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1

An interpretation of organometalic bond dissociation energies  

SciTech Connect

Organometallic bond dissociation energies (BDE) are incorporated into the E and C model with excellent results. Since the data are consistent with gas-phase systems, the fit supports claims that the enthalpies are relatively free of solvation contributions. The organometallic catimers (fragments forming the positive end of the dipole) include (CO){sub 5}Mn{sup 1},({eta}{sup 5}-(CH{sub 3}){sub 3}SiC{sub 5}H{sub 4}){sub 3}U{sup IV}-,({eta}{sup 5}C{sub 5}H{sub 5})(CO){sub 3}Mo{sup II}{sub 5}-,({eta}C{sub 5}(CH{sub 3}){sub 5})(P(CH{sub 3}{sub 3}){sub 2}Ru{sup II}-, (PCH{sub 2})CH{sub 2}P(C{sub 6}H{sub 5}){sub 2})(CH{sub 3})Pt{sup II}-,({eta}{sup 5}-C{sub 5}(CH{sub 3}){sub 5}){sub 2}Zr-, and 1/2({eta}{sup 5}-(C{sub 5}(CH{sub 3}){sub 5}){sub 2}Sm){sub 2{minus}}. The animers (fragments forming the negative end of the dipole) include organics, halogens, and inorganics. In addition to predicting and interpreting enthalpies, the resulting parameters for the radicals provide reactivity scales that can be used to interpret reactivity and physicochemical properties. Significant chemical insight results from the fit of the data to the ECT model. The parameters are used to reinterpret {sup 19}F chemical shifts in (F-Ph)Pt(P{sub 2}R{sub 3}){sub 2}-X, in terms of a {sigma}-only Pt-X bond. The earlier interpretation is one of the classic examples used to support metal-ligand {pi}-bonding interactions, Predicted bond energies are analyzed to indicate the metal properties that facilitate the CO insertion reaction. The analysis provides insights into the relative importance of electrostatic and covalent interactions.

Drago, R.S.; Wong, N.M.; Ferris, D.C. [Univ. of Florida, Gainesvile, FL (United States)

1992-01-01

2

Atomic contributions to bond dissociation energies in aliphatic hydrocarbons  

NASA Astrophysics Data System (ADS)

This paper explores the atomic contributions to the electronic vibrationless bond dissociation enthalpy (BDE) at 0K of the central C-C bond in straight-chain alkanes (CnH2n+2) and trans-alkenes (CnH2n) with an even number of carbon atoms, where n =2, 4, 6, 8. This is achieved using the partitioning of the total molecular energy according to the quantum theory of atoms in molecules by comparing the atomic energies in the intact molecule and its dissociation products. The study is conducted at the MP2(full)/6-311++G(d,p) level of theory. It is found that the bulk of the electronic energy necessary to sever a single C-C bond is not supplied by these two carbon atoms (the ?-carbons) but instead by the atoms directly bonded to them. Thus, the burden of the electronic part of the BDE is primarily carried by the two hydrogens attached to each of the ?-carbons and by the ?-carbons. The effect drops off rapidly with distance along the hydrocarbon chain. The situation is more complex in the case of the double bond in alkenes, since here the burden is shared between the ?-carbons as well as the atoms directly bonded to them, namely, again the ?-hydrogens and the ?-carbons. These observations may lead to a better understanding of the bond dissociation process and should be taken into account when locally dense basis sets are introduced to improve the accuracy of BDE calculations.

Matta, Chérif F.; Castillo, Norberto; Boyd, Russell J.

2006-11-01

3

On the C?H bond dissociation energy of acetylene  

NASA Astrophysics Data System (ADS)

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)

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

1990-04-01

4

Bond Dissociation Energies in Second-Row Compounds  

SciTech Connect

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. Heats of formation at 0 and 298 K are predicted for PF?, PF?, PF?O, SF?, SF?, SF?, SF?O, SF?O?, and SF?O as well as a number of radicals derived from these stable compounds on the basis of coupled cluster theory [CCSD(T)] calculations extrapolated to the complete basis set limit. In order to achieve near chemical accuracy (±1 kcal/mol), additional corrections were added to the complete basis set binding energies based on frozen core coupled cluster theory energies: a correction for core-valence effects, a correction for scalar relativistic effects, a correction for first-order atomic spin-orbit effects, and vibrational zero-point energies. The calculated values substantially reduce the error limits for these species. A detailed comparison of adiabatic and diabatic bond dissociation energies (BDEs) is made and used to explain trends in the BDEs. Because the adiabatic BDEs of polyatomic molecules represent not only the energy required for breaking a specific bond but also contain any reorganization energies of the bonds in the resulting products, these BDEs can be quite different for each step in the stepwise loss of ligands in binary compounds. For example, the adiabatic BDE for the removal of one fluorine ligand from the very stable closed-shell SF? molecule to give the unstable SF? radical is 2.8 times the BDE needed for the removal of one fluorine ligand from the unstable SF? radical to give the stable closed-shell SF? molecule. Similarly, the BDE for the removal of one fluorine ligand from the stable closed-shell PF?O molecule to give the unstable PF?O radical is higher than the BDE needed to remove the oxygen atom to give the stable closed-shell PF? molecule. The same principles govern the BDEs of the phosphorus fluorides and the sulfur oxofluorides. In polyatomic molecules, care must be exercised not to equate BDEs with the bond strengths of given bonds. The measurement of the bond strength or stiffness of a given bond represented by its force constant involves only a small displacement of the atoms near equilibrium and, therefore, does not involve any reorganization energies, i.e., it may be more appropriate to correlate with the diabatic product states.

Grant, Daniel J.; Matus, Myrna H.; Switzer, Jackson R.; Dixon, David A.; Francisco, Joseph S.; Christe, Karl O.

2008-04-10

5

The dissociative bond.  

PubMed

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

Gordon, Nirit

2013-01-01

6

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

E-print Network

stabilization enthalpies (RSE) and with BDE(C-H), the C-H bond dissociation energies for the corresponding sensitive to deviations from planarity and give better linear correlations with RSE and BDE(C-H). The correlations cover a range of more than 20 kcal/mol and are reliable predictors of RSE and BDE(C-H

Brocks, Jochen J.

7

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

E-print Network

A theory for calculating the surface-adsorbate bond dissociation energy from collision is presented for determining the bond dissociation energy, Do, of a surface-adsorbate complex from collision-induced desorption measurements. D, is calculated from the minimum collision energy required for desorption

Levis, Robert J.

8

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

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

9

Alfa and remote substituent effects on the homolytic dissociation energies of O–H bonds  

Microsoft Academic Search

In the study we used a number of high level theoretical methods to calculate the O–H bond dissociation energies (BDEs) as well as ? and remote para substituent effects on them. We found that only G3 and CBS-Q methods can be used to calculate the absolute O–H BDEs. Other methods including B3LYP, MP2, and CCSD(T), either open-shelled or close-shelled, significantly

Yao Fu; Lei Liu; Yi Mou; Bo-Lin Lin; Qing-Xiang Guo

2004-01-01

10

Computational study on the difference between the Co-C bond dissociation energy in methylcobalamin and adenosylcobalamin.  

PubMed

The bond dissociation energies of the Co-C bonds in the cobalamin cofactors methylcobalamin and adenosylcobalamin were calculated using the hybrid quantum mechanics/molecular mechanics method IMOMM (integrated molecular orbital and molecular mechanics). Calculations were performed on models of differing complexities as well as on the full systems. We investigated the origin of the different experimental values for the Co-C bond dissociation energies in methylcobalamin and adenosylcobalamin, and have provided an explanation for the difficulties encountered when we attempt to reproduce this difference in quantum chemistry. Additional calculations have been performed using the Miertus-Scrocco-Tomasi method in order to estimate the influence of solvent effects on the homolytic Co-C bond cleavage. Introduction of these solvation effects is shown to be necessary for the correct reproduction of experimental trends in bond dissociation energies in solution, which consequently have no direct correlation with dissociation processes in the enzyme. PMID:15986217

Dölker, Nicole; Morreale, Antonio; Maseras, Feliu

2005-08-01

11

Bond Dissociation Energies in Second-Row Compounds  

Microsoft Academic Search

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. Heats of formation at 0 and 298 K are predicted for PF, PF, PFO, SF, SF, SF, SFO, SFO, and

Daniel J. Grant; Myrna H. Matus; Jackson R. Switzer; David A. Dixon; Joseph S. Francisco; Karl O. Christe

2008-01-01

12

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

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

13

Influence of steric and intramolecular inductive effects on the variable trends in RX (R=Alkyl) bond dissociation energy  

Microsoft Academic Search

The question “why are the variation trends of R-X bond dissociation energy different?” is answered. The R-X bond dissociation\\u000a energy (BDE) may be influenced by three main factors: the C-X intrinsic bond energy, the 1,3 geminal repulsion, and the intramolecular\\u000a charge-induced dipole. In the presence of atom X, the variation trend of BDE in R-X (R= Me, Et, i-Pr, t-Bu)

ChenZhong Cao

2009-01-01

14

Comment on "the origin of anomalous bond dissociation energies of V +(H 2) n clusters"  

NASA Astrophysics Data System (ADS)

In a recent study, we reported experimental determinations of bond dissociation energies and entropies for V +(H 2) n ( n = 1 to 6) and suggested that a spin change from quintet to triplet occurs upon addition of the sixth H 2 ligand. A very recent theoretical paper by Niu et al. disputes this and concludes that the experimental results are consistent with purely quintet clusters (J. Niu, B.K. Rao, S.N. Khanna and P. Jena, Chem. Phys. Letters 230 (1994) 299). In this Comment, we restate our reasons for the proposed spin charge and argue that important aspects of the results of Niu et al. are incorrect.

Kemper, P. R.; Bushnell, J. E.; Maitre, P.; Bowers, M. T.

1995-08-01

15

Bond dissociation energies and radical stabilization energies: an assessment of contemporary theoretical procedures.  

PubMed

Various contemporary theoretical procedures have been tested for their accuracy in predicting the bond dissociation energies (BDEs) and the radical stabilization energies (RSEs) for a test set of 22 monosubstituted methyl radicals. The procedures considered include the high-level W1, W1', CBS-QB3, ROCBS-QB3, G3(MP2)-RAD, and G3X(MP2)-RAD methods, unrestricted and restricted versions of the double-hybrid density functional theory (DFT) procedures B2-PLYP and MPW2-PLYP, and unrestricted and restricted versions of the hybrid DFT procedures BMK and MPWB1K, as well as the unrestricted DFT procedures UM05 and UM05-2X. The high-level composite procedures show very good agreement with experiment and are used to evaluate the performance of the comparatively less expensive DFT procedures. RMPWB1K and both RBMK and UBMK give very promising results for absolute BDEs, while additionally restricted and unrestricted X2-PLYP methods and UM05-2X give excellent RSE values. UM05, UB2-PLYP, UMPW2-PLYP, UM05-2X, and UMPWB1K are among the less well performing methods for BDEs, while UMPWB1K and UM05 perform less well for RSEs. The high-level theoretical results are used to recommend alternative experimental BDEs for propyne, acetaldehyde, and acetic acid. PMID:18047305

Menon, Ambili S; Wood, Geoffrey P F; Moran, Damian; Radom, Leo

2007-12-27

16

Quantum chemical calculations of bond dissociation energies for COOH scission and electronic structure in some acids  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations are performed to investigate the equilibrium C—COOH bond distances and the bond dissociation energies (BDEs) for 15 acids. These compounds are studied by utilizing the hybrid density functional theory (DFT) (B3LYP, B3PW91, B3P86, PBE1PBE) and the complete basis set (CBS—Q) method in conjunction with the 6-311G** basis as DFT methods have been found to have low basis sets sensitivity for small and medium molecules in our previous work. Comparisons between the computational results and the experimental values reveal that CBS—Q method, which can produce reasonable BDEs for some systems in our previous work, seems unable to predict accurate BDEs here. However, the B3P86 calculated results accord very well with the experimental values, within an average absolute error of 2.3 kcal/mol. Thus, B3P86 method is suitable for computing the reliable BDEs of C—COOH bond for carboxylic acid compounds. In addition, the energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of studied compounds are estimated, based on which the relative thermal stabilities of the studied acids are also discussed.

Zeng, Hui; Zhao, Jun; Xiao, Xun

2013-02-01

17

C-H and N-H bond dissociation energies of small aromatic hydrocarbons  

SciTech Connect

A survey of computational methods was undertaken to calculate the homolytic bond dissociation energies (BDEs) of the C-H and N-H bonds in monocyclic aromatic molecules that are representative of the functionalities present in coal. These include six-membered rings (benzene, pyridine, pyridazine, pyrimidine, pyrazine) and five-membered rings (furan, thiophene, pyrrole, oxazole). By comparison of the calculated C-H BDEs with the available experimental values for these aromatic molecules, the B3LYP/6-31G(d) level of theory was selected to calculate the BDEs of polycyclic aromatic hydrocarbons (PAHs), including carbonaceous PAHs (naphthalene, anthracene, pyrene, coronene) and heteroatomic PAHs (benzofuran, benzothiophene, indole, benzoxazole, quinoline, isoquinoline, dibenzofuran, carbazole). The cleavage of a C-H or a N-H bond generates a {sigma} radical that is, in general, localized at the site from which the hydrogen atom was removed. However, delocalization of the unpaired electron results in {approximately} 7 kcal {center{underscore}dot} mol{sup {minus}1} stabilization of the radical with respect to the formation of phenyl when the C-H bond is adjacent to a nitrogen atom in the azabenzenes. Radicals from five-membered rings are {approximately} 6 kcal {center{underscore}dot} mol{sup {minus}1} less stable than those formed from six-membered rings due to both localization of the spin density and geometric factors. The location of the heteroatoms in the aromatic ring affects the C-H bond strengths more significantly than does the size of the aromatic network. Therefore, in general, the monocyclic aromatic molecules can be used to predict the C-H BDE of the large PAHs within 1 kcal {center{underscore}dot} mol{sup {minus}1}.

Barckholtz, C.; Barckholtz, T.A.; Hadad, C.M.

1999-01-27

18

PCM study of the solvent and substituent effects on bond dissociation energies of the C=NO bond  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations are used to estimate the equilibrium C=NO bond dissociation energies (BDEs) for eight X=NO molecule (X = CCl3, C6F5, CH3, CH3CH2, iC3H7, tC4H9, CH2CHCH2, and C6H5CH2). These compounds are studied by employing the hybrid density functional theory (B3LYP, B3PW91, B3P86) methods together with 6-31G** and 6-311G** basis sets and the complete basis set (CBS-QB3) method. The obtained results are compared with the available experimental results. It is demonstrated that B3P86/6-31G** and CBS-QB3 methods are accurate for computing the reliable BDEs for the X=NO molecule. Considering the inevitably computational cost of CBS-QB3 method and the reliability of the B3P86 calculations, B3P86 method with 6-31G** basis set may be more suitable to calculate the BDEs of the C=NO bond. The solvent effects on the BDEs of the C=NO bond are analyzed and it is shown that the C=NO BDEs in a vacuum computed by using B3PW91/6-311G** method are the closest to the computed values in acetontrile and the average solvent effect is 1.48 kcal/mol. Subsequently, the substituent effects of the BDEs of the C=NO bond are further analyzed and it is found that electron denoting group stabilizes the radical and as a result BDE decreases; whereas electron withdrawing group stabilizes the group state of the molecule and thus increases the BDE from the parent molecule.

Li, Xiao-Hong; Tang, Zheng-Xin; Yang, Xiang-Dong

19

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

SciTech Connect

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.

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

20

Bond dissociation energies and radical stabilization energies associated with model peptide-backbone radicals.  

PubMed

Bond dissociation energies (BDEs) and radical stabilization energies (RSEs) have been calculated for a series of models that represent a glycine-containing peptide-backbone. High-level methods that have been used include W1, CBS-QB3, U-CBS-QB3, and G3X(MP2)-RAD. Simpler methods used include MP2, B3-LYP, BMK, and MPWB1K in association with the 6-311+G(3df,2p) basis set. We find that the high-level methods produce BDEs and RSEs that are in good agreement with one another. Of the simpler methods, RBMK and RMPWB1K achieve good accuracy for BDEs and RSEs for all the species that were examined. For monosubstituted carbon-centered radicals, we find that the stabilizing effect (as measured by RSEs) of carbonyl substituents (CX=O) ranges from 24.7 to 36.9 kJ mol(-1), with the largest stabilization occurring for the CH=O group. Amino groups (NHY) also stabilize a monosubstituted alpha-carbon radical, with the calculated RSEs ranging from 44.5 to 49.5 kJ mol(-1), the largest stabilization occurring for the NH2 group. In combination, NHY and CX=O substituents on a disubstituted carbon-centered radical produce a large stabilizing effect ranging from 82.0 to 125.8 kJ mol(-1). This translates to a captodative (synergistic) stabilization of 12.8 to 39.4 kJ mol(-1). For monosubstituted nitrogen-centered radicals, we find that the stabilizing effect of methyl and related (CH2Z) substituents ranges from 25.9 to 31.7 kJ mol(-1), the largest stabilization occurring for the CH3 group. Carbonyl substituents (CX=O) destabilize a nitrogen-centered radical relative to the corresponding closed-shell molecule, with the calculated RSEs ranging from -30.8 to -22.3 kJ mol(-1), the largest destabilization occurring for the CH=O group. In combination, CH2Z and CX=O substituents at a nitrogen radical center produce a destabilizing effect ranging from -19.0 to -0.2 kJ mol(-1). This translates to an additional destabilization associated with disubstitution of -18.6 to -7.8 kJ mol(-1). PMID:16833974

Wood, Geoffrey P F; Moran, Damian; Jacob, Rebecca; Radom, Leo

2005-07-21

21

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

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

22

Renewable energy liberation by nonthermal intermolecular bond dissociation in water and ethanol  

NASA Astrophysics Data System (ADS)

Prior indication that renewable energy can be extracted from hydrogen bonds in water has led to several investigations of the energy balance when bulk liquid is converted into micron scale droplets by directional (nonthermal) forces. The demonstration of this effect has previously involved pulsed high current arcs in water which produce large electrodynamic forces. Here, we show that renewable energy is also liberated during the creation of droplets by electrostatic forces in electrohydrodynamic atomization (electrospray) experiments. Using both ethanol and water, the energy outputs, primarily the droplet kinetic energy, were always greater than the energy inputs, implying that stored energy was liberated from the liquid. The energetics of generic chemical bonding are investigated to demonstrate that although this discovery was not publicly anticipated, it is consistent with conventional theory. This experimental breakthrough should have a major impact on the quest for renewable energy sources, capable of powering electricity generators.

Graneau, N.; Verdoold, S.; Oudakker, G.; Yurteri, C. U.; Marijnissen, J. C. M.

2011-02-01

23

Estimation of the Rh-Rh bond dissociation energy in the (octaethylporphyrinato)rhodium(II) dimer by /sup 1/H NMR line broadening  

SciTech Connect

The octaethylporphyrin dimer ((OEP)Rh)/sub 2/ has been reported to have an interesting range of organometallic reactivity. An estimation of the Rh-Rh bond dissociation energy (BDE) in the dimer from /sup 1/H NMR line broadening studies is reported herein. This value for the dissociation energy has been used in deriving the (R-H)BDE in (OEP)Rh-H and the (Rh-C)BDE in (OEP)Rh-CHO. 19 references, 2 figures.

Wayland, B.B.; Coffin, V.L.; Farnos, M.D.

1988-07-27

24

Bond-specific dissociation following excitation energy transfer for distance constraint determination in the gas phase.  

PubMed

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

Hendricks, Nathan G; Lareau, Nichole M; Stow, Sarah M; McLean, John A; Julian, Ryan R

2014-09-24

25

Photodissociation measurements of bond dissociation energies: Tiz, Vi, Co,`, and Co;  

E-print Network

of predissociationthresholdsasbonddissociationenergiesandperiodictrendsin thebondingof the3d transition metal diatomic neutralsand monocationsare discussed. I. INTRODUCTION Investigationsinto the bonding of small transition metal clusters have beencarried out for many yearsnow. Part in these difficult elec- tronic systems.On one hand, d-orbital contributions to the bonding can strengthenthe bond

Morse, Michael D.

26

Bond-dissociation using hybrid DFT  

NASA Astrophysics Data System (ADS)

The calculation of potential curves and potential surfaces is the main approach for quantum chemical studies of reaction mechanisms. For a sufficient accuracy, qualitatively correct descriptions of bond cleavages and bond formations are required. When large models are used, such as for systems of biological interest, in practice the only available method is DFT. The most common variant is hybrid DFT with the B3LYP functional. In the present study, two cases of bond dissociation using B3LYP are discussed, one for the single O-O bond in hydrogen peroxide, the other one for the hextuple bond in the chromium dimer. Quite accurate results are obtained in both cases.

Siegbahn, Per E. M.; Blomberg, Margareta R. A.

27

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

E-print Network

(BDE) have been used to derive O-O bond strengths. From these data it was concluded that the strength. The BDE of the O-O bond in diacyl peroxides was estimated by this method to be only 30 ( 1 kcal/mol.1b corresponds to 50.5 kcal/mol for the BDE at 298 K ((H°298 - H°0) ) 1.79 kcal/mol).8c It has been assumed

Schlegel, H. Bernhard

28

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

NASA Astrophysics Data System (ADS)

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.

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

2014-01-01

29

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

PubMed

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

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

2014-01-28

30

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

SciTech Connect

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.

Oyeyemi, Victor B. [Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544 (United States)] [Department of Chemical and Biological Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Krisiloff, David B. [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States)] [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States); Keith, John A.; Libisch, Florian [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States)] [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Pavone, Michele [Department of Chemical Sciences, University of Napoli Federico II, Napoli 80120 (Italy)] [Department of Chemical Sciences, University of Napoli Federico II, Napoli 80120 (Italy); Carter, Emily A., E-mail: eac@princeton.edu [Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey 08544 (United States); Program in Applied and Computational Mathematics, Princeton University, Princeton, New Jersey 08544 (United States); Andlinger Center for Energy and the Environment, Princeton University, Princeton, New Jersey 08544 (United States)

2014-01-28

31

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

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.

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

32

Bond dissociation energies of c10 and c18 methyl esters from local multireference averaged-coupled pair functional theory.  

PubMed

We previously developed a fast, local, reduced scaling Cholesky-decomposed multireference averaged-coupled pair functional (CD-LMRACPF2) method, which takes advantage of the locality of dynamic correlation and numerical approximations such as Cholesky decomposition and integral screening. Motivated by the desire to study large biodiesel methyl ester molecules, here we validate CD-LMRACPF2 for the computation of bond dissociation energies (BDEs) in a suite of oxygenated molecules, and show that the low-cost method is very accurate compared to the conventional variant. We then demonstrate the power of CD-LMRACPF2 for fast and accurate computation of energies of molecules containing up to 13 second-row atoms within a polarized triple-? (cc-pVTZ) basis set. We use biodiesel methyl esters as a chemically interesting model system and furnish BDEs of C10 and C18 methyl esters, with the latter performed within a cc-pVDZ basis set. We describe trends in the BDEs and explain how structural (isomeric) differences affect BDEs, as well as discuss implications of BDE trends for biodiesel physical and chemical properties. PMID:25775253

Oyeyemi, Victor B; Dieterich, Johannes M; Krisiloff, David B; Tan, Ting; Carter, Emily A

2015-04-01

33

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

34

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

SciTech Connect

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

Carta, V.; Ciccioli, A., E-mail: guido.gigli@uniroma1.it, E-mail: andrea.ciccioli@uniroma1.it; Gigli, G., E-mail: guido.gigli@uniroma1.it, E-mail: andrea.ciccioli@uniroma1.it [Dipartimento di Chimica, Sapienza Università di Roma, p.le A. Moro 5, 00185 Roma (Italy)

2014-02-14

35

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

PubMed

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. PMID:24527913

Carta, V; Ciccioli, A; Gigli, G

2014-02-14

36

Linear free energy relationships in C-N bond dissociations in molecular ions of 4-substituted N-(2-furylmethyl)anilines in the gas phase.  

PubMed

The substituent effect on the reactivity of the C-N bond of molecular ions of 4-substituted N-(2-furylmethyl)anilines toward two dissociation pathways was studied. With this aim, six of these compounds were analyzed by mass spectrometry using electron ionization with energies between 7.8 and 69.9 eV. Also, the UB3LYP/6-31G (d,p) and UHF/6-31G (d, p) levels of theory were used to calculate the critical energies (reaction enthalpies at 0 K) of the processes that lead to the complementary ions [C(5)H(5)O](+) and [M - C(5)H(5)O](+), assuming structures that result from the heterolytic and homolytic C-N bond cleavages of the molecular ions, respectively. A kinetic approach proposed in the 1960s was applied to the mass spectral data to obtain the relative rate coefficients for both dissociation channels from ratios of the peak intensities of these ions. Linear relationships were obtained between the logarithms of the relative rate coefficients and the calculated critical energies and other thermochemical properties, whose slopes showed to be conditioned by the energy provided to the compounds within the ion source. Moreover, it was found that the dissociation that leads to [C(5)H(5)O](+) is a process strongly dependent upon the electron withdrawing or donating properties of the substituent, favored by those factors that destabilize the molecular ion. On the contrary, the dissociation that leads to [M - C(5)H(5)O](+) is indifferent to the polar electronic effects of the substituent. The abundance of both products was governed by the rule of Stevenson-Audier, according to which the major ion is the one of less negative electronic affinity. PMID:17687763

Solano Espinoza, Eduardo A; Stashenko, Elena; Martínez, Jairo; Mora, Uriel; Kouznetsov, Vladimir

2007-11-01

37

Bond dissociation energies of H{sub 2}NX compounds. Comparison with CH{sub 3}X, HOX, and FX compounds  

SciTech Connect

The bond dissociation energies (BDE) of H{sub 2}NNH{sub 2}, HONH{sub 2} and FNH{sub 2} have been calculated using Pople`s G1 procedure, and the known BDE for hydrazine is well reproduced. The BDE`s of MeX, H{sub 2}NX, HOX and FX derivatives where X = Me, H{sub 2}N, HO, and F, are compared, and the differences are related to changes in hybridization, internal Coulombic stabilization and lone pair-lone pair repulsion. 20 refs., 6 figs., 6 tabs.

Wiberg, K.B. [Yale Univ., New Haven CT (United States)

1992-07-09

38

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

PubMed

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. PMID:24832350

DiLabio, Gino A; Koleini, Mohammad

2014-05-14

39

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

SciTech Connect

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.

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

40

Co?C bond dissociation energy and reaction volume change of 2',5'-dideoxyadenosylcobalamin studied by laser-induced time-resolved photoacoustic calorimetry  

NASA Astrophysics Data System (ADS)

Time resolved photoacoustic calorimetry (PAC) was applied to a study of the photolysis of a coenzyme B 12 analog 2',5'-dideoxyadenosylcobalamin, which lacks an ?OH group at the 2' position of ribofuranose ring. In aqueous solution, we report for the first time the quantum yield ? d (0.25±0.02), Co?C bond dissociation energy (BDE; 31.8±2.5 kcal mol -1) and reaction volume change ?V R (6.5±0.5 ml mol -1) due to conformation changes of the corrin ring and its side chains accompanying the cleavage of the Co?C bond. These values for the analog are very similar to those for the natural cofactor. Based our results and previous studies, a possible explanation for the similarity in their structure and properties versus the large difference in their enzymatic activity is discussed.

Chen, Hao; Li, Gang; Zhang, Fei Fei; Sun, Li; Chen, Hui Lan; Zhang, Shu Yi

2003-10-01

41

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

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.

Salta, Zoi; Kosmas, Agnie Mylona [Department of Chemistry, University of Ioannina, Ioannina 45110 (Greece); Lesar, Antonija [Department of Physical and Organic Chemistry, Jožef Stefan Institute, Jamova 39, SI-1000, Ljubljana (Slovenia)

2014-10-06

42

Intrinsic affinities of alkali cations for 15-crown-5 and 18-crown-6: Bond dissociation energies of gas-phase M{sup +}-crown ether complexes  

SciTech Connect

Bond dissociation energies (BDEs) of M{sup +}[c-(C{sub 2}H{sub 4}O){sub 5}] and M{sup +}[c-(C{sub 2}H{sub 4}O){sub 6}] for M = Na, K, Rb, and Cs are reported. The BDEs are determined experimentally by analysis of the thresholds for collision-induced dissociation of the cation-crown ether complexes by xenon measured by using guided ion beam mass spectrometry. In all cases, the primary and lowest energy dissociation channel observed experimentally in endothermic loss of the ligand molecule. The cross section thresholds are interpreted to yield 0 and 298 K BDEs after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and unimolecular decay rates. For both 18-crown-6 and 15-crown-5, the BDEs decrease monotonically with increasing cation size. These results indicate that the intrinsic affinity of c-(C{sub 2}H{sub 4}O){sub 5} and c-(C{sub 2}H{sub 4}O){sub 6} for M{sup +} is determined principally by the charge density of the cation not by the ratio of the ionic radius to the cavity size. The BDEs reported here are in fair agreement with recent ab initio calculations at the MP2 level with 6-31+G* basis sets. The experimental values are systematically smaller than the computed values by 8 {+-} 2 kJ/mol per metal-oxygen interaction. The existence of less strongly bound isomers in the experimental apparatus for Rb{sup +}(15-crown-5) and Cs{sup +}(15-crown-5) appears likely, but their absence for Na{sup +} and K{sup +} complexes indicates interesting metal-dependent dynamics to the formation of such isomers.

More, M.B.; Ray, D.; Armentrout, P.B.

1999-01-20

43

A theoretical study of the change in homolytic bond dissociation energy on conversion of A-B to A-B sup + H  

SciTech Connect

The bond dissociation energies (BDE) for the homolytic cleavage of a number of isoelectronic A-B dimers have been calculated to third order in Moeller-Plesset perturbation theory with the 6-31G** basis set. In particular, BDE's have been calculated for A-B {yields} A* + *B, with A = CH{sub 3}, NH{sub 2}, OH, and F and B = CH{sub 3}, NH{sub 2}, OH, F, N{sup +}H{sub 3}, O{sup +}H{sub 2}, and F{sup +}H. It is shown that a substantial increase in the BDE occurs upon protonation of A-B and that the more electronegative the element B, the greater the change in BDE that accompanies the protonation of B. These trends are rationalized by application of the earlier discussions of Pauling and Allred and shown to be consistent with known chemical transformations.

Boyd, R.J.; Glover, J.N.M.; Pincock, J.A. (Dalhousie Univ., Halifax, Nova Scotia (Canada))

1989-07-05

44

Does Electron Capture Dissociation Cleave Protein Disulfide Bonds?  

PubMed Central

Peptide and protein characterization by mass spectrometry (MS) relies on their dissociation in the gas phase into specific fragments whose mass values can be aligned as ‘mass ladders’ to provide sequence information and to localize possible posttranslational modifications. The most common dissociation method involves slow heating of even-electron (M+n H)n+ ions from electrospray ionization by energetic collisions with inert gas, and cleavage of amide backbone bonds. More recently, dissociation methods based on electron capture or transfer were found to provide far more extensive sequence coverage through unselective cleavage of backbone N–C? bonds. As another important feature of electron capture dissociation (ECD) and electron transfer dissociation (ETD), their unique unimolecular radical ion chemistry generally preserves labile posttranslational modifications such as glycosylation and phosphorylation. Moreover, it was postulated that disulfide bond cleavage is preferred over backbone cleavage, and that capture of a single electron can break both a backbone and a disulfide bond, or even two disulfide bonds between two peptide chains. However, the proposal of preferential disulfide bond cleavage in ECD or ETD has recently been debated. The experimental data presented here reveal that the mechanism of protein disulfide bond cleavage is much more intricate than previously anticipated. PMID:24363980

Ganisl, Barbara; Breuker, Kathrin

2012-01-01

45

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

PubMed

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

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

2014-10-01

46

Measuring Bond Energy of an Ionic Compound  

NSDL National Science Digital Library

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.

2007-08-09

47

Three methods to measure RH bond energies  

SciTech Connect

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.

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

48

Enthalpies of formation, bond dissociation energies, and molecular structures of the n-aldehydes (acetaldehyde, propanal, butanal, pentanal, hexanal, and heptanal) and their radicals.  

PubMed

Aldehydes are important intermediates and products in a variety of combustion and gas-phase oxidation processes, such as in low-temperature combustion, in the atmosphere, and in interstellar media. Despite their importance, the enthalpies of formation and bond dissociation energies (BDEs) for the aldehydes are not accurately known. We have determined enthalpies of formation for acetaldehyde, propanal, and butanal from thermodynamic cycles, using experimentally measured reaction and formation enthalpies. All enthalpy values used for reference molecules and reactions were first verified to be accurate to within around 1 kcal mol-1 using high-level ab initio calculations. Enthalpies of formation were found to be -39.72 +/- 0.16 kcal mol-1 for acetaldehyde, -45.18 +/- 1.1 kcal mol-1 for propanal, and -49.27 +/- 0.16 kcal mol-1 for butanal. Enthalpies of formation for these three aldehydes, as well as for pentanal, hexanal, and heptanal, were calculated using the G3, G3B3, and CBS-APNO theoretical methods, in conjunction with bond-isodesmic work reactions. On the basis of the results of our thermodynamic cycles, theoretical calculations using isodesmic work reactions, and existing experimental measurements, we suggest that the best available formation enthalpies for the aldehydes acetaldehyde, propanal, butanal, pentanal, hexanal, and heptanal are -39.72, -45.18, -50.0, -54.61, -59.37, and -64.2 kcal mol-1, respectively. Our calculations also identify that the literature enthalpy of formation of crotonaldehyde is in error by as much as 1 kcal mol-1, and we suggest a value of -25.1 kcal mol-1, which we calculate using isodesmic work reactions. Bond energies for each of the bonds in the aldehydes up to pentanal were calculated at the CBS-APNO level. Analysis of the BDEs reveals the R-CH(2)CH=O to be the weakest bond in all aldehydes larger than acetaldehyde, due to formation of the resonantly stabilized vinoxy radical (vinyloxy radical/formyl methyl radical). It is proposed that the vinoxy radical as well as the more commonly considered formyl and acetyl radicals are important products of aldehyde combustion and oxidation, and the reaction pathways of the vinoxy, formyl, and acetyl radicals are discussed. Group additivity values for the carbon-oxygen-hydrogen groups common to the aldehydes are also determined. Internal rotor profiles and electrostatic potential surfaces are used to study the dipole induced dipole-dipole interaction in the synperiplanar conformation of propanal. It is proposed that the loss of this dipole-dipole interaction in RC(.-)HCH(2)CH=O radicals causes a ca. 1-2 kcal mol-1 decrease in the aldehyde C-H and C-C bond energies corresponding to RC(.-)HCH(2)CH=O radical formation. PMID:17134166

da Silva, Gabriel; Bozzelli, Joseph W

2006-12-01

49

Exploring the energy disposal immediately after bond-breaking in solution: the wavelength-dependent excited state dissociation pathways of para-methylthiophenol.  

PubMed

A wavelength-resolved (?pump = 295, 285, 270, and 267 nm) photodissociation study of para-methylthiophenol (p-MePhSH) in ethanol solution has been performed using femtosecond transient absorption (TA) spectroscopy, and the results compared with those from studies of the corresponding photodissociation in cyclohexane solution at 270 nm. Anisotropy spectra are used to identify the electronic character of the initially populated excited state(s). S-H bond fission is found to occur via the dissociative S2(1(1)??*) state, which can be populated directly, or by ultrafast nonradiative transitions from the S3(2(1)??*) state, or by very efficient tunneling from the S1(1(1)??*) state, depending on the excitation wavelength, in line with conclusions from previous gas-phase studies of this same molecular photodissociation (Oliver, T. A. A.; King, G. A.; Tew, D. P.; Dixon R. N.; Ashfold, M. N. R. J. Phys. Chem. A 2012, 116, 12444). p-MePhS radicals are observed on a time scale faster than the instrument response at all wavelengths, but the available time resolution affords a rare opportunity to explore the branching between different electronic states of a product (the à and X? states of the p-MePhS radical in this case). The present study provides estimates of this branching in the products formed immediately after the first pass through the conical intersection (CI) between the S2 and S0 states. At 270 nm, for example, we identify a marked population inversion in the radical products, in contrast to the reported gas phase behavior. The finding that the contrast in branching ratio is largest between cyclohexane solution and the gas phase, with ethanol being intermediate, can be rationalized by recognizing the differing distributions of the S-H torsion angle (relative to the ring plane) in a room temperature solution compared with those in a jet-cooled molecular beam. The available time resolution also allows exploration of the electronic quenching of nascent à state radicals as solvent motion encourages recrossing of the S2/S0 CI. The average separation distance, , between the H + p-MePhS products arising in successful dissociation events is seen to increase with decreasing photolysis wavelength. This finding accords with the previous gas phase results, which determined that most of the excess energy following population of the dissociative S2 state (directly, or by ultrafast coupling from the S3 state) is released as product translation, and the expectation that should scale with the total kinetic energy release. The present work also confirms that geminate recombination of the H + p-MePhS products leads not just to reformation of parent p-MePhSH molecules but also to alternative adducts wherein the H atom bonds to the benzene ring. Analysis of the present data and results of high level ab initio calculations together with recent UV-IR pump-probe measurements (Murdock, D.; Harris, S. J.; Karsili, T. N. V.; Greetham, G. M.; Clark, I. P.; Towrie, M.; Orr-Ewing, A. J.; Ashfold, M. N. R. J. Phys. Chem. Lett. 2012, 3, 3715) allows identification of the likely adduct structures. PMID:24047130

Zhang, Yuyuan; Oliver, Thomas A A; Das, Saptaparna; Roy, Anirban; Ashfold, Michael N R; Bradforth, Stephen E

2013-11-21

50

Dissociation energies and charge distribution of the Co-NO bond for nitrosyl-alpha,beta,gamma,delta-tetraphenylporphinatocobalt(II) and nitrosyl-alpha,beta,gamma,delta-tetraphenylporphinatocobalt(III) in benzonitrile solution.  

PubMed

The first two series of Co-NO bond dissociation enthalpies in benzonitrile solution were determined for 12 cobalt(II) nitrosyl porphyrins and for 12 cobalt(III) nitrosyl porphyrins by titration calorimetry with suitable thermodynamic cycles. The results display that the energy scales of the heterolytic Co(III)-NO bond dissociation, the homolytic Co(III)-NO bond dissociation, and the homolytic Co(II)-NO bond dissociation are 14.7-23.2, 15.1-17.5, and 20.8-24.6 kcal/mol in benzonitrile solution, respectively, which not only indicates that the thermodynamic stability of cobalt(II) nitrosyl porphyrins is larger than that of the corresponding cobalt(III) nitrosyl porphyrins for homolysis in benzonitrile solution but also suggests that both cobalt(III) nitrosyl porphyrins and cobalt(II) nitrosyl porphyrins are excellent NO donors, and in addition, cobalt(III) nitrosyl porphyrins are also excellent NO(+) contributors. Hammett-type linear free energy analyses suggest that the nitrosyl group carries negative charges of 0.49 +/- 0.06 and 0.27 +/- 0.04 in T(G)PPCo(II)NO and in T(G)PPCo(III)NO, respectively, which indicates that nitric oxide is an electron-withdrawing group both in T(G)PPCo(II)NO and in T(G)PPCo(III)NO, behaving in a manner similar to Lewis acids rather than to Lewis bases. The energetic and structural information disclosed in the present work is believed to furnish hints to the understanding of cobalt nitrosyl porphyrins' biological functions in vivo. PMID:12175249

Zhu, Xiao-Qing; Li, Qian; Hao, Wei-Fang; Cheng, Jin-Pei

2002-08-21

51

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

SciTech Connect

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

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

2011-04-21

52

Comments on reevaluation of the bond-dissociation energies (. Delta. H sub DBE ) for H-OH, H-OOH, H-OO sup minus , H-O sup sm bullet , H-OO sup minus , and H-OO sup sm bullet double prime  

SciTech Connect

In a recent letter by Sawyer, it was suggested that new values of the bond dissociation energies (BDE), defined for bond-breaking processes in the gas phase at 298 K, for a number of hydrogen- and oxygen-containing species could be determined from half-cell potentials. Discrepancies with accepted values for HO{sub 2} and HO{sub 2}{sup {minus}} were noted. We wish to point out that the bond dissociation energies for H-OO and H-OO{sup {minus}} that were derived by Sawyer are in serious disagreement with those established in the past decade by gas-phase chemical kinetics and photoelectron spectroscopy. These results were not cited by Sawyer. Moreover, computations utilizing half-cell potentials for the derivation of bond dissociation energies must account for substantial solvation effects. When properly calculated, these BDEs are, in fact, in accord with established values.

Golden, D.M. (SRI International, Menlo Park, CA (USA)); Bierbaum, V.M. (Univ. of Colorado, Boulder (USA)); Howard, C.J. (Aeronomy Laboratory, Boulder, CO (USA))

1990-06-28

53

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

PubMed Central

The oxidative modification of polyunsaturated fatty acids which occurs through enzymatic and non-enzymatic processes is typically initiated by the attachment of molecular oxygen to an unsaturated fatty acyl chain forming a lipid hydroperoxide (LOOH). Enzymatic pathways are critical for cellular homeostasis but aberrant lipid peroxidation has been implicated in important pathologies. Analysis of primary oxidation products such as hydroperoxides has proven challenging for a variety of reasons. While negative ion electrospray ionization has been used for the specific detection of some LOOH species, hydroperoxide dehydration in the ion source has been a significant drawback. Here we describe positive ion electrospray ionization of ammoniated 13-hydroperoxy-9Z,11E-octadecadienoyl cholesterol and 9-hydroperoxy-10E,12Z-octadecadienoyl cholesterol, [M + NH4]+, following normal phase high-pressure liquid-chromatography. Dehydration in the ion source was not prevalent and the ammoniated molecular ion was the major species observed. Collisionally induced dissociation of the two positional isomers yielded unique product ion spectra resulting from carbon-carbon cleavages along their acyl chains. Further investigation of this behavior revealed that complex collision induced dissociations were initiated by scission of the hydroperoxide bond that drove subsequent acyl chain cleavages. Interestingly some of the product ions retained the ammonium nitrogen through the formation of covalent carbon-nitrogen or oxygen-nitrogen bonds. These studies were carried out using hydroperoxy-octadecadienoate cholesteryl esters as model compounds, however the observed mechanisms of [LOOH+NH4]+ ionization and dissociation are likely applicable to the analysis of other lipid hydroperoxides and may serve as the basis for selective LOOH detection as well as aid in the identification of unknown lipid hydroperoxides. PMID:21472521

Hutchins, Patrick M.; Murphy, Robert C.

2013-01-01

54

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

PubMed

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. PMID:19405499

Hayes, Carrigan J; Hadad, Christopher M

2009-11-12

55

Combustion Pathways of the Alkylated Heteroaromatics: Bond Dissociation Enthalpies and Alkyl Group Fragmentations  

NASA Astrophysics Data System (ADS)

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.

Hayes, Carrigan J.; Hadad, Christopher M.

2009-04-01

56

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

SciTech Connect

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.

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

2009-11-15

57

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

SciTech Connect

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

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

2008-05-30

58

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

E-print Network

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

Fayer, Michael D.

59

Reconfiguration and dissociation of bonded hydrogen in silicon by energetic ions  

SciTech Connect

We report in situ infrared measurements of ion-induced reconfiguration and dissociation of bonded hydrogen associated with various defects in silicon at low temperatures. Defect-associated Si-H complexes were prepared by low-temperature proton implantation in silicon followed by room-temperature annealing. As a result of subsequent low-temperature {sup 3}He ion irradiation, we observed (1) ion-induced dissociation of Si-H complexes, (2) a notable difference in the dissociation rate of interstitial- and vacancy-type defects, and, unexpectedly, (3) the growth of bond-centered hydrogen, which is generally observed in association with low-temperature proton implantation. These findings provide insight into the mechanisms responsible for the dissociation of hydrogen bonds in silicon and thus have important implications for bond-selective nanoscale engineering and the long-term reliability of state-of-the-art silicon semiconductor and photovoltaic devices.

Nageswara Rao, S. V. S. [Department of Physics, Pondicherry University, Puducherry 605014 (India); Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Dixit, S. K. [Interdisciplinary Materials Science Program, Vanderbilt University, Nashville, Tennessee 37235 (United States); Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University, Tennessee TN 37235 (United States); Luepke, G. [Department of Applied Science, College of William and Mary, Williamsburg, Virginia 23187 (United States); Tolk, N. H. [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University, Tennessee TN 37235 (United States); Feldman, L. C. [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Interdisciplinary Materials Science Program, Vanderbilt University, Nashville, Tennessee 37235 (United States); Vanderbilt Institute of Nanoscale Science and Engineering, Vanderbilt University, Tennessee TN 37235 (United States); Institute for Advanced Materials Devices and Nanotechnology, Rutgers University, Piscataway, NJ 08901 (United States)

2011-01-15

60

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

E-print Network

in the most basic and important chemical and biological phenomena.1-3 The strength of hydrogen bonds lies: Chemical Exchange Two-Dimensional Infrared Vibrational Echo Spectroscopy Junrong Zheng, Kyungwon Kwak, Xin and dissociation (chemical exchange) of this type of three-centered hydrogen bond complex were observed in real

Fayer, Michael D.

61

High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formation of cobalt carbide (CoC) and its cation (CoC+).  

PubMed

The ionization energy (IE) of CoC and the 0 K bond dissociation energies (D0) and the heats of formation at 0 K (?H°f0) and 298 K (?H°f298) for CoC and CoC(+) are predicted by the wavefunction based coupled-cluster theory with single, double, triple and quadruple excitations (CCSDTQ) and complete basis set (CBS) approach. The CCSDTQ?CBS calculations presented here involve the approximation to the CBS limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy, high-order correlation, core-valence (CV) electronic, spin-orbit coupling, and scalar relativistic effect corrections. The present calculations provide the correct symmetry, (1)?(+), for the ground state of CoC(+). The CCSDTQ?CBS IE(CoC) = 7.740 eV is found in good agreement with the experimental IE value of 7.73467 ± 0.00007 eV, determined in a two-color laser photoion and pulsed field ionization-photoelectron study. This work together with the previous experimental and theoretical investigations support the conclusion that the CCSDTQ?CBS method is capable of providing reliable IE predictions for 3d-transition metal carbides, such as FeC, CoC, and NiC. Among the single-reference based coupled-cluster methods and multi-reference configuration interaction (MRCI) approach, the CCSDTQ and MRCI methods give the best predictions to the harmonic frequencies ?e (?e (+)) = 956 (992) and 976 (1004) cm(-1) and the bond lengths re (re (+)) = 1.560 (1.528) and 1.550 (1.522) A?, respectively, for CoC (CoC(+)) in comparison with the experimental values. The CCSDTQ?CBS calculations give the prediction of D0(Co(+)-C) - D0(Co-C) = 0.175 eV, which is also consistent with the experimental determination of 0.14630 ± 0.00014 eV. The theoretical results show that the CV and valence-valence electronic correlations beyond CCSD(T) wavefunction and the relativistic effect make significant contributions to the calculated thermochemical properties of CoC?CoC(+). For the experimental D0 and ?H(o) f0 values of CoC?CoC(+), which are not known experimentally, we recommend the following CCSDTQ?CBS predictions: ?H(o) f0(CoC) = 775.7 kJ?mol and ?H(o) f0(CoC(+)) = 1522.5 kJ?mol, ?H(o) f298(CoC) = 779.2 kJ?mol and ?H(o) 298(CoC(+)) = 1526.0 kJ?mol. PMID:23485289

Lau, Kai-Chung; Pan, Yi; Lam, Chow-Shing; Huang, Huang; Chang, Yih-Chung; Luo, Zhihong; Shi, Xiaoyu; Ng, C Y

2013-03-01

62

Effects of Peptide Backbone Amide-to-Ester Bond Substitution on the Cleavage Frequency in Electron Capture Dissociation and Collision-Activated Dissociation  

Microsoft Academic Search

Probing the mechanism of electron capture dissociation on variously modified model peptide polycations has resulted in discovering\\u000a many ways to prevent or reduce $$ {\\\\text{N}} - {{\\\\text{C}}_? } $$ bond fragmentation. Here we report on a rare finding of how to increase the backbone bond dissociation rate. In a number\\u000a of model peptides, amide-to-ester backbone bond substitution increased the frequency

Frank Kjeldsen; Roman A. Zubarev

2011-01-01

63

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

64

Redox-induced fluoride ligand dissociation stabilized by intramolecular hydrogen bonding.  

PubMed

Chemical reduction of a tripodal Cu(ii)-F complex containing pendent hydroxyl groups results in the partial dissociation of a F(-) ligand from Cu. The resulting Cu(i) complex is characterized as containing an outer sphere F(-) anion 'captured' by hydrogen bonds. The pendent hydroxyl groups were found to be crucial for reductive stability. PMID:25322967

Moore, Cameron M; Szymczak, Nathaniel K

2014-10-17

65

Theoretical dissociation energies for ionic molecules  

NASA Technical Reports Server (NTRS)

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.

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

1986-01-01

66

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

PubMed

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 Å and an axial-equatorial distance of 2.060 Å. 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

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

2012-04-10

67

Coupling of disulfide bond and distal histidine dissociation in human ferrous cytoglobin regulates ligand binding.  

PubMed

Earlier kinetics studies on cytoglobin did not assign functional properties to specific structural forms. Here, we used defined monomeric and dimeric forms and cysteine mutants to show that an intramolecular disulfide bond (C38-C83) alters the dissociation rate constant of the intrinsic histidine (H81) (?1000 fold), thus controlling binding of extrinsic ligands. Through time-resolved spectra we have unequivocally assigned CO binding to hexa- and penta-coordinate forms and have made direct measurement of histidine rebinding following photolysis. We present a model that describes how the cysteine redox state of the monomer controls histidine dissociation rate constants and hence extrinsic ligand binding. PMID:25601563

Beckerson, Penny; Reeder, Brandon J; Wilson, Michael T

2015-02-13

68

Dissociation energies of some high temperature molecules containing aluminum  

NASA Technical Reports Server (NTRS)

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.

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

1972-01-01

69

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

E-print Network

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

Reisler, Hanna

70

Ion kinetic energy distributions from dissociative photoionization of molecular hydrogen  

Microsoft Academic Search

The present note provides kinetic energy distributions for the dissociative photoionization of ground and vibrationally excited H2 to the dissociative continuum of the ls sigma-g state of H2(+). Continuum fractions for all possible v'' concerned are tabulated as well. The Franck-Condon factor (square of vibrational wavefunction overlap) is involved in the calculation of the probability of dissociative transitions of the

A. L. Ford; Kate Kirby Docken

1975-01-01

71

Calculation of systematic set of bond dissociation enthalpies of polyhalogenated benzenes  

Microsoft Academic Search

The bond dissociation enthalpies (BDEs) of polyhalogenated benzenes were calculated by using the G2M(CC), B3LYP\\/6-311G(2df,p), and B3LYP\\/6-311G(d,p) methods. The BDEs of C–H and C–X (X=F, Cl, and Br) calculated by these three methods well reproduced the experimental BDEs, within 1.2, 2.3, and 4.5kcal\\/mol, respectively. The analysis of the basis set dependence of the BDEs showed that the BDEs calculated by

Toshio Watanabe; Zun-Yao Wang; Ohgi Takahashi; Kenji Morihashi; Osamu Kikuchi

2004-01-01

72

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

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, ?H°f,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 ?fH°298 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

Auzmendi-Murua, Itsaso; Bozzelli, Joseph W

2014-05-01

73

Accurate In Bond Energies  

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

74

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

E-print Network

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.

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

2015-02-20

75

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

SciTech Connect

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.

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

2011-01-01

76

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

Microsoft Academic Search

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

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

2002-01-01

77

H-atom high-n Rydberg time-of-flight spectroscopy of C–H bond fission in acrolein dissociated at 193 nm  

Microsoft Academic Search

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

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

2002-01-01

78

Design of an infrared laser pulse to control the multiphoton dissociation of the Fe-CO bond in CO-heme compounds  

Microsoft Academic Search

Optimal control theory is used to design a laser pulse for the multiphoton dissociation of the Fe-CO bond in the CO-heme compounds. The study uses a hexacoordinated iron-porphyrin-imidazole-CO complex in its ground electronic state as a model for CO liganded to the heme group. The potential energy and dipole moment surfaces for the interaction of the CO ligand with the

Sitansh Sharma; Harjinder Singh; Jeremy N. Harvey; Gabriel G. Balint-Kurti

2010-01-01

79

Theoretical Study of the C-Cl Bond Dissociation Enthalpy and Electronic Structure of Substituted Chlorobenzene Compounds  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations were used to estimate the bond dissociation energies (BDEs) for 13 substituted chlorobenzene compounds. These compounds were studied by the hybrid density functional theory (B3LYP, B3PW91, B3P86) methods together with 6-31G** and 6-311G** basis sets. The results show that B3P86/6-311G** method is the best method to compute the reliable BDEs for substituted chlorobenzene compounds which contain the C-Cl bond. It is found that the C-Cl BDE depends strongly on the computational method and the basis sets used. Substituent effect on the C-Cl BDE of substituted chlorobenzene compounds is further discussed. It is noted that the effects of substitution on the C-Cl BDE of substituted chlorobenzene compounds are very insignificant. The energy gaps between the HOMO and LUMO of studied compounds are also investigated and from this data we estimate the relative thermal stability ordering of substituted chlorobenzene compounds.

Zhang, Rui-zhou; Li, Xiao-hong; Zhang, Xian-zhou

2009-06-01

80

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

NASA Technical Reports Server (NTRS)

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

Scott, Carl D.; Smalley, Richard E.

2002-01-01

81

Computational Study of Bond Dissociation Enthalpies for Lignin Model Compounds: $\\beta$-5 Arylcoumaran  

SciTech Connect

The biopolymer lignin is a potential source of valuable chemicals. The $\\beta$-5 linkage comprises $\\sim$10\\% of the linkages in lignin. Density Functional Theory (DFT) was used to calculate the $\\alpha$C-O and $\\alpha$C-$\\beta$C bond dissociation enthalpies (BDEs) for $\\beta$-5 models with varied substituents, which are important for understanding initial lignin decomposition. The $\\alpha$C-O ($\\alpha$C-$\\beta$C) BDEs were in the range of 40-44 (57-62) kcal/mol. The products resulting from either homolysis are bi-radicals with multi-determinant character in the singlet electronic state. Multiconfiguration self-consistent field (MCSCF) theory results were used to verify that unrestricted DFT and broken-symmetry DFT were sufficient to study these reactions.

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

2012-01-01

82

Computational study of bond dissociation enthalpies for lignin model compounds: ?-5 Arylcoumaran  

NASA Astrophysics Data System (ADS)

The biopolymer lignin is a potential source of valuable chemicals. The ?-5 linkage comprises ˜10% of the linkages in lignin. Density Functional Theory (DFT) was used to calculate the C?-O and C?-C? bond dissociation enthalpies (BDEs) for ?-5 models with varied substituents, which are important for understanding initial lignin decomposition. The C?-O (C?-C?) BDEs were in the range of 40-44 (57-62) kcal/mol. The products resulting from either homolysis are bi-radicals with multi-determinant character in the singlet electronic state. Multiconfiguration self-consistent field (MCSCF) theory results were used to verify that unrestricted DFT and broken-symmetry DFT were sufficient to study these reactions.

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

2012-08-01

83

Comparative computational analysis of some nitramine and difluoramine structures, dissociation energies and heats of formation  

NASA Astrophysics Data System (ADS)

Density functional methods have been used to compute the optimized geometries, dissociation energies, and gas phase heats of formation of several difluoramines (in which the -NF2 is attached to a nitrogen) and the corresponding nitramines. The -NF2 groups are found to be pyramidal, in contrast to the planarity of the -NO2. In each instance, one N-F bond length is at least 0.1 A longer than the other, while the N-N bonds are anomalously short. For the molecules and properties studied, the effects of -NO2 and -NF2 (on nitrogen) do not differ dramatically. Replacing -N-NO2 by -N-NF2 affects the dissociation energies of other N-NO2 and C-NO2 bonds only slightly (2-3 kcal/mole); however the N-NF2 bonds are 3-6 kcal/mole stronger than the N-NO2 that were replaced. The difluoramine heats of formation are less positive, by 15-17 kcal/mole, than those of the corresponding nitramines.

Politzer, Peter; Lane, Pat; Grice, M. E.; Concha, Monica C.; Redfern, Paul C.

1994-11-01

84

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

PubMed

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 alpha-helices with the recent experimental results on ECD of alpha-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 alpha-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 alpha-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[Single Bond]C(alpha) bond. The introduced here way of excitation energy generation and transfer may significantly advance ECD understanding and complement existing ECD mechanisms. PMID:19044894

Pouthier, Vincent; Tsybin, Yury O

2008-09-01

85

Energy and Entropy Effects in Dissociation of Peptide Radical Anions  

SciTech Connect

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

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

2012-04-15

86

Prediction of bond dissociation enthalpy of antioxidant phenols by support vector machine.  

PubMed

Antioxidants play crucial roles in scavenging oxidative damages arising from reactive oxygen species. Bond dissociation enthalpy (BDE) of phenolic O-H bond has well been accepted as an indicator of antioxidant activity since phenols donate the hydrogen atom to the free radicals thereby neutralizing its toxic effect. The BDEs from a data set of 39 antioxidant phenols were modeled using computationally inexpensive quantum chemical descriptors with multiple linear regression (MLR), partial least squares (PLS), and support vector machine (SVM). The molecular descriptors of the phenols were derived from calculations at the following theoretical levels: AM1, HF/3-21g(d), B3LYP/3-21g(d), and B3LYP/6-31g(d). Results indicated that when MLR and PLS were used as the regression methods, B3LYP/3-21g(d) gave the best performance with leave-one-out cross-validated correlation coefficients (r) of 0.917 and 0.921, respectively, while the semiempirical AM1 provided slightly lower r of 0.897 and 0.888, respectively. When SVM was used as the regression method no significant difference in the accuracy was observed for models using B3LYP/3-21g(d) and AM1 as indicated by r of 0.968 and 0.966, respectively. The quantitative structure-property relationship (QSPR) model of BDE discussed in this study offers great potential for the design of novel antioxidant phenols with robust properties. PMID:18499490

Nantasenamat, Chanin; Isarankura-Na-Ayudhya, Chartchalerm; Naenna, Thanakorn; Prachayasittikul, Virapong

2008-09-01

87

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

NASA Astrophysics Data System (ADS)

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.

Nam, Pham Cam; Nguyen, Minh Tho

2013-03-01

88

Discovery and mechanistic studies of facile N-terminal C?-C bond cleavages in the dissociation of tyrosine-containing peptide radical cations.  

PubMed

Fascinating N-terminal C?-C bond cleavages in a series of nonbasic tyrosine-containing peptide radical cations have been observed under low-energy collision-induced dissociation (CID), leading to the generation of rarely observed x-type radical fragments, with significant abundances. CID experiments of the radical cations of the alanyltyrosylglycine tripeptide and its analogues suggested that the N-terminal C?-C bond cleavage, yielding its [x2 + H](•+) radical cation, does not involve an N-terminal ?-carbon-centered radical. Theoretical examination of a prototypical radical cation of the alanyltyrosine dipeptide, using density functional theory calculations, suggested that direct N-terminal C?-C bond cleavage could produce an ion-molecule complex formed between the incipient a1(+) and x1(•) fragments. Subsequent proton transfer from the iminium nitrogen atom in a1(+) to the acyl carbon atom in x1(•) results in the observable [x1 + H](•+). The barriers against this novel C?-C bond cleavage and the competitive N-C? bond cleavage, forming the complementary [c1 + 2H](+)/[z1 - H](•+) ion pair, are similar (ca. 16 kcal mol(-1)). Rice-Ramsperger-Kassel-Marcus modeling revealed that [x1 + H](•+) and [c1 + 2H](+) species are formed with comparable rates, in agreement with energy-resolved CID experiments for [AY](•+). PMID:24678922

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

2014-04-24

89

Dissociation of OCS by high energy highly charged ion impact  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

90

Dissociation of OCS by high energy highly charged ion impact  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

91

Dissociation constants of weak acids from ab initio molecular dynamics using metadynamics: influence of the inductive effect and hydrogen bonding on pKa values.  

PubMed

The theoretical estimation of the dissociation constant, or pKa, of weak acids continues to be a challenging field. Here, we show that ab initio Car-Parrinello molecular dynamics simulations in conjunction with metadynamics calculations of the free-energy profile of the dissociation reaction provide reasonable estimates of the pKa value. Water molecules, sufficient to complete the three hydration shells surrounding the acid molecule, were included explicitly in the computation procedure. The free-energy profiles exhibit two distinct minima corresponding to the dissociated and neutral states of the acid, and the difference in their values provides the estimate for pKa. We show for a series of organic acids that CPMD simulations in conjunction with metadynamics can provide reasonable estimates of pKa values. The acids investigated were aliphatic carboxylic acids, chlorine-substituted carboxylic acids, cis- and trans-butenedioic acid, and the isomers of hydroxybenzoic acid. These systems were chosen to highlight that the procedure could correctly account for the influence of the inductive effect as well as hydrogen bonding on pKa values of weak organic acids. In both situations, the CPMD metadynamics procedure faithfully reproduces the experimentally observed trend and the magnitudes of the pKa values. PMID:25375645

Tummanapelli, Anil Kumar; Vasudevan, Sukumaran

2014-11-26

92

Describing static correlation in bond dissociation by KohnSham density functional theory  

E-print Network

dissociation in H2 in a spin-restricted Kohn­Sham formalism, i.e., without artificial symmetry breaking. We, as exemplified by the H2 + molecule, where 100% exact exchange mixing and zero correlation en- ergy would wave function. A famous example is the dissoci- ating H2 molecule. The proper singlet KS ground state

93

Multi-component molecular orbital study on positron attachment to alkali-metal hydride molecules: nature of chemical bonding and dissociation limits of [LiH; e+  

NASA Astrophysics Data System (ADS)

We have performed multi-component full-configuration interaction calculations to investigate the nature of chemical bonding of [LiH;e+] at the small and large internuclear distance. We discuss the importance of geometrical changes in positronic compounds induced by a positron attachment in terms of the virial theorem, with a comparison of the adiabatic- and vertical-positron affinity (PA). The systematic improvement of the PA values achieved by optimisation of (i) the molecular geometry and (ii) the positronic basis centre is also discussed. The stable dissociation channel of [LiH;e+] is compared with the ionic- and neutral-dissociation channels of its parent molecule LiH through the analysis of the potential energy curve and the electronic and positronic densities. The vertical PA as a function of is also presented, which is the difference between the potential energy curve of the parent molecule (LiH ? Li + H) and its positronic compound ([LiH; e+] ? Li + [H; e+]). Unlike the preceding study of [M. Mella et al., J. Chem. Phys. 113, 6154 (2000)], it took more than bohr to converge the vertical PA due to the long-range ionic bonding interaction.

Oyamada, Takayuki; Tachikawa, Masanori

2014-08-01

94

The dissociation energy of He2(+)  

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

95

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

PubMed

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

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

2014-11-26

96

Adhesive bonding using variable frequency microwave energy  

DOEpatents

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.

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

97

Adhesive bonding using variable frequency microwave energy  

DOEpatents

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.

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

1998-09-08

98

Adhesive bonding using variable frequency microwave energy  

DOEpatents

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.

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

1998-08-25

99

High energy collision-induced dissociation of alkali-metal ion adducts of crown ethers and acyclic analogs.  

PubMed

High energy collision-induced dissociation (CID) techniques were applied for structural elucidation of alkali-metal ion adducts of crown ethers. The CID of alkali-metal adducts of tetraglyme and hexaethylene glycol were also evaluated to contrast the fragmentation pathways of the cyclic ethers with those of acyclic analogs. A common fragmentation channel for alkali-metal ion adducts of all the ethers, which results in distonic radical cations, is the homolytic cleavage of carbon-carbon bonds. Additionally, dissociation by carbon-oxygen bond cleavages occurs, and these processes are analogous to the fragmentation pathways observed for simple protonated ethers. The proposed fragmentation pathways for alkali-metal ion adducts of crown ethers result mostly in odd-electron, acyclic product ions. Dissociation of the alkali-metal ion adducts of the acyclic ethers is dominated by losses of various neutral species after an initial hydride or proton transfer. The CID processes for all ethers are independent of the alkali-metal ion sizes; however, the extent of dissociation of the complexes to bare alkali-metal ions increases with the size of the metal. PMID:1385992

Maleknia, S; Brodbelt, J

1992-06-01

100

Homolytic dissociation in hydrogen-bonding liquids: energetics of the phenol O–H bond in methanol and the water O–H bond in water  

Microsoft Academic Search

The energetics of the phenol O–H bond in methanol and the water O–H bond in liquid water were investigated by microsolvation modelling and statistical mechanics Monte Carlo simulations. The microsolvation approach was based on density functional theory calculations. Optimised structures for clusters of phenol and the phenoxy radical with one and two methanol molecules are reported. By analysing the differential

S. G. Estácio; P. Cabral do Couto; R. C. Guedes; B. J. Costa Cabral; J. A. Martinho Simões

2004-01-01

101

Bond-Energy and Surface-Energy Calculations in Metals  

ERIC Educational Resources Information Center

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

Eberhart, James G.; Horner, Steve

2010-01-01

102

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

NASA Technical Reports Server (NTRS)

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

Scott, Carl D.; Smalley, Richard E.

2003-01-01

103

Imaging bond breaking and vibrational energy transfer in small water containing clusters  

NASA Astrophysics Data System (ADS)

This letter presents a brief overview of our recent experimental studies of state-to-state vibrational predissociation (VP) dynamics of small hydrogen bonded (H-bonded) clusters following vibrational excitation. Velocity map imaging (VMI) and resonance-enhanced multiphoton ionization (REMPI) are used to determine accurate bond dissociation energies (D0) of (H2O)2, (H2O)3, HCl-H2O and NH3-H2O. Pair-correlated product energy distributions from the VP of these complexes are also presented and compared to theoretical models. Further insights into mechanisms are obtained from the recent quasi-classical trajectory (QCT) calculations of Bowman and coworkers. The D0 values for (H2O)2 and (H2O)3 are in very good agreement with recent calculated values, and the results are used to estimate the contributions of cooperative interactions to the H-bonding network.

Samanta, Amit K.; Ch'ng, Lee C.; Reisler, Hanna

2013-06-01

104

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

SciTech Connect

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

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

105

Towards measuring the ionisation and dissociation energies of molecular hydrogen with  

E-print Network

Towards measuring the ionisation and dissociation energies of molecular hydrogen with sub, Accepted 26th January 2011 DOI: 10.1039/c0fd00035c The most precise determination of the ionisation Rydberg state. The values of the ionisation and dissociation energies obtained for H2, and for HD and D2

106

The vibrational energies of ozone up to the dissociation threshold: Dynamics calculations on an accurate potential energy surface  

E-print Network

The vibrational energies of ozone up to the dissociation threshold: Dynamics calculations present an ab initio potential energy surface for the ground electronic state of ozone. It is global, i. All bound states of nonrotating ozone up to more than 99% of the dissociation energy are calculated

Farantos, Stavros C.

107

A new determination of the dissociation energy of acetylene  

SciTech Connect

A new {ital upper} {ital bound} for the dissociation energy of acetylene, {ital D}{sup 0}{sub 0}(HCC--H) =529.89({plus minus}0.01) kJ/mol, has been determined by Stark anticrossing spectroscopy. The zero-pressure extrapolated (unimolecular) decay rates of levels of {ital S}{sub 1} ({ital {tilde A}} {sup 1}{ital A}{sub {ital u}}) {ital v}{sup {prime}}{sub 3}=2 and 3 (quanta of the {ital trans}-bending vibration) {ital increase} upon application of an electric field of 113 kV/cm. We attribute this increase in molecular decay rate to {ital predissociation} rather than any other Stark-induced nonradiative or radiative phenomenon. The lowest level ({ital v}{sup {prime}}{sub 3} =2, {ital J}{prime}=2, {ital K}{prime}=1) from which we have observed an increase in decay rate (i.e., predissociation) has an internal energy of 44 295.65 cm{sup {minus}1} relative to {ital v}=0, {ital J}=0 of {ital S}{sub 0} ({ital {tilde X}} {sup 1}{Sigma}{sup +}{sub {ital g}}). This corresponds to a value about 24 kJ/mol lower then the consensus {ital upper bound} result from four different recent experimental determinations (including one of ours) as well as current {ital ab nitio} results. The new value agrees, however, with earlier work and with recent modeling studies of acetylene pyrolysis kinetics.

Green, P.G.; Kinsey, J.L.; Field, R.W. (Department of Chemistry and George R. Harrison Spectroscopy Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (US))

1989-11-01

108

Effect of nanoscale surface roughness on the bonding energy of direct-bonded silicon wafers  

NASA Astrophysics Data System (ADS)

Direct wafer bonding of silicon wafers is a promising technology for manufacturing three-dimensional complex microelectromechanical systems as well as silicon-on-insulator substrates. Previous work has reported that the bond quality declines with increasing surface roughness, however, this relationship has not been quantified. This article explicitly correlates the bond quality, which is quantified by the apparent bonding energy, and the surface morphology via the bearing ratio, which describes the area of surface lying above a given depth. The apparent bonding energy is considered to be proportional to the real area of contact. The effective area of contact is defined as the area sufficiently close to contribute to the attractive force between the two bonding wafers. Experiments were conducted with silicon wafers whose surfaces were roughened by a buffered oxide etch solution (BOE, HF:NH4F=1:7) and/or a potassium hydroxide solution. The surface roughness was measured by atomic force microscopy. The wafers were direct bonded to polished "monitor" wafers following a standard RCA cleaning and the resulting bonding energy was measured by the crack-opening method. The experimental results revealed a clear correlation between the bonding energy and the bearing ratio. A bearing depth of ˜1.4 nm was found to be appropriate for the characterization of direct-bonded silicon at room temperature, which is consistent with the thickness of the water layer at the interface responsible for the hydrogen bonds that link the mating wafers.

Miki, N.; Spearing, S. M.

2003-11-01

109

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)

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.

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

2014-10-01

110

Enthalpy of formation of anisole: implications for the controversy on the O-H bond dissociation enthalpy in phenol.  

PubMed

Significant discrepancies in the literature data for the enthalpy of formation of gaseous anisole, ?fHmo(PhOCH3, g), have fueled an ongoing controversy regarding the most reliable enthalpy of formation of the phenoxy radical and of the gas phase O-H bond dissociation enthalpy, DHo(PhO-H), in phenol. In the present work ?fHmo(PhOCH3, g) was reassessed using a combination of calorimetric determinations and high-level (W2-F12) ab initio calculations. Static-bomb combustion calorimetry led to the standard molar enthalpy of formation of liquid anisole at 298.15 K, ?fHmo(PhOCH3, l) = ?(117.1 ± 1.4) kJ·mol(-1). The corresponding enthalpy of vaporization was obtained as, ?vapHmo(PhOCH3) = 46.41 ± 0.26 kJ·mol(-1), by Calvet-drop microcalorimetry. These results give ?fHmo(PhOCH3, g) = ?(70.7 ± 1.4) kJ·mol(-1), in excellent agreement with ?fHmo(PhOCH3, g) = ?(70.8 ± 3.2) kJ·mol(-1), obtained from the W2-F12 calculations. The ?fHmo(PhOCH3, g) here recommended leads to ?fHmo(PhO•, g) = 55.5 ± 2.4 kJ·mol(-)1 and DH°(PhO-H) = 368.1 ± 2.6 kJ·mol(-1). PMID:25340952

Simões, Ricardo G; Agapito, Filipe; Diogo, Hermínio P; da Piedade, Manuel E Minas

2014-11-20

111

Photoionization spectroscopy of dichromium and dimolybdenum: Ionization potentials and bond energies  

NASA Astrophysics Data System (ADS)

Photoionization spectroscopy has been used to probe molecular beams of laser-vaporized chromium (Cr2) and molybdenum (Mo2) dimers. Two-color photoionization efficiency spectroscopy has been used to determine the adiabatic ionization potential (IP) of Cr2 and Mo2 to be 56 449±8 cm-1 and 56 042±8 cm-1, respectively. The IP of Cr2 is combined with the IP of Cr [54 575.6±0.3 cm-1, Huber et al., Proc. R. Soc. London, Ser. A 342, 431 (1975)] and the bond energy of Cr2+ [10 200±500 cm-1, Su et al., Chem. Phys. Lett. 201, 199 (1993)] to yield a bond energy of 12 400±500 cm-1 for Cr2. One-color resonant two-photon ionization (R2PI) spectroscopy has been employed to probe the molybdenum dimer molecule in the energy region where its dissociation should occur. The dissociation limit has been ascribed to the threshold observed at 36 100±80 cm-1. This value is combined with the IP of Mo [57 204.3±0.3 cm-1, Rayner et al., J. Opt. Soc. Am. B 4, 900 (1987)] and Mo2 to yield a bond energy of 37 260±80 cm-1 for Mo2+.

Simard, Benoit; Lebeault-Dorget, Marie-Ange; Marijnissen, Adrian; ter Meulen, J. J.

1998-06-01

112

Study of N–H, O–H, and S–H bond dissociation enthalpies and ionization potentials of substituted anilines, phenols, and thiophenols  

Microsoft Academic Search

In this article, the study of 44 compounds representing various p-and m-substituted anilines, phenols and thiophenols is presented. These serve as model structures of amine, phenol and thiophenol types of antioxidants. Molecules and their radical structures were studied using DFT and semi-empirical PM3 and AM1 quantum chemical methods in order to calculate the N–H, O–H and S–H bond dissociation enthalpies

Erik Klein; Vladimír Lukeš; Zuzana Cibulková; Júlia Polovková

2006-01-01

113

DISSOCIATION ENERGIES OF MOLECULES WITH VERY HEAVY ATOMS FROM MASS SPECTROMETRY  

E-print Network

WITH VERY HEAVY ATOMS FROM MASS SPECTROMETRY Kenneth S.with Very Heavy Atoms from Mass Spectrometry Kenneth S.mass~spectrometric investigations Gingerich and associates have measured the dissociation energies of many molecules including heavy atoms.

PItzer, Kenneth S.

2013-01-01

114

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

PubMed

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

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

2013-04-15

115

Study of gas-phase O-H bond dissociation enthalpies and ionization potentials of substituted phenols - Applicability of ab initio and DFT/B3LYP methods  

NASA Astrophysics Data System (ADS)

In this paper, the study of phenol and 37 compounds representing various ortho-, para-, and meta-substituted phenols is presented. Molecules and their radical structures were studied using ab initio methods with inclusion of correlation energy and DFT in order to calculate the O-H bond dissociation enthalpies (BDEs) and vertical ionization potentials (IPs). Calculated BDEs and IPs were compared with available experimental values to ascertain the suitability of used methods, especially for the description of the substituent induced changes in BDE and IP. MP2, MP3, and MP4 methods do not give reliable results, since they significantly underestimate substituent induced changes in BDE and do not reflect distinct effect of substituents related to para and meta position correctly. DFT/B3LYP method reflects the effect of substituents on BDE satisfactorily, though ?BDEs are in narrower range than experimental values. BDE of phenol was calculated also using CCSD(T) method in various basis sets. Both, DFT and HF methods describe the effect of substituents on IP identically. However, DFT considerably underestimates individual values. HF method gives IPs in very good agreement with experimental data. Obtained results show that dependences of BDEs and IPs on Hammett constants of the substituents are linear. Linearity of DFT BDE vs. IP dependence is even better than the dependences on Hammett constants and obtained equations allow estimating of O-H BDEs of meta- and para-substituted phenols from calculated IPs.

Klein, Erik; Lukeš, Vladimír

2006-11-01

116

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

SciTech Connect

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.

Medford, Andrew

2012-02-16

117

Dissociation of ozonide in water  

SciTech Connect

The free energy of bond dissociation for ozonide ion radical is found to be lowered in aqueous solution by about 20 kcal/mol relative to that in the gas phase, based on electronic structure calculations. Explicit treatment of anion-water clusters indicates that the stronger hydrogen bonds to first-shell water molecules formed by O{sup {minus}} relative to O{sub 3}{sup {minus}} account for much of the lowering. Reaction field methods show that nonspecific electrostatic polarization of the bulk solvent further contributes noticeably to the lowering. The study clearly demonstrates that the aqueous free energy of ozonide bond dissociation is small, and probably endothermic. The best semitheoretical prediction of the actual value is 5 {+-} 5 kcal/mol.

Bentley, J.; Collins, J.Y.; Chipman, D.M.

2000-05-18

118

Metal-hydrogen bond energies in protonated transition-metal complexes  

SciTech Connect

Proton affinities of 20 organotransition-metal complexes in the gas phase are reported. For 16 of these complexes protonation occurs on the metal center. The corresponding metal-hydrogen homolytic bond dissociation energies were determined and these data summarized. All proton affinities were determined by the techniques of ion cyclotron resonance spectroscopy, by examining proton-transfer reactions in mixtures with compounds of known base strength. Ionization potentials are taken from a variety of sources and experimental procedures, as noted. The site of protonation in several of these compounds has been determined by either gas-phase or solution-phase studies. These results and their interpretations are presented. (AT)

Stevens, A.E.; Beauchamp, J.L.

1981-01-14

119

HD+ in a beam in intense pulsed laser fields: Dissociation and ionization with high-energy resolution of the fragments  

NASA Astrophysics Data System (ADS)

The isotopically mixed hydrogen molecular ion HD+ was investigated in intense pulsed laser fields with high, i.e., vibrational resolution of the fragments. An ion beam of HD+ with a translational energy of 11.1 keV was exposed to femtosecond laser pulses (100 fs) of intensities in the range from 1013 1015W/cm2 . Fragments from the two dissociation channels HD+?H+D+ , and HD+?D+H+ , as well as the Coulomb explosion channel, HD+?H++D++e- , were projected onto a two-dimensional multichannel plate detector to measure their velocity distributions. The fragments from the three channels were spatially clearly distinguished because of the different velocities of H (H+) and D (D+) fragments. Fragments from most of the populated vibrational states of HD+ can be discerned as well-resolved peaks in the speed and angular distributions. The typical light induced potential (LIP) effects such as bond softening and level shifting already observed in the studies of H2+ and D2+ are here also observed. In addition to these one-photon peaks, also peaks due to three- (net two-) and finally also to direct two-photon absorption, typical of the asymmetric HD+ , were found in the vibrationally resolved fragment spectra of the dissociation channels. Besides the fragments from one-photon bond softening, also fragments formed by two- and three-photon processes were found to have narrow angular distributions, in contrast to the approximately cos2 distribution of fragments from vibrational levels above the LIP crossing being fragmented by classical dissociation. The relative probability of the two dissociation channels was investigated, addressing the question of the higher electron affinity to the proton or the deuteron during the dissociation, but could not be decided because of too low accuracy here. The Coulomb explosion channel was also clearly discerned by its fragment velocities as well as the narrow angular distributions of H+ and D+ fragments, which is quite analogous to those found in the cases of H2+ and D2+ .

Kiess, Andreas; Pavi?i?, Domagoj; Hänsch, Theodor W.; Figger, Hartmut

2008-05-01

120

Low-Energy Collision-Induced Dissociation Mass Spectra of Protonated p-Toluenesulfonamides Derived from Aliphatic Amines  

NASA Astrophysics Data System (ADS)

Collision-induced fragmentation of protonated N-alkyl- p-toluenesulfonamides primarily undergo either an elimination of the amine to form CH3-(C6H4)-SO2 + cation ( m/z 155) or an alkene to form a cation for the protonated p-toluenesulfonamide ( m/z 172). To comprehend the fragmentation pathways, several deuterated analogs of N-decyl- p-toluenesulfonamides were prepared and evaluated. Hypothetically, two mechanisms, both of which involve ion-neutral complexes, can be envisaged. In one mechanism, the S-N bond fragments to produce an intermediate [sulfonyl cation/amine] complex, which dissociates to afford the m/z 155 cation (Pathway A). In the other mechanism, the C-N bond dissociates to produce a different intermediate complex. The fragmentation of this [ p-toluenesulfonamide/carbocation] complex eliminates p-toluenesulfonamide and releases the carbocation (Pathway B). Computations carried out by the Hartree-Fock method suggested that the Pathway B is more favorable. However, a peak for the carbocation is observed only when the carbocation formed is relatively stable. For example, the spectrum of N-phenylethyl- p-toluenesulfonamide is dominated by the peak at m/z 105 for the incipient phenylethyl cation, which rapidly isomerizes to the remarkably stable methylbenzyl cation. The peaks for the carbocations are weak or absent in the spectra of most of N-alkyl- p-toluenesulfonamides because alkyl carbocations, such as the decyl cation, rearrange to more stable secondary cations by 1,2-hydride and alkyl shifts. The energy freed is not dissipated, but gets internalized, causing the carbocation to dissociate either by transferring a proton to the sulfonamide or by releasing smaller alkenes to form smaller carbocations. The loss of the positional integrity in this way was proven by deuterium labeling experiments.

Bialecki, Jason B.; Weisbecker, Carl S.; Attygalle, Athula B.

2014-06-01

121

Dissociative-recombination product states and the dissociation energy D0 of Ne2+  

SciTech Connect

Final product states of Ne2+ dissociative recombination were studied using time-of-flight spectroscopy to determine the kinetic energies released. The dissociative recombination occurred in a sustained discharge in the presence of a variable magnetic field and discharge voltage, at pressures of 5-15 mTorr. Under different conditions various excited states were observed ranging from the lowest 3s metastable states to higher Rydbcrg states within 0.000 54 eV of the dissociation limit. From their narrow widths, it is deduced that these higher states arose from Ne2+ ions with subthermal energies. From two of these narrow distributions, we obtain an improved value for the dissociation limit D0(Ne2+)= 1.26±0.02 eV.

Hardy, K. A.; Peterson, J. R.; Ramos, G.; Sheldon, J. W.

1998-02-28

122

Theoretical study on the dissociation energies, ionization potentials and electron affinities of three perfluoroalkyl iodides  

NASA Astrophysics Data System (ADS)

Dissociation energies, ionization potentials and electron affinities of three perfluoroalkyl iodides, CF 3I, C 2F 5I, and i-C 3F 7I are calculated accurately with B3LYP, MP n ( n = 2-4), QCISD, QCISD(T), CCSD, and CCSD(T) methods. Calculations are performed by using large-core correlation-consistent pseudopotential basis set (SDB-aug-cc-pVTZ) for iodine atom. In all energy calculations, the zero point vibration energy is corrected. And the basis set superposition error is corrected by counterpoise method in the calculation of dissociation energy. Theoretical results are compared with the experimental values.

Cheng, Li; Shen, Zuochun; Lu, Jianye; Gao, Huide; Lü, Zhiwei

2005-11-01

123

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

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

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

2015-03-23

124

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

E-print Network

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

Thumm, Uwe

125

Excitation energy distributions and statistical dissociation of C702+ prepared in collisions with F+ ions at 3 keV  

NASA Astrophysics Data System (ADS)

The statistical dissociation of C702+ has been studied as a function of the internal energy using collision induced dissociation under energy control (CIDEC). Doubly charged ions C702+ were prepared in F+ (3 keV) + C70 ? F- + C702+ collisions. Up to seven successive evaporation of C2 have been observed in a time range of 1.7 ?s. The dissociation energies of C70-2m2+ (m=1-7) were determined using a statistical cascade model to reproduce the excitation energy distribution of C702+ parent ions for each dissociation channel. Results are in good agreement with previous theoretical calculations.

Brédy, R.; Ortéga, C.; Ji, M.; Chen, L.; Bernard, J.; Montagne, G.; Qian, D.; Li, B.; Ma, X.; Martin, S.

2014-04-01

126

7978 J. Phys. Chem. 1993,97, 7978-7987 Sequential Bond Energies of Cr(CO)t, x = 1-6  

E-print Network

difficulttostudy. An importantelement in characterizing these species is the bond dissociation energy (BDE toobtainaccuratesequential BDEs for Fe(CO),+ species. In the present work, we apply this technique to obtain sequential BDEs theother fragments. This observation suggests that the BDEs for loss of CO from thesespeciesare smallerthan

Clemmer, David E.

127

Proton affinities of the N- and C-terminal segments arising upon the dissociation of the amide bond in protonated peptides  

Microsoft Academic Search

Dissociation of the amide bonds in a protonated peptide leads to N-terminal sequence fragments with cyclic structures and\\u000a C-terminal sequence fragments with linear structures. The ionic fragments containing the N-terminus (b\\u000a n\\u000a ) have been shown to be protonated oxazolones, whereas those containing the C-terminus (y\\u000a n\\u000a ) are protonated linear peptides. The coproduced neutral fragments are cyclic peptides from

Michael J. Nold; Blas A. Cerda; Chrys Wesdemiotis

1999-01-01

128

Diffractive dissociation in proton-nucleus collisions at collider energies  

E-print Network

The cross section for the nuclear diffractive dissociation in proton-lead collisions at the LHC is estimated. Based on the current theoretical uncertainties for the single (target) diffactive cross section in hadron-hadron reactions one obtains sigma_SD(5.02 TeV) = 19.67 \\pm 5.41 mb and sigma_SD(8.8 TeV) = 18.76 \\pm 5.77 mb, respectively. The invariant mass M_X for the reaction pPb -> pX is also analyzed. Discussion is performed on the main theoretical uncertainties associated to the calculations.

G. Sampaio dos Santos; M. V. T. Machado

2014-10-23

129

Dissociative chemisorption of N2 on rhenium: Dynamics at high impact energies  

Microsoft Academic Search

The dissociative chemisorption of N2 on the (0001) rhenium crystal surface is studied theoretically at high impact energies. The dynamics of the molecule is accordingly treated classically excluding tunneling processes. This study extends previous low energy studies in three important ways: (1) all six degrees of freedom of the N2 molecule are considered; (2) lateral variations (corrugation) are included in

Niels E. Henriksen; Gert D. Billing; Flemming Y. Hansen

1990-01-01

130

Influence of Internal Energy Excitation and Molecular Dissociation on Normal Shock Structure  

NASA Astrophysics Data System (ADS)

In this work, we investigate internal energy excitation and dissociation under conditions characteristic of reentry flows using the Direct Simulation Monte Carlo method. For the purpose of studying these phenomena, a simple test case is used: a supersonic flow of nitrogen is decelerated through a standing shock wave, causing the internal energy modes of the N2 molecules to be excited and leading to partial dissociation of N2 . Downstream of the shock, the evolution of the translational, rotational and vibrational temperatures, as well as the fraction of atomic nitrogen are monitored. The results from the DSMC calculations are compared to continuum CFD calculations based on the Navier-Stokes equations.

Torres, E.; Munafó, A.; Magin, T.

2011-08-01

131

Fluorine hot atom oxidation of bismuth vapor. A comment on the evaluation of the BiF bond energy  

NASA Astrophysics Data System (ADS)

The energetics of the chemiluminescent reaction between bismuth dimers and fluorine atoms (T.C. Devore et al., Chem. Phys. 155 (1991) 423; 156 (1991) 156) has been evaluated to better refine a determination of the bismuth fluoride dissociation energy. By directly examining the spectrum of the SF 6 discharge used to generate the F atoms to establish the significant energy imparted to these dissociation products and by exploring F atom chemiluminescent reactions with known energetics, the F atom beam is established to have contributed a maximum of 0.8-0.9 eV to the chemiluminescent process. Based upon the observed population of the ?'=4 level of the BiF A0 + state resulting from the Bi 2 + F reaction, a BiF bond energy of 3.9 ± 0.2 eV is established. This value is slightly higher than a very recent evaluation of the BiF bond energy (Yoo et al., Chem. Phys. 166 (1992) 215) but disagrees with previous determinations in the literature. Many of the previous evaluations of the group 15 halide dissociation energies have been based on Birge—Sponer extrapolations. The data now available for BiF permits an evaluation of the nature of these extrapolations for this molecule. The limitations of these extrapolations and possible corrections for these shortcomings are presented.

Devore, T. C.; Gole, J. L.

1993-08-01

132

The Calculation of Accurate Metal-Ligand Bond Energies  

NASA Technical Reports Server (NTRS)

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.

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

1997-01-01

133

C?-C? chromophore bond dissociation in protonated tyrosine-methionine, methionine-tyrosine, tryptophan-methionine, methionine-tryptophan and their sulfoxide analogs.  

PubMed

C(?)-C(?) chromophore bond dissociation in some selected methionine-containing dipeptides induced by UV photons is investigated. In methionine containing dipeptides with tryptophan as the UV chromophore, the tryptophan side chain is ejected either as an ion or as a neutral fragment while in dipeptides with tyrosine, the tyrosine side chain is lost only as a neutral fragment. Mechanisms responsible for these fragmentations are proposed based on measured branching ratios and fragmentation times, and on the results of DFT/B3-LYP calculations. It appears that the C(?)-C(?) bond cleavage is a non-statistical dissociation for the peptides containing tyrosine, and occurs after internal conversion for those with tryptophan. The proposed mechanisms are governed by the ionization potential of the aromatic side chain compared to that of the rest of the molecule, and by the proton affinity of the aromatic side chain compared to that of the methionine side chain. In tyrosine-containing peptides, the presence of oxygen on sulfur of methionine presumably reduces the ionization potential of the peptide backbone, facilitating the loss of the side chain as a neutral fragment. In tryptophan-containing peptides, the presence of oxygen on methionyl-sulfur expedites the transfer of the proton from the side chain to the sulfoxide, which facilitates the loss of the neutral side chain. PMID:22722478

Sunil Kumar, S; Lucas, B; Soorkia, S; Barat, M; Fayeton, J A

2012-08-01

134

Facilitating protein disulfide mapping by a combination of pepsin digestion, electron transfer higher energy dissociation (EThcD), and a dedicated search algorithm SlinkS.  

PubMed

Disulfide bond identification is important for a detailed understanding of protein structures, which directly affect their biological functions. Here we describe an integrated workflow for the fast and accurate identification of authentic protein disulfide bridges. This novel workflow incorporates acidic proteolytic digestion using pepsin to eliminate undesirable disulfide reshuffling during sample preparation and a novel search engine, SlinkS, to directly identify disulfide-bridged peptides isolated via electron transfer higher energy dissociation (EThcD). In EThcD fragmentation of disulfide-bridged peptides, electron transfer dissociation preferentially leads to the cleavage of the S-S bonds, generating two intense disulfide-cleaved peptides as primary fragment ions. Subsequently, higher energy collision dissociation primarily targets unreacted and charge-reduced precursor ions, inducing peptide backbone fragmentation. SlinkS is able to provide the accurate monoisotopic precursor masses of the two disulfide-cleaved peptides and the sequence of each linked peptide by matching the remaining EThcD product ions against a linear peptide database. The workflow was validated using a protein mixture containing six proteins rich in natural disulfide bridges. Using this pepsin-based workflow, we were able to efficiently and confidently identify a total of 31 unique Cys-Cys bonds (out of 43 disulfide bridges present), with no disulfide reshuffling products detected. Pepsin digestion not only outperformed trypsin digestion in terms of the number of detected authentic Cys-Cys bonds, but, more important, prevented the formation of artificially reshuffled disulfide bridges due to protein digestion under neutral pH. Our new workflow therefore provides a precise and generic approach for disulfide bridge mapping, which can be used to study protein folding, structure, and stability. PMID:24980484

Liu, Fan; van Breukelen, Bas; Heck, Albert J R

2014-10-01

135

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

SciTech Connect

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})

Heger, Matthias; Suhm, Martin A.; Mata, Ricardo A., E-mail: rmata@gwdg.de [Georg-August-Universität Göttingen, Institut für Physikalische Chemie, Tammannstr. 6, 37077 Göttingen (Germany)

2014-09-14

136

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

SciTech Connect

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.

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

137

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

PubMed

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

Beck, John Frederick; Mo, Yirong

2007-01-15

138

Dissociative Adsorption of Molecules on Graphene and Silicene  

E-print Network

We study the interaction of H$_2$, O$_2$, CO, H$_2$O and OH molecules with the vacancy defects of graphene and silicene. Atoms around the bare vacancy reconstruct and specific chemically active sites are created. While H$_2$, O$_2$ and CO remain intact on both pristine graphene and silicene, these molecules can dissociate when they are placed at the close proximity of these chemically active sites and nucleate centers for the hydrogenation and oxygenation. Saturation of the dangling bonds at the defect sites by constituent atoms of dissociated molecules gives rise to significant modification of electronic and magnetic properties. We analyzed the mechanism of the dissociation and revealed a concerted action of surrounding host atoms together with dissociated molecules to lower the energy barrier needed for dissociation. The dissociations of H$_2$O and OH are hindered by high energy barriers. Our study suggests that graphene and silicene can be functionalized by creating meshes of single vacancy, where specific...

Gurel, H Hakan; Ciraci, S

2014-01-01

139

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

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

140

Dissociative energy flow, vibrational energy redistribution, and conformeric structural dynamics in bifunctional amine model systems.  

PubMed

Time-resolved multiphoton ionization mass spectrometry coupled with Rydberg Fingerprint Spectroscopy (RFS) has been used to analyze the structural and electronic dynamics of N,N-dimethylphenethylamine (PENNA) and N,N-dimethylcyclohexethylamine (CENNA). In PENNA, the molecule converts from 3p to 3s on a time scale of 149 fs, a process that is reflected in the mass spectrum as the onset of fragmentation. Once in 3s, the overall signal intensity of the PENNA 3s signal shows biexponential decay kinetics, which is attributed to the electronic curve crossing from the Rydberg state to a dissociative antibonding orbital of the ethylenic bridge. This curve crossing exemplifies a possible fragmentation pathway observed in electron capture dissociation of proteins. The initially fast reaction (1.3 ps) is greatly slowed down as a result of an apparent relaxation process with a 5.6 ps time constant. The electron binding energy of the 3s Rydberg state of PENNA is observed to shift with a time constant of 4.8 ps, which is correlated to a cation-? interaction driven conformeric rearrangement. PMID:20593860

Bush, Joseph C; Minitti, Michael P; Weber, Peter M

2010-10-28

141

THE JOURNAL OF CHEMICAL PHYSICS 135, 084104 (2011) Breaking the carbon dimer: The challenges of multiple bond dissociation  

E-print Network

of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom 2 Chemistry Department, Imperial College London to its multiple bond and significant multireference character even at equi- librium geometries,1,2 many

Alavi, Ali

2011-01-01

142

July 18, 2012 Qualified Energy Conservation Bond (QECB) Update: New  

E-print Network

July 18, 2012 Qualified Energy Conservation Bond (QECB) Update: New Guidance from the U, and local governments be given wide discretion in methods to conserve energy that may be financed with QECBs governments by providing them with access to subsidized financing to help promote energy-efficient policies

143

Predicted bond energies in peroxides and disulfides by density functional methods  

SciTech Connect

We have performed self-consistent linear combination of Gaussian-type orbitals-density functional calculations for the molecules YY, RY, RYY, RYR{prime}, RYYR, and RYYR{prime} with Y=O,S and R,R{prime}=H,CH{sub 3}. The structures were optimized within the local spin density approximation while the Y--Y, Y--C, and Y--H bond dissociation energies (BDE) were calculated with both a local exchange-correlation energy functional and a gradient corrected functional. Comparison of results obtained with the local and gradient corrected exchange-correlation functionals provides more experience on the successes and failures of gradient corrections. Trends in BDEs and the nature of bonding in oxygen and sulfur containing analog molecules are analyzed on the basis of two observations: (1) the O atom is more electronegative than S, C, and H atoms; (2) a S atom can have a valency larger than two and has a greater ability for multiple bonding than oxygen. Finally, comparison with a number of experimental results suggest that the C--S BDE in CH{sub 3}S, the S--S BDE in CH{sub 3}SSCH{sub 3}, and the enthalpy of formation of CH{sub 3}S should be reexamined.

Fournier, R.; DePristo, A.E. (Ames Laboratory-USDOE, Iowa State University, Ames, Iowa (United States). Department of Chemistry)

1992-01-15

144

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

PubMed

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

Munafò, A; Panesi, M; Magin, T E

2014-02-01

145

Relative dissociation energies of singly and doubly charged fullerene ions, Cnz+, for n = 52 to 70  

NASA Astrophysics Data System (ADS)

Relative activation energies for dissociation of fullerene ions Cnz+ into Cn-2z+ + C2 have been determined for z = 1 and 2, covering the size range 52 <= n <- 70. These data are derived from measured appearance energies of fragment ions, obtained by electron impact ionization of C70, with the help of the finite heat bath theory. The present results are compared with experimental and theoretical values for C2 loss reported in the literature.

Matt, S.; Echt, O.; Worgotter, R.; Scheier, P.; Klots, C. E.; Mark, T. D.

1997-11-01

146

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

E-print Network

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

Raji Heyrovska

2008-09-11

147

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

ERIC Educational Resources Information Center

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…

Sattar, Simeen

2011-01-01

148

Dissociative attachment and vibrational excitation in low-energy electron collisions with chlorine molecules  

NASA Astrophysics Data System (ADS)

In a combined experimental and theoretical effort, we have investigated dissociative attachment and vibrational excitation in low-energy electron collisions with chlorine molecules. Using the laser photoelectron attachment method, we have measured the energy dependence of the cross section sgrDA(E) for dissociative electron attachment (Cl- formation) over the range 0-195 meV with an energy width of 1-3 meV and for Rydberg electron transfer at high principal quantum numbers (n>67). Near zero energy, the cross section shows a behaviour compatible with the threshold law for p-wave attachment via the 2Sgru+ resonance, reaches a maximum around 50 meV and declines towards higher energies. These findings are in good agreement with the results of semi-empirical R-matrix calculations. Measured rate coefficients knl for Cl- formation due to electron transfer from K**(nl) Rydberg atoms were found to be nearly constant for high principal quantum numbers (n>67) in contrast to the behaviour expected within the quasi-free electron model for p-wave attachment. The R-matrix calculations are extended to describe electron attachment through the 2Pgrg and 2Pgru resonances, and recommended absolute cross sections for dissociative attachment to chlorine molecules at room temperature are provided over the energy range 0-9 eV. Furthermore, we predict cross sections for vibrationally inelastic electron scattering through the 2Sgru+, 2Pgrg and 2Pgru resonances.

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

2004-01-01

149

Natural bond orbital study on the strain energy in cyclotrisilane  

Microsoft Academic Search

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,

Ming-Chiu Ou; San-Yan Chu

1995-01-01

150

Why N2 Molecules with Thermal Energy Abundantly Dissociate on W(100) and Not on W(110)  

NASA Astrophysics Data System (ADS)

Low-energy N2 molecules easily dissociate on W(100) but not on W(110). In this Letter, the six-dimensional potential energy surface for the dissociation of N2 molecules on W(110) has been determined by density functional calculations. Results are compared to those of N2 dissociation on W(100). The difference in reactivity between the two faces is shown to arise from the characteristics of the potential energy surface far from the surface (>3Å) and not from the properties of a precursor well or those of the final atomic adsorption sites.

Alducin, M.; Díez Muiño, R.; Busnengo, H. F.; Salin, A.

2006-08-01

151

Kinetic energies of fragment ions produced by dissociative photoionization of NO  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

152

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

PubMed

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

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

2014-12-10

153

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

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 1–2 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.

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

2007-10-25

154

Dissociation of methanol by ion-impact  

NASA Astrophysics Data System (ADS)

The dissociation dynamics of multiply charged methanol molecules formed in collision with 1.2 MeV Ar8+projectiles is studied. Using coincidence mapping techniques, we can separate out the different dissociation pathways between carbon, oxygen and hydrogen ionic fragments as well as two- and three-body breakup events. Reactions involving intramolecular bond rearrangements within the CH3 group of the dissociative molecule are discussed in detail. A signature of hydrogen migration in doubly charged methanol is observed. Kinetic energy releases of different breakup channels are reported here and compared with values calculated from a Coulomb explosion model. The shape and orientation of the islands in the coincidence map give further information about the momentum balance in the fragmentation process of two- or many-body dissociation pathways.

de, Sankar; Roy, A.; Rajput, Jyoti; Ghosh, P. N.; Safvan, C. P.

2008-09-01

155

Bonding  

MedlinePLUS

... between teeth Make teeth look longer Change the shape or color of teeth Sometimes, bonding also is used to ... a color that will most closely match the color of the tooth. He or she will shape the tooth with a drill (handpiece) if necessary, ...

156

Collision-induced dissociation of fatty acid [M - 2H + Na]- ions: charge-directed fragmentation and assignment of double bond position.  

PubMed

The collision-induced dissociation (CID) of cationic fatty acid-metal ion complexes has been extensively studied and, in general, provides rich structural information. In particular, charge-remote fragmentation processes are commonly observed allowing the assignment of double bond position. In a previous manuscript, we presented two methods to doubly deprotonate polyunsaturated fatty acids to form anionic fatty acid-sodium ion complexes, referred to as [M - 2H + Na]?(-) ions. In the current manuscript, the CID behavior of these [M - 2H + Na]?(-) ions is investigated for the first time. Significantly, we also present a deuterium-labeling experiment, which excludes the possibility that deprotonation occurs predominately at the ?-carbon in the formation of fatty acid [M - H + NaF](-) ions. This supports our original proposal where deprotonation occurs at the bis-allylic positions of polyunsaturated fatty acids. CID spectra of polyunsaturated fatty acid [M - 2H + Na](-) ions display abundant product ions arising from acyl chain cleavages. Through the examination of fatty acid isomers, it is demonstrated that double bond position may be unequivocally determined for methylene-interrupted polyunsaturated fatty acids with three or more carbon-carbon double bonds. In addition, CID of [M - 2H + Na](-) ions was applied to 18:3 isomers of Nannochloropsis oculata and three isomers were tentatively identified: ?(9,12,15)18:3, ?(6,9,12)18:3, and ?(5,8,11)18:3. We propose that structurally-informative product ions are formed via charge-driven fragmentation processes at the site of the resonance-stabilized carbanion as opposed to charge-remote fragmentation processes, which could be inferred if deprotonation occurred predominately at the ?-carbon. PMID:25142324

Thomas, Michael C; Altvater, Jens; Gallagher, Thomas J; Nette, Geoffrey W

2014-11-01

157

Students' interdisciplinary reasoning about "high-energy bonds" and ATP  

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

158

The kinetic energy change on covalent bond formation  

PubMed Central

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

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

1981-01-01

159

Energy decomposition analysis of covalent bonds and intermolecular interactions.  

PubMed

An energy decomposition analysis method is implemented for the analysis of both covalent bonds and intermolecular interactions on the basis of single-determinant Hartree-Fock (HF) (restricted closed shell HF, restricted open shell HF, and unrestricted open shell HF) wavefunctions and their density functional theory analogs. For HF methods, the total interaction energy from a supermolecule calculation is decomposed into electrostatic, exchange, repulsion, and polarization terms. Dispersion energy is obtained from second-order Møller-Plesset perturbation theory and coupled-cluster methods such as CCSD and CCSD(T). Similar to the HF methods, Kohn-Sham density functional interaction energy is decomposed into electrostatic, exchange, repulsion, polarization, and dispersion terms. Tests on various systems show that this algorithm is simple and robust. Insights are provided by the energy decomposition analysis into H(2), methane C-H, and ethane C-C covalent bond formation, CH(3)CH(3) internal rotation barrier, water, ammonia, ammonium, and hydrogen fluoride hydrogen bonding, van der Waals interaction, DNA base pair formation, BH(3)NH(3) and BH(3)CO coordinate bond formation, Cu-ligand interactions, as well as LiF, LiCl, NaF, and NaCl ionic interactions. PMID:19586091

Su, Peifeng; Li, Hui

2009-07-01

160

Energy decomposition analysis of covalent bonds and intermolecular interactions  

NASA Astrophysics Data System (ADS)

An energy decomposition analysis method is implemented for the analysis of both covalent bonds and intermolecular interactions on the basis of single-determinant Hartree-Fock (HF) (restricted closed shell HF, restricted open shell HF, and unrestricted open shell HF) wavefunctions and their density functional theory analogs. For HF methods, the total interaction energy from a supermolecule calculation is decomposed into electrostatic, exchange, repulsion, and polarization terms. Dispersion energy is obtained from second-order Møller-Plesset perturbation theory and coupled-cluster methods such as CCSD and CCSD(T). Similar to the HF methods, Kohn-Sham density functional interaction energy is decomposed into electrostatic, exchange, repulsion, polarization, and dispersion terms. Tests on various systems show that this algorithm is simple and robust. Insights are provided by the energy decomposition analysis into H2, methane C-H, and ethane C-C covalent bond formation, CH3CH3 internal rotation barrier, water, ammonia, ammonium, and hydrogen fluoride hydrogen bonding, van der Waals interaction, DNA base pair formation, BH3NH3 and BH3CO coordinate bond formation, Cu-ligand interactions, as well as LiF, LiCl, NaF, and NaCl ionic interactions.

Su, Peifeng; Li, Hui

2009-07-01

161

Storing Renewable Energy in Chemical Bonds  

ScienceCinema

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.

Helm, Monte; Bullock, Morris

2014-06-13

162

Storing Renewable Energy in Chemical Bonds  

SciTech Connect

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.

Helm, Monte; Bullock, Morris

2013-03-27

163

Bonding energies of bitumen to tar sand mineral  

SciTech Connect

The bonding energy of bitumen in a tar sand was found by algebraically adding the heat of dissolution of bitumen on tar sand, heat of dissolution of recovered bitumen and the heat of wetting of extracted tar sand mineral. The value for an Asphalt Ridge tar sand was found to be 270 cal/mole. 6 refs., 3 figs.

Ensley, E.K.; Scott, M.A.

1986-03-01

164

Mixed mode energy release rates for adhesively bonded beam specimens  

Microsoft Academic Search

This paper presents closed-form solutions for the energy release rate and the mode ratio of an equal adherend adhesively bonded beam specimen subject to a mixed mode bending load. The developed expressions explicitly account for the thickness and the material properties of the adhesive layer using a beam on an elastic foundation model. The accuracy of the expressions is verified

G. Fernlund; J. K. Spelt; T Kevin O'Brien

1994-01-01

165

Hydrogen bond energy of the water dimer  

Microsoft Academic Search

Large scale ab initio molecular orbital calculations on the binding energy of the water dimer have been performed. These calculations extend the previous correlation consistent basis set work to include larger basis sets (up to 574 functions), and core\\/valence correlation effects have now been included. The present work confirms the earlier estimate of -4.9 kcal\\/mol as the MP2(FC) basis set

Martin W. Feyereisen; David Feller; David A. Dixon

1996-01-01

166

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

167

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

SciTech Connect

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

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

168

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

PubMed

Low energy electron (LEE) induced cytosine base release in a selected pyrimidine nucleotide, viz., 2'-deoxycytidine-3'-monophosphate is investigated using ab initio electronic structure methods and time dependent quantum mechanical calculations. It has been noted that the cytosine base scission is comparatively difficult process than the 3' C-O bond cleavage from the lowest ?* shape resonance in energy region <1 eV. This is mainly due to the high activation energy barrier associated with the electron transfer from the ?* orbital of the base to the ?* orbital of the glycosidic N-C bond. In addition, the metastable state formed after impinging LEE (0-1 eV) has very short lifetime (10 fs) which may decay in either of the two competing auto-detachment or dissociation process simultaneously. On the other hand, the selected N-C mode may cleave to form the cytosine base anion at higher energy regions (>2 eV) via tunneling of the glycosidic bond. Resonance states generated within this energy regime will exist for a duration of ~35-55 fs. Comparison of salient features of the two dissociation events, i.e., 3' C-O single strand break and glycosidic N-C bond cleavage in 3'-dCMPH molecule are also provided. PMID:25217918

Bhaskaran, Renjith; Sarma, Manabendra

2014-09-14

169

Strength of Chemical Bonds  

NASA Technical Reports Server (NTRS)

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

Christian, Jerry D.

1973-01-01

170

Heats of Formation and Bond Energies in Group III Compounds  

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

171

MULTIPHOTON DISSOCIATION OF POLY ATOMIC MOLECULES  

E-print Network

intensity and energy fluence, because the dissociation lifetimeintensities CF,I is not excited much beyond its dissociation energy, because the dissociation lifetimeintensity for pulse dura­ tions longer than 0.6 ns. We call this regime lifetime

Schulz, Peter A.

2010-01-01

172

Clean renewable energy bonds (CREBs) present a low-cost opportunity for public entities to issue bonds to finance  

E-print Network

bonds to finance renewable energy projects. The federal government lowers the cost of debt by providing makes cash inter- est payments. The federal government exempts this interest income from federal taxes credit rating. ·Tax credit bonds. The federal government provides the investor with tax credits in lieu

173

Higher-energy C-trap dissociation for peptide modification analysis.  

PubMed

Peptide sequencing is the basis of mass spectrometry-driven proteomics. Here we show that in the linear ion trap-orbitrap mass spectrometer (LTQ Orbitrap) peptide ions can be efficiently fragmented by high-accuracy and full-mass-range tandem mass spectrometry (MS/MS) via higher-energy C-trap dissociation (HCD). Immonium ions generated via HCD pinpoint modifications such as phosphotyrosine with very high confidence. Additionally we show that an added octopole collision cell facilitates de novo sequencing. PMID:17721543

Olsen, Jesper V; Macek, Boris; Lange, Oliver; Makarov, Alexander; Horning, Stevan; Mann, Matthias

2007-09-01

174

A big data approach to the ultra-fast prediction of DFT-calculated bond energies  

PubMed Central

Background The rapid access to intrinsic physicochemical properties of molecules is highly desired for large scale chemical data mining explorations such as mass spectrum prediction in metabolomics, toxicity risk assessment and drug discovery. Large volumes of data are being produced by quantum chemistry calculations, which provide increasing accurate estimations of several properties, e.g. by Density Functional Theory (DFT), but are still too computationally expensive for those large scale uses. This work explores the possibility of using large amounts of data generated by DFT methods for thousands of molecular structures, extracting relevant molecular properties and applying machine learning (ML) algorithms to learn from the data. Once trained, these ML models can be applied to new structures to produce ultra-fast predictions. An approach is presented for homolytic bond dissociation energy (BDE). Results Machine learning models were trained with a data set of >12,000 BDEs calculated by B3LYP/6-311++G(d,p)//DFTB. Descriptors were designed to encode atom types and connectivity in the 2D topological environment of the bonds. The best model, an Associative Neural Network (ASNN) based on 85 bond descriptors, was able to predict the BDE of 887 bonds in an independent test set (covering a range of 17.67–202.30 kcal/mol) with RMSD of 5.29 kcal/mol, mean absolute deviation of 3.35 kcal/mol, and R2?=?0.953. The predictions were compared with semi-empirical PM6 calculations, and were found to be superior for all types of bonds in the data set, except for O-H, N-H, and N-N bonds. The B3LYP/6-311++G(d,p)//DFTB calculations can approach the higher-level calculations B3LYP/6-311++G(3df,2p)//B3LYP/6-31G(d,p) with an RMSD of 3.04 kcal/mol, which is less than the RMSD of ASNN (against both DFT methods). An experimental web service for on-line prediction of BDEs is available at http://joao.airesdesousa.com/bde. Conclusion Knowledge could be automatically extracted by machine learning techniques from a data set of calculated BDEs, providing ultra-fast access to accurate estimations of DFT-calculated BDEs. This demonstrates how to extract value from large volumes of data currently being produced by quantum chemistry calculations at an increasing speed mostly without human intervention. In this way, high-level theoretical quantum calculations can be used in large-scale applications that otherwise would not afford the intrinsic computational cost. PMID:23849655

2013-01-01

175

Accurate Bond Energies of Hydrocarbons from Complete Basis Set Extrapolated Multi-Reference Singles and Doubles Configuration Interaction  

SciTech Connect

Quantum chemistry has become one of the most reliable tools for characterizing the thermochemical underpinnings of reactions, such as bond dissociation energies (BDEs). The accurate prediction of these particular properties (BDEs) are challenging for ab initio methods based on perturbative corrections or coupled cluster expansions of the single-determinant Hartree-Fock wave function: the processes of bond breaking and forming are inherently multi-configurational and require an accurate description of non-dynamical electron correlation. To this end, we present a systematic ab initio approach for computing BDEs that is based on three components: (1) multi-reference single and double excitation configuration interaction (MRSDCI) for the electronic energies; (2) a two-parameter scheme for extrapolating MRSDCI energies to the complete basis set limit; and (3) DFT-B3LYP calculations of minimumenergy structures and vibrational frequencies to account for zero point energy and thermal corrections. We validated our methodology against a set of reliable experimental BDE values of C*C and C*H bonds of hydrocarbons. The goal of chemical accuracy is achieved, on average, without applying any empirical corrections to the MRSDCI electronic energies. We then use this composite scheme to make predictions of BDEs in a large number of hydrocarbon molecules for which there are no experimental data, so as to provide needed thermochemical estimates for fuel molecules.

Oyeyemi, Victor B.; Pavone, Michele; Carter, Emily A.

2011-11-03

176

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

PubMed

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

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

2006-11-01

177

IR Spectra and Bond Energies Computed Using DFT  

NASA Technical Reports Server (NTRS)

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.

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

2000-01-01

178

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

PubMed

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

Lu, Tian; Chen, Feiwu

2013-04-11

179

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

NASA Astrophysics Data System (ADS)

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.

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

2015-04-01

180

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

Microsoft Academic Search

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

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

2005-01-01

181

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

ERIC Educational Resources Information Center

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 =…

Smith, Derek W.

2004-01-01

182

Controlling the bond scission sequence of oxygenates for energy applications  

NASA Astrophysics Data System (ADS)

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

Stottlemyer, Alan L.

183

Excitation energy transfer in covalently bonded porphyrin heterodimers  

NASA Astrophysics Data System (ADS)

We describe the photophysical properties of heterodimers that are formed by the free base 2-(2-carboxyvinyl)-5,10,15,20-tetraphenylporphyrin and the zinc complex of 5-( p-aminophenyl)-10,15,20-triphenylporphyrin and that are covalently bonded by the amide link. These dimers differ in the configuration of the double bond in the spacer group. We determine fluorescence quantum yields of heterodimers and their porphyrin components. The energy transfer rate constants have been estimated from the measured fluorescence lifetimes and fluorescence excitation spectra and, also, they have been calculated from the steady-state absorption and fluorescence spectra according to the Förster theory. We have found that the efficiency of the intramolecular energy transfer in heterodimers is 0.97-0.99, and the energy migration rate constants have been found to be (1.82-4.49) × 1010 s-1. The results of our investigation show that synthesized heterodimers can be used as efficient light-harvesting elements in solar energy conversion devices.

Paschenko, V. Z.; Konovalova, N. V.; Bagdashkin, A. L.; Gorokhov, V. V.; Tusov, V. B.; Yuzhakov, V. I.

2012-04-01

184

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

E-print Network

Cleavage of thymine N3­H bonds by low-energy electrons attached to base p* orbitals Magali The the effects of base p-stacking on the rates of such bond cleavages. To date, our results suggest that sugar­phosphate C­O bonds have the lowest barriers to cleavage, that attach- ment of electrons with energies below 2

Simons, Jack

185

The molecular dissociation of formaldehyde at medium photoexcitation energies: A quantum chemistry and direct quantum dynamics study  

SciTech Connect

The mechanisms of radiationless decay involved in the photodissociation of formaldehyde into H{sub 2} and CO have been investigated using complete active space self-consistent field (CASSCF) calculations and direct dynamics variational multiconfiguration Gaussian (DD-vMCG) quantum dynamics in the S{sub 1}, T{sub 1}, and S{sub 0} states. A commonly accepted scheme involves Fermi Golden Rule internal conversion from S{sub 1} followed by dissociation of vibrationally hot H{sub 2}CO in S{sub 0}. We recently proposed a novel mechanism [M. Araujo et al., J. Phys. Chem. A 112, 7489 (2008)] whereby internal conversion and dissociation take place in concert through a seam of conical intersection between S{sub 1} and S{sub 0} after the system has passed through an S{sub 1} transition barrier. The relevance of this mechanism depends on the efficiency of tunneling in S{sub 1}. At lower energy, an alternative scheme to internal conversion involves intersystem crossing via T{sub 1} to regenerate the reactant before the S{sub 0} barrier to dissociation. We propose here a previously unidentified mechanism leading directly to H{sub 2} and CO products via T{sub 1}. This channel opens at medium energies, near or above the T{sub 1} barrier to dissociation and still lower than the S{sub 1} barrier, thus making T{sub 1} a possible shortcut to molecular dissociation.

Araujo, Marta; Magalhaes, Alexandre L. [REQUIMTE, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto (Portugal); Lasorne, Benjamin [Institut Charles Gerhardt (UMR 5253), CNRS, Universite Montpellier 2, CC 1501, Place Eugene Bataillon, 34095 Montpellier (France); Department of Chemistry, Imperial College London, London SW7 2AZ (United Kingdom); Worth, Graham A. [School of Chemistry, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Bearpark, Michael J.; Robb, Michael A. [Department of Chemistry, Imperial College London, London SW7 2AZ (United Kingdom)

2009-10-14

186

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

E-print Network

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

Reif, Rafael

187

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

E-print Network

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

Schlegel, H. Bernhard

188

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

ERIC Educational Resources Information Center

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

Cooper, Melanie M.; Klymkowsky, Michael W.

2013-01-01

189

Dissociation mechanisms of the Ar trimer induced by a third atom in high-energy electron-impact ionization  

NASA Astrophysics Data System (ADS)

We experimentally studied the dissociation dynamics of a highly charged Ar3 cluster initiated by a high-energy electron. The dissociation patterns of the correlated ions from a two-body and a three-body Coulombic explosion (CE) of (Ar3)2+ suggest that predissociation alters the evolution of radiative charge transfer. The three-body CE in (Ar3)4+ and (Ar3)5+ is driven, after double ionization of one constituent Ar atom, by single ionization with a simultaneous interatomic Coulombic decay process.

Yan, S.; Zhang, P.; Ma, X.; Xu, S.; Tian, S. X.; Li, B.; Zhu, X. L.; Feng, W. T.; Zhao, D. M.

2014-06-01

190

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

NASA Astrophysics Data System (ADS)

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.

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

2007-11-01

191

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

E-print Network

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

Reisler, Hanna

192

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

PubMed

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

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

2012-02-01

193

Low-energy collision-induced dissociation of deprotonated dinucleotides: determination of the energetically favored dissociation pathways and the relative acidities of the nucleic acid bases  

Microsoft Academic Search

Fourier transform ion cyclotron resonance mass spectroscopy has been used to examine the collision-induced dissociation pathways of all 16 of the possible deprotonated dinucleotides. These quasimolecular ions were generated by cesium ion bombardment of a mixture of triethanolamine, ammonium hydroxide and the dinucleotide. Collisional activation using continuous off-resonance excitation permits observation of energetically-favorable dissociation pathways. Dissociation products were examined over

M. T. Rodgers; Sherrie Campbell; Elaine M. Marzluff; J. L. Beauchamp

1994-01-01

194

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

E-print Network

Low-Energy (0.1 eV) Electron Attachment S­S Bond Cleavage Assisted by Coulomb Stabilization and insights should be of substantial value to workers studying bond cleavage rates and fragmentation patterns Chem 102: 838­846, 2005 Key words: electron attachment; bond cleavage; disulfide bridge Correspondence

Simons, Jack

195

Absence of CO dissociation on Mo(112).  

PubMed

We revisit the problem of CO adsorption and thermal dissociation on the Mo(112) surface by means of density-functional calculations of binding energies, local densities of states, and CO vibrational frequencies for various configurations of equilibrated adlayers. The bridge-on-row adsorption sites on the Mo(112) surface are found to be the most favorable and CO molecules will occupy less stable in-furrow sites only after the completing of the first monolayer. At low coverages, CO molecules are tilted by approximately 40 degrees with respect to the normal to the surface (the beta state), but with increasing coverage, due to lateral interactions, attain an upright orientation with the carbon end down (the alpha state). The tilting of CO results in a significant elongation of the C-O bond (to 1.20 A) and, consequently, the C-O stretching vibration frequency decreases to 1159 cm(-1). Nonetheless, the beta state cannot be attributed to the precursor to CO dissociation, because the estimated potential barrier for the dissociation (approximately 2.8 eV) substantially exceeds the chemisorption energy (2.1 eV), which makes the thermally induced CO dissociation on Mo improbable. With estimated chemisorption energies, Monte Carlo simulations have shown that the two-peak shape of TPD spectra can be explained without involving the CO dissociation. We predict also that the lack of dissociation can be detected in photoemission studies for CO on Mo(112) by the presence of the -23 and -7 eV peaks, characteristic of chemisorbed CO, and absence of the -18 and -5 eV peaks characteristic of adsorbed O atoms. PMID:19425805

Yakovkin, I N; Petrova, N V

2009-05-01

196

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

SciTech Connect

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

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

2006-02-28

197

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

NASA Astrophysics Data System (ADS)

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.

Eisfeld, Wolfgang; Vieuxmaire, Olivier; Viel, Alexandra

2014-06-01

198

Interstellar Isomers: The Importance of Bonding Energy Differences  

E-print Network

We present strong detections of methyl cyanide, vinyl cyanide, ethyl cyanide and cyanodiacetylene molecules with the Green Bank Telescope (GBT) toward the Sgr B2(N) molecular cloud. Attempts to detect the corresponding isocyanide isomers were only successful in the case of methyl isocyanide for its J(K)=1(0)-0(0) transition, which is the first interstellar report of this line. To determine the spatial distribution of methyl isocyanide, we used archival Berkeley-Illinois-Maryland Association (BIMA) array data for the J(K)=4(K)-3(K) (K=0-3) transitions but no emission was detected. From ab initio calculations, the bonding energy difference between the cyanide and isocyanide molecules is >8500 cm^-1 (>12,000 K). That we detect methyl isocyanide emission with a single antenna (Gaussian beamsize(Omega_B)=1723 arcsec^2) but not with an interferometer (Omega_B=192 arcsec^2), strongly suggests that methyl isocyanide has a widespread spatial distribution toward the Sgr B2(N) region. Thus, large-scale, non-thermal processes in the surrounding medium may account for the conversion of methyl cyanide to methyl isocyanide while the LMH hot core, which is dominated by thermal processes, does not produce a significant amount of methyl isocyanide. Ice analog experiments by other investigators have shown that radiation bombardment of methyl cyanide can produce methyl isocyanide, thus supporting our observations. We conclude that isomers separated by such large bonding energy differences are distributed in different interstellar environments, making the evaluation of column density ratios between such isomers irrelevant unless it can be independently shown that these species are co-spatial.

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

2005-06-21

199

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

NASA Astrophysics Data System (ADS)

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).

Fabrikant, I.; Marienfeld, S.

2005-05-01

200

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

201

Dissociated methanol test results  

SciTech Connect

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.

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

1982-04-01

202

Dissociative ionization cross sections of CO2 at electron impact energy of 5 keV  

NASA Astrophysics Data System (ADS)

The dissociative ionization of CO2 induced by 5 keV electrons in two-body and three-body dissociative channels of CO22+ and CO23+ is identified by the ion—ion coincidence- method using a momentum imaging spectrometer. The partial ionization cross sections (PICSs) of different ionic fragments are measured and the results generally agree with the calculations made by a semi-empirical approach. Furthermore, the PICSs of the dissociative channels are also obtained by carefully considering the detection efficiency of the micro-channel plates and the total transmission efficiency of the time of flight system.

Wang, En-Liang; Shen, Zhen-Jie; Yang, Hong-Jiang; Tang, Ya-Guo; Shan, Xu; Chen, Xiang-Jun

2014-11-01

203

Nonstatistical bond breaking in the multiphoton ionization/dissociation of [Fe(CO){sub 5}]{sub m}Ar{sub n} clusters  

SciTech Connect

Photoionization of iron pentacarbonyl/argon clusters with 30 ps, 266 nm laser pulses results in the ultimate detection of iron ions solvated with argon atoms. Clusters such as Fe{sub m}{sup +}Ar{sub n} (m=1,2; n=1{endash}26) are readily observed following the laser-induced decarbonylation of the [Fe(CO){sub 5}]{sub m}Ar{sub n} species formed in the supersonic jet. An interesting intensity alternation of the Fe{sup +}Ar{sub n} ions is observed up to a magic number at n=6, after which a monotonically decreasing intensity pattern is noted. The pattern is similar to a more extensive spectrum (with additional magic numbers) observed in separate experiments where metallic iron is laser ablated into a supersonic flow of argon, krypton, or xenon, and the resulting cluster ions are detected in a reflectron mass spectrometer. In another experiment in the latter apparatus, the sputtering of iron into a mixture of carbon monoxide and argon shows the relative reactivity of Fe{sup +} to form Fe{sup +}Ar{sub n} and Fe{sup +}(CO){sub n} ions. Mechanisms for the energy disposal during the ionization/dissociation process are discussed. Additionally, the intensity pattern of iron{endash}rare gas clusters, Fe{sup +}(RG){sub n}, is discussed in the context of structural arguments which have previously been applied successfully to a large number of metal{endash}rare gas systems. {copyright} {ital 1998 American Institute of Physics.}

Bililign, S.; Feigerle, C.S.; Miller, J.C. [Biochemistry and Biophysics Section, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee37831-6125] [Biochemistry and Biophysics Section, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee37831-6125; [Department of Chemistry, University of Tennessee, Knoxville, Tennessee37996 (United States); Velegrakis, M. [Foundation for Research and Technology-Hellas, Institute of Electronic Structure and Laser, FORTH-IESL, P.O. Box 1527, Heraklion 71110, Crete (Greece)] [Foundation for Research and Technology-Hellas, Institute of Electronic Structure and Laser, FORTH-IESL, P.O. Box 1527, Heraklion 71110, Crete (Greece)

1998-04-01

204

Dissociative disorders.  

PubMed

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

Kihlstrom, John F

2005-01-01

205

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

SciTech Connect

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

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

2008-08-01

206

Influence of confinement on hydrogen bond energy. The case of the FH···NCH dimer.  

PubMed

The influence of the external pressure on the energy of the intermolecular hydrogen bond is investigated by modeling the pressure effects with helium atoms located at fixed points in space around the hydrogen bonded dimer. Several methods of estimating the energy of the H···N hydrogen bond in the He···FH···NCH···He model system are proposed. They show that the energy of the H···N hydrogen bond in this confined dimer decreases continuously with the reduction of the He···He distance, thus with the increase of the pressure effect exerted on the confined dimer. PMID:20738112

Jab?o?ski, Miros?aw; Solà, Miquel

2010-09-23

207

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

208

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

PubMed

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

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

2015-01-28

209

Theoretical investigation of the competitive mechanism between dissociation and ionization of H?? in intense field.  

PubMed

The competitive mechanism between dissociation and ionization of hydrogen molecular ion in intense field has been theoretically investigated by using an accurate non-Born-Oppenheimer method. The relative yield of fragments indicates that the dissociation and ionization channels are competitive with the increasing laser intensity from 5.0 × 10(13) to 2.0 × 10(14) W/cm(2). In the case of intensity lower than 1.0 × 10(14) W/cm(2), the dissociation channel is dominant, with a minor contribution from ionization. The mechanism of dissociation includes the contributions from the bond softening, bond hardening, below-threshold dissociation, and above-threshold dissociation, which are strongly dependent on the laser intensity and initial vibrational state. Furthermore, the ionization dominates over the dissociation channel at the highest intensity of 2.0 × 10(14) W/cm(2). The reasonable origin of ionization is ascribed as the above-threshold Coulomb explosion, which has been demonstrated by the space-time dependent ionization rate. Moreover, the competition mechanism between dissociation and ionization channels are displayed on the total kinetic energy resolved (KER) spectra, which could be tested at current experimental conditions. PMID:24806756

Yao, Hongbin; Zhao, Guangjiu

2014-10-01

210

Dissociative electron attachments to ethanol and acetaldehyde: A combined experimental and simulation study  

NASA Astrophysics Data System (ADS)

Dissociation dynamics of the temporary negative ions of ethanol and acetaldehyde formed by the low-energy electron attachments is investigated by using the anion velocity map imaging technique and ab initio molecular dynamics simulations. The momentum images of the dominant fragments O-/OH- and CH3- are recorded, indicating the low kinetic energies of O-/OH- for ethanol while the low and high kinetic energy distributions of O- ions for acetaldehyde. The CH3- image for acetaldehyde also shows the low kinetic energy. With help of the dynamics simulations, the fragmentation processes are qualitatively clarified. A new cascade dissociation pathway to produce the slow O- ion via the dehydrogenated intermediate, CH3CHO- (acetaldehyde anion), is proposed for the dissociative electron attachment to ethanol. After the electron attachment to acetaldehyde molecule, the slow CH3- is produced quickly in the two-body dissociation with the internal energy redistributions in different aspects before bond cleavages.

Wang, Xu-Dong; Xuan, Chuan-Jin; Feng, Wen-Ling; Tian, Shan Xi

2015-02-01

211

Dissociative electron attachments to ethanol and acetaldehyde: A combined experimental and simulation study.  

PubMed

Dissociation dynamics of the temporary negative ions of ethanol and acetaldehyde formed by the low-energy electron attachments is investigated by using the anion velocity map imaging technique and ab initio molecular dynamics simulations. The momentum images of the dominant fragments O(-)/OH(-) and CH3 (-) are recorded, indicating the low kinetic energies of O(-)/OH(-) for ethanol while the low and high kinetic energy distributions of O(-) ions for acetaldehyde. The CH3 (-) image for acetaldehyde also shows the low kinetic energy. With help of the dynamics simulations, the fragmentation processes are qualitatively clarified. A new cascade dissociation pathway to produce the slow O(-) ion via the dehydrogenated intermediate, CH3CHO(-) (acetaldehyde anion), is proposed for the dissociative electron attachment to ethanol. After the electron attachment to acetaldehyde molecule, the slow CH3 (-) is produced quickly in the two-body dissociation with the internal energy redistributions in different aspects before bond cleavages. PMID:25681915

Wang, Xu-Dong; Xuan, Chuan-Jin; Feng, Wen-Ling; Tian, Shan Xi

2015-02-14

212

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

PubMed Central

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 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 ion–dipole complex stabilization. PMID:20228960

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

2010-01-01

213

Conformational stability of disulfide bonds in redox processes  

NASA Astrophysics Data System (ADS)

The protein sulfur functions have numerous cellular fundamental roles. They are in charge of the maintenance of the cellular reduction potential, which in turn governs gene expression. In addition, the redox cycling of disulfide/thiol functions has a great importance in the protein folding-unfolding process, which governs the functioning of enzymes. In our previous studies, we showed that the redox properties of disulfide bonds differ considerably. An analysis of the structure of the disulfide bonds in several proteins in the Protein Data Bank indicated that there are two types of conformations. Thus, we have compared the structures of the anions in these two types of conformation and the SS bond dissociation energy of the anion. For both conformations, the SS bond length of the anion and the electronic affinity are very close. However, the bond dissociation energy (BDE) varies.

Houée-Levin, C.; Bergès, J.

2008-10-01

214

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

PubMed Central

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

Pauling, Linus; Kamb, Barclay

1986-01-01

215

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

Microsoft Academic Search

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

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

2009-01-01

216

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

Microsoft Academic Search

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

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

2009-01-01

217

Interstellar Isomers: The Importance of Bonding Energy Differences  

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

218

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

SciTech Connect

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.

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

219

Dissociation of a Product of a Surface Reaction in the Gas Phase: Xenon Difluoride Reaction with Si  

NASA Astrophysics Data System (ADS)

Xenon difluoride interacts with Si(100)2x1 at the dangling bond sites by atom abstraction whereby a dangling bond abstracts a F atom from XeF2, forming a Si-F bond and scattering the complementary XeF radical. The XeF fragment produced by this reaction follows either of two subsequent pathways. In one pathway, it interacts with the surface a second time, undergoing a second F atom abstraction reaction and giving rise to a second Si-F bond and a scattered Xe atom. In the other pathway, it scatters into the gas phase. Some of the XeF scattered into the gas phase is observed to dissociate. The dissociation arises from the partitioning of sufficient reaction exothermicity to the rovibrational continuum of the ground electronic state of XeF. The resulting F and Xe atoms are shown conclusively to arise from dissociation of gas phase XeF by demonstrating that the angle-resolved velocity distributions of F, Xe, and XeF conserve momentum, energy, and mass. The dissociation occurs when XeF is about 2 Å away from the surface. The XeF bond orientations at the time of dissociation are largely those where the F atom of the XeF fragment is pointing into the vacuum. This experiment documents the first observation of dissociation of a product of a surface reaction in the gas phase.

Ceyer, S. T.

2004-03-01

220

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

SciTech Connect

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

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

2014-03-28

221

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

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

222

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

PubMed

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

Jiang, Bin; Guo, Hua

2014-12-01

223

Theoretical studies on the dissociation reactions of chloromethyl peroxynitrate  

NASA Astrophysics Data System (ADS)

Using the CCSD(T)/cc-pVDZ//B3LYP/6-311G(2d,2p) method, we investigated the detailed potential energy surfaces for the unimolecular dissociation reactions of chloromethyl peroxynitrate (CH2ClO2NO2). The results show that there are four most stable isomers of CH2ClO2NO2, named IS1, IS2, IS3 and IS4. From these isomers, twenty unimolecular decomposition reaction channels have been studied and discussed. Among them, the predominant thermal decomposition pathways are those direct O-N bond rupture to produce o-cis-CH2ClO2?+NO2 or i-cis-CH2ClO2?+NO2. The corresponding O-N bond dissociation energies (BDEs) are 22.0, 22.0, 21.7 and 21.7 kcal/mol, respectively, in good agreement with the experimental results.

Wei, Wen-mei; Zheng, Ren-hui; Hou, Tao; Xu, Shuang-jun; Zhang, Sheng-hui

2014-03-01

224

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

SciTech Connect

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.

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

2009-03-23

225

Electron-induced ionization and dissociative ionization of iron pentacarbonyl molecules  

NASA Astrophysics Data System (ADS)

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.

Lacko, Michal; Papp, Peter; Wnorowski, Karol; Matejí?k, Štefan

2015-03-01

226

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

227

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

E-print Network

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

Houston, Paul L.

228

State-resolved spectroscopy of high vibrational levels of water up to the dissociative continuum.  

PubMed

We summarize here our experimental studies of the high rovibrational energy levels of water. The use of double-resonance vibrational overtone excitation followed by energy-selective photofragmentation and laser-induced fluorescence detection of OH fragments allowed us to measure previously inaccessible rovibrational energies above the seventh OH-stretch overtone. Extension of the experimental approach to triple-resonance excitation provides access to rovibrational levels via transitions with significant transition dipole moments (mainly OH-stretch overtones) up to the dissociation threshold of the O-H bond. A collisionally assisted excitation scheme enables us to probe vibrations that are not readily accessible via pure laser excitation. Observation of the continuous absorption onset yields a precise value for the O-H bond dissociation threshold, 41?145.94 ± 0.15?cm(-1). Finally, we detect long-lived resonances as sharp peaks in spectra above the dissociation threshold. PMID:22547240

Maksyutenko, Pavlo; Grechko, Maxim; Rizzo, Thomas R; Boyarkin, Oleg V

2012-06-13

229

CO dissociation on iron nanoparticles: Size and geometry effects  

NASA Astrophysics Data System (ADS)

The reactivity of 0.5-1.4 nm iron nanoparticles and corresponding bulk surfaces has been systematically studied using density functional theory. The study includes both ideally symmetric and more realistic rugged nanoparticles. The activation energies for CO dissociation vary between 1.1 and 2.1 eV. An increasing particle size and roughness result in lower activation energies. For a single particle, variations as large as 0.9 eV occur indicating the importance of local particle morphology. Depending on the nanoparticle size, geometry, and CO dissociation pathway the reaction rates span five orders of magnitude at conditions relevant for gas-phase chemical vapor deposition synthesis of carbon nanotubes. Studies on the smallest particles and bulk surfaces show that these systems cannot be used as reliable models for catalysis on larger iron nanoparticles. It has also been demonstrated that predictive d-band and linear-energy relationships cannot be used to explain the reactivity of iron for CO dissociation as reaction mechanisms vary from one particle to another. The changes in reaction mechanisms can be rationalized by the varying Fe-Fe bond lengths in different particles leading to changes in back-bonding between the iron surface and CO. CO dissociation on nano-sized iron seems to be more complex than that seen on more conventional non-magnetic noble metal particles.

Melander, Marko; Latsa, Ville; Laasonen, Kari

2013-10-01

230

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

E-print Network

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

Reisler, Hanna

231

Financing Public Sector Projects with Clean Renewable Energy Bonds; Fact Sheet Series on Financing Renewable Energy Projects, National Renewable Energy Laboratory (NREL)  

Microsoft Academic Search

Clean renewable energy bonds (CREBs) present a low-cost opportunity for public entities to issue bonds to finance renewable energy projects. The federal government lowers the cost of debt by providing a tax credit to the bondholder in lieu of interest payments from the issuer. Because CREBs are theoretically interest free, they may be more attractive than traditional tax-exempt municipal bonds.

C. Kreycik; J. Couglin

2009-01-01

232

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

E-print Network

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

Raji Heyrovska

2008-07-27

233

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

E-print Network

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

Heyrovska, Raji

2008-01-01

234

Diffraction Dissociation - 50 Years Later  

E-print Network

The field of Diffraction Dissociation, which is the subject of this workshop, began 50 years ago with the analysis of deuteron stripping in low energy collisions with nuclei. We return to the subject in a modern context- deuteron dissociation in $\\sqrt{s_{NN}}= 200$ GeV d-Au collisions recorded during the 2003 RHIC run in the PHENIX experiment. At RHIC energy, d$\\to$n+p proceeds predominantly (90%) through Electromagnetic Dissociation and the remaining fraction via the hadronic shadowing described by Glauber. Since the dissociation cross section has a small theoretical error we adopt this process to normalize other cross sections measured in RHIC.

Sebastian N. White

2005-07-18

235

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

236

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

SciTech Connect

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.

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

237

Exit angle, energy loss and internuclear distance distributions of H 2+ ions dissociated when traversing different materials  

NASA Astrophysics Data System (ADS)

We have performed computer simulations of the trajectory followed by each proton resulting from the dissociation of H 2+ molecules when traversing a thin solid target. We use the dielectric formalism to describe the forces due to electronic excitations in the medium, and we also consider the Coulomb repulsion between the pair of protons. Nuclear collisions with target nuclei are incorporated through a Monte Carlo code and the effect of the coherent scattering is taken into account by means of an effective force model. The distributions of exit angle, energy loss and internuclear separations of the protons fragments are discussed for the case of amorphous carbon and aluminum targets.

Garcia-Molina, Rafael; Abril, Isabel; Denton, Cristian D.; Arista, Néstor R.

2000-04-01

238

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

PubMed

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

Jacobsen, Heiko

2009-06-01

239

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

SciTech Connect

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.

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

2014-08-01

240

Toward accurate prediction of potential energy surfaces and the spectral density of hydrogen bonded systems  

NASA Astrophysics Data System (ADS)

Despite the considerable progress made in quantum theory and computational methods, detailed descriptions of the potential energy surfaces of hydrogen-bonded systems have not yet been achieved. In addition, the hydrogen bond (H-bond) itself is still so poorly understood at the fundamental level that it remains unclear exactly what geometry constitutes a “real” H-bond. Therefore, in order to investigate features essential for hydrogen bonded complexes, a simple, efficient, and general method for calculating matrix elements of vibrational operators capable of describing the stretching modes and the H-bond bridges of hydrogen-bonded systems is proposed. The derived matrix elements are simple and computationally easy to evaluate, which makes the method suitable for vibrational studies of multiple-well potentials. The method is illustrated by obtaining potential energy surfaces for a number of two-dimensional systems with repulsive potentials chosen to be in Gaussian form for the stretching mode and of the Morse-type for the H-bond bridge dynamics. The forms of potential energy surfaces of weak and strong hydrogen bonds are analyzed by varying the asymmetry of the Gaussian potential. Moreover, the choice and applicability of the selected potential for the stretching mode and comparison with other potentials used in the area of hydrogen bond research are discussed. The approach for the determination of spectral density has been constructed in the framework of the linear response theory for which spectral density is obtained by Fourier transform of the autocorrelation function of the dipole moment operator of the fast mode. The approach involves anharmonic coupling between the high frequency stretching vibration (double well potential) and low-frequency donor-acceptor stretching mode (Morse potential) as well as the electrical anharmonicity of the dipole moment operator of the fast mode. A direct relaxation mechanism is incorporated through a time decaying exponential according to Rösch and Ratner theory.

Rekik, Najeh

2014-03-01

241

Characterizing Changes in the Rate of Protein-Protein Dissociation upon Interface Mutation Using Hotspot Energy and Organization  

PubMed Central

Predicting the effects of mutations on the kinetic rate constants of protein-protein interactions is central to both the modeling of complex diseases and the design of effective peptide drug inhibitors. However, while most studies have concentrated on the determination of association rate constants, dissociation rates have received less attention. In this work we take a novel approach by relating the changes in dissociation rates upon mutation to the energetics and architecture of hotspots and hotregions, by performing alanine scans pre- and post-mutation. From these scans, we design a set of descriptors that capture the change in hotspot energy and distribution. The method is benchmarked on 713 kinetically characterized mutations from the SKEMPI database. Our investigations show that, with the use of hotspot descriptors, energies from single-point alanine mutations may be used for the estimation of off-rate mutations to any residue type and also multi-point mutations. A number of machine learning models are built from a combination of molecular and hotspot descriptors, with the best models achieving a Pearson's Correlation Coefficient of 0.79 with experimental off-rates and a Matthew's Correlation Coefficient of 0.6 in the detection of rare stabilizing mutations. Using specialized feature selection models we identify descriptors that are highly specific and, conversely, broadly important to predicting the effects of different classes of mutations, interface regions and complexes. Our results also indicate that the distribution of the critical stability regions across protein-protein interfaces is a function of complex size more strongly than interface area. In addition, mutations at the rim are critical for the stability of small complexes, but consistently harder to characterize. The relationship between hotregion size and the dissociation rate is also investigated and, using hotspot descriptors which model cooperative effects within hotregions, we show how the contribution of hotregions of different sizes, changes under different cooperative effects. PMID:24039569

Agius, Rudi; Torchala, Mieczyslaw; Moal, Iain H.; Fernández-Recio, Juan; Bates, Paul A.

2013-01-01

242

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

NASA Astrophysics Data System (ADS)

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.

Srivastava, Amit; Granek, Rony

2015-02-01

243

Communication: Rigorous calculation of dissociation energies (D0) of the water trimer, (H2O)3 and (D2O)3  

NASA Astrophysics Data System (ADS)

Using a recent, full-dimensional, ab initio potential energy surface [Y. Wang, X. Huang, B. C. Shepler, B. J. Braams, and J. M. Bowman, J. Chem. Phys. 134, 094509 (2011)], 10.1063/1.3554905 together with rigorous diffusion Monte Carlo calculations of the zero-point energy of the water trimer, we report dissociation energies, D0, to form one monomer plus the water dimer and three monomers. The calculations make use of essentially exact zero-point energies for the water trimer, dimer, and monomer, and benchmark values of the electronic dissociation energies, De, of the water trimer [J. A. Anderson, K. Crager, L. Fedoroff, and G. S. Tschumper, J. Chem. Phys. 121, 11023 (2004)], 10.1063/1.1799931. The D0 results are 3855 and 2726 cm-1 for the 3H2O and H2O + (H2O)2 dissociation channels, respectively, and 4206 and 2947 cm-1 for 3D2O and D2O + (D2O)2 dissociation channels, respectively. The results have estimated uncertainties of 20 and 30 cm-1 for the monomer plus dimer and three monomer of dissociation channels, respectively.

Wang, Yimin; Bowman, Joel M.

2011-10-01

244

Dissociation of a Product of a Surface Reaction in the Gas Phase: XeF2 Reaction with Si  

NASA Astrophysics Data System (ADS)

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

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

2004-05-01

245

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

PubMed

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

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

2015-01-21

246

Monte Carlo configuration interaction with perturbation corrections for dissociation energies of first row diatomic molecules: C2, N2, O2, CO, and NO  

NASA Astrophysics Data System (ADS)

Dissociation energies for the diatomic molecules C2, N2, O2, 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(103) from a FCI space of dimension O(1014), 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.

Kelly, Thomas P.; Perera, Ajith; Bartlett, Rodney J.; Greer, James C.

2014-02-01

247

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

PubMed Central

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

Li, Yilei; Zhu, Zhencai; Chen, Guoan

2014-01-01

248

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

PubMed

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

Li, Yilei; Zhu, Zhencai; Chen, Guoan

2014-01-01

249

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

E-print Network

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

Jones, William D.

250

Buried hydrophobic silicon bonding studied by high-energy x-ray reflectivity  

NASA Astrophysics Data System (ADS)

The non-conventional technique of high-energy x-ray reflectivity is used to investigate buried Si|Si interface obtained by hydrophobic wafer bonding. In this experiment the well-collimated beam is transmitted through the sample and is reflected by the bonding interface described by its density and width. Transmission x-ray reflectivity curves are fitted using this two-parameter model with a Gaussian or exponential profile to analyse the evolution of the bonding interface as a function of temperature from 250°C to 1100°C.

Buttard, D.; Rieutord, F.; Eymery, J.; Fournel, F.; Bataillou, B.

2003-05-01

251

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

Microsoft Academic Search

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 Si–Si bonds obtained for the compounds were then used to examine the rehybridization effect from the strain energy. A higher strain

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

2007-01-01

252

Photofragment translational spectroscopy of three body dissociations and free radicals  

SciTech Connect

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.

North, S.W.

1995-04-01

253

Isotope dependent, temperature regulated, energy repartitioning in a low-barrier, short-strong hydrogen bonded cluster  

SciTech Connect

We investigate and analyze the vibrational properties, including hydrogen/deuterium isotope effects, in a fundamental organic hydrogen bonded system using multiple experimental (infrared multiple photon dissociation and argon-tagged action spectroscopy) and computational techniques. We note a qualitative difference between the two experimental results discussed here and employ ab initio molecular dynamics simulations to explain these results. A deeper understanding of the differences between the isotopically labeled systems arises from an analysis of the simulated cluster spectroscopy and leads to a system-bath coupling interpretation. Specifically, when a few active modes, involving the shared hydrogen/deuterium stretch, are identified and labeled as “system,” with all other molecular vibrational modes being identified as “bath” modes, we find critical differences in the coupling between the system modes for the shared proton and shared deuteron cases. These differences affect the energy repartitioning between these modes resulting in a complex spectral evolution as a function of temperature. Furthermore, intensity borrowing across modes that are widely distributed in the frequency domain plays an important role on the simulated spectra.

Li, Xiaohu [Department of Chemistry, Indiana University, 800 E. Kirkwood Ave., Bloomington, Indiana 47405 (United States); Oomens, Jos [FOM Institute for Plasma Physics ‘Rijnhuizen’, Edisonbaan 14, 3439 MN Nieuwegein (Netherlands); Eyler, John R. [Department of Chemistry, University of Florida, Gainesville, Florida 32611 (United States); Moore, David T., E-mail: iyengar@indiana.edu, E-mail: david.moore@lehigh.edu [Department of Chemistry, Lehigh University, Bethlehem, Pennsylvania 18015 (United States); Iyengar, Srinivasan S., E-mail: iyengar@indiana.edu, E-mail: david.moore@lehigh.edu [Department of Chemistry, Indiana University, 800 E. Kirkwood Ave., Bloomington, Indiana 47405 (United States); Department of Physics, Indiana University, 727 E. Third St., Bloomington, Indiana 47405 (United States)

2010-06-28

254

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

Microsoft Academic Search

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 ?*

Jay K. Badenhoop; Steve Scheiner

1996-01-01

255

Dissociative electron attachment studies on acetone  

SciTech Connect

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

Prabhudesai, Vaibhav S., E-mail: vaibhav@tifr.res.in; Tadsare, Vishvesh; Ghosh, Sanat; Gope, Krishnendu; Davis, Daly; Krishnakumar, E. [Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005 (India)

2014-10-28

256

Dissociative electron attachment studies on acetone.  

PubMed

Dissociative electron attachment (DEA) to acetone is studied in terms of the absolute cross section for various fragment channels in the electron energy range of 0-20 eV. H(-) is found to be the most dominant fragment followed by O(-) and OH(-) with only one resonance peak between 8 and 9 eV. The DEA dynamics is studied by measuring the angular distribution and kinetic energy distribution of fragment anions using Velocity Slice Imaging technique. The kinetic energy and angular distribution of H(-) and O(-) fragments suggest a many body break-up for the lone resonance observed. The ab initio calculations show that electron is captured in the multi-centered anti-bonding molecular orbital which would lead to a many body break-up of the resonance. PMID:25362312

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

2014-10-28

257

Climate Change, Sustainable Energy, and Caron Finance: The Kyoto Bond  

Microsoft Academic Search

The Kyoto Protocol requires a 5.2% reduction of greenhouse gas emissions from developed countries. This is an important starting point both to prevent climate change and to start to implement new Sustainable Energy policy for a Sustainable Economy. At the local level (from regions to cities) lower cost\\/risk energy portfolios can be developed by adjusting the conventional mix of energy

Aldo Iacomellia; Emanuele Piccinno; Daniele Villoresi

258

Tuning the ionization energy of organic semiconductor films: the role of intramolecular polar bonds.  

PubMed

For the prototypical conjugated organic molecules pentacene and perfluoropentacene, we demonstrate that the surface termination of ordered organic thin films with intramolecular polar bonds (e.g., -H versus -F) can be used to tune the ionization energy. The collective electrostatics of these oriented bonds also explains the pronounced orientation dependence of the ionization energy. Furthermore, mixing of differently terminated molecules on a molecular length scale allows continuously tuning the ionization energy of thin organic films between the limiting values of the two pure materials. Our study shows that surface engineering of organic semiconductors via adjusting the polarity of intramolecular bonds represents a generally viable alternative to the surface modification of substrates to control the energetics at organic/(in)organic interfaces. PMID:18771262

Salzmann, Ingo; Duhm, Steffen; Heimel, Georg; Oehzelt, Martin; Kniprath, Rolf; Johnson, Robert L; Rabe, Jürgen P; Koch, Norbert

2008-10-01

259

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

SciTech Connect

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.

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

2013-01-15

260

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

PubMed

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

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

2013-01-15

261

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

PubMed Central

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

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

2008-01-01

262

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

PubMed Central

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

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

2013-01-01

263

Financing climate-friendly energy development through bonds  

Microsoft Academic Search

In this paper we review the various instruments that have been proposed and implemented for financing renewable energy and low-carbon technology projects, in both the developed and developing world, with a focus on private sector involvement. We consider their common features and compare their total impact so far with the scale of renewable energy funding likely to be needed over

John A Mathews; Sean Kidney

2012-01-01

264

Hydrogen bonding constrains free radical reaction dynamics at serine and threonine residues in peptides.  

PubMed

Free radical-initiated peptide sequencing (FRIPS) mass spectrometry derives advantage from the introduction of highly selective low-energy dissociation pathways in target peptides. An acetyl radical, formed at the peptide N-terminus via collisional activation and subsequent dissociation of a covalently attached radical precursor, abstracts a hydrogen atom from diverse sites on the peptide, yielding sequence information through backbone cleavage as well as side-chain loss. Unique free-radical-initiated dissociation pathways observed at serine and threonine residues lead to cleavage of the neighboring N-terminal C?-C or N-C? bond rather than the typical C?-C bond cleavage observed with other amino acids. These reactions were investigated by FRIPS of model peptides of the form AARAAAXAA, where X is the amino acid of interest. In combination with density functional theory (DFT) calculations, the experiments indicate the strong influence of hydrogen bonding at serine or threonine on the observed free radical chemistry. Hydrogen bonding of the side-chain hydroxyl group with a backbone carbonyl oxygen aligns the singly occupied ? orbital on the ?-carbon and the N-C? bond, leading to low-barrier ?-cleavage of the N-C? bond. Interaction with the N-terminal carbonyl favors a hydrogen-atom transfer process to yield stable c and z(•) ions, whereas C-terminal interaction leads to effective cleavage of the C?-C bond through rapid loss of isocyanic acid. Dissociation of the C?-C bond may also occur via water loss followed by ?-cleavage from a nitrogen-centered radical. These competitive dissociation pathways from a single residue illustrate the sensitivity of gas-phase free radical chemistry to subtle factors such as hydrogen bonding that affect the potential energy surface for these low-barrier processes. PMID:24605822

Thomas, Daniel A; Sohn, Chang Ho; Gao, Jinshan; Beauchamp, J L

2014-09-18

265

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

E-print Network

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

Ramaswamy, Ram

266

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

SciTech Connect

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

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

267

Looking for high energy density compounds among polynitraminepurines.  

PubMed

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

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

2013-09-01

268

Oxygen-oxygen bonds : catalytic redox pathways in energy storage  

E-print Network

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

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

2009-01-01

269

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

SciTech Connect

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.

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

1988-01-15

270

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

SciTech Connect

The total cross section has been measured for the electron induced dissociation of trimethyl (methylcyclopentadienyl) platinum (IV) [MeCpPt(IV)Me{sub 3}], 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 (4.2+-0.3x10{sup -17} cm{sup 2} on the a:C-Pt and 1.4+-0.1x10{sup -17} cm{sup 2} on the Au) that increases with increasing incident electron energy, reaching a maximum at around 150 eV (4.1+-0.5x10{sup -16} cm{sup 2} on the a:C-Pt and 2.3+-0.2x10{sup -16} cm{sup 2} 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)Me{sub 3}, 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.

Dorp, W. F. van [Department of Physics and Astronomy, Laboratory of Surface Modification, Rutgers, State University of New Jersey, Piscataway, New Jersey 08854-8019 (United States); Charged Particle Optics Group, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft (Netherlands); Wnuk, J. D.; Gorham, J. M.; Fairbrother, D. H. [Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Madey, T. E. [Department of Physics and Astronomy, Laboratory of Surface Modification, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854-8019 (United States); Hagen, C. W. [Charged Particle Optics Group, Faculty of Applied Sciences, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft (Netherlands)

2009-10-01

271

The Scalar Relativistic Contribution to Ga-Halide Bond Energies  

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

272

Molecular dynamics investigations of the dissociation of SiO2 on an ab initio potential energy surface obtained using neural network methods.  

PubMed

The neural network (NN) procedure to interpolate ab initio data for the purpose of molecular dynamics (MD) simulations has been tested on the SiO(2) system. Unlike other similar NN studies, here, we studied the dissociation of SiO(2) without the initial use of any empirical potential. During the dissociation of SiO(2) into Si+O or Si+O(2), the spin multiplicity of the system changes from singlet to triplet in the first reaction and from singlet to pentet in the second. This paper employs four potential surfaces. The first is a NN fit [NN(STP)] to a database comprising the lowest of the singlet, triplet, and pentet energies obtained from density functional calculations in 6673 nuclear configurations. The other three potential surfaces are obtained from NN fits to the singlet, triplet, and pentet-state energies. The dissociation dynamics on the singlet-state and NN(STP) surfaces are reported. The results obtained using the singlet surface correspond to those expected if the reaction were to occur adiabatically. The dynamics on the NN(STP) surface represent those expected if the reaction follows a minimum-energy pathway. This study on a small system demonstrates the application of NNs for MD studies using ab initio data when the spin multiplicity of the system changes during the dissociation process. PMID:16613454

Agrawal, Paras M; Raff, Lionel M; Hagan, Martin T; Komanduri, Ranga

2006-04-01

273

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

NASA Technical Reports Server (NTRS)

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

Altshuller, Aubrey P

1955-01-01

274

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

Microsoft Academic Search

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

N. Flocke; R. J. Bartlett

2003-01-01

275

Electronic structure, molecular bonding and potential energy surfaces  

SciTech Connect

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

Ruedenberg, K. [Ames Laboratory, IA (United States)

1993-12-01

276

The H2 dissociation on the BN, AlN, BP and AlP nanotubes: a comparative study.  

PubMed

The thermodynamic and kinetic feasibility of H(2) dissociation on the BN, AlN, BP and AlP zigzag nanotubes has been investigated theoretically by calculating the dissociation and activation energies. We determined the BN and AlP tubes to be inert toward H(2) dissociation, both thermodynamically and kinetically. The reactions are endothermic by 5.8 and 3 kcal mol(-1), exhibiting high activation energies of 38.8 and 30.6 kcal mol(-1), respectively. Our results indicated that H(2) dissociation is thermodynamically favorable on both PB and AlN nanotubes. However, in spite of the thermodynamic feasibility of H(2) dissociation on PB types, this process is kinetically unfavorable due to partly high activation energy. Generally, we concluded that among the four studied tubes, the AlN nanotube may be an appropriate model for H(2) dissociation process, from a thermodynamic and kinetic stand point. We also indicated that H(2) dissociation is not homolytic, rather it takes place via a heterolytic bond cleavage. In addition, a comparative study has been performed on the electrical and geometrical properties of the tubes. Our analysis showed that the electrical conductivity of tubes is as follows: BP>AlP>BN>AlN depending on how to combine the electron rich and electron poor atoms. PMID:21979405

Beheshtian, Javad; Soleymanabadi, Hamed; Kamfiroozi, Mohammad; Ahmadi, Ali

2012-06-01

277

Autocatalytic water dissociation on Cu(110) at near ambient conditions  

SciTech Connect

Autocatalytic dissociation of water on the Cu(110) metal surface is demonstrated based on X-ray photoelectron spectroscopy studies carried out in-situ under near ambient conditions of water vapor pressure (1 Torr) and temperature (275-520 K). The autocatalytic reaction is explained as the result of the strong hydrogen-bond in the H{sub 2}O-OH complex of the dissociated final state, which lowers the water dissociation barrier according to the Broensted-Evans-Polanyi relations. A simple chemical bonding picture is presented which predicts autocatalytic water dissociation to be a general phenomenon on metal surfaces.

Mulleregan, Alice; Andersson, Klas; Ketteler, Guido; Bluhm, Hendrik; Yamamoto, Susumu; Ogasawara, Hirohito; Pettersson, Lars G.M.; Salmeron, Miquel; Nilsson, Anders

2007-05-16

278

An energy criterion for determining d orbital contribution to adsorbate bonding to a transition metal: CO\\/Fe 12  

Microsoft Academic Search

Summary A new criterion is presented for determining the contribution of a particular class or group of orbitals to a chemical bond. The new criterion is the diatomic energy contribution of particular orbitals to a bond. In neglect to differential overlap methods the total energy may be decomposed entirely into monoatomic and diatomic terms. The contribution of the electrons ind

George Blyholder; Michael Lawless

1990-01-01

279

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

PubMed

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

Majerz, I; Olovsson, I

2007-10-01

280

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

PubMed

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

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

2013-01-28

281

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

SciTech Connect

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

Blancafort, Lluis [Institut de Quimica Computacional, Department de Quimica, Universitat de Girona, Campus de Montilivi, 17071 Girona (Spain); Gatti, Fabien [CTMM, Institut Charles Gerhardt Montpellier (UMR 5253), CC 1501, Universite Montpellier 2, 34095 Montpellier Cedex 05 (France); Meyer, Hans-Dieter [Theoretische Chemie, Ruprecht-Karls-Universitaet, Im Neuenheimer Feld 229, 69120 Heidelberg (Germany)

2011-10-07

282

The thermal dissociation of cholesterol esters using a 5.75-?m free-electron laser  

NASA Astrophysics Data System (ADS)

In order to estimate the optimum laser conditions for efficient dissociation of cholesterol ester in an arteriosclerotic region of blood vessels, we have invstigated the relationship between laser wavelength and power density on cholesterol ester dissociation using a mid infrared free electron laser (MIR-FEL). In this study, cholesteryl oleate, which is a typical cholesterol ester found in arteriosclerotic regions, was irradited with 5.75-?m-FELs, which cause vibration of ester bonds. Two results were obtained. (1) Ester dissociated depending on the absorption coefficient, and the macropulse duration was shorter than the thermal relaxation time, showing that ester bonds dissociated into carboxylic acid and cholesterol by macropulse-induced thermal effects without accompanying thermal diffusion, (2) Using a wavelength of 5.75-?m the maximum ester dissociation ratio was achieved under the optimum laser conditions of a macropulse energy density of 0.4-1.0 J/cm2. We conclude that MIR pulsed-lasers with a wavelegnth of 5.75 ?m can be useful for removal of cholesteryl lester in an arteriosclerotic region of blood vessels.

Fukami, Yuko; Awazu, Kunio

2003-07-01

283

Ab Initio Molecular Dynamics of High-Temperature Unimolecular Dissociation of Gas-Phase RDX and Its Dissociation Products.  

PubMed

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

Schweigert, Igor V

2015-03-26

284

Expanding the detectable HLA peptide repertoire using electron-transfer/higher-energy collision dissociation (EThcD)  

PubMed Central

The identification of peptides presented by human leukocyte antigen (HLA) class I is tremendously important for the understanding of antigen presentation mechanisms under healthy or diseased conditions. Currently, mass spectrometry-based methods represent the best methodology for the identification of HLA class I-associated peptides. However, the HLA class I peptide repertoire remains largely unexplored because the variable nature of endogenous peptides represents difficulties in conventional peptide fragmentation technology. Here, we substantially enhanced (about threefold) the identification success rate of peptides presented by HLA class I using combined electron-transfer/higher-energy collision dissociation (EThcD), reporting over 12,000 high-confident (false discovery rate <1%) peptides from a single human B-cell line. The direct importance of such an unprecedented large dataset is highlighted by the discovery of unique features in antigen presentation. The observation that a substantial part of proteins is sampled across different HLA alleles, and the common occurrence of HLA class I nested sets, suggest that the constraints of HLA class I to comprehensively present the health states of cells are not as tight as previously thought. Our dataset contains a substantial set of peptides bearing a variety of posttranslational modifications presented with marked allele-specific differences. We propose that EThcD should become the method of choice in analyzing HLA class I-presented peptides. PMID:24616531

Mommen, Geert P. M.; Frese, Christian K.; Meiring, Hugo D.; van Gaans-van den Brink, Jacqueline; de Jong, Ad P. J. M.; van Els, Cécile A. C. M.; Heck, Albert J. R.

2014-01-01

285

Vibrational Feshbach resonances in dissociative electron attachment to uracil  

NASA Astrophysics Data System (ADS)

Low-energy dissociative electron attachment to uracil molecules in the gas phase is partly controlled by interaction between the lowest ?* resonance with a dipole-supported anion state. We calculate this contribution using a combination of the finite element discrete model with the resonance R-matrix theory. Deuterated uracil is investigated, also, and a strong isotope effect is found. The results agree qualitatively and semiquantitatively with experimental data, but for a complete description of the process the interaction between a second N—H bond ?* resonance in the molecule and the second ?* resonance should be included.

Gallup, Gordon A.; Fabrikant, Ilya I.

2011-01-01

286

Molecular resonant dissociation of surface-adsorbed molecules by plasmonic nanoscissors  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

287

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

NASA Technical Reports Server (NTRS)

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.

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

1976-01-01

288

Coverage dependent water dissociative adsorption on Fe(110) from DFT computation.  

PubMed

Using density functional theory calculations and ab initio atomistic thermodynamics, H2O adsorption and dissociation on the Fe(110) p(4 × 4) surface at different coverages have been computed. At the lowest coverage, the adsorbed H2O, OH, O and H species can migrate easily on the surface. For (H2O)n adsorption, H2O molecules donating H atoms for H-bonding adsorb more strongly than those accepting H atoms for H-bonding. Monomeric H2O dissociation is favored both thermodynamically and kinetically. On nO pre-covered Fe(110) surfaces (n = 1-8), H2O dissociation is accessible for nO + H2O (n = 1-7) both kinetically and thermodynamically, while H2O desorption instead of dissociation occurs at n = 8. With the increased number of surface O atoms, H2 dissociative adsorption energies vary in a narrow range for n = 1-4 and decrease for n = 5-7, while at n = 8, the surface does not adsorb H2. At low OH coverage (n = 2, 4), OH groups are perpendicularly adsorbed without H-bonding, while for n? 6, adsorbed OH groups are linearly arranged and stabilized by H-bonding. The maximal OH coverage (n = 12) is 0.75 ML and the reasonable O coverage (n = 7) is 0.44 ML, in line with the experiment. The calculated desorption temperatures of H2O and H2 agree well with the available experimental data. These results provide fundamental insights into water-involved reactions catalyzed by iron and interaction mechanisms of water interaction with metal surfaces. PMID:25743027

Liu, Shaoli; Tian, Xinxin; Wang, Tao; Wen, Xiaodong; Li, Yong-Wang; Wang, Jianguo; Jiao, Haijun

2015-04-14

289

Dissociative Recombination without a Curve Crossing  

NASA Technical Reports Server (NTRS)

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(+).

Guberman, Steven L.

1994-01-01

290

Structural characterization of triacylglycerols as lithiated adducts by electrospray ionization mass spectrometry using low-energy collisionally activated dissociation on a triple stage quadrupole instrument  

Microsoft Academic Search

We describe features of tandem mass spectra of lithiated adducts of triacylglycerol (TAG) species obtained by electrospray\\u000a ionization mass spectrometry (ms) with low-energy collisionally activated dissociation (CAD) on a triple stage quadrupole\\u000a instrument. The spectra distinguish isomeric triacylglycerol species and permit assignment of the mass of each fatty acid\\u000a substituent and positions on the glycerol backbone to which substituents are

Fong-Fu Hsu; John Turk

1999-01-01

291

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

SciTech Connect

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.}

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

292

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

NASA Astrophysics Data System (ADS)

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

Hart-Smith, Gene; Raftery, Mark J.

2012-01-01

293

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

E-print Network

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

Ellison, Barney

294

Isotope dependent, temperature regulated, energy repartitioning in a low-barrier, short-strong hydrogen bonded cluster  

E-print Network

/deuterium isotope effects, in a fundamental organic hydrogen bonded system using multiple experimental infraredIsotope dependent, temperature regulated, energy repartitioning in a low-barrier, short-strong hydrogen bonded cluster Xiaohu Li,1 Jos Oomens,2 John R. Eyler,3 David T. Moore,4,a and Srinivasan S

Iyengar, Srinivasan S.

295

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

NASA Astrophysics Data System (ADS)

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.

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

2014-06-01

296

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

NASA Technical Reports Server (NTRS)

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.

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

1981-01-01

297

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

PubMed

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

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

2014-05-01

298

A theoretical study on the strength of the C-NO2 bond and ring strain upon the formation of the intermolecular H-bonding interaction between HF and nitro group in nitrocyclopropane, nitrocyclobutane, nitrocyclopentane or nitrocyclohexane.  

PubMed

As a follow-up to our investigation into the influence of H-bond on the C-NO2 trigger bond, a comparison of the effect of the H-bond on the ring strain energy with the C-NO2 bond dissociation energy was carried out in the HF complex with nitrocyclopropane, nitrocyclobutane, nitrocyclopentane, and nitrocyclohexane by using the DFT-B3LYP and MP2 (full) methods with the 6-311++G(2df,2p) and aug-cc-pVTZ basis sets. The C-NO2 bond length decreases with strengthening of trigger-bond while the ring perimeter increases companied by weakening of ring strain upon the complex formation. The H-bonding energy correlates well with the increment of ring perimeter and the change of ring bond angle. For nitrocyclopropane???HF, the effect of H-bond on the ring strain energy is notable, while for the other complex, it is negligible. Therefore, for nitrocyclopropane???HF, the origin of the change of explosive sensitivity might be due to the increment of the C-NO2 bond dissociation energy and decrease of the ring strain energy, while for the other complex, it might be only due to the strengthening of C-NO2 bond. The analysis of electron density shifts shows that the C-C bond in ring loses density while the C-NO2 bond gains density, leading to the weakened ring strain and strengthened C-NO2 bond, and thus the possibly reduced explosive sensitivity. PMID:25863689

Qiu, Wei; Ren, Fu-de; Shi, Wen-Jing; Wang, Yan-Hong

2015-05-01

299

Dependence of collision-induced dissociation energy on molecular degrees of freedom as a means to assess relative binding affinity in multivalent complexes.  

PubMed

In collision-induced dissociation mass spectrometry experiments, the collision energy required for dissociation linearly depends on the degrees of freedom in the precursor ion. The magnitude of the slope of this relationship previously has been shown to qualitatively correlate to the relative binding strength of a noncovalently bound, monovalent complex. The goal of the work presented here is to determine if a similar methodology can be applied for assessing relative binding strengths in multivalent species. We have tested the method on complexes formed from 18-crown-6 and a variety of protonated, primary alkylamines, [C(n)H(2n+1)NH(3)](+) (n=9, 12, 14, 16 and 18) and alkyldiamines, [H(3)NC(n)H(2n)NH(3)](2+) (n=3, 5, 6, 9 and 12), and compared our results with dissociation energies calculated using density functional theory at the B3LYP/6-31G* level. We found that the method correctly assessed the stronger crown ether/headgroup interaction in the two divalent species (1:1 and 2:1 complexes formed from the diaminoalkanes) compared with the weaker interaction in the monovalent species (1:1 complexes formed from mono-aminoalkanes). However, the experimental method could not distinguish between the binding strengths of the two divalent complexes, perhaps because their calculated dissociation energies were quite similar. Our preliminary results suggest that this method could potentially be used for a quick and simple analysis of binding strengths in multivalent species if the binding strengths of the species are significantly different from one another. PMID:21766373

Huffman, Carmen L; Williams, Melissa Lee; Benoist, D Michelle; Overstreet, Richard E; Jellen-McCullough, Emily E

2011-08-30

300

Dissociation of O2 molecule chemisorbed on Si1 - xGex/Si(001)  

NASA Astrophysics Data System (ADS)

Osbnd O bond breaking in O2 chemisorbed on addimers of perfect Si1 - xGex/Si(001) surface was investigated using ab initio calculations. A hybrid quantum mechanical-molecular mechanical approach (QM/MM) and a CASSCF(2;2)/N21-3** method were employed to simulate this reaction. The ability of such model to reproduce correct results was confirmed by additional calculation of dissociation barrier using different modifications of CASSCF method, basis set and surface clusters. The act of Osbnd O bond breaking was found to be energetically favorable only due to local surface stain, with an activation energy of 0.2 eV.

Grynchuk, A.; Koval, I.; Nakhodkin, M.

2014-05-01

301

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

SciTech Connect

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.

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

302

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

SciTech Connect

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.

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

303

Intermolecular hydrogen bond energies in crystals evaluated using electron density properties: DFT computations with periodic boundary conditions.  

PubMed

The hydrogen bond (H-bond) energies are evaluated for 18 molecular crystals with 28 moderate and strong O-H···O bonds using the approaches based on the electron density properties, which are derived from the B3LYP/6-311G** calculations with periodic boundary conditions. The approaches considered explore linear relationships between the local electronic kinetic G(b) and potential V(b) densities at the H···O bond critical point and the H-bond energy E(HB). Comparison of the computed E(HB) values with the experimental data and enthalpies evaluated using the empirical correlation of spectral and thermodynamic parameters (Iogansen, Spectrochim. Acta Part A 1999, 55, 1585) enables to estimate the accuracy and applicability limits of the approaches used. The V(b)-E(HB) approach overestimates the energy of moderate H-bonds (E(HB) < 60 kJ/mol) by ~20% and gives unreliably high energies for crystals with strong H-bonds. On the other hand, the G(b)-E(HB) approach affords reliable results for the crystals under consideration. The linear relationship between G(b) and E(HB) is basis set superposition error (BSSE) free and allows to estimate the H-bond energy without computing it by means of the supramolecular approach. Therefore, for the evaluation of H-bond energies in molecular crystals, the G(b) value can be recommended to be obtained from both density functional theory (DFT) computations with periodic boundary conditions and precise X-ray diffraction experiments. PMID:22786749

Vener, M V; Egorova, A N; Churakov, A V; Tsirelson, V G

2012-11-01

304

Comparison of collision-induced dissociation and electron-induced dissociation of singly protonated aromatic amino acids, cystine and related simple peptides using a hybrid linear ion trap–FT-ICR mass spectrometer  

Microsoft Academic Search

The gas-phase fragmentation reactions of singly protonated aromatic amino acids, their simple peptides as well as simple models for intermolecular disulfide bonds have been examined\\u000a using a commercially available hybrid linear ion trap–Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer.\\u000a Low-energy collision-induced dissociation (CID) reactions within the linear ion trap are compared with electron-induced dissociation\\u000a (EID) reactions within the FT-ICR

Hadi Lioe; Richard A. J. O’Hair

2007-01-01

305

Vibrationally bond-selected chemisorption of methane isotopologues on Pt(111) studied by reflection absorption infrared spectroscopy.  

PubMed

Reflection absorption infrared spectroscopy (RAIRS) was used to probe for vibrational bond-selectivity in the dissociative chemisorption of three partially deuterated methane isotopologues on a Pt(111) surface. While a combination of incident translational energy and thermal vibrational excitation produces a nearly statistical distribution of C-H and C-D bond cleavage products, we observe that laser excitation of an infrared active C-H stretch normal mode leads to highly selective dissociation of a C-H bond for CHD3, CH2D2, and CH3D. Our results show that vibrational energy redistribution between C-H and C-D stretch modes due to methane/surface interactions is negligible during the sub-picosecond collision time which indicates that vibrational bond-selectivity may be the rule rather than the exception in heterogeneous reactions of small polyatomic molecules. PMID:23230773

Chen, Li; Ueta, Hirokazu; Bisson, Régis; Beck, Rainer D

2012-01-01

306

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

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

307

TiCl, TiH and TiH+ Bond Energies, a Test of a Correlation Consistent Ti Basis Set  

NASA Technical Reports Server (NTRS)

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.

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

1999-01-01

308

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

SciTech Connect

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

Lei, Huaping; Wang, Caizhuang; Yao, Yongxin; Hupalo, Myron [Ames Laboratory, USDOE, Ames, Iowa 50011 (United States)] [Ames Laboratory, USDOE, Ames, Iowa 50011 (United States); Wang, Yangang [Ames Laboratory, USDOE, Ames, Iowa 50011 (United States) [Ames Laboratory, USDOE, Ames, Iowa 50011 (United States); Supercomputing Center of Computer Network Information Center, CAS, Beijing 100190 (China); McDougall, Dan; Tringides, Michael; Ho, Kaiming [Ames Laboratory, USDOE, Ames, Iowa 50011 (United States) [Ames Laboratory, USDOE, Ames, Iowa 50011 (United States); Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011 (United States)

2013-12-14

309

Controlling energy level offsets in organic/organic heterostructures using intramolecular polar bonds  

NASA Astrophysics Data System (ADS)

The impact of intramolecular polar bonds (IPBs) on the energy level alignment in layered systems of rodlike conjugated molecules standing on the substrate was investigated for pentacene (PEN) and perfluoropentacene (PFP) on SiO2 using ultraviolet photoelectron spectroscopy. A remarkably large energy offset of 1.75 eV was found between the highest occupied molecular orbital (HOMO) levels of PEN and PFP caused by IPBs at the surface of standing PFP layers. This large HOMO-level offset results in a narrow intermolecular energy gap of approximately 0.4 eV at the interface between PEN and PFP layers. However, the absence of significant spatial overlap of PEN and PFP electron wave functions across the layers suppresses interlayer optical transitions.

Duhm, Steffen; Salzmann, Ingo; Heimel, Georg; Oehzelt, Martin; Haase, Anja; Johnson, Robert L.; Rabe, Jürgen P.; Koch, Norbert

2009-01-01

310

Rovibrational energy and spectroscopic constant calculations of complexes pairing via dihydrogen bonds.  

PubMed

In the present investigation, we performed a thorough study of potential energy curves, rovibrational spectra, and spectroscopic constants for complexes pairing via dihydrogen bonds. In particular, we dealt with LiH[Symbol: see text][Symbol: see text][Symbol: see text]HX (X = F, CN, CCH, CCF, CCCl) complexes by employing accurate electronic energy calculations at the MP2/aug-cc-pVDZ level of theory. Following this, the Numerov method was applied to solve the nuclear Schrödinger equation, thus obtaining spectroscopic constants and rovibrational spectra. Good linear correlation between the magnitudes of the interaction energies for interaction of HX with LiH, and the most positive electrostatic potentials of hydrogen in HX, was established. PMID:25877527

Solimannejad, Mohammad; Jouypazadeh, Hamidreza; Farrokhpour, Hossein

2015-05-01

311

Diffraction dissociation at the LHC  

SciTech Connect

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.

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

312

10024 J. Am. Chem. SOC.1992, 114, 10024-10039 showing that bonding capabilities of silylene, germylene, and  

E-print Network

of planar (e2,,state 5B,). Finally, comparison of naked MoM'H,, with their penta- carbonylated homologous (CO)5Mo=M'H,, reveals that, as far as Mo-M' bond strengths and dissociation energies are concerned

Goddard III, William A.

313

First Experimental Constraint on the Fe59(n ,?)Fe60 Reaction Cross Section at Astrophysical Energies via the Coulomb Dissociation of Fe60  

NASA Astrophysics Data System (ADS)

The radionuclide Fe60 has been of great interest to the nuclear astrophysics community for over a decade. An initial discrepancy between the observed and modeled Galactic Fe60/Al26 ratio motivated numerous studies focused on the nucleosynthesis of these two isotopes, though the cross section of the primary astrophysical production reaction, Fe59(n ,?)Fe60, has remained purely theoretical. The present work offers a first experimental constraint on the Fe59(n ,?)Fe60 cross section at astrophysical energies, obtained indirectly via Coulomb dissociation, and demonstrates that the theoretical reaction rates used in present stellar models are not highly erroneous.

Uberseder, E.; Adachi, T.; Aumann, T.; Beceiro-Novo, S.; Boretzky, K.; Caesar, C.; Dillmann, I.; Ershova, O.; Estrade, A.; Farinon, F.; Hagdahl, J.; Heftrich, T.; Heil, M.; Heine, M.; Holl, M.; Ignatov, A.; Johansson, H. T.; Kalantar, N.; Langer, C.; Le Bleis, T.; Litvinov, Yu. A.; Marganiec, J.; Movsesyan, A.; Najafi, M. A.; Nilsson, T.; Nociforo, C.; Panin, V.; Pietri, S.; Plag, R.; Prochazka, A.; Rastrepina, G.; Reifarth, R.; Ricciardi, V.; Rigollet, C.; Rossi, D. M.; Savran, D.; Simon, H.; Sonnabend, K.; Streicher, B.; Terashima, S.; Thies, R.; Togano, Y.; Volkov, V.; Wamers, F.; Weick, H.; Weigand, M.; Wiescher, M.; Wimmer, C.; Winckler, N.; Woods, P. J.

2014-05-01

314

An alternative energy–size relationship to that proposed by Bond for the design and optimisation of grinding circuits  

Microsoft Academic Search

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

Stephen Morrell

2004-01-01

315

The Pairwise Correlated Generalized Valence Bond Model of Electronic Structure I; The Estimation of Pair Energies from Orbital Overlaps  

PubMed Central

A new method for the accurate a priori calculation of atomic and molecular energies is proposed. The new method agrees with experiment to within less than 1 kcal/mole in all cases examined thus far, and is applicable to excited states and to transition states for chemical reactions. Since the new method corrects the results of generalized valence bond calculations for the effects of electron pair correlations, we call the new method the pairwise correlated generalized valence bond method. PMID:16592172

Petersson, G. A.

1974-01-01

316

Influence of surface treatment on adherence energy of alloys used in bonded prosthetics.  

PubMed

Usually, shear or tensile tests are used to assess bond strengths between resin and metal. In this study, a cleavage test, the Double Cantilever Beam test, was performed to measure the adherence energy in air and in water between a 4-META resin, and five alloys (palladium, palladium-silver, gold, cobalt-chromium and nickel-chromium alloys) whose surfaces have been treated by sandblasting only or by two methods of silica coating (Silicoater MD, Rocatec) or by painting with a primer (V-Primer). Results showed that, after storage in water, it is difficult to divide the studied alloys into a dental base alloys group and a noble alloys group. Therefore, the silica coating has significantly limited the propagation of fissures in water. Higher values of adherence energy were recorded with the Rocatec system except with the palladium alloy which must be treated with the Silicoater MD system. The treatment with V-Primer was sensitive to hydrolytic attack. PMID:10373089

Moulin, P; Degrange, M; Picard, B

1999-05-01

317

The geometrical factor of infinitely long cylindrical ICR cells for collision energy-resolved mass spectrometry: appearance energies of EI 2 + (E = P, As, Sb, and Bi) from collision-induced dissociation of EI 3 + and [EI 2·ligand] + complexes  

Microsoft Academic Search

The geometrical factor ? of infinitely long cylindrical ICR cells is determined to employ collision energy-resolved mass spectrometry (CERMS) with a FT-ICR spectrometer. In case of four identical infinitely long cylindrical electrodes ? equals 0.90. A cylindrical ICR cell emulating infinitely long electrodes is used to study the energy-dependent collision-induced dissociation (CID) of EI3+ radical cations and [EI2·ligand]+ complexes with

Heinrich L. Sievers; Hans-Fr Grützmacher; Pablo Caravatti

1996-01-01

318

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

SciTech Connect

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.

Krishtal, A. [Fachbereich Chemie, Technische Universität Kaiserslautern, Erwin Schrödinger Straße 52, D-67663 Kaiserslautern (Germany)] [Fachbereich Chemie, Technische Universität Kaiserslautern, Erwin Schrödinger Straße 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

319

The dissociation dynamics of He...I 35Cl(B,v'=2,3) complexes with varying amounts of internal energy.  

PubMed

The He...I (35)Cl intermolecular vibrational levels with n'=0-6 that are bound within the He+ICl(B,v'=3) potential [A. B. McCoy, J. P. Darr, D. S. Boucher, P. R. Winter, M. D. Bradke, and R. A. Loomis, J. Chem. Phys. 120, 2677 (2004)] are identified in laser-induced fluorescence experiments performed at very low temperatures within a supersonic expansion. Comparisons of the positions and intensities of these lines with the excitation spectra, calculated using potential surfaces to describe the interactions between the helium atom and ICl in its ground and excited state, assist in the assignments. Based on these comparisons the excited state potential was rescaled so that the experimental and calculated J'=0 energies agree to within the experimental uncertainties for all but the lowest, n'=0, intermolecular level. Two-laser, action, and pump-probe spectroscopy experiments indicate that the bound He...I (35)Cl(B,v'=3) intermolecular vibrational levels undergo vibrational predissociation forming rotationally excited I (35)Cl(B,v'=2,j') products with distributions that depend upon the initial intermolecular vibrational level excited. Action spectra recorded in the ICl B-X, 2-0 region while monitoring the Deltav=0, I (35)Cl(B,v'=2) channel reveal two additional dissociation mechanisms for the He...I (35)Cl(B,v') excited state complexes: rotational predissociation of discrete metastable states lying slightly above the He+I (35)Cl(B,v'=2) asymptote and direct dissociation that occurs when the linear conformer is excited to the continuum of states above the same asymptote. The rotational predissociation pathway forms I (35)Cl(B,v'=2,j') products in all of the rotational states energetically accessible. The direct dissociation mechanism yields very cold rotational product state distributions; for instance, the average rotational energy in the product state distribution measured when the linear complexes are prepared 20 cm(-1) above the dissociation limit is only 1.51 cm(-1), representing only 7.6% of the available energy. PMID:15740259

Darr, Joshua P; Loomis, Richard A; McCoy, Anne B

2005-01-22

320

Theoretical investigation of the dissociation dynamics of vibrationally excited vinyl bromide on an ab initio potential-energy surface obtained using modified novelty sampling and feedforward neural networks. II. Numerical application of the method.  

PubMed

A previously reported method for conducting molecular dynamics simulations of gas-phase chemical dynamics on ab initio potential-energy surfaces using modified novelty sampling and feedforward neural networks is applied to the investigation of the unimolecular dissociation of vinyl bromide. The neural network is fitted to a database comprising the MP4(SDQ) energies computed for 71 969 nuclear configurations using an extended basis set. Dissociation rate coefficients and branching ratios at an internal excitation energy of 6.44 eV for all six open reaction channels are reported. The distribution of vibrational energy in HBr formed in three-center dissociation is computed and found to be in excellent accord with experimental measurements. Computational requirements for the electronic structure calculations, neural network training, and trajectory calculations are given. The weight and bias matrices required for implementation of the neural network potential are made available through the Supplementary Material. PMID:17919009

Malshe, M; Raff, L M; Rockley, M G; Hagan, M; Agrawal, Paras M; Komanduri, R

2007-10-01

321

Halide Abstraction from Halogenated Acetate Ligands by Actinyls: A Competition between Bond Breaking and Bond Making.  

PubMed

Transfer of halogen atoms from halogenated acetate ligands, CX3CO2 (X = F, Cl, Br), to actinyls, AnO2(2+) (An = U, Np, Pu) is stimulated by collision-induced dissociation (CID) in a quadrupole ion trap. CID of [AnO2(CF3CO2)3](-) complexes results exclusively in F atom transfer, concomitant with elimination of CF2CO2, to produce [(CF3CO2)2AnO2F](-), [(CF3CO2)AnO2F2](-), and [AnO2F3](-). This contrasts with CID of transition metal fluoroacetates for which CO2-elimination to produce organometallics is an important pathway, a disparity that can be attributed to the differing bond dissociation energies (BDEs) of the created metal-carbon and metal-fluorine bonds. The dominant pathway for CID of [AnO2(CF3CO2)(CCl3CO2)(CBr3CO2)](-) is Br-atom transfer to produce [(CF3CO2)(CCl3CO2)AnO2Br](-). The preferential formation of bromides, despite that the BDEs of An-F bonds are substantially greater than those of An-Br bonds, is attributed to the offsetting effect of higher BDEs for C-F versus C-Br bonds. The results for the trihaloacetates are similar for uranyl, neptunyl and plutonyl, indicating that for all three the An-X bond dissociation energies are sufficiently high that X atom transfer is overwhelmingly dominant. CID of [UO2(CH2XCO2)2(CX3CO2)](-) (X = F, Cl, Br) resulted in F-transfer only from CH2XCO2, but Cl- and Br-transfer from both CH2XCO2 and CX3CO2, a manifestation of the characteristic increase in BDE[C-F] in CHx-nFn species as n increases; the overall thermochemistry determines the observed CID processes, providing clear distinctions between fluorides and chlorides/bromides. The results of this work reveal the propensity of the actinides to form strong bonds with halogens, and suggest that there is not a large variation in actinyl-halogen BDEs between uranyl, neptunyl, and plutonyl. PMID:25766197

Dau, Phuong D; Gibson, John K

2015-04-01

322

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

PubMed

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

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

2015-04-15

323

Influence of warm air-drying on enamel bond strength and surface free-energy of self-etch adhesives.  

PubMed

We examined the effect of warm air-drying on the enamel bond strengths and the surface free-energy of three single-step self-etch adhesives. Bovine mandibular incisors were mounted in self-curing resin and then wet ground with #600 silicon carbide (SiC) paper. The adhesives were applied according to the instructions of the respective manufacturers and then dried in a stream of normal (23°C) or warm (37°C) air for 5, 10, and 20 s. After visible-light irradiation of the adhesives, resin composites were condensed into a mold and polymerized. Ten samples per test group were stored in distilled water at 37°C for 24 h and then the bond strengths were measured. The surface free-energies were determined by measuring the contact angles of three test liquids placed on the cured adhesives. The enamel bond strengths varied according to the air-drying time and ranged from 15.8 to 19.1 MPa. The trends for the bond strengths were different among the materials. The value of the ?S? component increased slightly when drying was performed with a stream of warm air, whereas that of the ?S? component decreased significantly. These data suggest that warm air-drying is essential to obtain adequate enamel bond strengths, although increasing the drying time did not significantly influence the bond strength. PMID:23841790

Shiratsuchi, Koji; Tsujimoto, Akimasa; Takamizawa, Toshiki; Furuichi, Tetsuya; Tsubota, Keishi; Kurokawa, Hiroyasu; Miyazaki, Masashi

2013-08-01

324

A mechanistic study of H2S adsorption and dissociation on Cu2O(1 1 1) surfaces: Thermochemistry, reaction barrier  

NASA Astrophysics Data System (ADS)

The interaction mechanism of H2S with different Cu2O(1 1 1) surfaces, including perfect, oxygen-vacancy and sulfur-containing surfaces, have been systematically studied using periodic density functional calculations. Different kinds of possible modes of H2S, as well as the resultant SH and S species adsorbed on these surfaces are identified. Two types of pathways via molecular and dissociative adsorption processes are mapped out. Our results show that sulfur species (H2S, SH and S) interact with surface Cu centers; H2S exists in the form of molecular adsorption on perfect and sulfur-containing surfaces; the dissociative adsorption of H2S occurs predominantly on oxygen-vacancy surface, suggesting that oxygen-vacancy exhibits a strong catalytic activity toward the dissociation of H2S. On the other hand, the dissociation processes of the molecular and dissociative adsorption H2S, leading to final product S species on these Cu2O(1 1 1) surfaces, show that the overall dissociation process is exothermic. Meanwhile, with respect to molecular adsorption H2S, the activation barrier and reaction energy of the overall dissociation process on perfect and oxygen-vacancy surfaces indicate that H2S can easily dissociate into S species. Importantly, in the case of dissociative adsorption of H2S, the dissociation of H2S into S species is a spontaneous process with respect to molecular adsorption H2S. However, on sulfur-containing surface, the presence of surface S atom goes against the Hsbnd S bond-breaking process both thermodynamically and kinetically. Finally, the vibrational frequencies for the adsorbed H2S, SH and S species on these surfaces have been obtained, which can be applied to guide surface vibrational spectroscopy in experiment.

Zhang, Riguang; Liu, Hongyan; Li, Jingrui; Ling, Lixia; Wang, Baojun

2012-10-01

325

Energy and angular distributions in dissociative photodetachment of O4 C. R. Sherwood, M. C. Garner, K. A. Hanold, K. M. Strong, and R. E. Continetti  

E-print Network

. O4 is known to photodestruct in the 200 to 1000 nm range from total cross-section measurements.8 Gas structure and electronic symmetry. Anisotropic prod- uct angular distributions have been observed in dissociative photoionization,3 dissociative electron-impact ionization,4 and dissociative electron attachment

Continetti, Robert E.

326

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

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.

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

327

Dissociation of dicarboxylate and disulfonate dianions  

NASA Astrophysics Data System (ADS)

Collision-induced dissociation (CID), along with infrared multiple photon dissociation/detachment (IRMPD) techniques, is utilized to study a series of doubly substituted aromatic dianions containing sulfonate and carboxylate functionalities (1,2- and 1,3-benzenedisulfonate, 1,5-naphthalenedisulfonate, 2,6-naphthalenedisulfonate, 4-sulfobenzoate, 2,6-naphthalenedicarboxylate, and terephthalate dianions). The molecules were chosen because of the electronegativity of the CO2 and SO3 moieties along with their varied spatial separation in order to investigate the effect of the repulsive Coulomb barrier (RCB) on the dianions' respective dissociation pathways. Density functional theory calculations of the structures, electron detachment and dissociation energies, as well as vibrational frequencies are performed. Calculated infrared active vibrational frequencies are largely in agreement with the IRMPD spectra which provide support for interpretations based upon computed energies. Calculated and experimental results show that fragmentation dominates over electron detachment as the lowest energy dissociation pathway for these systems and the nature of this dissociation is dictated by properties of the substituent group. CID and IRMPD of dianions with two sulfonate groups (SO3-) resulted in a single dissociation channel leading to observation of SO3- and its anion conjugate pair, whereas the carboxylate (CO2-) containing dianions dissociated via loss of one or both CO2 molecules and an electron. The SO3- collisional dissociation exhibited a clear energetic threshold toward ionic fragmentation with an isomeric dependence that is in reasonable agreement with a simple electrostatic model of the RCB, as well as with published reports on electron photodetachment. The loss of one or both CO2 units and an electron from CID of the carboxylate dianions appeared with no threshold (dissociation occurs with no collision gas), implying these dianions to be metastable toward the dissociation pathway. However, calculations show these ions to be energetically stable toward dissociation as well as electron detachment. More importantly, in the case of the 2,6-naphthalenedicarboxylate dianion, experiments performed at the FELIX Fourier-transform ion cyclotron resonance facility and the ELISA electrostatic storage ring, where ions are collisionally cooled prior to analysis, showed this ion to be stable (? >1.5 s). We conclude that the carboxylate (CO2-) containing dianions formed in the present CID experiment are electronically stable but vibrationally metastable due to internal energy imparted in the harsh electrospray conditions. The delocalized nature of the excess electrons associated with the carboxylate containing dianions may lead to circumvention of the RCB by dissociating via neutral fragmentation followed by (or accompanied by) electron detachment.

Ard, Shaun; Mirsaleh-Kohan, Nasrin; Steill, Jeffrey D.; Oomens, Jos; Nielsen, Steen Brøndsted; Compton, R. N.

2010-03-01

328

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

PubMed

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

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

329

Influence of Light Intensity on Surface Free Energy and Dentin Bond Strength of Core Build-up Resins.  

PubMed

SUMMARY Objective : We examined the influence of light intensity on surface free energy characteristics and dentin bond strength of dual-cure direct core build-up resin systems. Methods : Two commercially available dual-cure direct core build-up resin systems, Clearfil DC Core Automix with Clearfil Bond SE One and UniFil Core EM with Self-Etching Bond, were studied. Bovine mandibular incisors were mounted in acrylic resin and the facial dentin surfaces were wet ground on 600-grit silicon carbide paper. Adhesives were applied to dentin surfaces and cured with light intensities of 0 (no irradiation), 200, 400, and 600 mW/cm(2). The surface free energy of the adhesives (five samples per group) was determined by measuring the contact angles of three test liquids placed on the cured adhesives. To determine the strength of the dentin bond, the core build-up resin pastes were condensed into the mold on the adhesive-treated dentin surfaces according to the methods described for the surface free energy measurement. The resin pastes were cured with the same light intensities as those used for the adhesives. Ten specimens per group were stored in water maintained at 37°C for 24 hours, after which they were shear tested at a crosshead speed of 1.0 mm/minute in a universal testing machine. Two-way analysis of variance (ANOVA) and a Tukey-Kramer test were performed, with the significance level set at 0.05. Results : The surface free energies of the adhesive-treated dentin surfaces decreased with an increase in the light intensity of the curing unit. Two-way ANOVA revealed that the type of core build-up system and the light intensity significantly influence the bond strength, although there was no significant interaction between the two factors. The highest bond strengths were achieved when the resin pastes were cured with the strongest light intensity for all the core build-up systems. When polymerized with a light intensity of 200 mW/cm(2) or less, significantly lower bond strengths were observed. Conclusions : The data suggest that the dentin bond strength of core build-up systems are still affected by the light intensity of the curing unit, which is based on the surface free energy of the adhesives. On the basis of the results and limitations of the test conditions used in this study, it appears that a light intensity of >400 mW/cm(2) may be required for achieving the optimal dentin bond strength. PMID:24809538

Shimizu, Y; Tsujimoto, A; Furuichi, T; Suzuki, T; Tsubota, K; Miyazaki, M; Platt, Ja

2015-01-01

330

Aggregation-induced chemical reactions: acid dissociation in growing water clusters.  

PubMed

Understanding chemical reactivity at ultracold conditions, thus enabling molecular syntheses via interstellar and atmospheric processes, is a key issue in cryochemistry. In particular, acid dissociation and proton transfer reactions are ubiquitous in aqueous microsolvation environments. Here, the full dissociation of a HCl molecule upon stepwise solvation by a small number of water molecules at low temperatures, as relevant to helium nanodroplet isolation (HENDI) spectroscopy, is analyzed in mechanistic detail. It is found that upon successive aggregation of HCl with H(2)O molecules, a series of cyclic heteromolecular structures, up to and including HCl(H(2)O)(3), are initially obtained before a precursor state for dissociation, HCl(H(2)O)(3)···H(2)O, is observed upon addition of a fourth water molecule. The latter partially aggregated structure can be viewed as an "activated species", which readily leads to dissociation of HCl and to the formation of a solvent-shared ion pair, H(3)O(+)(H(2)O)(3)Cl(-). Overall, the process is mostly downhill in potential energy, and, in addition, small remaining barriers are overcome by using kinetic energy released as a result of forming hydrogen bonds due to aggregation. The associated barrier is not ruled by thermal equilibrium but is generated by athermal non-equilibrium dynamics. These "aggregation-induced chemical reactions" are expected to be of broad relevance to chemistry at ultralow temperature much beyond HENDI spectroscopy. PMID:21351796

Forbert, Harald; Masia, Marco; Kaczmarek-Kedziera, Anna; Nair, Nisanth N; Marx, Dominik

2011-03-23

331

Early Mechanistic Events in Biotin Dissociation from Streptavidin  

SciTech Connect

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

Hyre, D. E.

2002-01-01

332

Scattering angular distributions in collisionally activated dissociation of some high mass ions: Analysis of mass-analyzed ion kinetic energy peak shapes  

NASA Astrophysics Data System (ADS)

A method has been developed to determine scattering angular distribution in collisionally activated dissociation (CAD) of high mass ions by analyzing translational energy spectra recorded by mass-analyzed ion kinetic energy spectrometry. Scattering angular distributions have been obtained for CAD of C6F5I+?, Cr(CH3COCHCOCH3)+?3, and Cs5I+4 with He. Large energy losses observed in the translational energy spectra are attributed to the elastic energy transfer to the collision gas accompanying collisional deflection. Deflections of the parent ions get larger as the translational energy for relative motion in the center-of-mass coordinate system decreases. This has been explained by the reactive line-of-centers model. Either vibrational excitation via momentum transfer or vibronic excitation via nonadiabatic interaction is compatible with the experimental data. On the other hand, electronic excitation via the Franck-Condon process is not a feasible mechanism to explain the excitation process in CAD of high mass ions at keV translational energy.

Lee, Young Jin; Kim, Myung Soo

1995-10-01

333

Synthesis of Through-bond Energy Transfer Cassettes and Their Encapsulation in Silica and Calcium Phosphate Nanoparticles  

E-print Network

have synthesized a set of six through-bond energy transfer cassettes which emit in the 600-800 nm region with Fluorescein or BODIPY as donor and benzophenoxazine dye Nile Red or cyanine dye Cy5 as acceptor. Their photophysical properties in organic...

Jose, Jiney

2011-02-22

334

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

E-print Network

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

Reisler, Hanna

335

Isotope dependent, temperature regulated, energy repartitioning in a low-barrier, short-strong hydrogen bonded cluster  

E-print Network

Isotope dependent, temperature regulated, energy repartitioning in a low-barrier, short-strong hydrogen bonded cluster Xiaohu Li and Srinivasan S. Iyengar Department of Chemistry, Indiana University, Bloomington, IN 47405 Abstract We investigate and analyze the vibrational properties, including H/D isotope

Iyengar, Srinivasan S.

336

Bonding silicones with epoxies  

SciTech Connect

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.

Tira, J.S.

1980-01-01

337

Dissociative adsorption of CH3X (X = Br and Cl) on a silicon(100) surface revisited by density functional theory  

NASA Astrophysics Data System (ADS)

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.

Wang, Chen-Guang; Huang, Kai; Ji, Wei

2014-11-01

338

Identification of c-Type Heme-Containing Peptides Using Non-Activated Immobilized Metal Affinity Cchromatography Resin Enrichment and Higher-Energy Collisional Dissociation  

SciTech Connect

c-type cytochromes play essential roles in many biological activities of both prokaryotic and eukaryotic cells, including electron transfer, enzyme catalysis and induction of apoptosis. We report a novel enrichment strategy for identifying c-type heme-containing peptides that uses non-activated IMAC resin. The strategy demonstrated at least seven-fold enrichment for heme-containing peptides digested from a cytochrome c protein standard, and quantitative linear performance was also assessed for heme-containing peptide enrichment. Heme-containing peptides extracted from the periplasmic fraction of Shewanella oneidensis MR-1 were further identified using higher-energy collisional dissociation tandem mass spectrometry. The results demonstrated the applicability of this enrichment strategy to identify c-type heme-containing peptides from a highly complex biological sample, and at the same time, confirmed the periplasmic localization of heme-containing proteins during suboxic respiration activities of S. oneidensis MR-1.

Zhang, Haizhen; Yang, Feng; Qian, Weijun; Brown, Roslyn N.; Wang, Yuexi; Merkley, Eric D.; Park, Jea H.; Monroe, Matthew E.; Purvine, Samuel O.; Moore, Ronald J.; Shi, Liang; Fredrickson, Jim K.; Pasa-Tolic, Ljiljana; Smith, Richard D.; Lipton, Mary S.

2011-10-01

339

Benchmark binding energies of ammonium and alkyl-ammonium ions interacting with water. Are ammonium-water hydrogen bonds strong?  

NASA Astrophysics Data System (ADS)

Alkyl-ammonium ion/water interactions are investigated using high level quantum computations, yielding thermodynamics data in good agreement with gas-phase experiments. Alkylation and hydration lead to weaken the NHsbnd O hydrogen bonds. Upon complete hydration by four water molecules, their main features are close to those of the OHsbnd O bond in the isolated water dimer. Energy decomposition analyses indicate that hydration of alkyl-ammonium ions are mainly due to electrostatic/polarization effects, as for hard monoatomic cations, but with a larger effect of dispersion.

Vallet, Valérie; Masella, Michel

2015-01-01

340

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)

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.

Huang, Minsheng; Li, Zhenhuan

2013-12-01

341

The Effect of Carbon Monoxide Co-Adsorption on Ni-Catalysed Water Dissociation  

PubMed Central

The effect of carbon monoxide (CO) co-adsorption on the dissociation of water on the Ni(111) surface has been studied using density functional theory. The structures of the adsorbed water molecule and of the transition state are changed by the presence of the CO molecule. The water O–H bond that is closest to the CO is lengthened compared to the structure in the absence of the CO, and the breaking O–H bond in the transition state structure has a larger imaginary frequency in the presence of CO. In addition, the distances between the Ni surface and H2O reactant and OH and H products decrease in the presence of the CO. The changes in structures and vibrational frequencies lead to a reaction energy that is 0.17 eV less exothermic in the presence of the CO, and an activation barrier that is 0.12 eV larger in the presence of the CO. At 463 K the water dissociation rate constant is an order of magnitude smaller in the presence of the CO. This reveals that far fewer water molecules will dissociate in the presence of CO under reaction conditions that are typical for the water-gas-shift reaction. PMID:24287907

Mohsenzadeh, Abas; Borjesson, Anders; Wang, Jeng-Han; Richards, Tobias; Bolton, Kim

2013-01-01

342

Characterization of multiple-photon absorption and dissociation of polyatomic molecules  

SciTech Connect

A quantitative comparison of multiple-photon absorption (MPA) and dissociation (MPD) has been performed for experiments with a number of different polyatomic molecules. Appropriate normalization techniques for the absorption and dissociation parameters are formulated to account for the different conditions of the experiment and the molecular parameters. This procedure in a first approximation, accounts for the effects of independent variables such as gas pressure, optical bandwidth, optical pulse duration, excitation frequency, spectral width of the optical absorption band, absorption strength of the transition, bond strength, and the density of states in the molecule. The theoretical description of the dynamics of the absorbing ground state is considered and used to provide the rationale for the normalization procedure. The results of this analysis indicate that the functional dependence of the number of photons absorbed per molecule with fluence is qualitatively the same for the most molecules. Similarly, the probability for dissociation of most molecules can be related to the density of vibrational states, the bond strength, the number of photons absorbed per molecule, and the width of the absorbing transition. The functional relationships derived for MPA and MPD can be related to several theoretical aspects of the optical interaction process. In particular, the implications for the basic absorption mechanisms and the distribution of vibrational energy in the molecule will be addressed.

Judd, O.P.

1980-01-01

343

Bonding in silicates: Investigation of the Si L 2,3 edge by parallel electron energy-loss spectroscopy  

Microsoft Academic Search

The Si L2,3 core-loss edge can be used to probe the crystal chemistry around Si, providing information on the s- and d-like partial density of unoccupied states of the Si-O bonds. We present Si L 2,3 edges from 59 silicates, glasses, and amorphous materials acquired by parallel electron energy-loss spectroscopy (PEELS) with a transmission electron microscope (TEM) at an energy

LAURENCE A. J. GARVIE; PETER R. BUSECK

1999-01-01

344

On the existence and characteristics of ?-beryllium bonds.  

PubMed

The existence of ?-beryllium bonds explains the stability of the complexes between ethylene and acetylene and BeX2 (X = H, F, and Cl) derivatives. These linkers involve a significant charge transfer from the ?(CC) bonding orbitals into the empty p orbitals of Be and to a much smaller degree into the ?(BeH)* antibonding orbitals. The significant deformation of the BeX2 moiety and the slight deformation of the unsaturated hydrocarbon result in distortion energies as high as the dissociation energy of the complex. The ?-beryllium bonds are about four times stronger than conventional ?-hydrogen bonds and even stronger than the strongest ?-hydrogen bond reported to date in the literature. The topology of their electron density is characterized as being very flat in the bonding region between the ?-system and Be, which leads to topologically unstable structures close to catastrophe points. Among the functionals considered in our study M06 is the one that leads to values in better agreement with CCSD(T)/aug-cc-pVTZ calculations used as a reference. B3LYP underestimates some interactions, whereas M06-2X overestimates all of them. MP2 also yields good agreement with the CCSD(T) method. PMID:25026560

Villanueva, Estefanía Fernández; Mó, Otilia; Yáñez, Manuel

2014-09-01

345

Mutation Research 473 (2001) 211217 Total energy of deoxyguanosine bonded to  

E-print Network

, the bonding oc- curs between the carbon C8 of the guanosine and the nitrogen N2 of AAF. In the remaining instances the bond is formed between the nitrogen N2 of the guanosine and the carbon C3 of AAF. It has mechanics have been undertaken on AAF-modified guanosine and other modified base polymers [17

Besson, Morgan

346

Coordination-resolved local bond contraction and electron binding-energy entrapment of Si atomic clusters and solid skins  

SciTech Connect

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.

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

347

Identification of a Previously Unobserved Dissociative Ionization Pathway in Time-Resolved Photospectroscopy of the Deuterium Molecule  

NASA Astrophysics Data System (ADS)

A femtosecond vacuum ultraviolet (VUV) pulse with high spectral resolution (<200 meV ) is selected from the laser-driven high order harmonics. This ultrafast VUV pulse is synchronized with an infrared (IR) laser pulse to study dissociative ionization in deuterium molecules. At a VUV photon energy of 16.95 eV, a previously unobserved bond-breaking pathway is found in which the dissociation direction does not follow the IR polarization. We interpret it as corresponding to molecules predissociating into two separated atoms, one of which is photoionized by the following IR pulse. A time resolved study allows us to determine the lifetime of the intermediate predissociation process to be about 1 ps. Additionally, the dissociative ionization pathways show high sensitivity to the VUV photon energy. As the VUV photon energy is blueshifted to 17.45 eV, the more familiar bond-softening channel is opened to compete with the newly discovered pathway. The interpretation of different pathways is supported by the energy sharing between the electron and nuclei.

Cao, Wei; Laurent, Guillaume; Ben-Itzhak, Itzik; Cocke, C. Lewis

2015-03-01

348

Further Theoretical Evidence for Hydrogen-Assisted CO Dissociation on Ru(0001)  

SciTech Connect

Extensive calculations based on spin-polarized density functional theory were carried out to examine how CH{sub x} are formed from the dissociation of CO on Ru(0001) in the presence of hydrogen. Common pathways, such as the direct CO dissociation and H-assisted route leading to HCO or COH, including alternative routes that involve the formation of HCOH and CH{sub 2}O, were examined. The reaction energy and barrier for each elementary step were calculated. The calculations show that the carbide mechanism is not the main reaction pathway for the conversion of CO on Ru(0001). Complementary microkinetic simulations utilizing results from first-principles quantum mechanical calculations indicate that a branch starting from the hydrogenation of CO to HCOH (via COH intermediate) and subsequent C–O bond cleavage is more plausible.

Alfonso, Dominic R.

2013-10-10

349

Gas-Phase Dissociation Pathways of Multiply Charged Peptide Clusters  

PubMed Central

Numerous studies of cluster formation and dissociation have been conducted to determine properties of matter in the transition from the condensed phase to the gas phase using materials as diverse as atomic nuclei, noble gasses, metal clusters, and amino acids. Here, electrospray ionization is used to extend the study of cluster dissociation to peptides including leucine enkephalin with 7–19 monomer units and 2–5 protons, and somatostatin with 5 monomer units and 4 protons under conditions where its intramolecular disulfide bond is either oxidized or reduced. Evaporation of neutral monomers and charge separation by cluster fission are the competing dissociation pathways of both peptides. The dominant fission product for all leucine enkephalin clusters studied is a proton-bound dimer, presumably due to the high gas-phase stability of this species. The branching ratio of the fission and evaporation processes for leucine enkephalin clusters appears to be determined by the value of z2/n for the cluster where z is the charge and n the number of monomer units in the cluster. Clusters with low and high values of z2/n dissociate primarily by evaporation and cluster fission respectively, with a sharp transition between dissociation primarily by evaporation and primarily by fission measured at a z2/n value of ~0.5. The dependence of the dissociation pathway of a cluster on z2/n is similar to the dissociation of atomic nuclei and multiply charged metal clusters indicating that leucine enkephalin peptide clusters exist in a state that is more disordered, and possibly fluid, rather than highly structured in the dissociative transition state. The branching ratio, but not the dissociation pathway of [somatostatin5 + 4H]4+ is altered by the reduction of its internal disulfide bond indicating that monomer conformational flexibility plays a role in peptide cluster dissociation. PMID:14652186

Jurchen, John C.; Garcia, David E.; Williams, Evan R.

2005-01-01

350

Enhanced N2 dissociation on Ru-loaded inorganic electride.  

PubMed

Electrides, i.e. salts in which electrons serve as anions, are promising materials for lowering activation energies of chemical reactions. Ab initio simulations are used to investigate the effect of the electron anions in a prototype mayenite-based electride (C12A7:e(-)) on the mechanism of N2 dissociation. It is found that both atomic and molecular nitrogen species chemisorb on the electride surface and become negatively charged due to the electron transfer from the substrate. However, charging alone is not sufficient to promote dissociation of N2 molecules. In the presence of Ru, N2 adsorbs with the formation of a cis-Ru2N2 complex and the N-N bond weakens due to both the electron transfer from the substrate and interaction with Ru. This complex transforms into a more stable trans-Ru2N2 configuration, in which the N2 molecule is dissociated, with the calculated barrier of 116 kJ mol(-1) and the overall energy gain of 72 kJ mol(-1). In contrast, in the case of the stoichiometric mayentie, the cis-Ru2N2 is ~34 kJ mol(-1) more stable than the trans-Ru2N2, while the cis-trans transition has a barrier of 192 kJ mol(-1). Splitting of N2 is promoted by a combination of the strong electron donating power of C12A7:e(-), ability of Ru to capture N2, polarization of Ru clusters, and electrostatic interaction of negatively charged N species with the surface cations. PMID:24483141

Kuganathan, Navaratnarajah; Hosono, Hideo; Shluger, Alexander L; Sushko, Peter V

2014-02-12

351

Exceptional sensitivity of metal-aryl bond energies to ortho-fluorine substituents: influence of the metal, the coordination sphere, and the spectator ligands on M-C/H-C bond energy correlations.  

PubMed

DFT calculations are reported of the energetics of C-H oxidative addition of benzene and fluorinated benzenes, Ar(F)H (Ar(F) = C(6)F(n)H(5-n), n = 0-5) at ZrCp(2) (Cp = eta(5)-C(5)H(5)), TaCp(2)H, TaCp(2)Cl, WCp(2), ReCp(CO)(2), ReCp(CO)(PH(3)), ReCp(PH(3))(2), RhCp(PH(3)), RhCp(CO), IrCp(PH(3)), IrCp(CO), Ni(H(2)PCH(2)CH(2)PH(2)), Pt(H(2)PCH(2)CH(2)PH(2)). The change in M-C bond energy of the products fits a linear function of the number of fluorine substituents, with different coefficients corresponding to ortho-, meta-, and para-fluorine. The values of the ortho-coefficient range from 20 to 32 kJ mol(-1), greatly exceeding the values for the meta- and para-coefficients (2.0-4.5 kJ mol(-1)). Similarly, the H-C bond energies of Ar(F)H yield ortho- and para-coefficients of 10.4 and 3.4 kJ mol(-1), respectively, and a negligible meta-coefficient. These results indicate a large increase in the M-C bond energy with ortho-fluorine substitution on the aryl ring. Plots of D(M-C) vs D(H-C) yield slopes R(M-C/H-C) that vary from 1.93 to 3.05 with metal fragment, all in excess of values of 1.1-1.3 reported with other hydrocarbyl groups. Replacement of PH(3) by CO decreases R(M-C/H-C) significantly. For a given ligand set and metals in the same group of the periodic table, the value of R(M-C/H-C) does not increase with the strength of the M-C bond. Calculations of the charge on the aryl ring show that variations in ionicity of the M-C bonds correlate with variations in M-C bond energy. This strengthening of metal-aryl bonds accounts for numerous experimental results that indicate a preference for ortho-fluorine substituents. PMID:19453181

Clot, Eric; Mégret, Claire; Eisenstein, Odile; Perutz, Robin N

2009-06-10

352

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

PubMed

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

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

2015-01-21

353

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

NASA Astrophysics Data System (ADS)

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.

Paredes-Gil, Katherine; Jaque, Pablo

2015-01-01

354

Limitations for aggressively scaled CMOS Si devices due to bond coordination constraints and reduced band offset energies at Si-high- k dielectric interfaces  

NASA Astrophysics Data System (ADS)

The three chemical bonding effects at Si-dielectric interfaces that are important in substituting alternative gate dielectric materials for SiO 2 in aggressively scaled CMOS are (i) the character of the interface bonds, either isovalent with bond and nuclear charge balanced as in Si-SiO 2, or heterovalent, where there is an inherent mismatch between bond and nuclear charge, (ii) physical bonding constraints related to the average number of bonds/atom, Nav and (iii) reduced conduction band offset energies in transition metal (T-M) elemental and binary oxides that are derived from increased ionic bonding and d-state contributions to the lowest conduction bands. These effects are discussed with respect to several different emerging high- k materials including (i) nitrides, (ii) T-M oxides, (iii) alloys of SiO 2 and T-M oxides and (iv) Al 2O 3.

Lucovsky, Gerald; Phillips, James C.

2000-10-01

355

Phosphodiester and N-glycosidic bond cleavage in DNA induced by 4-15 eV electrons  

NASA Astrophysics Data System (ADS)

Thin molecular films of the short single strand of DNA, GCAT, were bombarded under vacuum by electrons with energies between 4 and 15 eV. Ex vacuo analysis by high-pressure liquid chromatography of the samples exposed to the electron beam revealed the formation of a multitude of products. Among these, 12 fragments of GCAT were identified by comparison with reference compounds and their yields were measured as a function of electron energy. For all energies, scission of the backbone gave nonmodified fragments containing a terminal phosphate, with negligible amounts of fragments without the phosphate group. This indicates that phosphodiester bond cleavage by 4-15 eV electrons involves cleavage of the C-O bond rather than the P-O bond. The yield functions exhibit maxima at 6 and 10-12 eV, which are interpreted as due to the formation of transient anions leading to fragmentation. Below 15 eV, these resonances dominate bond dissociation processes. All four nonmodified bases are released from the tetramer, by cleavage of the N-glycosidic bond, which occurs principally via the formation of core-excited resonances located around 6 and 10 eV. The formation of the other nonmodified products leading to cleavage of the phosphodiester bond is suggested to occur principally via two different mechanisms: (1) the formation of a core-excited resonance on the phosphate unit followed by dissociation of the transient anion and (2) dissociation of the CO bond of the phosphate group formed by resonance electron transfer from the bases. In each case, phosphodiester bond cleavage leads chiefly to the formation of stable phosphate anions and sugar radicals with minimal amounts of alkoxyl anions and phosphoryl radicals.

Zheng, Yi; Cloutier, Pierre; Hunting, Darel J.; Wagner, J. Richard; Sanche, Léon

2006-02-01

356

Dissociative recombination in aeronomy  

NASA Technical Reports Server (NTRS)

The importance of dissociative recombination in planetary aeronomy is summarized, and two examples are discussed. The first is the role of dissociative recombination of N2(+) in the escape of nitrogen from Mars. A previous model is updated to reflect new experimental data on the electronic states of N produced in this process. Second, the intensity of the atomic oxygen green line on the nightside of Venus is modeled. Use is made of theoretical rate coefficients for production of O (1S) in dissociative recombination from different vibrational levels of O2(+).

Fox, J. L.

1989-01-01

357

Low energy (0-4 eV) electron impact to N(2)O clusters: Dissociative electron attachment, ion-molecule reactions, and vibrational Feshbach resonances.  

PubMed

Electron attachment to clusters of N(2)O in the energy range of 0-4 eV yields the ionic complexes [(N(2)O)(n)O](-), [(N(2)O)(n)NO](-), and (N(2)O)(n) (-) . The shape of the ion yields of the three homologous series differs substantially reflecting the different formation mechanisms. While the generation of [(N(2)O)(n)O](-) can be assigned to dissociative electron attachment (DEA) of an individual N(2)O molecule in the target cluster, the formation of [(N(2)O)(n)NO](-) is interpreted via a sequence of ion molecule reactions involving the formation of O(-) via DEA in the first step. The nondecomposed complexes (N(2)O)(n) (-) 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(2)O)(n)O](-) and (N(2)O)(n) (-) 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(2)O clusters [E. Leber, S. Barsotti, J. Bo?mmels, J. M. Weber, I. I. Fabrikant, M.-W. Ruf, and H. Hotop, Chem. Phys. Lett. 325, 345 (2000)]. PMID:20969408

Vizcaino, Violaine; Denifl, Stephan; Märk, Tilmann D; Illenberger, Eugen; Scheier, Paul

2010-10-21

358

Low energy (0-4 eV) electron impact to N2O clusters: Dissociative electron attachment, ion-molecule reactions, and vibrational Feshbach resonances  

NASA Astrophysics Data System (ADS)

Electron attachment to clusters of N2O in the energy range of 0-4 eV yields the ionic complexes [(N2O)nO]-, [(N2O)nNO]-, and (N2O)n- . The shape of the ion yields of the three homologous series differs substantially reflecting the different formation mechanisms. While the generation of [(N2O)nO]- can be assigned to dissociative electron attachment (DEA) of an individual N2O molecule in the target cluster, the formation of [(N2O)nNO]- is interpreted via a sequence of ion molecule reactions involving the formation of O- via DEA in the first step. The nondecomposed complexes (N2O)n- 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 [(N2O)nO]- and (N2O)n- 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 N2O clusters [E. Leber, S. Barsotti, J. Bömmels, J. M. Weber, I. I. Fabrikant, M.-W. Ruf, and H. Hotop, Chem. Phys. Lett. 325, 345 (2000)].

Vizcaino, Violaine; Denifl, Stephan; Märk, Tilmann D.; Illenberger, Eugen; Scheier, Paul

2010-10-01

359

Bond energies and structures of ammonia-sulfuric acid positive cluster ions.  

PubMed

New particle formation in the atmosphere is initiated by nucleation of gas-phase species. The small molecular clusters that act as seeds for new particles are stabilized by the incorporation of an ion. Ion-induced nucleation of molecular cluster ions containing sulfuric acid generates new particles in the background troposphere. The addition of a proton-accepting species to sulfuric acid cluster ions can further stabilize them and may promote nucleation under a wider range of conditions. To understand and accurately predict atmospheric nucleation, the stabilities of each molecular cluster within a chemical family must be known. We present the first comprehensive measurements of the ammonia-sulfuric acid positive ion cluster system NH(4)(+)(NH(3))(n)(H(2)SO(4))(s). Enthalpies and entropies of individual growth steps within this system were measured using either an ion flow reactor-mass spectrometer system under equilibrium conditions or by thermal decomposition of clusters in an ion trap mass spectrometer. Low level ab initio structural calculations provided inputs to a master equation model to determine bond energies from thermal decomposition measurements. Optimized ab initio structures for clusters up through n = 3, s = 3 are reported. Upon addition of ammonia and sulfuric acid pairs, internal proton transfer generates multiple NH(4)(+) and HSO(4)(-) ions within the clusters. These multiple-ion structures are up to 50 kcal mol(-1) more stable than corresponding isomers that retain neutral NH(3) and H(2)SO(4) species. The lowest energy n = s clusters are composed entirely of ions. The addition of acid-base pairs to the core NH(4)(+) ion generates nanocrystals that begin to resemble the ammonium bisulfate bulk crystal starting with the smallest n = s cluster, NH(4)(+)(NH(3))(1)(H(2)SO(4))(1). In the absence of water, this cluster ion system nucleates spontaneously for conditions that encompass most of the free troposphere. PMID:22103290

Froyd, Karl D; Lovejoy, Edward R

2012-06-21

360

Influence of oxygen inhibition on the surface free-energy and dentin bond strength of self-etch adhesives.  

PubMed

We compared the surface free-energies and dentin bond strengths of single-step self-etch adhesives with and without an oxygen-inhibited layer. The labial dentin surfaces of bovine mandibular incisors were wet ground with #600-grit silicon carbide paper. The adhesives were applied to the ground dentin, light-irradiated, and the oxygen-inhibited layer was either retained or removed with ethanol. The surface free-energies were determined by measuring the contact angles of three test liquids placed on the cured adhesives. The dentin bond strengths of specimens with and without the oxygen-inhibited layer were measured. For all surfaces, the value of the estimated surface tension component was relatively constant at 35.5-39.8 mJ m(-2) . The value of the , Lewis acid component increased slightly when the oxygen-inhibited layer was removed, whereas that of the , Lewis base component decreased significantly. The bond strengths of the self-etch adhesives were significantly lower in specimens without an oxygen-inhibited layer (13.2-13.6 MPa) than in those with an oxygen-inhibited layer (17.5-18.4 MPa). These results indicate that the presence of an oxygen-inhibited layer in single-step self-etch adhesives with advanced photoinitiators promotes higher dentin bond strength. PMID:21896057

Koga, Kensaku; Tsujimoto, Akimasa; Ishii, Ryo; Iino, Masayoshi; Kotaku, Mayumi; Takamizawa, Toshiki; Tsubota, Keishi; Miyazaki, Masashi

2011-10-01

361

Influence of oxygen inhibition on the surface free energy and enamel bond strength of self-etch adhesives.  

PubMed

We compared the surface free energies and enamel bond strengths of single-step self-etch adhesives with and without an oxygen-inhibited layer. The adhesives were applied to the enamel surfaces of bovine incisors, light irradiated, and the oxygen-inhibited layer was either retained or removed with ethanol. The surface free energies and their components (?(S)(LW), ?(S)(+), and ?(S)(-)) were determined by measuring the contact angles of three test liquids placed on the cured adhesives. The enamel bond strengths of specimens with and without the oxygen-inhibited layer were measured. For all surfaces, the value of the estimated surface tension component ?(S)(LW) was relatively constant. The value of the ?(S)(+) component increased slightly when the oxygen-inhibited layer was removed, whereas that of the ?(S)(-) component decreased significantly. The enamel bond strengths of the self-etch adhesives were significantly lower in the specimens without an oxygen-inhibited layer. The oxygen-inhibited layer therefore appeared to promote higher enamel bond strength. PMID:22277602

Oyama, Koji; Tsujimoto, Akimasa; Otsuka, Eiichiro; Shimizu, Yusuke; Shiratsuchi, Koji; Tsubota, Keishi; Takamizawa, Toshiki; Miyazaki, Masashi

2012-02-01

362

Hydrophobic silicon wafer bonding  

NASA Astrophysics Data System (ADS)

Wafers prepared by an HF dip without a subsequent water rinse were bonded at room temperature and annealed at temperatures up to 1100 °C. Based on substantial differences between bonded hydrophilic and hydrophobic Si wafer pairs in the changes of the interface energy with respect to temperature, secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM), we suggest that hydrogen bonding between Si-F and H-Si across two mating wafers is responsible for room temperature bonding of hydrophobic Si wafers. The interface energy of the bonded hydrophobic Si wafer pairs does not change appreciably with time up to 150 °C. This stability of the bonding interface makes reversible room-temperature hydrophobic wafer bonding attractive for the protection of silicon wafer surfaces.

Tong, Q.-Y.; Schmidt, E.; Gösele, U.; Reiche, M.

1994-01-01

363

Financing Public Sector Projects with Clean Renewable Energy Bonds; Fact Sheet Series on Financing Renewable Energy Projects, National Renewable Energy Laboratory (NREL)  

SciTech Connect

Clean renewable energy bonds (CREBs) present a low-cost opportunity for public entities to issue bonds to finance renewable energy projects. The federal government lowers the cost of debt by providing a tax credit to the bondholder in lieu of interest payments from the issuer. Because CREBs are theoretically interest free, they may be more attractive than traditional tax-exempt municipal bonds. In February 2009, Congress appropriated a total of $2.4 billion for the "New CREBs" program. No more than one-third of the budget may be allocated to each of the eligible entities: governmental bodies, electric cooperatives, and public power providers. Applications for this round of "New CREBs" were due to the Internal Revenue Service (IRS) on August 4, 2009. There is no indication Congress will extend the CREBs program; thus going forward, only projects that are approved under the 2009 round will be able to issue CREBs. This factsheet explains the CREBs mechanism and provides guidance on procedures related to issuing CREBs.

Kreycik, C.; Couglin, J.

2009-12-01

364

Hallucinogens and Dissociative Drugs  

MedlinePLUS

... in bizarre or dangerous behavior. Hallucinogens such as LSD and psilocybin cause emotions to swing wildly and ... Take Hallucinogenic or Dissociative Drugs? How Do Hallucinogens (LSD and Psilocybin) Affect the Brain and Body? What ...

365

High-resolution study of dissociative electron attachment to dipolar molecules at low energies: CH2Br2 and CCl3Br  

NASA Astrophysics Data System (ADS)

Using the laser photoelectron attachment method with an energy width ? 1 meV at low energies (? 172 meV) and an electron beam method (energy width about 70 meV) at higher energies (up to 2 eV), we have determined absolute cross sections ?e (E) for dissociative electron attachment to the dipolar molecules CH2Br2 and CCl3Br by normalization to known electron attachment rate coefficients. At thresholds for vibrational excitation of the CH2Br2 molecule, the DA cross section exhibits pronounced structure due to coupling of the attachment process with scattering channels; below the ?3 = 1 onset for the symmetric CBr2 stretch vibration, a clear vibrational Feshbach resonance is observed. At low energies the cross sections ?e (E) show an energy dependence between E-1/2 and E-1, in essential agreement with predictions of an extended Vogt-Wannier (EVW) capture model which includes the long-range electron-dipole interaction in addition to the polarization force. The determined absolute values are, however, substantially smaller than those predicted by the EVW model. Semiempirical R-matrix calculations have been carried out which show that at low electron energies (E < 0.15 eV) Br- formation from CCl3Br proceeds by s-wave attachment to the anion ground state while a broad peak, observed around 0.6 eV and evolving predominantly into the Cl- channel, is due to an excited anion state. Comparisons are made with cross sections and rate coefficients obtained in previous photoelectron attachment work (TPSA) and in electron beam as well as swarm experiments. Based on our joint experimental results for ?e (E), we report the electron temperature dependence of the rate coefficients ke (Te) for free electron attachment involving a Maxwellian electron ensemble and a gas at room temperature (TG = 300 K).

Schramm, A.; Ruf, M.-W.; Stano, M.; Matejcik, S.; Fabrikant, I. I.; Hotop, H.

2002-10-01

366

Accounting for the differences in the structures and relative energies of the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I4 2+, the Se-I pi-bonded Se2I4 2+, and their higher-energy isomers by AIM, MO, NBO, and VB methodologies.  

PubMed

The bonding in the highly homoatomic np pi-np pi (n > or = 3)-bonded S2I42+ (three sigma + two pi bonds), the Se-I pi-bonded Se2I42+ (four sigma + one pi bonds), and their higher-energy isomers have been studied using modern DFT and ab initio calculations and theoretical analysis methods: atoms in molecules (AIM), molecular orbital (MO), natural bond orbital (NBO), and valence bond (VB) analyses, giving their relative energies, theoretical bond orders, and atomic charges. The aim of this work was to seek theory-based answers to four main questions: (1) Are the previously proposed simple pi*-pi* bonding models valid for S2I42+ and Se2I42+? (2) What accounts for the difference in the structures of S2I42+ and Se2I42+? (3) Why are the classically bonded isolobal P2I4 and As2I4 structures not adopted? (4) Is the high experimentally observed S-S bond order supported by theoretical bond orders, and how does it relate to high bond orders between other heavier main group elements? The AIM analysis confirmed the high bond orders and established that the weak bonds observed in S2I42+ and Se2I42+ are real and the bonding in these cations is covalent in nature. The full MO analysis confirmed that S2I42+ contains three sigma and two pi bonds, that the positive charge is essentially equally distributed over all atoms, that the bonding between S2 and two I2+ units in S2I42+ is best described by two mutually perpendicular 4c2e pi*-pi* bonds, and that in Se2I42+, two SeI2+ moieties are joined by a 6c2e pi*-pi* bond, both in agreement with previously suggested models. The VB treatment provided a complementary approach to MO analysis and provided insight how the formation of the weak bonds affects the other bonds. The NBO analysis and the calculated AIM charges showed that the minimization of the electrostatic repulsion between EI2+ units (E = S, Se) and the delocalization of the positive charge are the main factors that explain why the nonclassical structures are favored for S2I42+ and Se2I42+. The difference in the structures of S2I42+ and Se2I42+ is related to the high strength of the S-S pi bond compared to the weak S-I sigma bond and the additional stabilization from increased delocalization of positive charge in the structure of S2I42+ compared to the structure of Se2I42+. The investigation of the E2X42+ series (E = S, Se, Te; X = Cl, Br, I) revealed that only S2I42+ adopts the highly np pi-np pi (n > or = 3)-bonded structure, while all other dications favor the pi-bonded Se2I42+ structure. Theoretical bond order calculations for S2I42+ confirm the previously presented experimentally based bond orders for S-S (2.1-2.3) and I-I (1.3-1.5) bonds. The S-S bond is determined to have the highest reported S-S bond order in an isolated compound and has a bond order that is either similar to or slightly less than the Si-Si bond order in the proposed triply bonded [(Me3Si)2CH]2(iPr)SiSi triple bond SiSi(iPr)[CH(SiMe3)2]2 depending on the definition of bond orders used. PMID:17257010

Brownridge, Scott; Crawford, Margaret-Jane; Du, Hongbin; Harcourt, Richard D; Knapp, Carsten; Laitinen, Risto S; Passmore, Jack; Rautiainen, J Mikko; Suontamo, Reijo J; Valkonen, Jussi

2007-02-01

367

Chemical bonding, interface strength, and oxygen K electron-energy-loss near-edge structure of the Cu\\/Al2O3 interface  

Microsoft Academic Search

Chemical bondings and oxygen K electron-energy-loss near-edge structures (ELNES) of oxygen terminated Cu\\/Al2O3 heterointerfaces with hollow and on-top configurations were theoretically investigated by using a first principles orthogonalized linear combination of atomic orbitals method. From the chemical bonding analysis, it was found that the hollow configuration has stronger ionic and covalent bondings as compared with the on-top configuration, and the

Teruyasu Mizoguchi; Takeo Sasaki; Shingo Tanaka; Katsuyuki Matsunaga; Takahisa Yamamoto; Masanori Kohyama; Yuichi Ikuhara

2006-01-01

368

Chemical bonding, interface strength, and oxygen K electron-energy-loss near-edge structure of the Cu\\/AlâOâ interface  

Microsoft Academic Search

Chemical bondings and oxygen K electron-energy-loss near-edge structures (ELNES) of oxygen terminated Cu\\/AlâOâ heterointerfaces with hollow and on-top configurations were theoretically investigated by using a first principles orthogonalized linear combination of atomic orbitals method. From the chemical bonding analysis, it was found that the hollow configuration has stronger ionic and covalent bondings as compared with the on-top configuration, and the

Teruyasu Mizoguchi; Takeo Sasaki; Katsuyuki Matsunaga; Yuichi Ikuhara; Shingo Tanaka; Masanori Kohyama; Takahisa Yamamoto

2006-01-01

369

Effusive molecular beam study of C2H6 dissociation on Pt(111).  

PubMed

The dissociative sticking coefficient for C2H6 on Pt(111) has been measured as a function of both gas temperature (Tg) and surface temperature (Ts) using effusive molecular beam and angle-integrated ambient gas dosing methods. A microcanonical unimolecular rate theory (MURT) model of the reactive system is used to extract transition state properties from the data as well as to compare our data directly with supersonic molecular beam and thermal equilibrium sticking measurements. We report for the first time the threshold energy for dissociation, E0 = 26.5 +/- 3 kJ mol(-1). This value is only weakly dependent on the other two parameters of the model. A strong surface temperature dependence in the initial sticking coefficient is observed; however, the relatively weak dependence on gas temperature indicates some combination of the following (i) not all molecular excitations are contributing equally to the enhancement of sticking, (ii) that strong entropic effects in the dissociative transition state are leading to unusually high vibrational frequencies in the transition state, and (iii) energy transfer from gas-phase rovibrational modes to the surface is surprisingly efficient. In other words, it appears that vibrational mode-specific behavior and/or molecular rotations may play stronger roles in the dissociative adsorption of C2H6 than they do for CH4. The MURT with an optimized parameter set provides for a predictive understanding of the kinetics of this C-H bond activation reaction, that is, it allows us to predict the dissociative sticking coefficient of C2H6 on Pt(111) for any combination of Ts and Tg even if the two are not equal to one another. PMID:16570977

DeWitt, Kristy M; Valadez, Leticia; Abbott, Heather L; Kolasinski, Kurt W; Harrison, Ian

2006-04-01

370

Exploring the Nature of Silicon-Noble Gas Bonds in H3SiNgNSi and HSiNgNSi Compounds (Ng = Xe, Rn).  

PubMed

Ab initio and density functional theory-based computations are performed to investigate the structure and stability of H3SiNgNSi and HSiNgNSi compounds (Ng = Xe, Rn). They are thermochemically unstable with respect to the dissociation channel producing Ng and H3SiNSi or HSiNSi. However, they are kinetically stable with respect to this dissociation channel having activation free energy barriers of 19.3 and 23.3 kcal/mol for H3SiXeNSi and H3SiRnNSi, respectively, and 9.2 and 12.8 kcal/mol for HSiXeNSi and HSiRnNSi, respectively. The rest of the possible dissociation channels are endergonic in nature at room temperature for Rn analogues. However, one three-body dissociation channel for H3SiXeNSi and one two-body and one three-body dissociation channels for HSiXeNSi are slightly exergonic in nature at room temperature. They become endergonic at slightly lower temperature. The nature of bonding between Ng and Si/N is analyzed by natural bond order, electron density and energy decomposition analyses. Natural population analysis indicates that they could be best represented as (H3SiNg)+(NSi)- and (HSiNg)+(NSi)-. Energy decomposition analysis further reveals that the contribution from the orbital term (?Eorb) is dominant (ca. 67%-75%) towards the total attraction energy associated with the Si-Ng bond, whereas the electrostatic term (?Eelstat) contributes the maximum (ca. 66%-68%) for the same in the Ng-N bond, implying the covalent nature of the former bond and the ionic nature of the latter. PMID:25809612

Pan, Sudip; Saha, Ranajit; Chattaraj, Pratim K

2015-01-01

371

Chemical bonding in view of electron charge density and kinetic energy density descriptors.  

PubMed

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

Jacobsen, Heiko

2009-05-01

372

Dissociation of energy selected Sn(CH3)4(+), Sn(CH3)3Cl+, and Sn(CH3)3Br+ ions: evidence for isolated excited state dynamics.  

PubMed

The dissociation dynamics of Sn(CH(3))(4)(+), Sn(CH(3))(3)Cl(+), and Sn(CH(3))(3)Br(+) were investigated by threshold photoelectron photoion spectrometry using an electron imaging apparatus (iPEPICO) at the Swiss Light Source. The tetramethyltin ion was found to dissociate via Sn(CH(3))(4)(+) ? Sn(CH(3))(3)(+) + CH(3) ? Sn(CH(3))(2)(+) + 2CH(3), while the trimethyltin halide ions dissociated via methyl loss at low energies, and a competitive halogen loss at somewhat higher energies. The 0 K methyl loss onset for the three ions was found to be 9.410 ± 0.020 eV, 10.058 ± 0.020 eV, and 9.961 ± 0.020 eV, respectively. Statistical theory could not reproduce the observed onsets for the halogen loss steps in the halotrimethyltin ions. The halide loss signal as a function energy mimicked the excited state threshold photoelectron spectrum, from which we conclude that the halide loss from these ions takes place on an isolated excited state potential energy surface, which we describe by time dependent density functional calculations. The sequential loss of a second methyl group in the Sn(CH(3))(4)(+) ion, observed at about 3 eV higher energies than the first one, is also partially non-statistical. The derived product energy distribution resulting from the loss of the first methyl group is two-component with about 50% being statistical and the remainder associated with high translational energy products that peak at 2 eV. Time dependent DFT calculations show that a dissociative ?B state lies in the vicinity of the experimental measurements. We thus propose that 50% of the Sn(CH(3))(4)(+) ions produced in this energy range internally convert to the ?X state, on which they dissociate statistically, while the remainder dissociate directly from the repulsive ?B state leading to high kinetic energy products. PMID:21892510

Baer, Tomas; Guerrero, Andrés; Davalos, Juan Z; Bodi, Andras

2011-10-21

373

Unimolecular dissociations of C70+ and its noble gas endohedral cations Ne@C70+ and Ar@C70+: cage-binding energies for C2 loss.  

PubMed

The energetics and dynamics of unimolecular decompositions of C70+ and its noble gas endohedral cations, Ne@C70+ and Ar@C70+, have been studied using tandem mass spectrometry techniques. The high-resolution mass-analyzed ion kinetic energy (HR-MIKE) spectra for the unimolecular reactions of C70+, Ne@CC70+, and Ar@C70+ were recorded by scanning the electrostatic analyzer and using single-ion counting that was achieved by combination of an electron multiplier, amplifier/discriminator, and multichannel analyzer. These cations dissociate unimolecularly via loss of a C2 unit, and no endohedral atom is observed as fragment. The activation energies for C2 evaporation from Ne@C70+ and Ar@C70+ are lower than those for elimination of the endohedral noble gas atoms. The kinetic energy release distributions (KERDs) for the C2 evaporation have been measured and, by use of the finite heat bath theory (FHBT), the binding energies for the C2 emission have been deduced from the KERDs. The C2 evaporation energies increase in the order DeltaEvap(C70+) < DeltaEvap(Ne@C70+) < DeltaEvap(Ar@C70+), but no big difference in the cage binding was observed for C70+, Ne@C70+, and Ar@C70+, indicating incorporations of the Ne and Ar atoms into C70 contribute a little to the stability of C70 toward C2 loss, which is in good agreement with theoretical calculations but contrasts with the findings in their C60 analogues and in metallofullerenes that the decay energies of the filled fullerenes are much higher than those of the corresponding empty cages. PMID:16833319

Cao, Baopeng; Peres, Tikva; Cross, R James; Saunders, Martin; Lifshitz, Chava

2005-11-17

374

Dissociative Ionization of Benzene by Electron Impact  

NASA Technical Reports Server (NTRS)

We report a theoretical study of the dissociative ionization (DI) of benzene from the low-lying ionization channels. Our approach makes use of the fact that electron motion is much faster than nuclear motion and DI is treated as a two-step process. The first step is electron-impact ionization resulting in an ion with the same nuclear geometry as the neutral molecule. In the second step the nuclei relax from the initial geometry and undergo unimolecular dissociation. For the ionization process we use the improved binary-encounter dipole (iBED) model. For the unimolecular dissociation step, we study the steepest descent reaction path to the minimum of the ion potential energy surface. The path is used to analyze the probability of unimolecular dissociation and to determine the product distributions. Our analysis of the dissociation products and the thresholds of the productions are compared with the result dissociative photoionization measurements of Feng et al. The partial oscillator strengths from Feng et al. are then used in the iBED cross section calculations.

Huo, Winifred; Dateo, Christopher; Kwak, Dochan (Technical Monitor)

2002-01-01

375

Evaluation of Die-Attach Bonding Using High-Frequency Ultrasonic Energy for High-Temperature Application  

NASA Astrophysics Data System (ADS)

Room-temperature die-attach bonding using ultrasonic energy was evaluated on Cu/In and Cu/Sn-3Ag metal stacks. The In and Sn-3Ag layers have much lower melting temperatures than the base material (Cu) and can be melted through the heat generated during ultrasonic bonding, forming intermetallic compounds (IMCs). Samples were bonded using different ultrasonic powers, bonding times, and forces and subsequently aged at 300°C for 500 h. After aging, die shear testing was performed and the fracture surfaces were inspected by scanning electron microscopy. Results showed that the shear strength of Cu/In joints reached an upper plateau after 100 h of thermal aging and remained stable with aging time, whereas that of the Cu/Sn-3Ag joints decreased with increasing aging time. ?-Cu7In4 and (Cu,Au)11In9 IMCs were observed at the Cu/In joint, while Cu3Sn and (Ag,Cu)3Sn IMCs were found at the Cu/Sn-3Ag joint after reliability testing. As Cu-based IMCs have high melting temperatures, they are highly suitable for use in high-temperature electronics, but can be formed at room temperature using an ultrasonic approach.

Lee, Jong-Bum; Aw, Jie-Li; Rhee, Min-Woo

2014-09-01

376

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

PubMed

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

Angelina, Emilio L; Duarte, Darío J R; Peruchena, Nélida M

2013-05-01

377

Hydrogen Bond Lifetimes and Energetics for Solute/Solvent Complexes Studied with 2D-IR Vibrational Echo Spectroscopy  

E-print Network

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

Fayer, Michael D.

378

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

E-print Network

formation) in materials using force ®elds (FF) that properly describe multiple bonds at small distances the dissoci- ation and formation of chemical bonds. Although high- quality quantum mechanical (QM species on diamond surfaces [6±11], fullerene molecules scattering on dia- mond surfaces [12], mechanical

Goddard III, William A.

379

Dissociative dynamics of O2 on Ag(110).  

PubMed

We study the dissociative dynamics of O2 on Ag(110) by performing classical and quasiclassical trajectory calculations on an adiabatic six-dimensional potential energy surface (PES). The PES is constructed from the interpolation of a large set of energies that are calculated using spin-polarized density functional theory. The minimum energy barrier to dissociation amounts to 0.36 eV. This value, which is considerably lower than the barriers of about 1.1 eV found in the Ag(100) and Ag(111) surfaces, is in line with the measured much higher reactivity of the (110) surface. Our classical dynamics calculations show that under normal incidence conditions no significant dissociation occurs below an initial energy of 0.9 eV (0.6 eV in the quasiclassical calculations). This result is an indication of a very much reduced configurational space leading to dissociation and also explains why direct dissociation has not been observed experimentally at low incidence energies. Our calculations also show that for off-normal incidence, most of the dissociation takes place close to the long-bridge site, a region of the configurational space where the energy barriers to dissociation are higher than 0.7 eV, resulting in still lower dissociation probabilities. PMID:25767834

Lon?ari?, Ivor; Alducin, M; Juaristi, J I

2015-04-14

380

Atom abstraction and gas phase dissociation in the interaction of XeF2 with Si(100)  

NASA Astrophysics Data System (ADS)

Xenon difluoride reacts with Si(100)2×1 by single atom abstraction whereby a dangling bond abstracts a F atom from XeF2, scattering the complementary XeF product molecule into the gas phase, as observed in a molecular beam surface scattering experiment. Partitioning of the available reaction energy produces sufficient rovibrational excitation in XeF for dissociation of most of the XeF to occur. The resulting F and Xe atoms are shown to arise from the dissociation of gas phase XeF by demonstrating that the angle-resolved velocity distributions of F, Xe, and XeF conserve momentum, energy, and mass. Dissociation occurs within 2 Å of the surface and within a vibrational period of the excited XeF molecule. Approximately an equal amount of the incident XeF2 is observed to react by two atom abstraction, resulting in adsorption of a second F atom and scattering of a gas phase Xe atom. Two atom abstraction occurs for those XeF product molecules whose bond axes at the transition state are oriented within ±60° of the normal and with the F end pointed toward the surface.

Hefty, R. C.; Holt, J. R.; Tate, M. R.; Ceyer, S. T.

2008-12-01

381

B3LYP calculations of the potential energy surfaces of the thermal dissociations and the triplet ground state of pyrolysis products XN( x˜ 3?-) for halogen azides XN 3 (X: F, Cl, Br, I)  

NASA Astrophysics Data System (ADS)

Mechanisms of XN 3 (X: F, Cl, Br, I) dissociations are proposed based on B3LYP calculated potential energy surfaces. The energy gaps between the ground-state reactants XN3( x˜ 1A') and the intersystem crossing (ISC) points are only a little lower than respective potential energy barriers of the spin-allowed reactions, XN3( x˜ 1A')? XN(a 1?)+ N2( x˜ 1?g+) . The ISC point, therefore, is considered as a 'transition state' of the spin-forbidden reactions, XN3( x˜ 1A')? XN( x˜ 3?-)+ N2( x˜ 1?g+) . The methods of IRC and topological analysis of electron density are used to predict the thermal dissociation pathway of the reactions studied.

Zeng, Yanli; Meng, Lingpeng; Zheng, Shijun; Wang, Dianxun

2003-08-01

382

Diatomic silylynes, germylynes, stannylynes, and plumbylynes: structures, dipole moments, dissociation energies, and quartet-doublet gaps of EH and EX (E = Si, Ge, Sn, Pb; X = F, Cl, Br, I).  

PubMed

Systematic theoretical studies of the carbyne and halocarbyne analogues E-H and E-X (E = Si, Ge, Sn, Pb; X = F, Cl, Br, I) were carried out with ab initio coupled-cluster methods using very large basis sets. The (2)? state is the ground electronic state for all these compounds. The quartet-doublet energy separations, equilibrium distances, and dissociation energies for these species are predicted. The quartet-doublet splittings fall in the order EF > ECl > EBr > EI > EH for a given metal E; and PbX > GeX > SnX > SiX for the same halogen atom X. The dipole moments span a large range, from 0.08 debye (GeH) to 3.58 debye (PbCl). The dissociation energies range from 1.84 eV (PbH) to 6.15 eV (SiF). PMID:23731286

Li, Huidong; Feng, Hao; Sun, Weiguo; Xie, Yaoming; Schaefer, Henry F

2013-06-17

383

Tubulin bond energies and microtubule biomechanics determined from nanoindentation in silico  

E-print Network

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...

Kononova, Olga; Theisen, Kelly E; Marx, Kenneth A; Dima, Ruxandra I; Ataullakhanov, Fazly I; Grishchuk, Ekaterina L; Barsegov, Valeri

2015-01-01

384

A comparative study of Dissociative Ionization of N2 and CO  

NASA Astrophysics Data System (ADS)

A comparative study on the properties of charge symmetric dissociation (CSD) and charge asymmetric dissociation (CAD) of doubly ionized N2 and CO is performed. Kinetic energy release (KER) distributions resulting from the dissociation of doubly charged molecular ions are explained on the basis of calculated potential energy curves.

Pandey, Amrendra; Bapat, B.; Shamsundar, K. R.

2014-04-01

385

Ab initio non-Born-Oppenheimer simulations of rescattering dissociation of H2 in strong infrared laser fields  

NASA Astrophysics Data System (ADS)

We simulate the time-dependent Schrödinger equation and observe the rescattering dissociation of H2 in strong infrared laser fields. Two dissociation pathways are identified, i.e., the dissociation of H2+ in the 2 p ?u state and the dissociation of H2 in doubly excited states. The former accounts for larger proportions as the rescattering energy is larger. The kinetic energy release of dissociative fragments reflects the temporal internuclear distance at the moment the rescattering happens.

Li, Zhi-Chao; He, Feng

2014-11-01

386

State-resolved imaging of CO from propenal photodissociation: Signatures of concerted three-body dissociation  

NASA Astrophysics Data System (ADS)

State-selected DC sliced images of propenal photodissociation show clear signatures of a novel synchronous concerted three-body dissociation of propenal recently proposed by Lee and co-workers to give C2H2 + H2 + CO [S. H. Lee, C. H. Chin, C. Chaudhuri, ChemPhysChem 12, 753 (2011)]. Unlike any prior example of a concerted 3-body dissociation event, this mechanism involves breaking three distinct bonds and yields 3 distinct molecules. DC sliced images of CO fragments were recorded for a range of rotational levels for both v = 0 and v = 1. The results show formation of two distinct CO product channels having dissimilar translational energy distributions with characteristic rovibrational state distributions. The images for CO (v = 0) show a large contribution of slower CO fragments at lower rotational levels (J = 5-25). This slow component is completely absent from the v = 1 CO images. The images for the higher rotational levels of the v = 0 and v = 1 CO are nearly identical, and this provides a basis for decomposing the two channels for v = 0. The quantum state and translational energy distributions for the slow channel are readily assigned to the 3-body dissociation based on the properties of the transition state. The faster CO fragments dominating the higher rotational levels in both v = 0 and v = 1 are attributed to formation of CH3CH + CO, also in agreement with the inferences based on previous non-state-resolved measurements with supporting theoretical calculations.

Dey, Arghya; Fernando, Ravin; Suits, Arthur G.

2014-04-01

387

Coordination-resolved local bond relaxation, electron binding-energy shift, and Debye temperature of Ir solid skins  

NASA Astrophysics Data System (ADS)

Numerical reproduction of the measured 4f7/2 energy shift of Ir(1 0 0), (1 1 1), and (2 1 0) solid skins turns out the following: (i) the 4f7/2 level of an isolated Ir atom shifts from 56.367 eV to 60.332 eV by 3.965 eV upon bulk formation; (ii) the local energy density increases by up to 130% and the atomic cohesive energy decreases by 70% in the skin region compared with the bulk values. Numerical match to observation of the temperature dependent energy shift derives the Debye temperature that varies from 285.2 K (Surface) to 315.2 K (Bulk). We clarified that the shorter and stronger bonds between under-coordinated atoms cause local densification and quantum entrapment of electron binding energy, which perturbs the Hamiltonian and the core shifts in the skin region.

Bo, Maolin; Wang, Yan; Huang, Yongli; Yang, Xuexian; Yang, Yezi; Li, Can; Sun, Chang Q.

2014-11-01

388

Using Qualified Energy Conservation Bonds (QECBs) to Fund a Residential Energy Efficiency Loan Program: Case Study on Saint Louis County, MO  

SciTech Connect

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.

Zimring, Mark

2011-06-23

389

Dissociation and psychosis in dissociative identity disorder and schizophrenia.  

PubMed

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

Laddis, Andreas; Dell, Paul F

2012-01-01

390

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

Microsoft Academic Search

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 Møller-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

Yutaka Imamura; Takeshi Baba; Hiromi Nakai

2008-01-01

391

Hydrogen Sulfide Waste, Treatment By Microwave Plasma Dissociation  

Microsoft Academic Search

A new waste-treatment technology for hydrogen sulfide using a microwave-generated plasma to dissociate hydrogen sulfide appears to have a substantial economic edge over the current industrial technology. The advantage of the plasma process is that it can recover hydrogen, as well as sulfur, from hydrogen sulfide. Since the plasma process requires less energy to dissociate hydrogen sulfide than is needed

J. B. L. Harkness; A. J. Gorskl; E. J. Daniels

1990-01-01

392

Doorway mechanism for dissociative electron attachment to fructose Thomas Sommerfelda  

E-print Network

Doorway mechanism for dissociative electron attachment to fructose Thomas Sommerfelda Department, deoxyribose, and fructose have been shown to undergo dissociative electron attachment at threshold, that is, to fragment upon capture of a zero-energy electron. Here the electron acceptor properties of three fructose

Simons, Jack

393

A first-principles study of molecular oxygen dissociation at an electrode surface: a comparison of potential variation and coadsorption effects.  

PubMed

Influences of coadsorbed sodium and water, aqueous solvent, and electrode potential on the kinetics of O(2) dissociation over Pt(111) are systematically investigated using density functional theory models of vacuum and electrochemical interfaces. Na coadsorption alters the electronic states of Pt to stabilize the reactant (O(2)*), transition, and product (2O*) states by facilitating electron donation to oxygen, causing a more exothermic reaction energy (-0.84 eV for Na and O(2), -0.81 eV for isolated O(2)) and a decrease in dissociation barrier (0.39 eV for Na and O(2), 0.57 eV for isolated O(2)). Solvation decreases the reaction energy (-0.67 eV) due to enhanced hydrogen bond stabilization of O(2)* compared to 2O*. The influence of Na is less pronounced at the solvated interface (barrier decreases by only 0.11 eV) because H(2)O screens Na charge-donation. In the electrochemical model system, the dissociation energy becomes more exothermic and the barrier decreases toward more positive potentials. Potential-dependent behavior results from changes in interfacial dipole moment and polarizability between O(2)*, the dissociation transition state, and 2O*; each are influenced by changes in adsorption and hydrogen bonding. Coadsorption of Na in the solvated system dampens the dipole moment change between O(2)* and 2O* and significantly increases the polarizability at the dissociation transition state and for 2O*; the combination causes little change in the reaction energy but reduces the activation barrier by 0.08 eV at 0 V versus NHE. The potential-dependent behavior contrasts that determined at a constant surface charge or from an applied electric field, illustrating the importance of considering the electrochemical potential at the fully-solvated interface in determining reaction energetics, even for non-redox reactions. PMID:18563222

Wasileski, Sally A; Janik, Michael J

2008-07-01

394

Kinetic ion thermometers for electron transfer dissociation.  

PubMed

Peptide fragment ions of the z-type were used as kinetic ion thermometers to gauge the internal energy of peptide cation-radicals produced by electron transfer in the gas-phase. Electron transfer dissociation (ETD)-produced z2 ions containing the leucine residue, z2(Leu-Lys) and z2(Leu-Arg), were found to undergo spontaneous dissociation by loss of C3H7 that was monitored by time-resolved kinetic measurements on the time scale of the linear ion trap mass spectrometer. Kinetic modeling of the dissociations, including collisional cooling and product loss by neutralization, provided unimolecular rate constants for dissociation that were converted to the z ion internal energies using RRKM theory. The internal energy of z2(Leu-Lys) and z2(Leu-Arg) fragment ions was found to decrease with the increasing size of the precursor peptide ion, indicating vibrational energy partitioning between the ion and neutral fragments and ergodic behavior. The experimentally determined excitation in the peptide cation-radicals upon electron transfer (285-327 kJ mol(-1)) was found to be lower than that theoretically calculated from the reaction exothermicity. The reasons for this missing energy are discussed. PMID:25594857

Pepin, Robert; Ture?ek, František

2015-02-19

395

Dissociative adsorption of CH{sub 3}X (X = Br and Cl) on a silicon(100) surface revisited by density functional theory  

SciTech Connect

During the dissociative adsorption on a solid surface, the substrate usually participates in a passive manner to accommodate fragments produced upon the cleavage of the internal bond(s) of a (transient) molecular adsorbate. This simple picture, however, neglects the flexibility of surface atoms. Here, we report a Density Functional Theory study to revisit our early studies of the dissociative adsorption of CH{sub 3}X (X = Br and Cl) on Si(100). We have identified a new reaction pathway, which involves a flip of a silicon dimer; this new pathway agrees better with experiments. For our main exemplar of CH{sub 3}Br, insights have been gained using a simple model that involves a three-atom reactive center, Br-C-Si. When the silicon dimer flips, the interaction between C and Si in the Br-C-Si center is enhanced, evident in the increased energy-split of the frontier orbitals. We also examine how the dissociation dynamics of CH{sub 3}Br is altered on a heterodimer (Si-Al, Si-P, and Si-Ge) in a Si(100) surface. In each case, we conclude, on the basis of computed reaction pathways, that no heterodimer flipping is involved before the system transverses the transition state to dissociative adsorption.

Wang, Chen-Guang [Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials and Micro-nano Devices, Renmin University of China, Beijing 100872 (China); Lash Miller Chemical Laboratories, Department of Chemistry and Institute of Optical Sciences, University of Toronto, Toronto, Ontario M5S 3H6 (Canada); Huang, Kai, E-mail: khuang@chem.utoronto.ca, E-mail: wji@ruc.edu.cn [Lash Miller Chemical Laboratories, Department of Chemistry and Institute of Optical Sciences, University of Toronto, Toronto, Ontario M5S 3H6 (Canada); Ji, Wei, E-mail: khuang@chem.utoronto.ca, E-mail: wji@ruc.edu.cn [Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials and Micro-nano Devices, Renmin University of China, Beijing 100872 (China)

2014-11-07

396

Introduction to dissociative recombination  

NASA Technical Reports Server (NTRS)

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.

Guberman, Steven L.; Mitchell, J. Brian A.

1989-01-01

397

Dissociative Identity Disorder  

ERIC Educational Resources Information Center

Few psychological disorders in the Diagnostic Statistical Manual have generated as much controversy as Dissociative Identity Disorder (DID). For the past 35 years diagnoses of DID, previously referred to as Multiple Personality Disorder (MPD), have increased exponentially, causing various psychological researchers and clinicians to question the…

Schmidt, Tom

2007-01-01

398

Thermodynamic properties (enthalpy, bond energy, entropy, and heat capacity) and internal rotor potentials of vinyl alcohol, methyl vinyl ether, and their corresponding radicals.  

PubMed

Vinyl alcohols (enols) have been discovered as important intermediates and products in the oxidation and combustion of hydrocarbons, while methyl vinyl ethers are also thought to occur as important combustion intermediates. Vinyl alcohol has been detected in interstellar media, while poly(vinyl alcohol) and poly(methyl vinyl ether) are common polymers. The thermochemical property data on these vinyl alcohols and methyl vinyl ethers is important for understanding their stability, reaction paths, and kinetics in atmospheric and thermal hydrocarbon-oxygen systems. Enthalpies , entropies , and heat capacities (C(p)()(T)) are determined for CH(2)=CHOH, C(*)H=CHOH, CH(2)=C(*)OH, CH(2)=CHOCH(3), C(*)H=CHOCH(3), CH(2)=C(*)OCH(3), and CH(2)=CHOC(*)H(2). Molecular structures, vibrational frequencies, , and C(p)(T) are calculated at the B3LYP/6-31G(d,p) density functional calculation level. Enthalpies are also determined using the composite CBS-Q, CBS-APNO, and G3 methods using isodesmic work reactions to minimize calculation errors. Potential barriers for internal rotors are calculated at the B3LYP/6-31G(d,p) level and used to determine the hindered internal rotational contributions to entropy and heat capacity. The recommended ideal gas phase values calculated in this study are the following (in kcal mol(-1)): -30.0, -28.9 (syn, anti) for CH(2)=CHOH; -25.6, -23.9 for CH(2)=CHOCH(3); 31.3, 33.5 for C(*)H=CHOH; 27.1 for anti-CH(2)=C(*)OH; 35.6, 39.3 for C(*)H=CHOCH(3); 33.5, 32.2 for CH(2)=C(*)OCH(3); 21.3, 22.0 for CH(2)=CHOC(*)H(2). Bond dissociation energies (BDEs) and group additivity contributions are also determined. The BDEs reveal that the O-H, O-CH(3), C-OH, and C-OCH(3) bonds in vinyl alcohol and methyl vinyl ether are similar in energy to those in the aromatic molecules phenol and methyl phenyl ether, being on average around 3 kcal mol(-1) weaker in the vinyl systems. The keto-enol tautomerization enthalpy for the interconversion of vinyl alcohol to acetaldehyde is determined to be -9.7 kcal mol(-1), while the activation energy for this reaction is calculated as 55.9 kcal mol(-1); this is the simplest keto-enol tautomerization and is thought to be important in the reactions of vinyl alcohol. Formation of the formyl methyl radical (vinoxy radical/vinyloxy radical) from both vinyl alcohol and methyl vinyl ether is also shown to be important, and its reactions are discussed briefly. PMID:16789782

da Silva, Gabriel; Kim, Chol-Han; Bozzelli, Joseph W

2006-06-29

399

Chemical Bonds I  

ERIC Educational Resources Information Center

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)

Sanderson, R. T.

1972-01-01

400

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

NASA Astrophysics Data System (ADS)

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.

Fantner, Georg E.

2005-03-01

401

DFT study of sulfur derivatives of cumulenes and their protonated forms of interstellar interest and calculations of dissociation energies of protonated forms (SC(CH)C(n-2)S)(+) (n?=?3-8).  

PubMed

A theoretical study of the sulfur cumulenes SCnS (n?=?3-8), CnS ( n?=?1-8) and of their protonated forms (SCnS)H(+) and (CnS)H(+) that might exist in the interstellar environment, has been carried out by means of the standard B3LYP/6-311G** method. The geometries and relative energies of singlet and triplet states according to the number of carbons have been computed. Like neutral species, we have found that the ground state of the most stable protonated forms (SC(CH)Cn-2S)(+) and ((HC)Cn-1S)(+), alternates between a triplet state for the even series and a singlet state for the odd series. We provided the data needed to simulate infrared and microwave spectra (vibration frequencies, dipole moments, and rotational constants) for each protonated species (SCnS)H(+) and (CnS)H(+) and for each neutral CnS species. The computing of dissociation energies of the most stable protonated forms (SC(CH)Cn-2S)(+) (n?=?3-8) has shown that the lowest values are obtained for the dissociation of compounds with an even number of carbons, in their triplet state, which produce the observed fragments CS and C3S. The dissociation of even protonated forms requires less energy than for the odd protonated forms. PMID:24935110

Benmensour, Mohamed Ali; Djennane-Bousmaha, Sema; Boucekkine, Abdou

2014-07-01

402

Three dimensions of dissociative amnesia.  

PubMed

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

Dell, Paul F

2013-01-01

403

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

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.... The impurities were isobutylene, 0. 3/; t-butylbromide, = 0. 1F. ; and traces of one o ther unidentified compound. C. Analysis For g. l. c. analysis, a 0. 6 x 150 cm. column packed with 10/ CABX 550 on 60/80 chromosorb P. was used. At a column temperature...

Jirustithipong, Pongsiri

1975-01-01

404

Bonding Electronics and Energetics:. AN Approach Crossing the Barriers of Classical and Quantum Approximations  

NASA Astrophysics Data System (ADS)

The physical properties of a macroscopic system can be well described using classical approaches in terms of the Gibbs free energy or the continuum medium mechanics, for instances, that relate the detectable quantities directly to the external stimulus such as the temperature, pressure, chemical composition, electric and magnetic field, etc, without needing consideration of atomistic origins of the property change. At the atomic scale, quantum effect becomes dominant and the physical properties of a small object can be reliably optimized in computations by solving the Schüdinger equations or Newtonian motion of equations with a sum of averaged interatomic potentials as key factors. However, for a small system at the nanometer regime, both the classical and the quantum approaches encountered some difficulties. Recent exercises [1, 2] showed that the difficulties could be solved by considering the interatomic bond formation, dissociation, relaxation, and vibration and the associated energetic response of atoms and electrons and their consequences on the detectable quantities. It is possible to establish the functional dependence of a detectable quantity Q = Q (zi, di, Ei,m) on the bonding identities such as bond order, zi, bond length, di, bond energy, Ei, and bond nature indicator, m, and the response of the bonding identities to the external stimulus such as the coordination environment, temperature, pressure, etc. Progress made insofar is quite encouraging, which may evidence the essentiality of the approach that could describe the true situation and predict the performance of nanostructures. Note from Publisher: This article contains the abstract only.

Sun, Chang Qing

2008-12-01

405

DFT+U study on the oxygen adsorption and dissociation on CeO2-supported platinum cluster  

NASA Astrophysics Data System (ADS)

We investigated the reactivity of CeO2-supported Pt4 cluster (denoted as Pt4/CeO2(1 1 1)) toward O2 adsorption and dissociation as well as the geometry/electronic properties associated with such metal oxide supported cluster system using density functional theory and on-site Coulomb interaction correction via the Hubbard-like term, U (DFT+U). It was found that Pt4 binds strongly to CeO2(1 1 1) via PtOCe bonds which act as "anchors" between the surface and the cluster, confirming its non-sintering as found in experiments. The adsorption of the cluster involves net electron transfer to CeO2, however, charge redistribution also happens within the cluster (from Pt atom bonded to the surface to the Pt on top of the cluster). This charge couples to the top Pt leading to reduce its spin moment as compared to that of unsupported cluster. When O2 adsorbs on Pt4/CeO2(1 1 1), while it prefers Pt vertex site near the CeO2 surface, the OO bond elongation is more profound at the PtPt edges. The energy barrier for dissociating O2 from this edge site precursor state is smallest. A correlation between the OO bond length at the precursor state and the stability at the transition state is revealed. Finally, the barrier for dissociation in unsupported Pt4 is lower, indicating suppression of the cluster's reactivity due to the support. We attribute this to the hybridization of Pt-5d orbitals with O-2p orbitals in CeO2(1 1 1) leading to the broadening of Pt-5d states near the Fermi level.

Nguyen, Tien Quang; Escaño, Mary Clare Sison; Nakanishi, Hiroshi; Kasai, Hideaki; Maekawa, Hiroyoshi; Osumi, Kazuo; Sato, Kaoru

2014-01-01

406

Chemical Bonds  

NSDL National Science Digital Library

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.

The Concord Consortium

2011-12-11