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1

The Bond Dissociation Energies of 1-Butene  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

2

Bond Dissociation Energies of Organic Molecules  

E-print Network

to the enthalpy of reaction 1, rxnH298(1), which is by definition2 the bond dissociation enthalpy of the molecule.03 kcal mol-1, the forward reaction is determined to be exothermic since rxnH298(2) ) DH298(CH3CH2-H) - DH). By definition, it is the reaction enthalpy of the bond homolysis reaction 1, rxnH298(1), and thus depends

Ellison, Barney

3

Theoretical study of the bond dissociation energies of methanol  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

4

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

5

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

6

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

Microsoft Academic Search

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

Nicole Dölker; Antonio Morreale; Feliu Maseras

2005-01-01

7

Relationships for the impact sensitivities of energetic C-nitro compounds based on bond dissociation energy.  

PubMed

The ZPE-corrected C-NO(2) bond dissociation energies (BDEs(ZPE)) of a series of model C-nitro compounds and 26 energetic C-nitro compounds have been calculated using density functional theory methods. Computed results show that for C-nitro compounds the UB3LYP calculated BDE(ZPE) is less than the UB3P86 using the 6-31G** basis set, and the UB3P86 BDE(ZPE) changes slightly with the basis set varying from 6-31G** to 6-31++G**. For the series of model C-nitro compounds with different chemical skeletons, it is drawn from NBO analysis that the order of BDE(ZPE) is not only in line with that of the NAO bond order but also with that of the energy gap between C-NO(2) bonding and antibonding orbitals. It is found that for the energetic C-nitro compounds whose drop energies (Es(dr)) are below 24.5 J a good linear correlation exists between E(dr) and BDE(ZPE), implying that these compounds ignite through the C-NO(2) dissociation mechanism. After excluding the so-called trinitrotoluene mechanism compounds, a polynomial correlation of ln(E(dr)) with the BDE(ZPE) calculated at density functional theory levels has been established successfully for the 18 C-NO(2) dissociation energetic C-nitro compounds. PMID:20092267

Li, Jinshan

2010-02-18

8

THE JOURNAL OF CHEMICAL PHYSICS 134, 211101 (2011) Communication: Determination of the bond dissociation energy (D0)  

E-print Network

dissociation energy (D0) of the water dimer, (H2O)2, by velocity map imaging Blithe E. Rocher-Casterline, Lee C online 1 June 2011) The bond dissociation energy (D0) of the water dimer is determined by using state. Phys. 130, 144314 (2009)]. © 2011 American Institute of Physics. [doi:10.1063/1.3598339] The water

Reisler, Hanna

9

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

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

1991-01-01

10

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

11

Energy of N-H-bond dissociation in phenothiazines and diphenylamines  

NASA Astrophysics Data System (ADS)

Energies of the dissociation of N-H-bonds ( D N-H) in 3 phenothiazines, phenoxazine, phenoselenoazine, and 9 diphenylamines (AmH) are determined. The D N-H values are calculated from kinetic data by means of intersecting parabolas. The rate constants of the following types of reaction are used in calculations: RO{2/·} + Am i H, R· + Am i H, Am{/i ·} + PhMe2CH, and Am{/i ·} + ROOH. As a rule, the results obtained for the reactions of different types are in good agreement with each other and with the results obtained using other methods.

Denisov, E. T.; Denisova, T. G.

2014-04-01

12

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

13

Bond dissociation of the dipeptide dialanine and its derivative alanine anhydride induced by low energy electrons.  

PubMed

Dissociative electron attachment to dialanine and alanine anhydride has been studied in the gas phase utilizing a double focusing two sector field mass spectrometer. We show that low-energy electrons (i.e., electrons with kinetic energies from near zero up to 13 eV) attach to these molecules and subsequently dissociate to form a number of anionic fragments. Anion efficiency curves are recorded for the most abundant anions by measuring the ion yield as a function of the incident electron energy. The present experiments show that as for single amino acids (M), e.g., glycine, alanine, valine, and proline, the dehydrogenated closed shell anion (M-H)(-) is the most dominant reaction product. The interpretation of the experiments is aided by quantum chemical calculations based on density functional theory, by which the electrostatic potential and molecular orbitals are calculated and the initial electron attachment process prior to dissociation is investigated. PMID:21303118

Alizadeh, Elahe; Gschliesser, David; Bartl, Peter; Hager, Michaela; Edtbauer, Achim; Vizcaino, Violaine; Mauracher, Andreas; Probst, Michael; Märk, Tilmann D; Ptasi?ska, Sylwia; Mason, Nigel J; Denifl, Stephan; Scheier, Paul

2011-02-01

14

Bond dissociation of the dipeptide dialanine and its derivative alanine anhydride induced by low energy electrons  

NASA Astrophysics Data System (ADS)

Dissociative electron attachment to dialanine and alanine anhydride has been studied in the gas phase utilizing a double focusing two sector field mass spectrometer. We show that low-energy electrons (i.e., electrons with kinetic energies from near zero up to 13 eV) attach to these molecules and subsequently dissociate to form a number of anionic fragments. Anion efficiency curves are recorded for the most abundant anions by measuring the ion yield as a function of the incident electron energy. The present experiments show that as for single amino acids (M), e.g., glycine, alanine, valine, and proline, the dehydrogenated closed shell anion (M-H)- is the most dominant reaction product. The interpretation of the experiments is aided by quantum chemical calculations based on density functional theory, by which the electrostatic potential and molecular orbitals are calculated and the initial electron attachment process prior to dissociation is investigated.

Alizadeh, Elahe; Gschliesser, David; Bartl, Peter; Hager, Michaela; Edtbauer, Achim; Vizcaino, Violaine; Mauracher, Andreas; Probst, Michael; Märk, Tilmann D.; Ptasi?ska, Sylwia; Mason, Nigel J.; Denifl, Stephan; Scheier, Paul

2011-02-01

15

Isolation, Characterization of an Intermediate in an Oxygen Atom-Transfer Reaction, and the Determination of the Bond Dissociation Energy  

SciTech Connect

Redox reactions coupled with the formal loss or gain of an oxygen atom are ubiquitous in chemical processes. Such reactions proceed through the reduction of the donor center (XO) and the oxidation of the acceptor (Y) molecule. Among many examples of the metal centered oxygen atom transfer (OAT) reactivity, those involving molybdenum complexes have been widely investigated due to their involvement in mononuclear molybdenum enzymes. The heat of reaction of the overall atom transfer process can be expressed as a difference between the bond dissociation energies (BDEs) of the oxygen-donor(X) and oxygen-acceptor(Y) bond, i.e., H=DX=o-DY=O.

Nemykin, Victor N.; Laskin, Julia; Basu, Partha

2004-07-19

16

Theoretical Bond Dissociation Energies of Halo-Heterocycles: Trends and Relationships to Regioselectivity in Palladium-Catalyzed Cross-Coupling Reactions  

PubMed Central

Selectivity of the palladium-catalyzed cross-coupling reactions of heterocycles bearing multiple identical halogens is mainly determined by the relative ease of oxidative addition. This is related to both the energy to distort the carbon halogen bond to the transition-state geometry (related to the CX bond-dissociation energy) and to the interaction between the heterocycle ?* (LUMO) and PdL2 HOMO (J. Am. Chem. Soc. 2007, 129, 12664). The computed bond dissociation energies of a larger series of halo-heterocycles have been explored with B3LYP and higher accuracy G3B3 calculations. Quantitative trends in bond dissociation energies have been identified for five- and six-membered chloro and bromo substituted heterocycles with N, O, and S heteroatoms. PMID:19368385

Garcia, Yeimy; Schoenebeck, Franziska; Legault, Claude Y.; Merlic, Craig A.; Houk, K. N.

2009-01-01

17

A multivariate relationship for the impact sensitivities of energetic N-nitrocompounds based on bond dissociation energy.  

PubMed

The ZPE-corrected N-NO(2) bond dissociation energies (BDEs(ZPE)) of a series of model N-nitrocompounds and typical energetic N-nitrocompounds have been calculated using density functional theory methods. Computed results show that using the 6-31G** basis set the UB3LYP calculated BDE(ZPE) is similar to the B3PW91 but is less than the UB3P86 and that for both UB3P86 and UB3PW91 methods the 6-31G(**) calculated BDE(ZPE) is close to the 6-31++G(**). For the series of model N-nitrocompounds it is drawn from the NBO analysis that at the UB3LYP/6-31G(**) level the order of BDE(ZPE) is not only in line with that of bond order but also with that of the energy gap between N-NO(2) bond and antibond orbitals. For the typical energetic N-nitrocompounds the impact sensitivity is strongly related to the BDE(ZPE) indeed, and based on the BDEs(ZPE) calculated at different density functional theory levels this work has established a good multivariate correlation of impact sensitivity with molecular parameters, which provides a method to address the sensitivity problem. PMID:19819622

Li, Jinshan

2010-02-15

18

S-OO bond dissociation energies and enthalpies of formation of the thiomethyl peroxyl radicals CH3S(O)nOO (n=0,1,2)  

NASA Astrophysics Data System (ADS)

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, CH3S(O)2OO, which contains two sulfonic type oxygen atoms followed by the methylthiyl peroxyl radical, CH3SOO. The methylsulfinyl peroxyl radical, CH3S(O)OO, which contains only one sulfonic type oxygen shows the least stability with regard to dissociation to CH3S(O)+O2. This stabilization trend is nicely reflected in the variations of the S-OO bond distance which is found to be shortest in CH3S(O)2OO and longest in CH3S(O)OO.

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

2014-10-01

19

Theoretical study of bond distances and dissociation energies of actinide oxides AnO and AnO2.  

PubMed

In the present study we evaluated trends in the bond distances and dissociation enthalpies of actinide oxides AnO and AnO(2) (An = Th-Lr) on the basis of consistent computed data obtained by using density functional theory in conjunction with relativistic small-core pseudopotentials. Computations were carried out on AnO (An = Th-Lr) and AnO(2) (An = Np, Pu, Bk-Lr) species, while for the remaining AnO(2) species recent literature data (Theor. Chem. Acc. 2011, 129, 657) were utilized. The most important computed properties include the geometries, vibrational frequencies, dissociation enthalpies, and several excited electronic states. These molecular properties of the late actinide oxides (An = Bk-No) are reported here for the first time. We present detailed analyses of the bond distances, covalent bonding properties, and dissociation enthalpies. PMID:22471700

Kovács, Attila; Pogány, Peter; Konings, Rudy J M

2012-04-16

20

Effect of an external electric field on the dissociation energy and the electron density properties: The case of the hydrogen bonded dimer HF⋯HFa)  

NASA Astrophysics Data System (ADS)

The effect of a homogeneous external electric field parallel to the hydrogen bond in the FH⋯FH dimer has been studied by theoretical methods. The quantum theory of atoms in molecules methodology has been used for analyzing the electron distribution of the dimer, calculated with different hydrogen bond distances and external field magnitudes. It is shown that an electric field in the opposite direction to the dipole moment of the system strengthens the interaction due to a larger mutual polarization between both molecules and increases the covalent character of the hydrogen bond, while an external field in the opposite direction has the inverse effect. The properties of the complex at its equilibrium geometry with applied field have been calculated, showing that dependencies between hydrogen bond distance, dissociation energy, and properties derived from the topological analysis of the electron distribution are analogous to those observed in families of XDH⋯AY complexes. The application of an external field appears as a useful tool for studying the effect of the atomic environment on the hydrogen bond interaction. In the case of FH⋯FH, both the kinetic energy density and the curvature of the electron density along the hydrogen bond at the bond critical point present a surprisingly good linear dependence on the dissociation energy. The interaction energy can be modeled by the sum of two exponential terms that depend on both the hydrogen bond distance and the applied electric field. Moreover, as indicated by the resulting interaction energy observed upon application of different external fields, the equilibrium distance varies linearly with the external field, and the dependence of the dissociation energy on either the hydrogen bond distance or the external electric field is demonstrated to be exponential.

Mata, Ignasi; Molins, Elies; Alkorta, Ibon; Espinosa, Enrique

2009-01-01

21

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

22

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

23

High-accuracy coupled-cluster computations of bond dissociation energies in SH, H2S, and H2O  

NASA Astrophysics Data System (ADS)

The first and second bond dissociation enthalpies of H2S have been investigated at up to the CCSD(T)/aug-ccpV6Z level of theory. Corrections for core/valence electron correlation, anharmonic zero point vibrational energy and relativistic effects were followed by extrapolation to the complete basis set limit. Analysis of direct dissociation yields D0)(S-H=349.9 and D0)(HS-H=375.8 kJ mol-1. Together these imply an atomization enthalpy for H2S about 1 kJ mol-1 larger than literature evaluations. Consideration of exchange of a second H atom from OH to SH yields D0)(HS-H=376.2 kJ mol-1. The two computations of D0)(HS-H lie within 0.5 kJ mol-1 of a recent spectroscopic measurement of D0)(HS-H=376.24plus-or-minus0.05 kJ mol-1 [R. C. Shiell, X. K. Hu, Q. J. Hu, and J. W. Hepburn, J. Phys. Chem. A 104, 4339 (2000)]. The deuterated analogs SD and D2S are also considered. There is also accord to within 1.5 kJ mol-1 with D0)(S-H=348.4plus-or-minus0.8 kJ mol-1, which we derive from the experimental literature. We propose revised enthalpies of formation, Delta]fH0(2[Pi]3/2)SH=142.6[plus-or-minus0.8 kJ mol-1 and Delta]fH298.15)(SH=143.1[plus-or-minus0.8 kJ mol-1. The results suggest the dominant uncertainties in these high-level calculations come from the basis set extrapolation and scalar relativistic terms, and that both contribute about 1 kJ mol-1 uncertainty. We also obtain D0)(H-OH=492.6 kJ mol-1, which compares well with recent experiments.

Peebles, Lynda R.; Marshall, Paul

2002-08-01

24

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

25

Sequential bond energies and barrier heights for the water loss and charge separation dissociation pathways of Cd(2+)(H2O)n, n = 3-11.  

PubMed

The bond dissociation energies for losing one water from Cd(2+)(H(2)O)(n) complexes, n = 3-11, are measured using threshold collision-induced dissociation in a guided ion beam tandem mass spectrometer coupled with a thermal electrospray ionization source. Kinetic energy dependent cross sections are obtained for n = 4-11 complexes and analyzed to yield 0 K threshold measurements for loss of one, two, and three water ligands after accounting for multiple collisions, kinetic shifts, and energy distributions. The threshold measurements are converted from 0 to 298 K values to give the hydration enthalpies and free energies for sequentially losing one water from each complex. Theoretical geometry optimizations and single point energy calculations are performed on reactant and product complexes using several levels of theory and basis sets to obtain thermochemistry for comparison to experiment. The charge separation process, Cd(2+)(H(2)O)(n) ? CdOH(+)(H(2)O)(m) + H(+)(H(2)O)(n-m-1), is also observed for n = 4 and 5 and the competition between this process and water loss is analyzed. Rate-limiting transition states for the charge separation process at n = 3-6 are calculated and compared to experimental threshold measurements resulting in the conclusion that the critical size for this dissociation pathway of hydrated cadmium is n(crit) = 4. PMID:21428620

Cooper, Theresa E; Armentrout, P B

2011-03-21

26

OH bond dissociation energies in hydroquinones and 4-hydroxyphenoxyl radicals and effect of solvation on the kinetics of reactions involving hydroquinones and semiquinone radicals  

Microsoft Academic Search

The O-H bond dissociation energies (D\\u000a OH) in the molecules of 2,5-dimethylhydroquinone (1) and 2,5-di-tert-butylhydroquinone (2) and in the corresponding semiquinone radicals (5 and 8, respectively) were estimated by the method of intersecting parabolas (IP) from experimental data on the rate constants for\\u000a the reactions of these compounds with N-phenyl-1,4-benzoquinonemonoimine (3) and using the density functional B3LYP\\/6-31+G* quantum chemical calculations.

V. T. Varlamov; B. E. Krisyuk; A. V. Antonov

2005-01-01

27

Dissociation energy of molecules in dense gases  

NASA Technical Reports Server (NTRS)

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

Kunc, J. A.

1992-01-01

28

Accurate bond dissociation energy of water determined by triple-resonance vibrational spectroscopy and ab initio calculations  

NASA Astrophysics Data System (ADS)

Triple-resonance vibrational spectroscopy is used to determine the lowest dissociation energy, D0, for the water isotopologue HD16O as 41 239.7 ± 0.2 cm-1 and to improve D0 for H216O to 41 145.92 ± 0.12 cm-1. Ab initio calculations including systematic basis set and electron correlation convergence studies, relativistic and Lamb shift effects as well as corrections beyond the Born-Oppenheimer approximation, agree with the measured values to 1 and 2 cm-1 respectively. The improved treatment of high-order correlation terms is key to this high theoretical accuracy. Predicted values for D0 for the other five major water isotopologues are expected to be correct within 1 cm-1.

Boyarkin, Oleg V.; Koshelev, Maxim A.; Aseev, Oleg; Maksyutenko, Pavel; Rizzo, Thomas R.; Zobov, Nikolay F.; Lodi, Lorenzo; Tennyson, Jonathan; Polyansky, Oleg L.

2013-05-01

29

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

E-print Network

signal. Using a set of coupled kinetic equations, the time constants for hydrogen bond dissociationHydrogen Bond Dissociation and Reformation in Methanol Oligomers Following Hydroxyl Stretch hydrogen bond dissociation, following vibrational relaxation, decreases the concentration of methanol

Fayer, Michael D.

30

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

E-print Network

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

Peterson, Ellengene

31

Photodissociation of CS2 in the vacuum ultraviolet - Determination of bond dissociation energy from the lowest vibrational level of the ground state CS2.  

NASA Technical Reports Server (NTRS)

Photolysis in the vacuum ultraviolet results almost exclusively in the production of S(super-3)P atoms, which is in apparent violation of spin conservation. The threshold energy of incident photons required to produce fluorescence was used to calculate the bond dissociation energy (from the lowest vibrational level of the ground state), and the result agrees with the value previously derived from the photoionization of CS2. The fluorescence excitation spectrum shows peaks corresponding to Rydberg series I and II, indicating that the observed photodissociation of CS2 in the vacuum ultraviolet is mainly the result of predissociation from Rydberg states. The absorption coefficient of CS2 was measured in the region of 1200 to 1400 A.

Okabe, H.

1972-01-01

32

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

Microsoft Academic Search

Several photoionization experiments utilizing the positive ion cycle to derive the O-H bond energy converge to a consensus value of AE0(OH+\\/H2O)= 146117? 24 cm-1 (18.1162? 0.0030 eV). With the most accurate currently available ZEKE value. IE(OH)= 104989? 2 cm-1, corroborated by a number of photoelectron measurements,Error! Bookmark not defined.,Error! Bookmark not defined.,Error! Bookmark not defined.,Error! Bookmark not defined. this leads

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

2001-01-01

33

A quantitative relationship for the shock sensitivities of energetic compounds based on X-NO(2) (X=C, N, O) bond dissociation energy.  

PubMed

The ZPE-corrected X-NO(2) (X=C, N, O) bond dissociation energies (BDEs(ZPE)) of 11 energetic nitrocompounds of different types have been calculated employing density functional theory methods. Computed results show that using the 6-31G** basis set the UB3LYP calculated BDE(ZPE) is less than the UB3P86. For these typical energetic nitrocompounds the shock-initiated pressure (P(98)) is strongly related to the BDE(ZPE) indeed, and a polynomial correlation of ln(P(98)) with the BDE(ZPE) has been established successfully at different density functional theory levels, which provides a method to address the shock sensitivity problem. PMID:20447762

Li, Jinshan

2010-08-15

34

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

PubMed

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

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

2014-04-24

35

Determination of ion-ligand bond energies and ion fragmentation energies of electrospray-produced ions by collision-induced dissociation threshold measurements  

Microsoft Academic Search

A triple quadrupole mass spectrometer adapted for the determination of collision-induced dissociation (CID) threshold energies of ions produced by electrospray (ES) is described. The ES-produced ions are transferred from 1 atm atm a low pressure source, 10 Torr, where they can be partially declustered and after that thermalized by gas collisions. The ions entering the vacuum of the triple quadrupole

Stephen G. Anderson; Arthur T. Blades; John Klassen; Paul Kebarle

1995-01-01

36

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

37

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

38

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

39

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

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

40

Electron transfer dissociation (ETD) of peptides containing intrachain disulfide bonds.  

PubMed

The fragmentation chemistry of peptides containing intrachain disulfide bonds was investigated under electron transfer dissociation (ETD) conditions. Fragments within the cyclic region of the peptide backbone due to intrachain disulfide bond formation were observed, including: c (odd electron), z (even electron), c-33 Da, z+33 Da, c+32 Da, and z-32 Da types of ions. The presence of these ions indicated cleavages both at the disulfide bond and the N-C? backbone from a single electron transfer event. Mechanistic studies supported a mechanism whereby the N-C? bond was cleaved first, and radical-driven reactions caused cleavage at either an S-S bond or an S-C bond within cysteinyl residues. Direct ETD at the disulfide linkage was also observed, correlating with signature loss of 33 Da (SH) from the charge-reduced peptide ions. Initial ETD cleavage at the disulfide bond was found to be promoted amongst peptides ions of lower charge states, while backbone fragmentation was more abundant for higher charge states. The capability of inducing both backbone and disulfide bond cleavages from ETD could be particularly useful for sequencing peptides containing intact intrachain disulfide bonds. ETD of the 13 peptides studied herein all showed substantial sequence coverage, accounting for 75%-100% of possible backbone fragmentation. PMID:22161508

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

2012-02-01

41

Dissociative Low-Energy Electron Attachment to the C-S Bond of H3CSCH3 Influenced by Coulomb Stabilization  

NASA Astrophysics Data System (ADS)

In earlier works by our group, it was suggested that the presence of stabilizing Coulomb potentials can allow low-energy electrons (i.e., with kinetic energies <1 eV) to attach to [sigma]* orbitals of certain bonds and to thus cleave those bonds. In these earlier efforts, we focused on S-S bond cleavage and in breaking a variety of bonds that occur in typical peptides and proteins. In the present effort, we focus primarily on the stabilizing effects of nearby positive charges on the electron attachment process to dimethyl sulfide (DMS) to break one of the C-S bonds. Ab initio electronic structure calculations have been used to explore the influence of Coulomb potentials on the ability of low-energy electrons to directly attach to the [sigma]* orbital of the C-S bond and to effect bond cleavage, as well as to examine [sigma]* anion energy evolution as a function of C-S bond length.

Sobczyk, Monika; Skurski, Piotr; Simons, Jack

42

Kinetics and energetics of hydrogen bond dissociation in isolated acetic acid- d1 and - d4 and trifluoroactic acid dimers  

NASA Astrophysics Data System (ADS)

A quantitative determination of the rate constant, activation energy, entropy, and enthalpy of dissociation of hydrogen bonds in deuterated acetic acid- d1, - d4, and trifluoroacetic acid dimers in the gas phase was performed by resonant CO 2 laser photoacoustic spectroscopy. Within the experimental error, the kinetics and energetics of hydrogen bond dissociation were found to be independent of deuterium substitution of the hydroxy-hydrogen for pressures below 100 mbar. On the other hand, the dynamics, but not the energetics, of H bond dissociation are affected by the chemical nature of the rest group R (e.g., CH 3, CD 3, or CF 3) of the carboxylic acid.

Sauren, H.; Winkler, A.; Hess, P.

1995-06-01

43

Kinetics and energetics of hydrogen bond dissociation in isolated acetic acid- d 1 and - d 4 and trifluoroactic acid dimers  

Microsoft Academic Search

A quantitative determination of the rate constant, activation energy, entropy, and enthalpy of dissociation of hydrogen bonds in deuterated acetic acid-d1, -d4, and trifluoroacetic acid dimers in the gas phase was performed by resonant CO2 laser photoacoustic spectroscopy. Within the experimental error, the kinetics and energetics of hydrogen bond dissociation were found to be independent of deuterium substitution of the

H. Sauren; A. Winkler; P. Hess

1995-01-01

44

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

NASA Astrophysics Data System (ADS)

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

Hutchins, Patrick M.; Murphy, Robert C.

2011-05-01

45

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 of state-to-state vibrational pre- dissociation (VP) dynamics of small hydrogen bonded (H-bonded) clusters (REMPI) are used to determine accurate bond dissociation energies (D0) of (H2O)2, (H2O)3, HCl­H2O and NH3

Reisler, Hanna

46

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

E-print Network

near-dissociation behavior of the rotational constants BI.,Dl.,Hi,,... etc., to the asymptoticallyGround State D, Dissociation Energy from the Near-dissociation Behaviorof Rotational Level Spacings the dissociation energy of a diatomic molecule from the rotational term value(s) of a single vibrational level

Le Roy, Robert J.

47

Energy pulse bonding  

NASA Technical Reports Server (NTRS)

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

Smith, G. C.

1972-01-01

48

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

E-print Network

-- leads to spontaneous self-dissociation of a water molecule, producing spatially separated excess proton in the literature to designate the self- dissociation of water into ionic fragments. This is the first report of such water cluster configurations that can proceed to a lower energy state through self-dissociation. The (H2

Ciobanu, Cristian

49

Analysis of diatomic bond dissociation and formation in terms of the reaction force and the position-dependent reaction force constant  

Microsoft Academic Search

Bond dissociation and formation in diatomic molecules are analyzed in terms of the reaction force F(R) and the reaction force constant ?(R). These were determined for a group of 13 molecules from their extended-Rydberg potential energy functions V(R), which are of near-experimental quality. From F(R) and ?(R) comes a two-stage description of dissociation\\/formation. In dissociation, the first stage involves stretching

Jane S. Murray; Alejandro Toro-Labbé; Tim Clark; Peter Politzer

2009-01-01

50

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

SciTech Connect

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

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

2009-01-01

51

The Dissociation Energies of CH4 and C2H2 Revisited  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

52

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

53

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

ERIC Educational Resources Information Center

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

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

2008-01-01

54

Low energy electron induced dissociation in condensed diallyl disulfide  

NASA Astrophysics Data System (ADS)

Using a high sensitivity Time of Flight mass analyser we have measured the electron stimulated desorption (ESD) of anions and cations from multilayer thin films of diallyl disulfide (DADS) formed by condensation onto Pt and Kr substrates. Measurements were performed as a function of incident electron energy (Ei), film thickness and effective incident current. For Ei ? 15 eV the desorption yields of anions are the result of dissociative electron attachment (DEA) via several transient negative ions often associated with electron capture into C-S and S-S ?* bonds. The minimum incident energies observed for desorption of the anionic fragments H-, S-, CH2CHCH-2, and CH2CHCH2S- are compared to theoretical bond dissociation energies calculated using DFT methods. In comparison to gas-phase electron impact mass spectra, the yield of cationic fragments are dominated by desorption of low mass fragments although similar species are observed in both cases. Electron impact at higher electron energies on thicker films of DADS enhances desorption of larger fragment ions, including those formed by the scission and formation of multiple bonds.

Yildirim, Y.; Balcan, M.; Kinal, A.; Bass, A. D.; Cloutier, P.; Sanche, L.

2012-07-01

55

Qualifying Energy Conservation Bonds  

E-print Network

1Qualified Energy Construction Bonds (QECB’s) CATEE Conference December 18, 2013 ESL-KT-13-12-39 CATEE 2013: Clean Air Through Energy Efficiency Conference, San Antonio, Texas Dec. 16-18 • Originally authorized by the Energy Improvement & Extension... are QECB’s ESL-KT-13-12-39 CATEE 2013: Clean Air Through Energy Efficiency Conference, San Antonio, Texas Dec. 16-18 • 70% of allocation must be for public use, 30% of allocation MAY be used for a private activity • Representative projects include school...

Briggs, J.

2013-01-01

56

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

PubMed

The ionization energy (IE) of NiC and the 0 K bond dissociation energies (D(0)) and heats of formation at 0 K (?H(o)(f0)) and 298 K (?H(o)(f298)) for NiC and NiC(+) are predicted by the wavefunction based CCSDTQ(Full)/CBS approach and the multireference configuration interaction (MRCI) method with Davidson correction (MRCI+Q). The CCSDTQ(Full)/CBS calculations presented here involve the approximation to the complete basis set (CBS) limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy (ZPVE), high-order correlation, core-valence electronic (CV), spin-orbit coupling (SO), and scalar relativistic effect (SR) corrections. The present calculations provide the correct symmetry predictions for the ground states of NiC and NiC(+) to be (1)?(+) and (2)?(+), respectively. The CCSDTQ(Full)/CBS IE(NiC)=8.356 eV is found to compare favorably with the experimental IE value of 8.372 05±0.000 06 eV. The predicted IE(NiC) value at the MRCI+Q/cc-pwCV5Z level, including the ZPVE, SO, and SR effects is 8.00 eV, which is 0.37 eV lower than the experimental value. This work together with the previous experimental and theoretical investigations supports the conclusion that the CCSDTQ(Full)/CBS method is capable of providing reliable IE predictions for 3d-transition metal carbides, such as FeC and NiC. Furthermore, the CCSDTQ(Full)/CBS calculations give the prediction of D(0)(Ni-C)-D(0)(Ni(+)-C)=0.688 eV, which is also consistent with the experimental determination of 0.732 21±0.000 06 eV, whereas the MRCI+Q calculations (with relativistic and CV effects) predict a significantly lower value of 0.39 eV for D(0)(Ni-C)-D(0)(Ni(+)-C). The analysis of the correction terms shows 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 NiC/NiC(+). For the experimental D(0) and ?H(o)(f0) values of NiC/NiC(+), which are not known experimentally, we recommend the CCSDTQ(Full)/CBS predictions [D(0)(Ni-C)=4.048 eV, D(0)(Ni(+)-C)=3.360 eV, ?H(o)(f0)(NiC)=749.0 kJ/mol, and ?H(o)(f0)(NiC(+))=1555.1 kJ/mol]. PMID:20866136

Lau, Kai-Chung; Chang, Yih Chung; Shi, Xiaoyu; Ng, C Y

2010-09-21

57

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

PubMed

The ionization energy (IE) of FeC and the 0 K bond dissociation energies (D(0)) and the heats of formation at 0 K (DeltaH(o)(f0)) and 298 K (DeltaH(o)(f298)) for FeC and FeC(+) are predicted by the single-reference wave function based CCSDTQ(Full)/CBS approach, which involves the approximation to the complete basis set (CBS) limit at the coupled cluster level up to full quadruple excitations. The zero-point vibrational energy (ZPVE) correction, the core-valence electronic corrections (up to CCSDT level), spin-orbit couplings, and relativistic effects (up to CCSDTQ level) are included in the calculations. The present calculations provide the correct symmetry predictions for the ground states of FeC and FeC(+) to be (3)Delta and (2)Delta, respectively. We have also examined the theoretical harmonic vibrational frequencies of FeC/FeC(+) at the ROHF-UCCSD(T) and UHF-UCCSD(T) levels. While the UHF-UCCSD(T) harmonic frequencies are in good agreement with the experimental measurements, the ROHF-UCCSD(T) yields significantly higher harmonic frequency predictions for FeC/FeC(+). The CCSDTQ(Full)/CBS IE(FeC) = 7.565 eV is found to compare favorably with the experimental IE value of 7.59318 +/- 0.00006 eV, suggesting that the single-reference-based coupled cluster theory is capable of providing reliable IE prediction for FeC, despite its multireference character. The CCSDTQ(Full)/CBS D(0)(Fe(+)-C) and D(0)(Fe-C) give the prediction of D(0)(Fe(+)-C) - D(0)(Fe-C) = 0.334 eV, which is consistent with the experimental determination of 0.3094 +/- 0.0001 eV. The D(0) calculations also support the experimental D(0)(Fe(+)-C) = 4.1 +/- 0.3 eV and D(0)(Fe-C) = 3.8 +/- 0.3 eV determined by the previous ion photodissociation study. The present calculations also provide the DeltaH(o)(f0)(DeltaH(o)(f298)) predictions for FeC/FeC(+). The analysis of the correction terms in these calculations shows that the core-valence and valence-valence electronic correlations beyond CCSD(T) wave function and the relativistic effects make significant contributions to the calculated thermochemical properties of FeC/FeC(+). For the experimental D(0) and DeltaH(o)(f0) values of FeC/FeC(+), which are not known to high precision, we recommend the CCSDTQ(Full)/CBS predictions [D(0)(Fe-C) = 3.778 eV, D(0)(Fe(+)-C) = 4.112 eV, DeltaH(o)(f0)(FeC) = 760.8 kJ/mol and DeltaH(o)(f0)(FeC(+)) = 1490.6 kJ/mol] based on the ZPVE corrections using the experimental vibrational frequencies of FeC and FeC(+). PMID:19775110

Lau, Kai-Chung; Chang, Yih-Chung; Lam, Chow-Shing; Ng, C Y

2009-12-31

58

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

59

Dissociation energies of protonated water clusters  

Microsoft Academic Search

Relative abundances of positively ionized water clusters formed in a low-pressure electrical discharge as function of reduced electric field were obtained by using drift cell and quadrupole mass spectrometer. It was noticed that some clusters say with n ¼ 4 were more abundant than others, at comparable drift conditions. Dissociation energies have been derived from equilibrium conditions for relative clusters

E. Gazdaa Ziemczonek; G. P. Karwasz

60

Dissociation energies of protonated water clusters  

Microsoft Academic Search

Relative abundances of positively ionized water clusters formed in a low-pressure electrical discharge as function of reduced electric field were obtained by using drift cell and quadrupole mass spectrometer. It was noticed that some clusters say with n=4 were more abundant than others, at comparable drift conditions. Dissociation energies have been derived from equilibrium conditions for relative clusters abundances. The

T. Wróblewski; L. Ziemczonek; E. Gazda; G. P. Karwasz

2003-01-01

61

Hydrogen-bond symmetrization and molecular dissociation in hydrogen halids  

Microsoft Academic Search

Hydrogen chloride is a simple diatomic molecule forming a planar zig-zag chain of molecules connected by hydrogen bonds in the solid phase. Raman spectra were measured for solid HCl to 60 GPa at room temperature. The molecular stretching frequency falls toward zero at about 51 GPa, where the molecular vibrational peaks disappear and the lattice peaks remain. The spectral changes

K. Aoki; E. Katoh; H. Yamawaki; M. Sakashita; H. Fujihisa

1999-01-01

62

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

63

Topological study of intramolecular hydrogen bonding in beta-hydroxyethylperoxy radical and beta-hydroxyethoxy radical along its dissociation pathway.  

PubMed

The presence of intramolecular hydrogen bond (IHB) in beta-hydroxyethylperoxy and beta-hydroxyethoxy radicals was investigated using the QTAIM topological study on UB3LYP/6-311++G(2d,2p) charge densities. Only one of the two conformers of beta-hydroxyethylperoxy radical which were previously considered to present IHB displays a bond critical point (BCP) associated to an IHB. Furthermore, the atomic energies and electron populations indicate no evidence of IHB in the second conformer. Nevertheless, very small differences in molecular energies were obtained using several one-step and multi-step methods (G3, G3B3) between both conformers. No BCP is found between the hydroxyl hydrogen and the oxygen in the most stable conformer or in the transition state for the dissociation path of beta-hydroxyethoxy radical. However, a BCP is formed in the last steps of this path, thereby yielding H-bonded products. PMID:16240043

Mandado, Marcos; Mosquera, Ricardo A; Van Alsenoy, Christian

2005-09-21

64

The dissociation energy of N2  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

65

A Redetermination of the Dissociation Energy of MgO(+)  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

66

Probing hydrogen bond energies by mass spectrometry.  

PubMed

Mass spectrometry with desorption electrospray ionization (DESI) is demonstrated to be useful for probing the strength of hydrogen bonding, exemplified by various complexes of benzothiazoles and carboxylic acids in the solid state. Efficiencies for fragmentation of the complexes, quantified by collision-induced dissociation (CID) technology, correspond well with energies of the hydrogen bonds of O-H···N and N-H···O bridging each pair of benzothiazole and carboxylic acid. Linear correlations (with correlation factors of 0.8953 and 0.9928) have been established for the calibration curves of normalized collision energy at 100% fragmentation rate vs the length between donor and acceptor (in the hydrogen bond of O-H···N) as well as the slope of the fragmentation efficiency curve vs the average length difference between O-H···N and N-H···O in the complex. The mechanism responsible for determination of the hydrogen bonds is proposed on the basis of the experiments starting from the mixtures of the complexes as well as labeling with deuterium. As a complement of previously available methods (e.g., X-ray diffraction analysis), expectably, the proposed mass spectrometric method seems to be versatile for probing hydrogen bond energies. PMID:23550909

Su, Hai-Feng; Xue, Lan; Li, Yun-Hua; Lin, Shui-Chao; Wen, Yi-Mei; Huang, Rong-Bin; Xie, Su-Yuan; Zheng, Lan-Sun

2013-04-24

67

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

NASA Astrophysics Data System (ADS)

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

Pouthier, Vincent; Tsybin, Yury O.

2008-09-01

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

The Dissociation Enthalpies of Terminal (N O) Bonds in Organic Compounds  

NASA Astrophysics Data System (ADS)

Dissociation enthalpies of terminal (N-O) bonds, DH?(N-O), in amine N-oxides, nitrile N-oxides, pyridine N-oxides, quinoxaline 1,4-dioxides, furoxans, nitrones, azoxy-derivatives, azo-N,N-dioxides, nitro compounds, nitramines, and alkyl nitrates are calculated from published enthalpy of formation, enthalpy of sublimation, and enthalpy of vaporization data. For each class of organic compounds, the calculated DH?(N-O) values are critically evaluated. The derived DH?(N-O) values can be used to estimate enthalpies of formation of other molecules in each of these classes of organic compounds.

Acree, William E.; Pilcher, Geoffrey; Ribeiro da Silva, Maria D. M. C.

2005-06-01

70

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

71

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

72

Theoretical dissociation energies for the alkali and alkaline-earth monofluorides and monochlorides  

NASA Technical Reports Server (NTRS)

Spectroscopic parameters are accurately determined for the alkali and alkaline-earth monofluorides and monochlorides by means of ab initio self-consistent field and correlated wave function calculations. Numerical Hartree-Fock calculations are performed on selected systems to ensure that the extended Slater basis sets employed are near the Hartree-Fock limit. Since the bonding is predominantly electrostatic in origin, a strong correlation exists between the dissociation energy (to ions) and the spectroscopic parameter r(e). By dissociating to the ionic limits, most of the differential correlation effects can be embedded in the accurate experimental electron affinities and ionization potentials.

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

1986-01-01

73

Model-free determination of dissociation energies of polyatomic systems.  

PubMed

We describe and apply a new procedure that allows a direct determination of dissociation energies of polyatomic systems (clusters, fullerenes, polymers, and other molecules) without any modeling of the systems under investigation. As an example, we have determined the dissociation energies of a series of gold clusters Au(+)n. A comparison with values obtained from statistical models of unimolecular dissociation shows that these models significantly fail to describe the data. In contrast, the new method yields values which are an order of magnitude more accurate, thus allowing one to experimentally set benchmarks for any theory which attempts to describe activated processes. PMID:11461464

Vogel, M; Hansen, K; Herlert, A; Schweikhard, L

2001-07-01

74

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

75

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

76

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

77

Intrinsic defect formation in amorphous SiO2 by electronic excitation: Bond dissociation versus Frenkel mechanisms  

NASA Astrophysics Data System (ADS)

Two competing mechanisms of intrinsic defect formation in amorphous SiO2 (a-SiO2) , i.e., the vacancy-interstitial (Frenkel) mechanism and Si-O bond dissociation to form silicon and oxygen dangling bonds, were compared under ? -ray electronic excitation. The Frenkel mechanism was found to be dominant. The concentrations of both kinds of defects strongly correlate with the degree of the structural disorder of a-SiO2 , providing experimental evidence that both types of intrinsic defect pairs are formed mainly from the strained Si-O-Si bonds. The bond dissociation mechanism is more susceptible to the structural disorder than the vacancy-interstitial mechanism.

Kajihara, Koichi; Hirano, Masahiro; Skuja, Linards; Hosono, Hideo

2008-09-01

78

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

SciTech Connect

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

Dr. William Casey

2003-09-03

79

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

E-print Network

on their accuracy. In addition, multiple bond systems exhibit both large dynamical and static electron correlation electronic configurations on the other. Their interplay makes them prototypical of "strongly correlated across the entire dissociation reaction coordinate, as a prototypical example of a strongly correlated

Alavi, Ali

80

Quantum scattering calculations of energy transfer and dissociation of HCO in collisions with Ar  

SciTech Connect

We report a quantum scattering calculation of energy transfer and collision-induced dissociation of HCO in collisions with Ar. The HCO rotation is treated in the infinite order sudden approximation, and the HCO vibrations are treated by the coupled-channel method. Sixty {ital L}{sup 2} HCO vibrational wave functions are included in the coupled-channel basis, of which 15 correspond to bound HCO states for zero HCO angular momentum, and the remainder represent a discretized continuum, which includes ten resonances. A simple ``sum-of-pairs`` potential is used to describe the Ar--HCO interaction, and the HCO intramolecular potential is the previous Legendre polynomial fit to {ital ab} {ital initio} calculations. Vibrational state-specific and state-to-state cross sections, averaged over the orientation of Ar relative to the CO-bond axis, are calculated over a range of translational energies. Collision-induced dissociation cross sections to form H+CO from all HCO bound states are presented, and decomposed into components corresponding to dissociation via HCO resonances and dissociation via no``nresonance states. The energy transfer from selected initial states is also calculated as a function of initial relative translational energy. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

Pan, B.; Bowman, J.M. [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)

1995-12-08

81

Dissociation of C-H molecular bond of methane by pulse shaped ultra-intense laser field  

NASA Astrophysics Data System (ADS)

The effects of laser field and laser pulse width on the dissociation probability of C-H bond of CH4 have been investigated. Calculation of time dependent Schrödinger equation by grid spectral method is carried out and it is produced optimistic results in comparison to the earlier Quasi-classical calculations. The results show that there is an excellent match with experimental data. In this work, a number of results in the emerging field of laser with intensity of I = 8 × 1013 W cm-2 and pulse duration of 100 fs are presented. The present modulated field leads to more than 20% improvement in the dissociation probability.

Zare, S.; Irani, E.; Navid, H. A.; Dehghani, Z.; Anvari, A.; Sadighi-Bonabi, R.

2013-02-01

82

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

83

On the Determination of Monomer Dissociation Energies of Small Water Clusters from Photoionization Experiments  

Microsoft Academic Search

Recently, water monomer dissociation energies from neutral water clusters were estimated from the measured appearance energies resulting from vacuum ultraviolet photoionization. The monomer dissociation energies of neutral water clusters were determined via a thermodynamic cycle, which encompassed the experimentally measured appearance energies of the photoionized water clusters and the previously reported dissociation energies of protonated water clusters. A key approximation

Shawn M. Kathmann; Gregory K. Schenter; Sotiris S. Xantheas

2008-01-01

84

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

85

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

86

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

87

Co-C bond energies in adenosylcobinamide and methylcobinamide in the gas phase and in silico.  

PubMed

Essential to biological activity of adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl) is the Co-C bond cleavage step. Hence, we report an accurate determination of the homolytic gas-phase Co-C bond dissociation energies in the related adenosyl- and methylcobinamides (41.5 ± 1.2 and 44.6 ± 0.8 kcal/mol, respectively) utilizing an energy-resolved threshold collision-induced dissociation technique. This approach allows for benchmarking of electronic structure methods separate from (often ill-defined) solvent effects. Adequacy of various density functional theory methods has been tested with respect to the experimentally obtained values. PMID:24007238

Kobylianskii, Ilia J; Widner, Florian J; Kräutler, Bernhard; Chen, Peter

2013-09-18

88

Quantum Monte Carlo calculations of the dissociation energy of the water dimer  

Microsoft Academic Search

We report diffusion quantum Monte Carlo (DMC) calculations of the equilibrium dissociation energy De of the water dimer. The dissociation energy measured experimentally, D0, can be estimated from De by adding a correction for vibrational effects. Using the measured dissociation energy and the modern value of the vibrational energy Mas et al., [J. Chem. Phys. 113, 6687 (2000)] leads to

N. A. Benedek; I. K. Snook; M. D. Towler; R. J. Needs

2006-01-01

89

Electronic configuration and bond energy  

Microsoft Academic Search

Conclusions  The original interpretation of the method of molecular orbitals as a theory of valency, in which the single electron possesses\\u000a bonding power was based on the assumption that non-premoted electrons are bonding and premoted ones are anti-bonding or non-bonding.\\u000a This assumption is not the outcome of any requirements of theory but is an empirical postulate, which seeks justification\\u000a in experimental

R. K. Asundi; R. Samuel

1936-01-01

90

Site-specific protonation directs low-energy dissociation pathways of dinucleotides in the gas phase  

NASA Astrophysics Data System (ADS)

Fourier transform ion cyclotron resonance mass spectroscopy has been used to examine the low-energy collision-induced dissociation (CID) pathways of protonated dinucleotides. Collisional activation using continuous off-resonance excitation permits observation of energetically favorable dissociation pathways. Dissociation products were examined under multiple collision conditions over a range of average center-of-mass collision energies from 0 to 8.1 eV. Semiempirical calculations were performed using AM1 and PM3 methods to obtain gas-phase model structures of the protonated dinucleotides and their CID fragments. These calculations indicate that the proton is localized exclusively on one of the nucleic acid bases, with additional stabilization of some systems resulting from hydrogen bonding interactions between the bases. Protonated molecular ions dissociate to yield several characteristic products. The major fragmentation pathways are directed by the site of protonation leading to elimination of a protonated base, generally the 3'-terminus base. Exceptions are observed only in systems having thymine as the 3'-terminus base, where the major product is the protonated 5'-terminus base. These observations agree with the known relative proton affinities of the nucleic acid bases, and the existence of stable tautomeric structures of adenine, cytosine, and guanine which make these bases better leaving groups when protonated. In addition, application of statistical RRKM calculations to model the unimolecular dissociation dynamics of the reaction leading to the protonated 3'-terminus base provides an estimate of 1.9 eV for the activation energy associated with this major fragmentation pathway. In some systems, moderate yields of other fragment ions are also observed. Only minor yields of sequence ions are observed with these quasi-molecular ions. Reaction mechanisms accounting for the observed products are proposed.

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

1995-09-01

91

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

NASA Astrophysics Data System (ADS)

Dissociative photoionization of methyl bromide (CH3Br) 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 X2E of CH3Br+ is stable, and both A2A1 and B2E ionic excited states are fully dissociative to produce the unique fragment ion of CH3+. From TPEPICO 3D time-sliced velocity images of CH3+ dissociated from specific state-selected CH3Br+ ion, kinetic energy release distribution (KERD) and angular distribution of CH3+ fragment ion are directly obtained. Both spin-orbit states of Br(2P) atom can be clearly observed in fast dissociation of CH3Br+(A2A1) ion along C-Br rupture, while a KERD of Maxwell-Boltzmann profile is obtained in dissociation of CH3Br+(B2E) ion. With the aid of the re-calculated potential energy curves of CH3Br+ including spin-orbit coupling, dissociation mechanisms of CH3Br+ ion in A2A1 and B2E states along C-Br rupture are revealed. For CH3Br+(A2A1) ion, the CH3+ + Br(2P1/2) channel is occurred via an adiabatic dissociation by vibration, while the Br(2P3/2) formation is through vibronic coupling to the high vibrational level of X2E state followed by rapid dissociation. C-Br bond breaking of CH3Br+(B2E) ion can occur via slow internal conversion to the excited vibrational level of the lower electronic states and then dissociation.

Tang, Xiaofeng; Zhou, Xiaoguo; Sun, Zhongfa; Liu, Shilin; Liu, Fuyi; Sheng, Liusi; Yan, Bing

2014-01-01

92

Strength of hydrogen bond network takes crucial roles in the dissociation process of inhibitors from the HIV-1 protease binding pocket.  

PubMed

To understand the underlying mechanisms of significant differences in dissociation rate constant among different inhibitors for HIV-1 protease, we performed steered molecular dynamics (SMD) simulations to analyze the entire dissociation processes of inhibitors from the binding pocket of protease at atomistic details. We found that the strength of hydrogen bond network between inhibitor and the protease takes crucial roles in the dissociation process. We showed that the hydrogen bond network in the cyclic urea inhibitors AHA001/XK263 is less stable than that of the approved inhibitor ABT538 because of their large differences in the structures of the networks. In the cyclic urea inhibitor bound complex, the hydrogen bonds often distribute at the flap tips and the active site. In contrast, there are additional accessorial hydrogen bonds formed at the lateral sides of the flaps and the active site in the ABT538 bound complex, which take crucial roles in stabilizing the hydrogen bond network. In addition, the water molecule W301 also plays important roles in stabilizing the hydrogen bond network through its flexible movement by acting as a collision buffer and helping the rebinding of hydrogen bonds at the flap tips. Because of its high stability, the hydrogen bond network of ABT538 complex can work together with the hydrophobic clusters to resist the dissociation, resulting in much lower dissociation rate constant than those of cyclic urea inhibitor complexes. This study may provide useful guidelines for design of novel potent inhibitors with optimized interactions. PMID:21559397

Li, Dechang; Ji, Baohua; Hwang, Keh-Chih; Huang, Yonggang

2011-01-01

93

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

94

Theoretical determination of the alkali-metal superoxide bond energies  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

95

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

96

Dissociation in molecule-surface collisions  

Microsoft Academic Search

Dissociation at surfaces is a very important process, both scientifically and technologically. Dissociative chemisorption of molecules impinging at surfaces with thermal energies forms the basis of many processes, like catalysis. In thermal collisions it is evident that the kinetic energy of the impinging molecules is insufficient to break the molecular bond. Electronic processes occurring in the close proximity of the

A. W. Kleyn

1992-01-01

97

Mechanisms of Peptide Fragmentation from Time-and Energy-Resolved Surface-Induced Dissociation Studies: Dissociation of Angiotensin Analogs  

SciTech Connect

Energetics and mechanism of dissociation of singly protonated angiotensin III (RVYIHPF) and its analogs RVYIFPF, RVYIYPF, RVYIHAF, and RVYIHDF was studied using surface-induced dissociation (SID) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially configured for studying ion activation by collisions with surfaces. The energetics and dynamics of peptide fragmentation were deduced by modeling the time- and energy-resolved survival curves for each precursor ion using an RRKM based approach developed in our laboratory. Fragmentation mechanisms were inferred from comparison of time- and energy-resolved fragmentation efficiency curves (TFECs) of different fragment ions followed by RRKM modeling of dissociation of angiotensin III into six major families of fragment ions. Detailed modeling demonstrated that dissociation of these peptides is dominated by loss of ammonia from the precursor ion and characterized by a high energy barrier of 1.6 eV. Loss of NH3 and subsequent rearrangement of the MH-NH3 ion results in proton mobilization and release of ca. 30 kcal/mol into internal excitation of the MH-NH3 ion. The resulting highly excited ion accesses a variety of non-specific dissociation pathways with very high rate constants. Fast fragmentation of excited MH-NH3 ion forms a variety of abundant bn-NH3 and an-NH3 fragment ions. Abundant XH and HX internal fragments are also formed, reflecting the stability of histidine-containing diketopiperazine structures.

Laskin, Julia; Bailey, Thomas H.; Futrell, Jean H.

2006-03-01

98

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

NASA Astrophysics Data System (ADS)

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 the range of center of mass energies from 0 to the minimum energy required to bring about complete dissociation of the reactant ion which did not exceed 7.7eV for deprotonated parent ions and 8.8eV for fragment ions in any of the systems. Semiempirical calculations were performed using the PM3 method, a variant of the AM1 method, to obtain gas-phase model structures and energies of the deprotonated dinucleotides and their collision-induced dissociation fragments. The acidities of the nucleic acid bases and dimethyl phosphate were calculated using the AM1 method. The deprotonated quasimolecular ions dissociate to yield several characteristic products. The major products formed in all systems are the deprotonated 5'-terminus base, the ion resulting from loss of the neutral 5'-terminus base, or the metaphosphate anion, PO-3. Insight into the relative stabilities of the fragment ions is gained by comparing the product distributions observed in each of the systems. The relative yields of products involving either the 3'- or 5'-end of the molecule suggest the 3'-terminus base is stabilized through hydrogen bonding interaction with the phosphate group. The relative strength of this stabilization follows the order guanine > thymine > cytosine > adenine. Additionally, the relative abundances of the deprotonated nucleic acid fragments suggest that the relative acidities of the nucleic acid bases follow the order adenine > thymine > guanine > cytosine. Only minor yields of sequence ions in which one of the phosphate diester linkages is cleaved are observed with these quasimolecular ions. Reaction mechanisms which account for the observed products are proposed.

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

1994-10-01

99

Quantum Monte Carlo calculations of the dissociation energy of the water dimer  

Microsoft Academic Search

We report diffusion quantum Monte Carlo (DMC) calculations of the equilibrium dissociation energy De of the water dimer. The dissociation energy measured experimentally, D0, can be estimated from De by adding a correction for vibrational effects. Using the measured dissociation energy and the modern value of the vibrational energy Mas &etal;, [J. Chem. Phys. 113, 6687 (2000)] leads to De=5.00±0.7

N. A. Benedek; I. K. Snook; M. D. Towler; R. J. Needs

2006-01-01

100

Excitation and multiple dissociation of projectiles at intermediate energy  

SciTech Connect

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

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

1989-04-01

101

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

Microsoft Academic Search

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

Fong-Fu Hsu; John Turk

1999-01-01

102

Adhesive bonding using variable frequency microwave energy  

SciTech Connect

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

103

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

104

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

105

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

PubMed

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

Scott, Carl D; Smalley, Richard E

2003-01-01

106

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

107

Site-specific protonation directs low-energy dissociation pathways of dinucleotides in the gas phase  

Microsoft Academic Search

Fourier transform ion cyclotron resonance mass spectroscopy has been used to examine the low-energy collision-induced dissociation (CID) pathways of protonated dinucleotides. Collisional activation using continuous off-resonance excitation permits observation of energetically favorable dissociation pathways. Dissociation products were examined under multiple collision conditions over a range of average center-of-mass collision energies from 0 to 8.1 eV. Semiempirical calculations were performed using

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

1995-01-01

108

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

PubMed

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

Malli, Gulzari L

2006-02-21

109

Energy-Dependent Electron Activated Dissociation of Metal-Adducted Permethylated Oligosaccharides  

PubMed Central

The effects of varying the electron energy and cationizing agents on electron activated dissociation (ExD) of metal-adducted oligosaccharides were explored, using permethylated maltoheptaose as the model system. Across the examined range of electron energy, the metal-adducted oligosaccharide exhibited several fragmentation processes, including electron capture dissociation (ECD) at low energies, hot-ECD at intermediate energies, and electronic excitation dissociation (EED) at high energies. The dissociation threshold depended on the metal charge carrier(s), whereas the types and sequence spans of product ions were influenced by the metal-oligosaccharide binding pattern. Theoretical modeling contributed insight into the metal-dependent behavior of carbohydrates during low-energy ECD. When ExD was applied to a permethylated high mannose N-linked glycan, EED provided more structural information than either collision-induced dissociation (CID) or low-energy ECD, thus demonstrating its potential for oligosaccharide linkage analysis. PMID:22881449

Yu, Xiang; Huang, Yiqun; Lin, Cheng; Costello, Catherine E.

2013-01-01

110

Low-energy electron-induced chemistry of condensed-phase hexamethyldisiloxane: Initiating dissociative process and subsequent reactions  

NASA Astrophysics Data System (ADS)

Thin films of condensed hexamethyldisiloxane (HMDSO) have been exposed to electron irradiation at incident energies between 5 and 15 eV and analysed afterwards by thermal desorption spectrometry (TDS). Formation of products is observed at energies at and above 11 eV and quantified at 15 eV by comparison with reference samples of known composition. Gas-phase measurements aiming at detection of dissociative electron attachment (DEA) were, in addition, performed to obtain more insight into the dominant electron-induced dissociation channel expected to initiate further reactions in the condensed phase. Apart from CH4 which is the most obvious product present in exposed films of HMDSO, tetramethylsilane (TMS) and smaller amounts of C2H6 have been detected. The quantity of the products is by one to two orders of magnitude smaller than the amount of decomposed HMDSO. In addition, signals ascribed to unquantified amounts of larger siloxanes have been observed. The present results together with previous gas-phase results from literature suggest that dissociative ionisation leading to Si-C bond rupture and release of a methyl radical is the most important electron-driven initial reaction step. Possible mechanisms of the subsequent reactions induced by the fragments of the initial dissociation reaction are reviewed and discussed in relation to the observed product quantities.

Ipolyi, I.; Burean, E.; Hamann, T.; Cingel, M.; Matejcik, S.; Swiderek, P.

2009-05-01

111

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

112

The H2O2+ potential energy surfaces dissociating into H+/OH+: Theoretical analysis of the isotopic effect  

NASA Astrophysics Data System (ADS)

We present a detailed study of the potential energy surfaces of the water dication correlating asymptotically with O(P3) and O(D1). Using ab initio multireference configuration interaction method, we computed a large ensemble of data, which was used to generate a fit of each potential energy surface for bending angles ? ?80° degrees and OH distances ROH?1.0 a.u. The fit is used to investigate the dissociation dynamics along each potential energy surface for several initial geometries corresponding to Franck-Condon transition from neutral or singly ionized water molecule. For each case, we determine the dissociation channels and we compute the kinetic energy release and angular momentum distribution of the final arrangements. Among the eight potential energy surfaces investigated here, only the lowest triplet and the three lowest singlet can lead to the formation of bound residual fragment. The dissociation of HOD2+ presents a strong preference for OH rather than OD bond breakage. It is characterized by the isotopic ratio, defined as the number of OD+ over the number of OH+ residual fragments. This ratio depends strongly on the shape of each potential energy surface and on the initial conditions.

Gervais, B.; Giglio, E.; Adoui, L.; Cassimi, A.; Duflot, D.; Galassi, M. E.

2009-07-01

113

Threshold collision-induced dissociation and theoretical studies of hydrated Fe(II): binding energies and Coulombic barrier heights.  

PubMed

The first experimentally determined bond dissociation energies for losing water from Fe(2+)(H(2)O)(n) complexes, n = 4-11, are measured using threshold collision-induced dissociation (TCID) in a guided ion beam tandem mass spectrometer coupled to an electrospray ionization source that forms thermalized complexes. In this technique, absolute cross-sections for dissociation induced by collisions with Xe at systematically varied kinetic energies are obtained. After accounting for multiple collisions, kinetic shifts, and energy distributions, these cross-sections are analyzed to yield the energy thresholds for losing one, two, or three water ligands at 0 K. The 0 K threshold measurements are converted to 298 K values to give the hydration enthalpies and free energies for sequentially losing water ligands from each complex. Comparisons to previous results for hydration of Zn(2+) indicate that the bond energies are dominated by electrostatic interactions, with no obvious variations associated with the open shell of Fe(2+). Theoretical geometry optimizations and single-point energy calculations are performed using several levels of theory for comparison to experiment, with generally good agreement. In addition to water loss channels, the charge separation process generating hydrated FeOH(+) and protons is observed for multiple reactant complexes. Energies of the rate-limiting transition states are calculated at several levels of theory with density functional approaches (B3LYP and B3P86) disagreeing with MP2(full) results. Comparisons to our kinetic energy dependent cross-sections suggest that the energetics of the MP2(full) level are most accurate. PMID:22812673

Hofstetter, Theresa E; Armentrout, P B

2013-02-14

114

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.

115

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

SciTech Connect

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

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

2012-10-24

116

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

117

Determination of the substituent effect on the O-H bond dissociation enthalpies of phenolic antioxidants by the EPR radical equilibration technique.  

PubMed

The bond dissociation enthalpies (BDE) of several phenols containing electron-withdrawing substituents in the para position have been determined by means of the EPR radical equilibration technique. It has been found that CN, NO(2), CHO, COOR, and COOH induce an increase of the BDE value of the O-H bond, thus producing a worsening of the antioxidant activity of phenols, while Cl, Ph, and CH[double bond]CHPh show an opposite effect. The contributions of these substituents for the calculation of the BDE values in polysubstituted phenols by using the group additivity rule have also been derived. It is shown that this rule provides quite reliable predictions of bond strengths, so that the method can be conveniently used to estimate new data on substituted phenols. PMID:12098294

Brigati, Giovanni; Lucarini, Marco; Mugnaini, Veronica; Pedulli, Gian Franco

2002-07-12

118

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

E-print Network

for the production of clean fuels, the combustion of fuels, and the production of chemicals with improved energy efficiency and less pollution, and in developing better fuel cells and batteries. Thus, one would like and H-C bond energies in the corresponding gaseous alkanes was predicted on the basis of density

Campbell, Charles T.

119

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

120

Electron capture and transfer dissociation: Peptide structure analysis at different ion internal energy levels  

Microsoft Academic Search

We decoupled electron-transfer dissociation (ETD) and collision-induced dissociation of charge-reduced species (CRCID) events\\u000a to probe the lifetimes of intermediate radical species in ETD-based ion trap tandem mass spectrometry of peptides. Short-lived\\u000a intermediates formed upon electron transfer require less energy for product ion formation and appear in regular ETD mass spectra,\\u000a whereas long-lived intermediates require additional vibrational energy and yield product

Hisham Ben Hamidane; Diego Chiappe; Ralf Hartmer; Aleksey Vorobyev; Marc Moniatte; Yury O. Tsybin

2009-01-01

121

Diffractive dissociation in proton-nucleus collisions at collider energies  

NASA Astrophysics Data System (ADS)

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 mb and mb, respectively. The invariant mass MX for the reaction is also analyzed. Discussion is performed on the main theoretical uncertainties associated to the calculations.

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

2014-11-01

122

Bond resonance energy and verification of the isolated pentagon rule  

Microsoft Academic Search

The isolated pentagon rule (IPR) states that fullerenes with isolated pentagons are kinetically much more stable than their fused pentagon counterparts. This rule can be verified in terms of a graph-theoretically defined bond resonance energy. In general, a Ï bond shared by two pentagons has a large negative bond resonance energy, thus contributing significantly to the increase in kinetic instability

Jun-ichi Aihara; Jun Ichi

1995-01-01

123

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

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

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

PubMed

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

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

2011-08-28

126

Dissociative electron attachment to triflates.  

PubMed

Gas phase studies of dissociative electron attachment to simple alkyl (CF(3)SO(3)CH(3)) and aryl (C(6)H(5)SO(3)CF(3) and CF(3)SO(3)C(6)H(4)CH(3)) triflates, model molecules of nonionic photoacid generators for modern lithographic applications, were performed. The fragmentation pathways under electron impact below 10 eV were identified by means of crossed electron-molecular beam mass spectrometry. Major dissociation channels involved C-O, S-O, or C-S bond scissions in the triflate moiety leading to the formation of triflate (OTf(-)), triflyl (Tf(-)), or sulfonate (RSO(3)(-)) anions, respectively. A resonance leading to C-O bond breakage and OTf(-) formation in alkyl triflates occurred at electron energies about 0.5 eV lower than the corresponding resonance in aryl triflates. A resonance leading to S-O bond breakage and Tf(-) formation in aryl triflates occurred surprisingly at the same electron energies as C-O bond breakage. In case of alkyl triflates S-O bond breakage required 1.4 eV higher electron energies to occur and proceeded with substantially lower yields than in aryl triflates. C-S bond scission occurred for all presently studied triflates at energies close to 3 eV. PMID:22149794

Ptasi?ska, Sylwia; Gschliesser, David; Bartl, Peter; Janik, Ireneusz; Scheier, Paul; Denifl, Stephan

2011-12-01

127

Dissociative electron attachment to triflates  

NASA Astrophysics Data System (ADS)

Gas phase studies of dissociative electron attachment to simple alkyl (CF3SO3CH3) and aryl (C6H5SO3CF3 and CF3SO3C6H4CH3) triflates, model molecules of nonionic photoacid generators for modern lithographic applications, were performed. The fragmentation pathways under electron impact below 10 eV were identified by means of crossed electron-molecular beam mass spectrometry. Major dissociation channels involved C-O, S-O, or C-S bond scissions in the triflate moiety leading to the formation of triflate (OTf-), triflyl (Tf-), or sulfonate (RSO3-) anions, respectively. A resonance leading to C-O bond breakage and OTf- formation in alkyl triflates occurred at electron energies about 0.5 eV lower than the corresponding resonance in aryl triflates. A resonance leading to S-O bond breakage and Tf- formation in aryl triflates occurred surprisingly at the same electron energies as C-O bond breakage. In case of alkyl triflates S-O bond breakage required 1.4 eV higher electron energies to occur and proceeded with substantially lower yields than in aryl triflates. C-S bond scission occurred for all presently studied triflates at energies close to 3 eV.

Ptasi?ska, Sylwia; Gschliesser, David; Bartl, Peter; Janik, Ireneusz; Scheier, Paul; Denifl, Stephan

2011-12-01

128

A comparative study of the bonding energy in adhesive wafer bonding  

NASA Astrophysics Data System (ADS)

Adhesion energies are determined for three different polymers currently used in adhesive wafer bonding of silicon wafers. The adhesion energies of the polymer off-stoichiometry thiol-ene-epoxy OSTE+ and the nano-imprint resist mr-I 9150XP are determined. The results are compared to the adhesion energies of wafers bonded with benzocyclobutene, both with and without adhesion promoter. The adhesion energies of the bonds are studied by blister tests, consisting of delaminating silicon lids bonded to silicon dies with etched circular cavities, using compressed nitrogen gas. The critical pressure needed for delamination is converted into an estimate of the bond adhesion energy. The fabrication of test dies and the evaluation method are described in detail. The mean bond energies of OSTE+ were determined to be 2.1 and 20 J m-2 depending on the choice of the epoxy used. A mean bond energy of 1.5 J m-2 was measured for mr-I 9150XP.

Forsberg, F.; Saharil, F.; Haraldsson, T.; Roxhed, N.; Stemme, G.; van der Wijngaart, W.; Niklaus, F.

2013-08-01

129

ZEKE Photoelectron Spectroscopy of p-Fluorophenol···H2S/H2O Complexes and Dissociation Energy Measurement Using the Birge-Sponer Extrapolation Method.  

PubMed

In this work we have shown that the Birge-Sponer extrapolation method can be successfully used to determine the dissociation energies (D0) of noncovalently bound complexes. The O-H···S hydrogen-bonding interaction in the cationic state of the p-fluorophenol···H2S complex was characterized using zero kinetic energy (ZEKE) photoelectron spectroscopy. This is the first ZEKE report on the O-H···S hydrogen-bonding interaction. The adiabatic ionization energy (AIE) of the complex was determined as 65?542 cm(-1). Various intermolecular and intramolecular vibrational modes of the cation were assigned. A long progression was observed in the intermolecular stretching mode (?) of the complex with significant anharmonicity along this mode. The anharmonicity information was used to estimate the dissociation energy (D0) in the cationic state using the Birge-Sponer extrapolation method. The D0 was estimated as 9.72 ± 1.05 kcal mol(-1). The ZEKE photoelectron spectra of analogous complex FLP···H2O was also recorded for the sake of comparison. The AIE was determined as 64?082 cm(-1). The intermolecular stretching mode in this system, however, was found to be quite harmonic, unlike that in the H2S complex. The dissociation energies of both the complexes, along with those of a few benchmark systems, such as phenol···H2O and indole···benzene complexes, were computed at various levels of theory such as MP2 at the complete basis set limit, ?B97X-D, and CCSD(T). It was found that only the ?B97X-D level values were in excellent agreement with the experimental results for the benchmark systems for the ground as well as the cationic states. The dissociation energy of the (FLP···H2S)(+) complex determined by the Birge-Sponer extrapolation was about ?18% lower than that computed at the ?B97X-D level. PMID:25250474

Bhattacharyya, Surjendu; Wategaonkar, Sanjay

2014-10-01

130

Quantum-mechanical and QM\\/MM simulations of proton dissociation free energies in solution  

Microsoft Academic Search

Chemical reactions often occur in the presence of a solvent, in particular water for biological systems. To describe such processes a quantum mechanical (QM) description of the reaction site is needed, combined with a large number of solvent molecules that affect the reaction via their electrostatic fields and free energy effects of their long-range structure. We have simulated the dissociation

Noam Bernstein; Csilla Varnai; Monika Fuxreiter; G. Ábor Csányi

2011-01-01

131

Production of hydrogen, obtaining electric and thermal energy by water dissociation method  

Microsoft Academic Search

At present, the most widespread method of producing gaseous hydrogen is water electrolysis. However it requires the consumption of large amounts of electric energy and therefore the use of hydrogen as fuel is not economically efficient as compared with petroleum-based fuel.The author offers a new method for producing gaseous hydrogen which is called a water dissociation method. It is based

Vladimir Lipovestsky

2004-01-01

132

Classical dynamics of dissociative adsorption for a nonactivated system: The role of zero point energy  

Microsoft Academic Search

We present dissociative adsorption probabilities of H2 on Pd(111) computed with the classical trajectory method. We perform both classical (C) and quasiclassical (QC) calculations, the latter including, by contrast with the former, the initial zero point energy (ZPE) of H2. We analyze in detail the role played by the ZPE and demonstrate the strong and weak points of both C

H. F. Busnengo; C. Crespos; W. Dong; J. C. Rayez; A. Salin

2002-01-01

133

Overlap population density as an index of bond strength  

E-print Network

for the CH Series 19 20 20 21 23 VII Dissociation Energy and Overlap Population Density versus n for the CH Series 25 VIII Dissociation Energy and Stretching Force Constants versus n for the CH Series n n(N', N), d(N, N) and Bond Dissociation... constant as a measure of bond strength, 30 110 105 100 95 O O W HP 90 I I I I I . I 6. 25 6. 0 5. 75 5. 50 O n O 85 5. 0 80 4. 75 CH CH2 CH3 CH4 4. 5 EIGURE VIII DISSOCIATION ENERGY AND STRETCHING 1 Ol'CE CONSTANTS VEI'SUS n EOR...

Gallagher, Michael James

2012-06-07

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

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

136

Dissociation pressure measurements on salts proposed for thermochemical energy storage  

Microsoft Academic Search

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

R. W. Carling

1979-01-01

137

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

138

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

139

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

NASA Astrophysics Data System (ADS)

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 N2-N interactions. The coarse-grained model is constructed by lumping the rovibrational energy levels of the N2 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.

Munafò, A.; Panesi, M.; Magin, T. E.

2014-02-01

140

Classical dynamics of dissociative adsorption for a nonactivated system: The role of zero point energy  

NASA Astrophysics Data System (ADS)

We present dissociative adsorption probabilities of H2 on Pd(111) computed with the classical trajectory method. We perform both classical (C) and quasiclassical (QC) calculations, the latter including, by contrast with the former, the initial zero point energy (ZPE) of H2. We analyze in detail the role played by the ZPE and demonstrate the strong and weak points of both C and QC calculations. We show that ZPE is crucial in accelerating the molecules toward the surface through vibrational softening. However, at low energies, dynamic trapping is quenched in QC calculations by processes of vibration to rotation energy transfer that would be associated with closed channels in a quantum approach. In this study we use a new representation of the H2/Pd(111) potential energy surface (obtained by interpolation of ab initio data) with a significantly better accuracy in the entrance channel region which plays a decisive role in the dissociation dynamics.

Busnengo, H. F.; Crespos, C.; Dong, W.; Rayez, J. C.; Salin, A.

2002-05-01

141

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

142

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

143

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

Microsoft Academic Search

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

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

1995-01-01

144

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

145

Electron impact dissociative ionization of the CH2F2 molecule: cross sections, appearance potentials, nascent kinetic energy distributions and dissociation pathways  

Microsoft Academic Search

Ions produced by crossed-beam collisions of pulsed monoenergetic electrons and supersonic expansion molecules have been analysed by time-of-flight mass spectroscopy (TOF-MS) in order to determine the appearance potentials, absolute total, dissociative and parent ionization cross sections and nascent ion kinetic energy distributions. The electron impact study was conducted at incident electron energies up to 100 eV on the parent CH2F2

I. Torres; R. Martínez; M. N. Sánchez Rayo; F. Castaño

2000-01-01

146

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

SciTech Connect

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

Boily, Jean F.; Seward, Terry M.

2005-12-01

147

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

148

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

PubMed

The discrepancy between experimental and harmonically predicted shifts of the OH stretching fundamental of methanol upon hydrogen bonding to a second methanol unit is too large to be blamed mostly on diagonal and off-diagonal anharmonicity corrections. It is shown that a decisive contribution comes from post-MP2 electron correlation effects, which appear not to be captured by any of the popular density functionals. We also identify that the major deficiency is in the description of the donor OH bond. Together with estimates for the electronic and harmonically zero-point corrected dimer binding energies, this work provides essential constraints for a quantitative description of this simple hydrogen bond. The spectroscopic dissociation energy is predicted to be larger than 18 kJ/mol and the harmonic OH-stretching fundamental shifts by about -121 cm(-1) upon dimerization, somewhat more than in the anharmonic experiment (-111 cm(-1)). PMID:25217897

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

2014-09-14

149

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

PubMed

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

Andersson, Thomas; Broo, Anders; Evertsson, Emma

2014-07-01

150

Free energy perturbation study of water dimer dissociation kinetics  

Microsoft Academic Search

An efficient approach is described for using accurate ab initio calculations to determine the rates of elementary condensation and evaporation processes that lead to nucleation of aqueous aerosols. The feasibility of the method is demonstrated in an application to evaporation rates of water dimer at 230 K. The method, known as ABC-FEP (ab initio\\/classical free energy perturbation), begins with a

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

2004-01-01

151

Use of a single trajectory to study product energy partitioning in unimolecular dissociation: Mass effects for halogenated alkanes  

Microsoft Academic Search

A single trajectory (ST) direct dynamics approach is compared with quasiclassical trajectory (QCT) direct dynamics calculations for determining product energy partitioning in unimolecular dissociation. Three comparisons are made by simulating C2H5F-->HF+C2H4 product energy partitioning for the MP2\\/6-31G* and MP2\\/6-311++G** potential energy surfaces (PESs) and using the MP2\\/6-31G* PES for C2H5F dissociation as a model to simulate CHCl2CCl3-->HCl+C2Cl4 dissociation and its

Lipeng Sun; Kihyung Song; Donald W. Setser; William L. Hase

2006-01-01

152

Time-dependent wave-packet study of the direct low-energy dissociative recombination of HD+  

NASA Astrophysics Data System (ADS)

Wave-packet methods involving the numerical solution of the time-dependent Schrödinger equation have been used with great success in the calculation of cross sections for dissociative recombination of molecular ions by electron impact in the high energy region where the ``boomerang'' model [L. Dube and A. Herzenberg, Phys. Rev. A 11, 1314 (1975)] is valid. We extend this method to study low-energy dissociative recombination where this approximation is no longer appropriate. We apply the method to the ``direct'' low-energy dissociative recombination of HD+. Our results are in excellent agreement with calculations using the multichannel quantum defect method.

Orel, A. E.

2000-08-01

153

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

PubMed

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

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

2014-02-01

154

Ultrafast dissociation in polyhalogenated ethane: alternative mechanisms  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

155

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

156

Bond resonance energy and verification of the isolated pentagon rule  

SciTech Connect

The isolated pentagon rule (IPR) states that fullerenes with isolated pentagons are kinetically much more stable than their fused pentagon counterparts. This rule can be verified in terms of a graph-theoretically defined bond resonance energy. In general, a {pi} bond shared by two pentagons has a large negative bond resonance energy, thus contributing significantly to the increase in kinetic instability or chemical reactivity of the molecule. The existence of such highly antiaromatic local structures sharply distinguishes IPR-violating fullerenes from isolated-pentagon isomers. {pi}bonds shared by two pentagons are shared by many antiaromatic conjugated circuits but not by relatively small aromatic conjugated circuits. 39 refs., 3 figs., 5 tabs.

Aihara, Jun Ichi [Shizuoka Univ. (Japan)

1995-04-12

157

Collision-Induced Dissociation of Fatty Acid [M - 2H + Na]- Ions: Charge-Directed Fragmentation and Assignment of Double Bond Position  

NASA Astrophysics Data System (ADS)

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: ?9,12,1518:3, ?6,9,1218:3, and ?5,8,1118:3. 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.

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

2014-08-01

158

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

159

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

PubMed

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

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

2014-08-19

160

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

E-print Network

+ and of their dissociation products NO+ , HO- , and water were studied with the DFT methods B3LYP and MPW1PW91The Heterolytic Dissociation of Neutral and Protonated Nitrous Acid Hong Wu and Rainer GlaserJ/mol. The experimental heterolytic bond dissociation energy of E0 ) 917.80 kJ/mol for HONO and of H298 ) 77.3 k

Glaser, Rainer

161

Quasiclassical trajectory study of energy transfer and collision-induced dissociation in hyperthermal Ar + CH4 and Ar + CF4 collisions.  

PubMed

We present a study of energy transfer in collisions of Ar with methane and perfluoromethane at hyperthermal energies (E(coll) = 4-10 eV). Quasiclassical trajectory calculations of Ar + CX(4) (X = H, F) collisions indicate that energy transfer from reagents' translation to internal modes of the alkane molecule is greatly enhanced by fluorination. The reasons for the enhancement of energy transfer upon fluorination are shown to emerge from a decrease in the hydrocarbon vibrational frequencies of the CX(4) molecule with increasing the mass of the X atom, and to an increase of the steepness of the Ar-CX(4) intermolecular potential. At high collision energies, we find that the cross section of Ar + CF(4) collisions in which the amount of energy transfer is larger than needed to break a C-F bond is at least 1 order of magnitude larger than the cross sections of Ar + CH(4) collisions producing CH(4) with energy above the dissociation limit. In addition, collision-induced dissociation is detected in short time scales in the case of the fluorinated species at E(coll) = 10 eV. These results suggest that the cross section for degradation of fluorinated hydrocarbon polymers under the action of nonreactive hyperthermal gas-phase species might be significantly larger than that of hydrogenated hydrocarbon polymers. We also illustrate a practical way to derive intramolecular potential energy surfaces for bond-breaking collisions by improving semiempirical Hamiltonians based on grids of high-quality ab initio calculations. PMID:16833915

Troya, Diego

2005-07-01

162

Unimolecular dissociation of cyclohexene at extremely high temperatures: behavior of the energy-transfer collision efficiency  

SciTech Connect

The dissociation of cyclehexene has been observed in shock waves with the laser schlieren and pulsed laser flash absorption techniques over 1200-2000 K and 110-550 Torr, using 2% and 4% cyclohexene in krypton and 0.2% cyclohexene in argon. The inverse Diels-Alder molecular elimination to 1,3-butadiene and ethylene is clearly the dominant dissociation channel under all conditions. Rate constants derived for this reaction have a high precision, with rms deviations of only a few percent. Unimolecular falloff, although slight at the lowest temperatures, is clearly discernible for all temperatures. A simple RRKM calculation, using a nonspecific vibration model transition state, is fit to the measured rate constants, giving log k/sub infinity/ = 15.57 - 65.7 (kcal/mol)/2.303RT with a barrier of 61.9 kcal/mol. These RRKM calculations were performed with the energy-transfer collision efficiency derived from both fixed <..delta..E>/sub down/ and <..delta..E>/sub all/. A good fit is achieved with either below 1500 K, but above this a fixed <..delta..E>/sub down/ gives rates which are much too small, and this deficiency cannot be compensated by other changes, whereas a fixed <..delta..E>/sub all/ provides quite satisfactory agreement with the measurements for all conditions. This situation is similar to that indicated by other large molecule dissociations at extreme temperatures.

Kiefer, J.H.; Shah, J.N.

1987-05-21

163

Absolute cross sections for dissociative electron attachment and dissociative ionization of cobalt tricarbonyl nitrosyl in the energy range from 0 eV to 140 eV.  

PubMed

We report absolute dissociative electron attachment (DEA) and dissociative ionization (DI) cross sections for electron scattering from the focused electron beam induced deposition (FEBID) precursor Co(CO)(3)NO in the incident electron energy range from 0 to 140 eV. We find that DEA leads mainly to single carbonyl loss with a maximum cross section of 4.1 × 10(-16) cm(2), while fragmentation through DI results mainly in the formation of the bare metal cation Co(+) with a maximum cross section close to 4.6 × 10(-16) cm(2) at 70 eV. Though DEA proceeds in a narrow incident electron energy range, this energy range is found to overlap significantly with the expected energy distribution of secondary electrons (SEs) produced in FEBID. The DI process, on the other hand, is operative over a much wider energy range, but the overlap with the expected SE energy distribution, though significant, is found to be mainly in the threshold region of the individual DI processes. PMID:23387582

Engmann, Sarah; Stano, Michal; Papp, Peter; Brunger, Michael J; Matej?ík, Štefan; Ingólfsson, Oddur

2013-01-28

164

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

165

Potential energy curves via double electron-attachment calculations: Dissociation of alkali metal dimers  

NASA Astrophysics Data System (ADS)

The recently developed method [M. Musia?, J. Chem. Phys. 136, 134111 (2012)] to study double electron attached states has been applied to the description of the ground and excited state potential energy curves of the alkali metal dimers. The method is based on the multireference coupled cluster scheme formulated within the Fock space formalism for the (2,0) sector. Due to the use of the efficient intermediate Hamiltonian formulation, the approach is free from the intruder states problem. The description of the neutral alkali metal dimers is accomplished via attaching two electrons to the corresponding doubly ionized system. This way is particularly advantageous when a closed shell molecule dissociates into open shell subunits while its doubly positive cation generates the closed shell fragments. In the current work, we generate the potential energy curves for the ground and multiple excited states of the Li2 and Na2 molecules. In all cases the potential energy curves are smooth for the entire range of interatomic distances (from the equilibrium point to the dissociation limit). Based on the calculated potential energy curves, we are able to compute spectroscopic parameters of the systems studied.

Musia?, Monika; Kowalska-Szojda, Katarzyna; Lyakh, Dmitry I.; Bartlett, Rodney J.

2013-05-01

166

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

NSDL National Science Digital Library

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.

2013-09-07

167

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

168

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

169

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

170

Dissociative chemisorption of N 2 on rhenium: Dynamics at low impact energies  

NASA Astrophysics Data System (ADS)

The dissociative chemisorption of nitrogen on the (0001) rhenium surface is studied at low impact energies, where tunnelling processes are important. A quantum-classical model is used in which two coordinates, the distance from the surface and the vibrational coordinate, are treated quantum mechanically using the FFT (fast Fourier transform) technique. Also normal modes of the solid are quantized using a quantum boson approach and the remaining degrees of freedom are treated classically. Full corrugation of the surface and phonon coupling to infinite order as well as rotational motion of the diatom are included in the model.

Billing, Gert D.; Guldberg, Annette; Henriksen, Niels E.; Hansen, Flemming Y.

1990-10-01

171

The relative cross section and kinetic energy distribution of dissociation processes of methane by electron impact  

NASA Astrophysics Data System (ADS)

Electron-impact ionization and dissociation of methane (CH4) has been experimentally studied with a cold target recoil-ion momentum spectrometer. We report data for the formation of CHn+ (n = 0 ? 3) relative to that of CH4+ as a function of incident electron energy from 20 to 200 eV. Good agreements are achieved with previous studies. The kinetic energy distribution of the recoil-ions is presented and the average kinetic energy released (KER) was obtained for formation of CH3+. Taking advantages of the supersonic jet expansion, the thermal motion contribution to the kinetic energy distribution of the recoil-ions was reduced. The results agree better with theoretical data than those from previous experimental studies.

Wei, B.; Chen, Z.; Wang, X.; Lu, D.; Lin, S.; Hutton, R.; Zou, Y.

2013-11-01

172

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

E-print Network

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

Butler, Laurie J.

173

Dissociative electron attachment and electron energy-loss spectra of phenyl azide  

NASA Astrophysics Data System (ADS)

Electron-induced chemistry—dissociative electron attachment (DEA)—was studied for phenyl azide. The major fragment corresponded to the loss of N2 and formation of the phenylnitrene anion. This process has an onset already at zero kinetic energy of the incident electron and is interpreted as proceeding via the A''?* electronic ground state of the phenyl azide anion. Other fragments, N3- and CN-, were observed at higher energies and interpreted as proceeding via low-lying shape resonances or higher lying core-excited resonances. The interpretation of the dissociative attachment spectra was supported by an investigation of the excited electronic states of neutral phenyl azide by electron energy-loss spectroscopy and DFT/MRCI calculations, and a study of shape and core-excited resonances of the phenyl azide anion by means of electron transmission spectroscopy and of cross sections for vibrational and electronic excitation by electron impact. Interesting parallels and differences are found by comparing DEA of phenyl and benzyl azides with the corresponding chloro compounds.

Zivanov, S.; Ibanescu, B. C.; Paech, M.; Poffet, M.; Baettig, P.; Sergenton, A.-C.; Grimme, S.; Allan, M.

2007-01-01

174

A micro energy harvester with 3D wire bonded microcoils  

Microsoft Academic Search

We developed the first micro energy harvester with optimized wire bonded microcoils. The coils were fabricated with a fully automated process on PCB. The 3D coils enable to effectively use the magnetic field and generate an output power of 0.62 !W at 1 ms -2 within a total harvester volume of 0.46 cm 3 . With the coil wire thickness

C. Cepnik; U. Wallrabe

2011-01-01

175

Dissociation of disulfide-intact somatostatin ions: the roles of ion type and dissociation method.  

PubMed

The dissociation chemistry of somatostatin-14 was examined using various tandem mass spectrometry techniques including low-energy beam-type and ion trap collision-induced dissociation (CID) of protonated and deprotonated forms of the peptide, CID of peptide-gold complexes, and electron transfer dissociation (ETD) of cations. Most of the sequence of somatostatin-14 is present within a loop defined by the disulfide linkage between Cys-3 and Cys-14. The generation of readily interpretable sequence-related ions from within the loop requires the cleavage of at least one of the bonds of the disulfide linkage and the cleavage of one polypeptide backbone bond. CID of the protonated forms of somatostatin did not appear to give rise to an appreciable degree of dissociation of the disulfide linkage. Sequential fragmentation via multiple alternative pathways tended to generate very complex spectra. CID of the anions proceeded through CH(2)-S cleavages extensively but relatively few structurally diagnostic ions were generated. The incorporation of Au(I) into the molecule via ion/ion reactions followed by CID gave rise to many structurally relevant dissociation products, particularly for the [M+Au+H](2+) species. The products were generated by a combination of S-S bond cleavage and amide bond cleavage. ETD of the [M+3H](3+) ion generated rich sequence information, as did CID of the electron transfer products that did not fragment directly upon electron transfer. The electron transfer results suggest that both the S-S bond and an N-C(alpha) bond can be cleaved following a single electron transfer reaction. PMID:19630027

Mentinova, Marija; Han, Hongling; McLuckey, Scott A

2009-09-01

176

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

177

Comparison of collision-induced dissociation and electron-induced dissociation of singly charged mononucleotides  

E-print Network

covalent bond cleavages (similar or not to CID) with enhanced dissociation rate constants. ECD as well1 Comparison of collision-induced dissociation and electron-induced dissociation of singly-146" DOI : 10.1016/j.ijms.2012.01.015 #12;2 Abstract The dissociation of singly charged

178

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

NASA Astrophysics Data System (ADS)

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.

Bhaskaran, Renjith; Sarma, Manabendra

2014-09-01

179

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

180

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

181

Dissociative double photoionization of singly deuterated benzene molecules in the 26-33 eV energy range.  

PubMed

This work provides new experimental and theoretical results about the formation and dissociation of benzene dication. The experiment has been carried out by using a vacuum ultraviolet radiation from a synchrotron source together with a time-of-flight spectrometer and a position sensitive ion detector. Isotopically labeled benzene molecules with a single deuterium atom have been used in order to study the symmetric dissociation of the benzene dication, not well evident in previous experiments. A threshold of 30.1 ± 0.1 eV has been observed for this dissociation reaction. Moreover, the lifetime of the dissociation of the benzene metastable dication producing CH(3)(+) and C(5)H(3)(+) has been obtained as a function of the photon energy, by the use of a Monte Carlo trajectory analysis of the coincidence distributions. The determined lifetime is independent of the photon energy and has an average value of 0.75 ± 0.22 ?s. Theoretical calculations of the energy and structure of dissociation product ions have been also performed to provide crucial information about the dynamics of the charge separation reactions following the photoionization event. PMID:22010715

Alagia, M; Candori, P; Falcinelli, S; Mundim, M S P; Pirani, F; Richter, R; Rosi, M; Stranges, S; Vecchiocattivi, F

2011-10-14

182

Coulomb energy determination of a single Si dangling bond.  

PubMed

Determination of the Coulomb energy of single point defects is essential because changing their charge state critically affects the properties of materials. Based on a novel approach that allows us to simultaneously identify a point defect and to monitor the occupation probability of its electronic state, we unambiguously measure the charging energy of a single Si dangling bond with tunneling spectroscopy. Comparing the experimental result with tight-binding calculations highlights the importance of the particular surrounding of the localized state on the effective charging energy. PMID:21231404

Nguyen, T H; Mahieu, G; Berthe, M; Grandidier, B; Delerue, C; Stiévenard, D; Ebert, Ph

2010-11-26

183

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

184

Analysis of liquid metal embrittlement from a bond energy viewpoint  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

185

Structures, energies, and bonding in the water heptamer  

NASA Astrophysics Data System (ADS)

In this paper we report the geometries and properties of 38 distinct geometrical motifs located on the B3LYP/6-31+G(d), MP2/6-311++G(d, p) potential energy surfaces of the water heptamer. Binding energies of up to 45 kcal/mol are calculated. All motifs fall within 10 kcal/mol of the most stable conformation, with at least 13 structural patterns located no more than 3 kcal/mol above, leading to a very complex potential energy surface, populated by a multitude of motifs each one allowing large numbers of conformations. Cluster stability does not seem to be correlated with the number of hydrogen bonds. Compact structures are energetically favored by electronic energies with zero-point energy corrections, while more open structures are preferred when temperature and entropy are accounted for. The molecular interactions holding the clusters as discrete units lead to large binding energies but are not strong enough to cause significant changes in the geometries of the interacting monomers. Our results indicate that bonding in the water heptamers can be considered as largely non-shared interactions with contributions from intermediate character of increasing covalency.

Acelas, Nancy; Hincapié, Gina; Guerra, Doris; David, Jorge; Restrepo, Albeiro

2013-07-01

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

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

188

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

E-print Network

of coal combustion.6 Furan is also an impor- tant intermediate in the pyrolysis of biomass,7­10 where economy. Because of its importance in combustion chemistry and biomass pyrolysis, the thermochemistry­13 Conversion of biomass (and, more specifically, its major components--lignin, cel- lulose, and hemicellulose14

Lineberger, W. Carl

189

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

190

Hydrogen bonding Part 53. Correlation of differential scanning calorimetric data with IR and dissociation vapor pressure studies of transitions of hexamethonium chloride and bromide dihydrates and hexamethonium bromide monohydrate  

NASA Astrophysics Data System (ADS)

Differential scanning calorimetry of hexamethonium chloride dihydrate shows an endothermic transition of 2.70 kcal mol -1 at 36.81°C. This correlates well with the temperatures observed by IR spectra (36°C) and equilibrium dissociation vapor pressure studies (37°C) for the transition between Type I planar cluster and Type II extended linear HOH⋯Cl - hydrogen bonding, and with the value of 2.77 kcal mol -1 for this transition derived by Hess' law treatment of dissociation vapor pressure data. Differential scanning calorimetry of hexamethonium bromide shows a rapid endothermic transition of 2.38 kcal mol -1 at 35.15°C and a very slow endothermic transition of about 12-13 kcal mol -1 centered near 50°C. This latter endotherm corresponds to the transition between Type I and Type II HOH⋯Br - hydrogen bonding observed by IR and vapor pressure studies at 49°C. The nature of the 35.15°C endotherm is not known. Hexamethonium bromide also shows a third endotherm at 142.91°C, which presumably results from melting of hydrate in the sealed DSC cell. Combined analysis of differential scanning calorimetry and dissociation vapor pressure data predicts a value of about -13 kcal mol -1 for an exothermic disproportionation at 52°C of two hexamethonium bromide monohydrate to Type II dihydrate and anhydrous bromide.

Snider, Barbara L.; Harmon, Kenneth M.

1994-03-01

191

Resonant dissociative electron attachments to cysteine and cystine.  

PubMed

Shape-resonant electron attachments to cysteine and cystine and the subsequent dissociation dynamics are investigated with the single-center expansion potential scattering calculations. Selectivity of the direct bond cleavage at a given resonant state or by the specific resonant state coupling is demonstrated with the one-dimensional complex potential energy curves of the temporary anion (cysteine)(-). The wave function of the lowest shape resonant state of the temporary anion (cystine)(-) distinctly shows the localized anti-bond (S-S)* character, implying that this disulfide bond can be easily broken due to the low-energy electron resonant attachment. PMID:21785790

Wang, Yong-Feng; Tian, Shan Xi; Yang, Jinlong

2011-09-14

192

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

193

Defect effects on H2 dissociative adsorption on the Ni(100) surface  

Microsoft Academic Search

The dissociative adsorption of a hydrogen molecule on the nickel(100) surface with point defects is investigated using the embedded-atom method (EAM). The potential-energy surfaces (PES) for H2 dissociation on both perfect and imperfect Ni(100) surfaces are presented, based on total-energy calculations. it is clearly shown that as the H2 approaches the Ni(100) surface along the entrance channel, the H-H bond

Xie Jianjun; Jiang Ping; Zhang Kaiming

1994-01-01

194

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

195

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.

196

Use of a single trajectory to study product energy partitioning in unimolecular dissociation: mass effects for halogenated alkanes.  

PubMed

A single trajectory (ST) direct dynamics approach is compared with quasiclassical trajectory (QCT) direct dynamics calculations for determining product energy partitioning in unimolecular dissociation. Three comparisons are made by simulating C(2)H(5)F-->HF + C(2)H(4) product energy partitioning for the MP26-31G(*) and MP26-311 + + G(**) potential energy surfaces (PESs) and using the MP26-31G(*) PES for C(2)H(5)F dissociation as a model to simulate CHCl(2)CCl(3)-->HCl + C(2)Cl(4) dissociation and its product energy partitioning. The trajectories are initiated at the transition state with fixed energy in reaction-coordinate translation E(t) (double dagger). The QCT simulations have zero-point energy (ZPE) in the vibrational modes orthogonal to the reaction coordinate, while there is no ZPE for the STs. A semiquantitative agreement is obtained between the ST and QCT average percent product energy partitionings. The ST approach is used to study mass effects for product energy partitioning in HX(X = F or Cl) elimination from halogenated alkanes by using the MP26-31G(*) PES for C(2)H(5)F dissociation and varying the masses of the C, H, and F atoms. There is, at most, only a small mass effect for partitioning of energy to HX vibration and rotation. In contrast, there are substantial mass effects for partitioning to relative translation and the polyatomic product's vibration and rotation. If the center of mass of the polyatomic product is located away from the C atom from which HX recoils, the polyatomic has substantial rotation energy. Polyatomic products, with heavy atoms such as Cl atoms replacing the H atoms, receive substantial vibration energy that is primarily transferred to the wag-bend motions. For E(t) (double dagger) of 1.0 kcalmol, the ST calculations give average percent partitionings to relative translation, polyatomic vibration, polyatomic rotation, HX vibration, and HX rotation of 74.9%, 6.8%, 1.5%, 14.4%, and 2.4% for C(2)H(5)F dissociation and 39.7%, 38.1%, 0.2%, 16.1%, and 5.9% for a model of CHCl(2)CCl(3) dissociation. PMID:16483213

Sun, Lipeng; Park, Kyoyeon; Song, Kihyung; Setser, Donald W; Hase, William L

2006-02-14

197

Use of a single trajectory to study product energy partitioning in unimolecular dissociation: Mass effects for halogenated alkanes  

NASA Astrophysics Data System (ADS)

A single trajectory (ST) direct dynamics approach is compared with quasiclassical trajectory (QCT) direct dynamics calculations for determining product energy partitioning in unimolecular dissociation. Three comparisons are made by simulating C2H5F?HF+C2H4 product energy partitioning for the MP2/6-31G* and MP2/6-311++G** potential energy surfaces (PESs) and using the MP2/6-31G* PES for C2H5F dissociation as a model to simulate CHCl2CCl3?HCl+C2Cl4 dissociation and its product energy partitioning. The trajectories are initiated at the transition state with fixed energy in reaction-coordinate translation Et‡. The QCT simulations have zero-point energy (ZPE) in the vibrational modes orthogonal to the reaction coordinate, while there is no ZPE for the STs. A semiquantitative agreement is obtained between the ST and QCT average percent product energy partitionings. The ST approach is used to study mass effects for product energy partitioning in HX (X=ForCl) elimination from halogenated alkanes by using the MP2/6-31G* PES for C2H5F dissociation and varying the masses of the C, H, and F atoms. There is, at most, only a small mass effect for partitioning of energy to HX vibration and rotation. In contrast, there are substantial mass effects for partitioning to relative translation and the polyatomic product's vibration and rotation. If the center of mass of the polyatomic product is located away from the C atom from which HX recoils, the polyatomic has substantial rotation energy. Polyatomic products, with heavy atoms such as Cl atoms replacing the H atoms, receive substantial vibration energy that is primarily transferred to the wag-bend motions. For Et‡ of 1.0kcal /mol, the ST calculations give average percent partitionings to relative translation, polyatomic vibration, polyatomic rotation, HX vibration, and HX rotation of 74.9%, 6.8%, 1.5%, 14.4%, and 2.4% for C2H5F dissociation and 39.7%, 38.1%, 0.2%, 16.1%, and 5.9% for a model of CHCl2CCl3 dissociation.

Sun, Lipeng; Park, Kyoyeon; Song, Kihyung; Setser, Donald W.; Hase, William L.

2006-02-01

198

Theoretical electron density distributions for Fe- and Cu-sulfide earth materials: a connection between bond length, bond critical point properties, local energy densities, and bonded interactions.  

PubMed

Bond critical point and local energy density properties together with net atomic charges were calculated for theoretical electron density distributions, rho(r), generated for a variety of Fe and Cu metal-sulfide materials with high- and low-spin Fe atoms in octahedral coordination and high-spin Fe atoms in tetrahedral coordination. The electron density, rho(rc), the Laplacian, triangle down2rho(rc), the local kinetic energy, G(rc), and the oxidation state of Fe increase as the local potential energy density, V(rc), the Fe-S bond lengths, and the coordination numbers of the Fe atoms decrease. The properties of the bonded interactions for the octahedrally coordinated low-spin Fe atoms for pyrite and marcasite are distinct from those for high-spin Fe atoms for troilite, smythite, and greigite. The Fe-S bond lengths are shorter and the values of rho(rc) and triangle down2rho(rc) are larger for pyrite and marcasite, indicating that the accumulation and local concentration of rho(r) in the internuclear region are greater than those involving the longer, high-spin Fe-S bonded interactions. The net atomic charges and the bonded radii calculated for the Fe and S atoms in pyrite and marcasite are also smaller than those for sulfides with high-spin octahedrally coordinated Fe atoms. Collectively, the Fe-S interactions are indicated to be intermediate in character with the low-spin Fe-S interactions having greater shared character than the high-spin interactions. The bond lengths observed for chalcopyrite together with the calculated bond critical point properties are consistent with the formula Cu+Fe3+S2. The bond length is shorter and the rho(rc) value is larger for the FeS4 tetrahedron displayed by metastable greigite than those displayed by chalcopyrite and cubanite, consistent with a proposal that the Fe atom in greigite is tetravalent. S-S bond paths exist between each of the surface S atoms of adjacent slabs of FeS6 octahedra comprising the layer sulfide smythite, suggesting that the neutral Fe3S4 slabs are linked together and stabilized by the pathways of electron density comprising S-S bonded interactions. Such interactions not only exist between the S atoms for adjacent S8 rings in native sulfur, but their bond critical point properties are similar to those displayed by the metal sulfides. PMID:17274642

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

2007-03-01

199

Dissociative electron attachment to ?-alanine.  

PubMed

A detailed study on dissociative electron attachment (DEA) to ?-alanine (?A) in the gas phase is presented. Ion yields as a function of the incident electron energy from about 0 to 15 eV have been measured for most of the fragments. As for all ?-amino acids, the main reaction corresponds to the loss of a hydrogen atom, although many other fragments have been observed that involved more complex bond cleavages. Threshold energies have been calculated by using the G4(MP2) method for various decomposition reactions. Fragmentation pathways were also investigated to measure metastable decays of the intermediate fragment anion (?A-H)(-) by using the mass-analyzed ion kinetic energy (MIKE) scan technique. Comparisons with ?-alanine and other amino acids are made when relevant. PMID:21509925

Vizcaino, Violaine; Bartl, Peter; Gschliesser, David; Huber, Stefan E; Probst, Michael; Märk, Tilmann D; Scheier, Paul; Denifl, Stephan

2011-05-01

200

Does Nitric Acid Dissociate at the Aqueous Solution Surface?  

SciTech Connect

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

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

2011-11-03

201

A variational algebraic method used to study the full vibrational spectra and dissociation energies of some specific diatomic systems  

NASA Astrophysics Data System (ADS)

The algebraic method (AM) proposed by Sun et al. is improved to be a variational AM (VAM) to offset the possible experimental errors and to adapt to the individual energy expansion nature of different molecular systems. The VAM is used to study the full vibrational spectra {E?} and the dissociation energies De of 4HeH+-X1?+, 7Li2-13?g, Na2-C1?u, NaK-71?, Cs2-B1?u and 79Br2-?1g(3P2) diatomic electronic states. The results not only precisely reproduce all known experimental vibrational energies, but also predict correct dissociation energies and all unknown high-lying levels that may not be given by the original AM or other numerical methods or experimental methods. The analyses and the skill suggested here might be useful for other numerical simulations and theoretical fittings using known data that may carry inevitable errors.

Zhang, Yi; Sun, Weiguo; Fu, Jia; Fan, Qunchao; Ma, Jie; Xiao, Liantuan; Jia, Suotang; Feng, Hao; Li, Huidong

2014-01-01

202

A variational algebraic method used to study the full vibrational spectra and dissociation energies of some specific diatomic systems.  

PubMed

The algebraic method (AM) proposed by Sun et al. is improved to be a variational AM (VAM) to offset the possible experimental errors and to adapt to the individual energy expansion nature of different molecular systems. The VAM is used to study the full vibrational spectra {E?} and the dissociation energies De of (4)HeH(+)-X(1)?(+), (7)Li2-1(3)?g,Na2-C(1)?u,NaK-7(1)?, Cs2-B(1)?u and (79)Br2-?1g((3)P2) diatomic electronic states. The results not only precisely reproduce all known experimental vibrational energies, but also predict correct dissociation energies and all unknown high-lying levels that may not be given by the original AM or other numerical methods or experimental methods. The analyses and the skill suggested here might be useful for other numerical simulations and theoretical fittings using known data that may carry inevitable errors. PMID:24013115

Zhang, Yi; Sun, Weiguo; Fu, Jia; Fan, Qunchao; Ma, Jie; Xiao, Liantuan; Jia, Suotang; Feng, Hao; Li, Huidong

2014-01-01

203

Energy-resolved collision-induced dissociation studies of 1,10-phenanthroline complexes of the late first-row divalent transition metal cations: determination of the third sequential binding energies.  

PubMed

The third sequential binding energies of the late first-row divalent transition metal cations to 1,10-phenanthroline (Phen) are determined by energy-resolved collision-induced dissociation (CID) techniques using a guided ion beam tandem mass spectrometer. Five late first-row transition metal cations in their +2 oxidation states are examined including: Fe(2+), Co(2+), Ni(2+), Cu(2+), and Zn(2+). The kinetic energy dependent CID cross sections for loss of an intact Phen ligand from the M(2+)(Phen)3 complexes are modeled to obtain 0 and 298 K bond dissociation energies (BDEs) after accounting for the effects of the internal energy of the complexes, multiple ion-neutral collisions, and unimolecular decay rates. Electronic structure theory calculations at the B3LYP, BHandHLYP, and M06 levels of theory are employed to determine the structures and theoretical estimates for the first, second, and third sequential BDEs of the M(2+)(Phen)x complexes. B3LYP was found to deliver results that are most consistent with the measured values. Periodic trends in the binding of these complexes are examined and compared to the analogous complexes to the late first-row monovalent transition metal cations, Co(+), Ni(+), Cu(+), and Zn(+), previously investigated. PMID:23565706

Nose, Holliness; Chen, Yu; Rodgers, M T

2013-05-23

204

Dissociative electron attachment to triflates  

NASA Astrophysics Data System (ADS)

It is known that understanding of chemical transformations induced by low energy electrons reacting with photoresist components is crucial for effective design of chemically amplified resists in modern lithography. Therefore in present work gas phase studies on dissociative electron attachment to simple alkyl (CF3SO3CH3) and aryl (C6H5SO3CF3 and CF3SO3C6H4CH3) triflates were carried out. The fragmentation pathways under electron impact below 10 eV were identified by means of crossed electron-molecular beam mass spectrometry. Several reaction channels were observed upon an electron capture by the studied compounds, involving single or multiple bond cleavages or intramolecular rearrangement. Three main dissociation channels were observed that are C-O, S-O or C-S bond breakage in the triflate moiety leading to the formation of triflate (OTf), triflyl (Tf) or sulfonate (RSO3) anions, respectively. The results of this work can be helpful at later stage in the improvement of the image quality in post optical lithography processes.

Ptasinska, Sylwia; Gschliesser, David; Bartl, Peter; Ianik, Ireneusz; Scheier, Paul; Denifl, Stephan

2012-10-01

205

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

PubMed

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

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

2008-06-01

206

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

207

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

E-print Network

as shared covalent bonds. C­O and S­O bonded interactions classify as both intermediate and covalent bonded with a substantial component of covalent character and the C­O single-bonded interaction classifies as a covalent bond whereas their local electronic energy density values indicate that they are each covalent bonded

Crawford, T. Daniel

208

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

209

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

210

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

SciTech Connect

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

Petrignani, Annemieke; Altevogt, Simon; Berg, Max H.; Bing, Dennis; Grieser, Manfred; Hoffmann, Jens; Jordon-Thaden, Brandon; Krantz, Claude; Mendes, Mario B.; Novotny, Oldrich; Novotny, Steffen [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany); Buhr, Henrik [Department of Particle Physics, Weizmann Institute of Science, 76100 Rehovot (Israel); Kreckel, Holger [Columbia University, 550 West 120th Street, New York, New York 10027 (United States); Kokoouline, Viatcheslav [Department of Physics, University of Central Florida, Orlando, Florida 32816, USA, and Laboratoire Aime Cotton, CNRS, Universite Paris-Sud XI, F-91405 Orsay (France); Greene, Chris H. [Department of Physics and JILA, University of Colorado, Boulder, Colorado 80309-0440 (United States); Orlov, Dmitry A.; Repnow, Roland; Sorg, Tobias; Stuetzel, Julia; Wolf, Andreas

2011-03-15

211

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

212

Unimolecular dissociation of cyclohexene at extremely high temperatures: behavior of the energy-transfer collision efficiency  

Microsoft Academic Search

The dissociation of cyclehexene has been observed in shock waves with the laser schlieren and pulsed laser flash absorption techniques over 1200-2000 K and 110-550 Torr, using 2% and 4% cyclohexene in krypton and 0.2% cyclohexene in argon. The inverse Diels-Alder molecular elimination to 1,3-butadiene and ethylene is clearly the dominant dissociation channel under all conditions. Rate constants derived for

John H. Kiefer; Jatin N. Shah

1987-01-01

213

Unimolecular dissociation of aniline molecular ion  

NASA Astrophysics Data System (ADS)

The potential energy surface (PES) for dissociation of aniline ion was determined using density functional theory molecular orbital calculations at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level. On the basis of the PES obtained, kinetic analysis was performed by Rice-Ramsperger-Kassel-Marcus (RRKM) calculations. The RRKM dissociation rate constants agreed well with previous experimental data. The most favorable channel was formation of the cyclopentadiene ion by loss of HNC, occurring through consecutive ring opening and re-closure to a five-membered ring. Loss of H could compete with the HNC loss at high energy, which occurred by direct cleavage of an N-H bond or through ring expansion.

Choe, Joong Chul; Cheong, Nu Ri; Park, Seung Min

2009-01-01

214

Tuning of dissociative-adsorption processes on Cu{1 0 0} by controlling the kinetic energy of the impinging O 2 molecule  

NASA Astrophysics Data System (ADS)

Dissociative adsorption of hyperthermal O 2 molecules on Cu{1 0 0} was investigated by X-ray photoemission spectroscopy in conjunction with a synchrotron light source. From precise measurements of the O-uptake curves, it was found that the dissociative adsorption of hyperthermal O 2 molecules follows a simple Langmuir-type model and the reaction order depends on the incident energy. An O 2?- -mediated adsorption mechanism can interpret the incident-energy dependence of the reaction order. These results suggest the possibility of tuning dissociative adsorption via the selection of the incident kinetic energy of the impinging O 2 molecules.

Okada, Michio; Moritani, Kousuke; Yoshigoe, Akitaka; Teraoka, Yuden; Nakanishi, Hiroshi; Diño, Wilson Agerico; Kasai, Hideaki; Kasai, Toshio

2004-06-01

215

An isomer-specific high-energy collision-induced dissociation MS/MS database for forensic applications: a proof-of-concept on chemical warfare agent markers.  

PubMed

Spectra database search has become the most popular technique for the identification of unknown chemicals, minimizing the need for authentic reference chemicals. In the present study, an isomer-specific high-energy collision-induced dissociation (CID) MS/MS spectra database of 12 isomeric O-hexyl methylphosphonic acids (degradation markers of nerve agents) was created. Phosphonate anions were produced by the electrospray ionization of phosphonic acids or negative-ion chemical ionization of their fluorinated derivatives and were analysed in a hybrid magnetic-sector-time-of-flight tandem mass spectrometer. A centre-of-mass energy (E(com)) of 65?eV led to an optimal sequential carbon-carbon bond breakage, which was interpreted in terms of charge remote fragmentation. The proposed mechanism is discussed in comparison with the routinely used low-energy CID MS/MS. Even-mass (odd-electron) charge remote fragmentation ion series were diagnostic of the O-alkyl chain structure and can be used to interpret unknown spectra. Together with the odd-mass ion series, they formed highly reproducible, isomer-specific spectra that gave significantly higher database matches and probability factors (by 1.5 times) than did the EI MS spectra of the trimethylsilyl derivatives of the same isomers. In addition, ionization by negative-ion chemical ionization and electrospray ionization resulted in similar spectra, which further highlights the general potential of the high-energy CID MS/MS technique. PMID:21915956

Subramaniam, Raja; Östin, Anders; Nygren, Yvonne; Juhlin, Lars; Nilsson, Calle; Åstot, Crister

2011-09-01

216

A systematic theoretical study of water dissociation on clean and oxygen-preadsorbed transition metals  

Microsoft Academic Search

Water dissociation on clean and oxygen-preadsorbed transition metal surfaces was investigated by the DFT-GGA method. The total energy change and the reaction barrier were calculated with respect to the direct and oxygen-assisted cleavage of OH bonds of water. The calculated results showed periodic trends for water dissociation on both clean and oxygen-preadsorbed surfaces. On clean surfaces, the chemical activity for

Gui-Chang Wang; Shu-Xia Tao; Xian-He Bu

2006-01-01

217

Free Energy Profiles for H + Conduction along Hydrogen-Bonded Chains of Water Molecules  

Microsoft Academic Search

The molecular mechanism for proton conduction along hydrogen-bonded chains, or “proton wires,” is studied with free energy simulations. The complete transport of a charge along a proton wire requires two complementary processes: 1) translocation of an excess proton (propagation of an ionic defect), and 2) reorientation of the hydrogen-bonded chain (propagation of a bonding defect). The potential of mean force

Régis Pomès; Benoît Roux

1998-01-01

218

Threshold collision-induced dissociation: A guided ion beam study of energy transfer dynamics, lifetime effects, and applications  

NASA Astrophysics Data System (ADS)

A guided ion beam tandem mass spectrometer (GIB-TMS) instrument is used to study the dynamics and kinetics of collision induced dissociation (CID) processes in the threshold energy region. The dynamics of CID in the threshold energy region is investigated through integral and differential cross section measurements on the sequential dissociation of the Cr(CO)6+ system. The implementation of the method of measuring differential cross sections on this instrument is presented in detail. Energy transfer dynamics is discussed on the basis of differential cross section data. Experimental deposited energy distributions are compared to the predictions of the modified line-of-centers model used in modeling the kinetic energy dependence of CID. The kinetic shift effects encountered in the CID of C6H 4C12+ and n-C4H9C 6H5+ with Xe are investigated. Ab initio calculations are performed in order to complement the available information about the potential energy surfaces of these systems. CID threshold values are obtained by modeling the energy dependence of integral cross sections and accounting for kinetic and competitive shifts by using the RRKM theory. The selection of parameters used for calculation of dissociation rates by RRKM theory is discussed by comparing the energy dependence of the calculated rates with experimental data from literature. The energy dependencies of CID integral cross sections of the [OCS:C 2H2]+ system are analyzed using the present modeling procedures that account for kinetic and competitive shifts. The potential energy surface of the system is characterized in great detail by CID experiments with Xe and Ar, and by ab initio calculations.

Muntean, Felician

219

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

PubMed

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

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

2014-05-01

220

Structural studies on ceramides as lithiated adducts by low energy collisional-activated dissociation tandem mass spectrometry with electrospray ionization  

Microsoft Academic Search

We applied electrospray ionization (ESI) tandem quadrupole mass spectrometry to establish the fragmentation pathways of ceramides\\u000a under low energy collisional-activated dissociation (CAD) by studying more than thirty compounds in nine subclasses. The product-ion\\u000a spectra of the [M + Li]+ ions of ceramides contain abundant fragment ions that identify the fatty acyl substituent and the long-chain base (LCB) of\\u000a the molecules,

Fong-F. u Hsu; John Turk; Mary E. Stewart; Donald T. Downing

2002-01-01

221

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

222

Energy levels and charge distributions of nonideal dangling and floating bonds in amorphous Si  

NASA Astrophysics Data System (ADS)

Defect-state wave functions and energies are calculated for numerous configurations of nonideal dangling and floating bonds in a-Si with use of Bethe-lattice-terminated clusters and a tight-binding approach. The energy eigenvalue for the dangling bond is highly dependent on deviations from ideality while the wave-function amplitudes are much less so. Exactly the opposite holds for the floating bond. The experimental consequences of these calculations are discussed.

Fedders, P. A.; Carlsson, A. E.

1989-01-01

223

Dissociation of water on oxygen-covered Rh(111)  

SciTech Connect

The adsorption of water and coadsorption with oxygen on Rh(111) under ultrahigh vacuum conditions was studied using synchrotron-based photoemission and photoabsorption spectroscopy. Water adsorbs intact on the clean surface at temperatures below 154 K. Irradiation with x-rays, however, induces fast dissociation and the formation of a mixed OH+H{sub 2}O layer indicating that the partially dissociated layer is thermodynamically more stable. Coadsorption of water and oxygen at a coverage below 0.3 monolayers has a similar effect, leading to the formation of a hydrogen-bonded network of water and hydroxyl molecules at a ratio of 3:2. The partially dissociated layers are more stable than chemisorbed intact water with the maximum desorption temperatures up to 30 K higher. For higher oxygen coverage, up to 0.5 monolayers, water does not dissociate and an intact water species is observed above 160 K, which is characterized by an O 1s binding energy 0.6 eV higher than that of chemisorbed water and a high desorption temperature similar to the partially dissociated layer. The extra stabilization is most likely due to hydrogen bonds with atomic oxygen.

Shavorskiy, A.; Eralp, T.; Held, G. [Department of Chemistry, The University of Reading, Whiteknights, Reading RG6 6AD (United Kingdom); Ataman, E.; Isvoranu, C.; Schnadt, J.; Andersen, J. N. [Department of Synchrotron Radiation Research, Institute of Physics, Lund University, P.O. Box 118, S-221 00 Lund (Sweden)

2009-12-07

224

Dissociation of water on oxygen-covered Rh{111}  

NASA Astrophysics Data System (ADS)

The adsorption of water and coadsorption with oxygen on Rh{111} under ultrahigh vacuum conditions was studied using synchrotron-based photoemission and photoabsorption spectroscopy. Water adsorbs intact on the clean surface at temperatures below 154 K. Irradiation with x-rays, however, induces fast dissociation and the formation of a mixed OH+H2O layer indicating that the partially dissociated layer is thermodynamically more stable. Coadsorption of water and oxygen at a coverage below 0.3 monolayers has a similar effect, leading to the formation of a hydrogen-bonded network of water and hydroxyl molecules at a ratio of 3:2. The partially dissociated layers are more stable than chemisorbed intact water with the maximum desorption temperatures up to 30 K higher. For higher oxygen coverage, up to 0.5 monolayers, water does not dissociate and an intact water species is observed above 160 K, which is characterized by an O 1s binding energy 0.6 eV higher than that of chemisorbed water and a high desorption temperature similar to the partially dissociated layer. The extra stabilization is most likely due to hydrogen bonds with atomic oxygen.

Shavorskiy, A.; Eralp, T.; Ataman, E.; Isvoranu, C.; Schnadt, J.; Andersen, J. N.; Held, G.

2009-12-01

225

Dissociation of water on oxygen-covered Rh{111}.  

PubMed

The adsorption of water and coadsorption with oxygen on Rh{111} under ultrahigh vacuum conditions was studied using synchrotron-based photoemission and photoabsorption spectroscopy. Water adsorbs intact on the clean surface at temperatures below 154 K. Irradiation with x-rays, however, induces fast dissociation and the formation of a mixed OH+H(2)O layer indicating that the partially dissociated layer is thermodynamically more stable. Coadsorption of water and oxygen at a coverage below 0.3 monolayers has a similar effect, leading to the formation of a hydrogen-bonded network of water and hydroxyl molecules at a ratio of 3:2. The partially dissociated layers are more stable than chemisorbed intact water with the maximum desorption temperatures up to 30 K higher. For higher oxygen coverage, up to 0.5 monolayers, water does not dissociate and an intact water species is observed above 160 K, which is characterized by an O 1s binding energy 0.6 eV higher than that of chemisorbed water and a high desorption temperature similar to the partially dissociated layer. The extra stabilization is most likely due to hydrogen bonds with atomic oxygen. PMID:19968360

Shavorskiy, A; Eralp, T; Ataman, E; Isvoranu, C; Schnadt, J; Andersen, J N; Held, G

2009-12-01

226

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

2014-10-22

227

Hydrogen Bond Breaking and Reformation in Alcohol Oligomers Following Vibrational Relaxation of a Non-Hydrogen-Bond Donating Hydroxyl Stretch  

E-print Network

constants for hydrogen bond dissociation and reformation have been determined to be 2-3 ps for breaking propose a model in which hydrogen bond dissociation, following vibrational relaxation, increases. The observation of the same decay rates with and without hydrogen bond dissociation indicates that hydrogen bond

Fayer, Michael D.

228

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

229

A reduced radial potential energy function for the halogen bond and the hydrogen bond in complexes B···XY and B···HX, where X and Y are halogen atoms.  

PubMed

It is shown by considering 76 halogen- and hydrogen-bonded complexes BXY and BHX (where B is a Lewis base N2, CO, C2H2, C2H4, H2S, HCN, H2O, PH3 or NH3 and X, Y are F, Cl, Br or I) that the intermolecular stretching force constants k? (determined from experimental centrifugal distortion constants via a simple model) and the intermolecular dissociation energies D? (calculated at the CCSD(T)(F12*)/cc-pVDZ-F12 level of theory) are related by D? = C?k?, where C? = 1.50(3) × 10(3) m(2) mol(-1). This suggests that one-dimensional functions implying direct proportionality of D? and k?, (e.g. a Morse or Rydberg function) might serve as reduced radial potential energy functions for such complexes. PMID:24827860

Legon, Anthony C

2014-06-28

230

Dissociative recombination of LiH2+  

NASA Astrophysics Data System (ADS)

In this paper, we report results regarding how LiH2+ fragments as a result of a low-energy collision with an electron (dissociative recombination), a reaction that contains only elements and particles created during the very first phase of the universe. The collision-energy-dependent reaction rate and cross sections show detailed structures, more so than predicted by theory, suggesting significant rovibrational coupling in the ion and a complex reaction surface. From the structure of the molecule, the reaction predominantly results in the formation of Li + H2. However, 23% of the reaction flux leads to more interesting products, with 17% producing Li + 2H and 6% producing LiH + H. These last two channels break the strongest molecular bond in the system and, in the case of the latter channel, form a significantly weaker ionic bond. Possible reasons behind this interesting behavior are discussed, together with the interaction between the available reaction channels.

Thomas, R. D.; Ehlerding, A.; Geppert, W. D.; Hellberg, F.; Zhaunerchyk, V.; Larsson, M.; Bahati, E.; Bannister, M. E.; Fogle, M. R.; Vane, C. R.

2014-05-01

231

Making and Breaking Bonds  

NSDL National Science Digital Library

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

Consortium, The C.

2011-12-11

232

Energy deposition in iron pentacarbonyl ions undergoing surface-induced dissociation in a Fourier transform mass spectrometer.  

PubMed

Internal energy deposition into iron pentacarbonyl positive ions undergoing surface-induced dissociation (SID) in a Fourier transform mass spectrometer is estimated from the abundances and known critical energies of the product fragment ions. A narrow energy distribution, comparable to that reported in earlier BQ and tandem quadrupole SID studies of the same compound, is observed. As judged by the ratio of fragment ions to incident parent ions observed, SID of iron pentacarbonyl in the 3 T Fourier transform mass spectrometer is more efficient, but results in lower conversion of laboratory to internal energy. This may be a result of the more shallow collision incidence angle employed in the Fourier transform mass spectrometer measurements (a few degrees), which contrasts with the 32-60° collision angles used in the earlier BQ and tandem quadrupole mass spectrometry studies. Collision-induced dissociation with He under single collision conditions is also reported, Not unexpectedly, conversion of kinetic to internal energy was lower than found in a previous Fourier transform mass spectrometer study of the iron pentacarbonyl cation employing argon as collision gas under multiple collision conditions. PMID:24243054

Castoro, J A; Rucker, P V; Wilkins, C L

1992-05-01

233

Threshold collision-induced dissociation of Sr(2+)(H(2)O)(x) complexes (x=1-6): An experimental and theoretical investigation of the complete inner shell hydration energies of Sr(2+).  

PubMed

The sequential bond energies of Sr(2+)(H(2)O)(x) complexes, where x=1-6, are determined by threshold collision-induced dissociation using a guided ion beam tandem mass spectrometer equipped with an electrospray ionization source. The electrospray source produces an initial distribution of Sr(2+)(H(2)O)(x) complexes, where x=6-9. Smaller Sr(2+)(H(2)O)(x) complexes, where x=1-5, are accessed using a recently developed in-source fragmentation technique that takes place in the high pressure region of a rf-only hexapole ion guide. This work constitutes the first experimental study for the complete inner shell of any multiply charged ion. The kinetic energy dependent cross sections are determined over a wide energy range to monitor all possible dissociation products and are modeled to obtain 0 and 298 K binding energies for loss of a single water molecule. These binding energies decrease monotonically for the Sr(2+)(H(2)O) complex to Sr(2+)(H(2)O)(6). Our experimental results agree well with previous literature results obtained by equilibrium and kinetic studies for x=5 and 6. Because there has been limited theory for the hydration of Sr(2+), we also present an in-depth theoretical study on the energetics of the Sr(2+)(H(2)O)(x) systems by employing several levels of theory with multiple effective core potentials for Sr and different basis sets for the water molecules. PMID:20113029

Carl, D R; Chatterjee, B K; Armentrout, P B

2010-01-28

234

Threshold collision-induced dissociation of hydrated magnesium: experimental and theoretical investigation of the binding energies for Mg(2+)(H2O)x complexes (x=2-10).  

PubMed

The sequential bond energies of Mg(2+)(H2O)x complexes, in which x=2-10, are measured by threshold collision-induced dissociation in a guided ion beam tandem mass spectrometer. From an electrospray ionization source that produces an initial distribution of Mg(2+)(H2O)x complexes in which x=7-10, complexes down to x=3 are formed by using an in-source fragmentation technique. Complexes smaller than Mg(2+)(H2O)3 cannot be formed in this source because charge separation into MgOH(+)(H2O) and H3O(+) is a lower-energy pathway than simple water loss from Mg(2+)(H2O)3. The kinetic energy dependent cross sections for dissociation of Mg(2+)(H2O)x complexes, in which x=3-10, are examined over a wide energy range to monitor all dissociation products and are modeled to obtain 0 and 298 K binding energies. Analysis of both primary and secondary water molecule losses from each sized complex provides thermochemistry for the sequential hydration energies of Mg(2+) for x=2-10 and the first experimental values for x=2-4. Additionally, the thermodynamic onsets leading to the charge-separation products from Mg(2+)(H2O)3 and Mg(2+)(H2O)4 are determined for the first time. Our experimental results for x=3-7 agree well with quantum chemical calculations performed here and previously calculated binding enthalpies, as well as previous measurements for x=6. The present values for x=7-10 are slightly lower than previous experimental results and theory, but within experimental uncertainties. PMID:23239534

Carl, Damon R; Armentrout, Peter B

2013-03-18

235

Experimental investigation of the complete inner shell hydration energies of Ca2+: threshold collision-induced dissociation of Ca(2+)(H2O)x Complexes (x = 2-8).  

PubMed

The sequential bond energies of Ca(2+)(H(2)O)(x) complexes, where x = 1-8, are measured by threshold collision-induced dissociation (TCID) in a guided ion beam tandem mass spectrometer. From an electrospray ionization source that produces an initial distribution of Ca(2+)(H(2)O)(x) complexes where x = 6-8, complexes down to x = 2 are formed using an in-source fragmentation technique. Ca(2+)(H(2)O) cannot be formed in this source because charge separation into CaOH(+) and H(3)O(+) is a lower energy pathway than simple water loss from Ca(2+)(H(2)O)(2). The kinetic energy dependent cross sections for dissociation of Ca(2+)(H(2)O)(x) complexes, where x = 2-9, are examined over a wide energy range to monitor all dissociation products and are modeled to obtain 0 and 298 K binding energies. Analysis of both primary and secondary water molecule losses from each sized complex provides thermochemistry for the sequential hydration energies of Ca(2+) for x = 1-8 and the first experimental values for x = 1-4. Additionally, the thermodynamic onsets leading to the charge separation products from Ca(2+)(H(2)O)(2) and Ca(2+)(H(2)O)(3) are determined for the first time. Our experimental results for x = 1-6 agree well with previously calculated binding enthalpies as well as quantum chemical calculations performed here. Agreement for x = 1 is improved when the basis set on calcium includes core correlation. PMID:22452741

Carl, Damon R; Armentrout, P B

2012-04-19

236

Many-body energy decomposition of hydrogen-bonded glycine clusters in gas-phase  

Microsoft Academic Search

A detailed analysis of the many-body contribution to the interaction energies of the gas-phase hydrogen-bonded glycine clusters, (Gly)N, N=1–4 is presented. The energetics of the hydrogen-bonded dimer, trimer and tetramer complexes have been analyzed using density-functional theory. The magnitude of the two- through four-body energy terms have been calculated and compared. The relaxation energy and the two-body energy terms are

Puspitapallab Chaudhuri; Sylvio Canuto

2010-01-01

237

Accurate ab initio structure, dissociation energy, and vibrational spectroscopy of the F(-)-CH4 anion complex.  

PubMed

Accurate equilibrium structure, dissociation energy, global potential energy surface (PES), dipole moment surface (DMS), and the infrared vibrational spectrum in the 0-3000 cm(-1) range of the F(-)-CH4 anion complex have been obtained. The equilibrium electronic structure calculations employed second-order Møller-Plesset perturbation theory (MP2) and coupled-cluster (CC) method up to single, double, triple, and perturbative quadruple excitations using the aug-cc-p(C)VXZ [X = 2(D), 3(T), 4(Q), and 5] correlation-consistent basis sets. The best equilibrium geometry has been obtained at the all-electron CCSD(T)/aug-cc-pCVQZ level of theory. The dissociation energy has been determined based on basis set extrapolation techniques within the focal-point analysis (FPA) approach considering (a) electron correlation beyond the all-electron CCSD(T) level, (b) relativistic effects, (c) diagonal Born-Oppenheimer corrections (DBOC), and (d) variationally computed zero-point vibrational energies. The final D(e) and D0 values are 2398 +/- 12 and 2280 +/- 20 cm(-1), respectively. The global PES and DMS have been computed at the frozen-core CCSD(T)/aug-cc-pVTZ and MP2/aug-cc-pVTZ levels of theory, respectively. Variational vibrational calculations have been performed for CH4 and F(-)-CH4 employing the vibrational configuration interaction (VCI) method as implemented in Multimode. PMID:18651724

Czakó, Gábor; Braams, Bastiaan J; Bowman, Joel M

2008-08-14

238

Reaction pathway and free energy barrier for defect-induced water dissociation on the (101) surface of TiO2-anatase  

Microsoft Academic Search

The adsorption of a water molecule on a partially reduced TiO2 anatase (101) surface has been studied by first-principles molecular-dynamics simulations. At variance with the stoichiometric surface, dissociation of water close to the oxygen vacancy is energetically favored compared to molecular adsorption. However, no spontaneous dissociation was observed in a simulation of several picoseconds, indicating the presence of an energy

Antonio Tilocca; Annabella Selloni

2003-01-01

239

Dissociative Attachment of Low-Energy Electrons to Vibrationally Excited Hydrogen Molecules  

NASA Astrophysics Data System (ADS)

Dissociative electron attachment to hot hydrogen molecules is studied in the framework of nonlocal resonance model. The method based on the use of the Bateman approximation, well known in nuclear physics, is adapted for solving the Lippmann-Schwinger integral equation of the nonlocal resonance model and applied to the calculation of cross sections of inelastic resonant electron-molecule collisions. The proposed method is compared with the Schwinger-Lanczos algorithm used extensively for the treatment of these processes. It is shown that the Bateman approximation is very useful and efficient for treating the non-separable nonlocal potentials appearing in the integral kernels of the nonlocal resonance models. The calculated cross sections for the dissociative attachment of electrons to vibrationally excited hydrogen molecules are of importance for astrophysics.

Houfek, K.; ?ížek, M.; Horá?ek, J.

2002-01-01

240

H2S ultrafast dissociation probed by energy-selected resonant Auger electron-ion coincidence measurements.  

PubMed

We have studied the ultrafast dissociation of the H2S molecule upon S 2p3/2-->6a1 inner-shell excitation by combining high-resolution resonant Auger spectroscopy and energy-selected Auger electron-ion coincidence measurements. Auger final states have been correlated to the different fragmentation pathways (S+, HS+, and H2S+ ions). As an original result, we evidence a three-step mechanism to describe the resonant production of S+: the Auger recombination in the HS* fragment is followed for the A 3Pi and c 1Pi states by the S++H fragmentation mechanism. PMID:17887845

Le Guen, K; Miron, C; Céolin, D; Guillemin, R; Leclercq, N; Simon, M; Morin, P; Mocellin, A; Björneholm, O; Naves de Brito, A; Sorensen, S L

2007-09-21

241

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

242

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

243

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.; Fernandez-Recio, Juan; Bates, Paul A.

2013-01-01

244

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

PubMed Central

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 about chemical energy (which is also the way we talk about energy in everyday life); 2) the macroscopic approach to energy concepts that is common in physics and physical sciences; and 3) the failure of chemistry courses to explicitly link molecular with macroscopic energy ideas. From a constructivist perspective, it is unlikely that students can, without a coherent understanding of such a central concept, attain a robust and accurate understanding of new concepts. However, changes are on the horizon, guided by the increasing understanding that difficult concepts require coherent, well-designed learning progressions and the new National Research Council Framework for K–12 Science Education. We provide supporting evidence for our assertions and suggestions for an interdisciplinary learning progression designed to better approach the concept of bond energies, a first step in an understanding chemical energy and behavior of reaction systems that is central to biological systems. PMID:23737636

Cooper, Melanie M.; Klymkowsky, Michael W.

2013-01-01

245

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

Microsoft Academic Search

A second-generation potential energy function for solid carbon and hydrocarbon molecules that is based on an empirical bond order formalism is presented. This potential allows for covalent bond breaking and forming with associated changes in atomic hybridization within a classical potential, producing a powerful method for modelling complex chemistry in large many-atom systems. This revised potential contains improved analytic functions

Donald W. Brenner; Olga A. Shenderova; Judith A. Harrison; Steven J. Stuart; Boris Ni; Susan B. Sinnott

2002-01-01

246

Sacrificial bonds and hidden length dissipate energy as mineralized fibrils separate during bone fracture  

Microsoft Academic Search

Properties of the organic matrix of bone as well as its function in the microstructure could be the key to the remarkable mechanical properties of bone. Previously, it was found that on the molecular level, calcium-mediated sacrificial bonds increased stiffness and enhanced energy dissipation in bone constituent molecules. Here we present evidence for how this sacrificial bond and hidden length

Georg E. Fantner; Tue Hassenkam; Johannes H. Kindt; James C. Weaver; Henrik Birkedal; Leonid Pechenik; Jacqueline A. Cutroni; Geraldo A. G. Cidade; Galen D. Stucky; Daniel E. Morse; Paul K. Hansma

2005-01-01

247

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

2008-07-25

248

Large nonstatistical branching ratio in the dissociation of pentane-2,4-dione radical cation: an ab initio direct classical trajectory study.  

PubMed

The dissociation of pentane-2,4-dione radical cation has been studied by ab initio direct classical trajectory calculations at the MP2/6-31G(d) level of theory. A bond additivity correction has been used to improve the MP2 potential energy surface (BAC-MP2). A microcanonical ensemble was constructed using quasiclassical normal-mode sampling by distributing 10 kcal/mol of excess energy above ZPE for the transition state for the tautomerization of the enol with a terminal double bond, 4-hydroxypent-4-en-2-one radical cation, to the diketo form. A total of 244 trajectories were run starting from this transition state, yielding pentane-2,4-dione radical cation and depositing energy in the terminal CC bond. As a result, the branching ratio for dissociation of the terminal CC bond versus the interior CC bonds is significantly larger than expected from RRKM theory. The branching ratio for the dissociation of the two interior CC bonds is ?20:1, with the one closest to the activated methyl breaking more often. Since the two interior bonds are equivalent and should dissociate with equal probability, this branching ratio represents a very large deviation from statistical behavior. A simple kinetic scheme has been constructed to model the dissociation rates. The nonstatistical behavior is seen because the rate of energy flow within the molecule is comparable to or less than the rates of dissociation for the activated system. In addition to the expected dissociation products, some of the trajectories also lead to the formation of an ester-like product, prop-1-en-2-yl acetate radical cation. PMID:22893922

Zhou, Jia; Schlegel, Bernhard

2009-02-26

249

First-principles study of water adsorption and dissociation on the UO2 (1 1 1), (1 1 0) and (1 0 0) surfaces  

NASA Astrophysics Data System (ADS)

The adsorption and dissociation behaviors of water molecule on the UO2 (1 1 1), (1 1 0) and (1 0 0) surfaces were investigated using first-principles methods within the DFT+U framework. For a single water molecule at 1/4 ML coverage, the molecular adsorption exhibits comparable adsorption energies with the dissociative adsorption on the (1 1 1) surface, while it is far less stable than the dissociative adsorption on the (1 1 0) and (1 0 0) surfaces. We find that the adsorbed molecular and dissociative water tend to cluster on low-index UO2 surfaces by forming hydrogen-bond networks. The adsorption stability of water depends on the synergistic effect of hydrogen bonding interaction and steric effect between adsorbates. The mixed adsorption configuration of molecular and dissociative water in 1:1 mol ratio is found to be thermally more stable on the UO2 (1 1 1) and (1 1 0) surfaces.

Bo, Tao; Lan, Jian-Hui; Zhao, Yao-Lin; Zhang, Yu-Juan; He, Chao-Hui; Chai, Zhi-Fang; Shi, Wei-Qun

2014-11-01

250

Approaching the exact energy for H/sub 2/: Bond functions vs polarization functions  

SciTech Connect

Configuration interaction calculations are reported for hydrogen molecule. The relative efficiency of nuclear-centered polarization functions, verses mid-bond functions, in lowering the absolute energy of hydrogen molecule is examined.(AIP)

Wright, J.S.; Barclay, V.J.

1987-03-01

251

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

E-print Network

methodology and com- putational facilities, transition metal molecules remain diffi- cult systems for the electronic structure of the molecule is to be obtained. The bond energy is among the most diffi- cult

Morse, Michael D.

252

Fluorescein and Rosamine Derivatives as Donors/Acceptors for "Through-bond" Energy Transfer Cassettes  

E-print Network

A series of fluorescein and rosamine derivatives have been prepared and their spectroscopical properties analyzed to determine their usefulness as donor and/or acceptors in "through-bond" energy transfer systems. Such new systems have been tailored...

Castro, Juan C.

2010-07-14

253

The adsorption and dissociation of CO on Fe(111)  

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

254

Correction: A reduced radial potential energy function for the halogen bond and the hydrogen bond in complexes BXY and BHX, where X and Y are halogen atoms.  

PubMed

Correction for 'A reduced radial potential energy function for the halogen bond and the hydrogen bond in complexes BXY and BHX, where X and Y are halogen atoms' by Anthony C. Legon, Phys. Chem. Chem. Phys., 2014, 16, 12415-12421. PMID:25325573

Legon, Anthony C

2014-12-01

255

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

256

Interlayer contraction in Mg B2 upon replacement of Mg by Al: Effect of the covalent bond energy  

NASA Astrophysics Data System (ADS)

The partitioning of the cohesive energy which we derived recently from the total energy expression of density functional theory [J. Phys.: Condens. Matter 13, 11541 (2001)] allows us to quantify the energy Ecov that describes the covalent and the metallic bond energy in a periodic solid. We apply this methodology to analyze various bonds in MgB2 and AlB2 . We find that the experimentally observed interlayer contraction when going from MgB2 to AlB2 is consistent with the calculated larger Ecov energy of the Al-B bond compared to the Mg-B bond. We further explain this result by the filling of bonding states in the boron- p-Al-p bonds as revealed by the energy resolved covalent bond energy Ecov(E) .

Bester, Gabriel; Fähnle, Manfred

2005-09-01

257

Raman spectroscopic determination of the length, energy, Debye temperature, and compressibility of the C-C bond in carbon allotropes  

NASA Astrophysics Data System (ADS)

Raman phonon relaxation dynamics in carbon allotropes including graphene, carbon nanotube, C60, carbon nanobud, graphite, and diamond has been formulated in terms of the bond order-length-strength (BOLS) correlation. The length and energy responses of the representative bond to the change of coordination environment, pressure, and temperature determine intrinsically the Raman shifts. Reproduction of the measured results in quantitative information of the bond length, bond energy, mode cohesive energy, binding energy density, Debye temperature, and the compressibility of the C-C bond in each phase without needing involvement of the phonon scattering resonant processes or the mode Grüneisen constants.

Yang, X. X.; Zhou, Z. F.; Wang, Yan; Li, J. W.; Guo, N. G.; Zheng, W. T.; Peng, J. Z.; Sun, C. Q.

2013-06-01

258

Dissociative adsorption of O2 on Pt and Au surfaces: Potential-energy surfaces and electronic states  

NASA Astrophysics Data System (ADS)

Using density functional theory, we investigate the difference in the reactive pathways and potential-energy surfaces for the dissociative adsorption of oxygen (O2) on platinum (Pt) and gold (Au) surfaces. We found that the reactivity on Au surface can be improved by changing the surface structure. However, it does not exceed that on Pt surface. We also found that the difference of the reactivity can be attributed to the affinity between metal surface and oxygen atom, and not between metal surface and oxygen molecule. This conclusion is further corroborated by our calculated atom-projected density of states results, which show that the difference in reactivity comes from the difference in the hybridization strength between electrons of oxygen and those of the metal surface.

Yotsuhashi, Satoshi; Yamada, Yuka; Kishi, Tomoya; Diño, Wilson Agerico; Nakanishi, Hiroshi; Kasai, Hideaki

2008-03-01

259

Collision-induced dissociation of fluoropyridinide anions  

NASA Astrophysics Data System (ADS)

Collision-induced dissociation of ortho-fluoro, meta-fluoro, and 2,6-difluoropyridinide anions are studied using the selected ion flow tube technique. Structures and energetics of the reactants, transition states, and products are calculated at the MP4(SDQ)/6-31 + G(d) level of theory based on the B3LYP/6-311++G(d,p) and/or MP2/6-31 + G(d) optimized geometries. The monofluoropyridinide anions (C5NH3F-) dissociate almost exclusively via loss of an HF molecule, i.e., C5NH2- + HF at low collision energies, in addition to loss of F- at higher energies. 2,6-Difluoropyridinide anions (C5NH2F2-) dissociate via successive loss of HF molecules to form C5NHF- then C5N- depending on the collision energy. The CID results strongly suggest formation of ring-intact pyridynide structures (C5NH2-, C5NHF-) with a bent triple bond embedded in the azine ring systems. Calculated reaction energy diagrams are totally consistent with the experimental observations. Didehydropyridynides C5NH2- and C5NHF- have substantial barriers to decomposition. Tetradehydropyridynide C5N- is a highly strained ring system and metastable with a predicted barrier of about 5 kcal mol-1 (20 kJ mol-1) toward ring-opening to a linear NCCCCC- structure. The observed C5N- species is most likely the linear anion under experimental conditions; however, the ring-intact C5N- pyridynide is a highly energetic species releasing about 80 kcal mol-1 (340 kJ mol-1) of energy upon the ring-opening.

Kato, Shuji; Lineberger, W. Carl; Bierbaum, Veronica M.

2007-10-01

260

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

E-print Network

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

Alavi, Ali

261

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

262

The enthalpy of formation of fullerene fluoride C60F18 and the C-F bond energy  

NASA Astrophysics Data System (ADS)

The enthalpy of combustion of crystalline fullerene fluoride C60F18 was determined in an isoperibolic calorimeter with a rotating platinized bomb, and the enthalpy of formation of the compound was calculated. The enthalpy of sublimation of C60F18 measured earlier was used to calculate the enthalpy of formation of fullerene fluoride in the gas phase and the mean enthalpy of dissociation of C-F bonds in this compound.

Papina, T. S.; Luk'yanova, V. A.; Goryunkov, A. A.; Ioffe, I. N.; Gol'Dt, I. V.; Buyanovskaya, A. G.; Kabaeva, N. M.; Sidorov, L. N.

2007-10-01

263

Excited state dynamics of liquid water: Insight from the dissociation reaction following two-photon excitation  

E-print Network

We use transient absorption spectroscopy to monitor the ionization and dissociation products following two-photon excitation of pure liquid water. The two decay mechanisms occur with similar yield for an excitation energy of 9.3 eV, whereas the major channel at 8.3 eV is dissociation. The geminate recombination kinetics of the H and OH fragments, which can be followed in the transient absorption probed at 267 nm, provide a window on the dissociation dynamics at the lower excitation energy. Modeling the OH geminate recombination indicates that the dissociating H atoms have enough kinetic energy to escape the solvent cage and one or two additional solvent shells. The average initial separation of H and OH fragments is 0.7+-0.2 nm. Our observation suggests that the hydrogen bonding environment does not prevent direct dissociation of an O-H bond in the excited state. We discuss the implications of our measurement for the excited state dynamics of liquid water and explore the role of those dynamics in the ionizati...

Elles, C G; Crowell, R A; Shkrob, I A; Bradforth, Stephen E.; Crowell, Robert A.; Elles, Christopher G.; Shkrob, Ilya A.

2007-01-01

264

Dissociative recombination of CH4(+).  

PubMed

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

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

2013-10-01

265

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

266

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

PubMed

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

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

2014-11-21

267

Cis ?trans, trans ?cis isomerizations and N-O bond dissociation of nitrous acid (HONO) on an ab initio potential surface obtained by novelty sampling and feed-forward neural network fitting  

NASA Astrophysics Data System (ADS)

The isomerization and dissociation dynamics of HONO are investigated on an ab initio potential surface obtained by fitting the results of electronic structure calculations at 21 584 configurations by using previously described novelty sampling and feed-forward neural network (NN) methods. The electronic structure calculations are executed by using GAUSSIAN 98 with a 6-311G(d) basis set at the MP4(SDQ) level of accuracy. The average absolute error of the NN fits varies from 0.012eV (1.22kJmol-1) to 0.017eV (1.64kJmol-1). The average computation time for a HONO trajectory using a single NN surface is approximately 4.8s. These computation times compare very favorably with those required by other methods primarily because the NN fitting needs to be executed only one time rather than at every integration point. If the average result obtained from a committee of NNs is employed at each point rather than a single NN, increased fitting accuracy can be achieved at the expense of increased computational requirements. In the present investigation, we find that a committee comprising five NN potentials reduces the average absolute interpolation error to 0.0111eV (1.07kJmol-1). Cis-trans isomerization rates with total energy of 1.70eV (including zero point energy) have been computed for a variety of different initial distributions of the internal energy. In contrast to results previously reported by using an empirical potential, where cis ?trans to trans ?cis rate coefficient ratios at 1.70eV total energy were found to lie in the range of 2.0-12.9 depending on the vibration mode excited, these ratios on the ab initio NN potential lie in the range of 0.63-1.94. It is suggested that this result is a reflection of much larger intramode coupling terms present in the ab initio potential surface. A direct consequence of this increased coupling is a significant decrease in the mode specific rate enhancement when compared to results obtained by using empirical surfaces. All isomerizations are found to be first order in accordance with the results reported by using empirical potentials. The dissociation rate to NO +OH has been investigated at internal HONO energies of 3.10 and 3.30eV for different distributions of this energy among the six vibrational modes of HONO. These dissociations are also found to be first order. The computed dissociation rate coefficients exhibit only modest mode specific rate enhancement that is significantly smaller than that obtained on an empirical surface because of the much larger mode couplings present on the ab initio surface.

Le, Hung M.; Raff, Lionel M.

2008-05-01

268

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

269

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

E-print Network

excitation is the main mechanism in CID at kiloelectronvolt incident energy. Vibrational excitation also was the dominant excitation mechanism at kiloelectronvolt translational energy and that vibrational excitation via mechanism, i.e., vibrational excitation dominating at low collision energy and electronic excitation at high

Kim, Myung Soo

270

Dissociative Identity Disorder  

MedlinePLUS

Dissociative Identity Disorder What is dissociative identity disorder (DID)? Dissociative identity disorder (DID), previously referred to as ... among their possessions. What are the symptoms of DID? Often people living with DID are depressed or ...

271

A Vision of Interdisciplinary Education: Students' Reasoning about "High-Energy Bonds" and ATP  

E-print Network

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 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 nuanc...

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

2014-01-01

272

Spectroscopic constants of diatomic molecules computed correcting Hartree-Fock or general-valence-bond potential-energy curves with correlation-energy functionals  

NASA Astrophysics Data System (ADS)

The Kohn-Sham energy with exact exchange [using the exact Hartree-Fock (HF) exchange but an approximate correlation-energy functional] may be computed very accurately by adding the correlation obtained from the HF density to the total HF energy. Three density functionals are used: local spin density (LSD), LSD with self-interaction correction, and LSD with generalized gradient correction. This scheme has been extended (Lie-Clementi, Colle-Salvetti, and Moscardo-San-Fabian) to be used with general-valence-bond (GVB) energies and wave functions, so that the extra correlation included in the GVB energy is not counted again. The effect of all these approximate correlations on HF or GVB spectroscopic constants (Re,?e, and De) is studied. Approximate relations showing how correlation affects them are derived, and may be summarized as follows: (1) the effect on Re and ?e depends only on the correlation derivative at Re, and (2) the effect on De depends mainly on the correlation difference between quasidissociated and equilibrium geometries. A consequence is that all the correlation corrections tested here give larger ?e and De and shorter Re than the uncorrected HF or GVB values. This trend is correct for De for both HF and GVB. For Re and ?e, it is correct in most cases for GVB, but it often fails for the HF cases. A comparison is made with Kohn-Sham calculations with both exchange and correlation approximated. As a final conclusion, it is found that, within the present scheme, a qualitatively correct HF or GVB potential-energy curve, together with a correlation-energy approximation with correct dissociation behavior, is crucial for obtaining good estimates of spectroscopic constants.

Pérez-Jordá, José M.; San-Fabián, Emilio; Moscardó, Federico

1992-04-01

273

Explicitly correlated coupled cluster calculations of the dissociation energies and barriers to concerted hydrogen exchange of (HF)n oligomers (n=2,3,4,5)  

Microsoft Academic Search

The electronic dissociation energies and barriers to concerted hydrogen exchange of (HF)n oligomers with n = 2 ,...,5 are computed by means of a many-body decomposition of the total electronic energy. The one- and two-body terms are obtained from explicitly correlated coupled cluster calculations including singles, doubles, and a perturbative triples correction (CCSD(T)-R12), in a large Gaussian basis set consisting

Wim Klopper Martin Quack Martin A. Suhm

1998-01-01

274

High-energy collision-induced dissociation by MALDI TOF/TOF causes charge-remote fragmentation of steroid sulfates.  

PubMed

A method for structural elucidation of biomolecules dating to the 1980s utilized high-energy collisions (~10 keV, laboratory frame) that induced charge-remote fragmentations (CRF), a class of fragmentations particularly informative for lipids, steroids, surfactants, and peptides. Unfortunately, the capability for high-energy activation has largely disappeared with the demise of magnetic sector instruments. With the latest designs of tandem time-of-flight mass spectrometers (TOF/TOF), however, this capability is now being restored to coincide with the renewed interest in metabolites and lipids, including steroid-sulfates and other steroid metabolites. For these metabolites, structure determinations are required at concentration levels below that appropriate for NMR. To meet this need, we explored CRF with TOF/TOF mass spectrometry for two groups of steroid sulfates, 3-sulfates and 21-sulfates. We demonstrated that the current generation of MALDI TOF/TOF instruments can generate charge-remote fragmentations for these materials. The resulting collision-induced dissociation (CID) spectra are useful for positional isomer differentiation and very often allow the complete structure determination of the steroid. We also propose a new nomenclature that directly indicates the cleavage sites on the steroid ring with carbon numbers. PMID:24781458

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

2014-08-01

275

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

276

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

277

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

278

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

279

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

280

Dissociation of Bimolecular aIIbb3-Fibrinogen Complex under a Constant Tensile Force  

E-print Network

Dissociation of Bimolecular aIIbb3-Fibrinogen Complex under a Constant Tensile Force Rustem I the thermodynamics and kinetics of aIIbb3- fibrinogen bond formation and dissociation under constant unbinding forces

Barsegov, Valeri

281

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

282

Energy transfer mediated by asymmetric hydrogen-bonded interfaces†  

PubMed Central

Amidine-appended ferrocene derivatives form a supramolecular assembly with Ru(ii)(bpy-COOH) (L)22+ complexes (bpy-COOH is 4-CO2H-4?-CH3-bpy and L = bpy, 2,2?-bipyridine or btfmbpy, 4,4?-bis (trifluoromethyl)-2,2?-bipyridine). Steady-state, time-resolved spectroscopy and kinetic isotope effects establish that the metal-to-ligand charge transfer excited states of the Ru(ii) complexes are quenched by proton-coupled energy transfer (PCEnT). These results show that proton motion can be effective in mediating not only electron transfer (ET) but energy transfer (EnT) as well. PMID:24363889

Young, Elizabeth R.; Rosenthal, Joel

2013-01-01

283

Gold-catalyzed C(sp3)-H bond functionalization.  

PubMed

C-H bonds are ubiquitous in organic molecules. Homogenous gold-catalyzed direct functionalization of unsaturated C-H bonds has emerged as a powerful method in our synthetic toolbox. However, Csp(3)-H bonds have larger dissociation energy and lower proton acidity, and thus the efficient and exquisitely selective cleavage of this kind of chemical bonds for the formation of new carbon-carbon and carbon-heteroatom bonds is still a great challenge. In this tutorial review, we will highlight the recent achievements of gold-catalyzed oxidative and redox-neutral Csp(3)-H bond functionalization, which opens new avenues for economical and sustainable construction of fine chemicals. PMID:24853478

Xie, Jin; Pan, Changduo; Abdukader, Ablimit; Zhu, Chengjian

2014-08-01

284

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

285

The Generation of High Energy Ions by Photo-Induced Dissociation of Atomic Clusters  

Microsoft Academic Search

The interaction of an intense laser pulse of sub-picosecond duration with an atomic cluster larger than a few hundred atoms can be extremely energetic. The high local density within the cluster together with a dynamic dielectric resonance in the expanding cluster microplasma greatly enhance coupling of the laser to both ion and electron kinetic energies. In contrast to the few

R. A. Smith; J. W. G. Tisch; T. Ditmire; E. Springate; N. Hay; M. B. Mason; E. T. Gumbrell; A. J. Comley; L. C. Mountford; J. P. Marangos; M. H. R. Hutchinson

1999-01-01

286

Dynamics on the HOCO potential energy surface studied by dissociative photodetachment of HOCO-  

E-print Network

-consistent field/ multireference configuration interaction calculation with all 17 valence electrons and 13 valence potential energy surface PES for the ground electronic state X 2 A of the HOCO complex that governs the OH al. in 1987, using singly and doubly excited configuration inter- action calculations and a many

Continetti, Robert E.

287

Water adsorption and dissociation on BeO (001) and (100) surfaces  

E-print Network

Plateaus in water adsorption isotherms on hydroxylated BeO surfaces suggest significant differences between the hydroxylated (100) and (001) surface structures and reactivities. Density functional theory structures and energies clarify these differences. Using relaxed surface energies, a Wulff construction yields a prism crystal shape exposing long (100) sides and much smaller (001) faces. This is consistent with the BeO prisms observed when beryllium metal is oxidized. A water oxygen atom binds to a single surface beryllium ion in the preferred adsorption geometry on either surface. The water oxygen/beryllium bonding is stronger on the surface with greater beryllium atom exposure, namely the less-stable (001) surface. Water/beryllium coordination facilitates water dissociation. On the (001) surface, the dissociation products are a hydroxide bridging two beryllium ions and a metal coordinated hydride with some surface charge depletion. On the (100) surface, water dissociates into a hydroxide ligating a Be ato...

Gómez, M A; Kress, J D; Pratt, L R; Gomez, Maria A.; Kress, Joel D.; Pratt, Lawrence R.

2007-01-01

288

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

PubMed

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

Roux, María Victoria; Temprado, Manuel; Jiménez, Pilar; Dávalos, Juan Zenón; Notario, Rafael; Guzmán-Mejía, Ramón; Juaristi, Eusebio

2003-03-01

289

The energy of the intramolecular hydrogen bond in chloro-substituted N-methyl-salicylidene imines  

NASA Astrophysics Data System (ADS)

The energetic effects of the conformational rearrangement of eight Schiff bases, differently chloro-substituted, are discussed on the basis of the results of B3LYP/6-31+G(d,p) calculations. The proton transfer tautomers as well as "open"-non-hydrogen-bonded forms were considered. It was found, that the hydrogen-bonded forms have the lowest energy, but the second most stable were the proton transfer states with an O…H sbnd N intramolecular hydrogen bond. The proton transfer in Schiff bases dominates in comparison to other conformational rearrangements. This is important for the understanding of thermochromic and photochromic properties of these molecules. By using a thermodynamic cycle, the steric effects connected with chelate ring formation are estimated to be up to 5 kcal/mol, much higher than in related Mannich bases (˜1 kcal/mol) which do not form resonance assisted hydrogen bonds. Accounting these effects the "real" value of the energy of hydrogen bond formation was estimated to be 15 kcal/mol which increases with growing number of chlorine atoms up to 16.5 kcal/mol for 4,5,6-trichloro substitution.

Koll, A.; Karpfen, A.; Wolschann, P.

2007-11-01

290

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

291

Dissociation Channels of c-C4F8 to CF2 Radical in Reactive Plasma  

NASA Astrophysics Data System (ADS)

It has been generally assumed that octafluorocyclobutane (c-C4F8) is mainly decomposed to CF2 via C2F4 in etching process plasma. However, the detailed mechanism for the dissociations is yet ambiguous. In this paper we have calculated the probable dissociation pathways by using ab initio molecular orbital method. The results show that c-C4F8 is dissociated via the first triplet excited state T1(3A2), the fourth triplet excited state T4(32E) and the fourth singlet excited state S4(12E). One of the degenerate excited states of T4 and S4 is constituted by antibonding combination of two ? bonding orbital of C2F4. T1 state is constituted by antibonding combination of b1u antibonding ? orbital of C2F4. Therefore, in the case of the dissociation via S4 and T4 excited states c-C4F8 may dissociate to two C2F4, and in the case of the dissociation via T1 excited state c-C4F8 may dissociate to four CF2 radicals. It is also found that C3F5+ ion observed as the main peak in c-C4F8 process plasma is produced by electron collision with the slightly larger energy than the ionization threshold value. The main dissociation path of C2F4 is a vertical electron attachment. However, it is also found that dissociation pathways via 1B2g, 3B1u, and 3B2g excited states are very important and should not be ignored.

Hayashi, Toshio; Ishikawa, Kenji; Sekine, Makoto; Hori, Masaru; Kono, Akihiro; Suu, Koukou

2011-03-01

292

The dissociation dynamics of low lying triplet states in butane and butene molecules  

NASA Astrophysics Data System (ADS)

Butane, methylpropane, 1-,2-butene and isobutene are studied as a complete set of doubley methylated ethane and ethene molecules in order to probe the dissociation dynamics of their excited states. The butane and butene molecules are formed in electronically highly excited states by neutralization of their respective radical cations in collisions with alkali metal atoms. Processes that lead to dissociations into two fragments are measured with differential translational spectroscopy. it is found that the first triplet state is dominantly populated. Butanes exhibit direct dissociation of a carbon?carbon (C?C) bond via a repulsive state. Intramolecular vibrational energy redistribution (IVR) prior to dissociation is observed for the unsaturated butenes. For the butenes the C?C bond cleavage is even preceded by a hydrogen shift, resulting in molecular losses like methane and ethene. In this paper we stress the relations between the present results and optical excitation and electron scattering experiments. For butane the proposed dissociation via a repulsive triplet state is corroborated in ab initio calculations.

Beijersbergen, Jaap H. M.; de Koster, Chris. G.; van der Zande, Win J.; Kistemaker, Piet G.; Los, Joop

1992-02-01

293

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

294

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

295

Covalent bonding effect on the mean excitation energy of H2 with the local plasma model  

NASA Technical Reports Server (NTRS)

Chemical bonding is taken into account explicitly in the determination of the mean excitation energy (I) for stopping power of H2 with the local plasma approximation by employing molecular electronic wave functions for H2 for the first time. This procedure leads to a new value for IH2 that is higher than all accepted experimental and theoretical values.

Kamaratos, E.

1984-01-01

296

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

NASA Astrophysics Data System (ADS)

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

Mauguière, F. A. L.; Collins, P.; Ezra, G. S.; Wiggins, S.

2013-04-01

297

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

298

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

299

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

PubMed

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

Hart-Smith, Gene; Raftery, Mark J

2012-01-01

300

Structural determination of glycosphingolipids as lithiated adducts by electrospray ionization mass spectrometry using low-energy collisional-activated dissociation on a triple stage quadrupole instrument  

Microsoft Academic Search

Structural characterization of glycosphingolipids as their lithiated adducts using low-energy collisional-activated dissociation\\u000a (CAD) tandem mass spectrometry with electrospray ionization (ESI) is described. The tandem mass spectra contain abundant fragment\\u000a ions reflecting the long chain base (LCB), fatty acid, and the sugar constituent of the molecule and permit unequivocal identification\\u000a of cerebrosides, di-, trihexosyl ceramides and globosides. The major fragmentation pathways

Fong-Fu Hsu; John Turk

2001-01-01

301

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

302

Biradical thermochemistry from collision-induced dissociation threshold energy measurements. Absolute heats of formation of ortho-, meta-, and para-benzyne  

Microsoft Academic Search

The absolute heats of formation of 1,2-, 1,3-, and 1,4-dehydrobenzene (ortho, meta-, and para-benzyne) have been determined from measurements of the threshold energies for collision-induced dissociation (CID) of ortho, meta-, and para-chlorophenyl anions in a flowing afterglow-triple quadrupole apparatus. The 298 K heats of formation for ortho-, meta-, and para-benzyne derived in this manner are 106.6 [+-] 3.0, 122.0 [+-

Paul G. Wenthold; Robert R. Squires

1994-01-01

303

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

NASA Technical Reports Server (NTRS)

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

Jackels, C. F.

1985-01-01

304

Quantum enhancement of vibrational predissociation near the dissociation threshold  

NASA Astrophysics Data System (ADS)

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

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

2004-01-01

305

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

Microsoft Academic Search

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 HO-OH complex of the dissociated final state, which lowers the water dissociation

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

2007-01-01

306

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

307

Calculation of rate constants for dissociative attachment of low-energy electrons to hydrogen halides HCl, HBr, and HI and their deuterated analogs  

SciTech Connect

Calculations of rate constants for the process of dissociative attachment of low-energy electrons to hydrogen halides HCl, HBr, and HI and for the reverse process of associative detachment based on the nonlocal resonance model are reported. The calculated data are of importance for the modeling of plasma processes, environmental chemistry, etc. The calculated dissociative attachment rate constants are found to be in good agreement with existing experimental data. It is shown that at low temperatures the rate constants are very sensitive to small changes of the parameters of the nonlocal resonance model used for the calculation of the rate constants and represent a severe test of the theory. The isotopic effect and its dependence on the temperature is also discussed. The calculations of rate constants for the reverse process of associative detachment are also reported and discussed.

Houfek, Karel; Cizek, Martin; Horacek, Jiri [Institute of Theoretical Physics, Faculty of Mathematics and Physics, Charles University, V Holesovickach 2, 180 00 Prague 8 (Czech Republic)

2002-12-01

308

Estimation of individual binding energies in some dimers involving multiple hydrogen bonds using topological properties of electron charge density  

Microsoft Academic Search

Individual hydrogen bond (HB) energies have been estimated in several systems involving multiple HBs such as adenine–thymine and guanine–cytosine using electron charge densities calculated at X?H hydrogen bond critical points (HBCPs) by atoms in molecules (AIM) method at B3LYP\\/6-311++G?? and MP2\\/6-311++G?? levels. A symmetrical system with two identical H bonds has been selected to search for simple relations between ?HBCP

A. Ebrahimi; S. M. Habibi Khorassani; H. Delarami

2009-01-01

309

Dissociation and dissociative ionization of H2+ using the time-dependent surface flux method  

E-print Network

The time-dependent surface flux method developed for the description of electronic spectra [L. Tao and A. Scrinzi, New J. Phys. 14, 013021 (2012); A. Scrinzi, New J. Phys. 14, 085008 (2012)] is extended to treat dissociation and dissociative ionization processes of H2+ interacting with strong laser pulses. By dividing the simulation volume into proper spatial regions associated with the individual reaction channels and monitoring the probability flux, the joint energy spectrum for the dissociative ionization process and the energy spectrum for dissociation is obtained. The methodology is illustrated by solving the time-dependent Schr\\"{o}dinger equation (TDSE) for a collinear one-dimensional model of H2+ with electronic and nuclear motions treated exactly and validated by comparison with published results for dissociative ionization. The results for dissociation are qualitatively explained by analysis based on dressed diabatic Floquet potential energy curves, and the method is used to investigate the breakdow...

Yue, Lun

2014-01-01

310

Full-dimensional quantum calculations of the dissociation energy, zero-point, and 10 K properties of H7+/D7+ clusters using an ab initio potential energy surface.  

PubMed

Diffusion Monte Carlo (DMC) and path-integral Monte Carlo computations of the vibrational ground state and 10 K equilibrium state properties of the H7 (+)/D7 (+) cations are presented, using an ab initio full-dimensional potential energy surface. The DMC zero-point energies of dissociated fragments H5 (+)(D5 (+))+H2(D2) are also calculated and from these results and the electronic dissociation energy, dissociation energies, D0, of 752 ± 15 and 980 ± 14 cm(-1) are reported for H7 (+) and D7 (+), respectively. Due to the known error in the electronic dissociation energy of the potential surface, these quantities are underestimated by roughly 65 cm(-1). These values are rigorously determined for first time, and compared with previous theoretical estimates from electronic structure calculations using standard harmonic analysis, and available experimental measurements. Probability density distributions are also computed for the ground vibrational and 10 K state of H7 (+) and D7 (+). These are qualitatively described as a central H3 (+)/D3 (+) core surrounded by "solvent" H2/D2 molecules that nearly freely rotate. PMID:23862944

Barragán, Patricia; Pérez de Tudela, Ricardo; Qu, Chen; Prosmiti, Rita; Bowman, Joel M

2013-07-14

311

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

E-print Network

approximation and make predictions about the zero point energy ZPE for isotopically substituted molecules and their relative differ- ences ZPE . The shift of the ZPE between isotopologues is not di- rectly accessible . Therefore, D0 is a direct test of the BO approximation at high energies and an accurate measurement of ZPE

312

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

313

A temporal dissociation of energy liberation and high energy phosphate splitting during shortening in frog skeletal muscles  

PubMed Central

Measurements of the time course of high energy phosphate splitting and energy liberation were performed on rapidly shortening Rana pipiens skeletal muscles. In muscles contracting 30 times against small loads (less the 0.02P), the ratio of explained heat + work (H + W) (calculated from the measured high energy phosphate splitting) to observed H + W (from myothermal and mechanical measurements) was 0.68 +/- 0.08 and is in agreement with results obtained in isometric tetani of R. pipiens skeletal muscle. In lightly afterloaded muscles which were tetanized for 0.6a and whose metabolism was arrested at 3.0 s after the beginning of stimulation, a similar ratio of explained H + W to observed H + W was obtained. However, in identical contractions in which metabolism was arrested at 0.5-0.75 s after the beginning of stimulation, the ratio of explained H + W to observed H + W declined significantly to values ranging from 0.15 to 0.40. These results suggest that rapid shortening at the beginning of contraction induces a delay between energy production and measurable high energy phosphate splitting. This interpretation was tested and confirmed in experiments in which one muscle of a pair contracted isometrically while the other contracted against a small afterload. The afterload and stimulus pattern were arranged so that at the time metabolism was arrested, 0.5 s after the beginning of stimulation, the total energy production by both muscles was the same. Chemical analysis revealed that the isotonically contracting muscle spilt only 25% as much high energy phosphate as did the isometrically contracting muscle. PMID:1084912

1976-01-01

314

Primary events in photoacid dissociation Department of Physical Chemistry and the Fritz Haber Research Center, \\Lambda  

E-print Network

in the role of the solvent, e.g. water, in promoting acid dissociation and in the hydrogen­bond (HB) rearrangements which accompany it. Strong acids dissociate in water much too fast. Hence mixing cannot servePrimary events in photoacid dissociation Noam Agmon Department of Physical Chemistry and the Fritz

Agmon, Noam

315

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

NASA Astrophysics Data System (ADS)

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 H2 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 H2 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; Wang, Yangang; Hupalo, Myron; McDougall, Dan; Tringides, Michael; Ho, Kaiming

2013-12-01

316

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

317

ELECTRON INDUCED DISSOCIATION OF GLYCOSAMINOGLYCAN TETRASACCHARIDES  

PubMed Central

Electron detachment dissociation (EDD) Fourier transform mass spectrometry has recently been shown to be a powerful tool for examining the structural features of sulfated glycosaminoglycans (GAGs). The characteristics of GAG fragmentation by EDD include abundant cross-ring fragmentation primarily on hexuronic acid residues, cleavage of all glycosidic bonds, and the formation of even- and odd-electron product ions. GAG dissociation by EDD has been proposed to occur through the formation of an excited species that can undergo direct decomposition, or eject an electron which then undergoes dissociation. In this work, we perform electron induced dissociation (EID) on singly-charged GAGs to identify products that form via direct decomposition by eliminating the pathway of electron detachment. EID of GAG tetrasaccharides produces cleavage of all glycosidic bonds and abundant cross-ring fragmentation primarily on hexuronic acid residues, producing fragmentation similar to EDD of the same molecules, but distinctly different from the products of infrared multiphoton dissociation or collisionally activated decomposition. These results suggest that observed abundant fragmentation of hexuronic acid residues occurs due to their increased lability when they undergo electronic excitation. EID fragmentation of GAG tetrasaccharides results in both even- and odd-electron products. EID of heparan sulfate tetrasaccharide epimers produces identical fragmentation, in contrast to EDD, in which the epimers can be distinguished by their fragment ions. These data suggest that for EDD, electron detachment play a significant role in distinguishing glucuronic acid from iduronic acid. PMID:18657442

Wolff, Jeremy J.; Laremore, Tatiana N.; Aslam, Hammad; Linhardt, Robert J.; Amster, I. Jonathan

2008-01-01

318

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

319

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

320

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

PubMed

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

Kolli, Venkata; Dodds, Eric D

2014-05-01

321

Dissociative adsorption of pyrrole on Si(111)-(7×7)  

NASA Astrophysics Data System (ADS)

Pyrrole adsorption on Si(111)-(7×7) has been investigated using high-resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy, scanning tunneling microscopy (STM), and theoretical calculations. Compared to physisorbed pyrrole, chemisorption leads to the appearance of N-Si and Si-H vibrational features, together with the absence of N-H stretching mode. This clearly demonstrates the dissociative nature of pyrrole chemically binding on Si(111)-(7×7) through the breakage of N-H bond. Based on STM results, the resulting fragments of pyrrolyl and H atom are proposed to bind with an adatom and an adjacent rest atom, respectively. The STM images further reveal that the adsorption is site selective. The faulted center adatoms are most favored, followed by unfaulted center adatoms, faulted corner adatoms, and unfaulted corner adatoms. In addition, the chainlike pattern of reacted adatoms was observed, implying the possible existence of attractive interaction between adsorbed pyrrolyl and the precursor state. Theoretical calculation confirms that the dissociative adsorption with pyrrolyl bonded to an adatom and H atom to an adjacent rest atom is energetically favored compared to the associative cycloaddition involving the two ?-carbon atoms of pyrrole and an adatom-rest atom pair.

Yuan, Ze Liang; Chen, Xian Feng; Wang, Zhong Hai; Yong, Kian Soon; Cao, Yong; Xu, Guo Qin

2003-11-01

322

Comparison of DFT with Traditional Methods for the Calculation of Vibrational Frequencies and Bond Energies  

NASA Technical Reports Server (NTRS)

The vibrational frequencies of MO2 are computed at many levels of theory, including HF, B3LYP, BP86, CASSCF, MP2, and CCSD(T). The computed results are compared with the available experimental results. Most of the methods fail for at least one state of the systems considered. The accuracy of the results and the origin of the observed failures are discussed. The B3LYP bond energies are compared with traditional methods for a variety of systems, ranging from FeCOn+ to SiCln and its positive ions. The cases where B3LYP differs from the traditional methods are discussed.

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

1997-01-01

323

Single-Molecule Investigations of RNA Dissociation  

Microsoft Academic Search

Given the essential cellular roles for ribonucleic acids (RNAs) it is important to understand the stability of three-dimensional structures formed by these molecules. This study aims to investigate the dissociation energy landscape for simple RNA structures via atomic-force-microscopy-based single-molecule force-spectroscopy measurements. This approach provides details on the locations and relative heights of the energy barriers to dissociation, and thus information

Nicola H. Green; Philip M. Williams; Omar Wahab; Martyn C. Davies; Clive J. Roberts; Saul J. B. Tendler; Stephanie Allen

2004-01-01

324

Dissociation and Dissociative Identity Disorder: Treatment Guidelines and Cautions  

Microsoft Academic Search

?? ? Interest in dissociation and dissociative disorders has waxed and waned from the time of Janet’s (1889) landmark writings to contemporary attempts to understand dissociative phenomena in light of competing explanatory models and increasingly sophisticated experimental methods. From the eclipse of dissociation theory by early psychoanalytic theory, to the attack on dissociation by experimentalists later in the century (Rosenberg,

Steven Jay Lynn; Oliver Fassler; Joshua A. Knox; Scott O. Lilienfeld

325

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  

NASA Astrophysics Data System (ADS)

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 6.44eV 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.

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

2007-10-01

326

Dissociation of dicarboxylate and disulfonate dianions.  

PubMed

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 CO(2) and SO(3) 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 (SO(3)(-)) resulted in a single dissociation channel leading to observation of SO(3)(-) and its anion conjugate pair, whereas the carboxylate (CO(2)(-)) containing dianions dissociated via loss of one or both CO(2) molecules and an electron. The SO(3)(-) 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 CO(2) 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 (tau>1.5 s). We conclude that the carboxylate (CO(2)(-)) 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. PMID:20210392

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

2010-03-01

327

Measurement of in-situ hydrate dissociation properties. Final technical report, October 1, 1983-October 1, 1985  

SciTech Connect

In order to recover gas from hydrate reserves, it is necessary for heat to flow in order to dissociate the water bonds in the hydrate structure. The question of heat flow is central to any inhibitor injection, or dissociation by hot fluids because the molecules in the resulting fluid phases have more energy than those still trapped in the solid hydrate phase. The source of the energy given to the fluid molecules may be the reserve itself, the surrounding earth, or hot fluids such as steam or geothermal brines. In this work, we measured the rate of hydrate dissociation as a function of heat input, at low, constant pressure. We also measured the thermodynamic parameters of heat capacity and heat of dissociation, which we then used in two mathematical models we generated for hydrate dissociation. The more complex mathematical model (both heat and mass transfer) was shown to collapse to the simpler model (heat transfer alone controlling) for the cases of practical interest. The heat transfer controlled, moving boundary model was demonstrated to fit all of the hydrate dissociation data within 10%, with no adjustable parameters in the model. This a priori prediction of hydrate dissociation measurements represents the state-of-the-art in accuracy. We have proposed the follow-on work of measurement and modelling of the dissociation of hydrates in sediments, together with the completion of the measurement of hydrate thermal conductivity in sediment. If funded, the follow-on work should allow a quantitative prediction of the production rates of gas from hydrates. 6 refs., 2 figs.

Sloan, E.D.; Selim, M.S.

1985-12-01

328

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

Microsoft Academic Search

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

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

2008-01-01

329

Dissociative recombination in aeronomy  

Microsoft Academic Search

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

J. L. Fox

1989-01-01

330

Radiative Capture versus Coulomb Dissociation  

SciTech Connect

Measurements of the Coulomb dissociation of 8B have been used to infer the rate of the inverse radiative proton capture on 7Be. The analysis is usually based on the assumptions that the two processes are related by detailed balance and described by E1 transitions. However, there are corrections to this relation. The Coulomb form factors for the two processes, for example, are not identical. There are also E2 transitions and higher-order effects in the Coulomb dissociation, and the nuclear induced breakup cannot always be ignored. While adding first-order E2 transitions enhances the decay energy spectrum, the other mechanisms cause a suppression at low relative energies. The net result may accidentally be close to the conventional first-order E1 calculation, but there are differences which cannot be ignored if accuracies of 10% or better are needed.

Esbensen, Henning [Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

2006-03-13

331

A simple non-empirical procedure for spin-component-scaled MP2 methods applied to the calculation of the dissociation energy curve of noncovalently-interacting systems.  

PubMed

We present a simple and non-empirical method to determine optimal scaling coefficients, within the (spin-component)-scaled MP2 approach, for calculating intermolecular potential energies of noncovalently-interacting systems. The method is based on an observed proportionality between (spin-component) MP2 and CCSD(T) energies for a wide range of intermolecular distances and allows us to compute with high accuracy a large portion of the dissociation curve at the cost of a single CCSD(T) calculation. The accuracy of the present procedure is assessed for a series of noncovalently-interacting test systems: the obtained results reproduce CCSD(T) quality in all cases and definitely outperform conventional MP2, CCSD and SCS-MP2 results. The difficult case of the beryllium dimer is also considered. PMID:23942763

Grabowski, Ireneusz; Fabiano, Eduardo; Della Sala, Fabio

2013-10-01

332

High-energy collision induced dissociation fragmentation pathways of peptides, probed using a multiturn tandem time-of-flight mass spectrometer 'MULTUM-TOF/TOF'  

SciTech Connect

A new multiturn tandem time-of-flight (TOF) mass spectrometer 'MULTUM-TOF/TOF' has been designed and constructed. It consists of a matrix-assisted laser desorption/ionization ion source, a multiturn TOF mass spectrometer, a collision cell, and a quadratic-field ion mirror. The multiturn TOF mass spectrometer can overcome the problem of precursor ion selection in TOF, due to insufficient time separation between two adjacent TOF peaks, by increasing the number of cycles. As a result, the total TOF increases with the increase in resolving power. The quadratic-field ion mirror allows temporal focusing for fragment ions with different kinetic energies. Product ion spectra from monoisotopically selected precursor ions of angiotensin I, substance P, and bradykinin have been obtained. The fragment ions observed are mainly the result of high-energy collision induced dissociation.

Toyoda, Michisato; Giannakopulos, Anastassios E.; Colburn, Alex W.; Derrick, Peter J. [Department of Physics, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043 (Japan); Institute of Mass Spectrometry, Department of Chemistry, University of Warwick, Coventry CV4 7AL (United Kingdom)

2007-07-15

333

Role of bonding and coordination in the atomic structure and energy of diamond and silicon grain boundaries  

Microsoft Academic Search

The high-temperature equilibrated atomic structures and energies of large-unit-cell grain boundaries (GB{close_quote}s) in diamond and silicon are determined by means of Monte-Carlo simulations using Tersoff{close_quote}s potentials for the two materials. Silicon provides a relatively simple basis for understanding GB structural disorder in a purely sp³ bonded material against which the greater bond stiffness in diamond combined with its ability to

P. Keblinski; D. Wolf; S. R. Phillpot; H. Gleiter

1998-01-01

334

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

NASA Astrophysics Data System (ADS)

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.; Van Alsenoy, C.; Geerlings, P.

2014-05-01

335

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

PubMed

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. PMID:24832251

Krishtal, A; Van Alsenoy, C; Geerlings, P

2014-05-14

336

Dissociative recombination and dissociative excitation of 4HeH+: Absolute cross sections and mechanisms  

NASA Astrophysics Data System (ADS)

Absolute cross sections have been determined for the dissociative recombination and dissociative excitation of 4HeH+ for electron energies below 40 eV. The dissociative recombination cross section is in semiquantitative agreement with recent theoretical results by Sarpal, Tennyson, and Morgan [J. Phys. B 27, 5943 (1994)] and Guberman [Phys. Rev. A 49, R4277 (1994); in XIXth International Conference on the Physics of Electronic and Atomic Collisions, Whistler, Canada, AIP Conf. Proc. No. 360, edited by L. J. Dube, J. B. A. Mitchell, J. W. McConkey, and C. E. Brion (AIP, New York, 1995), p. 307]. The calculated resonant structure below a collision energy of 1 eV was not fully reproduced by the experiment. The quantum states of the dissociative recombination products at 0 eV collision energy have been determined; ground-state helium and excited hydrogen atoms (n=2) are dominantly formed, in agreement with recent predictions by Guberman. The dissociative excitation has an onset around 10 eV and follows the shape of the dissociative recombination cross section, illustrating that both processes start with the formation of doubly excited neutral states that lie in the ionization continuum as well as in the dissociation continuum. The dissociative excitation cross section is in quite good agreement with recent calculations by Orel and Kulander.

Strömholm, C.; Semaniak, J.; Rosén, S.; Danared, H.; Datz, S.; van der Zande, W.; Larsson, M.

1996-10-01

337

Products of Dissociative Recombination in the Ionosphere  

NASA Technical Reports Server (NTRS)

SRI International undertook a novel experimental measurement of the product states formed by dissociative ro-combination (DR) of C2(+), NO(+), and N2(+) as a function of both electron energy and reactant ion vibrational level. For these measurements we used a recently developed experimental technique for measuring dissociation product distributions that allows both the branching ratios to be accurately determined and the electronic and ro-vibrational state composition of the reactant ions to be specified. DR is the dominant electron loss mechanism in all regions of the ionosphere. In this process, electron attachment to the molecular ion produces an unstable neutral molecule that rapidly dissociates.

Cosby, Philip

1996-01-01

338

Nano-Bonding of Silicon Oxides-based surfaces at Low Temperature: Bonding Interphase Modeling via Molecular Dynamics and Characterization of Bonding Surfaces Topography, Hydro-affinity and Free Energy  

NASA Astrophysics Data System (ADS)

In this work, a new method, "Nanobonding(TM)" [1,2] is conceived and researched to bond Si-based surfaces, via nucleation and growth of a 2 D silicon oxide SiOxHx interphase connecting the surfaces at the nanoscale across macroscopic domains. Nanobonding cross-bridges two smooth surfaces put into mechanical contact in an O2/H 2O mixed ambient below T ?200 °C via arrays of SiOxH x molecules connecting into a continuous macroscopic bonding interphase. Nano-scale surface planarization via wet chemical processing and new spin technology are compared via Tapping Mode Atomic Force Microscopy (TMAFM) , before and after nano-bonding. Nanobonding uses precursor phases, 2D nano-films of beta-cristobalite (beta-c) SiO2, nucleated on Si(100) via the Herbots-Atluri (H-A) method [1]. beta-c SiO2 on Si(100) is ordered and flat with atomic terraces over 20 nm wide, well above 2 nm found in native oxides. When contacted with SiO2 this ultra-smooth nanophase can nucleate and grow domains with cross-bridging molecular strands of hydroxylated SiOx, instead of point contacts. The high density of molecular bonds across extended terraces forms a strong bond between Si-based substrates, nano- bonding [2] the Si and silica. A new model of beta-cristobalite SiO2 with its <110> axis aligned along Si[100] direction is simulated via ab-initio methods in a nano-bonded stack with beta-c SiO2 in contact with amorphous SiO2 (a-SiO2), modelling cross-bridging molecular bonds between beta-c SiO2 on Si(100) and a-SiO2 as during nanobonding. Computed total energies are compared with those found for Si(100) and a-SiO2 and show that the presence of two lattice cells of !-c SiO2 on Si(100) and a-SiO2 lowers energy when compared to Si(100)/ a-SiO 2 Shadow cone calculations on three models of beta-c SiO2 on Si(100) are compared with Ion Beam Analysis of H-A processed Si(100). Total surface energy measurements via 3 liquid contact angle analysis of Si(100) after H-A method processing are also compared. By combining nanobonding experiments, TMAFM results, surface energy data, and ab-initio calculations, an atomistic model is derived and nanobonding is optimized. [1] US Patent 6,613,677 (9/2/03), 7,851,365 (12/14/10), [2] Patent Filed: 4/30/09, 10/1/2011

Whaley, Shawn D.

339

Design Optimization of Energy-Efficient Hydrophobic Wafer-bonded III-V/Si Semiconductor Optical Amplifiers  

E-print Network

of Electrical and Computer Engineering, University of California, One Shields Ave., Davis, California 95616 USA) (b) energy band diagram of optimal In(1-x)GaxAsyP(1-y) composition bonding interface (c) current flow transport, optical gain computation, and optical wave-guiding are considered. The energy band diagram shows

Yoo, S. J. Ben

340

Increase in dissociation rate constants of cardiotonic steroid-brain (Na+ + K+)-ATPase complexes by reduction of the unsaturated lactone.  

PubMed

Several cardiotonic steroids have been modified by reduction of the unsaturated lactone and their interactions with the sodium- and potassium-activated ATPase ((Na+ + K+)-ATPase) have been investigated. Reduction of the unsaturated lactone results in a decrease in binding affinity due primarily to an increase in the dissociation rate constant concomitant with a decrease in the activation free energy of dissociation. This decrease in activation free energy is about 2 to 4 kcal, which is approximately equal to the energy of one hydrogen bond. It is suggested that the increase in dissociation rate due to reduction of the unsaturated lactone may make possible the use of these compounds as affinity ligands for purification of the (Na+ + K+)-ATPase or an ouabain-binding fragment. PMID:127794

Clark, A F; Swanson, P D; Stahl, W L

1975-12-25

341

Scaling of the critical free length for progressive unfolding of self-bonded graphene  

NASA Astrophysics Data System (ADS)

Like filled pasta, rolled or folded graphene can form a large nanocapsule surrounding a hollow interior. Use as a molecular carrier, however, requires understanding of the opening of such vessels. Here, we investigate a monolayer sheet of graphene as a theoretical trial platform for such a nanocapsule. The graphene is bonded to itself via aligned disulfide (S-S) bonds. Through theoretical analysis and atomistic modeling, we probe the critical nonbonded length (free length, Lcrit) that induces fracture-like progressive unfolding as a function of folding radius (Ri). We show a clear linear scaling relationship between the length and radius, which can be used to determine the necessary bond density to predict mechanical opening/closing. However, stochastic dissipated energy limits any exact elastic formulation, and the required energy far exceeds the dissociation energy of the S-S bond. We account for the necessary dissipated kinetic energy through a simple scaling factor (?), which agrees well with computational results.

Kwan, Kenny; Cranford, Steven W.

2014-05-01

342

Dissociation of copper(II) ternary complexes containing cystine.  

PubMed

The collision-induced dissociations are reported for Cu(II) complexes containing 1,4,7-triazacyclononane (tacn) as the auxiliary ligand and a peptide containing one cystine residue. For six of the complexes examined, cleavage of the S-S bond in the peptide was the dominant fragmentation pathway. The exceptions were for complexes containing the largest peptides, (GlyCys'Gly)(2) and (GlyGlyCys')(2) (Cys' = NHCH(CH(2)S)CO, one half of the cystine residue; terminal H and OH are implicit), for which proton transfer to the auxiliary ligand was the major channel. Cleavage of the C-S bond was observed, but was a minor channel for all complexes. The radical cation (Cys')(2)(*+) was not observed although the complementary ion [Cu(I)(tacn)](+) was present in moderate abundance. Density functional calculations (at B3LYP/6-311++G(d,p)) gave low barriers to fragmentation of (Cys')(2)(*+) by homolytic fission of the C-S bond of the canonical ion (barrier 16.5 kcal mol(-1)) and of the structure at the global minimum, a captodative ion (barrier 17.2 kcal mol(-1)). Peptide radical cations (GlyCys')(2)(*+), (GlyCys'Gly)(2)(*+), (GlyGlyCys')(2)(*+) and (GlyCys'(Cys')Gly)(*+) were observed in low abundances; the first two of these ions dissociated predominantly by fragmentation of the S-S bond, while the other two preferentially cleaved at an amide bond. No cleavage of the C-S bond was observed for the peptide radical cations. Density functional calculations at B3LYP/6-31G(d) established that the cystine in [Cu(II)(tacn)(Cys')(2)](*2+) is bound as a zwitterion through the carboxylate anion with the proton on the distal amino group. The lowest energy complex containing a canonical cystine, coordinated through the carbonyl oxygen and the amino group of the same Cys', is 8.3 kcal mol(-1) higher in enthalpy. PMID:20539872

Ke, Yuyong; Zhao, Junfang; Siu, K W Michael; Hopkinson, Alan C

2010-08-21

343

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

344

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

345

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

346

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

347

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

PubMed

During the dissociative adsorption on a solid surface, the substrate usually participates in a passive manner to accommodate fragments produced upon the cleavage of the internal bond(s) of a (transient) molecular adsorbate. This simple picture, however, neglects the flexibility of surface atoms. Here, we report a Density Functional Theory study to revisit our early studies of the dissociative adsorption of CH3X (X = Br and Cl) on Si(100). We have identified a new reaction pathway, which involves a flip of a silicon dimer; this new pathway agrees better with experiments. For our main exemplar of CH3Br, insights have been gained using a simple model that involves a three-atom reactive center, Br-C-Si. When the silicon dimer flips, the interaction between C and Si in the Br-C-Si center is enhanced, evident in the increased energy-split of the frontier orbitals. We also examine how the dissociation dynamics of CH3Br is altered on a heterodimer (Si-Al, Si-P, and Si-Ge) in a Si(100) surface. In each case, we conclude, on the basis of computed reaction pathways, that no heterodimer flipping is involved before the system transverses the transition state to dissociative adsorption. PMID:25381532

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

2014-11-01

348

Low-energy (0.1 eV) electron attachment S?S bond cleavage assisted by Coulomb stabilization  

NASA Astrophysics Data System (ADS)

Electron capture by the ion H3C-S-S-CH2-CH2-NH +3 at either the -NH +3 site (to form the Rydberg radical H3C-S-S-CH2-CH2-NH3) or into the S-S antibonding ?* orbital is shown to be able to produce the same S-S bond fragmentation products H3C-S and HS-CH2-CH2-NH2, albeit by very different pathways. Capture into the S-S ?* orbital is, in the absence of the nearby positive site, endothermic by approximately 0.9 eV and leads to an electronically metastable anion that can undergo dissociation or autodetachment. In contrast, in the presence of the stabilizing Coulomb potential provided by the nearby NH +3 site, electron attachment into the S-S ?* orbital is rendered exothermic. As a result, as we have shown in this paper, the effective cross sections for forming the H3C-S and HS-CH2-CH2-NH2 products via attachment at the -NH +3 and S-S ?* sites are predicted to be comparable for our model compound. Moreover, we predict that the ?* site will become more amenable to electron attachment compared with the -NH +3 site for compounds in which the distance between the S-S bond and the protonated amine is larger than in our cation. These findings and insights should be of substantial value to workers studying bond cleavage rates and fragmentation patterns in gaseous positively charged samples of peptides and proteins.

Sawicka, Agnieszka; Berdys-Kocha?ska, Joanna; Skurski, Piotr; Simons, Jack

349

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

350

Formation and Dissociation of Transient Molecular States with Ultrafast X Rays  

NASA Astrophysics Data System (ADS)

We report the first pump-probe spectra using 1 keV pulses from LCLS to excite N2 in delayed coincidence with 800 nm laser pulses. The relative timing between the pump and probe was controlled to within 100 femtoseconds. We determined the timing based on the rapid formation of nitrogen dications by x-ray core ionization and subsequent Auger relaxation into a quasi-bound final state. Our operating photon energy primarily photoionized K-shell electrons. KLL Auger relaxation rapidly follows, frequently leaving the molecule in one of several quasi-bound dicationic states. We subsequently triggered dissociation of these quasi-bound states by dressing the dications in the optical laser field, thus bond-softening the potentials into dissociation.

Glownia, James; Cryan, James; Bucksbaum, Philip; Coffee, Ryan

2010-03-01

351

Dissociation of Highly Excited Molecules  

NASA Astrophysics Data System (ADS)

A survey of the spectroscopy and dynamics of the dissociation of highly excited molecules is presented with emphasis on superexcited molecules by electron- and photon-impact.(See review articles: a) Y. Hatano, The Physics of Electronic and Atomic Collisions, eds., L. J. Dube et al., AIP Press, New York (1995) pp.67-88; b) N.Kouchi et al., J. Phys. B, 30, 2319 (1997); c) Y. Hatano, Dynamics of Excited Molecules, ed., K. Kuchitsu, Elsevier, Amsterdam (1994) Chapter 6.) Topics will include newly developed experimental methods covering two-dimensional spectroscopy of photodissociation(M. Ukai et al., Phys. Rev. Lett., 74, 239 (1995).) (S. Machida et al., J. Phys. Chem. A. 101, 656 (1997).) (A. Ehresmann et al., J. Phys. B, 29, 3629 (1996).), and coincident electron-energy-loss spectroscopy of the dissociation dynamics of highly excited molecules.(T. Odagiri et al., J. Phys. B, 28, L465 (1995).)(T. Odagiri et al., J. Phys. B, 29, 1829 (1996).) The measurement of absolute photoionization quantum yields will also be discussed.(K. Kameta et al., J. Chem. Phys., 99, 2487 (1993).) Comparative studies of electron- and photon-impact dissociative excitation of molecules will be summarized. The molecules studied are H_2, N_2, O_2, CO, CO_2, N_2O, hydrocarbons, and some Si-containing compounds.

Hatano, Yoshihiko

1997-10-01

352

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

E-print Network

is comparably small, due to their cancellation through the flip-flop-type energy exchanges among water molecules the melting from ice to liquid, water absorbs the latent heat 80 Cal/g, about 1.4 kcal/mol, and hydrogen bonds in pica second time scale, sometimes reaching up to 20 kcal/mol, associated with these collec- tive

Ramaswamy, Ram

353

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/deuterium isotope effects, in a fundamental organic hydrogen bonded system using multiple experimental infrared the isotopically labeled systems arises from an analysis of the simulated cluster spectroscopy and leads

Iyengar, Srinivasan S.

354

A molecular orbital study of bonding and ionization energies in pentavalent uranium imide/amide complexes  

SciTech Connect

Discrete variational local density functional (X{alpha}) calculations on the model complexes ((RN)U(NR{sub 2}){sub 3}) (R = H (1), SiH{sub 3} (2)) have been performed in order to investigate the electronic structure of uranium amido/imido complexes. Special emphasis is placed on the energy ordering of the highest lying levels formed by U 5f orbitals and by out-of-plane N 2p{sub {pi}} orbitals. Orbital relaxations are also estimated by studying the fragments NR and NR{sub 2} with R = H and R = SiMe{sub 3} in order to allow a comparison of the model compounds 1 and 2 with the measured photoelectron spectrum of the complex ((Me{sub 3}SiN)U(N(SiMe{sub 3}){sub 2}){sub 3}). The ionization energies corresponding to the N 2p{sub {pi}} MOs are calculated in the order N 2p{sub {pi}} (amido) < N 2p{sub {pi}} (imido). The calculated level ordering is rationalized by comparing the order of the two types of U-N bonds and the charge distributions of the corresponding ligands. Taking the calculated ordering as well as the character of the molecular orbitals into account, a new assignment of the observed photoelectron spectra is given based on a comparison of He I and He II spectra.

Bowmaker, G.A.; Goerling, A.; Haeberlen, O.; Roesch, N. (Technische Univ. Muenchen, Garching (Germany)); Goodman, G.L. (Argonne National Lab., IL (United States)); Ellis, D.E. (Northwestern Univ., Evanston, IL (United States))

1992-02-19

355

Laser adiabatic manipulation of the bond length of diatomic molecules with a single chirped pulse.  

PubMed

We propose and test numerically a scheme for controlling the bond distance in a diatomic molecule that requires the use of a single chirped pulse. The laser prepares a superposition state of both nuclear and electronic degrees of freedom, where the main character of the electronic wave function is that of an excited dissociative state. The main limitation of the scheme is the need of ultra broadband pulses, where the bandwidth must be of the order of the dissociation energy to achieve large bond elongations. The scheme can be used to deform the bond during the laser excitation to an arbitrary large and constant value, or to allow slow time-dependent bond elongations. Additionally, the scheme can be used to prepare highly excited vibrational wave packets in the ground potential after the pulse is switched off, at the expense of losing some population that dissociates. These wave packets are initially localized at the outer well of the potential, at energies controllable by the excitation process. PMID:21495751

Chang, Bo Y; Shin, Seokmin; Santamaria, Jesus; Sola, Ignacio R

2011-04-14

356

Single-Molecule Investigations of RNA Dissociation  

PubMed Central

Given the essential cellular roles for ribonucleic acids (RNAs) it is important to understand the stability of three-dimensional structures formed by these molecules. This study aims to investigate the dissociation energy landscape for simple RNA structures via atomic-force-microscopy-based single-molecule force-spectroscopy measurements. This approach provides details on the locations and relative heights of the energy barriers to dissociation, and thus information upon the relative kinetic stabilities of the formed complexes. Our results indicate that a simple dodecamer RNA helix undergoes a forced dissociation process similar to that previously observed for DNA oligonucleotides. Incorporating a UCU bulge motif is found to introduce an additional energy barrier closer to the bound state, and also to destabilize the duplex. In the absence of magnesium ions a duplex containing this UCU bulge is destabilized and a single, shorter duplex is formed. These results reveal that a bulge motif impacts upon the forced dissociation of RNA and produces an energy landscape sensitive to the presence of magnesium ions. Interestingly, the obtained data compare well with previously reported ensemble measurements, illustrating the potential of this approach to improve our understanding of RNA stability and dissociation kinetics. PMID:15189877

Green, Nicola H.; Williams, Philip M.; Wahab, Omar; Davies, Martyn C.; Roberts, Clive J.; Tendler, Saul J. B.; Allen, Stephanie

2004-01-01

357

Dissociative Electron Attachment to DNA X. Pan, P. Cloutier, D. Hunting, and L. Sanche*  

E-print Network

rings with the bases guanine and cytosine, and adenine and thymine, respectively, bonded to a phosphate of repeated sugar-phosphate units hydrogen bonded together by the four bases, covalently linked to the sugar- tion of a basic component in a dissociative state; e.g., for fragmentation of a covalent hydrogen bond

Simons, Jack

358

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

NASA Astrophysics Data System (ADS)

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

Simons, Jack

2010-01-01

359

Energy barriers between H-bonded and stacked structures of 9-methyladenine...1-methylthymine and 9-methylguanine...1-methylcytosine complexes.  

PubMed

The transition structures (TS) between H-bonded (H) and stacked (S) structures of 9-methyladenine...1-methylthymine and 9-methylguanine...1-methylcytosine base pairs were localized at the DFT-D/TZVP potential energy surface. The energy barrier between the S and TS structures is considerably higher for the former pair than for the latter, which makes localization of the stacked structure of this pair possible. PMID:20066299

Cerný, Jirí; Hobza, Pavel

2010-01-21

360

Dissociative electron attachment to the H2O molecule. I. Complex-valued potential-energy surfaces for the 2B1, 2A1, and 2B2 metastable states of the water anion  

E-print Network

We present the results of calculations defining global, three-dimensional representations of the complex-valued potential-energy surfaces of the doublet B1, doublet A1, and doublet B2 metastable states of the water anion that underlie the physical process of dissociative electron attachment to water. The real part of the resonance energies is obtained from configuration-interaction calculations performed in a restricted Hilbert space, while the imaginary part of the energies (the widths) is derived from complex Kohn scattering calculations. A diabatization is performed on the 2A1 and 2B2 surfaces, due to the presence of a conical intersection between them. We discuss the implications that the shapes of the constructed potential-energy surfaces will have upon the nuclear dynamics of dissociative electron attachment to H2O. This work originally appeared as Phys Rev A 75, 012710 (2007). Typesetting errors in the published version have been corrected here.

Haxton, Daniel J; Rescigno, T N

2007-01-01

361

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

362

Imaging the molecular dynamics of dissociative electron attachment to water  

SciTech Connect

Momentum imaging experiments on dissociative electron attachment to the water molecule are combined with ab initio theoretical calculations of the angular dependence of the quantum mechanical amplitude for electron attachment to provide a detailed picture of the molecular dynamics of dissociation attachment via the two lowest energy Feshbach resonances. The combination of momentum imaging experiments and theory can reveal dissociation dynamics for which the axial recoil approximation breaks down and thus provides a powerful reaction microscope for DEA to polyatomics.

Adaniya, Hidihito; Rudek, B.; Osipov, Timur; Haxton, Dan; Weber, Thorsten; Rescigno, Thomas N.; McCurdy, C.W.; Belkacem, Ali

2009-10-19

363

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

NASA Astrophysics Data System (ADS)

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; Wang, Yan; Huang, Yongli; Zhang, Xi; Zhang, Ting; Li, Can; Sun, Chang Q.

2014-04-01

364

Dissociation pressure measurements on salts proposed for thermochemical energy storage. [MgClâ\\/HâO; CaClâ\\/NHâ  

Microsoft Academic Search

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

Carling

1979-01-01

365

Dissociation of alkane ionized molecules  

NASA Astrophysics Data System (ADS)

The subject of investigation is the fragmentation of variously charged molecular ions arising in col-lisions of several kiloelectronvolt H+, He2+, and Ar6+ ions with molecules of the simplest alkanes (from methane to butane). Using the method of time-of-flight mass spectrometry, the formation cross sections of dissociation-induced fragment ions are measured. The dissociation takes place when an incident ion captures an electron from a methane, ethane, or propane molecule. The role of additional ionization of the molecule, which accompanies the electron capture by the incident ion, is elucidated. The kinetic energy spectrum for protons resulting from the fragmentation of multiply charged alkane ions is determined. The most plausible kinetic energies of protons depending on the degree of ionization and molecule size fall into the range 1-25 eV. It is shown that, when the molecule loses several electrons, the kinetic energies of protons are governed by Coulomb interaction between all fragment ions and are determined by their flying apart from the relative spatial arrangement of corresponding atoms in a parent molecule.

Afrosimov, V. V.; Baranova, L. A.; Basalaev, A. A.; Panov, M. N.; Smirnov, O. V.; Tulub, A. V.

2010-03-01

366

Substituent effect on the energy barrier for ?-bond formation from ?-single-bonded species, singlet 2,2-dialkoxycyclopentane-1,3-diyls  

PubMed Central

Summary Background: Localized singlet diradicals are in general quite short-lived intermediates in processes involving homolytic bond-cleavage and formation reactions. In the past decade, long-lived singlet diradicals have been reported in cyclic systems such as cyclobutane-1,3-diyls and cyclopentane-1,3-diyls. Experimental investigation of the chemistry of singlet diradicals has become possible. The present study explores the substituents and the effect of their substitution pattern at the C(1)–C(3) positions on the lifetime of singlet octahydropentalene-1,3-diyls to understand the role of the substituents on the reactivity of the localized singlet diradicals. Results: A series of singlet 2,2-dialkoxy-1,3-diaryloctahydropentalene-1,3-diyls DR were generated in the photochemical denitrogenation of the corresponding azoalkanes AZ. The ring-closed products CP, i.e., 3,3-dialkoxy-2,4-diphenyltricyclo[3.3.0.02,4]octanes, were quantitatively obtained in the denitrogenation reaction. The first-order decay process (k = 1/?) was observed for the fate of the singlet diradicals DR (?max ? 580–590 nm). The activation parameters, ?H ‡ and ?S ‡, for the ring-closing reaction (?-bond formation process) were determined by the temperature-dependent change of the lifetime. The energy barrier was found to be largely dependent upon the substituents Ar and Ar’. The singlet diradical DRf (Ar = 3,5-dimethoxyphenyl, OCH2Ar’ = OCH2(3,5-dimethoxyphenyl)) was the longest-lived, ?293 = 5394 ± 59 ns, among the diradicals studied here. The lifetime of the parent diradical DR (Ar = Ph, OCH2Ar’ = OCH3) was 299 ± 2 ns at 293 K. Conclusion: The lifetimes of the singlet 1,3-diyls are found to be largely dependent on the substituent pattern of Ar and Ar’ at the C(1)–C(3) positions. Both the enthalpy and entropy effect were found to play crucial roles in increasing the lifetime. PMID:23766808

Ye, Jianhuai; Fujiwara, Yoshihisa

2013-01-01

367

Adhesive-Bonded Composite Joint Analysis with Delaminated Surface Ply Using Strain-Energy Release Rate  

NASA Technical Reports Server (NTRS)

This paper presents an analytical model to determine the strain energy release rate due to an interlaminar crack of the surface ply in adhesively bonded composite joints subjected to axial tension. Single-lap shear-joint standard test specimen geometry with thick bondline is followed for model development. The field equations are formulated by using the first-order shear-deformation theory in laminated plates together with kinematics relations and force equilibrium conditions. The stress distributions for the adherends and adhesive are determined after the appropriate boundary and loading conditions are applied and the equations for the field displacements are solved. The system of second-order differential equations is solved to using the symbolic computation tool Maple 9.52 to provide displacements fields. The equivalent forces at the tip of the prescribed interlaminar crack are obtained based on interlaminar stress distributions. The strain energy release rate of the crack is then determined by using the crack closure method. Finite element analyses using the J integral as well as the crack closure method are performed to verify the developed analytical model. It has been shown that the results using the analytical method correlate well with the results from the finite element analyses. An attempt is made to predict the failure loads of the joints based on limited test data from the literature. The effectiveness of the inclusion of bondline thickness is justified when compared with the results obtained from the previous model in which a thin bondline and uniform adhesive stresses through the bondline thickness are assumed.

Chadegani, Alireza; Yang, Chihdar; Smeltzer, Stanley S. III

2012-01-01

368

Intriguing Role of a Quaternary Ammonium Cation in the Dissociation Chemistry of Keggin Polyoxometalate Anions  

NASA Astrophysics Data System (ADS)

The gas-phase fragmentations of a series of Keggin polyoxometalate anions with molecular formula of TBAn[XM12O40] (X = P, Si; M = Mo, W) were studied by electrospray ionization tandem mass spectrometry. The bare polyoxoanions [XM12O40]n- as well as the non-covalent complexes {TBA[XM12O40]}(n-1)- and {TBAm[XM12O40]2}3- displayed characteristic dissociation pathways. Fragmentation of [XM12O40]n- led to pairs of complementary product anions whose total stoichiometry and charge matched those of the precursor anion, consistent with the previous study by Ma et al. The nature of the non-covalent interaction between [XM12O40]n- and TBA+ was addressed in detail via the example of {TBA[XM12O40]}(n-1)-. The non-covalent interaction [1] primarily dominated by the Coulombic attraction of the opposite charges completely changed the dissociation chemistry of [XM12O40]n-. The non-covalent complexes {TBA[XM12O40]}(n-1)- and {TBAm[XM12O40]2}3-, formed by the charge reduction during the electrospray process, underwent distinct dissociation routes: {TBA[XM12O40]}(n-1)- fragmented to give rise to its product ion {(C4H9)[XM12O40]}(n-1)- by cleaving the N-C covalent bond inside the TBA+ cation whereas {TBAm[XM12O40]2}3- dissociated into a pair of product ions, {TBAi[XM12O40]}2- and {TBAm-i[XM12O40]}-, by breaking the non-covalent bond between [XM12O40]n- and TBA+. In addition, energy-variable CID was used to map the relative stabilities of the ion clusters in the gas phase, which was in excellent agreement with the relative orders of thermal stability in the condensed phase.

Cao, Jie; Li, Chenchen; Zhang, Zhengxiang; Xu, Chong; Yan, Jie; Cui, Fengyun; Hu, Changwen

2012-02-01

369

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

370

Performance of multireference and equation-of-motion coupled-cluster methods for potential energy surfaces of low-lying excited states: Symmetric and asymmetric dissociation of water  

NASA Astrophysics Data System (ADS)

Multireference (MR), general-model-space (GMS), state-universal (SU) coupled-cluster (CC) method that considers singly (S) and doubly (D) excited cluster amplitudes relative to the reference configurations spanning the model space (GMS SU CCSD), as well as its externally corrected (ec) version (N,M)-CCSD that employs N-reference MR CISD as an external source of higher-than-pair cluster amplitudes in a M-reference GMS CCSD, are employed to investigate low-lying states of the water molecule. The emphasis is on a generation of several low lying states belonging to the same symmetry species. Cuts of the potential energy surface (PES) corresponding to the breaking of a single OH bond and leading to the OH+H fragments, as well as the simultaneous breaking of both bonds into the O+2H are considered. Relying on a simple ab initio model that enables a comparison with the exact full configuration interaction energies, the performance of the GMS-based methods is assessed in the whole relevant range of internuclear separations. It is shown that the ec (N,M)-CCSD version provides best results for both the singlet and the triplet states considered. The same cuts of the PES are then explored using a realistic aug-cc-pVTZ basis set. For triplets, the use of high-spin (MS=1) references is to be preferred.

Li, Xiangzhu; Paldus, Josef

2010-07-01

371

VUV Photoionization and Dissociation of Tyramine and Dopamine: the Joint Experimental and Theoretical Studies  

NASA Astrophysics Data System (ADS)

Photon induced dissociation investigations of neutral tyramine and dopamine are carried out with synchrotron vacuum ultraviolet photoionization mass spectrometry and theoretical calculations. At low photon energy only molecular ions are measured by virtue of nearthreshold photoionization. While increasing photon energy to 11.7 eV or more, four distinct fragment ions are obtained for tyramine and dopamine, respectively. Besides, the ionization energies of tyramine and dopamine are determined to be 7.98±0.05 and 7.67±0.05 eV by measuring the photoionization efficiency curves of corresponding molecular ions. With help of density function theory calculations, the detailed fragmentation pathways are established as well. These two molecular cations have similar aminoethyl group elimination pathways, C7H8O2+· (m/z=124) and C7H8O+· (m/z=108) are supposed to be generated by the McLafferty rearrangement via ?-hydrogen (?-H) shift inducing ?-fission. And CH2NH2+ is proposed to derive from the direct fission of C7-C8 bond. Besides, the McLafferty rearrangement and the C7-C8 bond fission are validated to be dominant dissociation pathways for tyramine and dopamine cations.

Guo, Hui-jun; Ye, Li-li; Jia, Liang-yuan; Zhang, Li-dong; Qi, Fei

2012-02-01

372

Role of bonding and coordination in the atomic structure and energy of diamond and silicon grain boundaries  

SciTech Connect

The high-temperature equilibrated atomic structures and energies of large-unit-cell grain boundaries (GB{close_quote}s) in diamond and silicon are determined by means of Monte-Carlo simulations using Tersoff{close_quote}s potentials for the two materials. Silicon provides a relatively simple basis for understanding GB structural disorder in a purely sp{sup 3} bonded material against which the greater bond stiffness in diamond combined with its ability to change hybridization in a defected environment from sp{sup 3} to sp{sup 2} can be elucidated. We find that due to the purely sp{sup 3}-type bonding in Si, even in highly disordered, high-energy GB{close_quote}s at least 80{percent} of the atoms are fourfold coordinated in a rather dense confined amorphous structure. By contrast, in diamond even relatively small bond distortions exact a considerable price in energy that favors a change to sp{sup 2}-type local bonding; these competing effects translate into considerably more ordered diamond GB{close_quote}s; however, at the price of as many as 80{percent} of the atoms being only threefold coordinated. Structural disorder in the Si GB{close_quote}s is therefore partially replaced by coordination disorder in the diamond GB{close_quote}s. In spite of these large fractions of three-coordinated GB carbon atoms, however, the three-coordinated atoms are rather poorly connected amongst themselves, thus likely preventing any type of graphite-like electrical conduction through the GB{close_quote}s. {copyright} {ital 1998 Materials Research Society.}

Keblinski, P.; Wolf, D.; Phillpot, S.R. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Keblinski, P.; Gleiter, H. [Forschungszentrum Karlsruhe, 76021 Karlsruhe (Germany)

1998-08-01

373

Dissociative Reactions to Incest.  

ERIC Educational Resources Information Center

In contrast to Freud's later and revised view of the etiology of hysterical, or dissociative, symptoms, it is now known that real, and not fantasized, sexual experiences in childhood are experienced in disociative symptomatology. It is useful to understand that incest involves both traumatic events, that is, incidents of sexual violation per se,…

Hall, J. Mark

374

Pathological Dissociation as Measured by the Child Dissociative Checklist  

ERIC Educational Resources Information Center

The component structure of the Child Dissociative Checklist was examined among abused children. A factor described as pathological dissociation emerged that was predicted by participants being male. There also were differences in pathological dissociation between groups of sexually abused and physically abused children. Replication of this factor…

Wherry, Jeffrey N.; Neil, Debra A.; Taylor, Tamara N.

2009-01-01

375

Dissociative photoionization of methyl chloride studied with threshold photoelectron-photoion coincidence velocity imaging  

NASA Astrophysics Data System (ADS)

Utilizing threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging, dissociation of state-selected CH3Cl+ ions was investigated in the excitation energy range of 11.0-18.5 eV. TPEPICO time-of-flight mass spectra and three-dimensional time-sliced velocity images of CH3+ dissociated from CH3Cl+(A2A1 and B2E) ions were recorded. CH3+ was kept as the most dominant fragment ion in the present energy range, while the branching ratio of CH2Cl+ fragment was very low. For dissociation of CH3Cl+(A2A1) ions, a series of homocentric rings was clearly observed in the CH3+ image, which was assigned as the excitation of umbrella vibration of CH3+ ions. Moreover, a dependence of anisotropic parameters on the vibrational states of CH3+(11A') provided a direct experimental evidence of a shallow potential well along the C-Cl bond rupture. For CH3Cl+(B2E) ions, total kinetic energy released distribution for CH3+ fragmentation showed a near Maxwell-Boltzmann profile, indicating that the Cl-loss pathway from the B2E state was statistical predissociation. With the aid of calculated Cl-loss potential energy curves of CH3Cl+, CH3+ formation from CH3Cl+(A2A1) ions was a rapid direct fragmentation, while CH3Cl+(B2E) ions statistically dissociated to CH3+ + Cl via internal conversion to the high vibrational states of X2E.

Tang, Xiaofeng; Zhou, Xiaoguo; Wu, Manman; Liu, Shilin; Liu, Fuyi; Shan, Xiaobin; Sheng, Liusi

2012-01-01

376

Development of bonding methods and energy absorption of sandwich panels for thermoplastic advanced composites.  

E-print Network

??Given their high strength-to-weight and stiffness-to-weight ratios, sandwich composites continue to be considered for automotive applications. Thermoplastic materials, while difficult to bond, have an increased… (more)

Haslam, Erik Bravant

2012-01-01

377

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

378

Assessment of hydrogen bonding effect on ionization of water from ambient to supercritical region-MD simulation approach  

NASA Astrophysics Data System (ADS)

We present a novel, molecular dynamics (MD) simulation based, strategy to analyze how the degree of hydrogen bonding may influence the ionization and dissociation of water upon heating from ambient to supercritical temperatures. Calculations show a negligible change in the ionization energy up to 200 °C. At higher temperatures the ionization energy increases due to the decreasing degree of hydrogen bonding. The influence of density (pressure) is pronounced in the supercritical region. The ionization is more energy consuming in the less dense fluid. We also show that high temperature and low density may promote dissociation of the electronically excited water molecules. Implications on the initial radiation chemical yields of the hydrated electron, hydrogen atom and hydroxyl radical are discussed.

Swiatla-Wojcik, D.; Mozumder, A.

2014-04-01

379

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

380

Dissociation of CH4 at High Pressures and Temperatures  

E-print Network

Dissociation of CH4 at High Pressures and Temperatures: Diamond Formation in Giant Planet Interiors. Dissociation of CH4 at high pressures and temperatures can influence the energy budgets of planets containing substantial amounts of CH4, water, and ammonia, such as Uranus and Neptune. The luminosities and strong

Kruger, Michael - Department of Physics, University of Missouri

381

Polarization induced water molecule dissociation below the first-order electronic-phase transition temperature  

E-print Network

Hydrogen produced from the photocatalytic splitting of water is one of the reliable alternatives to replace the polluting fossil and the radioactive nuclear fuels. Here, we provide unequivocal evidence for the existence of blue- and red-shifting O$-$H covalent bonds within a single water molecule adsorbed on MgO surface as a result of asymmetric displacement polarizabilities. The adsorbed H-O-H on MgO gives rise to one weaker H-O bond, while the other O-H covalent bond from the same adsorbed water molecule compensates this effect with a stronger bond. The weaker bond (nearest to the surface), the interlayer tunneling electrons and the silver substrate are shown to be the causes for the smallest dissociative activation energy on MgO monolayer. The origin that is responsible to initiate the splitting mechanism is proven to be due to the changes in the polarizability of an adsorbed water molecule, which are further supported by the temperature-dependent static dielectric constant measurements for water below the...

Arulsamy, Andrew Das; Elersic, Kristina; Modic, Martina; Subramani, Uma Shankar

2011-01-01

382

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

PubMed

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

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

2005-07-01

383

Novel C?-C? bond cleavages of tryptophan-containing peptide radical cations.  

PubMed

In this study, we observed unprecedented cleavages of the C(?)-C(?) bonds of tryptophan residue side chains in a series of hydrogen-deficient tryptophan-containing peptide radical cations (M(•+)) during low-energy collision-induced dissociation (CID). We used CID experiments and theoretical density functional theory (DFT) calculations to study the mechanism of this bond cleavage, which forms [M - 116](+) ions. The formation of an ?-carbon radical intermediate at the tryptophan residue for the subsequent C(?)-C(?) bond cleavage is analogous to that occurring at leucine residues, producing the same product ions; this hypothesis was supported by the identical product ion spectra of [LGGGH - 43](+) and [WGGGH - 116](+), obtained from the CID of [LGGGH](•+) and [WGGGH](•+), respectively. Elimination of the neutral 116-Da radical requires inevitable dehydrogenation of the indole nitrogen atom, leaving the radical centered formally on the indole nitrogen atom ([Ind](•)-2), in agreement with the CID data for [WGGGH](•+) and [W(1-CH3)GGGH](•+); replacing the tryptophan residue with a 1-methyltryptophan residue results in a change of the base peak from that arising from a neutral radical loss (116 Da) to that arising from a molecule loss (131 Da), both originating from C(?)-C(?) bond cleavage. Hydrogen atom transfer or proton transfer to the ?-carbon atom of the tryptophan residue weakens the C(?)-C(?) bond and, therefore, decreases the dissociation energy barrier dramatically. PMID:22135037

Song, Tao; Hao, Qiang; Law, Chun-Hin; Siu, Chi-Kit; Chu, Ivan K

2012-02-01

384

The dissociation of diatomic molecules at surfaces  

Microsoft Academic Search

We present an exposition of the various theoretical models currently in use for describing the dynamics of molecular dissociation at surfaces. We begin by outlining the representations of the nuclear and electronic dynamics and how these define the potential energy surfaces for the interactions. Strategies for solving the nuclear motion follow with particular emphasis being paid to a quantum description

G. R. Darling; S. Holloway

1995-01-01

385

Coulomb dissociation of [sup 11]Li  

SciTech Connect

Kinematically complete measurements for Coulomb dissociation of [sup 11]Li into [sup 9]Li+2[ital n] were made at 28 MeV/nucleon. The [ital n]-[ital n] correlation function suggests a large source size for the two-neutron emission. The electromagnetic excitation spectrum of [sup 11]Li has a peak, as anticipated in low-energy dipole resonance models, but a large post-breakup Coulomb acceleration of the [sup 9]Li fragment is observed, indicating a very short lifetime of the excited state and favoring direct breakup as the dissociation mechanism.

Ieki, K.; Sackett, D.; Galonsky, A.; Bertulani, C.A.; Kruse, J.J.; Lynch, W.G.; Morrissey, D.J.; Orr, N.A.; Schulz, H.; Sherrill, B.M.; Sustich, A.; Winger, J.A. (National Superconducting Cyclotron Laboratory and Department of Physics, Michigan State Unversity, East Lansing, Michigan 48824 (United States)); Deak, F.; Horvath, A.; Kiss, A. (Department of Atomic Physics, Eoetvoes University, Puskin utca 5-7 H-1088 Budapest 8 (Hungary)); Seres, Z. (KFKI Research Institute for Particle and Nuclear Physics of the Hungarian Academy of Sciences, H-1525 Budapest 114 (Hungary)); Kolata, J.J. (Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556 (United States)); Warner, R.E. (Department of Physics, Oberlin College, Oberlin, Ohio 44074 (United States)); Humphrey, D.L. (Department of Physics, Western Kentucky University, Bowling Green, Kentucky 42101 (United States))

1993-02-08

386

Molecular dissociation in hot, dense hydrogen  

SciTech Connect

We present a path-integral Monte Carlo study of dissociation in dense hydrogen (1.75{le}{ital r}{sub {ital s}}{le}2.2, with {ital r}{sub {ital s}} the Wigner sphere radius). As the temperature is lowered from 10{sup 5} to 5000 K, a molecular hydrogen gas forms spontaneously from a neutral system of protons and electrons. At high density, {ital r}{sub {ital s}}{lt}2.0, thermally activated dissociation is accompanied by decreasing pressure, signaling the presence of a first order transition and critical point. The decrease in electron kinetic energy during dissociation is responsible for the pressure decrease and transition. At lower density the phase transition disappears. {copyright} {ital 1996 The American Physical Society.}

Magro, W.R.; Ceperley, D.M.; Pierleoni, C.; Bernu, B. [Theory Center and Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853 (United States)] [Theory Center and Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853 (United States); [National Center for Supercomputing Applications and Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States); [Dipartimento di Fisica, Universita de L`Aquila I-67100 L`Aquila (Italy); [INFM, sezione di Roma I, 00185 Roma (Italy); [Laboratoire de Physique Theorique des Liquides, Universite P. et M. Curie, 75252 Paris Cedex 05 (France)

1996-02-01

387

Ion Induced Dissociation Dynamics of Acetylene  

NASA Astrophysics Data System (ADS)

We report the results of dissociation dynamics of multiply charged acetylene molecules formed in collision with 1.2 MeV Ar8+ projectiles. Using the coincidence map, we found the evidence for molecular deformation due to a vibrationally active transition state of multiply charged C2H2 under the impact of low energy projectiles. 'Butterfly-like' structures are observed in the coincidence spectra between hydrogen and carbon ionic fragments. Such structures can be generated by numerical simulations and are found to originate from the bending motion of the dissociating molecule. From the measured slopes of the coincidence islands for carbon atomic fragments and theoretical values determined from the charge and momentum distribution of the correlated particles, we observe a diatom-like behavior of the C-C charged complex during dissociation of multiply charged acetylene. This is a signature of sequentiality in the breakup dynamics of this multiply charged molecular species.

De, Sankar

2009-03-01

388

Modeling the electron-impact dissociation of methane  

NASA Astrophysics Data System (ADS)

The product yield of the electron-impact dissociation of methane has been studied with a combination of three theoretical methods: R-matrix theory to determine the electronically inelastic collisional excitation cross sections, high-level electronic structure methods to determine excited states energies and derivative couplings, and trajectory surface hopping (TSH) calculations to determine branching in the dissociation of the methane excited states to give CH3, CH2, and CH. The calculations involve the lowest 24 excited-state potential surfaces of methane, up to the ionization energy. According to the R-matrix calculations, electron impact preferentially produces triplet excited states, especially for electron kinetic energies close to the dissociation threshold. The potential surfaces of excited states are characterized by numerous avoided and real crossings such that the TSH calculations show rapid cascading down to the lowest excited singlet or triplet states, and then slower the dissociation of these lowest states. Product branching for electron-impact dissociation was therefore estimated by combining the electron-impact excitation cross sections with TSH product branching ratios that were obtained from the lowest singlet and triplet states, with the singlet dissociation giving a comparable formation of CH2 and CH3 while triplet dissociation gives CH3 exclusively. The overall branching in electron-impact dissociation is dominated by CH3 over CH2. A small branching yield for CH is also predicted.

Zió?kowski, Marcin; Vikár, Anna; Mayes, Maricris Lodriguito; Bencsura, Ákos; Lendvay, György; Schatz, George C.

2012-12-01

389

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.

390

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

391

Differential cross sections for the dissociative single and double excitations resulting in H(2p) formation in electron-CH4 collisions at 80 eV incident electron energy  

NASA Astrophysics Data System (ADS)

The differential cross sections for the dissociative single and double excitations resulting in H(2p) formation with the excitation energy of 19-46 eV in electron-CH4 collisions have been measured as a function of electron scattering angle in the range 4°-48° at 80 eV incident electron energy by means of angle-resolved electron energy-loss spectroscopy in coincidence with detecting Lyman-? photons. This is the first measurement of the differential cross sections for the dissociative double excitations as a function of electron scattering angle in electron-molecule collisions. Their fractions have been compared with those at the optical limit calculated from the density of the dipole oscillator strength for the emission of Lyman-? photons previously measured by our group. The dissociative double excitations in 80 eV electron collisions seem to be brought about in a very different way from those at the optical limit where they arise from the electron correlation in a methane molecule. The differential cross sections have also been discussed in terms of momentum transfer, leading to a universal curve.

Yachi, Kazufumi; Odagiri, Takeshi; Ishikawa, Lisa; Nakazato, Tomoharu; Tsuchida, Toshinori; Ohno, Naruhito; Kitajima, Masashi; Kouchi, Noriyuki

2010-08-01

392

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

of 48-50 C, detector temperature of 120'C, a helium flow rate of 25 ml/min, and a filament current of 145 ma. ; the retention times (min) were as follows: air, 1. 2; isobutylene, 1. 6; 3-iodo-Z- methyl-propene, 3, 6; t-butylbromide, 6. 1; and iso...-BuBr was left, and more than 90 mole per cent of isobutylene was formed and small amounts of t-BuBr and 3-iodo-2-methyl-propene were also found. However no quantitative analysis was made for the last two compounds. But one can calculate the amount of t...

Jirustithipong, Pongsiri

2012-06-07

393

Psychophysiology of dissociated consciousness.  

PubMed

Recent study of consciousness provides an evidence that there is a limit of consciousness, which presents a barrier between conscious and unconscious processes. This barrier likely is specifically manifested as a disturbance of neural mechanisms of consciousness that through distributed brain processing, attentional mechanisms and memory processes enable to constitute integrative conscious experience. According to recent findings a level of conscious integration may change during certain conditions related to experimental cognitive manipulations, hypnosis, or stressful experiences that can lead to dissociation of consciousness. In psychopathological research the term dissociation was proposed by Pierre Janet for explanation of processes related to splitting of consciousness due to traumatic events or during hypnosis. According to several recent findings dissociation of consciousness likely is related to deficits in global distribution of information and may lead to heightened levels of "neural complexity" that reflects brain integration or differentiation based on numbers of independent neural processes in the brain that may be specifically related to various mental disorders. PMID:24850082

Bob, Petr

2014-01-01

394

A Comparative Ab Initio Study of the Primary Hydration and Proton Dissociation of Various Imide and Sulfonic Acid Ionomers  

SciTech Connect

We compare the role of neighboring group substitutions on proton dissociation of hydrated acidic moieties suitable for proton exchange membranes through electronic structure calculations. Three pairs of ionomers containing similar electron withdrawing groups within the pair were chosen for the study: two fully fluorinated sulfonyl imides (CF3SO2NHSO2CF3 and CF3CF2SO2NHSO2CF3), two partially fluorinated sulfonyl imides (CH3SO2NHSO2CF3 and C6H5SO2NHSO2CF2CF3), and two aromatic sulfonic acid based material s (CH3C6H4SO3H and CH3 OC6 - H3OCH3C6H4SO3H). Fully optimized counterpoise (CP) corrected geometries were obtained for each ionomer fragment with the inclusion of water molecules at the B3LYP/6-311G** level of density functional theory. Spontaneous proton dissociation was observed upon addition of three water molecules in each system, and the transition to a solvent-separated ion pair occurred when four water molecules were introduced. No considerable quantitative or qualitative differences in proton dissociation, hydrogen bond networks formed, or water binding energies were found between systems containing similar electron withdrawing groups. Each of the sulfonyl imide ionomers exhibited qualitatively similar results regarding proton dissociation and separation. The fully fluorinated sulfonyl imides, however, showed a greater propensity to exist in dissociated and ion-pair separated states at low degrees of hydration than the partially fluorinated sulfonyl imides. This effect is due to the additional electron withdrawing groups providing charge stabilization as the dissociated proton migrates away from the imide anion.

Clark II, Jeffrey K.; Paddison, Stephen J.; Eikerling, Michael; Dupuis, Michel; Zawodzinski, Jr., Thomas A.

2012-03-29

395

Collisionally-activated dissociation in hyperthermal surface ionization of cholesterol  

NASA Astrophysics Data System (ADS)

Cholesterol in a hydrogen-seeded supersonic molecular beam was scattered from a continuously oxidized rhenium foil. The hyperthermal surface scattering exhibited efficient molecular ionization with a controlled amount of molecular ion dissociation. At 5.3 eV incident molecular kinetic energy the hyperthermal surface ionization mass spectrum was dominated by the parent molecular ion. Upon the increase of the molecular kinetic energy, a gradual increase in the degree of ion dissociation was observed. At 22eV incident kinetic energy the parent ion was completely dissociated and the mass spectrum was dominated by an extensive consecutive fragmentation. An efficient kinetic-vibrational energy transfer was observed, and it is extimated to be over 18% of the available incident kinetic energy. The implication for surface collisionally-activated dissociation of polyatomic ions is discussed. Rhenium oxide is suggested as an optimal surface for this purpose, as well as for the hyperthermal surface ionization of neutral species.

Dagan, Shai; Danon, Albert; Amirav, Aviv

1992-03-01

396

Volume 4, number 9 CHEMICAL PHYSICSLETTERS 15 &uluary 1970 HYDROGEN-BOND ENERGY NONADDITIVITY IN WATER *  

E-print Network

. The value of accurate quantum-mechanic- al computation of electron cloud deformations in molecular clusters calculations based on point-charge and multipole- expansion models have been carried out to exam- ine which included only the four electrons di- rectly involved in the hydrogen-bonded system

Stillinger, Frank

397

Aircraft surface coatings study: Energy efficient transport program. [sprayed and adhesive bonded coatings for drag reduction  

NASA Technical Reports Server (NTRS)

Surface coating materials for application on transport type aircraft to reduce drag, were investigated. The investigation included two basic types of materials: spray on coatings and adhesively bonded films. A cost/benefits analysis was performed, and recommendations were made for future work toward the application of this technology.

1979-01-01

398

Reactive molecular dynamic simulations of hydrocarbon dissociations on Ni(111) surfaces  

NASA Astrophysics Data System (ADS)

Empirical potential parameters for H, C and Ni elements have been developed for the ReaxFF force field in order to study the decomposition of small hydrocarbon molecules on nickel using molecular dynamics simulations. These parameters were optimized using the geometrical and energetic information obtained from density functional (DFT) calculations on a subset of hydrogen and methane reactions with nickel (111) surfaces. The resulting force field was then used to obtain a molecular perspective of the dynamics of the methane dissociative adsorption on Ni(111) as well as two other small alkane molecules, ethane and n-butane. NVT simulations of dissociative adsorption of methane over a range of temperatures enabled the estimation of the sticking coefficient for the adsorption as well as the activation energy of the first C-H bond breaking. The rate constants of each elementary step (both forward and reverse) of CHx dissociation on Ni(111) were obtained by monitoring the surface species and a microkinetic model was constructed as a result. Qualitative analyses of the simulations of ethane and n-butane decompositions on Ni(111) demonstrate that such reactive MD technique can also be used to obtain useful information on complex reaction networks.

Liu, Bin; Lusk, Mark T.; Ely, James F.

2012-03-01

399

Transient Mobility of Oxygen Adatoms upon O2 Dissociation on Reduced TiO2 (110)  

SciTech Connect

Tracking the same region of the reduced TiO2 (110) surface by scanning tunneling microscopy before and after oxygen exposure at room temperature confirms that O2 molecules dissociate only at the bridging oxygen vacancies, with one O atom healing a vacancy and other O atom bonding at the neighboring Ti site as an adatom. Majority (~81%) of O adatoms are found separated from the original vacancy positions, by up to two lattice constants along [001] direction. Since at room temperature the thermal diffusion of O adatoms has been found to be rather small, with experimentally estimated activation energy of ~1.1 eV, we conclude that observed lateral distribution of the oxygen adatoms is attained through a nonthermal, transient mobility in the course of O2 dissociation. Unlike for other known cases of the dissociation of the diatomic molecules where both “hot” adatoms accommodate at the equivalent sites, in the studied system the oxygen atoms filling the vacancies are locked into the bridging oxygen rows and only the O adatoms are relatively free to move. The transient motion of the hyperthermal oxygen adatoms on the TiO2 (110) surface occurs exclusively along the Ti troughs.

Du, Yingge; Dohnalek, Zdenek; Lyubinetsky, Igor

2008-02-21

400

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

401

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

402

ELECTRON DETACHMENT DISSOCIATION OF DERMATAN SULFATE OLIGOSACCHARIDES  

PubMed Central

The structural characterization of glycosaminoglycans (GAG) oligosaccharides has been a longstanding challenge in the field of mass spectrometry. In this work, we present the application of electron detachment dissociation (EDD) Fourier transform mass spectrometry to the analysis of dermatan sulfate (DS) oligosaccharides up to 10 residues in length. The EDD mass spectra of DS oligosaccharides were compared to their infrared multiphoton dissociation (IRMPD) mass spectra. EDD produces more abundant fragmentation than IRMPD with far less loss of SO3 from labile sulfate modifications. EDD cleaves all glycosidic bonds, yielding both conventional glycosidic bond fragmentation as well as satellite peaks resulting from the additional loss of 1 or 2 hydrogen atoms. EDD also yields more cross-ring fragmentation than IRMPD. For EDD, abundant cross-ring fragmentation in the form of A- and X-ions is observed, with 1,5Xn cleavages occurring for all IdoA residues and many of the GalNAc4S residues, except at the reducing and nonreducing ends. In contrast, IRMPD produces only A-type cross-ring fragmentation for long oligosaccharides (dp6 – dp10). As all the structurally informative fragment ions observed by IRMPD appear as a subset of the peaks found in the EDD mass spectrum, EDD shows great potential for the characterization of GAG oligosaccharides using a single tandem mass spectrometry experiment. PMID:18055211

Wolff, Jeremy J.; Laremore, Tatiana N.; Busch, Alexander M.; Linhardt, Robert J.; Amster, I. Jonathan

2009-01-01

403

The Dissociative Recombination of OH(+)  

NASA Technical Reports Server (NTRS)

Theoretical quantum chemical calculations of the cross sections and rates for the dissociative recombination of the upsilon = 0 level of the ground state of OH(+) show that recombination occurs primarily along the 2 (2)Pi diabatic route. The products are 0((1)D) and a hot H atom with 6.1 eV kinetic energy. The coupling to the resonances is very small and the indirect recombination mechanism plays only a minor role. The recommended value for the rate coefficient is (6.3 +/- 0.7) x 10(exp -9)x (T(e)/1300)(exp -0.48) cu.cm/s for 10 less than T(e) less than 1000 K.

Guberman, Steven L.

1995-01-01

404

A fluorine bomb calorimetric determination of the standard molar enthalpy of formation of silicon disulfide SiS 2(cr) at the temperature 298.15 K. Enthalpies of dissociation of Si–S bonds  

Microsoft Academic Search

A synthesis of high-purity silicon disulfide SiS2is described, and the F.t.-Raman spectrum of the solid is reported for the first time. The standard massic energy of reaction of SiS2(cr) with fluorine was measured in a bomb calorimeter. The combustion reaction was shown to proceed as follows: SiS2(cr)+8F2(g)=SiF4(g)+2SF6(g). The derived standard molar enthalpy of formation is: ?fHmo(SiS2, cr, 298.15 K)=?(254.6±2.9) kJ·mol?1.

Iwona Tomaszkiewicz; G. A. Hope; P. A. G. O'Hare

1997-01-01

405

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

PubMed

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

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

2012-09-01

406

A novel salt bridge mechanism highlights the need for nonmobile proton conditions to promote disulfide bond cleavage in protonated peptides under low-energy collisional activation.  

PubMed

The gas-phase fragmentation mechanisms of small models for peptides containing intermolecular disulfide links have been studied using a combination of tandem mass spectrometry experiments, isotopic labeling, structural labeling, accurate mass measurements of product ions, and theoretical calculations (at the MP2/6-311 + G(2d,p)//B3LYP/3-21G(d) level of theory). Cystine and its C-terminal derivatives were observed to fragment via a range of pathways, including loss of neutral molecules, amide bond cleavage, and S-S and C-S bond cleavages. Various mechanisms were considered to rationalize S-S and C-S bond cleavage processes, including charge directed neighboring group processes and nonmobile proton salt bridge mechanism. Three low-energy fragmentation pathways were identified from theoretical calculations on cystine N-methyl amide: (1) S-S bond cleavage dominated by a neighboring group process involving the C-terminal amide N to form either a protonated cysteine derivative or protonated sulfenyl amide product ion (44.3 kcal mol(-1)); (2) C-S bond cleavage via a salt bridge mechanism, involving abstraction of the alpha-hydrogen by the N-terminal amino group to form a protonated thiocysteine derivative (35.0 kcal mol(-1)); and (3) C-S bond cleavage via a Grob-like fragmentation process in which the nucleophilic N-terminal amino group forms a protonated dithiazolidine (57.9 kcal mol(-1)). Interestingly, C-S bond cleavage by neighboring group processes have high activation barriers (63.1 kcal mol(-1)) and are thus not expected to be accessible during low-energy CID experiments. In comparison to the energetics of simple amide bond cleavage, these S-S and C-S bond cleavage reactions are higher in energy, which helps rationalize why bond cleavage processes involving the disulfide bond are rarely observed for low-energy CID of peptides with mobile proton(s) containing intermolecular disulfide bonds. On the other hand, the absence of a mobile proton appears to "switch on" disulfide bond cleavage reactions, which can be rationalized by the salt bridge mechanism. This potentially has important ramifications in explaining the prevalence of disulfide bond cleavage in singly protonated peptides under MALDI conditions. PMID:17462910

Lioe, Hadi; O'Hair, Richard A J

2007-06-01

407

Enhancing the quality of H/D exchange measurements with mass spectrometry detection in disulfide-rich proteins using electron capture dissociation.  

PubMed

Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) has become a potent technique to probe higher-order structures, dynamics, and interactions of proteins. While the range of proteins amenable to interrogation by HDX MS continues to expand at an accelerating pace, there are still a few classes of proteins whose analysis with this technique remains challenging. Disulfide-rich proteins constitute one of such groups: since the reduction of thiol-thiol bonds must be carried out under suboptimal conditions (to minimize the back-exchange), it frequently results in incomplete dissociation of disulfide bridges prior to MS analysis, leading to a loss of signal, inadequate sequence coverage, and a dramatic increase in the difficulty of data analysis. In this work, the dissociation of disulfide-linked peptide dimers produced by peptic digestion of the 80 kDa glycoprotein transferrin in the course of HDX MS experiments is carried out using electron capture dissociation (ECD). ECD results in efficient cleavage of the thiol-thiol bonds in the gas phase on the fast LC time scale and allows the deuterium content of the monomeric constituents of the peptide dimers to be measured individually. The measurements appear to be unaffected by hydrogen scrambling, even when high collisional energies are utilized. This technique will benefit HDX MS measurements for any protein that contains one or more disulfides and the potential gain in sequence coverage and spatial resolution would increase with disulfide bond number. PMID:24820935

Bobst, Cedric E; Kaltashov, Igor A

2014-06-01