV) and are in good agreement with experimental data. This result can be obtained only when correlation effects are taken into

  8. Potential energy surfaces for CH bond cleavage reactions

    SciTech Connect

    Harding, L.B.

    1996-12-31

    Ab initio, multi-reference, configuration interaction calculations are reported for CH{sub 4}{leftrightarrow}CH{sub 3}+H, CH{sub 3}F{leftrightarrow}CH{sub 2}F+H, CH{sub 2}F{sub 2}{leftrightarrow}CHF{sub 2}+H, and CHF{sub 3}{leftrightarrow}CF{sub 3}+H. Two equivalent, barrier-less paths are found for the CH{sub 3}+H recombination, two inequivalent, barrier-less paths are found for the CH{sub 2}F+H and CHF{sub 2}+H recombinations (depending on which side of the radical the H atom approaches), and only one barrier-less path is found for the CF{sub 3}+H recombination. Minimum energy path for H atom approaching CF{sub 3} from the concave side is predicted to have a barrier of 27 kcal/mole. Both minimum energy path energies and transitional frequencies as function of R{sub CH} for all 4 reactions are predicted to be similar.

  9. Controlling the subtle energy balance in protic ionic liquids: dispersion forces compete with hydrogen bonds.

    PubMed

    Fumino, Koichi; Fossog, Verlaine; Stange, Peter; Paschek, Dietmar; Hempelmann, Rolf; Ludwig, Ralf

    2015-02-23

    The properties of ionic liquids are determined by the energy-balance between Coulomb-interaction, hydrogen-bonding, and dispersion forces. Out of a set of protic ionic liquids (PILs), including trialkylammonium cations and methylsulfonate and triflate anions we could detect the transfer from hydrogen-bonding to dispersion-dominated interaction between cation and anion in the PIL [(C6 H13 )3 NH][CF3 SO3 ]. The characteristic vibrational features for both ion-pair species can be detected and assigned in the far-infrared spectra. Our approach gives direct access to the relative strength of hydrogen-bonding and dispersion forces in a Coulomb-dominated system. Dispersion-corrected density functional theory (DFT) calculations support the experimental findings. The dispersion forces could be quantified to contribute about 2.3?kJ?mol(-1) per additional methylene group in the alkyl chains of the ammonium cation. PMID:25639210

  10. Interlayer bonding energy of layered minerals: Implication for the relationship with friction coefficient

    NASA Astrophysics Data System (ADS)

    Sakuma, Hiroshi; Suehara, Shigeru

    2015-04-01

    The frictional strength of layered minerals is an important component of fault slip physics. A low-friction coefficient of these minerals has been attributed to the interlayer bonding energy (ILBE) of their weak interlayer bonding. The ILBE used for discussing the friction coefficient is based on a simple electrostatic calculation; however, the values should be revisited by precise calculations based on quantum mechanics. In this study, the ILBEs of layered minerals were calculated by using the density functional theory (DFT) method with van der Waals correction. The ILBEs calculated by the simple electrostatic method for hydrogen-bonding minerals such as kaolinite, lizardite, gibbsite, and brucite strongly overestimated the reliable energies calculated by the DFT method. This result should be ascribed to the inaccurate approximation of the point charges at the basal plane. A linear relationship between the experimentally measured friction coefficients of layered minerals and the ILBEs determined by the simple method was not confirmed by using the reliable ILBEs calculated by our DFT method. The results, however, do not remove the possibility of a relationship between interlayer bonding energy and the friction coefficient because the latter, used for comparing the former, was obtained through experiments conducted under various conditions.

  11. Rovibrational internal energy transfer and dissociation of N2(1?g+)-N(4S(u)) system in hypersonic flows.

    PubMed

    Panesi, Marco; Jaffe, Richard L; Schwenke, David W; Magin, Thierry E

    2013-01-28

    A rovibrational collisional model is developed to study energy transfer and dissociation of N(2)((1)?(g)(+)) molecules interacting with N((4)S(u)) atoms in an ideal isochoric and isothermal chemical reactor. The system examined is a mixture of molecular nitrogen and a small amount of atomic nitrogen. This mixture, initially at room temperature, is heated by several thousands of degrees Kelvin, driving the system toward a strong non-equilibrium condition. The evolution of the population densities of each individual rovibrational level is explicitly determined via the numerical solution of the master equation for temperatures ranging from 5000 to 50,000 K. The reaction rate coefficients are taken from an ab initio database developed at NASA Ames Research Center. The macroscopic relaxation times, energy transfer rates, and dissociation rate coefficients are extracted from the solution of the master equation. The computed rotational-translational (RT) and vibrational-translational (VT) relaxation times are different at low heat bath temperatures (e.g., RT is about two orders of magnitude faster than VT at T = 5000 K), but they converge to a common limiting value at high temperature. This is contrary to the conventional interpretation of thermal relaxation in which translational and rotational relaxation timescales are assumed comparable with vibrational relaxation being considerable slower. Thus, this assumption is questionable under high temperature non-equilibrium conditions. The exchange reaction plays a very significant role in determining the dynamics of the population densities. The macroscopic energy transfer and dissociation rates are found to be slower when exchange processes are neglected. A macroscopic dissociation rate coefficient based on the quasi-stationary distribution, exhibits excellent agreement with experimental data of Appleton et al. [J. Chem. Phys. 48, 599-608 (1968)]. However, at higher temperatures, only about 50% of dissociation is found to take place under quasi-stationary state conditions. This suggest the necessity of explicitly including some rovibrational levels, when solving a global kinetic rate equation. PMID:23387589

  12. Fracture energy vs. internal bond strength mechanical characterization of wood-based panels

    Microsoft Academic Search

    Jrn Rathke; Gerhard Sinn; Michael Harm; Alfred Teischinger; Martin Weigl; Ulrich Mller

    2012-01-01

    A new testing method measuring the specific fracture energy of wood-based panels in Mode I is proposed. Three types of wood-based panels, i.e. oriented strand board (OSB), particleboard (PB) and medium density fibreboard (MDF) are investigated, using fracture energy and the industrial European standard method of internal bond strength according to EN 319. Double cantilever beam specimens are notched in

  13. Electronegativities in situ, bond hardnesses, and charge-transfer components of bond energies from the topological theory of atoms in molecules

    SciTech Connect

    Cioslowski, J.; Mixon, S.T. (Florida State Univ., Tallahassee (United States))

    1993-02-10

    Rigorous definitions for electronegativities of atoms and functional groups in molecules, bond hardnesses, and the charge-transfer components of the bond energies are proposed. The definitions rely upon values of total energies and their derivatives calculated for molecules composed of fragments with a controlled degree of charge transfer. Such calculations, in which the atomic or fragment charges are obtained with the help of the topological theory of atoms in molecules, are easily accomplished by adding appropriate Lagrange multiplier terms to the electronic Hamiltonian. Numerical examples that are given for 23 different systems indicate that the bond hardnesses are mostly transferable, but because of the electric field generated by the molecular environment the electronegativity differences are not. 27 refs., 1 fig., 1 tab.

  14. 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.

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

    PubMed

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

    2014-05-01

    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. PMID:24671142

  16. 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(+).

  17. 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. [J. R. Macdonald Laboratory, Physics Department, Kansas State University, Manhattan, Kansas 66506 (United States)

    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 +}.

  18. Dissociative phenomenology of dissociative identity disorder.

    PubMed

    Dell, Paul F

    2002-01-01

    The goal of this study was to investigate the dissociative phenomenology of dissociative identity disorder (DID). The Multidimensional Inventory of Dissociation (MID) was administered to 34 patients with DID, 23 patients with dissociative disorder not otherwise specified (DDNOS), 52 patients with mixed psychiatric disorders, and 58 normal individuals. DID patients obtained significantly higher scores than the other three groups on 27 dissociation-related variables. DDNOS patients had significantly higher scores than normals and mixed psychiatric patients on 17 and 15 dissociation-related variables, respectively. The findings of the present study are virtually identical to a large body of replicated findings about the dissociative phenomenology of DID. This broad range of dissociation-related phenomena, which routinely occurs in individuals with DID, is largely absent from the DSM-IV-TR account of DID. Factor analysis of the 11 dimensions of dissociation that are measured by the MID extracted only one factor that accounted for 85% of the variance. It was concluded that dissociation is a unifactorial taxon or natural type that has different aspects or epiphenomena (i.e., amnesia, depersonalization, voices, trance, etc.). PMID:11838024

  19. Reaction of Sc + , Ti + , and V + with CO. MC + and MO + bond energies

    NASA Astrophysics Data System (ADS)

    Clemmer, D. E.; Elkind, J. L.; Aristov, N.; Armentrout, P. B.

    1991-09-01

    The reactions of Sc+, Ti+, and V+ with CO are studied as a function of translational energy in a guided-ion-beam tandem mass spectrometer. Formation of both metal-carbide and metal-oxide ions are observed and rationalized by a direct atom abstraction mechanism. At high energies, the ScC+ and ScO+ cross sections exhibit additional features that are unusual but can be explained by an impulsive pairwise mechanism and formation of excited-state product ions, respectively. Thresholds of the reaction cross sections are interpreted to give the 0 K bond energies (in eV) D0(ScC+)=3.340.06, D0(TiC+)=4.050.24, D0(VC+)=3.870.14, D0(ScO+)=7.110.08, D0(TiO+)=6.880.07, and D0(VO+)=5.810.17. Additional studies are used to help verify the bond energy for ScO+ and yield a recommended value of 7.140.11 eV. The nature of the bonding in MO+ and MC+ is discussed and compared for these three metal ions.

  20. Direct dissociative chemisorption of alkanes on Pt(111): Influence of molecular complexity

    SciTech Connect

    Weaver, Jason F. [Department of Chemical Engineering, Stanford University, Stanford, California 94305 (United States)] [Department of Chemical Engineering, Stanford University, Stanford, California 94305 (United States); Krzyzowski, Michael A. [Department of Chemical Engineering, Stanford University, Stanford, California 94305 (United States)] [Department of Chemical Engineering, Stanford University, Stanford, California 94305 (United States); Madix, Robert J. [Department of Chemical Engineering, Stanford University, Stanford, California 94305 (United States)] [Department of Chemical Engineering, Stanford University, Stanford, California 94305 (United States)

    2000-01-01

    The direct dissociative chemisorption of ethane, propane, n-butane, isobutane, and neopentane on Pt(111) was investigated as a function of the initial translational energy, E{sub T}, polar angle of incidence, {theta}{sub i}, initial vibrational temperature, and surface temperature using supersonic molecular beam techniques. For each alkane, the initial probability for direct dissociative chemisorption scales with the initial normal energy of the alkanes, E{sub n}=E{sub T} cos{sup 2} {theta}{sub i}, and is independent of both the surface temperature and initial vibrational energy of the alkanes under the experimental conditions employed. Above initial normal energies of approximately 125 kJ/mol, at constant E{sub n}, the dissociation probability decreases with increasing chain length of the C{sub 2}-C{sub 4} linear alkanes; however, the dissociation probability of neopentane is greater than that of isobutane, and both isobutane and neopentane are more reactive than n-butane. By assuming that cleavage of primary C-H bonds is the dominant reaction pathway for all of the alkanes investigated here, the trends in reactivity are best explained by considering the differences in the steric factors for primary C-H bond cleavage for these alkanes. Secondary C-H bond cleavage does appear to contribute to the reactivity of propane and n-butane but only at the highest energies examined. Additionally, the reaction probabilities of each of these alkanes were estimated using a statistical model recently proposed by Ukrainstev and Harrison [J. Chem. Phys. 101, 1564 (1994)]. Assuming cleavage of only primary C-H bonds, the trends in reactivity for ethane, propane, n-butane, and isobutane were qualitatively reproduced by the statistical model; however, except for ethane, which was used to obtain the necessary parameters for the theory, there was poor quantitative agreement, and the predictions for neopentane were significantly lower than the measured values. The model also predicts that the dissociation probability is enhanced by increasing the energy in all vibrational modes, which is inconsistent with the experimental results. Thus, we believe that direct alkane dissociation would be better described using a dynamical rather than statistical approach. (c) 2000 American Institute of Physics.

  1. 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.

  2. A potential-energy surface study of the 2A1 and low-lying dissociative states of the methoxy radical

    NASA Technical Reports Server (NTRS)

    Jackels, C. F.

    1985-01-01

    Accurate, ab initio quantum chemical techniques are applied in the present study of low lying bound and dissociative states of the methoxy radical at C3nu conformations, using a double zeta quality basis set that is augmented with polarization and diffuse functions. Excitation energy estimates are obtained for vertical excitation, vertical deexcitation, and system origin. The rate of methoxy photolysis is estimated to be too small to warrant its inclusion in atmospheric models.

  3. Fully integrated micro electromagnetic vibration energy harvesters with micro-patterning of bonded magnets

    Microsoft Academic Search

    K. Tao; G. Ding; P. Wang; Z. Yang; Y. Wang

    2012-01-01

    This paper presents the fabrication and characterization of a novel fully integrated micro electromagnetic vibration energy harvester using micro-patterning of bonded magnets. The magnetic material utilized is a polymer composite, consisting of a commercially available NdFeB powder dispersed in epoxy resin to a weight loading percentage of 90%. The prototype is fabricated using UV-LIGA technology and microelectroplating technology. The whole

  4. Coulomb-assisted dissociative electron attachment: application to a model peptide.

    PubMed

    Sobczyk, Monika; Anusiewicz, Iwona; Berdys-Kochanska, Joanna; Sawicka, Agnieszka; Skurski, Piotr; Simons, Jack

    2005-01-13

    The fragmentation of positively charged gas-phase samples of peptides is used to infer the primary structure of such molecules. In electron capture dissociation (ECD) experiments, very low-energy electrons attach to the sample and rupture bonds to effect the fragmentation. It turns out that ECD fragmentation tends to produce cleavage of very specific types of bonds. In earlier works by this group, it has been suggested that the presence of positive charges produces stabilizing Coulomb potentials that allow low-energy electrons to exothermically attach to sigma orbitals of certain bonds and thus to cleave those bonds. In the present effort, the stabilizing effects of Coulomb potentials due to proximal positive charges are examined for a small model peptide molecule that contains a wide range of bond types. Direct attachment of an electron to the sigma orbitals of eight different bonds as well as indirect sigma bond cleavage, in which an electron first binds to a carbonyl C=O pi orbital, are examined using ab initio methods. It is found that direct attachment to and subsequent cleavage of any of the eight sigma bonds is not likely except for highly positively charged samples. It is also found that attachment to a C=O pi orbital followed by cleavage of the nitrogen-to-alpha-carbon bond is the most likely outcome. Interestingly, this bond cleavage is the one that is seen most commonly in ECD experiments. So, the results presented here seem to offer good insight into one aspect of the ECD process, and they provide a means by which one can estimate (on the basis of a simple Coulomb energy formula) which bonds may be susceptible to cleavage by low-energy electron attachment. PMID:16839114

  5. Dynamic strength of molecular adhesion bonds.

    PubMed Central

    Evans, E; Ritchie, K

    1997-01-01

    In biology, molecular linkages at, within, and beneath cell interfaces arise mainly from weak noncovalent interactions. These bonds will fail under any level of pulling force if held for sufficient time. Thus, when tested with ultrasensitive force probes, we expect cohesive material strength and strength of adhesion at interfaces to be time- and loading rate-dependent properties. To examine what can be learned from measurements of bond strength, we have extended Kramers' theory for reaction kinetics in liquids to bond dissociation under force and tested the predictions by smart Monte Carlo (Brownian dynamics) simulations of bond rupture. By definition, bond strength is the force that produces the most frequent failure in repeated tests of breakage, i.e., the peak in the distribution of rupture forces. As verified by the simulations, theory shows that bond strength progresses through three dynamic regimes of loading rate. First, bond strength emerges at a critical rate of loading (> or = 0) at which spontaneous dissociation is just frequent enough to keep the distribution peak at zero force. In the slow-loading regime immediately above the critical rate, strength grows as a weak power of loading rate and reflects initial coupling of force to the bonding potential. At higher rates, there is crossover to a fast regime in which strength continues to increase as the logarithm of the loading rate over many decades independent of the type of attraction. Finally, at ultrafast loading rates approaching the domain of molecular dynamics simulations, the bonding potential is quickly overwhelmed by the rapidly increasing force, so that only naked frictional drag on the structure remains to retard separation. Hence, to expose the energy landscape that governs bond strength, molecular adhesion forces must be examined over an enormous span of time scales. However, a significant gap exists between the time domain of force measurements in the laboratory and the extremely fast scale of molecular motions. Using results from a simulation of biotin-avidin bonds (Izrailev, S., S. Stepaniants, M. Balsera, Y. Oono, and K. Schulten. 1997. Molecular dynamics study of unbinding of the avidin-biotin complex. Biophys. J., this issue), we describe how Brownian dynamics can help bridge the gap between molecular dynamics and probe tests. Images FIGURE 2 PMID:9083660

  6. EVIDENCE FOR CO DISSOCIATION ON RHODIUM SURFACES

    SciTech Connect

    Castner, D.G.; Dubois, L.H.; Sexton, B.A.; Somorjai, G.A.

    1980-06-01

    Carbon monoxide adsorbs molecularly on rhodium surfaces at 300K, but if the rhodium samples are heated in the presence of carbon monoxide, there is evidence for carbon-oxygen bond breaking at step and/or defect sites. The effects of step and defect site density, subsurface oxygen concentration, and oxygen dissolution into the rhodium lattice on CO dissociation are discussed.

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

    SciTech Connect

    Jost, R. [Grenoble High Magnetic Field Laboratory, MPI-FKF and CNRS, BP 166, F-38042 Grenoble Cedex 09 (France)] [Grenoble High Magnetic Field Laboratory, MPI-FKF and CNRS, BP 166, F-38042 Grenoble Cedex 09 (France); Joyeux, M. [Laboratoire de Spectrometrie Physique, CNRS UMR 5588, Universite Joseph Fourier-Grenoble I, BP 87, F-38402 St Martin dHeres Cedex (France)] [Laboratoire de Spectrometrie Physique, CNRS UMR 5588, Universite Joseph Fourier-Grenoble I, BP 87, F-38402 St Martin dHeres Cedex (France); Skokov, S.; Bowman, J. [Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322 (United States)] [Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322 (United States)

    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.}

  8. Students' reasoning about "high-energy bonds" and ATP: A vision of interdisciplinary education

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    As interdisciplinary courses are developed, instructors and researchers have to grapple with questions of how students should make connections across disciplines. We explore the issue of interdisciplinary reconciliation (IDR): how students reconcile seemingly contradictory ideas from different disciplines. While IDR has elements in common with other frameworks for the reconciliation of ideas across contexts, it differs in that each disciplinary idea is considered canonically correct within its own discipline. The setting for the research is an introductory physics course for biology majors that seeks to build greater interdisciplinary coherence and therefore includes biologically relevant topics such as adenosine triphosphate (ATP) and chemical bond energy. In our case-study 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 students justifying context-dependent modeling choices, showing nuance in articulating how system choices may be related to disciplinary problems of interest. This represents a desired end point of IDR, in which students can build coherent connections between concepts from different disciplines while understanding each concept in its own disciplinary context. Our case study also illustrates elements of the instructional environment that play roles in the process of IDR.

  9. Dissociation of Hydrogen Chloride and Proton Transfer in Liquid Glycerol: An Ab Initio Molecular Dynamics Study

    E-print Network

    Dellago, Christoph

    , a time scale consistent with recent molecular beam experiments. The dissociation of the hydrochloric acid of hydrogen bonds in a Grotthus-like fashion. I. Introduction The dissociation and dissolution of acidsDissociation of Hydrogen Chloride and Proton Transfer in Liquid Glycerol: An Ab Initio Molecular

  10. 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.

  11. 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. [Joint Institute for Nuclear Research (Russian Federation)] [Joint Institute for Nuclear Research (Russian Federation); Alikulov, S. S. [A. Kodirii Jizzakh State Pedagogical Institute (Uzbekistan)] [A. Kodirii Jizzakh State Pedagogical Institute (Uzbekistan); Artemenkov, D. A. [Joint Institute for Nuclear Research (Russian Federation)] [Joint Institute for Nuclear Research (Russian Federation); Bekmirzaev, R. N. [A. Kodirii Jizzakh State Pedagogical Institute (Uzbekistan)] [A. Kodirii Jizzakh State Pedagogical Institute (Uzbekistan); Bradnova, V.; Zarubin, P. I., E-mail: zarubin@lhe.jinr.ru; Zarubina, I. G.; Kondratieva, N. V.; Kornegrutsa, N. K.; Krivenkov, D. O.; Malakhov, A. I. [Joint Institute for Nuclear Research (Russian Federation)] [Joint Institute for Nuclear Research (Russian Federation); Olimov, K. [Uzbek Academy of Sciences, Institute for Physics and Technology (Uzbekistan)] [Uzbek Academy of Sciences, Institute for Physics and Technology (Uzbekistan); Peresadko, N. G.; Polukhina, N. G. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)] [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation); Rukoyatkin, P. A.; Rusakova, V. V.; Stanoeva, R. [Joint Institute for Nuclear Research (Russian Federation)] [Joint Institute for Nuclear Research (Russian Federation); Kharlamov, S. P. [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)] [Russian Academy of Sciences, Lebedev Physical Institute (Russian Federation)

    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.

  12. Molecular engineering of fracture energy dissipating sacrificial bonds into cellulose nanocrystal nanocomposites.

    PubMed

    McKee, Jason R; Huokuna, Johannes; Martikainen, Lahja; Karesoja, Mikko; Nyknen, Antti; Kontturi, Eero; Tenhu, Heikki; Ruokolainen, Janne; Ikkala, Olli

    2014-05-12

    Even though nanocomposites have provided a plethora of routes to increase stiffness and strength, achieving increased toughness with suppressed catastrophic crack growth has remained more challenging. Inspired by the concepts of mechanically excellent natural nanomaterials, one-component nanocomposites were fabricated involving reinforcing colloidal nanorod cores with polymeric grafts containing supramolecular binding units. The concept is based on mechanically strong native cellulose nanocrystals (CNC) grafted with glassy polymethacrylate polymers, with side chains that contain 2-ureido-4[1H]-pyrimidone (UPy) pendant groups. The interdigitation of the grafts and the ensuing UPy hydrogen bonds bind the nanocomposite network together. Under stress, UPy groups act as sacrificial bonds: simultaneously providing adhesion between the CNCs while allowing them to first orient and then gradually slide past each other, thus dissipating fracture energy. We propose that this architecture involving supramolecular binding units within side chains of polymer grafts attached to colloidal reinforcements opens generic approaches for tough nanocomposites. PMID:24706578

  13. Angular dependence of hydrogen bond energy in neutral and charged systems containing CH and NH proton donors

    NASA Astrophysics Data System (ADS)

    Nepal, Binod; Scheiner, Steve

    2015-06-01

    The effects of angular distortions on the H-bond energy are computed in both neutral and ionic complexes. F3CH, NCH, and HNCH+ are taken as CH donors and HCNH, HCNH+, and NH4+ are NH donors. Ionic complexes are more strongly bound and suffer a greater loss of H-bond energy upon angular distortion. However, when bending force constants k are normalized against intrinsic H-bond strength Eb, the k/Eb ratios are similar, only slightly larger for NH than for CH donors, and with only small perturbations caused by overall charge. The source of destabilization arising from angular deformation is traced to exchange repulsion.

  14. Primary photodissociation pathways of epichlorohydrin and analysis of the CC bond fission channels from an O,,3

    E-print Network

    Butler, Laurie J.

    to acrolein and dissociate. The paper then analyzes the dynamics of the C3H5O radical produced from CCl bond and vibrational energy imparted to the radical intermediate and the resulting competition between the H+acrolein

  15. Calorimetric study of the oxygen bond energy in a binary V?Ti catalyst and individual vanadium and titanium oxides

    Microsoft Academic Search

    V. M. Bondareva; T. V. Andrushkevich; Yu. D. Pankratiev

    1997-01-01

    Bond energy of oxygen in a binary V?Ti catalyst and individual V and Ti oxides has been studied by the calorimetric method.\\u000a The samples studied were shown to be significantly different in bond energy, homogeneity of surface oxygen and mobility of\\u000a the bulk one. Vanadium and titanium oxides appeared to interact in the binary system to form an active surface

  16. Threshold collision-induced dissociation of diatomic molecules: A case study of the energetics and dynamics of O{sub 2}{sup -} collisions with Ar and Xe

    SciTech Connect

    Ahu Akin, F.; Ree, Jongbaik; Ervin, Kent M.; Hyung, Kyu Shin [Department of Chemistry and Chemical Physics Program, University of Nevada, Reno, Nevada 89557 (United States); Department of Chemistry Education, College of Education, Chonnam National University, Kwangju 500-757 (Korea, Republic of); Department of Chemistry and Chemical Physics Program, University of Nevada, Reno, Nevada 89557 (United States)

    2005-08-08

    The energetics and dynamics of collision-induced dissociation of O{sub 2}{sup -} with Ar and Xe targets are studied experimentally using guided ion-beam tandem mass spectrometry. The cross sections and the collision dynamics are modeled theoretically by classical trajectory calculations. Experimental apparent threshold energies are 2.1 and 1.1 eV in excess of the thermochemical O{sub 2}{sup -} bond dissociation energy for argon and xenon, respectively. Classical trajectory calculations confirm the observed threshold behavior and the dependence of cross sections on the relative kinetic energy. Representative trajectories reveal that the bond dissociation takes place on a short time scale of about 50 fs in strong direct collisions. Collision-induced dissociation is found to be remarkably restricted to the perpendicular approach of Ar/Xe to the molecular axis of O{sub 2}{sup -}, while collinear collisions do not result in dissociation. The higher collisional energy-transfer efficiency of xenon compared with argon is attributed to both mass and polarizability effects.

  17. 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.

  18. An application of the full CCSDT coupled-cluster method to potential energy curves: The CH 4?CH 3+H dissociation

    NASA Astrophysics Data System (ADS)

    Sosa, C.; Noga, J.; Purvis, G. D., III; Bartlett, R. J.

    1988-12-01

    The potential energy surface for the dissociation of methane CH 4?CH 3+H is investigated using many-body perturbation theory (MBPT) and coupled-cluster (CC) methods including full CCSDT. Full fourth-order MBPT(4) based upon an unrestricted Hartree-Fock reference function shows the characteristic rise in the 1.5-3.0 region due to spin contamination. The full CCSDT and its approximations based on a restricted Hartree-Fock sum higher-order correlation effects even in the 3.0-5.0 range, where degeneracy effects are quite large, essentially recovering all the MR-CI correlation energy.

  19. Analysis of CO hydrogenation pathways using the bond-order-conservation method

    SciTech Connect

    Shustorovich, E. (Eastman Kodak Co., Rochester, NY (USA)); Bell, A.T. (Univ. of California, Berkeley (USA))

    1988-10-01

    The bond-order-conservation (BOC) method has been used to identify the energetics associated with the hydrogenation of CO over (111) surfaces of Ni, Pd, and Pt. In the formation of CH{sub 4}, the C-O bond of CO is cleaved. BOC calculations for Ni indicate that cleavage of the C-O bond occurs primarily by direct dissociation of molecularly adsorbed CO. The activation energy for direct dissociation of CO on Pd and Pt is significantly greater than that for hydrogen assisted dissociation, and hence the latter process is more significant. The BOC calculations indicate that for these metals the species from which C-O bond cleavage occurs is CH{sub 3}O{sub 5}. Because the activation barriers for CH{sub 3}O{sub 5} dissociation and hydrogenation to form CH{sub 3}OH are close for Pd and Pt, these metals are effective catalysts for both CH{sub 4} and CH{sub 3}OH synthesis. By contrast, the BOC method predicts that CH{sub 4} should be the principal product formed over Ni. 36 refs.

  20. 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.

  1. Diffraction dissociation at the LHC

    SciTech Connect

    Jenkovszky, Laszlo [Bogolyubov Institute for Theoretical Physics (BITP), Ukrainian National Academy of Sciences 14-b, Metrolohichna str., Kiev, 03680, Ukraine and Wigner Research Centre for Physics, Hungarian Academy of Sciences 1525 Budapest, POB 49 (Hungary); Orava, Risto [Institute of Physics, Division of Elementary Particle Physics, P.O. Box 64 (Gustaf Haellstroeminkatu 2a), FI-00014 University of Helsinki, Finland and CERN, CH-1211 Geneva 23 (Switzerland); Salii, Andrii [Bogolyubov Institute for Theoretical Physics (BITP), Ukrainian National Academy of Sciences 14-b, Metrolohichna str., Kiev, 03680 (Ukraine)

    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.

  2. Dissociation energies of six NO2 isotopologues by laser induced fluorescence spectroscopy and zero point energy of some

    E-print Network

    .56 cm 1 for 14 N16 O2 to 25 171.80 cm 1 for 15 N18 O2 . The zero point energy for the NO2 isotopologues energies and the calculated zero point energies of the parent NO2 isotopologue and of the NO product s we. The canonical perturbation theory was then used to calculate the zero point energy of all stable isotopologues

  3. Resonant Dissociative Recombination of ArH^+

    NASA Astrophysics Data System (ADS)

    Ngassam, V.; Orel, A. E.

    2008-05-01

    The rate coefficient for the ArH^+ dissociative recombination with electrons has been measured at the ASTRID storage ring in Denmark. The rate coefficient, as a function of the electron energy, displays several broad peaks between 5 and 35 eV. The first peak is due to dissociative recombination via the capture of the incoming electron by doubly excited Rydberg states converging to the excited state of the ion (Ar^+ ^2P + H ^1S). We will present the results of electron scattering calculations using the Complex Kohn variational method which were carried out to determine the positions and autoionization widths of the resonant states. These parameters were used in a time-dependent wave packet calculation to describe the dissociation dynamics. We also explore the low energy region where the non-adiabatic couplings between the ion, the Rydberg and the valence states drive dissociative recombination. The cross sections and dissociation rates will be compared to the available experimental data.

  4. Geometrical structures, vibrational frequencies, force constants and dissociation energies of isotopic water molecules (H2O, HDO, D2O, HTO, DTO, and T2O) under dipole electric field

    Microsoft Academic Search

    Shun-Ping Shi; Quan Zhang; Li Zhang; Rong Wang; Zheng-He Zhu; Gang Jiang; Yi-Bei Fu

    2011-01-01

    The dissociation limits of isotopic water molecules are derived for the ground state. The equilibrium geometries, the vibrational frequencies, the force constants and the dissociation energies for the ground states of all isotopic water molecules under the dipole electric fields from -0.05 a.u. to 0.05 a.u. are calculated using B3P86\\/6-311++G(3df,3pf). The results show that when the dipole electric fields change

  5. Dissociative Electron Attachment to Phosphoric Acid Esters: The Direct Mechanism for Single Strand Breaks in DNA

    SciTech Connect

    Koenig, Constanze; Kopyra, Janina; Bald, Ilko; Illenberger, Eugen [Institut fuer Chemie und Biochemie - Physikalische und Theoretische Chemie, Freie Universitaet Berlin, Takustrasse 3, D-14195 Berlin (Germany)

    2006-07-07

    We use dibutyl phosphate to simulate the behavior of the phosphate group in DNA towards the attack of low energy electrons. We find that the compound undergoes effective dissociative electron attachment within a low energy resonant feature at 1 eV and a further resonance peaking at 8 eV. The dissociative electron attachment (DEA) reactions are associated with the direct cleavage of the C-O and the P-O bond but also the excision of the PO{sup -}, PO{sub 3}{sup -}, H{sub 2}PO{sub 3}{sup -} units. For the phosphate group coupled in the DNA network these reactions represent single strand breaks. We hence propose that the most direct mechanism of single strand breaks occurring in DNA at subexcitation energies (<4 eV) is due to DEA directly to the phosphate group.

  6. Electron shuttling in electron transfer dissociation

    NASA Astrophysics Data System (ADS)

    Neff, Diane; Smuczynska, Sylwia; Simons, Jack

    2009-06-01

    Ab initio electronic structure calculations have been performed on two model systems containing a disulfide linkage and one or two positively charged sites, aimed at gaining further insight into how and where electrons attach to positively charged peptides under electron capture (ECD) and electron transfer dissociation (ETD) mass spectroscopy conditions. Couplings among electronic states involving (i) an entrance-channel with the excess electron residing on a donor anion interacting with the positively charged peptide, (ii) a state in which the electron has been transferred to the SS [sigma]* orbital to cause bond cleavage, and (iii) a manifold of states in which the electron has been transferred to a ground- or excited-Rydberg orbital on a positive site. The results of this study suggest that specific excited Rydberg states play a key role in effecting electron shuttling to the SS [sigma]* orbital. The excited-Rydberg orbitals close in energy to the SS [sigma]* orbital and with sufficient radial extent to span the distance between the positive site and the SS [sigma]* orbital play the key role. Then, when the anion donor, excited-Rydberg, and SS [sigma]* orbitals achieve spatial proximity and similarity in energies, one can have what is termed here a shuttle of an electron from the donor to the SS [sigma]* orbital, which results in SS bond cleavage. For the singly and doubly charged systems studied here, it was the 3p and 3d Rydberg orbitals, respectively, that met these criteria of spatial and energetic proximity. For other peptides having different charge states, it will be other Rydberg orbitals that meet these criteria because the relative energies of the SS [sigma]* and Rydberg orbitals are governed by the (different) Coulomb stabilizations these orbitals experience. However, the evidence suggests that it is not very high-energy Rydberg states but states with 3 < n < 10 that are involved in the rate limiting steps in ECD, ETD, and ECID experiments.

  7. 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.

  8. Energy and critical ionic-bond parameter of a 3D large-radius bipolaron

    SciTech Connect

    Lakhno, V. D., E-mail: lak@impb.psn.r [Russian Academy of Sciences, Institute of Mathematical Problems of Biology (Russian Federation)

    2010-05-15

    A theory of a strong-coupling large-radius bipolaron has been developed. The possibility of the formation of 3D bipolarons in high-temperature superconductors is discussed. For the bipolaron energy, the lowest variational estimate has been obtained at {alpha} > 8, where {alpha} is the electron-phonon coupling constant. The critical ionic-bond parameter {eta}{sub c} = {epsilon}{sub {infinity}/{epsilon}0}, where {epsilon}{sub {infinity}} and {epsilon}{sub 0} are the high-frequency and static dielectric constants, has been found to be {eta}{sub c} = 0.2496.

  9. Dissociative recombination of dications

    NASA Astrophysics Data System (ADS)

    Seiersen, K.; Heber, O.; Jensen, M. J.; Safvan, C. P.; Andersen, L. H.

    2003-07-01

    Dissociative recombination (DR) of doubly-charged positive ions has been studied at the heavy ion storage ring ASTRID. Low-energy electrons were scattered on the dication of the N2 molecule, and the absolute cross section was measured in the energy range of 10-4-50 eV. From the measured cross section, a thermal rate coefficient of 5.810-7 cm3 s-1 at 300 K was extracted. Furthermore, we present new results on the CO2+ DR rate, and a summary and comparison of measured DR rate coefficients for both the singly and doubly-charged ions of CO, CO2, and N2 is presented.

  10. An alternative energysize relationship to that proposed by Bond for the design and optimisation of grinding circuits

    Microsoft Academic Search

    Stephen Morrell

    2004-01-01

    Despite reservations of a number of researchers concerning the applicability of Bond's equation for relating specific energy to the size reduction of rocks, his approach has become an industry standard.Data from a large number of pilot and full-scale autogenous (AG), semi-autogenous (SAG) and ball mill circuits are used to show that Bond's equation does not hold over the particle size

  11. Catalytic enhancement in dissociation of nitric oxide over rhodium and nickel small-size clusters: a DFT study.

    PubMed

    Chang, Chun-Chih; Ho, Jia-Jen

    2014-03-21

    We applied density-functional theory (DFT) to investigate the adsorption and dissociation of NO on Rh19 and Ni19 clusters with a double-icosahedral (DI) structure. The transition structures of the NO dissociating on the potential-energy surfaces were derived using the nudged-elastic-band (NEB) method. The adsorption energies of NO molecules on the rhombus-center region of DI clusters are -2.53 eV and -2.78 eV with the N-O bond elongated to 1.33 and 1.35 , respectively, on Ni19 and Rh19, compared to 1.16 of the gaseous NO counterpart. The barriers to dissociation of N-O on both DI-Rh19 (Ea = 0.24 eV) and DI-Ni19 (Ea = 0.42 eV) clusters are small, indicating that the rhombus-center region of DI metal clusters might activate the scission of the N-O bond. To understand the interaction between these nanocluster catalysts and their adsorbates, we calculated the electronic properties including the local densities of states, orbital evolution of the adsorbates and interaction energies; the results indicate that a profound catalytic behavior for bond scission is observed in this unique rhombus-center region of DI metal-nanoclusters. PMID:24499741

  12. Determination of Hydrogen Bond Structure in Water versus Aprotic Environments To Test the Relationship Between Length and Stability.

    PubMed

    Sigala, Paul A; Ruben, Eliza A; Liu, Corey W; Piccoli, Paula M B; Hohenstein, Edward G; Martnez, Todd J; Schultz, Arthur J; Herschlag, Daniel

    2015-05-01

    Hydrogen bonds profoundly influence the architecture and activity of biological macromolecules. Deep appreciation of hydrogen bond contributions to biomolecular function thus requires a detailed understanding of hydrogen bond structure and energetics and the relationship between these properties. Hydrogen bond formation energies (?Gf) are enormously more favorable in aprotic solvents than in water, and two classes of contributing factors have been proposed to explain this energetic difference, focusing respectively on the isolated and hydrogen-bonded species: (I) water stabilizes the dissociated donor and acceptor groups much better than aprotic solvents, thereby reducing the driving force for hydrogen bond formation; and (II) water lengthens hydrogen bonds compared to aprotic environments, thereby decreasing the potential energy within the hydrogen bond. Each model has been proposed to provide a dominant contribution to ?Gf, but incisive tests that distinguish the importance of these contributions are lacking. Here we directly test the structural basis of model II. Neutron crystallography, NMR spectroscopy, and quantum mechanical calculations demonstrate that O-HO hydrogen bonds in crystals, chloroform, acetone, and water have nearly identical lengths and very similar potential energy surfaces despite ?Gf differences >8 kcal/mol across these solvents. These results rule out a substantial contribution from solvent-dependent differences in hydrogen bond structure and potential energy after association (model II) and thus support the conclusion that differences in hydrogen bond ?Gf are predominantly determined by solvent interactions with the dissociated groups (model I). These findings advance our understanding of universal hydrogen-bonding interactions and have important implications for biology and engineering. PMID:25871450

  13. Empirical valence bond models for reactive potential energy surfaces: a parallel multilevel genetic program approach.

    PubMed

    Bellucci, Michael A; Coker, David F

    2011-07-28

    We describe a new method for constructing empirical valence bond potential energy surfaces using a parallel multilevel genetic program (PMLGP). Genetic programs can be used to perform an efficient search through function space and parameter space to find the best functions and sets of parameters that fit energies obtained by ab initio electronic structure calculations. Building on the traditional genetic program approach, the PMLGP utilizes a hierarchy of genetic programming on two different levels. The lower level genetic programs are used to optimize coevolving populations in parallel while the higher level genetic program (HLGP) is used to optimize the genetic operator probabilities of the lower level genetic programs. The HLGP allows the algorithm to dynamically learn the mutation or combination of mutations that most effectively increase the fitness of the populations, causing a significant increase in the algorithm's accuracy and efficiency. The algorithm's accuracy and efficiency is tested against a standard parallel genetic program with a variety of one-dimensional test cases. Subsequently, the PMLGP is utilized to obtain an accurate empirical valence bond model for proton transfer in 3-hydroxy-gamma-pyrone in gas phase and protic solvent. PMID:21806098

  14. Vibrational state controlled bond cleavage in the photodissociation of isocyanic acid (HNCO)

    NASA Astrophysics Data System (ADS)

    Brown, Steven S.; Berghout, H. Laine; Crim, F. Fleming

    1995-06-01

    We report the bond selected photodissociation of isocyanic acid (HNCO). This molecule dissociates from its first excited singlet state, breaking either the N-H bond to form H+NCO (X 2?) or the C-N bond to form NH (a 1?)+CO (1?+). The threshold for production of NH lies about 3900 cm-1 above that of NCO, and we detect both of these channels by laser induced fluorescence on either the NH or the NCO fragment. Dissociating the molecule out of a vibrationally excited state on its ground electronic surface containing four quanta of N-H stretch (4?1) enhances the efficiency of the NCO channel over the NH channel by a factor of at least 20. We reach this conclusion by comparing the results of such a vibrationally mediated photodissociation experiment to those from a conventional single photon dissociation at the same total energy (about 1000 cm-1 above the threshold for the NH channel). Our estimate of the branching ratio in the one photon dissociation at this energy is roughly ?NCO/?NH?20, and it grows to ?NCO/?NH?400 in the vibrationally mediated photodissociation.

  15. Differentiation and quantitation of isomeric dipeptides by low-energy dissociation of copper(II)-bound complexes.

    PubMed

    Tao, W A; Wu, L; Cooks, R G

    2001-05-01

    Application of the kinetic method based on the dissociation of transition metal centered cluster ions is extended from chiral analysis (Tao, W. A.; Zhang, D.; Nikolaev, E. N.; Cooks, R. G. J. Am. Chem. Soc. 2000, 122, 10598) to quantitative analysis of isomeric mixtures, including those with Leu/Ile substitutions. Copper(II)-bound complexes of pairs of peptide isomers are generated by electrospray ionization mass spectrometry and the trimeric complex [CuII(ref)2(A) - H]+ (analyte A, a mixture of isomeric peptides; reference compound ref, usually a peptide) is caused to undergo collisional dissociation. Competitive loss of the neutral reference compound or the neutral analyte yields two ionic products and the ratio of rates of the two competitive dissociations, viz. the product ion branching ratio R is shown to depend strongly on the regiochemistry of the analyte in the precursor [CuII(A)(ref)2 - H]+ complex ion. Calibration curves are constructed by relating the branching ratio measured by the kinetic method, to the isomeric composition of the mixture to allow rapid quantitative isomer analysis. PMID:11349946

  16. 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.

  17. Inflight dissociation of zircon in air plasma

    NASA Astrophysics Data System (ADS)

    Yugeswaran, S.; Ananthapadmanabhan, P. V.; Thiyagarajan, T. K.; Selvarajan, V.; Nair, Janardhanan

    2010-02-01

    Thermal dissociation of zircon can be conveniently carried out in a plasma reactor, which is characterized by high temperature, high energy density and high quench rate. Zirconia is recovered from this partially dissociated zircon by alkali leaching. Dissociation of zircon has been conventionally carried out in argon gas, which is expensive. The present paper reports experimental results on thermal dissociation of zircon in air plasma medium. Process simulation for 'inflight' dissociation of zircon in air plasma medium is also presented. The experimental system consists of a central hollow graphite electrode, which acts as the cathode and a graphite anode. The material to be processed is fed centrally through the cathode. The unique feature of the system is that it uses air as the working gas to generate the thermal plasma. The system has been used to study in-flight dissociation of zircon in the thermal plasma jet. Dissociation was carried out over 10-25 kW power range. Results of the study indicate that complete dissociation of zircon to ZrO2 and silica could be accomplished at 25 kW in air plasma.

  18. 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.

  19. Chemistry at molecular junctions: Rotation and dissociation of O2 on the Ag(110) surface induced by a scanning tunneling microscope

    NASA Astrophysics Data System (ADS)

    Roy, Sharani; Mujica, Vladimiro; Ratner, Mark A.

    2013-08-01

    The scanning tunneling microscope (STM) is a fascinating tool used to perform chemical processes at the single-molecule level, including bond formation, bond breaking, and even chemical reactions. Hahn and Ho [J. Chem. Phys. 123, 214702 (2005), 10.1063/1.2131064] performed controlled rotations and dissociations of single O2 molecules chemisorbed on the Ag(110) surface at precise bias voltages using STM. These threshold voltages were dependent on the direction of the bias voltage and the initial orientation of the chemisorbed molecule. They also observed an interesting voltage-direction-dependent and orientation-dependent pathway selectivity suggestive of mode-selective chemistry at molecular junctions, such that in one case the molecule underwent direct dissociation, whereas in the other case it underwent rotation-mediated dissociation. We present a detailed, first-principles-based theoretical study to investigate the mechanism of the tunneling-induced O2 dynamics, including the origin of the observed threshold voltages, the pathway dependence, and the rate of O2 dissociation. Results show a direct correspondence between the observed threshold voltage for a process and the activation energy for that process. The pathway selectivity arises from a competition between the voltage-modified barrier heights for rotation and dissociation, and the coupling strength of the tunneling electrons to the rotational and vibrational modes of the adsorbed molecule. Finally, we explore the "dipole" and "resonance" mechanisms of inelastic electron tunneling to elucidate the energy transfer between the tunneling electrons and chemisorbed O2.

  20. 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

  1. Bonding of resin cements to a metal substrate: influence of pretreatment on the adherence energy.

    PubMed

    Asmussen, E; Attal, J P; Degrange, M

    1996-01-01

    The adherence of resin cements to restoration as well as tooth structure is of prime importance for the longevity of cemented restorations. It was the aim of the study to investigate the effect of an acid and a base primer on (i) surface polarity of a nonprecious alloy and on (ii) adherence energy of resin cements bonded to the alloy. The beams were pretreated with a 3% acetone solution of either maleic acid or N,N-diethanol-p-toluidine, and the solvent evaporated. The polarity was determined by means of measurements of contact angles. The adherence energy was measured by means of the wedge test, according to which 2 beams were glued together with the resin cement. A wedge was introduced between the joined beams to create a fissure, and on the basis of the length of the fissure, the adherence energy was calculated. It was found that the polar component of the surface free energy of the alloy increased as a consequence of the pretreatments. The results also showed that the pretreatments gave rise to an increase in adherence energy of 11-15 J/m2, equivalent to relative increases of 22-54%. The observed increases in adherence energy may be due to an increase in polar interactions at the interface between adhesive and substrate. PMID:9021331

  2. Evaluating interaction energies of weakly bonded systems using the Buckingham-Hirshfeld method

    SciTech Connect

    Krishtal, A. [Fachbereich Chemie, Technische Universitt Kaiserslautern, Erwin Schrdinger Strae 52, D-67663 Kaiserslautern (Germany)] [Fachbereich Chemie, Technische Universitt Kaiserslautern, Erwin Schrdinger Strae 52, D-67663 Kaiserslautern (Germany); Van Alsenoy, C. [Department of Chemistry, University of Antwerp, Universiteitsplein 1, B2610 Antwerp (Belgium)] [Department of Chemistry, University of Antwerp, Universiteitsplein 1, B2610 Antwerp (Belgium); Geerlings, P. [Algemene Chemie, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels (Belgium)] [Algemene Chemie, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels (Belgium)

    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.

  3. Energy level(s) of the dissociation product of the 1.014 eV photoluminescence copper center in n-type silicon determined by photoluminescence and deep-level transient spectroscopy

    NASA Astrophysics Data System (ADS)

    Nakamura, Minoru; Murakami, Susumu; Udono, Haruhiko

    2013-07-01

    The annealing behavior of copper centers in n-type silicon diffused with dilute copper was measured by photoluminescence (PL) and deep-level transient spectroscopy (DLTS) to investigate the energy level (or levels) of the dissociation product center of the 1.014 eV PL copper center. Among several DLTS peaks that appeared by the annealing, only the energy level at Ec - 0.16 eV (Ec: bottom energy of the conduction band) was suggested as the double acceptor level of the dissociation product center. From the disagreement between the measured energy levels of the dissociation product center and the estimated acceptor levels of substitutional copper (Cus), Cus was judged to be inappropriate for the origin of the product center.

  4. The catalytic adsorption and dissociation of carbon dioxide on a double icosahedral Ru19 nanocluster - A theoretical study

    NASA Astrophysics Data System (ADS)

    Li, Han-Jung; Yeh, Chen-Hao; Ho, Jia-Jen

    2013-10-01

    Using density-functional theory, we investigated the adsorption and dissociation of CO2 on Ru19 clusters of nm size. According to our results, the CO2 molecule adsorbed on the rhombus-center region of a double icosahedral Ru19 nanocluster has the largest adsorption energy, -1.48 eV, and the greatest elongation of C-O bond. Dissociating the first C-O bond of a CO2 molecule we got a reaction barrier of 0.78 eV, smaller than that of adsorbed on otherwise octahedral and low-symmetry Ru19 cluster structures. To understand the electronic properties, we calculated the electron localization functions and local densities of states, and the result was explicable.

  5. An investigation of the dissociation of complexes of triethylene tetramine with first-row transition-metal dications by electrospray ionization tandem mass spectrometry: Remote C C bond activation

    Microsoft Academic Search

    Janna Anichina; Diethard K. Bohme

    2007-01-01

    Electrospray ionization mass spectrometry is employed to probe the complexation and dissociation of the first-row transition-metal dications with triethylene tetramine that originate in water\\/methanol solutions of the corresponding metal salts and the ligand. The major complex ions emerging from the ESI source were observed to be ML2+, ML(CH3OH)2+, M(LH)+, MLCl+ and MLNO3+ (M=Mn, Fe, Co, Ni, Cu, Zn and L=triethylene

  6. Energy-resolved collision-induced dissociation pathways of model N-linked glycopeptides: implications for capturing glycan connectivity and peptide sequence in a single experiment.

    PubMed

    Kolli, Venkata; Dodds, Eric D

    2014-05-01

    Tandem mass spectrometry (MS/MS) of glycopeptides stands among the principal analytical approaches for assessing protein glycosylation in a site-specific manner. The aims of such experiments are often to determine the monosaccharide connectivity of the glycan, the amino acid sequence of the peptide, and the site of glycan attachment. This level of detail is often difficult to achieve using any single ion dissociation method; however, precedent does exist for use of collision-induced dissociation (CID) to establish either the connectivity of the oligosaccharide or the sequence of the polypeptide depending upon the applied collision energy. Unfortunately, the relative energy requirements for glycan and peptide cleavage have not been thoroughly characterized with respect to specific physicochemical characteristics of the precursor ions. This report describes case studies on the energy-resolved CID pathways of model tryptic glycopeptides derived from Erythrina cristagalli lectin and bovine ribonuclease B. While glycopeptide ions having disparate physical and chemical characteristics shared strikingly similar qualitative responses to increasing vibrational energy deposition, the absolute collision energies at which either glycan or peptide fragmentations were accessed varied substantially among the precursor ions examined. Nevertheless, these data suggest that the energy requirements for peptide and glycan cleavage may be somewhat predictable based on characteristics of the precursor ion. The practical usefulness of these observations was demonstrated through implementation of online collision energy modulation such that both glycan and peptide fragmentation were captured in the same spectrum, providing near-exhaustive glycopeptide characterization in a single experiment. Overall, these results highlight the potential to further extend the capabilities of CID in the context of glycoproteomics. PMID:24618751

  7. The vibrational dynamics of 3D HOCl above dissociation

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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.

  8. The vibrational dynamics of 3D HOCl above dissociation.

    PubMed

    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. PMID:25833576

  9. Gauging the applicability of ONIOM (MO\\/MO) methods to weak chemical interactions in large systems: hydrogen bonding in alcohol dimers

    Microsoft Academic Search

    Gregory S Tschumper; Keiji Morokuma

    2002-01-01

    The applicability of two-layer ONIOM methods to hydrogen bonding has been systematically investigated. The structures of 12 hydrogen bonded dimers composed of water, methanol, ethanol and n-propanol have been optimized using second-order MllerPlesset perturbation theory (MP2) in conjunction with a double-? basis set with polarization and diffuse functions on all atoms, denoted DZP++. The dissociation energies (both counterpoise corrected and

  10. Contemporary concepts of dissociation.

    PubMed

    Avdibegovi?, Esmina

    2012-10-01

    The concept of dissociation was developed in the late 19th century by Pierre Janet for conditions of "double consciousness" in hypnosis, hysteria, spirit possession and mediumship. He defined dissociation as a deficit in the capacity of integration of two or more different "systems of ideas and functions that constitute personality", and suggested that it can be related to a genetic component, to severe illness and fatigue, and particularly to experiencing adverse, potentially traumatizing events. By the late 20th century, various and often contradictory concepts of dissociation were suggested, which were either insufficient or exceedingly including when compared to the original idea. Currently, dissociation is used to describe a wide range of normal and abnormal phenomena as a process in which behaviour, thoughts and emotions can become separated one from another. A complete presentation of mechanisms involved in dissociation is still unknown. Scientific research on basic processes of dissociation is derived mainly from studies of hypnosis and post-traumatic stress disorder. Given the controversies in modern concepts of dissociation, some researchers and theorists suggest return to the original understanding of dissociation as a basic premise for the further development of the concept of dissociation. PMID:23114818

  11. Dissociating people from nature.

    PubMed

    Chatterjee, Rhitu

    2008-10-15

    Conservation measures that dissociate people from their native landscape can destroy traditional ecological knowledge and hurt the very biodiversity that the conservation policies aim to protect. PMID:18983073

  12. 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. [Department of Chemistry and James Franck Institute, University of Chicago, Chicago, Illinois 60637 (United States)

    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.

  13. Energetic multifunctionalized nitraminopyrazoles and their ionic derivatives: ternary hydrogen-bond induced high energy density materials.

    PubMed

    Yin, Ping; Parrish, Damon A; Shreeve, Jean'ne M

    2015-04-15

    Diverse functionalization was introduced into the pyrazole framework giving rise to a new family of ternary hydrogen-bond induced high energy density materials. By incorporating extended cationic interactions, nitramine-based ionic derivatives exhibit good energetic performance and enhanced molecular stability. Performance parameters including heats of formation and detonation properties were calculated by using Gaussian 03 and EXPLO5 v6.01 programs, respectively. It is noteworthy to find that 5-nitramino-3,4-dinitropyrazole, 4, has a remarkable measured density of 1.97 g cm(-3) at 298 K, which is consistent with its crystal density (2.032 g cm(-3), 150 K), and ranks highest among azole-based CHNO compounds. Energetic evaluation indicates that, in addition to the molecular compound 4, some ionic derivatives, 9, 11, 12, 17, 19, and 22, also have high densities (1.83-1.97 g cm(-3)), excellent detonation pressures and velocities (P, 35.6-41.6 GPa; vD, 8880-9430 m s(-1)), as well as acceptable impact and friction sensitivities (IS, 4-30 J; FS, 40-240 N). These attractive features highlight the application potential of nitramino hydrogen-bonded interactions in the design of advanced energetic materials. PMID:25807076

  14. Evaluation of segmented active constrained layer damping treatments that include bonding layer strain energy

    NASA Astrophysics Data System (ADS)

    Cento, Peter F.; Kawiecki, Grzegorz

    2001-08-01

    The primary objective of this study is to develop a more accurate research and design tool than those in the currently available literature for active constrained layer damping treatments applied in bending. A five layer beam finite element model is presented that includes bonding layer strain energy and extends current finite element models for Euler-Bernoulli beams with segmented active constrained layer damping treatments. Active constrained layer damping utilizes modern piezoelectric materials as the constraining layer for these types of damping treatments. Preliminary studies have confirmed that strains in the bonding layers can have a significant effect on damping ratios at the fundamental modal frequency, especially when relatively thin compliant piezo materials are used for constraining layers. Previous researchers that have developed three layer finite element models assumed perfect no-slip adhesion between adjacent surfaces of the beam, viscoelastic layer, and constraining layer. In certain instances this can contribute to reduced accuracy when predicting damping. The effectiveness of the finite element model is validated experimentally for both active and passive constraining layers. The damping is represented using an elastic displacement fields (ADF) to model the frequency dependent stiffness and damping properties in viscoelastic materials as developed by Lesieutre and Bianchini.

  15. 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., E-mail: jim.greer@tyndall.ie [Tyndall National Institute, University College Cork, Dyke Parade, Lee Maltings, Cork (Ireland); Perera, Ajith; Bartlett, Rodney J. [Quantum Theory Project, 2234 New Physics Building 92, PO Box 118435, University of Florida at Gainesville, Gainesville, Florida 32611-8435 (United States)] [Quantum Theory Project, 2234 New Physics Building 92, PO Box 118435, University of Florida at Gainesville, Gainesville, Florida 32611-8435 (United States)

    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.

  16. Bond energies, reaction volumes, and kinetics for ?- and ?-complexes of MoCO5L.

    PubMed

    Gittermann, Shannon M; Letterman, Roger G; Jiao, Tianjie; Leu, Ging-Long; DeYonker, Nathan J; Webster, Charles Edwin; Burkey, Theodore J

    2011-08-18

    The photosubstitution reactions of molybdenum hexacarbonyl with ? and ? donor ligands were investigated using photoacoustic calorimetry and computational methods in a series of linear alkane solvents (pentane, hexane, heptane, octane, decane, and dodecane). The results show that reaction volumes make a significant contribution to the photoacoustic signal and must be considered during thermodynamic calculations based on photoacoustic measurements. The enthalpies of CO substitution by an alkane solvent and subsequent substitution by each Lewis base were determined. Corresponding Mo-L bond energies (kcal mol(-1)) were calculated: L = linear alkanes (13), triethylsilane (26), 1-hexyne (27), 1-hexene (27), and benzene (17). The relative energies are in agreement with computational results. The experimental reaction volume for CO substitution by alkane was positive (15 mL mol(-1)) and negative or close to zero for alkane substitution by a Lewis base (for example, -11 mL mol(-1) for triethylsilane and 3.6 mL mol(-1) for benzene). The errors in the experimental and computational reaction volumes are large and often comparable to the reaction volumes. An improved calibration of the methods as well as a better understanding of the underlying physics involved is needed. For the Lewis bases reported in this study, the second-order rate constants for the displacement of a coordinated alkane are less than diffusion control (5 10(6)-4 10(7) M(-1) s(-1)) and decrease monotonically with the alkane chain length. The rate constants correlate better with steric effects than with bond energies. An interchange mechanism is consistent with the results. PMID:21780751

  17. Mechanisms for S-S and N-C ? bond cleavage in peptide ECD and ETD mass spectrometry

    NASA Astrophysics Data System (ADS)

    Simons, Jack

    2010-01-01

    This Letter reviews efforts made to elucidate the mechanism by which electron-capture and electron-transfer dissociation bond cleavages occur in mass spectrometry. The primary issues include where in the parent ion the electron initially attaches, whether the energy released in this initial electron-capture step is key to determining which bonds will cleave, whether the electron can migrate from the site to which it initially attaches to other sites in the parent ion, and, if so, over what distances and at what rates, and why, in polypeptides, one finds disulfide and N-C ? bond cleavage primarily.

  18. 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.

  19. 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.

  20. Chemical bonding of nitrogen in low energy high flux implanted austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Riviere, J. P.; Cahoreau, M.; Meheust, P.

    2002-05-01

    AISI 304L austenitic stainless steel was implanted at 400 C with 1.2 keV nitrogen ions using a high beam current density of 1 mA/cm2. The nitrogen depth profile, structure, and chemical composition in the modified surface layer were determined by nuclear reaction analysis (NRA) and x-ray diffraction (XRD). The chemical bonding of Fe, Cr atoms with nitrogen was investigated by x-ray photoelectron spectroscopy (XPS). For a treatment time of 1 h, the formation of a thick nitrided layer of about 3.5 ?m with a high nitrogen content (20 at. %) is observed by NRA. The nitrogen depth profile is characterized by a nearly flat shape over a thickness of 2.5 ?m followed by an abrupt decrease. XRD spectra show the formation in the nitrided layer of a phase usually called expanded austenite ?N, which corresponds fairly well with a nitrogen solid solution of the fcc structure containing a high density of stacking faults. The XPS study of the Cr2p3/2, Fe2p3/2, and N 1s binding states indicate clearly the preferential bonding of chromium with nitrogen with a binding energy of about 1 eV. This value, which is lower than the expected one for chromium nitride CrN, would be characteristic of the binding energy of nitrogen with Cr in the ?N expanded austenite phase. Moreover, it has been found that the atomic ratio N/Cr in the nitride layer deduced from both NRA and XPS is very close to 1. These experimental results support the specific role of chromium in the mechanisms of atomic transport of nitrogen over long distances at moderate temperature in austenitic stainless steels.

  1. Evidence for site-specific intra-ionic hydrogen/deuterium exchange in the low-energy collision-induced dissociation product ion spectra of protonated small molecules generated by electrospray ionisation.

    PubMed

    Holman, Stephen W; Wright, Patricia; Wells, Neil J; Langley, G John

    2010-04-01

    The experimental investigation of site-specific intra-ionic hydrogen/deuterium (H/D) exchange in the low-energy collision-induced dissociation (CID) product ion spectra of protonated small molecules generated by electrospray ionisation (ESI) is presented. The observation of intra-ionic H/D exchange in such ions under low-energy CID conditions has hitherto been rarely reported. The data suggest that the intra-ionic H/D exchange takes place in a site-specific manner between the ionising deuteron, localised at either a tertiary amine or a tertiary amine-N-oxide, and a gamma-hydrogen relative to the nitrogen atom. Nuclear magnetic resonance (NMR) spectroscopy measurements showed that no H/D exchange takes place in solution, indicating that the reaction occurs in the gas phase. The compounds analysed in this study suggested that electron-withdrawing groups bonded to the carbon atom bearing the gamma-hydrogen can preclude exchange. The effect of the electron-withdrawing group appears dependent upon its electronegativity, with lower chi value groups still allowing exchange to take place. However, the limited dataset available in this study prevented robust conclusions being drawn regarding the effect of the electron-withdrawing group. The observation of site-specific intra-ionic H/D exchange has application in the area of structural elucidation, where it could be used to introduce an isotopic label into the carbon skeleton of a molecule containing specific structural features. This could increase the throughput, and minimise the cost, of such studies due to the obviation of the need to produce a deuterium-labelled analogue by synthetic means. PMID:20069530

  2. Dissociated methanol test results

    Microsoft Academic Search

    J. G. Finegold; J. T. McKinnon

    1982-01-01

    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

  3. Bonding silicones with epoxies

    SciTech Connect

    Tira, J.S.

    1980-01-01

    It is shown that silicones, both room temperature vulcanizing (RTV) and millable rubber (press cured) can be successfully bonded to other materials using plasma treatment and epoxy adhesives. The plasma treatment using dry air atmosphere increases the surface energy of the silicone and thus provides a lower water contact angle. This phenomenon allows the epoxy adhesive to wet the silicone surface and ultimately bond. Bond strengths are sufficiently high to result in failures in the silicone materials rather than the adhesive bond.

  4. Energy-resolved collision-induced dissociation cross sections of 2:1 bis-oxazoline copper complexes. Nonbonded interactions and nonlinear effects.

    PubMed

    Zocher, Eva; Dietiker, Rolf; Chen, Peter

    2007-03-01

    Absolute ligand binding energies are determined for the 2:1 complexes of bis-oxazoline ligands and Cu(I) in the gas phase by the fitting of energy-resolved collision-induced dissociation cross sections. The complexes were chosen for their occurrence in asymmetric catalysis for which the phenomenon of nonlinear effects is explained by differences in stability for homochiral and heterochiral complexes. Pseudo-enantiomeric ligands are used so that mass spectrometric measurements can be employed. The measurements find that the sterically similar, but electronically different, isopropyl versus phenyl substituents lead to a different stability ordering of the homo- versus heterochiral complexes, which then leads to the prediction of nonlinear effects in asymmetric catalysis by the complexes with isopropyl-substituted ligands. The origin of the difference in stability order is found in noncovalent interactions between the phenyl groups on the ligands, which are poorly described by DFT calculations. PMID:17288414

  5. Narrative, dialogue, and dissociation.

    PubMed

    Gedo, Paul M

    2014-02-01

    This paper explores dissociative phenomena as disruptions of dialogue between persons, and disruptions of internal narratives. A dissociating patient temporarily loses ability to convey his or her inner experience to the therapist. The disconnection between dialogue and internal experience can mislead both participants, or distract them from underlying connotations. Dissociation also disrupts the patient's sense of internal coherence and internal conversation. Dissociation represents a regression to an early, preverbal mode of (internal and external) communication. The challenge for the dyad is to restore dialogue and then to discern the multiply determined meanings of the dissociative communication. This therapeutic work allows the patient to achieve a more coherent sense of self and of his or her life course. PMID:24555552

  6. 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 OH bond that is closest to the CO is lengthened compared to the structure in the absence of the CO, and the breaking OH 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

  7. Dissociative electron attachment in nanoscale ice films: Temperature and morphology effects

    SciTech Connect

    Simpson, W.C.; Sieger, M.T.; Orlando, T.M. [W. R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, M/S K8-88, Richland, Washington 99352 (United States)] [W. R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, M/S K8-88, Richland, Washington 99352 (United States); Parenteau, L.; Nagesha, K.; Sanche, L. [Canadian Medical Research Group in Radiation Sciences, Faculty of Medicine, University of Sherbrooke, Sherbrooke, Quebec, Canada, J1H 5N4 (CANADA)] [Canadian Medical Research Group in Radiation Sciences, Faculty of Medicine, University of Sherbrooke, Sherbrooke, Quebec, Canada, J1H 5N4 (CANADA)

    1997-11-01

    The electron-stimulated desorption (ESD) of D{sup {minus}} ions from condensed D{sub 2}O films is investigated. Three low-energy peaks are observed which are identified as arising from excitation of {sup 2}B{sub 1}, {sup 2}A{sub 1}, and {sup 2}B{sub 2} dissociative electron attachment (DEA) resonances. A fourth, higher energy feature is also seen in the D{sup {minus}} yield which is likely due to the formation of a transient anion state that dissociates and/or decays into a dissociative excited state. The energies and ion yields of the resonances vary with the temperature and morphology of the D{sub 2}O film. Below 60 K, the work function of the ice films changes with temperature and the DEA resonances shift in energy. The D{sup {minus}} ESD yield generally increases with temperature, but it deviates from this trend at temperatures corresponding to structural phase transitions in ice. The ({sup 2}B{sub 1}) D{sup {minus}} temperature dependence is remarkably similar to that observed for the ESD of low-energy D{sup +} ions from D{sub 2}O ice, even though the two originate from different electronic excitations. These results are attributed to thermally induced changes in the hydrogen bonding network, which changes the lifetimes of the predissociative states that lead to ESD and which also allows for the reorientation of surface molecules. {copyright} {ital 1997 American Institute of Physics.}

  8. Dissociative recombination of the acetaldehyde cation, CH(3)CHO(+).

    PubMed

    Vigren, Erik; Hamberg, Mathias; Zhaunerchyk, Vitali; Kaminska, Magdalena; Thomas, Richard D; Trippel, Sebastian; Zhang, Mingwu; Kashperka, Iryna; Ugglas, Magnus Af; Walsh, Catherine; Wester, Roland; Semaniak, Jacek; Larsson, Mats; Geppert, Wolf D

    2010-10-01

    The dissociative recombination of the acetaldehyde cation, CH(3)CHO(+), has been investigated at the heavy ion storage ring CRYRING at the Manne Siegbahn Laboratory in Stockholm, Sweden. The dependence of the absolute cross section of the reaction on the relative kinetic energy has been determined and a thermal rate coefficient of k(T) = (1.5 0.2) 10(-6) (T/300)(-0.700.02) cm(3) s(-1) has been deduced, which is valid for electron temperatures between ?10 and 1000 K. The branching fractions of the reaction were studied at ?0 eV relative kinetic energy and we found that breaking one of the bonds between two of the heavy atoms occurs in 72 2% of the reactions. In the remaining events the three heavy atoms stay in the same product fragment. While the branching fractions are fairly similar to the results from an earlier investigation into the dissociative recombination of the fully deuterated acetaldehyde cation, CD(3)CDO(+), the thermal rate coefficient is somewhat larger for CH(3)CHO(+). Astrochemical implications of the results are discussed. PMID:20714489

  9. 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 719 monomer units and 25 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

  10. Theoretical Electron Density Distributions for Fe-and Cu-Sulfide Earth Materials: A Connection between Bond Length, Bond Critical Point Properties, Local Energy Densities,

    E-print Network

    Downs, Robert T.

    interactions. The bond lengths observed for chalcopyrite together with the calculated bond critical point is larger for the FeS4 tetrahedron displayed by metastable greigite than those displayed by chalcopyrite

  11. Dissociative recombination of protonated methanol.

    PubMed

    Geppert, W D; Hamberg, M; Thomas, R D; Osterdahl, F; Hellberg, F; Zhaunerchyk, V; Ehlerding, A; Millar, T J; Roberts, H; Semaniak, J; af Ugglas, M; Kllberg, A; Simonsson, A; Kaminska, M; Larsson, M

    2006-01-01

    The branching ratios of the different reaction pathways and the overall rate coefficients of the dissociative recombination reactions of CH3OH2+ and CD3OD2+ have been measured at the CRYRING storage ring located in Stockholm, Sweden. Analysis of the data yielded the result that formation of methanol or deuterated methanol accounted for only 3 and 6% of the total rate in CH3OH2+ and CD3OD2+, respectively. Dissociative recombination of both isotopomeres mainly involves fragmentation of the C-O bond, the major process being the three-body break-up forming CH3, OH and H (CD3, OD and D). The overall cross sections are best fitted by sigma = 1.2 +/- 0.1 x 10(-15) E(-1.15 +/- 0.02) cm2 and sigma = 9.6 +/- 0.9 x 10(-16) E(-1.20 +/- 0.02) cm2 for CH3OH2+ and CD3OD2+, respectively. From these values thermal reaction rate coefficients of k(T) = 8.9 +/- 0.9 x 10(-7) (T/300)(-0.59 +/- 0.02) cm3 s(-1) (CH3OH2+) and k(T) = 9.1 +/- 0.9 x 10(-7) (T/300)(-0.63 +/- 0.02) cm3 s(-1) (CD3OD2+) can be calculated. A non-negligible formation of interstellar methanol by the previously proposed mechanism via radiative association of CH3+ and H2O and subsequent dissociative recombination of the resulting CH3OH2+ ion to yield methanol and hydrogen atoms is therefore very unlikely. PMID:17191449

  12. 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 CO bond cleavage is more plausible.

  13. Dissociative recombination study of Na+ (D2O) in a storage ring.

    PubMed

    Zhaunerchyk, Vitali; Ehlerding, Anneli; Geppert, Wolf D; Hellberg, Fredrik; Thomas, Richard D; Larsson, Mats; Viggiano, Albert A; Arnold, Susan T; Osterdahl, Fabian; Hlavenka, Peter

    2004-12-01

    The dissociative recombination of Na(+)(D(2)O) ion has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The cross section has been measured as a function of center-of-mass energy ranging from 1 meV to 0.1 eV and found to have an E(-1.37) dependence. The rate coefficient has been deduced to be (2.3+/-0.32)x10(-7)(T(e)/300)(-0.95+/-0.01) cm(3) s(-1) for T(e)=50-1000 K. The branching ratios have been measured at 0 eV. Of the four energetically accessible dissociation channels, three channels are found to occur although the channel that breaks the weak Na(+)-D(2)O bond is by far dominant. PMID:15549929

  14. Initiation stage of alkene metathesis: Insights from natural bond orbital and charge decomposition analyses

    NASA Astrophysics Data System (ADS)

    Paredes-Gil, Katherine; Jaque, Pablo

    2015-01-01

    The Rusbnd PR3 bonds of 1-2(a-b)-PC, Rudbnd CHPh bonds of 1a-b, 2-Inact/Act and 1a-b, 2-RCB were analyzed by charge decomposition (CDA) and natural bond orbital (NBO). We have found that the dissociation step of the Rusbnd PR3 bond is driven by charge transfer, while the RCB by polarization effects. Furthermore, the ?(Cipso)-?*(Rudbnd C) interaction was associated with delocalization effects in the benzylidene ring. Likewise, the nature of the rotameric changes in the carbene was studied through the resonance stabilization energy (ENLW). 2 presented a lower ?ENLW (Inactive ? Active) than 1a-b, which confirms that the delocalization effects are related to a low carbene rotameric energy.

  15. Energy partitioning in CO2 laser induced multiphoton dissociations: Energy of X/CF2 and X/CFCl from CF2CFCl

    NASA Astrophysics Data System (ADS)

    Stephenson, John C.; Bialkowski, Stephen E.; King, David S.

    1980-01-01

    We have measured the vibrational (v), rotational (J,K), and translational energy, (ET), of the X CF2 and X CFCl fragments formed in the CO2 laser induced multiphoton dissociation of CF2CFCl (chlorotrifluoroethylene): CF2CFCl?CF2 (v,J,K)+CFCl(v,J,K)+ET(v,J,K), which was the only detectable reaction path for CF2CFCl. More vibrational energy (Ev) appears in CF2 than in CFCl. Direct spectroscopic measurements of populations in levels 0energy in ?2, and the vibrational temperature which characterizes the nascent distribution is Tv(?2) =1860250 K. A vibrational relaxation method was used to accurately determine fo, the fraction of CF2 and CFCl molecules initially formed in the ground vibrational level. The measurements of fo showed that the energy in the stretching modes (?1 and ?3) of CF2 is not characterized by this Tv(?2); if the energy in ?1 and ?3 is also thermal, it must be characterized by a lower temperature: Tv(?1 and ?3) ?1100 K. For the CFCl product, direct spectroscopic measurement of the relative populations in ?2=1 and ?2=0 are consistent with Tv (?2) =1550300 K. However, the measured fo for CFCl was consistent with a thermal distribution characterized by a lower vibrational temperature. Values of fo for CF2 were measured as a function of laser fluence for the condition where the reactant was extremely dilute (XCF2CFCl<10-5) in a high pressure (119 Torr) of Ar buffer gas. These measurements showed that the fraction of CF2 product molecules formed in vibrationally excited states decreased from 76% to 53% as the fluence decreased by a factor of 5.5, from 30 J cm-2 to 5.7 J cm-2. This decrease in Ev reflects a change in the ratio of laser excitation rate to vibrational deactivation rate for the CF2CFCl reactant. Under conditions where collisions are unimportant, the initial rotational energy in the CF2 was probed and found to be consistent with a thermal distribution characterized by a rotational temperature TR=1550150 K. The translational energy ET was the same for CF2 fragments formed with no vibrational energy and for those formed in the ?2=5 level with Ev=3320 cm-1, and ET was also the same for products formed with little rotational excitation (ER?40 cm-1) and for those born with substantially higher rotational energy (ER=240 cm-1). The kinetic energy of the products is less than that observed in the photodissociation of CF2HC1.

  16. 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

  17. Experimental and Theoretical Investigations of Energy Transfer and Hydrogen-Bond Breaking in Small Water and HCl Clusters

    E-print Network

    Reisler, Hanna

    Experimental and Theoretical Investigations of Energy Transfer and Hydrogen-Bond Breaking in Small Water and HCl Clusters Amit K. Samanta, Gabor Czako, Yimin Wang, John S. Mancini, Joel M. Bowman, Institute of Chemistry, Eotvos University, P.O. Box 32, H-1518 Budapest 112, Hungary CONSPECTUS: Water

  18. 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.

  19. Assessment of diffusion-bonded KTP crystals for efficient, low pulse energy conversion from 1 to 2 microm.

    PubMed

    Perrett, Brian J; Mason, Paul D; Orchard, David A

    2006-06-20

    Diffusion bonded (DB) walk-off compensated KTP crystals offer an alternative nonlinear medium for efficient 1 to 2 microm conversion within optical parametric oscillators (OPOs) at low pulse energies. Spatial variations in optical absorption and transmission values measured at 2 mum are reported for two DB-KTP crystals. Finally, a comparison is made between the conversion efficiency obtained from a degenerate 1 microm pumped OPO using a single 20 mm KTP crystal and an equivalent length DB-KTP crystal consisting of two bonded 10 mm crystals. PMID:16778951

  20. Dissociative Identity Disorder

    PubMed Central

    2009-01-01

    A brief description of the controversies surrounding the diagnosis of dissociative identity disorder is presented, followed by a discussion of the proposed similarities and differences between dissociative identity disorder and borderline personality disorder. The phenomenon of autohypnosis in the context of early childhood sexual trauma and disordered attachment is discussed, as is the meaning of alters or alternate personalities. The author describes recent neurosciences research that may relate the symptoms of dissociative identity disorder to demonstrable disordered attention and memory processes. A clinical description of a typical patient presentation is included, plus some recommendations for approaches to treatment. PMID:19724751

  1. Dissociative symptoms and epilepsy.

    PubMed

    Medford, Nick

    2014-01-01

    This article considers the relationship between various types of dissociative symptoms, including symptoms of depersonalization, derealization, and conversion disorders, and epilepsy. After introductory remarks concerning dissociation, this relationship is discussed through two main themes: firstly, the phenomenology and mechanisms of so-called 'dreamy states' in epilepsy and their closest analogs in psychiatric disorders, and secondly, the similarities and differences between epileptic seizures and psychogenic nonepileptic attacks. Although epileptic and dissociative symptoms may appear similar to observers, they arise through different mechanisms and have different experiential qualities. PMID:24196397

  2. 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 NgN bond, implying the covalent nature of the former bond and the ionic nature of the latter. PMID:25809612

  3. 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 [Key Laboratory of Low-Dimensional Materials and Application Technologies, Xiangtan University, Hunan 411105 (China); Wang, Yan, E-mail: ywang8@hnust.edu.cn, E-mail: ecqsun@ntu.edu.sg [Key Laboratory of Low-Dimensional Materials and Application Technologies, Xiangtan University, Hunan 411105 (China); School of Information and Electronic Engineering, Hunan University of Science and Technology, Hunan 411201 (China); Zhang, Xi [School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Li, Can [Center for Coordination Bond Engineering, School of Materials Science and Engineering, China Jiliang University, Hangzhou 330018 (China); Sun, Chang Q., E-mail: ywang8@hnust.edu.cn, E-mail: ecqsun@ntu.edu.sg [Key Laboratory of Low-Dimensional Materials and Application Technologies, Xiangtan University, Hunan 411105 (China); School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Center for Coordination Bond Engineering, School of Materials Science and Engineering, China Jiliang University, Hangzhou 330018 (China)

    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.

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

    E-print Network

    Simons, Jack

    odore 1 , Monika Sobczyk, Jack Simons * Chemistry Department and Henry Eyring Center for Theoretical Chemistry, University of Utah, Salt Lake City, UT 84112, USA Received 9 April 2006; accepted 8 May 2006 or to phosphate P@O p* orbitals to cleave sugarphosphate CO bonds or basesugar N1C bonds. We also studied

  5. Vibrationally mediated photodissociation of isocyanic acid (HNCO): Preferential N-H bond fission by excitation of the reaction coordinate

    NASA Astrophysics Data System (ADS)

    Brown, Steven S.; Metz, Ricardo B.; Berghout, H. Laine; Crim, F. Fleming

    1996-10-01

    We report the bond selected photodissociation of HNCO from a vibrationally excited state containing three quanta of N-H stretch (3?1) and demonstrate that initial vibrational state preparation strongly influences the photochemical branching in HNCO, producing either NCO (X 2?) from cleavage of the N-H bond or NH (a 1?) from cleavage of the C-N bond. Initial excitation of the N-H dissociation coordinate by excitation of the N-H stretching overtone enhances the probability for breaking the N-H bond in the electronically excited state. Compared to isoenergetic photolysis of the ground vibrational state, photodissociation of the 3?1 state alters the NCO quantum yield by roughly a factor of 4 at the largest photolysis energy used in this work, changing the channel that breaks the N-H bond from the minor to the major dissociation pathway. In addition, the experiment measures the quantum yields for production of NCO (?NCO) in the one-photon dissociation at three different photolysis wavelengths and provides a correction for the influence of photodissociation from vibrationally and rotationally excited states.

  6. 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 is well-known. In the present paper, we derive an experimental dissociation energy of nitrous acid based on the homolytic dissociation energy of nitrous acid, the electron affinity of OH, and the ionization energy of NO

  7. 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

  8. The interplay between interface structure, energy level alignment and chemical bonding strength at organic-metal interfaces.

    PubMed

    Willenbockel, M; Lftner, D; Stadtmller, B; Koller, G; Kumpf, C; Soubatch, S; Puschnig, P; Ramsey, M G; Tautz, F S

    2015-01-21

    What do energy level alignments at metal-organic interfaces reveal about the metal-molecule bonding strength? Is it permissible to take vertical adsorption heights as indicators of bonding strengths? In this paper we analyse 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) on the three canonical low index Ag surfaces to provide exemplary answers to these questions. Specifically, we employ angular resolved photoemission spectroscopy for a systematic study of the energy level alignments of the two uppermost frontier states in ordered monolayer phases of PTCDA. Data are analysed using the orbital tomography approach. This allows the unambiguous identification of the orbital character of these states, and also the discrimination between inequivalent species. Combining this experimental information with DFT calculations and the generic Newns-Anderson chemisorption model, we analyse the alignments of highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) with respect to the vacuum levels of bare and molecule-covered surfaces. This reveals clear differences between the two frontier states. In particular, on all surfaces the LUMO is subject to considerable bond stabilization through the interaction between the molecular ?-electron system and the metal, as a consequence of which it also becomes occupied. Moreover, we observe a larger bond stabilization for the more open surfaces. Most importantly, our analysis shows that both the orbital binding energies of the LUMO and the overall adsorption heights of the molecule are linked to the strength of the chemical interaction between the molecular ?-electron system and the metal, in the sense that stronger bonding leads to shorter adsorption heights and larger orbital binding energies. PMID:25475998

  9. Total energies and bonding for crystallographic structures in titanium-carbon and tungsten-carbon systems

    SciTech Connect

    Price, D.L.; Cooper, B.R.

    1989-03-15

    A full-potential linearized muffin-tin orbital calculation is presented of titanium-carbon systems in a variety of crystallographic forms. The calculated electronic structure, total energies, and equilibrium lattice constants are determined for the ground-state NaCl structure of TiC and for prototype superlattice structures, and these results are discussed in terms of the nature of bonding found in TiC. Similar calculations are also given for WC in two of these crystalline forms, and the differing ground-state structure and equilibrium lattice constants in these two carbide materials are related to the behavior of those metallic d states which are occupied in WC and unoccupied in TiC. The behavior of these one-electron states, which stabilize WC in a simple hexagonal form, is similar to the calculated behavior of associated states in the prototype superlattice Ti-C structures, and these states are found to play a similar role in determining the structural characteristics in these systems. Some of the properties and probable stability of the various crystalline forms are also discussed in terms of our results.

  10. 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.

  11. The sequential dissociation of protonated polyethylene glycols.

    PubMed

    Hester, Thomas H; McCraney, Kendra K; Castillo, Daniel E; Goebbert, Daniel J

    2013-04-01

    Early investigations of protonated polyethylene glycol fragmentation suggested the dissociation mechanism includes both direct and sequential processes. Experiments designed to study the proposed mechanisms of sequential dissociation are absent from the literature. In order to obtain additional experimental details about the fragmentation reactions, the dissociation of protonated polyethylene glycol was studied by energy-dependent collision-induced dissociation (CID). Key fragment ions were separated by mass differences corresponding to the loss of single monomer units. Several fragment ions were also generated by in-source fragmentation and studied by CID. These experiments indicate the primary ions undergo sequential dissociation by the loss of either one or two monomer units. The results suggest that at least two different mechanisms must be considered to explain the sequential dissociation of protonated polyethylene glycols. The reaction involving the elimination of two subunits suggests the loss of a six-membered 1,4-dioxane product, while the elimination of a single subunit involves the loss of acetaldehyde by a 1,2-hydride shift rearrangement. PMID:23584939

  12. Resonant Infrared Multiple Photon Dissociation Spectroscopy of Anionic Nucleotide Monophosphate Clusters.

    PubMed

    Ligare, Marshall R; Rijs, Anouk M; Berden, Giel; Kabel?, Martin; Nachtigallova, Dana; Oomens, Jos; de Vries, Mattanjah S

    2015-06-25

    We report mid-infrared spectra and potential energy surfaces of four anionic, 2'-deoxynucleotide-5'-monophosphates (dNMPs) and the ionic DNA pairs [dGMP-dCMP-H](1-), [dAMP-dTMP-H](1-) with a total charge of the complex equal to -1. We recorded IR action spectra by resonant IR multiple-photon dissociation (IRMPD) using the FELIX free electron laser. The potential energy surface study employed an on-the-fly molecular dynamics quenching method (MD/Q), using a semiempirical AM1 method, followed by an optimization of the most stable structures using density functional theory. By employing infrared multiple-photon dissociation (IRMPD) spectroscopy in combination with high-level computational methods, we aim at a better understanding of the hydrogen bonding competition between the phosphate moieties and the nucleobases. We find that, unlike in multimer double stranded DNA structures, the hydrogen bonds in these isolated nucleotide pairs are predominantly formed between the phosphate groups. This intermolecular interaction appears to exceed the stabilization energy resulting from base pairing and directs the overall cluster structure and alignment. PMID:26004928

  13. 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

  14. On the Use of a Driven Wedge Test to Acquire Dynamic Fracture Energies of Bonded Beam Specimens

    SciTech Connect

    Dillard, David A. [Virginia Polytechnic Institute and State University (Virginia Tech); Pohilt, David [Engineering Science and Mechanics Department, Virginia Tech, Blacksburg, VA, USA; Jacob, George Chennakattu [ORNL; Starbuck, Michael [Materials Science and Engineering Department, University of Tennessee, Knoxville, TN, USA; Rakesh, Kapania [Aerospace and Ocean Engineering Department, Virginia Tech, Blacksburg, VA, USA

    2011-01-01

    A driven wedge test is used to characterize the mode I fracture resistance of adhesively bonded composite beam specimens over a range of crosshead rates up to 1 m/s. The shorter moment arms (between wedge contact and crack tip) significantly reduce inertial effects and stored energy in the debonded adherends, when compared with conventional means of testing double cantilever beam (DCB) specimens. This permitted collecting an order of magnitude more crack initiation events per specimen than could be obtained with end-loaded DCB specimens bonded with an epoxy exhibiting significant stick-slip behavior. The localized contact of the wedge with the adherends limits the amount of both elastic and kinetic energy, significantly reduces crack advance during slip events, and facilitates higher resolution imaging of the fracture zone with high speed imaging. The method appears to work well under both quasi-static and high rate loading, consistently providing substantially more discrete fracture events for specimens exhibiting pronounced stick-slip failures. Deflections associated with beam transverse shear and root rotation for the shorter beams were not negligible, so simple beam theory was inadequate for obtaining qualitative fracture energies. Finite element analysis of the specimens, however, showed that fracture energies were in good agreement with values obtained from traditional DCB tests. The method holds promise for use in dynamic testing and for characterizing bonded or laminated materials exhibiting significant stick slip behavior, reducing the number of specimens required to characterize a sufficient number of fracture events.

  15. Reactions of fourth-period metal ions (Ca + - Zn + ) with O2: Metal-oxide ion bond energies

    NASA Astrophysics Data System (ADS)

    Fisher, Ellen R.; Elkind, J. L.; Clemmer, D. E.; Georgiadis, R.; Loh, S. K.; Aristov, N.; Sunderlin, L. S.; Armentrout, P. B.

    1990-08-01

    Reactions of Ca+, Zn+ and all first-row atomic transition metal ions with O2 are studied using guided ion beam techniques. While reactions of the ground states of Sc+, Ti+, and V+ are exothermic, the remaining metal ions react with O2 in endothermic processes. Analyses of these endothermic reactions provide new determinations of the M+-O bond energies for these eight elements. Source conditions are varied such that the contributions of excited states of the metal ions can be explicitly considered for Mn+, Co+, Ni+, and Cu+. Results (in eV) at 0 K are D0(Ca+-O)= 3.570.05, D0(Cr+-O)=3.720.12, D0(Mn+-O)=2.950.13, D0(Fe+-O)=3.530.06 (reported previously), D0(Co+-O)=3.320.06, D0(Ni+-O) =2.740.07, D0(Cu+-O)=1.620.15, and D0(Zn+-O)=1.650.12. These values along with literature data for neutral metal oxide bond energies and ionization energies are critically evaluated. Periodic trends in the ionic metal oxide bond energies are compared with those of the neutral metal oxides and those of other related molecules.

  16. Branching ratios for the dissociative recombination of hydrocarbon ions

    NASA Astrophysics Data System (ADS)

    Mitchell, J. B. A.; Angelova, G.; Rebrion-Rowe, C.; Novotny, O.; LeGarrec, J. L.; Bluhme, H.; Seiersen, K.; Svendsen, A.; Andersen, L. H.

    2005-01-01

    Branching ratios for the recombination of hydrocarbon ions have been measured using the ASTRID storage ring electron cooler. These studies have concentrated upon the competition of channels where the carbon skeleton of the molecule is left intact with other channels where carbon-carbon bonds are broken. A discussion of the effects of initial molecular structure on the resulting dissociation pattern is given.

  17. Hyposexuality and Hypersexuality Secondary to Childhood Trauma and Dissociation

    Microsoft Academic Search

    Mark F. Schwartz; Lori Galperin

    2002-01-01

    Childhood trauma can influence the bonding between the caretaker and the infant and thereby structure the stress response threshold. The capacity to utilize others as a form of self-soothing is determined by early attachments and also is critical to one's response to developmental stresses. The quality of early attachments strongly affects the capacity for adult intimacy. Early trauma and dissociative

  18. Somatoform dissociation in depersonalization disorder.

    PubMed

    Simeon, Daphne; Smith, Rebecca J; Knutelska, Margaret; Smith, Lisa M

    2008-01-01

    Along with psychoform dissociation, somatoform dissociation has been put forth as a core aspect of dissociative states, possibly as reliable as psychoform dissociation in the screening for dissociative disorders. The goal of this study was to investigate the prominence and correlates of somatoform dissociation in one of the major Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev.) dissociative disorders, depersonalization disorder (DPD). A total of 54 adults with DPD and 47 healthy control participants free of lifetime Axis I and II disorders were administered the 20-item Somatoform Dissociation Questionnaire (SDQ) as well as the Dissociative Experiences Scale, the Cambridge Depersonalization Scale, and the Childhood Trauma Questionnaire-Short Form. Somatoform dissociation scores were statistically significantly, but clinically only modestly, elevated in the DPD as compared to the healthy control group. SDQ items significantly elevated in the DPD group were mostly perceptual in nature. Depersonalization scores were significantly correlated with somatoform dissociation in the DPD group, whereas absorption and amnesia scores were not. With respect to childhood interpersonal trauma, although emotional abuse was significantly associated with depersonalization severity, none of the 5 categories of trauma were significantly associated with somatoform dissociation in the DPD group. In conclusion, somatoform dissociation is modest in DPD, and the SDQ is a weak instrument for the screening of dissociation in this disorder, detecting only one third of the sample when using the traditional SDQ cutoff score of 30. PMID:19042782

  19. 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...

  20. Formation and binding energies of vacancies in the Al(111) surface: Density functional theory calculations confirm simple bond model

    NASA Astrophysics Data System (ADS)

    Zhu, Yan; Zheng, Wengen; Pan, Yan; Pan, Yanfei; Liu, Tao; Zhou, Xvguang; Shi, Daning; Shi, Yangguang; Wei, Xinyuan

    2015-07-01

    In terms of the density functional calculations on an Al(111) surface, we obtained reasonable results for the convergence of the formation energy of mono-vacancies with depth or supercell size and binding energy for di-vacancies in the first layer with supercell size. The formation energy of a mono-vacancy increases with the increase in the number of layers and the supercell size, and converges to the third layer and to a 4 4 supercell respectively. The binding energy of a di-vacancy on the surface will decrease with the supercell size. However, the lowest formation energy of a mono-vacancy and highest binding energy is in a 3 3 supercell because of the dimer formed by its two nearest neighbour Al atoms between two adjacent vacancies. The results are compatible with simple bond model theory, and the binding energy in a 2 2 supercell is in accord with experimental results.

  1. Adherence-fracture energy of a glass-bonded thick-film conductor: effect of firing conditions

    Microsoft Academic Search

    P. F. Becher; W. L. Newell

    1977-01-01

    The effect of firing conditions on the adherence of a glass-bonded Pt-Au printed thick film conductor to a 96 wt % Al2O3 substrate was determined by a fracture mechanics measurement of the critical fracture energy for catastrophic thick film-substrate separation. The technique also demonstrated that separation by slow crack growth (delayed failure) occurred in this system. Analysis of the thick

  2. Chemical applications of density functional theory: F -3 anion dissociation (F -3 ? F 2 + F -)

    NASA Astrophysics Data System (ADS)

    Sosa, Carlos; Lee, Chengteh; Fitzgerald, George; Eades, Robert A.

    1993-08-01

    The molecular structure and binding energies have been computed for F 2 and F -3. Local spin density (LSD) calculations were performed with the LSD Dirac exchange functional and with the Vosko, Wilk and Nusair correlation energy functional (VWN). Non-local corrections were estimated with different exchange-correlation energy functionals. The equilibrium bond lengths are within 0.01 to 0.03 of wave function-based ab initio results. Dissociation energies appear to be overestimated within the local density approximation. Density functional methods predict the F -3 anion to be bound by about 50.0 5 kcal/mol. Vibrational frequencies were computed with VWN, LYP, B?P, B?LYP and PW energy functionals.

  3. Inferring modules of functionally interacting proteins using the Bond Energy Algorithm

    PubMed Central

    Watanabe, Ryosuke LA; Morett, Enrique; Vallejo, Edgar E

    2008-01-01

    Background Non-homology based methods such as phylogenetic profiles are effective for predicting functional relationships between proteins with no considerable sequence or structure similarity. Those methods rely heavily on traditional similarity metrics defined on pairs of phylogenetic patterns. Proteins do not exclusively interact in pairs as the final biological function of a protein in the cellular context is often hold by a group of proteins. In order to accurately infer modules of functionally interacting proteins, the consideration of not only direct but also indirect relationships is required. In this paper, we used the Bond Energy Algorithm (BEA) to predict functionally related groups of proteins. With BEA we create clusters of phylogenetic profiles based on the associations of the surrounding elements of the analyzed data using a metric that considers linked relationships among elements in the data set. Results Using phylogenetic profiles obtained from the Cluster of Orthologous Groups of Proteins (COG) database, we conducted a series of clustering experiments using BEA to predict (upper level) relationships between profiles. We evaluated our results by comparing with COG's functional categories, And even more, with the experimentally determined functional relationships between proteins provided by the DIP and ECOCYC databases. Our results demonstrate that BEA is capable of predicting meaningful modules of functionally related proteins. BEA outperforms traditionally used clustering methods, such as k-means and hierarchical clustering by predicting functional relationships between proteins with higher accuracy. Conclusion This study shows that the linked relationships of phylogenetic profiles obtained by BEA is useful for detecting functional associations between profiles and extending functional modules not found by traditional methods. BEA is capable of detecting relationship among phylogenetic patterns by linking them through a common element shared in a group. Additionally, we discuss how the proposed method may become more powerful if other criteria to classify different levels of protein functional interactions, as gene neighborhood or protein fusion information, is provided. PMID:18559112

  4. The relationship between bond ionicity, lattice energy, coefficient of thermal expansion and microwave dielectric properties of Nd(Nb1-xSbx)O4 ceramics.

    PubMed

    Zhang, Ping; Zhao, Yonggui; Wang, Xiuyu

    2015-06-28

    The crystalline structure refinement, chemical bond ionicity, lattice energy and coefficient of thermal expansion were carried out for Nd(Nb1-xSbx)O4 ceramics with a monoclinic fergusonite structure to investigate the correlations between the crystalline structure, phase stability, bond ionicity, lattice energy, coefficient of thermal expansion, and microwave dielectric properties. The bond ionicity, lattice energy, and coefficient of thermal expansion of Nd(Nb1-xSbx)O4 ceramics were calculated using a semiempirical method based on the complex bond theory. The phase structure stability varied with the lattice energy which was resulted by the substitution constant of Sb(5+). With the increasing of the Sb(5+) contents, the decrease of Nb/Sb-O bond ionicity was observed, which could be contributed to the electric polarization. The ?r had a close relationship with the Nb/Sb-O bond ionicity. The increase of the Qf and |?f| values could be attributed to the lattice energy and the coefficient of thermal expansion. The microwave dielectric properties of Nd(Nb1-xSbx)O4 ceramics with the monoclinic fergusonite structure were strongly dependent on the chemical bond ionicity, lattice energy and coefficient of thermal expansion. PMID:25997635

  5. Is the decrease of the total electron energy density a covalence indicator in hydrogen and halogen bonds?

    PubMed

    Angelina, Emilio L; Duarte, Daro J R; Peruchena, Nlida 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

  6. 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

  7. Electron attachment step in electron capture dissociation (ECD) and electron transfer dissociation (ETD).

    PubMed

    Anusiewicz, Iwona; Berdys-Kochanska, Joanna; Simons, Jack

    2005-07-01

    We have made use of classical dynamics trajectory simultions and ab 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)) to a model system that contained both an S-S bond that is cleaved and a -NH(3)(+) positively charged site. We used a Landau-Zener-Stueckelberg curve-crossing approximation to estimate the ETD rates for electron transfer from a CH(3)(-) anion to the -NH(3)(+) Rydberg orbital or the S-S sigma* orbital. We draw conclusions about ECD from our ETD results and from known experimental electron-attachment cross sections for cations and sigma-bonds. We predict the cross section for ETD at the positive site of our model compound to be an order of magnitude larger than that for transfer to the Coulomb-stabilized S-S bond site. We also predict that, in ECD, the cross section for electron capture at the positive site will be up to 3 orders of magnitude larger than that for capture at the S-S bond site. These results seem to suggest that attachment to such positive sites should dominate in producing S-S bond cleavage in our compound. However, we also note that cleavage induced by capture at the positive site will be diminished by an amount that is related to the distance from the positive site to the S-S bond. This dimunition can render cleavage through Coulomb-assisted S-S sigma* attachment competitive for our model compound. Implications for ECD and ETD of peptides and proteins in which SS or N-C(alpha) bonds are cleaved are also discussed, and we explain that such events are most likely susceptible to Coulomb-assisted attachment, because the S-S sigma* and C=O pi* orbitals are the lowest-lying antibonding orbitals in most peptides and proteins. PMID:16833914

  8. Bonding Model for Transition Metal and Rare Earth Monoxides and Laser Spectroscopy of Nickel-Oxide

    NASA Astrophysics Data System (ADS)

    Srdanov, Vojislav I.

    We discovered that, for the transition metal and the rare earth monoxide series, the sum of the ionization potential of the metal, the energy of the lowest ( ...np) configuration of the metal ion and the thermochemical dissociation energy of the molecule adds up to a constant number. The correlation is particularly striking for the rare earth monoxides where the standard deviation is less than 1%. Based on this correlation we developed a new bonding scheme common for both the transition metal and rare earth monoxides. We propose that the bonding is invariant within the series and consists of an ionic and a covalent contribution. In our model a covalent contribution to the bonding of the inner-core d and f orbitals is negligible. This is in contrast to the current paradigm regarding the significant role of the d orbitals in the bonding in the first and second row transition metal oxides. Our model also appears to be in conflict with the M^{2+} O^{2-} ligand-field bonding model currently accepted for the rare earth monoxides. Based on the empirical correlation and the proposed bonding mechanism, however, we give a number of predictions regarding yet unmeasured fundamental quantities of some of the oxides such as permanent dipole moments, dissociation energies and equilibrium bond distances. We also present the results of the first high resolution laser spectroscopic study of the NiO molecule. Several bands in the green spectral region were found to originate from the ground state of NiO; their analysis allowed us to determine the following fundamental parameters: Ground state symmetry: ^3Sigma^-; Vibrational frequency: omega_{ rm e} = 8.39.1 cm^{ -1}; Equilibrium distance: r_ {rm e} = 1.627 A. With this work the determination of the ground state parameters for the first row transition metal oxides is now complete.

  9. 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.

  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. 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

  12. 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

  13. The correlations among bond ionicity, lattice energy and microwave dielectric properties of (Nd1-xLax)NbO4 ceramics.

    PubMed

    Zhang, Ping; Zhao, Yonggui; Li, Lingxia

    2015-06-24

    (Nd1-xLax)NbO4 ceramics were prepared via a conventional solid-state reaction route and the correlations among bond ionicity, lattice energy, phase stability and microwave dielectric properties were investigated. The diffraction patterns showed that the (Nd1-xLax)NbO4 ceramics possessed a monoclinic fergusonite structure. The chemical bond ionicity, bond covalency and lattice energy were calculated using the empirical method. The phase structure stability varied with the lattice energy which resulted due to the substitution content of La(3+) ions. With the increase of La(3+) ion contents, the decrease of Nd/La-O bond ionicity was observed, which could be attributed to the electric polarization. ?r has a close relationship with the Nd/La-O bond covalency. The increase of the Q f values and ?f values could be attributed to the change in the lattice energy. The microwave dielectric properties of (Nd1-xLax)NbO4 ceramics with a monoclinic fergusonite structure were strongly dependent on the chemical bond ionicity, bond covalency and lattice energy. PMID:26063124

  14. Dissociation pressure measurements on salts proposed for thermochemical energy storage. [MgCl\\/HO; CaCl\\/NH

    Microsoft Academic Search

    Carling

    1979-01-01

    Sandia Laboratories, Livermore, has been conducting research pertaining to the development of chemical heat pumps. Promising current models of chemical heat pumps employ salt hydrates, ammoniates, or methanolates for energy storage. The efficient operation of a chemical heat pump depends strongly upon the reaction energies and pressure\\/temperature relationships of these salts. Unfortunately, most of the needed data are either old,

  15. 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 [Institut fuer Ionenphysik und Angewandte Physik, Leopold Franzens-Universitaet Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria); Illenberger, Eugen [Institut fuer Chemie und Biochemie-Physikalische und Theoretische Chemie, Freie Universitaet Berlin, Takustrasse 3, D-14195 Berlin (Germany)

    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)].

  16. Accurate calculations of bond-breaking energies in C 60 using the three-layered ONIOM method

    Microsoft Academic Search

    Robert D. J Froese; Keiji Morokuma

    1999-01-01

    The three-layered ONIOM method was used to calculate the adiabatic singlettriplet (S0?T1) and singletquintet (S0?Q) energy splittings in C60 fullerene. The ONIOM(G2MS:ROMP2\\/6-31G(d):ROHF\\/6-31G) calculation gives a value of 35.1 for the S0?T1 splitting, in good agreement with the experimental value of 36.1 kcal\\/mol. For accurate bond energies, for which typically a coupled-cluster level of theory is required, the ONIOM appears to

  17. 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)

  18. PBGA wire bonding development

    Microsoft Academic Search

    W. K. Shu

    1996-01-01

    In a PBGA package, the existence of a glass transition temperature of 170~215C for PCB substrate puts an upper ceiling to the usable wire bond temperature. The low thermal conductivity of PCB substrate and the need for a thicker material make fine pad pitch wire bonding even more difficult to do. To compensate for the limitation in thermal energy, high

  19. 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.

  20. Determination of a chemisorption bond strength by direct measurement of the threshold energy for collision-induced desorption: Ammonia on Pt{111}

    NASA Astrophysics Data System (ADS)

    Szulczewski, Gregory; Levis, Robert J.

    1994-12-01

    Direct measurement of the threshold desorption energy for collision-induced desorption is used to determine a chemisorption bond energy. In this experiment the absolute cross section for desorption is measured using x-ray photoelectron spectroscopy as a function of the impact energy between a translationally energetic Ar atom and an ammonia molecule chemisorbed to a Pt{111} single crystal. For this adsorbate-surface system the threshold desorption energy is found to be 1.80.17 eV and is independent of the angle of incidence of the Ar beam. Using a classical energy transfer mechanism this threshold energy is found to correspond to a bond energy of 1.40.13 eV. This represents an upper limit for the bond strength assuming maximum energy transfer between Ar and NH3 and no internal excitation of the adsorbate at the desorption threshold.

  1. A theoretical study of the ionic dissociation of HF, HCl, and H2S in water clusters

    NASA Astrophysics Data System (ADS)

    Lee, Chengteh; Sosa, Carlos; Planas, Marc; Novoa, Juan J.

    1996-05-01

    The ionic dissociation of HF, HCl, and H2S in water is examined using density functional theory (DFT), Hartree-Fock (HF), and Mller-Plesset theory to second order (MP2). The calculations show that HF, HCl, and H2S form fully dissociated stable clusters with four water molecules. Each cluster appears to be stabilized by the formation of six hydrogen bonds. These calculations also indicate that a minimum of four water molecules are required to form stable structures in which positive and negative ions coexist in the cluster. The hydrogen transfer between the acid and water molecules is very similar to the mechanism proposed for hydrogen transfer in water solutions. The binding energies of the hydrated hydrofluoric acid, hydrated hydrochloric acid, and hydrated hydrogen disulfide estimated with B-LYP are 37.51, 41.17, and 20.68 kcal/mol, respectively.

  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. 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

  4. Chemical Bonds

    NSDL National Science Digital Library

    The Concord Consortium

    2011-12-11

    Electrons are key to forming the two broad categories of chemical bonds: covalent and ionic. Atoms, which have a nucleus surrounded by electrons, are represented in several different ways. In the Chemical Bonds activity, students explore the different kinds of chemical bonds that can form, ranging from non-polar covalent to ionic. In the model depicted above students adjust the electronegativity of two atoms and see the effect it has on electron distribution and bond type.

  5. Reaction of SC+, Ti+, and V+ with CO. MC+ and MO+ bond energies D. E. Clemmer, J. L. Elkind,") N. Aristov,b) and P. B. Armentrout")

    E-print Network

    Clemmer, David E.

    Reaction of SC+, Ti+, and V+ with CO. MC+ and MO+ bond energies D. E. Clemmer, J. L. Elkind,") N (Received 16April 1991;accepted28 May 1991) The reactionsof SC+ , Ti + , and V + with CO are studiedasa.Thresholdsof the reaction crosssectionsare interpreted to give the 0 K bond energies(in eV) DO(ScC+ ) = 3.34f 0.06,D'(Ti

  6. Natural bond orbital-based energy density analysis for correlated methods: Second-order Mller-Plesset perturbation and coupled-cluster singles and doubles

    Microsoft Academic Search

    Yutaka Imamura; Takeshi Baba; Hiromi Nakai

    2008-01-01

    Natural bond orbital-based energy density analysis (NBO-EDA), which split energies into atomic and bonding contributions, is proposed for correlated methods such as coupled-cluster singles and doubles (CCSD) and second-order Mller-Plesset (MP2) perturbation. Applying NBO-EDA for CCSD and MP2 to ethylene and the Diels-Alder reaction, we are successful in obtaining useful knowledge regarding electron correlation of pi- and sigma-type orbitals, and

  7. J/psi dissociation and Adler's theorem

    E-print Network

    A. Bourque; C. Gale; K. L. Haglin

    2005-09-05

    Effective Lagrangian models of charmonium have recently been used to estimate dissociation cross sections with light hadrons. Detailed study of the symmetry properties reveals possible shortcomings relative to chiral symmetry. We therefore propose a new Lagrangian and point out distinguishing features amongst the different approaches. Using the newly proposed Lagrangian, which exhibits SU_L(4) X SU_R(4) symmetry and complies with Adler's theorem, we find dissociation cross sections with pions that are reduced in an energy dependent way, with respect to cases where the theorem is not fulfilled.

  8. Spontaneous Exciton Dissociation in Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Kumamoto, Y.; Yoshida, M.; Ishii, A.; Yokoyama, A.; Shimada, T.; Kato, Y. K.

    2014-03-01

    Simultaneous photoluminescence and photocurrent measurements on individual single-walled carbon nanotubes reveal spontaneous dissociation of excitons into free electron-hole pairs. The correlation of luminescence intensity and photocurrent shows that a significant fraction of excitons are dissociating before recombination. Furthermore, the combination of optical and electrical signals also allows for extraction of the absorption cross section and the oscillator strength. Our observations explain the reasons why photoconductivity measurements in single-walled carbon nanotubes are straightforward despite the large exciton binding energies.

  9. Spontaneous exciton dissociation in carbon nanotubes.

    PubMed

    Kumamoto, Y; Yoshida, M; Ishii, A; Yokoyama, A; Shimada, T; Kato, Y K

    2014-03-21

    Simultaneous photoluminescence and photocurrent measurements on individual single-walled carbon nanotubes reveal spontaneous dissociation of excitons into free electron-hole pairs. The correlation of luminescence intensity and photocurrent shows that a significant fraction of excitons are dissociating before recombination. Furthermore, the combination of optical and electrical signals also allows for extraction of the absorption cross section and the oscillator strength. Our observations explain the reasons why photoconductivity measurements in single-walled carbon nanotubes are straightforward despite the large exciton binding energies. PMID:24702413

  10. Probe stiffness regulates receptor-ligand bond lifetime under force

    NASA Astrophysics Data System (ADS)

    Zhang, Yan; L, ShouQin; Long, Mian

    2011-05-01

    Receptor-ligand bond dissociation under applied force is crucial to elucidate its biological functionality when the molecular bond is usually connected to a mechanical probe. While the impact of probe stiffness, k, on bond rupture force has recently attracted more and more attention, the mechanism of how it affects the bond lifetime, however, remains unclear. Here we quantified the dissociation lifetime of selectin-ligand bond using an optical trap assay with low stiffness ranging from 3.510-3 to 4.710-2 pN/nm. Our results indicated that bond lifetime yielded distinct distributions with different probe stiffness, implying the stochastic feature of bond dissociation. It was also found that the mean lifetime varied with probe stiffness and that the catch bond nature was visualized at k?3.010-2 pN/nm. This work furthered the understanding of the forced dissociation of selectin-ligand bond at varied probe stiffness, which is physiologically relevant to the tethered rolling of leukocytes under blood flow.

  11. Differentiation of complex lipid isomers by radical-directed dissociation mass spectrometry.

    PubMed

    Pham, Huong T; Ly, Tony; Trevitt, Adam J; Mitchell, Todd W; Blanksby, Stephen J

    2012-09-01

    Contemporary lipidomics protocols are dependent on conventional tandem mass spectrometry for lipid identification. This approach is extremely powerful for determining lipid class and identifying the number of carbons and the degree of unsaturation of any acyl-chain substituents. Such analyses are however, blind to isomeric variants arising from different carbon-carbon bonding motifs within these chains including double bond position, chain branching, and cyclic structures. This limitation arises from the fact that conventional, low energy collision-induced dissociation of even-electron lipid ions does not give rise to product ions from intrachain fragmentation of the fatty acyl moieties. To overcome this limitation, we have applied radical-directed dissociation (RDD) to the study of lipids for the first time. In this approach, bifunctional molecules that contain a photocaged radical initiator and a lipid-adducting group, such as 4-iodoaniline and 4-iodobenzoic acid, are used to form noncovalent complexes (i.e., adduct ions) with a lipid during electrospray ionization. Laser irradiation of these complexes at UV wavelengths (266 nm) cleaves the carbon-iodine bond to liberate a highly reactive phenyl radical. Subsequent activation of the nascent radical ions results in RDD with significant intrachain fragmentation of acyl moieties. This approach provides diagnostic fragments that are associated with the double bond position and the positions of chain-branching in glycerophospholipids, sphingomyelins and triacylglycerols and thus can be used to differentiate isomeric lipids differing only in such motifs. RDD is demonstrated for well-defined lipid standards and also reveals lipid structural diversity in olive oil and human very-low density lipoprotein. PMID:22881372

  12. Plasma assisted dissociation of hydrogen sulfide

    Microsoft Academic Search

    K. Gutsol; T. Nunnally; A. Rabinovich; A. Fridman; A. Starikovskiy; A. Gutsol; A. Kemoun

    Dissociation of hydrogen sulfide has been studied in four different discharges: AC corona, dielectric barrier, streamer, and contracted glow discharge. All experiments were done in a single geometry, close to a plug flow reactor, with the goal of fair comparison. The performance of corona discharge and DBD was studied in the initial gas temperature range of 3001200K. A specific energy

  13. Dissociative recombination of small carbon cluster cations

    NASA Astrophysics Data System (ADS)

    Heber, O.; Seiersen, K.; Bluhme, H.; Svendsen, A.; Andersen, L. H.; Maunoury, L.

    2006-02-01

    The dissociative recombination of small cluster cations with free, zero-energy electrons was studied at the ASTRID storage ring. It was found that only two-body fragmentation channels contribute: C+C2 for C3+ , C2+C2 and C+C3 for C4+ . For C5+ and C6+ the final channels were also characterized by two-body fragmentation, but the specific channels were not identified because of limited mass resolution. It is being speculated whether cluster ions larger than C6+ may undergo recombination without dissociation. These clusters have a large heat capacity and a correspondingly lower temperature after electron capture. The decay of the intermediate neutral clusters may be influenced by infrared emission, which provides cooling and prevents dissociation.

  14. Dissociative recombination of small carbon cluster cations

    SciTech Connect

    Heber, O.; Seiersen, K.; Bluhme, H.; Svendsen, A.; Andersen, L. H.; Maunoury, L. [Department of Particle Physics, Weizmann Institute of Science, 76100, Rehovot (Israel); Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark); CIRIL, Avenue Henri Becquerel, Boite Postale 5133, 14070 Caen cedex 5 (France)

    2006-02-15

    The dissociative recombination of small cluster cations with free, zero-energy electrons was studied at the ASTRID storage ring. It was found that only two-body fragmentation channels contribute: C+C{sub 2} for C{sub 3}{sup +}, C{sub 2}+C{sub 2} and C+C{sub 3} for C{sub 4}{sup +}. For C{sub 5}{sup +} and C{sub 6}{sup +} the final channels were also characterized by two-body fragmentation, but the specific channels were not identified because of limited mass resolution. It is being speculated whether cluster ions larger than C{sub 6}{sup +} may undergo recombination without dissociation. These clusters have a large heat capacity and a correspondingly lower temperature after electron capture. The decay of the intermediate neutral clusters may be influenced by infrared emission, which provides cooling and prevents dissociation.

  15. Calculations of the relative free energies of aqueous solvation of several fluorocarbons: A test of the bond potential of mean force correction

    NASA Astrophysics Data System (ADS)

    Gough, Craig A.; Pearlman, David A.; Kollman, Peter

    1993-12-01

    The relative free energies of aqueous solvation of several fluorinated derivatives of methane were calculated using the free energy perturbation (FEP) method. The calculations in general duplicated the experimental free energies with relatively good accuracy, but the calculation of the bond potential of mean force (bond-PMF) contribution [D. A. Pearlman and P. A. Kollman, J. Chem. Phys. 94, 4532 (1991)] was necessary in order to get the most satisfactory agreement with experiment. In particular, it was necessary to use this contribution to obtain even qualitatively correct results for the relative free energies of hydration of methane and tetrafluoromethane. The reasons for this are discussed in terms of the accurate calculation of the effect of the size of the solute. In addition, it is noted that the bond-PMF contribution is important even for FEP calculations not involving large changes in size, such as the ethanol to ethane perturbation, if the length of a bond to a disappearing atom is changed during the perturbation. The relative free energy of aqueous solvation for ethanol and ethane was calculated to demonstrate that if the bond between the oxygen and the hydroxyl hydrogen being removed is ``shrunken'' during the perturbation without including the bond-PMF correction, the calculated free energy is too low by 3 kcal/mol.

  16. 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.

  17. 898 Ind. Eng. Chem. Res., Vol. 27, No. 5, 1988 the compounds having a wide range dissociation energies.

    E-print Network

    Skogestad, Sigurd

    energies. However, our data of phenolic resin decompositionindicate that there is good qualitative for coal liquefaction was evaluated using phenolic resin as an Australian brown coal model. The choice of a phenolic resin as a model for the lique- faction of Yallourn coal at 440 "C under nitrogen allowed

  18. 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., E-mail: ihsanas@yahoo.com [Department of Physics, Jerash University, Jerash-26150 (Jordan); Hamad, B. A. [Department of Physics, The University of Jordan, Amman-11942 (Jordan)] [Department of Physics, The University of Jordan, Amman-11942 (Jordan)

    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 IrC and IrIr 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.

  19. 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.

  20. Dissociative Recombination and Excitation of CH 5 +: Absolute Cross Sections and Branching Fractions

    Microsoft Academic Search

    J. Semaniak; A. Larson; A. Le Padellec; C. Stroemholm; M. Larsson; S. Rosen; R. Peverall; H. Danared; N. Djuric; G. H. Dunn; S. Datz

    1998-01-01

    The heavy-ion storage ring CRYRING was used to measure the absolute dissociative recombination and dissociative excitation cross sections for collision energies below 50 eV. Deduced thermal rates coefficients are consistent with previous beams data but are lower by a factor of 3 than the rates measured by means of the flowing afterglow Langmuir probe technique. A resonant structure in dissociative

  1. Dissociative Recombination and Excitation of CH{sup +} : Absolute Cross Sections and Branching Fractions

    Microsoft Academic Search

    J. Semaniak; A. Larson; A. Le Padellec; C. Stroemholm; M. Larsson; S. Rosen; R. Peverall; H. Danared; N. Djuric; G. H. Dunn; S. Datz

    1998-01-01

    The heavy-ion storage ring CRYRING was used to measure the absolute dissociative recombination and dissociative excitation cross sections for collision energies below 50 eV. Deduced thermal rates coefficients are consistent with previous beams data but are lower by a factor of 3 than the rates measured by means of the flowing afterglow Langmuir probe technique. A resonant structure in dissociative

  2. A Fracture Resisting Molecular Interaction in Trabecular Bone: Sacrificial Bonds and Hidden Length Dissipate Energy as Mineralized Fibrils Separate

    NASA Astrophysics Data System (ADS)

    Fantner, Georg E.

    2005-03-01

    A molecular energy dissipation mechanism in the form of sacrificial bonds and hidden length was previously found in bone constituent molecules of which the efficiency increased with the presence of Ca^2+ ions in the experimental solution. Here we present evidence for how this sacrificial bond-hidden length mechanism contributes to the mechanical properties of the bone composite. From investigations into the nanoscale arrangement of the bone constituents in combination with pico-Newton adhesion force measurements between mineralized collagen fibrils, based on single molecule force spectroscopy, we find evidence that bone consists of mineralized collagen fibrils and a non fibrillar organic matrix which acts as a ``glue'' that holds the mineralized fibrils together. We propose that this ``glue'' resists the separation of mineralized collagen fibrils. Like in the case of the sacrificial bonds in single molecules, the effectiveness of this ``glue'' increases with the presence of Ca^2+ ions. We further investigate how this molecular scale strengthening mechanism increases the fracture toughness of the macroscopic material.

  3. Structural studies on protein O-fucosylation by electron capture dissociation

    NASA Astrophysics Data System (ADS)

    Mormann, Michael; Macek, Boris; de Peredo, Anne Gonzalez; Hofsteenge, Jan; Peter-Katalinic, Jasna

    2004-05-01

    The low energy dissociation technique electron capture dissociation has been applied to a series of thrombospondin and properdin derived O-fucosylated glycopeptides. Followed by capture of an electron by multiply protonated precursor ions [M+nH]n+ reduced odd electron radical cations [M+nH](n-1)[radical sign]+ were generated. The latter mainly fragment by cleavage of the N---C[alpha] bonds of the peptide chain without loss of the labile sugar moiety allowing an unambiguous assignment of the glycosylation site. Apart from peptide backbone cleavages, side chain losses of aminocarbonylmethyl and aminocarbonylmethylthiyl radicals from carboxyamidomethylated cysteins are observed. The N---C[alpha] bond cleavage is greatly reduced on both sides of alkylated Cys. However, fragment ions that are formed by secondary fragmentations of z-type radical cations containing N-terminal cystein give rise to even electron z---[radical sign]SCH2CONH2 ions. The potential of the high mass accuracy for the identification of the protein modification topology has been fully explored.

  4. Study of the kinetics of the gas-phase, iodine catalyzed elimination of HBr from isobutylbromide: the tertiary C-H bond dissociation energy in isobutylbromide.

    E-print Network

    Jirustithipong, Pongsiri

    1975-01-01

    ( I) and thence to vacuum pump (N2). After purification (see section B, P. 15) 1-bromo- 2-methyl-propane (isobutylbromide) was stored in sample bulb, (M&). The temperature of the reaction vessel was measured at a point approximately 1 cm. from... to 92%%d pure. It was purified by the following procedure. A sample ( Z-3 c . c . ) was washed repeatedly with distilled water ( this removed t-butyl bromide by preferential hydrolysis and isobutylene by hydration), then degassed on the vacuum line...

  5. Bond-alternating Hckel-Mbius and related, twisted linear, cyclic and helical systemstheir molecular orbitals, energies and phase correlation upon dissociation

    Microsoft Academic Search

    Ying-Nan Chiu

    1983-01-01

    Cyclic group formalism and screw symmetry operation are used to clarify and generalize the definition of Hckel and Mbius systems. It is shown that the Mbius ring system has half-integral pseudo-angular momentum similar to that of spin space, and that applications of Mbius electronics to chemical reactions have been based on truncated single-circle Mbius rings which have unique beginning and

  6. Decisive role of the energetics of dissociation products in the adsorption of water on O/Ru(0001)

    SciTech Connect

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

    2008-10-15

    Using density-functional theory they found that, depending on coverage, coadsorbed oxygen can act both as a promoter and as an inhibitor of the dissociation of water on Ru(0001), the transition between these two behaviors occurring at (0.2 M). The key factor that determines this transition is the adsorption energy of the reaction products, OH in particular. The chemistry of this coadsorbed system is dictated by the effective coordination of the Ru atoms that participate in the bonding of the different species. In particular, they observed that a low coverage of oxygen increases the adsorption energy of the OH fraction on the Ru surface. This surprising extra stabilization of the OH with the coadsorption of oxygen can be understood in the context of the metallic bonding and could well correspond to a general trend for the coadsorption of electronegative species on metallic surfaces.

  7. Bridging the momentum distribution and the potential energy surface of protons in hydrogen bonds

    Microsoft Academic Search

    Joseph Morrone; Lin Lin; Roberto Car; Michele Parrinello

    2010-01-01

    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

  8. Force-Induced LysozymeHyHEL5 Antibody Dissociation and Its Analysis by Means of a Cooperative Binding Model

    PubMed Central

    Katletz, Stefan; Stroh, Cordula; Rankl, Christian; Titulaer, Urbaan M.; Hinterdorfer, Peter

    2010-01-01

    Abstract Dynamic force spectroscopy probes the kinetic properties of molecules interacting with each other such as antibody-antigen, receptor-ligand, etc. In this article, a statistical model for the dissociation of such cooperative systems is presented. The partner molecules are assumed to be linked by a number of relatively weak bonds that can be grouped together into cooperative units. Single bonds are assumed to open and close statistically. Our model was used to analyze molecular recognition experiments of single receptor-ligand pairs in which the two molecules are brought into contact using an atomic force microscope, which leads to the formation of a strong and specific bond. Then a prescribed time-dependent force is applied to the complex and the statistical distribution of forces needed to pull the molecules completely apart is measured. This quantity is also calculated from our model. Furthermore, its dependence on the model parameters, such as binding free energy, number of bonds and groups, number of cooperative elementary bonds and degree of cooperativity within a group, influence of the force on the binding free energy, and the rate of change of the pulling force, is determined. PMID:20655861

  9. Efficient C-H Bond Activations via O2 Cleavage by a Dianionic Cobalt(II) Complex.

    PubMed

    Nguyen, Andy I; Hadt, Ryan G; Solomon, Edward I; Tilley, T Don

    2014-07-01

    A dianionic, square planar cobalt(II) complex reacts with O2 in the presence of acetonitrile to give a cyanomethylcobalt(III) complex formed by C-H bond cleavage. Interestingly, PhIO and p-tolylazide react similarly to give the same cyanomethylcobalt(III) complex. Competition studies with various hydrocarbon substrates indicate that the rate of C-H bond cleavage greatly depends on the p Ka of the C-H bond, rather than on the C-H bond dissociation energy. Kinetic isotope experiments reveal a moderate KIE value of ca. 3.5 using either O2 or PhIO. The possible involvement of a cobalt(IV) oxo species in this chemistry is discussed. PMID:25071930

  10. [A dissociative patient].

    PubMed

    de Jongh, A; Abkhezr, S; Broers, D L M

    2009-08-01

    A 45-year-old woman attended a centre for special dental care. Initially, it seemed that the patient suffered from an extreme form of dental anxiety. However, the fact that she displayed 'dissociations' suggested that she had a severe psychiatric disorder, in this case Dissociative Identity Disorder. The key feature of this condition is a dysfunction of the normal integrative functions of identity, memory and consciousness. In such instances it is recommended to contact a psychologist or psychiatrist and the referring care provider to consider the consequences of the psychiatric condition regarding informed consent, treatment plan and actual treatment. Because it was not likely that the patient would respond to an intervention specifically aimed to reduce anxiety in the dental setting, dental treatment under general anesthesia was the best suited option. PMID:19739405

  11. Quantification of the bond-angle dispersion by Raman spectroscopy and the strain energy of amorphous silicon

    NASA Astrophysics Data System (ADS)

    Roura, P.; Farjas, J.; Roca i Cabarrocas, P.

    2008-10-01

    A thorough critical analysis of the theoretical relationships between the bond-angle dispersion in a-Si,??, and the width of the transverse optical Raman peak, ?, is presented. It is shown that the discrepancies between them are drastically reduced when unified definitions for ?? and ? are used. This reduced dispersion in the predicted values of ?? together with the broad agreement with the scarce direct determinations of ?? is then used to analyze the strain energy in partially relaxed pure a-Si. It is concluded that defect annihilation does not contribute appreciably to the reduction of the a-Si energy during structural relaxation. In contrast, it can account for half of the crystallization energy, which can be as low as 7 kJ/mol in defect-free a-Si.

  12. 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

  13. Ultrafast C(Spiro)-O dissociation via a conical intersection drives spiropyran to merocyanine photoswitching.

    PubMed

    Prager, Stefan; Burghardt, Irene; Dreuw, Andreas

    2014-02-27

    The mechanism of the photochemical conversion of spiropyran to merocyanine is investigated theoretically. Calculations were performed at TD-DFT/?B97XD/cc-pVDZ level of theory, which shows good agreement with the reference RI-CC2 method. A two-dimensional scan of the potential energy surface has been performed along the C-O distance and the central torsion angle in the ground state and in the first excited state, where the reaction takes place. Starting at the Franck-Condon geometry, the energy of the first excited state decreases in the direction of the C-O dissociation while the ground-state energy increases. This leads to a barrierless C-O bond dissociation in the first excited state. While relaxing on the S1 PES toward longer C-O distances, the torsion angle hardly changes, but other coordinates start to vary, leading to a conical intersection of the ground state and the first excited state at a C-O distance of about 3.4 . Passing the conical intersection, the reaction continues on the ground-state PES. At these large C-O distances, either barrierless Cspiro-O rebinding occurs that quenches spiropyran isomerization or rotation around the central torsion angle occurs that leads to merocyanine. For the latter an energy barrier of 0.1 eV must be overcome explaining the low quantum yield of spiropyran to merocyanine photoswitching. PMID:24467195

  14. Evaluation of the Influence of Amino Acid Composition on the Propensity for Collision-Induced Dissociation of Model Peptides Using Molecular Dynamics Simulations

    SciTech Connect

    Cannon, William R.; Taasevigen, Danny J.; Baxter, Douglas J.; Laskin, Julia

    2007-09-01

    The dynamical behavior of model peptides was evaluated with respect to their ability to form internal proton donor-acceptor pairs using molecular dynamics simulations. The proton donor-acceptor pairs are postulated to be prerequisites for peptide bond cleavage resulting in formation of b and y ions during low energy collision-induced dissociation in tandem mass spectrometry (MS/MS). The simulations for the polyalanine pentamer Ala5H+ were compared to experimental data from collision energy-resolved surface induced dissociation (SID) studies. The results of the simulation are insightful into the events that likely lead up to the fragmentation of peptides. 9-mer polyalanine-based model peptides were used to examine the dynamical effect of each of the 20 common amino acids on the probability to form donor-acceptor pairs at labile peptide bonds. A continuous range of probabilities was observed as a function of the substituted amino acid. However, the location of the peptide bond involved in the donor-acceptor pair plays a critical role in the dynamical behavior. This influence of position on the probability of forming a donor-acceptor pair would be hard to predict from statistical analyses on experimental spectra of aggregate, diverse peptides. In addition, the inclusion of basic side chains in the model peptides alters the probability of forming donor-acceptor pairs across the entire backbone. In this case there are still more ionizing protons than basic residues, but the side chains of the basic amino acids form stable hydrogen bond networks with the peptide carbonyl oxygens and thus act to prevent free access of mobile protons to labile peptide bonds. It is clear from the work that the identification of peptides from low-energy CID using automated computational methods should consider the location of the fragmenting bond as well as the amino acid composition.

  15. 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.

  16. Hydrogen-bonded OH and OD overtone bands and potential energy curve of methanol

    Microsoft Academic Search

    Hiroshi Morita; Saburo Nagakura

    1974-01-01

    The absorption spectra of CH3OH, CH3OD, CD3OH, and CD3OD as pure liquids and as carbon tetrachloride solutions were measured in the 3,850 - 16,600cm-1 region. In addition to the various combination bands, the higher overtone bands of the hydrogen-bonded O-H stretching vibration of self-associated methanols were observed at ~6470, 9300-9700, and 12,200 - 12,700 cm-1 with broad half-widths of ~700,

  17. Determination of S-H Bond Strengths in Dimolybdenum Tetrasulfide Complexes

    SciTech Connect

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

    2009-02-09

    Homolytic solution bond dissociation free energies (sBDFEs) for S-H bonds have been determined for soluble dimolybdenum tetrasulfide complexes through thermochemical cycles using electrochemical potentials and pKa values, all measured in acetonitrile. For [Cp*Mo(? S)(? SMe)2(? SH)MoCp*]+ (S4Me2H+), [Cp*Mo(? S)(? SMe)(? SH)2MoCp*]+ (S4MeH2+), and [Cp*Mo(? S)(? SH)3MoCp*]+ (S4H3+), the pKa values were determined to be 5.6 ? 0.4, 5.3 ? 0.3, and 4.9 ? 0.3, respectively. The E1/2 values for S4Me2+/o, S4MeH+/o, and S4H2+/o were measured to be -0.02 ? 0.02, +0.04 ? 0.05, and +0.07 ? 0.07 V vs FeCp2+/o, respectively. Using these experimental values, the homolytic S-H sBDFE for each S4RRH+ to S4RR+ reaction was determined to be 60.8 ? 1.0, 61.8 ? 1.6, and 61.9 ? 2.0 kcal/mol for S4Me2H+, S4MeH2+, and S4H3+ respectively. These sBDFE values can be used to estimate gas phase bond dissociation enthalpies of 65.6, 66.6, and 66.7 kcal/mol, respectively. The gas phase bond dissociation enthalpy for the analogous complex, Cp2Mo2S4Me2H+ was determined to be 64.9 kcal/mol by electronic structure calculations. Solid state structures are presented for S4MeH and S4H2. The Pacific Northwest National Laboratory is operated y Battelle for the U.S. Department of Energy.

  18. The chemical bonds in MeSb2O4 (Me = Mn, Ni, Fe, Zn) isomorphous compounds: Thermal expansion, force constants, energies

    Microsoft Academic Search

    J. R. Gavarri; R. Chater; J. Zilkowski

    1988-01-01

    The various chemical bonds (Me-O, Sb-O) in the MeSb2O4 isomorphous compounds (Me = Mn, Ni, Fe, Zn) are characterized by four quantities: the interatomic distance (rij), the force constant (fij), the thermal expansion (alphaij = 1\\/r dr\\/dT), the bond energy. Using structural evolution data (neutron diffraction) and Raman infrared spectroscopic studies at low temperature (5-300 K), it has been possible

  19. 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.

  20. A footprint study of bond initiation in gold wire crescent bonding

    Microsoft Academic Search

    Y. n. Zhou; X. Li; N. J. Noolu

    2005-01-01

    The morphological features of the crescent bond footprints on the substrate after peeling the wire off were studied to gain an understanding of the effect of process parameters on the crescent bond formation. In the absence of any ultrasonic energy, metallurgical bonding initiated at the peripheral regions of the crescent bond. The bond strength improved at higher substrate temperatures and

  1. The dissociation of transplantable tumors.

    PubMed

    Noel, J S; Zucker, R M; Wu, N C; Demaray, S Y

    1977-07-01

    Four animal transplantable solid tumors, composed of varying morphologic architecture and intercellular specializations, were studied by light and electron microscopy. These tumors were dissociated into viable single cell populations using a combination of mechanical and enzymatic methods. The conditions necessary for optimal dissociation consisted of (a) preparation of the tumor to maximize the tissue surface area, (b) enzymatic digestion with continuous agitation and (c) additional agitation to release loosely attached cells. Other factors that influenced the dissociation were optimized and discussed. PMID:197162

  2. Crystallographic studies evidencing the high energy tolerance to disrupting the interface disulfide bond of thioredoxin 1 from white leg shrimp Litopenaeus vannamei.

    PubMed

    Campos-Acevedo, Adam A; Rudio-Piera, Enrique

    2014-01-01

    Thioredoxin (Trx) is a small 12-kDa redox protein that catalyzes the reduction of disulfide bonds in proteins from different biological systems. A recent study of the crystal structure of white leg shrimp thioredoxin 1 from Litopenaeus vannamei (LvTrx) revealed a dimeric form of the protein mediated by a covalent link through a disulfide bond between Cys73 from each monomer. In the present study, X-ray-induced damage in the catalytic and the interface disulfide bond of LvTrx was studied at atomic resolution at different transmission energies of 8% and 27%, 12.8 keV at 100 K in the beamline I-24 at Diamond Light Source. We found that at an absorbed dose of 32 MGy, the X-ray induces the cleavage of the disulfide bond of each catalytic site; however, the interface disulfide bond was cleaved at an X-ray adsorbed dose of 85 MGy; despite being the most solvent-exposed disulfide bond in LvTrx (~50 2). This result clearly established that the interface disulfide bond is very stable and, therefore, less susceptible to being reduced by X-rays. In fact, these studies open the possibility of the existence in solution of a dimeric LvTrx. PMID:25517346

  3. [Dissociative disorders and affective disorders].

    PubMed

    Montant, J; Adida, M; Belzeaux, R; Cermolacce, M; Pringuey, D; Da Fonseca, D; Azorin, J-M

    2014-12-01

    The phenomenology of dissociative disorders may be complex and sometimes confusing. We describe here two cases who were initially misdiagnosed. The first case concerned a 61 year-old woman, who was initially diagnosed as an isolated dissociative fugue and was actually suffering from severe major depressive episode. The second case concerned a 55 year-old man, who was suffering from type I bipolar disorder and polyvascular disease, and was initially diagnosed as dissociative fugue in a mooddestabilization context, while it was finally a stroke. Yet dissociative disorders as affective disorder comorbidity are relatively unknown. We made a review on this topic. Dissociative disorders are often studied through psycho-trauma issues. Litterature is rare on affective illness comorbid with dissociative disorders, but highlight the link between bipolar and dissociative disorders. The later comorbidity often refers to an early onset subtype with also comorbid panic and depersonalization-derealization disorder. Besides, unipolar patients suffering from dissociative symptoms have more often cyclothymic affective temperament. Despite the limits of such studies dissociative symptoms-BD association seems to correspond to a clinical reality and further works on this topic may be warranted. PMID:25550242

  4. Computational study of substituent effects on the interaction energies of hydrogen-bonded Watson-Crick cytosine: guanine base pairs.

    PubMed

    Xue, Chunxia; Popelier, Paul L A

    2008-04-24

    The substituent effects on interaction energies of hydrogen-bonded DNA Watson-Crick base pairs in the gas phase were captured in a model using ab initio descriptors (at the B3LYP/6-311+G(2d,p) level). While forming a noncovalently bonded complex with unsubstituted guanine (G), cytosine (C) carried 42 possible substituents both at the C6 position (C6X:G) and at the C5 position (C5X:G). We rationalize why complexes possessing a more strongly electron-withdrawing group in CX form less stable base pairs. Multivariate linear regression constructed the quantitative relationships between the interaction energies of the complexes and the descriptors, which were drawn from quantum chemical topology (QCT). For the C6X dataset, the best model yielded r2 = 0.93 and a root-mean-square (rms) energy of 0.53 kJ/mol for the 28 complexes in the training set. This model was evaluated by an external test set (14 complexes), yielding an r2 value of 0.96 and an rms error of 0.42 kJ/mol. For the C5X dataset, the QCT descriptors generated a linear model, with r2 values of 0.92 and 0.97 and rms values of 1.69 and 1.24 kJ/mol for the training set (31 compounds) and the external test set (11 compounds), respectively. The models built here could therefore be useful for the assessment of the interaction energy of C6X:G and C5X:G purely from monomeric data. PMID:18373374

  5. Dissociation dynamics in the dissociative electron attachment to carbon dioxide

    NASA Astrophysics Data System (ADS)

    Nag, Pamir; Nandi, Dhananjay

    2015-05-01

    Dissociative electron attachment (DEA) to gas phase CO2 has been probed using a velocity slice imaging technique. DEA to CO2 produces only an O- ionic fragment and shows two major resonances located at 4.4 and 8.2 eV, respectively. The kinetic energy and angular distribution of the O- ions are measured around the second resonance with higher efficiency and sensitivity that provide details of the DEA dynamics. The kinetic energy distributions are in good agreement with the previous reports. However, the distinct angular distributions show substantial difference from the two recent studies within the limited electron energies. Our angular distribution results show two negative ion resonant states are involved in the underlying DEA process at the entire electron energies over the second resonance. We discussed the recent conflicting findings in the angular distribution results. The forward-backward asymmetry observed in the angular distributions is explained due to the interference effect of different partial waves associated with the attaching electron.

  6. 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

  7. Control of chemical reactions and synthesis by low-energy electrons.

    PubMed

    Bhler, Esther; Warneke, Jonas; Swiderek, Petra

    2013-12-21

    Controlling the outcome of reactions is a central issue of chemical research. Physical tools can achieve this if they are able to precisely dissociate specific bonds of a molecule. However, to control synthesis, such tools must induce the formation of new bonds between two reactants to yield a more complex product. In the ideal case of an atom efficient synthesis, this product would contain all or at least most of the initial material. An electron beam is a physical tool that is capable of preparing molecules in reactive states or, at low electron energies, of initiating highly selective bond dissociation. The resulting fragments in turn can react with other molecules to yield stable products. This tutorial review focuses in particular on such low-energy electron-initiated molecular syntheses and their applications in the modification of surfaces. It thus emphasizes strategies towards the controlled and predictable formation of more complex products from small reactants initiated by interaction with low-energy electrons either through selective bond dissociation or formation of specific reactive molecular species. However, selective bond dissociation is not always desirable. This is briefly illustrated by the case of electron beam induced deposition where additional strategies may be required to control product formation. PMID:24088739

  8. Effects of high angular momentum on the unimolecular dissociation of CD2CD2OH: theory and comparisons with experiment.

    PubMed

    McKown, Benjamin G; Ceriotti, Michele; Womack, Caroline C; Kamarchik, Eugene; Butler, Laurie J; Bowman, Joel M

    2013-10-24

    This paper explores the dynamics of a highly rotationally and vibrationally excited radical, CD2CD2OH. The radical is produced from the 193 nm photodissociation of 2-bromoethanol-d4, so it is imparted with high angular momentum and high vibrational energy and subsequently dissociates to several product channels. This paper focuses on characterizing its angular momentum and modeling its effect on the product channels, including the HOD + vinyl-d3 product channel resulting from a frustrated dissociation of the radical originally en route to OH + ethene-d4 that instead results in D atom abstraction. Our impulsive model of the initial photodissociation shows that, for some cases, upward of 200 au of angular momentum is imparted, which greatly affects the dynamics of the competing product channels. Using a permutationally invariant potential energy surface and quasiclassical trajectories, we simulated the dissociation dynamics of CD2CD2OH and compared these results to those of Kamarchik et al. (J. Phys. Chem. Lett. 2010, 1, 3058-3065), who studied the dynamics of CH2CH2OH with zero angular momentum. We found that the recoil translational energy distribution for radicals that dissociated to OH + C2D4 matched experiment closely only when high angular momentum of the initial radical was explicitly included in the trajectory calculations. Similarly, the rate constant for dissociation changes when rotational energy was added to the vibrational energy in the initial conditions. Lastly, we applied the sketch-map dimensionality reduction technique to analyze mechanistic information leading to the vinyl + water product channel. Projecting the ab initio intrinsic reaction coordinates onto the lower dimensional space identified with sketch map offers new insight into the dynamics when one looks at the simulated trajectories in the lower dimensional space. Further analysis shows that the transition path resembles a frustrated dissociation of the OH + ethene radical adduct, followed instead by branching to vinyl + water when the leaving OH group encounters a nearby D atom on the ethene moiety. This characterization is in accord with the one made previously. We show that the transition path bifurcation between the two similar channels occurs at carbon-oxygen distances and oxygen-abstracted deuterium distances of 2-2.5 controlled by the C-O-D bond angle with large angles preferentially branching to the water plus vinyl product state. The experimental branching ratios were not reproduced by theory, however, due partly to the insufficient quality of the fitted potential surface. We also have evidence of a minor product channel, HD + vinoxy-d3, from our molecular dynamics simulations that allows us to assign the HD signal in prior experimental work. PMID:24124756

  9. Dissociative processes in electron-molecular ion collisions

    NASA Astrophysics Data System (ADS)

    Djuric, Nada; Dunn, Gordon H.

    1998-10-01

    There is renewed interest in dissociation of molecular ions, primarily due to needs for modeling plasma generators for etching and deposition and for modeling edge plasmas for fusion reactors. At the same time, there are improvements in experimental techniques; e.g. use of heavy-ion storage rings has opened possibilities in dissociation studies of vibrationally relaxed molecular ions. At electron energies below the dissociation energy (D_e) of a molecular ion, the most importanat process is dissociative recombination (DR). Once the energy is above D_e, dissociative excitation (DE) is allowed, and at even higher energies dissociative ionization (DI) is energetically possible. In JILA we set up an apparatus wherein light fragment ions from DE of heteronuclear molecular ions are detected. In the heavy-ion storage ring at Stockholm (CRYRING) detection of neutral fragments was used for DE and DR studies. We will discuss the techniques and give examples of DE and DI obtainet at JILA and CRYRING [1,2,3]. Work supported in part by the Office of Fusion Energy of the U. S. DOE under Contract No. DE-A105-86ER53237 with NIST and in part by the Swedish Natural Science Research Council. 1. N. Djuric et al., Phys. Rev. A 56, 2887 (1997). 2. J. Semaniak et al., Ap. J. 498, 886 (1998). 3. J. R. Peterson et al., J. Chem. Phys. 108, 1978 (1998)

  10. Energetics of Intermolecular Hydrogen Bonds in a Hydrophobic Protein Cavity

    NASA Astrophysics Data System (ADS)

    Liu, Lan; Baergen, Alyson; Michelsen, Klaus; Kitova, Elena N.; Schnier, Paul D.; Klassen, John S.

    2014-05-01

    This work explores the energetics of intermolecular H-bonds inside a hydrophobic protein cavity. Kinetic measurements were performed on the gaseous deprotonated ions (at the -7 charge state) of complexes of bovine ?-lactoglobulin (Lg) and three monohydroxylated analogs of palmitic acid (PA): 3-hydroxypalmitic acid (3-OHPA), 7-hydroxypalmitic acid (7-OHPA), and 16-hydroxypalmitic acid (16-OHPA). From the increase in the activation energy for the dissociation of the (Lg + X-OHPA)7- ions, compared with that of the (Lg + PA)7- ion, it is concluded that the -OH groups of the X-OHPA ligands participate in strong (5 - 11 kcal mol-1) intermolecular H-bonds in the hydrophobic cavity of Lg. The results of molecular dynamics (MD) simulations suggest that the -OH groups of 3-OHPA and 16-OHPA act as H-bond donors and interact with backbone carbonyl oxygens, whereas the -OH group of 7-OHPA acts as both H-bond donor and acceptor with nearby side chains. The capacity for intermolecular H-bonds within the Lg cavity, as suggested by the gas-phase measurements, does not necessarily lead to enhanced binding in aqueous solution. The association constant (Ka) measured for 7-OHPA [(2.3 0.2) 105 M-1] is similar to the value for the PA [(3.8 0.1) 105 M-1]; Ka for 3-OHPA [(1.1 0.3) 106 M-1] is approximately three-times larger, whereas Ka for 16-OHPA [(2.3 0.2) 104 M-1] is an order of magnitude smaller. Taken together, the results of this study suggest that the energetic penalty to desolvating the ligand -OH groups, which is necessary for complex formation, is similar in magnitude to the energetic contribution of the intermolecular H-bonds.

  11. Dissociation of cyclohexene and 1,4-cyclohexadiene in a molecular beam

    SciTech Connect

    Zhao, X.; Continetti, R.E.; Yokoyama, A.; Hintsa, E.J.; Lee, Y.T. (Materials and Chemical Sciences Division, Lawrence Berkeley Laboratory and Department of Chemistry, University of California, Berkeley, California 94720 (US))

    1989-10-01

    Molecular-beam photofragmentation translational spectroscopy of cyclohexene and 1,4-cyclohexadiene was carried out using 193 nm and IR multiphoton excitation. At 193 nm, both the retro-Diels--Alder reaction of cyclohexene and H{sub 2} elimination from both molecules were observed in the ground electronic state, indicating the occurrence of internal conversion from the initially excited electronic states. The retro-Diels--Alder reaction is shown to be concerted up to an internal energy higher than 148 kcal/mol. Hydrogen-atom elimination was also observed for both molecules following 193 nm excitation. The H atom is eliminated from an excited state of cyclohexene and is assigned to be from a carbon adjacent to the double bond, with a corresponding C--H bond energy of 87{plus minus}3 kcal/mol. It is shown that the peak of the translational energy distribution for concerted dissociation in the ground state is determined mainly by the dynamics of the potential-energy release along the reaction coordinate, and is not sensitive to either the amount of internal energy or the form of excitation.

  12. Oxidative addition of the C-I bond on aluminum nanoclusters.

    PubMed

    Sengupta, Turbasu; Das, Susanta; Pal, Sourav

    2015-07-28

    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. PMID:26123032

  13. XUV Pump - XUV Probe Studies of Bond Forming Processes in Polyatomic Molecules

    NASA Astrophysics Data System (ADS)

    Shivaram, Niranjan; Champenois, Elio; Cryan, James; Wright, Travis; Yang, Chan-Shan; Belkacem, Ali

    2014-05-01

    Extreme-ultraviolet (XUV) high-order harmonics along with strong-field femtosecond near infra-red (NIR) laser pulses have been used to perform time-resolved pump-probe studies of ionization and fragmentation dynamics in atomic and molecular systems. With the availability of high pulse energy femtosecond laser systems it is now possible to generate high-harmonics with enough flux to perform XUV pump - XUV probe experiments. Here, we use high harmonics generated from a state-of-the-art 30 mJ, 1 KHz femtosecond NIR laser system to study dissociation dynamics in Sulfur hexa-fluoride (SF6). We focus mainly on dissociation channels above the first ionization threshold where neutral molecular Fluorine (F2) is eliminated from SF6. Using photo-ion and photo-electron spectroscopy we time-resolve the formation of a chemical bond. Supported by Chemical Sciences, Geosciences and Biosciences division of BES/DOE.

  14. Vibrational Spectroscopy and Thermal Desorption Spectroscopy Studies of Adsorbate Hydrogen Bonding and Surface Chemistry on PLATINUM(111) and NICKEL(111)

    NASA Astrophysics Data System (ADS)

    Gao, Quanyin

    1991-07-01

    Adsorbate-adsorbate interactions, hydrogen bonding and surface reactions, have been studied using Fourier transform reflection absorption infrared spectroscopy (FTRAIR), high resolution electron energy loss spectroscopy (HREELS) and thermal desorption spectroscopy. On Ni(111), the HREELS results reveal that for theta < 0.5, formamide molecules (HCONH_2) are dissociatively adsorbed as eta^2( _{rm C,O})-CONH_2 at 90K. At theta~0.85, non-dissociative adsorption occurs. The hydrogen bonding among adsorbates has been observed for theta > 0.5 characterized by the red shift and peak broadening of the upsilon _{rm a}(NH_2 ) and upsilon_{s}(NH_2) modes as well as enhanced intensity of the omega(NH _2) mode. The results from FTRAIRS, HREELS and TDS reveal two thermal decomposition channels. One leads to the production of NH_3 and CO. The other yields isocyanic acid (HNCO). Possible precursors related to hydrogen bonding effects have been discussed. On Pt(111), dissociative adsorption of HCONH _2 forming NH_3 and CO are found at low dosages at 170K. At saturation monolayer coverages, hydrogen-bonding interactions between the chemisorbed molecules result in 263 cm^{-1} red-shifting of the upsilon(NH _2) vibrational frequency and linewidth broadening of the upsilon_{s}(NH_2) and upsilon_{rm a}(NH _2) modes. For HCOND_2, the linewidths of the corresponding modes are reduced. The isotope effect for linewidth is discussed. Acetic acid (CH_3COOH, CH_3COOD and ^{13 }CD_3COOH(D)) adsorption and reaction have been studied on Pt(111). The HREELS results indicate that for theta< 0.3, dissociative adsorption occurs forming eta ^2(O,O)-CH_3COO. Molecular adsorption occurs at theta~ 0.5 with a finger print peak at ~923 cm^{-1} for CH _3COOH H-bonded dimers. The hydrogen bond energy are estimated to be ~7.3 kcal/mole and the bond length (R_{ rm O{cdots}{cdot}O }) to be of ~2.68 A. Thermal desorption spectroscopy and HREELS results reveal that on Pt(111), acetic acid decomposes into CO and H _2 as the major products upon heating.

  15. Graded representations in behavioral dissociations

    Microsoft Academic Search

    Yuko Munakata

    2001-01-01

    Why do people sometimes seem to know things when they are tested in one way, while seeming unaware of this information when tested in a different way? Such task-dependent behaviors, or dissociations, often occur in infants and children, and in adults following brain damage. To explain these dissociations, researchers have posited separable knowledge systems that are differentially tapped by various

  16. 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.

  17. Anti-Arrhenius cleavage of covalent bonds in bottlebrush macromolecules on substrate

    PubMed Central

    Lebedeva, Natalia V.; Nese, Alper; Sun, Frank C.; Matyjaszewski, Krzysztof; Sheiko, Sergei S.

    2012-01-01

    Spontaneous degradation of bottlebrush macromolecules on aqueous substrates was monitored by atomic force microscopy. Scission of C?C covalent bonds in the brush backbone occurred due to steric repulsion between the adsorbed side chains, which generated bond tension on the order of several nano-Newtons. Unlike conventional chemical reactions, the rate of bond scission was shown to decrease with temperature. This apparent anti-Arrhenius behavior was caused by a decrease in the surface energy of the underlying substrate upon heating, which results in a corresponding decrease of bond tension in the adsorbed macromolecules. Even though the tension dropped minimally from 2.16 to 1.89nN, this was sufficient to overpower the increase in the thermal energy (kBT) in the Arrhenius equation. The rate constant of the bond-scission reaction was measured as a function of temperature and surface energy. Fitting the experimental data by a perturbed Morse potential V=V0(1-e-?x)2-fx, we determined the depth and width of the potential to be V0=14119kJ/mol and ?-1=0.180.03?, respectively. Whereas the V0 value is in reasonable agreement with the activation energy Ea=80220kJ/mol of mechanical and thermal degradation of organic polymers, it is significantly lower than the dissociation energy of a C?C bond De=350kJ/mol. Moreover, the force constant Kx=2?2V0=1.450.36kN/m of a strained bottlebrush along its backbone is markedly larger than the force constant of a C?C bond Kl=0.44kN/m, which is attributed to additional stiffness due to deformation of the side chains. PMID:22645366

  18. 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.

  19. Ab initio molecular dynamics simulation study of dissociative electron attachment to dialanine conformers.

    PubMed

    Feng, Wen-Ling; Tian, Shan Xi

    2015-03-12

    Dissociative electron attachment (DEA) processes of six low-lying conformers (1-6) of dialanine in the gas phase are investigated by using ab initio molecular dynamics simulations. The incoming electron is captured and primarily occupies the virtual molecular orbital ?*, which is followed by the different dissociation processes. The electron attachments to conformers 1 and 2 having the stronger N-HN and O-HO intramolecular hydrogen bonds do not lead to fragmentations, but two different backbone bonds are broken in the DEAs to conformers 3 (or 4) and 6, respectively. It is interesting that the hydrogen abstraction of -NH from the terminal methyl group -CH3 is found in the roaming dissociation of the temporary anion of conformer 3. The present simulations enable us to have more insights into the peptide backbone bond breaks in the DEA process and demonstrate a promising way toward understanding of the radiation damages of complicated biological system. PMID:25679256

  20. Multiple-Bond Kinetics from Single-Molecule Pulling Experiments: Evidence for Multiple NCAM Bonds

    PubMed Central

    Hukkanen, E. J.; Wieland, J. A.; Gewirth, A.; Leckband, D. E.; Braatz, R. D.

    2005-01-01

    The kinetic parameters of single bonds between neural cell adhesion molecules were determined from atomic force microscope measurements of the forced dissociation of the homophilic protein-protein bonds. The analytical approach described provides a systematic procedure for obtaining rupture kinetics for single protein bonds from bond breakage frequency distributions obtained from single-molecule pulling experiments. For these studies, we used the neural cell adhesion molecule (NCAM), which was recently shown to form two independent protein bonds. The analysis of the bond rupture data at different loading rates, using the single-bond full microscopic model, indicates that the breakage frequency distribution is most sensitive to the distance to the transition state and least sensitive to the molecular spring constant. The analysis of bond failure data, however, motivates the use of a double-bond microscopic model that requires an additional kinetic parameter. This double-bond microscopic model assumes two independent NCAM-NCAM bonds, and more accurately describes the breakage frequency distribution, particularly at high loading rates. This finding agrees with recent surface-force measurements, which showed that NCAM forms two spatially distinct bonds between opposed proteins. PMID:16100278

  1. Dissociative Recombination of NeH+

    NASA Astrophysics Data System (ADS)

    Florescu, Anca; Orel, A. E.; Mitchell, J. B. A.; Novotny, O.; Angelova, G.; Legarrec, J. L.; Rebrion-Rowe, C.; Svendsen, A.; Andersen, L. H.

    2004-09-01

    The dissociative recombination of NeH^+ has been measured using the ASTRID storage ring. NeH^+ does not have a curve crossing with the ion ground state but recombination can occur at higher energies via excitation to neutral rydberg states lying below excited ion states. These have been modeled theoretically using a wave packet method and preliminary results show good agreement with experiment.

  2. A periodic Energy Decomposition Analysis (pEDA) method for the Investigation of Chemical Bonding in Extended Systems

    E-print Network

    Raupach, Marc

    2015-01-01

    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 binding energy between two fragments (e.g. the adsorption energy of a molecule on a surface) into several well-defined terms: preparation, electrostatic and dispersion interaction, Pauli repulsion and orbital relaxation energies. The pEDA presented here for an AO-based implementation 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 th...

  3. 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.

  4. Intriguing Mass Spectrometric Behavior of Guanosine Under Low Energy Collision-Induced Dissociation: H 2 O Adduct Formation and Gas-Phase Reactions in the Collision Cell

    Microsoft Academic Search

    Robin Tuytten; Filip Lemire; Walter Van Dongen; Eddy L. Esmans; Erwin Witters; Wouter Herrebout; Benjamin Van Der Veken; Ed Dudley; Russell P. Newton

    2005-01-01

    An in-depth study of the fragmentation pathway of guanosine was conducted by using an in-source collision-induced dissociation\\u000a high-mass accuracy tandem mass spectrometry experiment. The equivalent of MS4 data, a level of information normally achieved on ion trap instruments, was obtained on a Q-TOF mass spectrometer. The combination\\u000a of the features of high-resolution, accuracy, and in-source CID permitted the unambiguous elucidation

  5. Asymmetric charge partitioning upon dissociation of DNA duplexes.

    PubMed

    Madsen, James A; Brodbelt, Jennifer S

    2010-07-01

    Upon collisional activation, a series of DNA duplexes exhibited a significant degree of asymmetric dissociation with respect to charge partitioning among the single strands. That is, the charge states of the single strand product ions did not equal q/2 for even precursor charge states or (q + 1)/2 and (q-1)/2 for odd precursor charge states (where q is the charge of the precursor). The factors that affect this asymmetric charge partitioning were assessed. The smaller, lower charged duplexes resulted in more symmetric dissociation compared with larger duplexes in higher charge states, which displayed a high degree of asymmetry upon dissociation. The composition of the duplexes influenced charge partitioning, with those containing a greater number of A/T base pairs showing more symmetric dissociation relative to the more G/C rich duplexes. The use of higher collisional energies resulted in significantly more asymmetric dissociation. Comparisons were made with the dissociation behavior previously studied for protein noncovalent complexes and past studies of the gas-phase conformations and dissociation of DNA complexes. PMID:20356762

  6. An ab initio study of the dissociation of HNCO in the S1 electronic state

    NASA Astrophysics Data System (ADS)

    Stevens, Jonathan E.; Cui, Qiang; Morokuma, Keiji

    1998-01-01

    Regions of the S1 potential energy surface of HNCO relevant to N-H and C-N bond photodissociation have been investigated with ab initio calculations. Geometries of minima and transition states on S1 as well as those of the product photofragments and the HNCO ground state have been optimized with the CASSCF method, and their energies calculated with MRSDCI and CASPT2 methods. Deep planar trans and cis minima exist on the S1 surface, and are connected by transition states for isomerization. The S0?S1 electronic transition is brighter for trans configurations than for cis, and the initial excitation and dynamics are most likely to proceed through trans configurations. The N-H fission on S1 has a substantial barrier; it occurs more easily through the planar cis transition state, which is about 20 kcal/mol above the dissociation threshold, than through the trans transition state. The C-N fission on S1 can take place both via the planar trans and the planar cis transition state with a low barrier over the dissociation threshold; the reverse barrier is estimated to be a few kcal/mol.

  7. 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

  8. Overcoming lability of extremely long alkane carbon-carbon bonds through dispersion forces.

    PubMed

    Schreiner, Peter R; Chernish, Lesya V; Gunchenko, Pavel A; Tikhonchuk, Evgeniya Yu; Hausmann, Heike; Serafin, Michael; Schlecht, Sabine; Dahl, Jeremy E P; Carlson, Robert M K; Fokin, Andrey A

    2011-09-15

    Steric effects in chemistry are a consequence of the space required to accommodate the atoms and groups within a molecule, and are often thought to be dominated by repulsive forces arising from overlapping electron densities (Pauli repulsion). An appreciation of attractive interactions such as van der Waals forces (which include London dispersion forces) is necessary to understand chemical bonding and reactivity fully. This is evident from, for example, the strongly debated origin of the higher stability of branched alkanes relative to linear alkanes and the possibility of constructing hydrocarbons with extraordinarily long C-C single bonds through steric crowding. Although empirical bond distance/bond strength relationships have been established for C-C bonds (longer C-C bonds have smaller bond dissociation energies), these have no present theoretical basis. Nevertheless, these empirical considerations are fundamental to structural and energetic evaluations in chemistry, as summarized by Pauling as early as 1960 and confirmed more recently. Here we report the preparation of hydrocarbons with extremely long C-C bonds (up to 1.704?), the longest such bonds observed so far in alkanes. The prepared compounds are unexpectedly stable--noticeable decomposition occurs only above 200?C. We prepared the alkanes by coupling nanometre-sized, diamond-like, highly rigid structures known as diamondoids. The extraordinary stability of the coupling products is due to overall attractive dispersion interactions between the intramolecular HH contact surfaces, as is evident from density functional theory computations with and without inclusion of dispersion corrections. PMID:21921913

  9. Detachment of agglutinin-bonded red blood cells. II. Mechanical energies to separate large contact areas.

    PubMed Central

    Evans, E.; Berk, D.; Leung, A.; Mohandas, N.

    1991-01-01

    As detailed in a companion paper (Berk, D., and E. Evans. 1991. Biophys. J. 59:861-872), a method was developed to quantitate the strength of adhesion between agglutinin-bonded membranes without ambiguity due to mechanical compliance of the cell body. The experimental method and analysis were formulated around controlled assembly and detachment of a pair of macroscopically smooth red blood cell surfaces. The approach provides precise measurement of the membrane tension applied at the perimeter of an adhesive contact and the contact angle theta c between membrane surfaces which defines the mechanical leverage factor (1-cos theta c) important in the definition of the work to separate a unit area of contact. Here, the method was applied to adhesion and detachment of red cells bound together by different monoclonal antibodies to red cell membrane glycophorin and the snail-helix pomatia-lectin. For these tests, one of the two red cells was chemically prefixed in the form of a smooth sphere then equilibrated with the agglutinin before the adhesion-detachment procedure. The other cell was not exposed to the agglutinin until it was forced into contact with the rigid cell surface by mechanical impingement. Large regions of agglutinin bonding were produced by impingement but no spontaneous spreading was observed beyond the forced contact. Measurements of suction force to detach the deformable cell yielded consistent behavior for all of the agglutinins: i.e., the strength of adhesion increased progressively with reduction in contact diameter throughout detachment. This tension-contact diameter behavior was not altered over a ten-fold range of separation rates. In special cases, contacts separated smoothly after critical tensions were reached; these were the highest values attained for tension. Based on measurements reported in another paper (Evans et al. 1991. Biophys. J. 59:838-848) of the forces required to rupture molecular-point attachments, the density of cross-bridges was estimated with the assumption that the tension was proportional to the discrete rupture force x the number of attachments per unit length. These estimates showed that only a small fraction of agglutinin formed cross-bridges at initial assembly and increased progressively with separation. When critical tension levels were reached, it appeared that nearly all local agglutinin was involved as cross-bridges. Because one cell surface was chemically fixed, receptor accumulation was unlikely; thus, microscopic "roughness" and steric repulsion probably modulated formation of cross-bridges on initial contact. To counter the steric repulsion, adhesive contacts were exposed to solutions of a high molecular weight polymer to draw the surfaces together by osmotic dehydration of the adhesion gap. These stresses exceeded initial mechanical assembly stresses by up to three orders of magnitude. As expected, the strength of adhesion was greatly enhanced by the added impingement stress. Images FIGURE 1 PMID:2065189

  10. Dissociative recombination of the deuterated acetaldehyde ion, CD3CDO(+): product branching fractions, absolute cross sections and thermal rate coefficient.

    PubMed

    Vigren, Erik; Kami?ska, Magdalena; Hamberg, Mathias; Zhaunerchyk, Vitali; Thomas, Richard D; Semaniak, Jacek; Danielsson, Mathias; Larsson, Mats; Geppert, Wolf D

    2007-06-14

    Dissociative recombination of the deuterated acetaldehyde ion CD3CDO(+) has been studied at the heavy-ion storage ring CRYRING, located at the Manne Siegbahn Laboratory, Stockholm, Sweden. Product branching fractions together with absolute DR cross-sections were measured. The branching fractions were determined at a relative collision energy between the ions and the electrons of approximately 0 eV. With a probability of 34% the DR events resulted in no ruptures of bonds between heavy atoms (i.e. no breakage of the C-C bond or the C[double bond, length as m-dash]O bond). In the remaining 66% of the events one of the bonds between the heavy atoms was broken. The energy-dependent cross-section for the DR reaction was measured between approximately 0 and 1 eV relative kinetic energy. In the energy region between 1 meV and 0.2 eV the absolute cross section could be fitted by the expression sigma(E) = 6.8 x 10(-16)E(-1.28) cm(2), whereas in the energy interval between 0.2 and 1 eV the data were best fitted by sigma(E) = 4.1 x 10(-16)E(-1.60) cm(2). From these cross section data the thermal rate coefficient (as a function of the electron temperature), alpha(T) = 9.2 x 10(-7) (T/300)(-0.72) cm(3) s(-1) was obtained. PMID:17538730

  11. Are major dissociative disorders characterized by a qualitatively different kind of dissociation?

    PubMed

    Rodewald, Frauke; Dell, Paul F; Wilhelm-Gossling, Claudia; Gast, Ursula

    2011-01-01

    A total of 66 patients with a major dissociative disorder, 54 patients with nondissociative disorders, and 30 nonclinical controls were administered the Structured Clinical Interview for DSM-IV Dissociative Disorders-Revised, the Dissociative Experiences Scale, the Multidimensional Inventory of Dissociation, and the Symptom Checklist 90-Revised. Dissociative patients reported significantly more dissociative and nondissociative symptoms than did nondissociative patients and nonclinical controls. When general psychopathology was controlled, the dissociation scores of dissociative patients were still significantly higher than those of both other groups, whereas the dissociation scores of nondissociative patients and nonclinical controls no longer differed. These findings appear to be congruent with a typological model of dissociation that distinguishes between 2 qualitatively different kinds of dissociation. Specifically, the results of this study suggest that the dissociation that occurs in major dissociative disorders (i.e., dissociative identity disorder [DID] and dissociative disorder not otherwise specified, Type 1 [DDNOS-1]) is qualitatively different from the dissociation that occurs in persons who do not have a dissociative disorder. In contrast to previous research, the dissociation of persons who do not have a dissociative disorder is not limited to absorption; it covers a much wider range of phenomena. The authors hypothesize that different mechanisms produce the dissociation of persons with DID and DDNOS-1 as opposed to the dissociation of persons who do not have a dissociative disorder. PMID:21240735

  12. Dissociative chemisorption of methane on Ni and Pt surfaces: mode-specific chemistry and the effects of lattice motion.

    PubMed

    Nave, Sven; Tiwari, Ashwani K; Jackson, Bret

    2014-10-16

    The dissociative chemisorption of methane on metal surfaces is of great practical and fundamental interest. Not only is it the rate-limiting step in the steam re-forming of natural gas, but also the reaction exhibits interesting mode-specific behavior and a strong dependence on the temperature of the metal. Electronic structure methods are used to explore this reaction on various Ni and Pt surfaces, with a focus on how the transition state is modified by motion of the metal lattice atoms. These results are used to construct models that explain the strong variation in reactivity with substrate temperature, shown to result primarily from changes in the dissociation barrier height with lattice motion. The dynamics of the dissociative chemisorption of CH4 on Ni and Pt is explored, using a fully quantum approach based on the reaction path Hamiltonian that includes all 15 molecular degrees of freedom and the effects of lattice motion. Agreement with experiment is good, and vibrational excitation of the molecule is shown to significantly enhance reactivity. The efficacy for this is examined in terms of the vibrationally nonadiabatic couplings, mode softening, mode symmetry, and energy localization in the reactive bond. PMID:25153478

  13. O-HS hydrogen bonds conform to the acid-base formalism.

    PubMed

    Bhattacharyya, Surjendu; Bhattacherjee, Aditi; Shirhatti, Pranav R; Wategaonkar, Sanjay

    2013-08-29

    Hydrogen bonding interaction between the ROH hydrogen bond donor and sulfur atom as an acceptor has not been as well characterized as the O-HO interaction. The strength of O-HO interactions for a given donor has been well documented to scale linearly with the proton affinity (PA) of the H-bond acceptor. In this regard, O-HO interactions conform to the acid-base formalism. The importance of such correlation is to be able to estimate molecular property of the complex from the known thermodynamic data of its constituents. In this work, we investigate the properties of O-HS interaction in the complexes of the H-bond donor and sulfur containing acceptors of varying proton affinity. The hydrogen bonded complexes of p-Fluorophenol (FP) with four different sulfur containing acceptors and their oxygen analogues, namely H2O/H2S, MeOH/MeSH, Me2O/Me2S and tetrahydrofuran (THF)/tetrahydrothiophene (THT) were characterized in regard to its S1-S0 excitation spectra and the IR spectra. Two-color resonantly enhanced multiphoton ionization (2c-R2PI), resonant ion-dip infrared (RIDIR) spectroscopy, and IR-UV hole burning spectroscopic techniques were used to probe the hydrogen bonds in the aforementioned complexes. The spectroscopic data along with the ab initio calculations were used to deduce the strength of the O-HS hydrogen bonding interactions in these system relative to that in the O-HO interactions. It was found that, despite being dominated by the dispersion interaction, the O-HS interactions conform to the acid-base formalism as in the case of more conventional O-HO interactions. The dissociation energies and the red shifts in the O-H stretching frequencies correlated very well with the proton affinity of the acceptors. However, the O-HS interaction did not follow the same correlation as that in the O-HO H-bond. The energy decomposition analysis showed that the dissociation energies and the red shifts in the O-H stretching frequencies follow a unified correlation if these two parameters were correlated with the sum of the charge transfer and the exchange component of the total binding energy. PMID:23947570

  14. Mechanisms of and effect of coadsorption on water dissociation on an oxygen vacancy of the MgO(100) surface.

    PubMed

    Wang, Yan; Nguyen, Hung N; Truong, Thanh N

    2006-07-24

    The dissociation mechanism of a water molecule at an oxygen vacancy on the MgO(100) surface was studied by using the embedded cluster method at the DFT/B3 LYP level, while the energetic information was refined by using the IMOMO method at the CCSD level. We found that a water molecule initially adsorbs on one of the magnesium ions surrounding the vacancy site with a binding energy of 15.98 kcal mol(-1). It then can dissociate on the MgO(100) surface along two possible dissociation pathways. One pathway produces a hydroxyl group bonded to the original magnesium with a proton filling the vacancy via a transition state with a barrier of 4.67 kcal mol(-1) relative to the adsorbed water configuration. The other pathway yields two hydroxy groups; the hydroxy group originally belonging to the water molecule fills the vacancy, while the hydrogen atom binds with the surface oxygen to form the other hydroxy group. Hydrogen atoms of these hydroxy groups can recombine to form a hydrogen molecule and the surface is healed. Although the barrier (14.09 kcal mol(-1)) of the rate-controlling step of the latter pathway is higher than that of the former one, the energies of all of its stationary points are lower than that of the separated reactants (H(2)O+cluster). The effects of water coadsorption are modeled by placing an additional water molecule near the active center, which suggests that the more coadsorbed water molecules further stabilize the hydroxy species and prevent the hydrogen molecule formation through the latter pathway. The results support the photoemission spectral evidence of water dissociation on the defective MgO(100) surface at low water coverage. PMID:16729339

  15. Quantum chemical study of mechanisms of dissociation and isomerization reactions in some molecules and radicals of astrophysical significance: Cyanides and related molecules

    NASA Astrophysics Data System (ADS)

    Gupta, V. P.; Sharma, Archna

    2006-09-01

    A theoretical study of the mechanism of photodecomposition in carbonyl cyanide, diethynyl ketone, acetyl cyanide and formyl cyanide has been conducted using density functional and MP2 theories. A complete analysis of the electronic spectra of these molecules in terms of nature, energy and intensity of electronic transitions has been provided by time-dependent density functional theory. Mixing coefficients and main configurations of the electronic states have been used to identify the states leading to the photodecomposition process. While the Rydberg state ^1(n,3s) is involved in the dissociation of formyl cyanide and acetyl cyanide, the ?^*_{CC}/?^*_{CN} states are involved in the case of carbonyl cyanide and diethynyl ketone. In all cases, however, stepwise decomposition process is preferred over the concerted reaction process. Based on potential energy curves for bond dissociation and the transition state and IRC studies, it is found that besides the direct dissociation of carbonyl cyanide, a photoisomerization process through a non-planar transition state may also occur resulting in the formation of a stable and planar isomer CNC(O)CN. A complete vibrational analysis of the higher energy isomer has been conducted and several new fundamental bands are predicted. Some of the earlier experimental results on the photodecomposition mechanism and energies of photofragments in carbonyl cyanide and acetyl cyanide have also been rationalized.

  16. 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.

  17. Spontaneous exciton dissociation in carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Yoshida, Masahiro; Kumamoto, Yusuke; Ishii, Akihiro; Yokoyama, Akio; Shimada, Takashi; Kato, Yuichiro K.

    2014-03-01

    Simultaneous photoluminescence and photocurrent measurements on individual single-walled carbon nanotubes reveal spontaneous dissociation of excitons into free electron-hole pairs.[2] A simple model is constructed to consistently describe the excitation power and voltage dependence of the photoluminescence and photocurrent. Using this model, we find that a significant fraction of excitons are dissociating before recombination. Furthermore, the combination of optical and electrical signals also allows for extraction of the absorption cross section and the oscillator strength. Our observations explain the reasons for photoconductivity measurements in single-walled carbon nanotubes being straightforward despite the large exciton binding energies. Work supported by KAKENHI, SCOPE, KDDI Foundation, and the Photon Frontier Network Program of MEXT, Japan.

  18. Characterization of metallic foil joints using diffusion bonding and diffusion soldering in micro-technology-based energy and chemical systems

    SciTech Connect

    Gabriel, Michael (Oregon State Univ.); Paul, Brian K. (Oregon State Univ.); Wilson, Rick D.; Alman, David E.

    2001-01-10

    The several 316 stainless steel mesoscopic devices were made using diffusing bonding and diffusion soldering. Tensile strength, pressure drop of the devices were measured, and metallurgical examinations were made of the joints. Continuous bonds were observed in both diffusion bonded and diffusion soldered samples. Strengths of the diffusion soldered samples were up to 80% of the strength of the Ag(sub3) Sn joint material or 125 MPa. The pressure drop in diffusion soldered samples was 0.76 psi at the highest flow rates of 2.08 L/min. Diffusion bonded joints had strengths of up to 700 MPa but the back pressures were higher at all flow rates.

  19. Quasi-diabatic representations of adiabatic potential energy surfaces coupled by conical intersections including bond breaking: a more general construction procedure and an analysis of the diabatic representation.

    PubMed

    Zhu, Xiaolei; Yarkony, David R

    2012-12-14

    The analytic representation of adiabatic potential energy surfaces and their nonadiabatic interactions is a key component of accurate, fully quantum mechanical descriptions of nonadiabatic dynamics. In this work, we describe extensions of a promising method for representing the nuclear coordinate dependence of the energies, energy gradients, and derivative couplings of N(state) adiabatic electronic states coupled by conical intersections. The description is based on a vibronic coupling model and can describe multichannel dissociation. An important feature of this approach is that it incorporates information about the geometry dependent interstate derivative couplings into the fitting procedure so that the resulting representation is quantifiably quasi diabatic and quasi diabatic in a least squares sense. The reported extensions improve both the rate of convergence and the converged results and will permit the optimization of nonlinear parameters including those parameters that govern the placement of the functions used to describe multichannel dissociation. Numerical results for a coupled quasi-diabatic state representation of the photodissociation process NH(3)+hv ? NH(2)+H illustrate the potential of the improved algorithm. A second focus in this numerical example is the quasi-diabatic character of the representation which is described and analyzed. Special attention is paid to the immediate vicinity of the conical intersection seam. PMID:23249048

  20. Water's Hydrogen Bond Strength

    E-print Network

    Martin Chaplin

    2007-06-10

    Water is necessary both for the evolution of life and its continuance. It possesses particular properties that cannot be found in other materials and that are required for life-giving processes. These properties are brought about by the hydrogen bonded environment particularly evident in liquid water. Each liquid water molecule is involved in about four hydrogen bonds with strengths considerably less than covalent bonds but considerably greater than the natural thermal energy. These hydrogen bonds are roughly tetrahedrally arranged such that when strongly formed the local clustering expands, decreasing the density. Such low density structuring naturally occurs at low and supercooled temperatures and gives rise to many physical and chemical properties that evidence the particular uniqueness of liquid water. If aqueous hydrogen bonds were actually somewhat stronger then water would behave similar to a glass, whereas if they were weaker then water would be a gas and only exist as a liquid at sub-zero temperatures. The overall conclusion of this investigation is that water's hydrogen bond strength is poised centrally within a narrow window of its suitability for life.

  1. Dissociative photoionization of ClN3 using high-resolution synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Quinto-Hernandez, Alfredo; Lee, Yin-Yu; Huang, Tzu-Ping; Pan, Wan-Chen; Lin, Jim-Min, Jr.; Bobadova-Parvanova, Petia; Morokuma, Keiji; Samartzis, Petros C.; Wodtke, Alec M.

    2007-09-01

    High-resolution synchrotron-radiation-based photoionization mass spectrometry was applied to study the dissociative photoionization of ClN3 under collision-free molecular beam conditions at ionization energies between 10 and 17 eV. No parent ion (ClN3+) could be detected under our experimental conditions. This suggests that the ground and excited states of ClN3+ are weakly bound or repulsive, a conclusion supported by electronic structure calculations also reported here. We recorded photoionization yield spectra at m/z = 49, 42, 35 and 14 from which we extracted the appearance potentials for NCl+, N3+, Cl+, and N+. The appearance potential of NCl+ (10.17 0.02 eV) observed here is close to the previously reported ionization potential of ClN3 obtained form photoelectron spectroscopy. Using the theoretically calculated binding energy of ClN3+ (0.2 eV), we derive an estimate of the adiabatic ionization potential of ClN3 = 9.97 0.02 eV. The measured appearance potentials for N3+, Cl+, and N+ provide three independent determinations of the Cl-N bond energy in ClN3, which agree within their respective error limits. The observations of this work are consistent with a new value of the N-Cl bond energy in ClN3, D0(Cl-N3) = 1.86 0.05 eV, 0.3 eV lower than previously reported values, which are however experimentally derived upper limits. The bond energy reported here is consistent with high level ab initio (CCSD(T)) electronic structure calculations extrapolated to the complete basis set limit, which yield a value: D0(Cl-N3) = 1.87 eV.

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

    E-print Network

    energy structure minimizes the formal charges. Also, for triatomic molecules, the central atom of electron pairs 2. Guess possible structures 3. Place one electron pair between each pair of atoms 4 to Lewis Theory 1. Radicals: Radicals have an odd number of electrons; biradicals have two unpaired

  3. Mild and Robust Redox-Neutral Pd/C-Catalyzed Lignol ?-O-4' Bond Cleavage Through a Low-Energy-Barrier Pathway.

    PubMed

    Galkin, Maxim V; Dahlstrand, Christian; Samec, Joseph S M

    2015-07-01

    A Pd/C catalyzed redox neutral C?O bond cleavage of 2-aryloxy-1-arylethanols has been developed. The reactions are carried out at 80?C, in air, using a green solvent system to yield the aryl ketones in near quantitative yields. Addition of catalytic amounts of a hydrogen source to the reaction mixture activates the catalyst to proceed through a low energy barrier pathway. Initial studies support a transfer hydrogenolysis reaction mechanism that proceeds through an initial dehydrogenation followed by an enol adsorption to Pd/C and a reductive C?O bond cleavage. PMID:25925736

  4. 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

  5. Insulation bonding test system

    NASA Technical Reports Server (NTRS)

    Beggs, J. M.; Johnston, G. D.; Coleman, A. D.; Portwood, J. N.; Saunders, J. M.; Redmon, J. W.; Porter, A. C. (inventors)

    1984-01-01

    A method and a system for testing the bonding of foam insulation attached to metal is described. The system involves the use of an impacter which has a calibrated load cell mounted on a plunger and a hammer head mounted on the end of the plunger. When the impacter strikes the insulation at a point to be tested, the load cell measures the force of the impact and the precise time interval during which the hammer head is in contact with the insulation. This information is transmitted as an electrical signal to a load cell amplifier where the signal is conditioned and then transmitted to a fast Fourier transform (FFT) analyzer. The FFT analyzer produces energy spectral density curves which are displayed on a video screen. The termination frequency of the energy spectral density curve may be compared with a predetermined empirical scale to determine whether a igh quality bond, good bond, or debond is present at the point of impact.

  6. A theoretical study of the structure and bonding of UOX4 (X = F, Cl, Br, I) molecules: the importance of inverse trans influence.

    PubMed

    Kovcs, Attila; Konings, Rudy J M

    2006-02-13

    During nitroxide-mediated polymerization (NMP) in the presence of a nitroxide R2(R1)NO*, the reversible formation of N-alkoxyamines [P-ON(R1)R2] reduces significantly the concentration of polymer radicals (P*) and their involvement in termination reactions. The control of the livingness and polydispersity of the resulting polymer depends strongly on the magnitude of the bond dissociation energy (BDE) of the C-ON(R1)R2 bond. In this study, theoretical BDEs of a large series of model N-alkoxyamines are calculated with the PM3 method. In order to provide a predictive tool, correlations between the calculated BDEs and the cleavage temperature (T(c)), and the dissociation rate constant (k(d)), of the N-alkoxyamines are established. The homolytic cleavage of the N-OC bond is also investigated at the B3P86/6-311++G(d,p)//B3LYP/6-31G(d), level. Furthermore, a natural bond orbital analysis is carried out for some N-alkoxyamines with a O-C-ON(R1)R2 fragment, and the strengthening of their C-ON(R1)R2 bond is interpreted in terms of stabilizing anomeric interactions. PMID:16463335

  7. Distortion-triggered loss of long-range order in solids with bonding energy hierarchy.

    PubMed

    Kolobov, A V; Krbal, M; Fons, P; Tominaga, J; Uruga, T

    2011-04-01

    An amorphous-to-crystal transition in phase-change materials like Ge-Sb-Te is widely used for data storage. The basic principle is to take advantage of the property contrast between the crystalline and amorphous states to encode information; amorphization is believed to be caused by melting the materials with an intense laser or electrical pulse and subsequently quenching the melt. Here, we demonstrate that distortions in the crystalline phase may trigger a collapse of long-range order, generating the amorphous phase without going through the liquid state. We further show that the principal change in optical properties occurs during the distortion of the still crystalline structure, upsetting yet another commonly held belief that attributes the change in properties to the loss of long-range order. Furthermore, our results suggest a way to lower energy consumption by condensing phase change inducing energy into shorter pulses or through the use of coherent phonon excitation. PMID:21430691

  8. Distortion-triggered loss of long-range order in solids with bonding energy hierarchy

    NASA Astrophysics Data System (ADS)

    Kolobov, A. V.; Krbal, M.; Fons, P.; Tominaga, J.; Uruga, T.

    2011-04-01

    An amorphous-to-crystal transition in phase-change materials like Ge-Sb-Te is widely used for data storage. The basic principle is to take advantage of the property contrast between the crystalline and amorphous states to encode information; amorphization is believed to be caused by melting the materials with an intense laser or electrical pulse and subsequently quenching the melt. Here, we demonstrate that distortions in the crystalline phase may trigger a collapse of long-range order, generating the amorphous phase without going through the liquid state. We further show that the principal change in optical properties occurs during the distortion of the still crystalline structure, upsetting yet another commonly held belief that attributes the change in properties to the loss of long-range order. Furthermore, our results suggest a way to lower energy consumption by condensing phase change inducing energy into shorter pulses or through the use of coherent phonon excitation.

  9. Effects of Multiple-Bond Ruptures on Kinetic Parameters Extracted from Force Spectroscopy Measurements: Revisiting Biotin-Streptavidin Interactions

    PubMed Central

    Guo, Senli; Ray, Chad; Kirkpatrick, Andrea; Lad, Nimit; Akhremitchev, Boris B.

    2008-01-01

    Force spectroscopy measurements of the rupture of the molecular bond between biotin and streptavidin often results in a wide distribution of rupture forces. We attribute the long tail of high rupture forces to the nearly simultaneous rupture of more than one molecular bond. To decrease the number of possible bonds, we employed hydrophilic polymeric tethers to attach biotin molecules to the atomic force microscope probe. It is shown that the measured distributions of rupture forces still contain high forces that cannot be described by the forced dissociation from a deep potential well. We employed a recently developed analytical model of simultaneous rupture of two bonds connected by polymer tethers with uneven length to fit the measured distributions. The resulting kinetic parameters agree with the energy landscape predicted by molecular dynamics simulations. It is demonstrated that when more than one molecular bond might rupture during the pulling measurements there is a noise-limited range of probe velocities where the kinetic parameters measured by force spectroscopy correspond to the true energy landscape. Outside this range of velocities, the kinetic parameters extracted by using the standard most probable force approach might be interpreted as artificial energy barriers that are not present in the actual energy landscape. Factors that affect the range of useful velocities are discussed. PMID:18621812

  10. Hot hole-induced dissociation of NO dimers on a copper surface

    NASA Astrophysics Data System (ADS)

    Garca Rey, Natalia; Arnolds, Heike

    2011-12-01

    We use reflection-absorption infrared spectroscopy (RAIRS) to study the photochemistry of NO on Cu(110) in the UV-visible range. We observe that the only photoactive species of NO on Cu(110) is the NO dimer, which is asymmetrically bound to the surface. RAIRS shows that photoinduced dissociation proceeds via breaking of the weak N-N bond of the dimer, photodesorbing one NOg to the gas phase and leaving one NOads adsorbed on the surface in a metastable atop position. We model the measured wavelength-dependent cross sections assuming both electron- and hole-induced processes and find that the photochemistry can be described by either electron attachment to a level 0.3 eV above the Fermi energy EF or hole attachment to a level 2.2 eV below EF. While there is no experimental or theoretical evidence for an electron attachment level so close to EF, an occupied NO-related molecular orbital is known to exist at EF - 2.52 eV on the Cu(111) surface [I. Kinoshita, A. Misu, and T. Munakata, J. Chem. Phys. 102, 2970 (1995)]. We, therefore, propose that photoinduced dissociation of NO dimers on Cu(110) in the visible wavelength region proceeds by the creation of hot holes at the top of the copper d-band.

  11. 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 [Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C (Denmark)

    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)

  12. Hot hole-induced dissociation of NO dimers on a copper surface

    SciTech Connect

    Garcia Rey, Natalia; Arnolds, Heike [Surface Science Research Centre, University of Liverpool, Oxford Road, Liverpool L69 3BX (United Kingdom)

    2011-12-14

    We use reflection-absorption infrared spectroscopy (RAIRS) to study the photochemistry of NO on Cu(110) in the UV-visible range. We observe that the only photoactive species of NO on Cu(110) is the NO dimer, which is asymmetrically bound to the surface. RAIRS shows that photoinduced dissociation proceeds via breaking of the weak N-N bond of the dimer, photodesorbing one NO{sub g} to the gas phase and leaving one NO{sub ads} adsorbed on the surface in a metastable atop position. We model the measured wavelength-dependent cross sections assuming both electron- and hole-induced processes and find that the photochemistry can be described by either electron attachment to a level 0.3 eV above the Fermi energy E{sub F} or hole attachment to a level 2.2 eV below E{sub F}. While there is no experimental or theoretical evidence for an electron attachment level so close to E{sub F}, an occupied NO-related molecular orbital is known to exist at E{sub F}- 2.52 eV on the Cu(111) surface [I. Kinoshita, A. Misu, and T. Munakata, J. Chem. Phys. 102, 2970 (1995)]. We, therefore, propose that photoinduced dissociation of NO dimers on Cu(110) in the visible wavelength region proceeds by the creation of hot holes at the top of the copper d-band.

  13. Site-selective dissociation processes of cationic ethanol conformers: the role of hyperconjugation.

    PubMed

    Li, Weixing; Hu, Yongjun; Liu, Fuyi; Shan, Xiaobin; Sheng, Liusi

    2014-08-28

    In present report, we explored hyperconjugation effects on the site- and bond-selective dissociation processes of cationic ethanol conformers by the use of theoretical methods (including configuration optimizations, natural bond orbital (NBO) analysis, and density of states (DOS) calculations, etc.) and the tunable synchrotron vacuum ultraviolet (SVUV) photoionization mass spectrometry. The dissociative mechanism of ethanol cations, in which hyperconjugative interactions and charge-transfer processes were involved, was proposed. The results reveal C?-H and C-C bonds are selectively weakened, which arise as a result of the hyperconjugative interactions ?C?-H ? p in the trans-conformer and ?C-C ? p in gauche-conformer after being ionized. As a result, the selective bond cleavages would occur and different fragments were observed. PMID:25080068

  14. Temperature dependence of internal motions of protein side-chain NH3(+) groups: insight into energy barriers for transient breakage of hydrogen bonds.

    PubMed

    Zandarashvili, Levani; Iwahara, Junji

    2015-01-20

    Although charged side chains play important roles in protein function, their dynamic properties are not well understood. Nuclear magnetic resonance methods for investigating the dynamics of lysine side-chain NH3(+) groups were established recently. Using this methodology, we have studied the temperature dependence of the internal motions of the lysine side-chain NH3(+) groups that form ion pairs with DNA phosphate groups in the HoxD9 homeodomain-DNA complex. For these NH3(+) groups, we determined order parameters and correlation times for bond rotations and reorientations at 15, 22, 28, and 35 C. The order parameters were found to be virtually constant in this temperature range. In contrast, the bond-rotation correlation times of the NH3(+) groups were found to depend strongly on temperature. On the basis of transition state theory, the energy barriers for NH3(+) rotations were analyzed and compared to those for CH3 rotations. Enthalpies of activation for NH3(+) rotations were found to be significantly higher than those for CH3 rotations, which can be attributed to the requirement of hydrogen bond breakage. However, entropies of activation substantially reduce the overall free energies of activation for NH3(+) rotations to a level comparable to those for CH3 rotations. This entropic reduction in energy barriers may accelerate molecular processes requiring hydrogen bond breakage and play a kinetically important role in protein function. PMID:25489884

  15. Hopping approach towards exciton dissociation in conjugated polymers

    SciTech Connect

    Emelianova, E. V.; Auweraer, M. van der [Laboratory for Molecular Dynamics and Spectroscopy, KU Leuven, Celestijnenlaan 200F, B-3001 Heverlee-Leuven (Belgium); Institute for Nanoscale Physics and Chemistry (INPAC), Celestijnenlaan 200D, B-3001 Leuven (Belgium); Baessler, H. [Institute of Physical, Macromolecular and Nuclear Chemistry and Materials Science Center, Philipps University, D-35032 Marburg (Germany)

    2008-06-14

    By employing random walk an analytic theory for the dissociation of singlet excitons in a random organic solid, for instance, a conjugated polymer, has been developed. At variance of conventional three-dimensional Onsager theory, it is assumed that an exciton with finite lifetime can first transfer endothermically an electron to an adjacent site, thereby generating a charge transfer state whose energy is above the energy of that of the initial exciton. In a second step the latter can fully dissociate in accordance with Onsager's concept Brownian motion. The results indicate that, depending of the energy required for the first jump, the first jump contributes significantly to the field dependence of the dissociation yield. Disorder weakens the temperature dependence of the yield dramatically and precludes extracting information on the exciton binding energy from it.

  16. Dissociative disorders in DSM-5.

    PubMed

    Spiegel, David; Lewis-Fernndez, 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

  17. Quantum mechanical calculations on the potential energy surface for the formation of xenon dichloride and the nature of the (n5-cyclopentadienyl) dicarbonyliron-arene bond

    E-print Network

    Richardson, Nancy Arline

    1993-01-01

    QUANTUM MECHANICAL CALCULATIONS ON THE POTENTIAL ENERGY SURFACE FOR THE FORMATION OF XENON DICHLORIDE AND THE NATURE OF THE (tis- CYCLOPENTADIENYL) DICARBONYLIRON-ARENE BOND A Thesis by NANCY ARLINE RI~SON Submitted to the Office of Graduate... Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August 1993 Major Subject: Chemistry QUANTUM MECHANICAL CALCULATIONS ON THE POTENTIAL ENERGY SURFACE FOR THE FORMATION OF XENON...

  18. A quinone-assisted photoformation of energy-rich chemical bonds

    NASA Technical Reports Server (NTRS)

    Fox, S. W.; Adachi, T.; Stillwell, W.

    1980-01-01

    In a study of biochemical means of solar energy conversion, ADP and inorganic phosphates were converted to ATP by white light in the nonaqueous solvent dimethylformamide in the presence of tetrachloro-p-quinone or ubiquinone. Conversion of ADP to ATP has been accomplished in aqueous suspension by the use of cell-like structures aggregated from poly(aspartic acid, glutamic acid, tyrosine). This is believed to occur through the formation of dopaquinone in the peptide structure during illumination. The way in which the quantitative yield of ATP has been influenced by pH and by added substances, such as FeCl2, was studied.

  19. Thermodynamics of water dimer dissociation in the primary hydration shell of the iodide ion with temperature-dependent vibrational predissociation spectroscopy.

    PubMed

    Wolke, Conrad T; Menges, Fabian S; Ttsch, Niklas; Gorlova, Olga; Fournier, Joseph A; Weddle, Gary H; Johnson, Mark A; Heine, Nadja; Esser, Tim K; Knorke, Harald; Asmis, Knut R; McCoy, Anne B; Arismendi-Arrieta, Daniel J; Prosmiti, Rita; Paesani, Francesco

    2015-03-12

    The strong temperature dependence of the I(-)(H2O)2 vibrational predissociation spectrum is traced to the intracluster dissociation of the ion-bound water dimer into independent water monomers that remain tethered to the ion. The thermodynamics of this process is determined using van't Hoff analysis of key features that quantify the relative populations of H-bonded and independent water molecules. The dissociation enthalpy of the isolated water dimer is thus observed to be reduced by roughly a factor of three upon attachment to the ion. The cause of this reduction is explored with electronic structure calculations of the potential energy profile for dissociation of the dimer, which suggest that both reduction of the intrinsic binding energy and vibrational zero-point effects act to weaken the intermolecular interaction between the water molecules in the first hydration shell. Additional insights are obtained by analyzing how classical trajectories of the I(-)(H2O)2 system sample the extended potential energy surface with increasing temperature. PMID:25647222

  20. High-energy and low-energy collision-induced dissociation of protonated flavonoids generated by MALDI and by electrospray ionization

    NASA Astrophysics Data System (ADS)

    March, Raymond E.; Li, Hongxia; Belgacem, Omar; Papanastasiou, Dimitris

    2007-04-01

    Product ion mass spectra of a series of nine protonated flavonoids have been observed by electrospray ionization combined with quadrupole/time-of-flight (ESI QTOF), and matrix-assisted laser desorption ionization combined either with quadrupole ion trap (MALDI QIT) tandem mass spectrometry or time-of-flight tandem mass spectrometry (MALDI TOF ReTOF). The compounds examined are 3,6-, 3,2'-, and 3,3'-dihydoxyflavone, apigenin (5,7,4'-trihydroxyflavone), luteolin (5,7,3',4'-tetrahydroxyflavone), apigenin-7-O-glucoside, hesperidin (5,7,3'-trihydroxy-4'-methoxyflavanone), daidzen (7,4'-dihydroxyisoflavone), and rutin (quercitin-3-O-rutinoside) where quercitin is 3,5,7,3',4'-pentahydroxyflavone; sodiated rutin was examined also. The center-of-mass energies in ESI QTOF and MALDI QIT are similar (1-4 eV) and their product ion mass spectra are virtually identical. In the MALDI TOF ReTOF instrument, center-of-mass energies range from 126-309 eV for sodiated rutin to protonated dihydroxyflavones, respectively. Due to the high center-of-mass energies available with the MALDI TOF ReTOF instrument, some useful structural information may be obtained; however, with increasing precursor mass/charge ratio, product ion mass spectra become simplified so as to be of limited structural value. Electronic excitation of the protonated (and sodiated) species examined here offers an explanation for the very simple product ion mass spectra observed particularly for glycosylated flavonoids.