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1

Bond Dissociation Energies--A Continuing Story,  

National Technical Information Service (NTIS)

Most modern bond dissociation energies are obtained from kinetic rather than thermodynamic studies. This requires assumptions sometimes explicit and sometimes implicit which always require close scrutiny. Three case histories are examined spanning the per...

S. W. Benson

1987-01-01

2

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

3

Thermochemistry and bond dissociation energies of ketones.  

PubMed

Ketones are a major class of organic chemicals and solvents, which contribute to hydrocarbon sources in the atmosphere, and are important intermediates in the oxidation and combustion of hydrocarbons and biofuels. Their stability, thermochemical properties, and chemical kinetics are important to understanding their reaction paths and their role as intermediates in combustion processes and in atmospheric chemistry. In this study, enthalpies (?H°(f 298)), entropies (S°(T)), heat capacities (C(p)°(T)), and internal rotor potentials are reported for 2-butanone, 3-pentanone, 2-pentanone, 3-methyl-2-butanone, and 2-methyl-3-pentanone, and their radicals corresponding to loss of hydrogen atoms. A detailed evaluation of the carbon-hydrogen bond dissociation energies (C-H BDEs) is also performed for the parent ketones for the first time. Standard enthalpies of formation and bond energies are calculated at the B3LYP/6-31G(d,p), B3LYP/6-311G(2d,2p), CBS-QB3, and G3MP2B3 levels of theory using isodesmic reactions to minimize calculation errors. Structures, moments of inertia, vibrational frequencies, and internal rotor potentials are calculated at the B3LYP/6-31G(d,p) density functional level and are used to determine the entropies and heat capacities. The recommended ideal gas-phase ?H°(f 298), from the average of the CBS-QB3 and G3MP2B3 levels of theory, as well as the calculated values for entropy and heat capacity are shown to compare well with the available experimental data for the parent ketones. Bond energies for primary, secondary, and tertiary radicals are determined; here, we find the C-H BDEs on carbons in the ? position to the ketone group decrease significantly with increasing substitution on these ? carbons. Group additivity and hydrogen-bond increment values for these ketone radicals are also determined. PMID:22668341

Hudzik, Jason M; Bozzelli, Joseph W

2012-06-14

4

Characterization of CF bonds with multiple-bond character: bond lengths, stretching force constants, and bond dissociation energies.  

PubMed

Isoelectronic C=F(+) and C=O bonds contained in fluoro-substituted carbenium ions, aldehydes, and ketones are investigated with regard to their bond properties by utilizing the vibrational spectra of these molecules. It is demonstrated that bond dissociation energies (BDEs), bond lengths, vibrational stretching frequencies, and bond densities are not reliable descriptors of the bond strength. The latter is related to the intrinsic BDE, which corresponds to nonrelaxed dissociation products retaining the electronic structure and geometry they have in the molecule. It is shown that the harmonic stretching force constants k(a) of the localized internal coordinate vibrations (adiabatic vibrational modes) reflect trends in the intrinsic BDEs. The k(a) values of both CO and CF bonds are related to the bond lengths through a single exponential function. This observation is used to derive a common bond order n for 46 CO- and CF-containing molecules that reliably describes differences in bonding. CF bonds in fluorinated carbenium ions possess bond orders between 1.3 and 1.7 as a result of significant pi back-bonding from F to C, which is sensitive to electronic effects caused by substituents at the carbenium center. Therefore, the strength of the C=F(+) bond can be used as a sensor for (hyper)conjugation and other electronic effects influencing the stability of the carbenium ion. The diatomic C=F(+) ion has a true double bond due to pi donation from the F atom. The characterization of CF bonds with the help of adiabatic stretching modes is also applied to fluoronium ions (n = 0.3-0.6) and transition states involving CF cleavage and HF elimination (n = 0.7-0.8). PMID:19152353

Kraka, Elfi; Cremer, Dieter

2009-03-01

5

Bond Dissociation Energies in Second-Row Compounds  

SciTech Connect

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

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

2008-04-10

6

The dissociative bond.  

PubMed

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

Gordon, Nirit

2013-01-01

7

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

Microsoft Academic Search

Correlations of various indices of the stability and reactivity of carbon-centered radicals with ESR hyperfine splitting constants have been examined. For a large number of mono- and disubstituted radicals there is a moderately good linear correlation of R-proton hyperfine splitting constants (a(HR)) with radical stabilization enthalpies (RSE) and with BDE(C-H), the C-H bond dissociation energies for the corresponding parent compounds

Jochen J. Brocks; Hans-Dieter Beckhaus; Athelstan L. J. Beckwith; Christoph Ruchardt

1998-01-01

8

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

9

Accurate dissociation energies of O-H...O hydrogen-bonded 1-naphthol.solvent complexes  

NASA Astrophysics Data System (ADS)

Accurate O-H...O hydrogen-bond dissociation energies were measured for the supersonic-jet-cooled complexes 1-naphthol.S with S=D2O, ethanol, oxirane, and oxetane. A mass-selective pump-dump-probe method was used, combining stimulated emission pumping with resonant two-photon ionization and ion-dip techniques. The ground-state dissociation energies D0(S0) are 5.83+/-0.13 kcal/mol for d1-1-naphthol.D2O, 7.94+/-0.02 kcal/mol for 1-naphthol.ethanol, 7.71+/-0.14 kcal/mol for 1-naphthol.oxirane and >8.17 kcal/mol for 1-naphthol.oxetane. The D0's increase by 5%-7% upon excitation of 1-naphthol to the S1 state. These dissociation energies are compared to those of the analogous complexes with S=H2O, methanol, NH3, and ND3 [Chem. Phys. Lett. 246, 291 (1996)]. The trends in D0 are compared to the electric dipole moments ?, molecular polarizabilities ?, and gas-phase proton affinities of the H bond acceptor molecules. For the O-containing acceptors, the D0's correlate well with ?, but the only good overall correlation for both O- and N-containing acceptors was found between the dissociation energies and proton affinities.

Wickleder, Claudia; Henseler, Debora; Leutwyler, Samuel

2002-02-01

10

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

11

Calculation of bond dissociation energies for large molecules using locally dense basis sets  

NASA Astrophysics Data System (ADS)

A method is given for the calculation of gas-phase bond dissociation energies (BDEs) for relatively large molecules. The method combines the use of locally dense basis sets (LDBS) with density functional theory, using the B3LYP functional. For water and propene, primary and secondary regions are defined and the BDE is tested for consistency with respect to full (primary basis) calculations. Results obtained with LDBS closely approach the limit of using large basis sets throughout. An application of biochemical interest is the determination of the O-H BDE of ?-tocopherol, which contains 81 atoms.

DiLabio, G. A.; Wright, J. S.

1998-11-01

12

Bond dissociation free energy as a general parameter for flavonoid radical scavenging activity.  

PubMed

Notwithstanding multiple mechanisms of radical scavenging (RS), measured RS activities (RSA) of flavonoids are usually related to O-H bond dissociation enthalpy (BDE) for hydrogen atom transfer (HAT). For 12 flavonoids the reaction free energies were calculated for: (1) HAT, (2) single electron transfer-proton transfer (SET-PT) and (3) sequential proton loss electron transfer (SPLET) in gas and aqueous phases. Aqueous free energies, like bond dissociation (BDFEaq), ionisation (IFEaq) and deprotonation (?Gdeprot,aq) free energies were estimated using thermochemical cycles. While in gas HAT is a RS mechanism (BDFEg

Stepani?, Višnja; Gall Trošelj, Koraljka; Lu?i?, Bono; Markovi?, Zoran; Ami?, Dragan

2013-11-15

13

Determination of the C4-H bond dissociation energies of NADH models and their radical cations in acetonitrile.  

PubMed

Heterolytic and homolytic bond dissociation energies of the C4-H bonds in ten NADH models (seven 1,4-dihydronicotinamide derivatives, two Hantzsch 1,4-dihydropyridine derivatives, and 9,10-dihydroacridine) and their radical cations in acetonitrile were evaluated by titration calorimetry and electrochemistry, according to the four thermodynamic cycles constructed from the reactions of the NADH models with N,N,N',N'-tetramethyl-p-phenylenediamine radical cation perchlorate in acetonitrile (note: C9-H bond rather than C4-H bond for 9,10-dihydroacridine; however, unless specified, the C9-H bond will be described as a C4-H bond for convenience). The results show that the energetic scales of the heterolytic and homolytic bond dissociation energies of the C4-H bonds cover ranges of 64.2-81.1 and 67.9-73.7 kcal mol(-1) for the neutral NADH models, respectively, and the energetic scales of the heterolytic and homolytic bond dissociation energies of the (C4-H)(.+) bonds cover ranges of 4.1-9.7 and 31.4-43.5 kcal mol(-1) for the radical cations of the NADH models, respectively. Detailed comparison of the two sets of C4-H bond dissociation energies in 1-benzyl-1,4-dihydronicotinamide (BNAH), Hantzsch 1,4-dihydropyridine (HEH), and 9,10-dihydroacridine (AcrH(2)) (as the three most typical NADH models) shows that for BNAH and AcrH(2), the heterolytic C4-H bond dissociation energies are smaller (by 3.62 kcal mol(-1)) and larger (by 7.4 kcal mol(-1)), respectively, than the corresponding homolytic C4-H bond dissociation energy. However, for HEH, the heterolytic C4-H bond dissociation energy (69.3 kcal mol(-1)) is very close to the corresponding homolytic C4-H bond dissociation energy (69.4 kcal mol(-1)). These results suggests that the hydride is released more easily than the corresponding hydrogen atom from BNAH and vice versa for AcrH(2), and that there are two almost equal possibilities for the hydride and the hydrogen atom transfers from HEH. Examination of the two sets of the (C4-H)(.+) bond dissociation energies shows that the homolytic (C4-H)(.+) bond dissociation energies are much larger than the corresponding heterolytic (C4-H)(.+) bond dissociation energies for the ten NADH models by 23.3-34.4 kcal mol(-1); this suggests that if the hydride transfer from the NADH models is initiated by a one-electron transfer, the proton transfer should be more likely to take place than the corresponding hydrogen atom transfer in the second step. In addition, some elusive structural information about the reaction intermediates of the NADH models was obtained by using Hammett-type linear free-energy analysis. PMID:12584702

Zhu, Xiao-Qing; Li, Hai-Rong; Li, Qian; Ai, Teng; Lu, Jin-Yong; Yang, Yuan; Cheng, Jin-Pei

2003-02-17

14

Sequential bond energies of Pt +(NH 3) x ( x=1–4) determined by collision-induced dissociation and theory  

Microsoft Academic Search

The sequential bond energies of Pt+(NH3)x (x=1–4) are determined by collision-induced dissociation (CID) with Xe using guided-ion beam tandem mass spectrometry. Analysis of the kinetic energy-dependent cross sections includes consideration of multiple ion–neutral collisions, the internal energies of the complexes, and the dissociation lifetimes. We obtain the following 0K bond energies in eV (kJ\\/mol): 2.84±0.12 (274±12), 2.71±0.10 (261±10), 0.80±0.05 (77±5),

R. Liyanage; M. L. Styles; R. A. J. O’Hair; P. B. Armentrout

2003-01-01

15

Bond dissociation energies of organophosphorus compounds: an assessment of contemporary ab initio procedures.  

PubMed

Thermodynamic properties of phosphorus-containing compounds were investigated using high-level ab initio computations. An extended set of contemporary density functional theory (DFT) procedures was assessed for their ability to accurately predict bond dissociation energies of a set of phosphoranyl radicals. The results of meta- and double-hybrids as well as more recent methods, in particular M05, M05-2X, M06, and M06-2X, were compared with benchmark G3(MP2)-RAD values. Standard heats of formation, entropies, and heat capacities of a set of ten organophosphorus compounds were determined and the low-cost BMK functional was found to provide results consistent with available experimental data. In addition, bond dissociation enthalpies (BDEs) were computed using the BMK, M05-2X, and SCS-ROMP2 procedure. The three methods give the same stability trend. The BDEs of the phosphorus(III) molecules were found to be lower than their phosphorus(V) counterparts. Overall, the following ordering is found: BDE(P-OPh) < BDE(P-CH(3)) < BDE(P-Ph) < BDE(P-OCH(3)). PMID:20141194

Hemelsoet, Karen; Van Durme, Frederick; Van Speybroeck, Veronique; Reyniers, Marie-Françoise; Waroquier, Michel

2010-03-01

16

On the dissociation energies and bonding in NiCO + and TiCO +  

NASA Astrophysics Data System (ADS)

Ab initio calculations on the NiCO + and TiCO + molecules are carried out using large Gaussian basis sets and extensive treatment of electron correlation. The NiCO + molecule is found to have a 2? + ground state with a 2? state only 2.1 kcal/mole higher in energy. The 4? and 4? states of TiCO + are almost degenerate, but the 4? state has a substantially greater bond length due to a larger contribution from the Ti + (3d 24s 1) occupation. The Ni +-CO structure is about 11 and 28 kcal/mole more stable than the Ni +-OC and the T-shaped structures, respectively. The dissociation energy De of the Ni +-CO structure is computed to be 34.3 kcal/mole, suggesting that the experimental value of 48±2 kal/mole is substantially too large. The corresponding De of TiCO + is 28 kcal/mole.

Bauschlicher, Charles W.; Barnes, Leslie A.

1988-09-01

17

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

PubMed

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

Zhao, Yongyu; Bordwell, Frederick G.

1996-09-20

18

Collision-induced dissociation of Ni sup + sub n ( n =2--18) with Xe: Bond energies, geometrical structures, and dissociation pathways  

SciTech Connect

The kinetic energy dependence of the collision-induced dissociation (CID) of Ni{sup +}{sub {ital n}} ({ital n}=2--18) with xenon is studied by using a guided ion beam mass spectrometer. Bond energies of nickel cluster ions, {ital D}{sup 0}(Ni{sup +}{sub {ital n}{minus}1}--Ni), are determined from measurements of the CID thresholds. Bond energies for neutral nickel clusters, {ital D}{sup 0}(Ni{sub {ital n}{minus}1}--Ni), are derived by combining these ionic bond energies with literature values of ionization energies for Ni{sub {ital n}}. Both {ital D}{sup 0}(Ni{sup +}{sub {ital n}{minus}1}--Ni) and {ital D}{sup 0}(Ni{sub {ital n}{minus}1}--Ni) are found to increase nonmonotonically as a function of cluster size, with local maxima at {ital n}=3, 7, and 13 for ionic clusters and at {ital n}=6 and 13 for neutral clusters. Examination of the cluster size dependence of nickel cluster bond energies leads to speculations on the likely cluster geometric structures. Examination of the general dissociation behavior over a broad collision energy range shows that nickel cluster ions dissociate primarily by sequential atom loss, although exceptions are noted.

Lian, L.; Su, C.; Armentrout, P.B. (Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States))

1992-05-15

19

Trends in bond dissociation energies of alcohols and aldehydes computed with multireference averaged coupled-pair functional theory.  

PubMed

As part of our ongoing investigation of the combustion chemistry of oxygenated molecules using multireference correlated wave function methods, we report bond dissociation energies (BDEs) in C1-C4 alcohols (from methanol to the four isomers of butanol) and C1-C4 aldehydes (from methanal to butanal). The BDEs are calculated with a multireference averaged coupled-pair functional-based scheme. We compare these multireference BDEs with those derived from experiment and single-reference methods. Trends in BDEs for the alcohols and aldehydes are rationalized by considering geometry relaxations of dissociated radical fragments, resonance stabilization, and hyperconjugation. Lastly, we discuss the conjectured association between bond strengths and rates of hydrogen abstraction by hydroxyl radicals. In general, abstraction reaction rates are higher at sites where the C-H bond energies are lower (and vice versa). However, comparison with available rate data shows this inverse relationship between bond strengths and abstraction rates does not hold at all temperatures. PMID:24708179

Oyeyemi, Victor B; Keith, John A; Carter, Emily A

2014-05-01

20

Bond Dissociation Energies for Substituted Polycyclic Aromatic Hydrocarbons and Their Cations  

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

21

Collision-induced dissociation of Fe sub n sup + ( n =2--19) with Xe: Bond energies, geometric structures, and dissociation pathways  

SciTech Connect

The kinetic energy dependence of the collision-induced dissociation (CID) of Fe{sup +}{sub {ital n}} ({ital n}=11--19) with Xe is studied by using a guided ion beam mass spectrometer. As previously reported for smaller iron cluster ions, these iron cluster ions dissociate exclusively by evaporation, the sequential loss of Fe atoms. Bond energies for the larger iron cluster ions {ital D}{sup 0}(Fe{sup +}{sub {ital n}{minus}1}--Fe), {ital n}=11--19, as well as updated values for the smaller cluster ions, {ital n}=2--10, are reported. These energies are derived after explicit consideration of the effect of secondary collisions between Fe{sup +}{sub {ital n}} and Xe, and of the lifetimes of the energized iron cluster ions. Bond energies for neutral iron clusters are derived by combining these ionic bond energies with literature ionization energies for Fe{sub {ital n}}. Except for the dimers, we find that the bond energies of ionic and neutral iron clusters are very similar and change nonmonotonically as a function of cluster size, with local maxima at {ital n}=6, 7, 13, 15, and 19; and local minima at {ital n}=8, 14, and 18. Evidence for the existence of weakly bound isomers of iron cluster ions is also observed.

Lian, L.; Su, C.; Armentrout, P.B. (Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States))

1992-09-15

22

Collision-induced dissociation of Ti sup + sub n ( n =2--22) with Xe: Bond energies, geometric structures, and dissociation pathways  

SciTech Connect

The kinetic energy dependence of the collision-induced dissociation (CID) of Ti{sup +}{sub {ital n}} ({ital n}=2--22) with Xe is studied by using a guided ion beam mass spectrometer. Examination of the CID cross section behavior over a broad collision energy range demonstrates that Ti{sup +}{sub {ital n}} clusters dissociate exclusively by sequential loss of Ti atoms. Bond energies of ionic titanium clusters, {ital D}{sup 0}(Ti{sup +}{sub {ital n}{minus}1}--Ti), are determined from measurements of the CID thresholds. {ital D}{sup 0}(Ti{sup +}{sub {ital n}{minus}1}--Ti) are found to change significantly as a function of cluster size, with local maxima at {ital n}=7, 13, and 19. This pattern of highly stable cluster ions suggests that titanium cluster ions favor icosahedral structures.

Lian, L.; Su, C.; Armentrout, P.B. (Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States))

1992-09-15

23

Application of density functional theory \\/Hartree-Fock hybrid methods. Geometries and bond dissociation energies of Al + complexes  

Microsoft Academic Search

A mixture of Hartree-Fock exchange and density functional theory exchange-correlation treatment has been applied to determine the geometry and bond dissociation energies (BDEs) of cationic Al+-X complexes (X = CH3, NH3, H2O, OH, HF, HCN, HNC, CO, CN, CH2O, CO2, N2, O2, and F2). By using the local spin density approximation and the ‘Becke-3-Lee-Young-Parr’ functionals each combined with three different

Detlef Stöckigt

1996-01-01

24

Collision-induced CH bond dissociation in highly excited toluene  

NASA Astrophysics Data System (ADS)

The bond dissociation of highly excited toluene colliding with argon has been studied by use of classical trajectory procedures. All 39 stretches and bends of toluene are included in the model. Both methyl and adjacent ring CH bonds, each with the initial vibrational energy 0.10 eV below the dissociation threshold, are in interaction with Ar. The dissociation probabilities are PCH methyl = 0.14 and PCH ring = 0.19 at 300 K. The CH methyl bond dissociation is a result of the Ar-CH methyl collision transferring a large amount of energy (? kT) via the T ? V pathway. The activation of CH ring toward dissociation occurs through a series of small steps gaining energy intramolecularly from the methyl end. The Ar-CH ring interaction is unimportant in transferring energy to the CH ring stretch and in turn causing the bond dissociation.

Ree, J.; Kim, Y. H.; Shin, H. K.

2004-08-01

25

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

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

26

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

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

27

Communication: The highest frequency hydrogen bond vibration and an experimental value for the dissociation energy of formic acid dimer.  

PubMed

The highest frequency hydrogen bond fundamental of formic acid dimer, ?(24) (B(u)), is experimentally located at 264 cm(-1). FTIR spectra of this in-plane bending mode of (HCOOH)(2) and band centers of its symmetric D isotopologues (isotopomers) recorded in a supersonic slit jet expansion are presented. Comparison to earlier studies at room temperature reveals the large influence of thermal excitation on the band maximum. Together with three B(u) combination states involving hydrogen bond fundamentals and with recent progress for the Raman-active modes, this brings into reach an accurate statistical thermodynamics treatment of the dimerization process up to room temperature. We obtain D(0) = 59.5(5) kJ/mol as the best experimental estimate for the dimer dissociation energy at 0 K. Further improvements have to wait for a more consistent determination of the room temperature equilibrium constant. PMID:22519308

Kollipost, F; Wugt Larsen, R; Domanskaya, A V; Nörenberg, M; Suhm, M A

2012-04-21

28

Theoretical calculation of bond dissociation energies and heats of formation for nitromethane and polynitromethanes with density functional theory  

NASA Astrophysics Data System (ADS)

The C bond NO2 bond dissociation energies (BDEs) and the heats of formation (HOFs) of nitromethane and polynitromethanes (dinitromethane, trinitromethane, and tetranitromethane) system in gas phase at 298.15 K were calculated theoretically. Density functional theory (DFT) B3LYP, B3P86, B3PW91, and PBE0 methods in combination with different basis sets were employed. It was found that the C bond NO2 bond BDEs can be improved from B3LYP to B3PW91 to B3P86 or PBE0 functional. Levels of theory employing B3P86 and PBE0 functionals were found to be sufficiently reliable without the presence of diffusion functions. As the number of NO2 groups on the same C atom increases, the PBE0 functional performs better than the B3P86 functional. Regarding the calculated HOFs, all four functionals can yield satisfactory results with deviations of <2 kcal mol-1 from experimental ones for CH2(NO2)2 and CH(NO2)3, when the diffusion functions are not augmented. For the C(NO2)4 molecule, the large basis sets augmented with polarization functions and diffusion functions are required to yield a good result.

Su, Xinfang; Cheng, Xinlu; Liu, Yonggang; Li, Qinghuan

29

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

30

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

SciTech Connect

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

Ruscic, Branko (Argonne National Laboratory); Wagner, Albert F. (Argonne Naitonal Laboratory); Harding, Lawerence B. (Argonne National Laboratory); Asher, Robert L. (Argonne National Laboratory); Feller, David F. (BATTELLE (PACIFIC NW LAB)); Dixon, David A. (BATTELLE (PACIFIC NW LAB)); Peterson, Kirk A. (WASHINGTON STATE UNIV TC); Song, Yang (Ames Laboratory); Qian, Ximei (Ames Laboratory); Ng, C Y. (Iowa State University); Liu, Jianbo (Lawrence Berkeley National Laboratory); Wenwu, Chen (Lawrence Berkeley National Laboratory)

2001-12-01

31

Establishment of heterolytic and homolytic Y-NO2 bond dissociation energy scales of nitro-containing compounds in acetonitrile: chemical origin of NO2 release and capture.  

PubMed

The first heterolytic and homolytic N(O)-NO(2) bond dissociation energy scales of three types Y-nitro (Y = N, O) compounds and corresponding radical anions in acetonitrile were established by using titration calorimetry combined with relevant electrochemical data through proper thermodynamic cycles. PMID:18307353

Li, Xin; Zhu, Xiao-Qing; Zhang, Fan; Wang, Xiao-Xiao; Cheng, Jin-Pei

2008-03-21

32

Photodissociation measurements of bond dissociation energies: Ti[sup +][sub 2], V[sup +][sub 2], Co[sup +][sub 2], and Co[sup +][sub 3  

SciTech Connect

The bond dissociation energies of Ti[sup +][sub 2], V[sup +][sub 2], Co[sup +][sub 2], and Co[sup +][sub 3] have been measured from the sudden onset of predissociation in the photodissociation spectra of these molecules, yielding values of [ital D][sup [circ

Russon, L.M.; Heidecke, S.A.; Birke, M.K.; Conceicao, J.; Morse, M.D.; Armentrout, P.B. (Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States))

1994-04-01

33

A Promising Tool to Achieve Chemical Accuracy for Density Functional Theory Calculations on Y-NO Homolysis Bond Dissociation Energies  

PubMed Central

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

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

2012-01-01

34

Determination of N-NO bond dissociation energies of N-methyl-N-nitrosobenzenesulfonamides in acetonitrile and application in the mechanism analyses on NO transfer.  

PubMed

The heterolytic and homolytic N-NO bond dissociation energies of seven substituted N-methyl-N-nitrosobenzenesulfonamides (abbreviated as G-MNBS, G = p-OCH(3), p-CH(3), p-H, p-Cl, p-Br, 2,5-2Cl, m-NO(2)) in acetonitrile solution were evaluated for the first time by using titration calorimetry and relative thermodynamic cycles according to Hess' law. The results show that the energetic scales of the heterolytic and homolytic N-NO bond dissociation energies of G-MNBS in acetonitrile solution cover the ranges from 44.3 to 49.5 and from 33.0 to 34.9 kcal/mol for the neutral G-MNBS, respectively, which indicates that N-methyl-N-nitrosobenzenesulfonamides are much easier to release a NO radical (NO(*)) than to release a NO cation (NO(+)). The estimation of the heterolytic and homolytic (N-NO)(-)(*) bond dissociation energies of the seven G-MNBS radical anions in acetonitrile solution gives the energetic ranges of -15.8 to -12.9 and -3.1 to 1.8 kcal/mol for the (N-NO)(-)(*) bond homolysis and heterolysis, respectively, which means that G-MNBS radical anions are very unstable at room temperature and able to spontaneously or easily release a NO radical or NO anion (NO(-)), but releasing a NO radical is easier than releasing NO anion. These determined N-NO bond dissociation energies of G-MNBS and their radical anions have been successfully used in the mechanism analyses of NO transfer from G-MNBS to 3,6-dibromocarbazole and the reactions of NO with the substituted N-methyl-benzenesulfonamide nitranions (G-MBSN(-)) in acetonitrile solution. PMID:15725027

Zhu, Xiao-Qing; Hao, Wei-Fang; Tang, Hui; Wang, Chun-Hua; Cheng, Jin-Pei

2005-03-01

35

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

36

Two important factors influencing shock sensitivity of nitro compounds: Bond dissociation energy of X–NO 2 (X = C, N, O) and Mulliken charges of nitro group  

Microsoft Academic Search

DFT\\/BLYP\\/DNP is employed to calculate bond dissociation energy of X–NO2 (X=C, N, O) and Mulliken charges of nitro group of 14 kinds of nitro compounds, and partial least squares approximation is applied to linearly fit their shock initiation pressure (p90%,TMD). It is found that the fitted values are in good agreement with the experimental shock initiation pressures. The fitted model

Bisheng Tan; Xinping Long; Rufang Peng; Hongbo Li; Bo Jin; Shijin Chu; Haishan Dong

2010-01-01

37

Guided ion beam studies of the reactions of V{sub n}{sup +} (n=2{endash}17) with O{sub 2}: Bond energies and dissociation pathways  

SciTech Connect

The kinetic energy dependence of the reactions of V{sub n}{sup +} (n=2{endash}17) with oxygen is studied using a guided ion beam mass spectrometer. In all but the smallest clusters, the primary reaction process at low energies is the formation of a vanadium cluster dioxide ion which then loses one or two vanadium atoms or a vanadium oxide diatom (VO). Vanadium atom loss is the preferred reaction pathway for large clusters (n{ge}5), whereas loss of VO is more favorable for the smallest reactant clusters (n{le}4). As the collision energy is increased, these primary products dissociate further by loss of additional vanadium atoms. Bond dissociation energies of the vanadium cluster oxides are determined by analysis of the kinetic energy dependence of several different products. The effect of oxygen atoms on the stabilities of vanadium cluster ions is discussed and compared with bulk phase thermochemistry. {copyright} {ital 1998 American Institute of Physics.}

Xu, J.; Rodgers, M.T.; Griffin, J.B.; Armentrout, P.B. [Department of Chemistry, University of Utah, Salt Lake City, Utah84112 (United States)] [Department of Chemistry, University of Utah, Salt Lake City, Utah84112 (United States)

1998-06-01

38

Mechanistic Investigation of Phosphate Ester Bond Cleavages of Glycylphosphoserinyltryptophan Radical Cations under Low-Energy Collision-Induced Dissociation  

NASA Astrophysics Data System (ADS)

Under the conditions of low-energy collision-induced dissociation (CID), the canonical glycylphosphoserinyltryptophan radical cation having its radical located on the side chain of the tryptophan residue ([G p SW]•+) fragments differently from its tautomer with the radical initially generated on the ?-carbon atom of the glycine residue ([G• p SW]+). The dissociation of [G• p SW]+ is dominated by the neutral loss of H3PO4 (98 Da), with backbone cleavage forming the [b2 - H]•+/y1 + pair as the minor products. In contrast, for [G p SW]•+, competitive cleavages along the peptide backbone, such as the formation of [G p SW - CO2]•+ and the [c2 + 2H]+/[z1 - H]•+ pair, significantly suppress the loss of neutral H3PO4. In this study, we used density functional theory (DFT) to examine the mechanisms for the tautomerizations of [G• p SW]+ and [G p SW]•+ and their dissociation pathways. Our results suggest that the dissociation reactions of these two peptide radical cations are more efficient than their tautomerizations, as supported by Rice-Ramsperger-Kassel-Marcus (RRKM) modeling. We also propose that the loss of H3PO4 from both of these two radical cationic tautomers is preferentially charge-driven, similar to the analogous dissociations of even-electron protonated peptides. The distonic radical cationic character of [G• p SW]+ results in its charge being more mobile, thereby favoring charge-driven loss of H3PO4; in contrast, radical-driven pathways are more competitive during the CID of [G p SW]•+.

Quan, Quan; Hao, Qiang; Song, Tao; Siu, Chi-Kit; Chu, Ivan K.

2013-04-01

39

Sequential bond energies of Fe+ (CO2)n, n = 1-5, determined by threshold collision-induced dissociation and ab initio theory.  

PubMed

Collision-induced dissociation of the Fe+ (CO2)n complexes for n = 1-5 is studied using kinetic energy dependent guided ion beam mass spectrometry. In all cases, the primary products are endothermic loss of an intact neutral ligand from the complex. The cross section thresholds are interpreted to yield 0 K bond energies after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and unimolecular decay rates. These values are compared with density functional theoretical values for all five complexes. Theory provides bond energies in reasonable agreement with experiment for n = 1-4 and predictions for the infrared spectroscopy of these complexes that agree nicely with experimental results of Gregoire and Duncan (J. Chem. Phys. 2002, 117, 2120). Our thermochemical results are also compared with the Fe+ (CO)n and Fe+ (N2)n complexes, previously studied. PMID:16354023

Armentrout, P B; Koizumi, Hideya; MacKenna, Meghan

2005-12-22

40

Dipole effects on cation-pi interactions: absolute bond dissociation energies of complexes of alkali metal cations to N-methylaniline and N,N-dimethylaniline.  

PubMed

Threshold collision-induced dissociation of M (+)( nMA) x with Xe is studied using guided ion beam mass spectrometry, where nMA = N-methylaniline and N, N-dimethylaniline and x = 1 and 2. M (+) includes the following alkali metal cations: Li (+), Na (+), K (+), Rb (+), and Cs (+). In all cases, the primary dissociation pathway corresponds to the endothermic loss of an intact nMA ligand. The primary cross section thresholds are interpreted to yield 0 and 298 K bond dissociation energies (BDEs) for ( nMA) x-1 M (+)-( nMA) after accounting for the effects of multiple ion-neutral collisions, the internal and kinetic energy distributions of the reactants, and the dissociation lifetimes. Density functional theory calculations at the B3LYP/6-31G* level of theory are used to determine the structures of these complexes, which are also used in single-point calculations at the MP2(full)/6-311+G(2d,2p) level to determine theoretical BDEs. The results of these studies are compared to previous studies of the analogous M (+)(aniline) x complexes to examine the effects of methylation of the amino group on the binding interactions. Comparisons are also made to a wide variety of cation-pi complexes previously studied to elucidate the contributions that ion-dipole, ion-induced-dipole, and ion-quadrupole interactions make to the overall binding. PMID:18698747

Hallowita, Nuwan; Carl, Damon R; Armentrout, P B; Rodgers, M T

2008-09-01

41

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

42

The low-energy unimolecular reaction rate constants for the gas phase, Ni+-mediated dissociation of the C-C sigma bond in acetone.  

PubMed

The time dependence of the gaseous unimolecular decomposition of the jet-cooled adduct ion, Ni+-OC(CH3)2, was monitored through selective detection of the Ni+CO fragment ion. Various resolved amounts of energy in the range 15600-18800 cm(-1) were supplied to initiate the dissociation reaction through absorption of laser photons by the title molecular complex. First-order rate constants, k(E), ranged from 113000 to 55000 s(-1) and decreased with decreasing amounts of internal excitation. The energy used to initiate the reaction is well below that required to fragment C-C sigma bonds and indicates the necessity of the Ni+ cation to induce bond activation and fragmentation. These measurements are carried out in a unique apparatus and represent the first direct kinetic study of such catalytic type reactions. PMID:19725574

Castleberry, Vanessa A; Dee, S Jason; Villarroel, Otsmar J; Laboren, Ivanna E; Frey, Sarah E; Bellert, Darrin J

2009-10-01

43

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

NASA Astrophysics Data System (ADS)

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

DiLabio, Gino A.; Koleini, Mohammad

2014-05-01

44

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

PubMed

Dispersion-correcting potentials (DCPs) are atom-centered Gaussian functions that are applied in a manner that is similar to effective core potentials. Previous work on DCPs has focussed on their use as a simple means of improving the ability of conventional density-functional theory methods to predict the binding energies of noncovalently bonded molecular dimers. We show in this work that DCPs developed for use with the LC-?PBE functional along with 6-31+G(2d,2p) basis sets are capable of simultaneously improving predicted noncovalent binding energies of van der Waals dimer complexes and covalent bond dissociation enthalpies in molecules. Specifically, the DCPs developed herein for the C, H, N, and O atoms provide binding energies for a set of 66 noncovalently bonded molecular dimers (the "S66" set) with a mean absolute error (MAE) of 0.21 kcal/mol, which represents an improvement of more than a factor of 10 over unadorned LC-?PBE/6-31+G(2d,2p) and almost a factor of two improvement over LC-?PBE/6-31+G(2d,2p) used in conjunction with the "D3" pairwise dispersion energy corrections. In addition, the DCPs reduce the MAE of calculated X-H and X-Y (X,Y = C, H, N, O) bond dissociation enthalpies for a set of 40 species from 3.2 kcal/mol obtained with unadorned LC-?PBE/6-31+G(2d,2p) to 1.6 kcal/mol. Our findings demonstrate that broad improvements to the performance of DFT methods may be achievable through the use of DCPs. PMID:24832350

DiLabio, Gino A; Koleini, Mohammad

2014-05-14

45

Pressure catalyzed bond dissociation in an anthracene cyclophane photodimer.  

PubMed

The anthracene cyclophane bis-anthracene (BA) can undergo a [4 + 4] photocycloaddition reaction that results in a photodimer with two cyclobutane rings. We find that the subsequent dissociation of the dimer, which involves the rupture of two carbon-carbon bonds, is strongly accelerated by the application of mild pressures. The reaction kinetics of the dimer dissociation in a Zeonex (polycycloolefin) polymer matrix were measured at various pressures and temperatures. Biexponential reaction kinetics were observed for all pressures, consistent with the presence of two different isomers of bis(anthracene). One of the rates showed a strong dependence on pressure, yielding a negative activation volume for the dissociation reaction of ?V(++) = -16 Å(3). The 93 kJ/mol activation energy for the dissociation reaction at ambient pressure is lowered by more than an order of magnitude from 93 to 7 kJ/mol with the application of modest pressure (0.9 GPa). Both observations are consistent with a transition state that is stabilized at higher pressures, and a mechanism for this is proposed in terms of a two-step process where a flattening of the anthracene rings precedes rupture of the cyclobutane rings. The ability to catalyze covalent bond breakage in isolated small molecules using compressive forces may present opportunities for the development of materials that can be activated by acoustic shock or stress. PMID:22486461

Jezowski, Sebastian R; Zhu, Lingyan; Wang, Yaobing; Rice, Andrew P; Scott, Gary W; Bardeen, Christopher J; Chronister, Eric L

2012-05-01

46

Theoretical study of GeH sub n , AsH sub n , and SeH sub n : Bond dissociation energies  

SciTech Connect

{ital Ab} {ital initio} molecular orbital theory (Moller--Plesset perturbation theory to fourth order and new basis sets developed for Ge, As, and Se) is used to calculate the atomization energies of GeH{sub {ital n}}({ital n}=1--4), AsH{sub {ital n}}({ital n}=1--3), and SeH{sub {ital n}}({ital n}=1--2). Good agreement is found with the experimental bond dissociation energies of these hydrides derived from recent photoionization studies. The theoretical energies are combined with experimental data on the isolated atoms to determine ideal enthalpies of formation at 0 K for these hydrides, which are expected to have an accuracy of about {plus minus}3 kcal/mol ({plus minus}0.15 eV).

Binning, R.C. Jr. (Department of Chemistry and Physics, Carlow College, Pittsburgh, Pennsylvania 15213 (USA)); Curtiss, L.A. (Chemical Technology Division/Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439-4837 (USA))

1990-02-01

47

Cation-ether complexes in the gas phase: Bond dissociation energies and equilibrium structures of Li{sup +} (1,2-dimethoxyethane){sub x}, x= 1 and 2, and Li{sup +}(12-crown-4)  

SciTech Connect

Bond dissociation energies, equilibrium structures, and harmonic vibrational frequencies are reported for Li{sup +}(DXE), where DXE= CH{sub 3}O(CH{sub 2}){sub 2}OCH{sub 3}, Li{sup +}(DXE){sub 2}, and Li{sup +}(12-crown-4). The bond dissociation energies are determined experimentally by analysis of the thresholds for collision-induced dissociation of the cation-ether complexes by xenon (measured using guided ion beam mass spectroscopy) and computationally by ab initio electronic structure calculations. For Li{sup +}(DXE){sub x}, x= 1 and 2, the primary and lowest energy dissociation channel observed experimentally is endothermic loss of one dimethoxyethane molecule. For Li{sup +}(12-crown-4), the primary dissociation channel is endothermic loss of the intact crown ether, although ligand fragmentation is also observed. The cross section thresholds are interpreted to yield 0 and 298 K bond energies after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and unimolecular decay rates. The calculated and experimentally-derived bond energies are in good agreement for Li{sup +}(DXE), are in reasonable agreement for Li{sup +}(12-crown-4), and differ by 32{+-}12 kJ/mol for Li{sup +}(DXE){sub 2}. The equilibrium structures are determined primarily by strong electrostatic and polarization interactions between Li{sup +} and the ligands. 65 refs., 7 figs., 5 tabs.

Ray, D.; Feller, D.; Glendening, E.D. [Pacific Northwest National LAb., Richland, WA (United States)] [Pacific Northwest National LAb., Richland, WA (United States); More, M.B.; Armentrout, P.B. [Univ. of Utah, Salt Lake City, UT (United States)] [Univ. of Utah, Salt Lake City, UT (United States)

1996-10-03

48

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

49

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

PubMed

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

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

2014-01-14

50

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

SciTech Connect

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

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

1999-01-20

51

Fourier transform-ion cyclotron resonance study of the gas-phase acidities of germane and methylgermane; Bond dissociation energy of germane.  

PubMed

An accurate gas-phase acidity for germane (enthalpy scale, equivalent to the proton affinity of GeH3 (-)), ?H acid (o)(GeH4) = 1502.0 ± 5.1 kJ mol(-1), is obtained by constructing a consistent acidity ladder between GeH4, and H2S by using Fourier transform-ion cyclotron resonance spectrometry, and 0 and 298.15 K values for the first bond dissociation energy of GeH4 are proposed: D0 (o)(H3Ge-H) = 352 ± 9 kJ mol(-1); D (o)(H3Ge-H) = 358 ± 9 kJ mol(-1), respectively. These results are compared with experimental and theoretical data reported in the literature. Methylgermane was found to be a weaker acid than germane by approximately 35 kJ mol(-1): ?H acid (o) = 1536.6 kJ mol(-1). PMID:24234744

Decouzon, M; Gal, J F; Gayraud, J; Maria, P C; Vaglio, G A; Volpe, P

1993-01-01

52

Cation-ether complexes in the gas phase: Bond dissociation energies and equilibrium structures of Li{sup +}[O(CH{sub 3}){sub 2}]{sub x}, x=1-4  

SciTech Connect

Bond dissociation energies, equilibrium structures, and harmonic vibrational frequencies of Li{sup +}[O(CH{sub 3}){sub 2}]{sub x}, x=1-4, are reported. The bond dissociation energies are determined experimentally by analysis of the thresholds for collision-induced dissociation of the cation-ether complexes by xenon (measured using guided ion beam mass spectrometry) and computationally by ab initio electronic structure calculation at the RHF and MP2 levels of theory. In all cases, the primary and lowest energy dissociation channel observed experimentally is endothermic loss of one ether molecule. The cross-section thresholds are interpreted to yield 0 and 298 K bond energies after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and unimolecular decay rates. The experimental and theoretical bond energies are in good agreement with previous experimental results. Some of the discrepancies disappear at the complete basis set limit. The equilibrium structures are determined primarily by strong electrostatic and polarization interactions. Charge transfer interactions are also important, as indicated by natural energy decomposition analysis of the calculated wave functions. 59 refs., 6 figs., 5 tabs.

More, M.B.; Armentrout, P.B. [Univ. of Utah, Salt Lake City, UT (United States)] [Univ. of Utah, Salt Lake City, UT (United States); Glendening, E.D.; Ray, D.; Feller, D. [Pacific Northwest Lab., Richland, WA (United States)] [Pacific Northwest Lab., Richland, WA (United States)

1996-02-01

53

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

54

Does Electron Capture Dissociation Cleave Protein Disulfide Bonds?  

PubMed Central

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

Ganisl, Barbara; Breuker, Kathrin

2012-01-01

55

The impact of carbon-hydrogen bond dissociation energies on the prediction of the cytochrome P450 mediated major metabolic site of drug-like compounds.  

PubMed

Cytochrome P450 is a family of enzymes which is estimated to be responsible for over 75% of phase I drug metabolism. In this process carbon hydrogen bonds (C-H) are broken for hydroxylation indicating that the bond dissociation energy (BDE) plays a pivotal role. A host of experimentally derived C-H BDEs were benchmarked against their theoretical counterparts and an excellent correlation was found (R(2) = 0.9746, n = 100). The C-H BDEs were calculated for fifty drugs with known major hydrogen abstraction sites. Of those twelve (24%) had their major metabolic site at the lowest C-H BDE. The most prominent factor in determining the metabolic site is the presence of tertiary and secondary amine moieties (44%). Other features such as lipophilicity and steric accessibility of the pertinent molecular scaffolds are also important. Nevertheless, out of the 586 C-H BDEs calculated the average of the major hydrogen abstraction sites are statistically significantly lower by 6.9-12.8 kcal/mol (p-value = 7.257 × 10(-9)). This means that C-H BDEs are an indispensable component in building reliable models of first pass metabolism of xenobiotics. PMID:22960693

Drew, Kurt L M; Reynisson, Jóhannes

2012-10-01

56

Establishment of the C-NO bond dissociation energy scale in solution and its application in analyzing the trend of NO transfer from C-nitroso compound to thiols.  

PubMed

The first set of experimentally determined C-NO bond homolytic and heterolytic dissociation enthalpies in solution is derived by using direct titration calorimetry combined with appropriate electrode potentials through thermodynamic cycles. The homolytic bond dissociation energy scale (BDEs) of the corresponding C-NO bonds in the gas phase was also calculated at the MP2/6-311+G**//B3LYP/6-31G* level and BP86/6-31G*//B3LYP/6-31G* level of theory for the purpose of comparison. The C-NO and S-NO bond thermodynamic parameters were used to predict the trend of NO transfer from C-nitroso substrates to thiols in acetonitrile solution. PMID:19453157

Li, Xin; Deng, Hui; Zhu, Xiao-Qing; Wang, Xiaoxiao; Liang, Hao; Cheng, Jin-Pei

2009-06-19

57

Communication: Determination of the bond dissociation energy (D0) of the water dimer, (H2O)2, by velocity map imaging  

NASA Astrophysics Data System (ADS)

The bond dissociation energy (D0) of the water dimer is determined by using state-to-state vibrational predissociation measurements following excitation of the bound OH stretch fundamental of the donor unit of the dimer. Velocity map imaging and resonance-enhanced multiphoton ionization (REMPI) are used to determine pair-correlated product velocity and translational energy distributions. H2O fragments are detected in the ground vibrational (000) and the first excited bending (010) states by 2 + 1 REMPI via the C~ 1B1 (000) <-- X~ 1A1 (000 and 010) transitions. The fragments' velocity and center-of-mass translational energy distributions are determined from images of selected rovibrational levels of H2O. An accurate value for D0 is obtained by fitting both the structure in the images and the maximum velocity of the fragments. This value, D0 = 1105 +/- 10 cm-1 (13.2 +/- 0.12 kJ/mol), is in excellent agreement with the recent theoretical value of D0 = 1103 +/- 4 cm-1 (13.2 +/- 0.05 kJ/mol) suggested as a benchmark by Shank et al. [J. Chem. Phys. 130, 144314 (2009)].

Rocher-Casterline, Blithe E.; Ch'ng, Lee C.; Mollner, Andrew K.; Reisler, Hanna

2011-06-01

58

Free energy calculations of gramicidin dimer dissociation.  

PubMed

Molecular dynamics simulations, combined with umbrella sampling, is used to study how gramicidin A (gA) dimers dissociate in the lipid bilayer. The potential of mean force and intermolecular potential energy are computed as functions of the distance between center of masses of the two gA monomers in two directions of separation: parallel to the bilayer surface and parallel to the membrane normal. Results from this study show that the dissociation of gA dimers occurs via lateral displacement of gA monomers followed by tilting of dimers with respect to the lipid bilayer normal. It is found that the dissociation energy of gA dimers in the dimyristoylphosphatidylcholine bilayer is 14 kcal mol(-1) (~22 kT), which is approximately equal to the energy of breaking six intermolecular hydrogen bonds that stabilize the gA channel dimer. PMID:21988458

Wanasundara, Surajith N; Krishnamurthy, Vikram; Chung, Shin-Ho

2011-11-24

59

Periodic trends in transition metal-hydrogen, metal-carbon, and metal-oxygen bond dissociation energies. Correlation with reactivity and electronic structure  

SciTech Connect

Results of ion beam experiments in which an examination of the translational energy dependence of endothermic reactions yielded bond energies for metal hydrides, methyls, carbenes, and oxides are summarized for these compounds of Cr, Mn, Fe, Co, Ni, and Zn. The data indicate a close correlation of metal-ligand bond energies with the electronic configuration of the metal ion. On the basis of the noted correlations, some predictions of bond energies of the other transition metals are made. (BLM)

Armentrout, P.B.; Halle, L.F.; Beauchamp, J.L.

1981-10-21

60

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

PubMed

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

Auzmendi-Murua, Itsaso; Bozzelli, Joseph W

2012-07-19

61

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

PubMed

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

da Silva, Gabriel; Bozzelli, Joseph W

2006-12-01

62

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

63

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

PubMed

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

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

2013-11-21

64

Improving the Accuracy of Density Functional Theory (DFT) Calculation for Homolysis Bond Dissociation Energies of Y-NO Bond: Generalized Regression Neural Network Based on Grey Relational Analysis and Principal Component Analysis  

PubMed Central

We propose a generalized regression neural network (GRNN) approach based on grey relational analysis (GRA) and principal component analysis (PCA) (GP-GRNN) to improve the accuracy of density functional theory (DFT) calculation for homolysis bond dissociation energies (BDE) of Y-NO bond. As a demonstration, this combined quantum chemistry calculation with the GP-GRNN approach has been applied to evaluate the homolysis BDE of 92 Y-NO organic molecules. The results show that the ull-descriptor GRNN without GRA and PCA (F-GRNN) and with GRA (G-GRNN) approaches reduce the root-mean-square (RMS) of the calculated homolysis BDE of 92 organic molecules from 5.31 to 0.49 and 0.39 kcal mol?1 for the B3LYP/6-31G (d) calculation. Then the newly developed GP-GRNN approach further reduces the RMS to 0.31 kcal mol?1. Thus, the GP-GRNN correction on top of B3LYP/6-31G (d) can improve the accuracy of calculating the homolysis BDE in quantum chemistry and can predict homolysis BDE which cannot be obtained experimentally.

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

2011-01-01

65

Collision-induced dissociation studies of Fe(m)O(n) (+) : Bond energies in small iron oxide cluster cations, Fe(m)O(n) (+) (m=1-3, n=1-6).  

PubMed

A variety of iron oxide cluster cations is synthesized in a laser vaporization ion source. The kinetic energy dependence of the collision-induced dissociation (CID) of mass selected Fe(m)O(n) (+) (m=1-3, n=1-6) clusters with Xe is studied in this work using a guided ion beam tandem mass spectrometer. Examination of the general dissociation behavior over a broad collision energy range (0-15 eV) shows that iron oxide clusters can dissociate via evaporation of neutral Fe and O atoms as well as fission by loss of neutral O(2), FeO, FeO(2), Fe(2)O(2), and Fe(2)O(3) fragments. Such fission pathways, which are not observed in the CID studies of pure Fe cluster cations and most other pure transition metal cluster cations, result from the strong iron oxygen bonds. In general, the predominant dissociation pathways are found to correlate with the oxidation state of the iron in the cluster. Thresholds for loss of neutral Fe, O, O(2), FeO, FeO(2), Fe(2)O(2), and Fe(2)O(3) from various iron oxide cluster cations are quantitatively determined. These values are used to determine bond energies and heats of formation for both neutral and cationic iron oxide clusters in this size range. PMID:19831444

Li, Ming; Liu, Shu-Rong; Armentrout, P B

2009-10-14

66

Determination of the electron affinities of alpha- and beta-naphthyl radicals using the kinetic method with full entropy analysis. The C-H bond dissociation energies of naphthalene.  

PubMed

The C - H bond dissociation energies for naphthalene were determined using a negative ion thermochemical cycle involving the gas-phase acidity (Delta H (acid)) and electron affinity (EA) for both the alpha- and beta-positions. The gas-phase acidity of the naphthalene alpha- and beta-positions and the EAs of the alpha- and beta-naphthyl radicals were measured in the gas phase in a flowing after glow-triple quadrupole apparatus. A variation of the Cooks kinetic method was used to measure the EAs of the naphthyl radicals by collision-induced dissociation of the corresponding alpha- and beta-naphthylsulfinate adducts formed by reactions in the flow tube portion of the instrument. Calibration references included both pi and sigma radicals, and full entropy analysis was performed over a series of calibration curves measured at collision energies ranging from 3.5 to 8 eV (center-of-mass). The measured EAs are 33.0 +/- 1.4 and 31.4 +/- 1.0 kcal mol(-1) (1 kcal = 4.184 kJ) for the alpha- and beta-naphthyl radicals, respectively. The gas-phase acidities for naphthalene were measured by the DePuy silane cleavage method, which utilizes the relative abundances of aryldimethylsiloxides and trimethylsiloxide that result from competitive cleavages from a proposed penta coordinate hydroxysiliconate intermediate. The measured acidities are 394.0 +/- 5.0 and 397.6 +/- 4.8 kcal mol(-1) for the alpha- and beta- positions, respectively. The C - H bond dissociation energies calculated from the thermochemical cycle are 113.4 +/- 5.2 and 115.4 +/- 4.9 kcal mol(-1) for the alpha- and beta-positions, respectively. These energies are, to within experimental error, indistinguishable and are approximately the same as the first bond dissociation energy for benzene. PMID:11433533

Lardin, H A; Squires, R R; Wenthold, P G

2001-06-01

67

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

PubMed

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

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

2002-08-21

68

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

69

Cation-ether complexes in the gas phase: Bond dissociation energies of Na{sup +}(dimethyl ether){sub x}, x = 1-4; Na{sup +}(1,2-dimethoxyethane){sub x}, x = 1 and 2; and Na{sup +}(12-crown-4)  

SciTech Connect

Bond dissociation energies of Na{sup +}[O(CH{sub 3}){sub 2}]{sub x}, x = 1-4; Na{sup +}[(CH{sub 2}OCH{sub 3}){sub 2}]{sub x}, x = 1 and 2; and Na{sup +}[c-(C{sub 2}H{sub 4}O){sub 4}] are reported. The bond dissociation energies are determined experimentally by analysis of the thresholds for collision-induced dissociation of the cation-ether complexes by xenon measured using guided ion beam mass spectrometry. In all cases, the primary and lowest energy dissociation channel observed experimentally is endothermic loss of one ligand molecule. The cross section thresholds are interpreted to yield 0 and 298 K bond dissociation energies after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and unimolecular decay rates. Trends in the bond dissociation energies determined by experiment and recent theoretical ab initio calculations are in good agreement. Our best experimental values, which have an average uncertainty of {+-}7 kJ/mol, are lower than the theoretical values by 7 {+-} 5 kJ/mol per metal-oxygen interaction. These values are compared with bond dissociation energies for the comparable lithium cation-ether complexes. This comparison reveals the thermodynamic consequences of ligand-ligand repulsion. 51 refs., 5 figs., 4 tabs.

More, M.B.; Armentrout, P.B. [Univ. of Utah, Salt Lake City, UT (United States)] [Univ. of Utah, Salt Lake City, UT (United States); Ray, D. [Pacific Northwest National Lab., Richland, WA (United States)] [Pacific Northwest National Lab., Richland, WA (United States)

1997-01-30

70

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

SciTech Connect

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

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

2011-04-21

71

Dissociation energy and dynamics of water clusters  

NASA Astrophysics Data System (ADS)

The state-to-state vibrational predissociation (VP) dynamics of water clusters were studied following excitation of a vibrational mode of each cluster. Velocity-map imaging (VMI) and resonance-enhanced multiphoton ionization (REMPI) were used to determine pair-correlated center-of-mass translational energy distributions. Product energy distributions and dissociation energies were determined. Following vibrational excitation of the HCl stretch fundamental of the HCl-H2O dimer, HCl fragments were detected by 2 + 1 REMPI via the f 3?2(nu' = 0) ? X 1Sigma+(nu'' = 0) and V1Sigma + (nu' = 11 and 12) ? X1Sigma+ (nu'' = 0) transitions. REMPI spectra clearly show HCl from dissociation produced in the ground vibrational state with J'' up to 11. The fragments' center-of-mass translational energy distributions were determined from images of selected rotational states of HCl and were converted to rotational state distributions of the water cofragment. All the distributions could be fit well when using a dimer dissociation energy of bond dissociation energy D0 = 1334 +/- 10 cm--1. The rotational distributions in the water cofragment pair-correlated with specific rotational states of HCl appear nonstatistical when compared to predictions of the statistical phase space theory. A detailed analysis of pair-correlated state distributions was complicated by the large number of water rotational states available, but the data show that the water rotational populations increase with decreasing translational energy. H2O fragments of this dimer were detected by 2 + 1 REMPI via the C˜1B1(000) ? X˜1A1(000) transition. REMPI clearly shows that H2O from dissociation is produced in the ground vibrational state. The fragment's center-of-mass translational energy distributions were determined from images of selected rotational states of H2O and were converted to rotational state distributions of the HCl cofragment. The distributions gave D0 = 1334 +/- 10 cm --1 and show a clear preference for rotational levels in the HCl fragment that minimize translational energy release. The usefulness of 2 + 1 REMPI detection of water fragment is discussed. The hydrogen bonding in water is dominated by pair-wise dimer interactions, and the predissociation of the water dimer following vibrational excitation is reported. The measured D0 values of (H 2O)2 and (D2O)2, 1105 and 1244 +/- 10 cm--1, respectively, are in excellent agreement with the calculated values of 1103 and 1244 +/- 5 cm--1. Pair-correlated water fragment rovibrational state distributions following vibrational predissociation of (H2O)2 and (D2O) 2 were obtained upon excitation of the hydrogen bonded OH and OD stretch fundamentals, respectively. Quasiclassical trajectory calculations, using an accurate full-dimensional potential energy surface, are in accord with and help to elucidate experiment. Experiment and theory find predominant excitation of the fragment bending mode upon hydrogen bond breaking. A minor channel is also observed in which both fragments are in the ground vibrational state and are highly rotationally excited. The theoretical calculations reveal equal probability of bending excitation in the donor and acceptor subunits, which is a result of interchange of donor and acceptor roles. The rotational distributions associated with the major channel, in which one water fragment has one quantum of bend, and the minor channel with both water fragments in the ground vibrational state are calculated, and are in agreement with experiment. (Abstract shortened by UMI.)

Ch'ng, Lee Chiat

72

Evidence for a lower enthalpy of formation of hydroxyl radical and a lower gas-phase bond dissociation energy of water.  

SciTech Connect

There are two experimental approaches to determining {Delta}H{sub f0}{sup o}(OH), which produce values of this key thermodynamic quantity that differ by >0.5 kcal/mol. The apparent uncertainty of the positive ion cycle approach resides in the measurement of the appearance energy of OH{sup +} from H{sub 2}O, while the uncertainty of the spectroscopic approach resides in the determination of the dissociation energy of OH(A{sup 2}{Sigma}{sup +}). In this note we present an independent experimental determination of the appearance energy that confirms the accuracy and enhances the precision of the existing positive ion cycle value for {Delta}H{sub f0}{sup o}(OH). We also present electronic structure calculations of the OH(A{sup 2}{Sigma}{sup +}) potential energy curve, which suggest that the extrapolation method used to obtain the spectroscopic dissociation energy is in error. Finally, we present the largest ab initio electronic structure calculations ever performed for {Delta}H{sub f0}{sup o}(OH) that have an apparent uncertainty much less than 0.5 kcal/mol and support only the positive ion cycle value. Although all major thermochemical tables recommend a value of {Delta}H{sub f0}{sup o}(OH) based on the spectroscopic approach, the correct value is that of the positive ion cycle, {Delta}H{sub f0}{sup o}(OH) = 8.83 {+-} 0.09 kcal/mol, D{sub 0}(H-OH) = 117.57 {+-} 0.09 kcal/mol, and D{sub 0}(OH) = 101.79 {+-} 0.09 kcal/mol.

Ruscic, B.; Feller, D.; Dixon, D.; Peterson, K.; Harding, L.; Asher, R.; Wagner, A.; Chemistry; PNNL; Washington State Univ.

2001-01-11

73

The Effect of Hydrogen on the Bonding and Dissociation of Carbon Monoxide on AN IRON(100) Surface  

NASA Astrophysics Data System (ADS)

Adsorption and coadsorption of CO and H _2 on Fe(100) was studied using the following six methods: Temperature programmed desorption (TPD), x -ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), high resolution electron energy loss spectroscopy (HREELS), single reflection Fourier transform infrared spectroscopy (FTIR) and low-energy electron diffraction (LEED). The binding and dissociation of CO on a clean and hydrogen presaturated Fe(100) surface were investigated to provide better understanding of the first step in the Fischer-Tropsch synthesis, an important industrial catalytic reaction for converting CO and hydrogen to hydrocarbon. CO adsorbs molecularly on the clean surface in three states alpha_1, alpha_2 and alpha_3 . At temperatures above 350 K but below 440 K, CO is bound to the surface only in the highly perturbed alpha_3 state (pi -bonded geometry). The CO alpha_3 molecules are believed to occupy the 4-fold hollow sites. When the surface temperature is raised above 440 K, a fraction of the alpha_3 desorbs and the remainder dissociates. The dissociation fragments replace the CO alpha_3 molecules in the 4-fold hollow sites. These fragments recombine at higher temperatures and appear as beta CO. The bonding and dissociation of CO in the alpha_3 received more attention because it is believed that this state is a precursor to dissociation. A model describing the partitioning between desorption and dissociation is proposed in which the dissociation fragments displace the strongly bound CO in the beta -bonded state. The stoichiometry of this reaction at saturation requires that only half the original CO adsorbed in the beta-bonded CO state can dissociate. Presaturating the surface with hydrogen affects the bonding and dissociation of CO on the iron surface. One effect is to weaken CO-Fe bonds which results in a very weakly bound state (alpha^' _1). In addition to the alpha ^'_1 state, presaturating the surface with hydrogen results in isolating the alpha^'_2 state. Another effect of preadsorbed hydrogen appears in the alpha_3 state. The ratio of dissociation to desorption changes and suggests that hydrogen may induce island formation in the CO adlayer. Both factors, weakening CO-Fe bonds and influencing the dissociation/desorption ratio, might play an important role in the Fischer-Tropsch synthesis.

Nassir, Mohamed Husain

1993-01-01

74

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

75

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

SciTech Connect

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

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

2008-05-30

76

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

PubMed

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

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

2012-07-14

77

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

78

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

NASA Astrophysics Data System (ADS)

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 ?Hof0 values of CoC/CoC+, which are not known experimentally, we recommend the following CCSDTQ/CBS predictions: ?Hof0(CoC) = 775.7 kJ/mol and ?Hof0(CoC+) = 1522.5 kJ/mol, ?Hof298(CoC) = 779.2 kJ/mol and ?Ho298(CoC+) = 1526.0 kJ/mol.

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

2013-03-01

79

Selectivity of bond-breaking in electron-induced dissociation of hydrocarbon films on Au surfaces  

NASA Astrophysics Data System (ADS)

Electron-induced dissociation (EID) processes in organic and polymer films are important in a variety of applications. One scientific issue concerns the selectivity of low-energy electron bombardment to cleave a single C-H bond in hydrocarbon condensed films or adsorbed layers. We have undertaken combined TPD and FT-IRAS studies to identify and determine the purity of the surface species produced by EID of cyclohexane and benzene films on Au(1 1 1). Experimental evidence strongly supports a conclusion that EID of cyclohexane and benzene monolayer and multilayer films using incident electrons with an energy of 30 eV can be used to cleave a single C-H bond and produce a single chemisorbed product with high selectivity. An important consequence of these observations is that a variety of adsorbed hydrocarbon intermediates on Au(1 1 1) and other metal surfaces can be prepared in this manner, spectroscopically characterized, and used in studies to advance the understanding of chemical bonding, reactions and catalysis at surfaces.

Syomin, Denis; Koel, Bruce E.

2001-10-01

80

High-Level ab Initio Predictions for the Ionization Energy, Bond Dissociation Energies, and Heats of Formations of Iron Carbide (FeC) and Its Cation (FeC+)  

NASA Astrophysics Data System (ADS)

The ionization energy (IE) of FeC and the 0 K bond dissociation energies (D0) and the heats of formation at 0 K (?H°f0) and 298 K (?H°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? and 2?, 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 D0(Fe+-C) and D0(Fe-C) give the prediction of D0(Fe+-C) - D0(Fe-C) = 0.334 eV, which is consistent with the experimental determination of 0.3094 ± 0.0001 eV. The D0 calculations also support the experimental D0(Fe+-C) = 4.1 ± 0.3 eV and D0(Fe-C) = 3.8 ± 0.3 eV determined by the previous ion photodissociation study. The present calculations also provide the ?Hof0(?Hof298) 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 D0 and ?Hof0 values of FeC/FeC+, which are not known to high precision, we recommend the CCSDTQ(Full)/CBS predictions [D0(Fe-C) = 3.778 eV, D0(Fe+-C) = 4.112 eV, ?Hof0(FeC) = 760.8 kJ/mol and ?Hof0(FeC+) = 1490.6 kJ/mol] based on the ZPVE corrections using the experimental vibrational frequencies of FeC and FeC+.

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

2009-09-01

81

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

NASA Astrophysics Data System (ADS)

The current state (December 1990) of ab initio theory is reviewed, with special emphasis on electron correlation methods. A new family of Gaussian basis sets, the 'combined bond-polarization' basis sets, is introduced. Relative to common large basis sets, binding energies can be computed either with comparable accuracy (+/-2 kcal/mol) at much reduced computational cost, or with much greater accuracy (+/-0.12 kcal/mol per bond) at comparable cost. Several issues relating to basis set superposition error are discussed. Subsequently, a number of cluster molecules relevant in materials science and astrophysics are studied. For B_3, B_2N, and BN_2, the first published data whatsoever are presented. A literature disagreement on the dissociation energy of N_3 is resolved by large-scale ab initio calculations. Accurate spectroscopic constants for the lowest few states of SiC and BN are obtained, as well as JANAF-style thermodynamic functions up to 6000 K. An ad hoc reparametrization of MNDO for C_{rm n} clusters leads to much improved results, including very accurate harmonic frequencies. A comparison of computed frequencies, infrared intensities, and isotope shifts- -both ab initio and ad hoc MNDO--with available infrared data of argon-trapped carbon vapor leads to a completely revised assignment of these latter experimental frequencies. The latter has been instrumental in the experimental identification and characterization of C_4,C _5,C_7, and C _9. The ground state of C_4 , a long-standing issue in the literature, has been shown to be cyclic by ab initio calculations using large basis sets; an error in the experimental heat of formation has also been corrected. A definitive characterization of the C_3^{+} ion, a 'problem molecule' in quantum chemistry, has been given using a variety of single- and multi-reference correlation treatments. It is also shown that single excitations have an unusually large effect on the geometry and harmonic frequency of spin-contaminated radicals. Finally, a critical analysis, both theoretically and numerically, of size-consistency correction for limited configuration interaction has been made.

Martin, Jan M. L.

82

Collision Induced Dissociation Products of Disulfide-bonded Peptides: Ions Result from the Cleavage of More than One Bond  

PubMed Central

Disulfide bonds are a posttranslational modification (PTM) that can be scrambled or shuffled to non-native bonds during recombinant expression, sample handling, or sample purification. Currently, mapping of disulfide bonds is difficult due, to various sample requirements and data analysis difficulties. One step towards facilitating this difficult work is developing a better understanding of how disulfide-bonded peptides fragment during Collision Induced Dissociation (CID). Most automated analysis algorithms function based on the assumption that the preponderance of product ions observed during the dissociation of disulfide-bonded peptides result from the cleavage of just one peptide bond, and in this report we tested that assumption by extensively analyzing the product ions generated when several disulfide-bonded peptides are subjected to CID on a QTOF instrument. We found that one of the most common types of product ions generated resulted from two peptide bond cleavages, or a double cleavage. We found that for several of the disulfide-bonded peptides analyzed, the number of double cleavage product ions outnumbered those of single cleavages. The influence of charge state and precursor ion size was investigated, to determine if those parameters dictated the amount of double cleavage product ions formed. It was found in this sample set that no strong correlation existed between the charge state or peptide size and the portion of product ions assigned as double cleavages. This data shows that these ions could account for many of the product ions detected in CID data of disulfide bonded peptides. We also showed the utility of double cleavage product ions on a peptide with multiple cysteines present. Double cleavage products were able to fully characterize the bonding pattern of each cysteine where typical single b/y cleavage products could not.

Clark, Daniel F; Go, Eden P; Toumi, Melinda L; Desaire, Heather

2012-01-01

83

Collision Induced Dissociation Products of Disulfide-Bonded Peptides: Ions Result from the Cleavage of More Than One Bond  

NASA Astrophysics Data System (ADS)

Disulfide bonds are a post-translational modification (PTM) that can be scrambled or shuffled to non-native bonds during recombinant expression, sample handling, or sample purification. Currently, mapping of disulfide bonds is not easy because of various sample requirements and data analysis difficulties. One step towards facilitating this difficult work is developing a better understanding of how disulfide-bonded peptides fragment during collision induced dissociation (CID). Most automated analysis algorithms function based on the assumption that the preponderance of product ions observed during the dissociation of disulfide-bonded peptides result from the cleavage of just one peptide bond, and in this report we tested that assumption by extensively analyzing the product ions generated when several disulfide-bonded peptides are subjected to CID on a quadrupole time of flight (QTOF) instrument. We found that one of the most common types of product ions generated resulted from two peptide bond cleavages, or a double cleavage. We found that for several of the disulfide-bonded peptides analyzed, the number of double cleavage product ions outnumbered those of single cleavages. The influence of charge state and precursor ion size was investigated, to determine if those parameters dictated the amount of double cleavage product ions formed. It was found in this sample set that no strong correlation existed between the charge state or peptide size and the portion of product ions assigned as double cleavages. These data show that these ions could account for many of the product ions detected in CID data of disulfide bonded peptides. We also showed the utility of double cleavage product ions on a peptide with multiple cysteines present. Double cleavage products were able to fully characterize the bonding pattern of each cysteine where typical single b/ y cleavage products could not.

Clark, Daniel F.; Go, Eden P.; Toumi, Melinda L.; Desaire, Heather

2011-03-01

84

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

85

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.

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

1989-01-01

86

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

87

Dissociation Thresholds of Low-Energy Molecular Ions on a Cu(111) Surface  

NASA Astrophysics Data System (ADS)

The dissociation thresholds of polyatomic SF5+ and BF2+ ions on Cu(111) surface have been investigated in the incident energy range of 2 200 eV. The mass and kinetic energy of scattered ions were analyzed simultaneously using a quadrupole mass analyzer equipped with a 45° sector field energy filter. For SF5+ ion irradiation, dissociated species (SF4+ and F-) began to emerge at an energy of 15±2 eV, and the irradiated ions further dissociated into SF3+ at 50±2 eV. These energies are substantially higher than the bond strength of S F for free SF6 molecules (3.3 eV). These results suggest that the translational-vibrational energy transfer during the collision process greatly affects the observed dissociation threshold. Similar results are also observed for BF2+ irradiation.

Yamamoto, Hiroyuki; Baba, Yuji; Sasaki, Teikichi

1998-09-01

88

The C-N dissociation energies of nitrobenzene and nitrotoluene radical anions and neutrals  

NASA Astrophysics Data System (ADS)

The C-N dissociation energies of the radical anions of nitrobenzene and all three nitrotoluene isomers were determined by measuring the appearance energy of the NO2 fragment from collision induced dissociation in a tandem mass spectrometer. The dissociation energy of nitrobenzene radical anion is 1.99 ± 0.16 eV, o-nitrotoluene radical anion is 1.91 ± 0.14 eV, m-nitrotoluene radical anion is 2.01 ± 0.17, and p-nitrotoluene radical anion is 2.06 ± 0.21 eV. All anion bond energies are lower than the neutral C-N bond energies by at least 1 eV.

Pruitt, Carrie Jo M.; Goebbert, Daniel J.

2013-08-01

89

Three modes of dissociation of H bonds in hydrogen-bond dominated solids  

Microsoft Academic Search

ICE, paper and regenerated cellulose, Nylon (unstretched and lightly stretched), and to a certain extent natural cellulose, lignin and wool are typical examples of hydrogen-bond dominated solids (whose mechanical properties are mostly controlled by the density and characteristics of the hydrogen bond). Previously1 I have shown that for these materials, Young's modulus E is related to N, the effective number

Alfred H. Nissan

1976-01-01

90

Carbon-halogen bond dissociation at copper surfaces: Alkyl radicals versus metal alkyls  

Microsoft Academic Search

In this thesis, ultra-high vacuum techniques, electron spectroscopies, and mass spectrometry are applied to study the formation of alkyl radicals and surface-bound alkyl groups during the dissociation of carbon-halogen bonds on atomically-clean, single crystal copper surfaces. Straight-chain alkyl halides of one to five carbons in length (C[sub 1]-C[sub 5]) have been investigated on Cu(111) and Cu(100) surfaces. The initiating step

Lin; Jong-Liang

1993-01-01

91

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

92

Switching from molecular to dissociative adsorption with vibrational energy: ethylene on Ag(0 0 1)  

Microsoft Academic Search

We show that vibrational energy can be used to tune the chemisorption state of an adsorbed molecule. When dosing C2H4 with a supersonic molecular beam on Ag(001) we demonstrate by vibrational spectroscopy that, with increasing nozzle temperature, TN, firstly no stable adsorption occurs, then a ?-bonded configuration is populated, switching finally to a more strongly, undissociated, di-?-bonded state. Direct dissociation

L. Vattuone; L. Savio; U. Valbusa; M. Rocca

2000-01-01

93

A three-dimensional potential energy surface for dissociative adsorption and associative desorption at metal electrodes  

Microsoft Academic Search

A simple model is constructed to calculate the potential energy surface of dissociative adsorption and associative desorption reactions at the metal\\/solution interface. The model is based on an extension of the Anderson-Newns Hamiltonian and has three reaction coordinates; the bond length or the distance between the fragments, the distance from the surface, and the generalized solvent coordinate familiar from the

Marc T. M. Koper; Gregory A. Voth

1998-01-01

94

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

PubMed

Bond dissociation and formation in diatomic molecules are analyzed in terms of the reaction force F(R) and the reaction force constant kappa(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 kappa(R) comes a two-stage description of dissociation/formation. In dissociation, the first stage involves stretching of the bond, which is opposed by an increasingly negative retarding force F(R). This reaches a minimum and then begins to weaken in the second stage, which is the transition from stretched molecule to free atoms. Bond formation begins with the reverse transition, driven by a positive F(R) which reaches a maximum for the stretched molecule and then becomes a decreasing restoring force. In the stages in which the system is a stretched molecule, kappa(R) is positive with its maximum at the equilibrium bond length; it is zero at the minimum or maximum of F(R), and negative throughout the transition stages, going through a minimum. kappa(R) <0 has been found to characterize the transition portion of a reaction. This description of dissociation/formation is reinforced by computed B3LYP and Hartree-Fock force constants at different atom separations for the singlet molecules. Hartree-Fock wave function stability assessments suggest that, for the single-bonded singlet molecules, the onset of electron unpairing in dissociation comes in the neighborhood of the F(R) minimum. PMID:19052782

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

2009-06-01

95

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

96

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

97

Ionization energy of methylene revisited: Improved values for the enthalpy of formation of CH{sub 2} and the bond dissociation energy of CH{sub 3} via simultaneous solution of the local thermochemical network  

SciTech Connect

The appearance energy of the CH{sub 2}{sup +} fragment from CH{sub 2}CO has been carefully remeasured and fitted by a model curve, producing EA{sub 0}(CH{sub 2}{sup +}/CH{sub 2}CO) = 13.743 and 0.005 eV. This value can be sequentially propagated through selected thermochemical cycles to yield individual values for EI(CH{sub 2}), D{sub 0}(H-CH{sub 2}), {Delta}H{degree}{sub f0}(CH{sub 2}), and {Delta}H{degree}{sub f0}(CH{sub 2}CO). A set of values with a statistically larger weight is produced by analyzing a local thermochemical network, which combines the present measurement with thirteen other experimental determinations from the literature and encompasses the enthalpies of formation of CH{sub 3}, CH{sub 3}{sup +}, CH{sub 2}, CH{sub 2}{sup +}, and CH{sub 2}CO. The recommended simultaneously adjusted thermochemical values are: {Delta}H{degree}{sub f0}(CH{sub 3}) = 35.86 {+-} 0.07 kcal/mol (35.05 {+-} 0.07 kcal/mol at 298 K), {Delta}H{degree}{sub f0}(CH{sub 3}{sup +}) = 262.73 {+-} 0.06 kcal/mol (261.83 {+-} 0.06 kcal/mol at 298 K), {Delta}H{degree}{sub f0}(CH{sub 2}) = 93.18 {+-} 0.20 kcal/mol (93.31 {+-} 0.20 kcal/mol at 298 K), {Delta}H{degree}{sub f0}(CH{sub 2}{sup +}) = 332.92 {+-} 0.19 kcal/mol (333.04 {+-} 0.19 kcal/mol at 298 K), {Delta}H{degree}{sub f0}(CH{sub 2}CO) = {minus}11.10 {+-} 0.21 kcal/mol ({minus}11.85 {+-} 0.21 kcal/mol at 298 K), as well as D{sub 0}(H{sub 3}C-H) = 103.42 {+-} 0.03 kcal/mol (104.99 {+-} 0.03 kcal/mol at 298 K), D{sub 0}(H{sub 2}C-H) = 108.95 {+-} 0.20 kcal/mol (110.35 {+-} 0.20 kcal/mol at 298 K), D{sub 0}(H{sub 2}C{double{underscore}bond}CO) = 77.08 {+-} 0.02 kcal/mol (78.73 {+-} 0.02 kcal/mol at 298 K), EI(CH{sub 3}) = 9.3830 {+-} 0.0005 eV, and EI(CH{sub 2}) = 10.3962 {+-} 0.0036 eV. These values are in excellent agreement with current and several previous experimental measurements. The recommended enthalpy of formation of CH{sub 2} implies that the reaction of singlet methylene with water is essentially thermoneutral (to within {+-}0.2 kcal/mol) at 0 and 298 K, and slightly endothermic (0.5 {+-} 0.2 kcal/mol) at 1,000 K.

Ruscic, B.; Litorja, M.; Asher, R.L.

1999-10-28

98

Erratum : Ionization energy of methylene revisited : improved values for the enthalpy of formation of CH{sub 2} and the bond dissociation Energy of CH{3} via simultaneous solution of the local thermochemical network.  

SciTech Connect

The appearance energy of the CH{sub 2}{sup +} fragment from CH{sub 2}CO has been carefully remeasured and fitted by a model curve, producing EA{sub 0}(CH{sub 2}{sup +}/CH{sub 2}CO) = 13.743 {+-} 0.005 eV. This value can be sequentially propagated through selected thermochemical cycles to yield individual values for El(CH{sub 2}), D{sub 0}(H-CH{sub 2}), {Delta}H{sup o}{sub f 0}(CH{sub 2}CO). A set of values with a statistically larger weight is produced by analyzing a local thermochemical network, which combines the present measurement with thirteen other experimental determinations from the literature and encompasses the enthalpies of formation of CH{sub 3}, CH{sub 3}{sup +}, CH{sub 2}, CH{sub 2}{sup +}, and CH{sub 2}CO. The recommended simultaneously adjusted thermochemical values are: {Delta}H{sup o}{sub f 0}(CH{sub 3}) = 35.86 {+-} 0.07 kcal/mol (35.05 {+-} 0.07 kcal/mol at 298 K), {Delta}H{sup o}{sub f 0}(CH{sub 3}{sup +}) = 262.73 {+-} 0.06 kcal/mol (261.83 {+-} 0.06 kcal/mol at 298 K), {Delta}H{sup o}{sub f 0}(CH{sub 2}) = 93.18 {+-} 0.20 kcal/mol (93.31 {+-} 0.20 kcal/mol at 298 K), {Delta}H{sup o}{sub f 0}(CH{sub 2}{sup +}) = 332.92 {+-} 0.19 kcal/mol (333.04 {+-} 0.19 kcal/mol at 298 K), {Delta}H{sup o}{sub f 0}(CH{sub 2}CO) = -11.10 {+-} 0.21 kcal/mol (-11.85 {+-} 0.21 kcal/mol at 298 K), as well as D{sub 0}(H{sub 3}C-H) = 103.42 {+-} 0.03 kcal/mol (104.99 {+-} 0.03 kcal/mol at 298 K), D{sub 0}(H{sub 2}C-H) = 108.95 {+-} 0.20 kcal/mol (110.35 {+-} 0.20 kcal/mol at 298 K), D{sub 0}(H{sub 2}C{double_bond}CO) = 77.08 {+-} 0.02 kcal/mol (78.73 {+-} 0.02 kcal/mol at 298 K), El(CH{sub 3}) = 9.3830 {+-} 0.0005 eV, and El(CH{sub 2}) = 10.3962 {+-} 0.0036 eV. These values are in excellent agreement with current and several previous experimental measurements. The recommended enthalpy of formation of CH{sub 2} implies that the reaction of singlet methylene with water is essentially thermoneutral (to within {+-}0.2 kcal/mol) at 0 and 298 K, and slightly endothermic (0.5 {+-} 0.2 kcal/mol) at 1000 K.

Ruscic, B.; Litorja, M.; Asher, R.; Chemistry

1999-01-01

99

Choice of Bond Dissociation Enthalpies on which to Base the Stabilization Energies of Simple Radicals: DH(R-H)is Preferred because DH(R-Me) is Perturbed by Changes in Chain Branching  

SciTech Connect

The relative stabilization energies of radicals, SE(R ), along the simple series methyl/ethyl/i-propyl/t-butyl are known to vary in spread and even direction dependent on which dissociation enthalpies, DH(R-X), they are based on. Using a highly electronegative X is recognized as unwise, but it is not clear whether a choice of X = Me or X = R might not be preferred over the almost universal use of R = H. The enthalpies of isomerization of C4 radical pairs that vary only in the substitution pattern at the radical center but not in carbon skeleton illustrate that R = H is indeed the better choice. Comparisons in the context of recent predictive models for alkane and radical stability indicate that, while relative DH(R-H) values highlight the desired difference in substitution pattern at the radical center, relative DH(R-Me) values are perturbed by differences in skeletal branching or protobranching which are well-known to affect thermochemistry. As a result, SE(R ) values derived from relative DH(R-Me) values are consistently too small. The same pattern is illustrated for prim, sec, and tert allylic and benzylic radicals (larger SE(R )) and for the parent vinyl, phenyl, and ethynyl radicals (negative SE(R )).

Poutsma, Marvin L [ORNL

2008-01-01

100

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

101

The dissociation energy of the hydrogen molecule  

Microsoft Academic Search

On the basis of new absorption spectra of H2, HD and D2 taken at liquid nitrogen temperature with a 10.5-m vacuum grating spectrograph, the dissociation limits of these molecules near 850 Å were redetermined. It has been found that previous work was more strongly affected by overlapping lines and lack of resolution than was suspected at the time. Even with

G. Herzberg

1970-01-01

102

Ionization energy of methylene revisited: Improved values for the enthalpy of formation of CHâ and the bond dissociation energy of CHâ via simultaneous solution of the local thermochemical network  

Microsoft Academic Search

The appearance energy of the CHâ{sup +} fragment from CHâCO has been carefully remeasured and fitted by a model curve, producing EAâ(CHâ{sup +}\\/CHâCO) = 13.743 and 0.005 eV. This value can be sequentially propagated through selected thermochemical cycles to yield individual values for EI(CHâ), Dâ(H-CHâ), ÎH°{sub f0}(CHâ), and ÎH°{sub f0}(CHâCO). A set of values with a statistically larger weight is

B. Ruscic; M. Litorja; R. L. Asher

1999-01-01

103

Dissociative chemisorption and energy transfer for methane on Ir(111).  

PubMed

A 3-parameter local hot spot model of gas-surface reactivity is employed to analyze and predict dissociative sticking coefficients for CH(4) incident on Ir(111) under varied nonequilibrium and equilibrium conditions. One Ir surface oscillator and the molecular vibrations, rotations, and translational energy directed along the surface normal are treated as active degrees of freedom in the 14 dimensional microcanonical kinetics. The threshold energy for CH(4) dissociative chemisorption on Ir(111) derived from modeling molecular beam experiments is E(0) = 39 kJ/mol. Over more than 4 orders of magnitude of variation in sticking, the average relative discrepancy between the beam and theoretically derived sticking coefficients is 88%. The experimentally observed enhancement in dissociative sticking as beam translational energies decrease below approximately 10 kJ/mol is consistent with a parallel dynamical trapping/energy transfer channel that likely fails to completely thermalize the molecules to the surface temperature. This trapping-mediated sticking, indicative of specific energy transfer pathways from the surface under nonequilibrium conditions, should be a minor contributor to the overall dissociative sticking at thermal equilibrium. Surprisingly, the CH(4) dissociative sticking coefficient predicted for Ir(111) surfaces at thermal equilibrium, based on the molecular beam experiments, is roughly 4 orders of magnitude higher than recent measurements on supported nanoscale Ir catalysts at 1 bar pressure, which suggests that substantial improvements in catalyst turnover rates may be possible. PMID:16852257

Abbott, Heather L; Harrison, Ian

2005-05-26

104

Protonated water clusters. Hartree-Fock study of dissociation energies  

NASA Astrophysics Data System (ADS)

A complete set of protonated water clusters conformers up to n = 8 have been evaluated by ab-initio Hartree-Fock method in 6-311G** molecular orbitals basis set and with quadratic complete basis set method. Configurations of ground-state conformers are in a good accord with those available in literature but present dissociation energies for the light clusters agree better with experimental values. A tentative analysis of experimental conditions for observation of certain clusters is presented in comparison to selected formation paths of clusters. Dissociation energies show a broad range of values.

Wróblewski, T.; Karwasz, G. P.

2013-10-01

105

Kinetic-energy release in the dissociation of CO2 +  

Microsoft Academic Search

The kinetic-energy release distributions of the fragment ions (C+ and O+) produced in dissociative double photoionization of carbon monoxide have been determined by analyzing the photoion–photoion coincidence (PIPICO) spectra measured in the region h?=39–100 eV by use of a time-of-flight (TOF) mass spectrometer and synchrotron radiation. At low excitation energies (39–46.5 eV), low kinetic-energy components were observed, which cannot be

Toshio Masuoka

1994-01-01

106

Kinetic-energy release in the dissociation of NO2 +  

Microsoft Academic Search

Kinetic-energy release distributions of the fragment ions (N+ and O+) produced in dissociative double photoionization of nitric oxide have been determined by analyzing the photoion–photoion coincidence (PIPICO) spectra measured in the region 42–100 eV by use of a time-of-flight mass spectrometer and synchrotron radiation. At low excitation energies (42–46 eV), low kinetic-energy components were observed, which cannot be explained by

Toshio Masuoka

1994-01-01

107

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

108

Kinetic-energy release in the dissociation of CO22 +  

Microsoft Academic Search

The kinetic-energy release distributions (KERDs) of the fragment ion pairs (O++CO+ and C++O+) produced in dissociative double photoionization of carbon dioxide have been determined by analyzing the photoion–photoion coincidence spectra measured in the region h?=40–100 eV by use of a time-of-flight mass spectrometer and synchrotron radiation. The mechanism of the three-body dissociation (CO2+2?C++O++O) has been examined to take place sequentially

Toshio Masuoka; Eiken Nakamura; Atsunari Hiraya

1996-01-01

109

Bimodal kinetic energy release in the unimolecular dissociation of energy-selected formic acid ion  

Microsoft Academic Search

Threshold photoelectron-photoion coincidence mass spectrometry is used to study the dissociation of HCOOH(+) and DCOOH(+). Detailed breakdown diagrams are obtained over internal molecular ion energies less than 8 eV. Also, kinetic energy release distributions for HCO(+) and DCO(+) are extracted using a multiple linear regression method. The average kinetic energy releases for the dissociation to the products in the ground

Toshihide Nishimura; G. G. Meisels; Yoshio Niwa

1989-01-01

110

The entropic and enthalpic contributions to force-dependent dissociation kinetics of the pyrophosphate bond.  

PubMed

We report quantum-chemical calculations of the activation free energy of solvolysis of the pyrophosphate bond in a conformationally flexible reactant coupled to a constraining potential. The results reveal a significant contribution of conformational entropy to the force-dependent kinetics of even a fairly small reactant, suggesting that accurate predictions or molecular interpretation of localized reaction kinetics in stretched polymers may require explicit consideration of their force-dependent conformational heterogeneity. We further show that modeling the conformational space of the reactant and the transition state as collections of overlapping harmonic wells accurately predicts the force-dependent activation free energy up to 2 nN without detailed quantum-chemical computations. An estimate of the activation energies is obtained from the minimal (Eyring-Bell-Evans) model using the local coordinate common to all nucleophilic displacement reactions. PMID:22107035

Hermes, Matthew; Boulatov, Roman

2011-12-21

111

A pass too far: dissociation of internal energy selected paracyclophane cations, theory and experiment.  

PubMed

The vacuum ultraviolet (VUV) photoionization and dissociative photoionization of three hydroxy-substituted [2.2]paracyclophane derivatives were studied yielding adiabatic ionization energies and dissociative photoionization energies (appearance energies). The simplest dissociation pathway is the breaking of both CH(2)-CH(2) bridge units and fragmenting the molecular ion in half to yield xylylene neutral and cationic fragments. The experimental data show that this process is outcompeted by a faster, higher energy channel, possibly yielding cyclooctatetraene derivatives. The role of the reaction coordinate, the effect of large amplitude motions on the density of states function at low and high energies and the temperature dependent 'population gap' in the internal energy distribution in large molecules are discussed in the context of applying statistical models to the dissociation. Computational approaches to the binding energy of paracyclophanes are marred with pitfalls. Noncovalent interactions play a major role in keeping paracyclophanes bound by some 200 kJ mol(-1) with respect to the two xylylene motifs, and the covalent CH(2)-CH(2) bonds are mostly counteracted by the geometric strain. The stabilizing effects are twofold: first, paracyclophanes are aromatic compounds, whereas xylylenes are not. Thus, the aromaticity of the molecule is induced by dimerization. Second, dispersive ?-? interactions also stabilize the molecule. We evaluated 23 different computational chemistry approaches, and found that very few of the favorably scaling ones give an adequate description of this system. Among the DFT functionals tested, only PBE-D3 and perhaps M06-2X yielded consistently accurate results, comparable with MP3 and CCSD, or the G4 and CBS-QB3 composite methods. MP2 results in general suffer from significant overbonding. PMID:22847148

Hemberger, Patrick; Bodi, Andras; Schon, Christof; Steinbauer, Michael; Fischer, Kathrin H; Kaiser, Conrad; Fischer, Ingo

2012-09-14

112

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

113

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

114

Electron-induced dissociation of monolayer C 2H 5Cl on Ag(111). Electron energy dependence  

NASA Astrophysics Data System (ADS)

Electron-induced dissociation (EID) of monolayer C 2H 5Cl on Ag(111) has been studied using a novel low-energy photoelectron source. As a function of electron energy, the C?Cl bond dissociation cross section drops by more than an order of magnitude between 0.5 and 3 eV. It rises again by an order of magnitude between 8 and 12 eV, and then rises slowly to 50 eV. Above 8 eV, the EID cross section is attributed mainly to n(Cl) and ?(CCl) valence level ionization, whereas between 0.5 and 3 eV, it is attributed to dissociative electron attachment.

Liu, Z.-M.; Zhou, X.-L.; White, J. M.

1992-10-01

115

Absolute cross sections and kinetic energy release distributions for electron-impact dissociation of HD2+  

Microsoft Academic Search

Absolute cross sections results are reported for electron impact dissociative excitation and ionization of HD2+ in the electron energy range from threshold to 2.5 keV. Direct and resonant dissociative excitation is found to dominate the production of possible ionic products in the low energy region. Dissociative ionization is observed for H+ and D+ products only. The lowness of dissociative ionization

P. Defrance; J. J. Jureta; J. Lecointre; X. Urbain

2009-01-01

116

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

117

Angular distributions of collision induced dissociation: Dependence on kinetic energy release  

Microsoft Academic Search

Collisions between molecular-ion projectiles and atomic targets at energies of a few keV\\/amu lead predominantly to dissociative capture (DC) and collision-induced dissociation (CID). The CID process can be driven by electronic or vibrational excitation. The angular distribution of electronic CID, defined as the dissociation yield versus the angle between the molecular dissociation axis and the beam direction, is predicted by

Kevin Carnes; Ben Berry; Wania Wolff; Nora G. Johnson; A. Max Sayler; Bishwanath Gaire; Mohammad Zohrabi; Jarlath McKenna; Itzik Ben-Itzhak

2010-01-01

118

The dissociation dynamics of energy-selected neopentylamine ions  

NASA Astrophysics Data System (ADS)

The dissociation dynamics of energy-selected neopentylamine cations, (CH3)3CCH2NH2+, were studied using threshold photoelectron photoion coincidence (TPEPICO) spectroscopy in which ion time-of-flight (TOF) distributions are recorded as a function of the ion internal energy. The lowest energy pathway, producing the CH3NH3+ ion, involves a rearrangement of the molecular ion. The 0 K dissociation onsets for the production of the CH3NH3+, CH2NH2+, and (CH3)2CCH2NH2+ ions have been determined to be 9.54 ± 0.05, 9.647 ± 0.025 and 9.90 ± 0.1 eV, respectively. Because the heat of formation of the CH2NH2+ + t-C4H9 products are established, we can use the measured onset of 9.647 eV for this reaction to establish the neopentylamine . This result is used in a group additivity scheme to estimate the neopentyl alcohol heat of formation as . Both of these results are strongly supported by a series of isodesmic reactions calculated at the G3B3 and CBS-APNO levels. This is the first reported experimental heat of formation of the neopentylamine and the first reported heat of formation of the neopentyl alcohol.

Shuman, Nicholas S.; Kercher, James P.; Baer, Tomas

2008-11-01

119

Absolute cross sections and kinetic energy release distributions for electron-impact dissociation of HD2+  

NASA Astrophysics Data System (ADS)

Absolute cross sections results are reported for electron impact dissociative excitation and ionization of HD2+ in the electron energy range from threshold to 2.5 keV. Direct and resonant dissociative excitation is found to dominate the production of possible ionic products in the low energy region. Dissociative ionization is observed for H+ and D+ products only. The lowness of dissociative ionization signals both for HD+ and for D2+ indicate that molecular ions are dominantly formed in dissociative states, a situation which totally contrasts with the D3+isotopomer case.

Defrance, P.; Jureta, J. J.; Lecointre, J.; Urbain, X.

2009-11-01

120

Promotion effect of metal oxides on CO bond dissociation in CO hydrogenation over Rh\\/SiO 2 Catalyst — possible role of partially reduced state cations  

Microsoft Academic Search

In CO hydrogenation over Rh\\/SiO2 catalysts, the effect of additive metal oxides on C-O bond dissociation was studied by using pulse surface reaction rate\\u000a analysis (PSRA). The addition of oxides of Al, Ti, Cr, V, and Mn resulted in an increase in the rate constant for the dissociation\\u000a according to this sequence, while the oxides of Cu, Zn, and Ag

Hajime Kato; Masaki Nakashima; Yoshihiko Mori; Toshiaki Mori; Tadashi Hattori; Yuichi Murakami

1995-01-01

121

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. 26 figs.

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

1998-08-25

122

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. 26 figs.

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

1998-09-08

123

Adhesive bonding using variable frequency microwave energy  

DOEpatents

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

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

1998-01-01

124

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

SciTech Connect

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

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

2013-02-14

125

Unimolecular dissociation of energy-selected ethyl formate ions  

NASA Astrophysics Data System (ADS)

The unimolecular dissociation of ethyl formate ions has been investigated using threshold photoelectron photoion coincidence mass spectrometry. The fragment ions appearing at low internal energies are C2H4CO+ and C2H4·+, whose appearance potentials are higher than the ionization energy of the ethyl formate molecule by 0.18 eV and 0.28 eV respectively. Observed decay rates for the formation of C2H4CO+ were found to be different to those of C2H4·+, although the direct fragmentation mechanism indicates that they should be identical. Furthermore, the rate constants predicted by RRKM/QET calculations are 104-105 times higher than the observed rate constants for both ions. The different decay rates probably result from different isomerization processes. One of the reaction channels is a stepwise McLafferty rearrangement involving a distonic intermediate, with charge retention on the olefin.

Zha, Qingmei; Nishimura, Toshihide; Meisels, G. G.

1992-10-01

126

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

Microsoft Academic Search

The standard local density approximation and generalized gradient approximations fail to properly describe the dissociation of an electron pair bond, yielding large errors (on the order of 50 kcal\\/mol) at long bond distances. To remedy this failure, a self-consistent Kohn-Sham (KS) method is proposed with the exchange-correlation (xc) energy and potential depending on both occupied and virtual KS orbitals. The

M. Grüning; O. V. Gritsenko; E. J. Baerends

2003-01-01

127

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

Microsoft Academic Search

The standard local density approximation and generalized gradient approximations fail to properly describe the dissociation of an electron pair bond, yielding large errors (on the order of 50 kcal\\/mol) at long bond distances. To remedy this failure, a self-consistent Kohn–Sham (KS) method is proposed with the exchange-correlation (xc) energy and potential depending on both occupied and virtual KS orbitals. The

O. V. Gritsenko; E. J. Baerends

2003-01-01

128

Gas-phase acidities and O-H bond dissociation enthalpies of phenol, 3-methylphenol, 2,4,6-trimethylphenol, and ethanoic acid.  

PubMed

Energy-resolved, competitive threshold collision-induced dissociation (TCID) methods are used to measure the gas-phase acidities of phenol, 3-methylphenol, 2,4,6-trimethylphenol, and ethanoic acid relative to hydrogen cyanide, hydrogen sulfide, and the hydroperoxyl radical using guided ion beam tandem mass spectrometry. The gas-phase acidities of Delta(acid)H298(C6H5OH) = 1456 +/- 4 kJ/mol, Delta(acid)H298(3-CH3C6H4OH) = 1457 +/- 5 kJ/mol, Delta(acid)H298(2,4,6-(CH3)3C6H2OH) = 1456 +/- 4 kJ/mol, and Delta(acid)H298(CH3COOH) = 1457 +/- 6 kJ/mol are determined. The O-H bond dissociation enthalpy of D298(C6H5O-H) = 361 +/- 4 kJ/mol is derived using the previously published experimental electron affinity for C6H5O, and thermochemical values for the other species are reported. A comparison of the new TCID values with both experimental and theoretical values from the literature is presented. PMID:16942044

Angel, Laurence A; Ervin, Kent M

2006-09-01

129

Theoretical enthalpies of formation and O H bond dissociation enthalpy of an ?-tocopherol model and its free radical  

NASA Astrophysics Data System (ADS)

Using DFT computations (B3LYP and BHandHLYP functionals) with isodesmic reactions as working chemical reactions, and extended basis sets with diffuse functions, the standard enthalpies of formation of an ?-tocopherol model (where the aliphatic chain and the neighbour methyl group have been changed to hydrogen atoms) and its free radical ?-tocopheroxy were theoretically estimated for the first time: -79.4 ± 2.0, and -54.9 ± 2.0 kcal mol -1, respectively. These enthalpies of formation correspond to the O-H bond dissociation enthalpy of BDE(O-H)=76.6 ± 2.0 kcal mol -1, in excellent agreement with the gas-phase experimental value for natural ?-tocopherol, which lends confidence to the method and model used.

Espinosa-García, J.

2004-04-01

130

C-H bond activation over metal oxides: A new insight into the dissociation kinetics from density functional theory  

NASA Astrophysics Data System (ADS)

The C-H activation on metal oxides is a fundamental process in chemistry. In this paper, we report a density functional theory study on the process of the C-H activation of CH4 on Pd(111), Pt(111), Ru(0001), Tc(0001), Cu(111), PdO(001), PdO(110), and PdO(100). A linear relationship between the C-H activation barrier and the chemisorption in the dissociation final state on the metal surfaces is obtained, which is consistent with the work in the literature. However, the relationship is poor on the metal oxide surfaces. Instead, a strong linear correlation between the barrier and the lattice O-H bond strength is found on the oxides. The new linear relationship is analyzed and the physical origin is identified.

Li, Hui-Ying; Guo, Yang-Long; Guo, Yun; Lu, Guan-Zhong; Hu, P.

2008-02-01

131

The photo-dissociation of the pyrrole-ammonia complex--the role of hydrogen bonding in Rydberg states photochemistry.  

PubMed

The photochemistry of the pyrrole-ammonia cluster is analyzed theoretically. Whereas in neat pyrrole the dominant photochemical reaction is H-atom cleavage, recent experiments show that in pyrrole-ammonia clusters the major reaction is H-transfer to form the NH(4) radical (solvated by ammonia molecules in the case of large clusters) and the pyrrolyl radical. A mechanism involving the hydrogen-bonded Rydberg state is offered to account for these results and verified computationally. Two minima are located on the lowest excited singlet PES. Both of them are Rydberg states, one leads to the formation of NH(4) and pyrrolyl radicals, the other is connected to the ??* state through a relatively high barrier, leading to a 3-body dissociation reaction to form a pyrrolyl radical, ammonia and an H-atom. The former is the energetically and statistically preferred one. PMID:22337489

Zilberg, Shmuel; Kahan, Anat; Haas, Yehuda

2012-07-01

132

Kinetic-energy release in CO dissociation caused by fast F4+ impact  

Microsoft Academic Search

The dissociation of CO caused by 1-MeV\\/amu F4+ impact has been studied using the coincidence time-of-flight technique. The kinetic energy released during the dissociation of COQ+ into ion pairs Cq1+ and Oq+2 was determined from the measured difference in the times of flight of the two charged fragments. The kinetic-energy distributions of CO2+ dissociating into C+ and O+ as a

I. Ben-Itzhak; S. G. Ginther; Vidhya Krishnamurthi; K. D. Carnes

1995-01-01

133

Chemical activation of molecules by metals: Experimental studies of electron distributions and bonding. Technical progress report, March 1, 1989--September 30, 1991.  

National Technical Information Service (NTIS)

The formal relationship between measured molecular ionization energies and thermodynamic bond dissociation energies has been developed into a single equation which unifies the treatment of covalent bonds, ionic bonds, and partially ionic bonds. This relat...

D. L. Lichtenberger

1991-01-01

134

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

135

Possible mechanisms for protecting NC[alpha] bonds in helical peptides from electron-capture (or transfer) dissociation  

NASA Astrophysics Data System (ADS)

Ab initio electronic structure simulations are carried out on small alanine-based peptide fragments with an excess electron added to a Coulomb-stabilized amide OCN [pi]* orbital that forms a CO- radical anion center. A focus of the study is to determine to what extent and by what means helix-involved NC[alpha] bonds are "protected" against cleavage compared to similar bonds in non-helical peptides. The primary findings, many of which support earlier suggestions, include: (1) There is little or no increase in the energy barriers for NC[alpha] bond cleavage caused by an amino acid being in a helix where its carbonyl oxygen is involved in a hydrogen bond to an HN bond of an amino acid displaced by one helix turn. (2) When an electron attaches to a helix-involved Coulomb-stabilized OCN [pi]* orbital and the NC[alpha] bond cleaves, three hydrogen bonds act to bind together the c and z fragment ions. One of these hydrogen bonds is especially strong (ca. 16 kcal mol-1) because it involves a negatively charged oxygen center. This suggests that the "protection" against NC[alpha] cleavage of helix-involved amino acids may, as others suggested earlier, result 6rom the strong hydrogen bonding that binds the c and z fragment ions. (3) When an electron attaches to a helix-involved OCN [pi]* orbital, an electron can migrate to the [pi]* orbital of another amino acid one turn down the helix, but only by overcoming a barrier. After migrating to a new amino acid, NC[alpha] cleavage can occur at the latter site, also in line with what earlier workers have suggested. Suggestions of experiments that might test the hypotheses treated here are also put forth.

Skurski, Piotr; Sobczyk, Monika; Jakowski, Jacek; Simons, Jack

2007-09-01

136

Short-Lived Quantum Entanglement of Protons and Dissociation of C-H Bonds in Condensed Matter -- a New Effect  

NASA Astrophysics Data System (ADS)

In earlier neutron Compton scattering (NCS) experiments on H2O/D2O mixtures at T ? 298 K we observed, for the first time, a striking "anomalous" decrease of the ratio ?H/?D of the total scattering cross sections of H and D. This "anomaly" was found to depend strongly on the H/D composition of the liquid. Extending recent NCS results obtained from solid polystyrene, we present here new results concerning the quantum dynamics and dissociation of C-H bonds (at T ? 298 K) in: (a) liquid benzene and C6H6/C6D6 mixtures; (b) fully protonated and partially deuterated polystyrene; and (c) liquid mixtures of H-acetone (CH3COCH3) and D-acetone (CD3COCD3). The considered NCS effect was given a theoretical explanation based on short-lived protonic quantum entanglement (QE) and decoherence. The variety of the new results suggests that, in the short-time scale of the NCS experiment, protonic quantum dynamics is strongly correlated with that of electronic degrees of freedom participating in the various chemical bonds.

Chatzidimitriou-Dreismann, C. A.; Abdul-Redah, T.

2002-10-01

137

Neutral and ionic metal methyl bond energies: Zn  

SciTech Connect

Zinc methyl and zinc methyl ion are two competing products studied in the ion beam reactions of Zn/sup +/ with a series of alkanes. While ion beam techniques have long been used to provide bond dissociation energies for ionic transition metal species, including MCH/sub 3//sup +/, this study is one of the first to test the reliability of the technique. In addition, improved instrumentation makes possible the determination of both ionic and neutral bond energies. We determine D/sup 0/(Zn/sup +/-CH/sub 3/) = 3.06 +- 0.14 eV (70.6 +- 3.2 kcal/mol) and D/sup 0/(Zn-CH/sub 3/) = 0.84 +- 0.14 eV (19.4 +- 3.2 kcal/mol), both in excellent agreement with the available literature. Coupled with literature thermochemistry, this latter value implies that D/sup 0/(CH/sub 3/Zn-CH/sub 3/) = 69.5 +- 3.2 kcal/mol. General features of the reaction cross sections and branching ratios are discussed in terms of a simple qualitative molecular orbital picture.

Georgiadis, R.; Armentrout, P.B.

1986-04-30

138

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

139

Hydration Energies of Zinc(II): Threshold Collision-Induced Dissociation Experiments and Theoretical Studies  

NASA Astrophysics Data System (ADS)

The first experimentally determined sequential bond dissociation energies of Zn2+(H2O)n complexes, where n = 6-10, are measured using threshold collision-induced dissociation in a guided ion beam tandem mass spectrometer coupled with an electrospray ionization source. Kinetic energy dependent cross sections are obtained and analyzed to yield 0 K threshold measurements for the loss of one and two water ligands after accounting for multiple collisions, kinetic shifts, and energy distributions. The threshold measurements are then converted from 0 to 298 K values to give the hydration energies for sequentially losing one water from each parent complex. Theoretical geometry optimizations and single-point energy calculations are performed using several levels of theory for comparison to experiment. Although different levels of theory disagree on the ground-state conformation of most complexes examined here leading to potential ambiguities in the final thermochemical values, calculations at the MP2(full) level provide the best agreement with experiment. On this basis, the present experiments are most consistent with the inner solvent shell of Zn2+ being five waters, except for Zn2+(H2O)6 where all waters bind directly to the metal ion. The charge separation process, Zn2+(H2O)n ? ZnOH+(H2O)m + H+(H2O)n-m-1, which is in competition with the loss of water from the parent complex, is also observed for n = 6-8. These processes are analyzed in detail in the following paper.

Cooper, Theresa E.; Carl, D. R.; Armentrout, P. B.

2009-11-01

140

Hydration energies of zinc(II): threshold collision-induced dissociation experiments and theoretical studies.  

PubMed

The first experimentally determined sequential bond dissociation energies of Zn(2+)(H(2)O)(n) complexes, where n = 6-10, are measured using threshold collision-induced dissociation in a guided ion beam tandem mass spectrometer coupled with an electrospray ionization source. Kinetic energy dependent cross sections are obtained and analyzed to yield 0 K threshold measurements for the loss of one and two water ligands after accounting for multiple collisions, kinetic shifts, and energy distributions. The threshold measurements are then converted from 0 to 298 K values to give the hydration energies for sequentially losing one water from each parent complex. Theoretical geometry optimizations and single-point energy calculations are performed using several levels of theory for comparison to experiment. Although different levels of theory disagree on the ground-state conformation of most complexes examined here leading to potential ambiguities in the final thermochemical values, calculations at the MP2(full) level provide the best agreement with experiment. On this basis, the present experiments are most consistent with the inner solvent shell of Zn(2+) being five waters, except for Zn(2+)(H(2)O)(6) where all waters bind directly to the metal ion. The charge separation process, Zn(2+)(H(2)O)(n) --> ZnOH(+)(H(2)O)(m) + H(+)(H(2)O)(n-m-1), which is in competition with the loss of water from the parent complex, is also observed for n = 6-8. These processes are analyzed in detail in the following paper. PMID:19904969

Cooper, Theresa E; Carl, D R; Armentrout, P B

2009-12-10

141

Dissociative double ionization of CO2: dynamics, energy levels, and lifetime.  

PubMed

In a kinematically complete experiment on the dissociative double ionization of CO2 by electron impact, spontaneous and metastable decay have been observed via the channel CO2(2+) --> CO+ + O+. The metastable decay shows a lifetime of 5.8 +/- 1.5 micros. The measured kinetic energy release spectrum of the dissociation shows one broad peak. To understand the observed features, ab initio potential energy surface (PES) for the ground electronic state of CO2(2+) was computed using a multireference configuration interaction method and a correlation-consistent polarized-valence quadruple-zeta basis set, for a range of internuclear distances and O-C-O bond angles, and an analytic fit of the PES was obtained. The computed PES clearly indicates the metastability of the dication and yields a barrier height and an asymptotic limit in fair agreement with the reported data. A time-dependent quantum mechanical approach was used to compute the ground vibrational state wave function of CO2 in its ground electronic state. Assuming a Franck-Condon transition, the same function was taken to be the initial wave function at time t = 0 for the time evolution on the fitted PES for the ground electronic state of CO2(2+). The autocorrelation function was computed and Fourier transformed to obtain the excitation spectrum. Upon convolution with the instrument resolution function, the kinetic energy release spectrum was obtained, in good agreement with the experimental results, particularly at lower energies. The discrepancies at higher energies are attributed to the noninclusion of the excited states of CO2(2+) in the dynamical study. PMID:17497762

Sharma, Vandana; Bapat, B; Mondal, Jagannath; Hochlaf, M; Giri, Kousik; Sathyamurthy, N

2007-10-18

142

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

143

Kinetic-energy release in CO dissociation caused by fast F[sup 4+] impact  

Microsoft Academic Search

The dissociation of CO caused by 1-MeV\\/amu F[sup 4+] impact has been studied using the coincidence time-of-flight technique. The kinetic energy released during the dissociation of CO[sup [ital Q]+] into ion pairs C[sup [ital q

I. Ben-Itzhak; S. G. Ginther; Vidhya Krishnamurthi; K. D. Carnes

1995-01-01

144

Resonant structure of low-energy H3+ dissociative recombination  

NASA Astrophysics Data System (ADS)

High-resolution dissociative recombination rate coefficients of rotationally cool and hot H3+ 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 380-130+50 K and that this is the lowest rotational temperature so far realized in storage-ring rate-coefficient measurements on H3+. 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.; Novotný, Old?ich; Novotny, Steffen; Orlov, Dmitry A.; Repnow, Roland; Sorg, Tobias; Stützel, Julia; Wolf, Andreas; Buhr, Henrik; Kreckel, Holger; Kokoouline, Viatcheslav; Greene, Chris H.

2011-03-01

145

An intrinsic radical stability scale from the perspective of bond dissociation enthalpies: a companion to radical electrophilicities.  

PubMed

Bond dissociation enthalpies (BDEs) of a large series of molecules of the type A-B, where a series of radicals A ranging from strongly electrophilic to strongly nucleophilic are coupled with a series of 8 radicals (CH2OH, CH3, NF2, H, OCH3, OH, SH, and F) also ranging from electrophilic to nucleophilic, are computed and analyzed using chemical concepts emerging from density functional theory, more specifically the electrophilicities of the individual radical fragments A and B. It is shown that, when introducing the concept of relative radical electrophilicity, an (approximately) intrinsic radical stability scale can be developed, which is in good agreement with previously proposed stability scales. For 47 radicals, the intrinsic stability was estimated from computed BDEs of their combinations with the strongly nucleophilic hydroxymethyl radical, the neutral hydrogen atom, and the strongly electrophilic fluorine atom. Finally, the introduction of an extra term containing enhanced Pauling electronegativities in the model improves the agreement between the computed BDEs and the ones estimated from the model, resulting in a mean absolute deviation of 16.4 kJ mol(-1). This final model was also tested against 82 experimental values. In this case, a mean absolute deviation of 15.3 kJ mol(-1) was found. The obtained sequences for the radical stabilities are rationalized using computed spin densities for the radical systems. PMID:18937409

De Vleeschouwer, Freija; Van Speybroeck, Veronique; Waroquier, Michel; Geerlings, Paul; De Proft, Frank

2008-11-21

146

The binding energy and bonding in dialane.  

PubMed

The binding energy of dialane, Al2H6, has been measured using mass spectrometric techniques to be 33 +/- 5 kcal/mol. This represents the first measurement of the thermochemical properties of dialane, which has only recently been observed in low-temperature matricies. High-level quantum mechanical calculations give a binding energy in agreement with the measured value. Experimental and quantum mechanical calculations show that dialane is chemically similar to diborane, B2H6, even though the bonding for these two systems shows significant differences. PMID:16104745

Goebbert, Daniel J; Hernandez, Heriberto; Francisco, Joseph S; Wenthold, Paul G

2005-08-24

147

Energy and Rate Determinations to Activate the C-C ?-BOND of Acetone by Gaseous NI^+  

NASA Astrophysics Data System (ADS)

A unique application of a custom fabricated photodissociation spectrometer permits the determination of thermodynamic properties (activation energies), reaction rates, and mechanistic details of bare metal cation mediated C-C ?-bond activation in the gas phase. Specifically, the products and rates resulting from the unimolecular decomposition of the Ni^+Acetone (Ni^+Ac) adduct are monitored after absorption of a known amount of energy. The three dissociative products which are observed in high yield are Ni^+, Ni^+CO, and CH3CO^+. The latter two fragment ions result from the activation of a C-C ?-bond. It was found that minimally 14 000 cm^{-1} of energy must be deposited into the adduct ion to induce C-C bond breakage. Preliminary results for the Ni^+ activation of the C-C ?-bond of acetone indicate that there are (at least) two low energy reaction coordinates leading to C-C bond breakage. The lower energy pathway emerges from the doublet ground state with an upper limit to the activation energy of 14 000 cm^{-1} and reaction rate ?0.14 molecules/?s. The higher energy path is assumed to be along the quartet reaction coordinate with a minimum activation energy of 18 800 cm^{-1} (relative to the ground state) and a slightly slower reaction rate.

Castleberry, Vanessa A.; Dee, S. Jason; Villarroel, Otsmar J.; Laboren, Ivanna E.; Frey, Sarah E.; Bellert, Darrin J.

2009-06-01

148

A method for measurements of neutral fragments kinetic energies released to a specific dissociation threshold: optical translational spectroscopy  

Microsoft Academic Search

The optical translational spectroscopy technique, based on the principles of fast ion beam laser spectroscopy (FIBLAS) and translational spectroscopy, allows the kinetic energies study of neutral fragments released through free dissociation of a neutral molecule. This method presents interesting features such as near-threshold energy measurements and selection of a specific dissociation limit. The fragments resulting from free dissociation (not induced)

A. Roney; C. Frigon; M. Larzillière

1999-01-01

149

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

150

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

151

Kinetic-energy release in the dissociative double photoionization of OCS  

Microsoft Academic Search

Synchrotron radiation and the photoion-photoion coincidence (PIPICO) spectra were used to investigate the kinetic-energy release (KER) distributions of fragment ions produced in the dissociative double photoionization of the OCS molecule over the energy region of the valence orbitals. Analyses of PIPICO spectra yield new information on the dissociation dynamics of the OCS(2+) ion, including the KER distributions, their dependence on

Toshio Masuoka; Inosuke Koyano; Norio Saito

1992-01-01

152

How low can you go? Minimum energy pathways for O2 dissociation on Pt(111).  

PubMed

Many DFT studies of O(2) dissociation on Pt(111) give conflicting information on preferred paths and final states. Here we report large p(4 × 4) unit cell minimum energy pathway evaluations and compare O(2) adsorption and dissociated states on Pt(111). Calculations reveal how the pathways for O(2) dissociation starting from top-fcc-bridge, top-hcp-bridge, and top-bridge-top sites are interconnected. They also provide a direct reaction pathway for the dissociation of an O(2) molecule from a top-fcc-bridge into an hcp and an fcc site, which is consistent with low temperature scanning tunneling microscope experiments. Such a pathway is shown to be considerably perturbed by the presence of co-adsorbed oxygen atoms. We quantify the coverage dependence through the construction of a Brønsted-Evans-Polanyi relationship relating the O(2) dissociation activation energies to the binding energies of the dissociated O atoms. We also show that all pathways starting from a top-fcc-bridge site give the smallest barriers for O(2) dissociation. PMID:23093349

McEwen, J-S; Bray, J M; Wu, C; Schneider, W F

2012-12-28

153

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

154

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

155

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

NASA Astrophysics Data System (ADS)

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

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

1992-07-01

156

Influence of nitrogroups positions in molecules of various classes of explosives on results of quantum-chemical calculation of dissociation energy  

NASA Astrophysics Data System (ADS)

Results of quantum-chemical calculation of dissociation energies of nitrogroups in molecules of various classes of explosives such as aliphatic and aromatic nitrocompounds (C-NO2), aliphatic, heterocyclic (N-NO2) and aromatic (C-NO2, N-NO2) amines, nitrates of spirits (O-NO2) are presented. Molecules more than thirty explosives, from nitromethane to octogen and PETN are examined. Calculations were carried out with the use of the Gaussian 98 program. The density functional theory (DFT) method with the B3LYP combined functional was applied. Several basic sets of electronic functions, from the widely used polarizing 6-31G(d) basic set to the extremely large multifunctional 6-311++G(3df, 3pd) basic set, were used in calculations. The values of lengths of corresponding bonds and other structural and energetic characteristics of examined molecules are also deduced. Influence of structural isomerism and conformation was considered. The general tendencies of influence of nitrogroups positions in the molecules of explosives on the values of dissociation energy of the bonds were discoverd. For the majority of the considered molecules the certain interrelation of the dissociation energy of the weakest bond and the sensitivity to impact of corresponding explosive was recorded.

Golubev, Vladimir

2005-07-01

157

Kinetic energy distributions and line profile measurements of dissociation products of water upon electron impact  

Microsoft Academic Search

The Doppler line profiles of H Ly-? (1216 Å) and O I (1302 Å and 1152 Å) resulting from electron impact dissociative excitation of H2O have been measured with a high-resolution (?\\/?? = 50,000) ultraviolet spectrometer. The line profiles are used to calculate the kinetic energy distribution of the hydrogen atoms produced in dissociative excitation and ionization of H2O at

Oleg P. Makarov; Joseph M. Ajello; Prahlad Vattipalle; Isik Kanik; M. C. Festou; Anil Bhardwaj

2004-01-01

158

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

159

Middle School Chemistry: Energy Levels, Electrons, and Covalent Bonding  

NSDL National Science Digital Library

This multimedia lesson for Grades 7-8 features eight animations and a hands-on lab to explore the role of valence electrons in covalent bonding. The multimedia approach provides an opportunity to visualize the attractions between atoms that result in covalent bonds. The lab investigation uses a 9-volt battery, alligator clips, and pencils to show how electrical energy can break the covalent bonds in water molecules. Editor's Note: Covalent bonding occurs when electrons are shared between atoms; ionic bonding occurs when electrons are transferred between atoms. The processes are quite different. This module very effectively explores both formation and breaking of covalent bonds. Allow two class periods.

Galvan, Patti; Kessler, Jim

2011-08-17

160

Low-energy collision-induced dissociation mass spectra of protonated p-toluenesulfonamides derived from aliphatic amines.  

PubMed

Collision-induced fragmentation of protonated N-alkyl-p-toluenesulfonamides primarily undergo either an elimination of the amine to form CH3-(C6H4)-SO2(+) cation (m/z 155) or an alkene to form a cation for the protonated p-toluenesulfonamide (m/z 172). To comprehend the fragmentation pathways, several deuterated analogs of N-decyl-p-toluenesulfonamides were prepared and evaluated. Hypothetically, two mechanisms, both of which involve ion-neutral complexes, can be envisaged. In one mechanism, the S-N bond fragments to produce an intermediate [sulfonyl cation/amine] complex, which dissociates to afford the m/z 155 cation (Pathway A). In the other mechanism, the C-N bond dissociates to produce a different intermediate complex. The fragmentation of this [p-toluenesulfonamide/carbocation] complex eliminates p-toluenesulfonamide and releases the carbocation (Pathway B). Computations carried out by the Hartree-Fock method suggested that the Pathway B is more favorable. However, a peak for the carbocation is observed only when the carbocation formed is relatively stable. For example, the spectrum of N-phenylethyl-p-toluenesulfonamide is dominated by the peak at m/z 105 for the incipient phenylethyl cation, which rapidly isomerizes to the remarkably stable methylbenzyl cation. The peaks for the carbocations are weak or absent in the spectra of most of N-alkyl-p-toluenesulfonamides because alkyl carbocations, such as the decyl cation, rearrange to more stable secondary cations by 1,2-hydride and alkyl shifts. The energy freed is not dissipated, but gets internalized, causing the carbocation to dissociate either by transferring a proton to the sulfonamide or by releasing smaller alkenes to form smaller carbocations. The loss of the positional integrity in this way was proven by deuterium labeling experiments. PMID:24676895

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

2014-06-01

161

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

162

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

163

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

Microsoft Academic Search

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

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

2004-01-01

164

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

NASA Astrophysics Data System (ADS)

An experimental study of the dissociative photodetachment (DPD) dynamics of HOCO- and DOCO- at a photon energy of 3.21 eV has been carried out to probe the potential energy surface of the HOCO free radical and the dynamics of the OH+CO-->H+CO2 reaction. These photoelectron-photofragment coincidence experiments allow the identification of photodetachment processes leading to the production of stable HOCO free radicals and both the H+CO2 and OH+CO dissociation channels on the neutral surface. Isotopic substitution by deuterium in the parent ion is observed to reduce the product branching ratio for the D+CO2 channel, consistent with tunneling playing a role in this dissociation pathway. Other isotope effects on the detailed partitioning of kinetic energy between photoelectrons and photofragments are also discussed. The results are compared to recent theoretical predictions of this DPD process, and evidence for the involvement of vibrationally excited HOCO- anions is discussed.

Lu, Zhou; Hu, Qichi; Oakman, Jonathan E.; Continetti, Robert E.

2007-05-01

165

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

166

Municipal bond financing of solar energy facilities  

Microsoft Academic Search

The application of the laws of municipal bond financing to solar facilities is examined. The type of facilities under consideration are outlined. The general legal principles of municipal securities financing are discussed. The effect of recent decisions applying antitrust liability to municipal corporations is also discussed. Five specific types of municipal bonds are explained. The application of Section 103 of

1979-01-01

167

Guided ion beam and theoretical studies of sequential bond energies of water to sodium cysteine cation.  

PubMed

Absolute bond dissociation energies of water to sodium cysteine (Cys) cations and cysteine to hydrated sodium cations are determined experimentally by collision-induced dissociation of Na(+)Cys(H(2)O)(x), where x = 1-4, complexes with xenon in a guided ion beam mass spectrometer. Experimental results show that the binding energies of water and cysteine to the complexes decrease monotonically with increasing number of water molecules. Quantum chemical calculations at three different levels show reasonable agreement with the experimental bond energies. The calculations indicate that the primary binding site for Na(+) changes from charge-solvated tridentate chelation at the amino nitrogen, carbonyl oxygen, and sulfur side-chain for x = 0 and 1 to the C terminus of zwitterionic cysteine for x = 4, whereas different levels of theory provide conflicting predictions for x = 2 and 3. The first solvent shell of Na(+)Cys is found to be complete at four waters. This is fewer than needed for the aliphatic amino acid glycine, because the functionalized side-chain of Cys provides an internal solvation site, a binding motif that probably applies for most other functionalized amino acids. PMID:20607166

Ye, Sha Joshua; Armentrout, P B

2010-11-01

168

Bonding  

NSDL National Science Digital Library

Bonding Purpose: To review the 3 Types of Bonds and the 4 Intermolecular Forces. Assignment: Answer the following questions on a separate piece of paper: 1) List the 3 types of bonding, give descriptions and one example of each 2) List the 4 intermolecular forces and draw examples of each. Be ...

Cutting, Mrs.

2008-03-08

169

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

PubMed

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

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

2012-08-01

170

Dynamics of dissociative scattering: Hyperthermal energy collisions of state-selected OCS+ on Ag(111)  

Microsoft Academic Search

The dynamics of dissociation and negative ion formation have been investigated for the hyperthermal energy scattering of state-selected OCS+(X 2&Pgr;x, &ugr;1, &ugr;2, &ugr;3) on Ag(111). Experiments reveal the effect that collision energy and internal energy have on the formation of scattered ionic products. An analysis of the appearance threshold and fragment velocity distribution for each scattered product channel [S?(2P), O?(2P),

J. R. Morris; G. Kim; T. L. O. Barstis; R. Mitra; D. C. Jacobs

1997-01-01

171

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

SciTech Connect

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

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

2011-03-01

172

Comparison of hexamethyldisiloxane dissociation processes in plasma.  

PubMed

Different hexamethyldisiloxane (HMDSO) dissociation processes are investigated by means of absorption spectroscopy and mass spectrometry. All of these processes are expected to occur in plasma containing Ar-HMDSO gas mixture. We successively study interactions of the HMDSO molecule with electrons (energy ranges from 15 to 70 eV), with Ar((3)P(2)) metastable species (internal energy 11.55 eV) and with VUV photon (7.3 to 10.79 eV). The studies of HMDSO interactions with Ar((3)P(2)) and VUV photon provide new results concerning the dissociation pathways and the collision cross-sections. In the case of Ar((3)P(2)), the dissociation mechanisms result mainly in Si-C or Si-O bond breaking, producing SiMe(2,1) radicals. Less efficient mechanisms involve also Si-C and Si-O bond breaking producing Me, Si(2)Me(5)O, or SiMe(3), on one hand, and, on the other hand, Si-C and C-H bond breaking producing Si(2)Me(4)OH. In the case of photon interaction, the dissociation process is more selective and mainly produces Si(2)OMe(5) pentadisiloxane and methyl radicals due to Si-C bond breaking. Si-O bond breaking produces also SiMe(3) in a lower concentration. Dissociation cross-section values of HMDSO ranging from ? = 45 × 10(-20) m(2) to 180 × 10(-20) m(2) and from ? = 0.7 × 10(-22) m(2) to 18.3 × 10(-22) m(2), correspond to a global dissociation mechanism by Ar((3)P(2)) collision and to a selective dissociation mechanism (producing Si(2)OMe(5) and Me) by VUV photon interaction, respectively. All results are compared and discussed. PMID:22812650

Jauberteau, J L; Jauberteau, I

2012-09-01

173

[Vibrational levels and dissociation energies of diatomic systems using algebraic method].  

PubMed

The fixed order in the algebraic method (AM) suggested by Sun et al. is changed to be a flexible one in the vibrational energy expansion because the order of diatomic potential energy expansion may not be a constant. The AM with a flexible order was used to tackle the possible "butterfly effect" that may be encountered in spectroscopic computations, and to study the full vibrational levels {E(v)} and the dissociation energies D(e) for N2 - a'(1) sigma(u)(-), Li2(+) - 2 2sigma(g)(+), 4HeD(+) - X 1sigma(-) and 39K 85Rb- (2) 3sigma(+) electronic systems. The results reproduced all known experimental vibrational energies, and predicted correct dissociation energies and all unknown high-lying levels that may not be given if one uses original AM. The calculations showed that the modified AM can be extended to study the full vibrational spectra for many more diatomic systems. PMID:22497117

Zhang, Yi; Sun, Wei-guo; Fu, Jia; Fan, Qun-chao; Feng, Hao; Li, Hui-dong

2012-01-01

174

Dissociation of aliphatic hydrocarbons excited by electrons: Translational energy distributions of the excited hydrogen atom  

NASA Astrophysics Data System (ADS)

The Doppler profiles of the Balmer lines produced in collisions of ethane, propane, pentane and hexane with electrons have been measured precisely and the translational energy distributions of H* ( n = 3, 4) have been obtained. There are four major dissociation processes for all these molecules, just as in the case of methane. Their translational energy distributions and threshold energies correspond well with those of methane. The translational energy distributions of H* ( n = 3, 4) agree qualitatively with those of H + and the high-Rydberg atom. Thus, these molecules and fragments display qualitatively similar dissociation behavior and the core ion model is valid. However, there are some systematic differences related to the size of the molecules. The emission cross sections were determined separately for H* ( n = 3) with different translational energies.

Ogawa, Teiichiro; Tsuboi, Toshiyuki; Nakashima, Keiji

1991-10-01

175

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

176

Total cross sections and kinetic energy release for the electron impact dissociation of H+2 and D+2  

Microsoft Academic Search

Absolute total cross sections have been measured for electron impact dissociative excitation and dissociative ionization of H+2 and D+2 in the energy range 5-3000 eV. The vibrational population of the primary H+2 beam has been analysed by dissociative charge exchange on a potassium target, and is in good agreement with the measurements of von Busch and Dunn (1972 Phys. Rev.

M. O. Abdellahi El Ghazaly; J. Jureta; X. Urbain; P. Defrance

2004-01-01

177

Relativistic contributions to ionization energies and bond lengths  

Microsoft Academic Search

The interchange theorem of double perturbation theory permits two equivalent approaches for the determination and discussion of relativistic changes of ionization energies and bond lengths. Electron density differences due to ionization and bond length variation, respectively, at the nonrelativistic level, or alternatively density differences due to relativity, have to be taken into account ; either may be used for explaining

W. H. E. Schwarz; S. Y. Chu; F. Mark

1983-01-01

178

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

179

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

PubMed

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

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

2010-10-28

180

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

181

Noncatalytic dissociation of MgO by laser pulses towards sustainable energy cycle  

NASA Astrophysics Data System (ADS)

We succeeded in dissociating MgO using laser pulses without a reducing agent. The energy efficiency from laser to magnesium reaction energy exceeded 42.5%. Although 1 kW CO2 cw laser and Nd-YAG pulse laser are used in this experiment, the laser can be pumped by natural resources such as solar light or wind power. Thus natural resources are stored in the form of magnesium, which can be used through the reaction with water whenever we need the energy, and thus a renewable energy system will be established. This paper reports the preliminary experiments of MgO reduction toward a sustainable energy cycle.

Yabe, T.; Mohamed, M. S.; Uchida, S.; Baasandash, C.; Sato, Y.; Tsuji, M.; Mori, Y.

2007-06-01

182

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

183

Structure and dissociation energy of weakly bound H2n+1+ (n = 5-8) complexes  

NASA Astrophysics Data System (ADS)

The geometrical parameters, vibrational frequencies, and dissociation energies for H2n+1+ (n = 5-8) clusters have been investigated using high level ab initio quantum mechanical techniques with large basis sets. The highest level of theory employed in this study is TZ2P CCSD(T). The C1 structure of H15+ is predicted to be a global minimum, while the Cs structure of H15+ is calculated to be a transition state. Harmonic vibrational frequencies are also determined at the DZP and TZ2P CCSD levels of theory. The dissociation energies, De, for H2n+1+ (n = 5-8) have been predicted using energy differences at each optimized geometry, and zero-point vibrational energies (ZPVEs) are considered to compare with experimental values. The dissociation energies (Do) have been predicted to be 1.69, 1.65, 1.65, and 1.46 kcal · mol for H11+, H13+, H15+ (C1 symmetry) and H17+, respectively, at the TZ2P CCSD(T) level of theory.

Seo, Hyun-Il; Sun, Ju-Yong; Shin, Chang-Ho; Kim, Seung-Joon

184

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

PubMed

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

Beck, John Frederick; Mo, Yirong

2007-01-15

185

Reply to comment on `The enthalpy of the O H bond homolytic dissociation: Basis-set extrapolated density functional theory and coupled cluster calculations'  

NASA Astrophysics Data System (ADS)

Based on a recent re-evaluation of the O-H bond dissociation enthalpy (BDE) of phenol by Mulder et al. as 86.7 ± 0.7 kcal/mol, Di Labio and Mulder put under dispute the reliability of basis-set extrapolated coupled cluster calculations with single and double excitations (CCSD) for predicting the gas-phase BDEs of phenol and cathecol. Here, we stress again that our results support the experimental values for phenol recommended by Santos and Simões (88.7 kcal/mol) and by DeTuri and Erwin (90.1 ± 3.1 kcal/mol). We also verified that perturbative inclusion of triple excitations do not change our previous conclusions. We provide further elements that indicate why the recommended value of Mulder et al. for the phenol O-H BDE is not a definitive reference value.

Cabral, B. J. Costa; Canuto, Sylvio

2006-01-01

186

Kinetic energy releases upon dissociation of endohedral fullerene cations  

NASA Astrophysics Data System (ADS)

Kinetic energy release distributions are reported for the emission of C 2 from the positive ions of C 60, Ne@C 60, C 82 and La@C 82. Finite heat bath theory was applied to deduce the C 2 binding (vaporization) energies, ?Evap. The results obtained are: ?Evap(C 60+) = 7.1 ± 0.5 eV, ?Evap(Ne@C 60+) = 7.4 ± 0.5 eV; ?Evap(C 82+) = 6.1 ± 0.4 eV and ?Evap(La@C 82+) = 7.3 ± 0.4 eV. The endohedral neon atom has a minor effect on the cage binding, while lanthanum has a relatively strong effect.

Laskin, J.; Jimenez-Vazquez, H. A.; Shimshi, R.; Saunders, M.; de Vries, M. S.; Lifshitz, C.

1995-08-01

187

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. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:1949-1955, 2014. PMID:24823496

Andersson, Thomas; Broo, Anders; Evertsson, Emma

2014-07-01

188

Converging multidimensional rovibrational variational calculations: the dissociation energy of (HF) 2  

NASA Astrophysics Data System (ADS)

We report large scale quantum mechanical calculations for the ground state energy E0 and for the dissociation energy D0 of the HF dimer on the SQSBDE potential energy surface of Quack and Suhm. A value of 4593.13 cm -1 is obtained for E0 by a large scale variational basis set expansion and confirmed by very accurate quantum Monte Carlo calculations giving E0 of 4593.15±0.03 cm -1. The noticeably higher ground state energies computed in previous variational studies are explained by the use of suboptimal HF eigenfunctions. The new estimated value of D0 is 1058.00 cm -1.

Mladenovi?, Mirjana; Lewerenz, Marius

2000-04-01

189

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

190

Dissociation of molecules in intense laser beam  

NASA Astrophysics Data System (ADS)

Dissociation of molecules in the strong laser beam at the intensity of 1013-1014 W/cm2 is investigated. Experimentally, the fragmentation of neutral molecules, CH4, C2H4, C4H8; and the disintegration of molecular ions, CH{4/+} are studied by fluorescence spectroscopy and mass spectroscopy respectively. Some new phenomena, the strong dependence on the laser intensity, the universal dissociation, and the thorough fragmentation, are found in the fragmentation, and cannot be explained by the existing theories, as Coulomb Explosion theory or Re-scattering theory. We have suggested two new theories. The Super-excited State (SES) theory interprets the neutral fragmentation of molecules, which is stimulated to the SES by intense laser pulse. The Morse potential energy surface of the SES shows that either direct dissociation or pre-dissociation can take place in the SESs. Another theory, the theory of Field-assisted Dissociation (FAD) interprets the fragmentation of ionic molecules. According to this theory, the electric field of the laser pulse is involved directly to the dissociation process. QCT calculations for the trajectories moving on the dressed PES are performed. The result shows that the chemical bond which is parallel to the laser field vector undergo dissociation spontaneously. The dissociation takes place around 100 fs, which is in agreement with the ultrafast measurement in the pump-probe experiment.

Liu, Kai; Song, Di; Kong, Fanao

2009-08-01

191

Kinetics of GPIbalpha-vWF-A1 tether bond under flow: effect of GPIbalpha mutations on the association and dissociation rates.  

PubMed

The interaction between platelet glycoprotein (GP) Ib-IX-V complex and von Willebrand factor (vWF) is the first step of the hemostatic response to vessel injury. In platelet-type von Willebrand disease, two mutations, G233V and M239V, have been described within the Cys209-Cys248 disulfide loop of GPIbalpha that compromise hemostasis by increasing the affinity for vWF. We have earlier shown that converting other residues in this region to valine alters the affinity of GPIbalpha for vWF, with mutations K237V and Q232V, respectively, showing the greatest increase and decrease in affinity. Here, we investigated further the effect of these two mutations on the kinetics of the GPIbalpha interaction with the vWF-A1 domain under dynamic flow conditions. We measured the cellular on- and off-rate constants of Chinese hamster ovary cells expressing GPIb-IX complexes containing wild-type or mutant GPIbalpha interacting with vWF-A1-coated surfaces at different shear stresses. We found that the gain-of-function mutant, K237V, rolled very slowly and continuously on vWF-A1 surface while the loss-of-function mutant, Q232V, showed fast, saltatory movement compared to the wild-type (WT). The off-rate constants, calculated based on the analysis of lifetimes of transient tethers formed on surfaces coated with limiting densities of vWF-A1, revealed that the Q232V and K237V dissociated 1.25-fold faster and 2.2-fold slower than the WT. The cellular on-rate constant of WT, measured in terms of tethering frequency, was threefold more and threefold less than Q232V and K237V, respectively. Thus, the gain- and loss-of-function mutations in GPIbalpha affect both the association and dissociation kinetics of the GPIbalpha-vWF-A1 bond. These findings are in contrast to the functionally similar selectin bonds where some of the mutations have been reported to affect only the dissociation rate. PMID:14645097

Kumar, R Anand; Dong, Jing-fei; Thaggard, Jenny A; Cruz, Miguel A; López, José A; McIntire, Larry V

2003-12-01

192

Structural elucidation of O -linked glycopeptides by high energy collision-induced dissociation  

Microsoft Academic Search

O-linked glycopeptides that bear a GalNAc core with and without the presence of sialic acid have been analyzed by high energy\\u000a collision-induced dissociation (CID). We show that the CID spectra from the glycosylated precursor ions contain sufficient\\u000a information to identify the peptide sequence and to determine the glycosylated site(s). Asialo O-linked glycopeptides, previously prepared from a tryptic digest of bovine

K. F. Medzihradszkyaff; B. L. Gillece-Castroaff; R. R. Townsendaff; A. L. Burlingameaff; M. R. Hardyaff

1996-01-01

193

Absolute cross sections and kinetic energy release distributions for electron impact ionization and dissociation of CD+  

Microsoft Academic Search

Absolute cross sections for electron impact dissociative excitation and ionization of CD+ leading to the formation of ionic products (D+, C+, C2+ and C3+) are reported in the energy range from their respective thresholds to 2.5 keV. Around the maximum, cross sections are found to be (10.5 ± 1.0) × 10-17 cm2, (20.6 ± 3.5) × 10-17 cm2, (1.20 ±

J. Lecointre; S. Cherkani-Hassani; D. S. Belic; J. J. Jureta; K. Becker; H. Deutsch; T. D. Märk; M. Probst; R. K. Janev; P. Defrance

2007-01-01

194

Benchmark theoretical study on the dissociation energy of chlorine.  

PubMed

The currently accepted D(0)((35)Cl(2)) is 239.221 ± 0.001 kJ/mol, whereas popular theoretical model chemistries provide values in the range of 233-247 kJ/mol, and even the so-called high-accuracy protocols can yield values as low as 237.9 kJ/mol and as high as 240.1 kJ/mol for D(0)((35)Cl(2)). The aim of this study was to uncover the sources of error inherent in the theoretical approaches. Therefore, a coupled-cluster-based composite model chemistry was utilized that included contributions of up to pentuple excitations, as well as corrections beyond the nonrelativistic and Born-Oppenheimer approximations. In our calculations, correlation consistent basis set families were used up to octuple-? basis sets. It was found that the following factors, in order of significance, can be identified as the most important error sources: (i) the considerably large relativistic contributions carrying large uncertainties, (ii) the very slow convergence of the Møller-Plesset (MP2) correlation energy (with the octuple-? basis set, it still contains an error of a few tenth of a kJ/mol), (iii) the slow convergence of the coupled-cluster singles and doubles (CCSD) contribution (it needs a octuple-? basis set to converge within 0.1 kJ/mol), and (iv) the relatively large basis set (quadruple-?) needed in the calculation of an accurate perturbative quadruples contribution. It is also notable that, for chlorine, the use of a quintuple-? basis set for the Hartree-Fock energy, the MP2 correlation energy, and for the CCSD and perturbative triples contributions, which is the usual treatment in almost every high-accuracy model chemistry, resulted in the overestimation of all of these contributions (altogether about by 1.8 kJ/mol). However, this overestimation is accidentally compensated by (i) using an inappropriate, small basis set for the valence electron contribution due to quadruple excitations (?1.2 kJ/mol), (ii) neglecting the effects of core electron contributions due to quadruple excitations (?0.2 kJ/mol), and (iii) neglecting relativistic effects beyond the scalar relativistic treatment (?0.3 kJ/mol). The most reliable theoretical estimate for D(0)((35)Cl(2)) obtained in this study, 239.27 ± 1.30 kJ/mol, differs by only 0.05 kJ/mol from the most accurate experimental result. This study also underpins the effect of relativistic contributions, which precludes current model chemistries to enter the range of sub-kJ/mol accuracy for second-row systems. PMID:21604724

Csontos, József; Kállay, Mihály

2011-07-01

195

Metal cation dependence of interactions with amino acids: bond energies of Cs+ to Gly, Pro, Ser, Thr, and Cys.  

PubMed

The interactions of cesium cations with five amino acids (AA) including glycine (Gly), proline (Pro), serine (Ser), threonine (Thr), and cysteine (Cys) are examined in detail. Experimentally, the bond dissociation energies (BDEs) are determined using threshold collision-induced dissociation of the Cs(+)(AA) complexes 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. Bond dissociation energies (0 K) of 93.3 ± 2.5, 107.9 ± 4.6, 102.3 ± 4.1, 105.4 ± 4.3, and 96.8 ± 4.2 kJ/mol are determined for complexes of Cs(+) with Gly, Pro, Ser, Thr, and Cys, respectively. Quantum chemical calculations are conducted at the B3LYP, B3P86, MP2(full), and M06 levels of theory with geometries and zero-point energies calculated at the B3LYP level using both HW*/6-311+G(2d,2p) and def2-TZVPPD basis sets. Results obtained using the former basis sets are systematically low compared to the experimental bond energies, whereas the latter basis sets show good agreement. For Cs(+)(Gly), theory predicts the ground-state conformer has the cesium cation binding to the carbonyl group of the carboxylic acid. For Cs(+)(Pro), the secondary nitrogen accepts the carboxylic acid hydrogen to form the zwitterionic structure, and the metal cation binds to both oxygens. Cs(+)(Ser), Cs(+)(Thr), and Cs(+)(Cys) are found to have tridentate binding at the MP2(full) level, whereas the density functional approaches slightly prefer bidentate binding of Cs(+) at the carboxylic acid moiety. Comparison of these results to those for the smaller alkali cations provides insight into the trends in binding affinities and structures associated with metal cation variations. PMID:22452793

Armentrout, P B; Chen, Yu; Rodgers, M T

2012-04-26

196

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

197

Bond energy decomposition analysis for subsystem density functional theory.  

PubMed

We employed an explicit expression for the dispersion (D) energy in conjunction with Kohn-Sham (KS) density functional theory and frozen-density embedding (FDE) to calculate interaction energies between DNA base pairs and a selected set of amino acid pairs in the hydrophobic core of a small protein Rubredoxin. We use this data to assess the accuracy of an FDE-D approach for the calculation of intermolecular interactions. To better analyze the calculated interaction energies we furthermore propose a new energy decomposition scheme that is similar to the well-known KS bond formation analysis [F. M. Bickelhaupt and E. J. Baerends, Rev. Comput. Chem. 15, 1 (2000)], but differs in the electron densities used to define the bond energy. The individual subsystem electron densities of the FDE approach sum to the total electron density which makes it possible to define bond energies in terms of promotion energies and an explicit interaction energy. We show that for the systems considered only a few freeze-and-thaw cycles suffice to reach convergence in these individual bond energy components, illustrating the potential of FDE-D as an efficient method to calculate intermolecular interactions. PMID:23485283

Beyhan, S Maya; Götz, Andreas W; Visscher, Lucas

2013-03-01

198

Dissociation free-energy profiles of specific and nonspecific DNA-protein complexes.  

PubMed

DNA-binding proteins recognize DNA sequences with at least two different binding modes: specific and nonspecific. Experimental structures of such complexes provide us a static view of the bindings. However, it is difficult to reveal further mechanisms of their target-site search and recognition only from static information because the transition process between the bound and unbound states is not clarified by static information. What is the difference between specific and nonspecific bindings? Here we performed adaptive biasing force molecular dynamics simulations with the specific and nonspecific structures of DNA-Lac repressor complexes to investigate the dissociation process. The resultant free-energy profiles showed that the specific complex has a sharp, deep well consistent with tight binding, whereas the nonspecific complex has a broad, shallow well consistent with loose binding. The difference in the well depth, ~5 kcal/mol, was in fair agreement with the experimentally obtained value and was found to mainly come from the protein conformational difference, particularly in the C-terminal tail. Also, the free-energy profiles were found to be correlated with changes in the number of protein-DNA contacts and that of surface water molecules. The derived protein spatial distributions around the DNA indicate that any large dissociation occurs rarely, regardless of the specific and nonspecific sites. Comparison of the free-energy barrier for sliding [~8.7 kcal/mol; Furini J. Phys. Chem. B 2010, 114, 2238] and that for dissociation (at least ~16 kcal/mol) calculated in this study suggests that sliding is much preferred to dissociation. PMID:23713479

Yonetani, Yoshiteru; Kono, Hidetoshi

2013-06-27

199

Covalent bonding: the fundamental role of the kinetic energy.  

PubMed

This work addresses the continuing disagreement between two prevalent schools of thought concerning the mechanism of covalent bonding. According to Hellmann, Ruedenberg, and Kutzelnigg, a lowering of the kinetic energy associated with electron delocalization is the key stabilization mechanism. The opposing view of Slater, Feynman, and Bader has maintained that the source of stabilization is electrostatic potential energy lowering due to electron density redistribution to binding regions between nuclei. Despite the large body of accurate quantum chemical work on a range of molecules, the debate concerning the origin of bonding continues unabated, even for H2(+), the simplest of covalently bound molecules. We therefore present here a detailed study of H2(+), including its formation, that uses a sequence of computational methods designed to reveal the relevant contributing mechanisms as well as the spatial density distributions of the kinetic and potential energy contributions. We find that the electrostatic mechanism fails to provide real insight or explanation of bonding, while the kinetic energy mechanism is sound and accurate but complex or even paradoxical to those preferring the apparent simplicity of the electrostatic model. We further argue that the underlying mechanism of bonding is in fact of dynamical character, and analyses that focus on energy do not reveal the origin of covalent bonding in full clarity. PMID:23859401

Bacskay, George B; Nordholm, Sture

2013-08-22

200

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

NASA Astrophysics Data System (ADS)

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 2?u, 2?+g(I), and 2?+x(II) (x=g and/or u) states of O-*2. We also find evidence for an additional resonance, namely the 2?+u(I), positioned at about 10 eV above the neutral ground state in the Franck-Condon region, and dissociating into O-+O(3P). The measurements suggest that the autodetachment lifetimes of the 2?+u(I) and 2?+g(II) states may be longer than previously suggested. It is also observed that the effects of electron energy loss (EEL) in the solid prior to DEA, O- scattering in the solid after dissociation, and the charge-induced polarization energy of the solid, broaden the Ek distributions, shift them to lower anion energies, and result in additional structure in them. The effects of EEL on the desorption dynamics of O- are estimated from high-resolution electron-energy-loss spectra and excitation functions for losses in the vicinity of the Schumann-Runge continuum of the physisorbed O2 molecules. We find indications for an enhancement of the optically forbidden X 3?-g-->A 3?+u transition, and observe that the gas-phase Rydberg bands, for energy losses above 7 eV, are not distinguishable in the condensed phase.

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

1995-01-01

201

Collision-induced dissociation and theoretical studies of K + complexes with ammonia: a test of theory for potassium ions  

Microsoft Academic Search

The sequential bond energies of K+ with ammonia are determined using collision-induced dissociation (CID) with xenon gas in a guided ion beam tandem mass spectrometer. The kinetic energy dependences of the CID cross-sections are analyzed to give 0 and 298K bond energies for the successive loss of ammonia after accounting for multiple collisions, internal energy, and dissociation lifetimes. We also

Christopher Iceman; P. B Armentrout

2003-01-01

202

Absolute cross-sections and kinetic energy release distributions for electron-impact dissociation of D+3  

NASA Astrophysics Data System (ADS)

Absolute cross-sections for electron-impact dissociation of D+3 leading to the formation of D+ and D+2 products have been measured by applying the animated electron-ion beam method in the energy range from the respective thresholds up to 2.5 keV. The maximum total cross-sections are observed to be (13.9 ± 1.1) × 10-17 cm2 and (8.2 ± 0.1) × 10-17 cm2 (around 50 eV) for D+ and for D+2 fragments, respectively. The present results are in a satisfactory agreement with those of experiments performed at storage ring facilities in the low energy range (<30 eV). The data of D+ formation especially show resonant dissociative excitation playing a significant role in the collision energy range below the vertical excitation energy for the lowest electronic transition. The yields of fast D+ and D+2 ions have been measured; these energetic dissociations are mainly ascribed to dissociative ionization. For each fragment, absolute cross-sections are determined separately for dissociative excitation and for dissociative ionization processes. Kinetic energy release distributions are seen to extend from 0 to 16 eV both for D+ and for D+2 fragments. Present energy thresholds and kinetic energy release results are compared with available published data, allowing in some cases identification of fragmentation patterns and of molecular states contributing to observed processes.

Lecointre, J.; Abdellahi El Ghazaly, M. O.; Jureta, J. J.; Belic, D. S.; Urbain, X.; Defrance, P.

2009-04-01

203

Unimolecular and collision-induced dissociation study of CS2+2 with Ar at high collision energy  

Microsoft Academic Search

Mass-analyzed kinetic energy spectroscopy (MIKES) has been used to study the unimolecular and collision-induced dissociation (CID) of CS2+2 ions in collision with argon at 6 keV ion energy. When analyzed in center-of-mass (CM) co-ordinates, MIKES spectra of CS+ and S+ fragment ions are shown to originate from four dynamically distinguishable reaction pathways. They may be broadly classified as electron-capture-induced dissociation

X. D. Zhou; A. K. Shukla; R. E. Tosh; J. H. Futrell

1997-01-01

204

Absolute cross sections and kinetic energy release distributions for electron-impact dissociative excitation and ionization of NeD+  

NASA Astrophysics Data System (ADS)

Absolute cross sections for electron impact dissociative excitation and ionization of NeD+ leading to the formation of singly and multiply charged products (D+, Ne+, Ne2+ and Ne3+) are reported, in the energy range from their respective thresholds to 2.5 keV. The animated crossed-beams method is used. For singly charged fragments, absolute cross sections are obtained separately for dissociative excitation and for dissociative ionization. Dissociative excitation is seen to be restricted to the low-energy range (<300 eV) and the D+ formation dominates over the Ne+ one. At the maximum (around 35 eV), absolute cross sections for dissociative excitation are found to be (3.6 ± 0.8) × 10-17 cm2 and (6.3 ± 1.4) × 10-17 cm2 for Ne+ and D+, respectively; the corresponding appearance energies are (9.1 ± 0.5) eV and (10.0 ± 0.5) eV. The absolute cross section for dissociative ionization (Ne++D+ formation) is found to be (7.1 ± 1.4) × 10-17 cm2, around 155 eV, and the threshold energy is (26.8 ± 0.5) eV. For multiply charged products, absolute cross sections are found, around the maximum, to be (5.4 ± 0.5) × 10-18 cm2 and (18.2 ± 2.6) × 10-20 cm2 for Ne2+ and Ne3+, respectively; the corresponding thresholds are (53.1 ± 1.0) eV and (132 ± 5) eV. Kinetic energy release distributions are determined for each detected ionic product. The presented potential energy curves correspond to dissociation channels, which are significant for the discussion of present results. At fixed electron energy, the cross sections for the various ionization channels are seen to decrease exponentially with the potential energy of each dissociated ion pair.

Lecointre, J.; Jureta, J. J.; Mitchell, J. B. A.; Ngassam, V.; Orel, A. E.; Defrance, P.

2008-02-01

205

Unimolecular and collision-induced dissociation study of CS 2+ 2 with Ar at high collision energy  

Microsoft Academic Search

Mass-analyzed kinetic energy spectroscopy (MIKES) has been used to study the unimolecular and collision-induced dissociation (CID) of CS2+2 ions in collision with argon at 6 keV ion energy. When analyzed in center-of-mass (CM) co-ordinates, MIKES spectra of CS+ and S+ fragment ions are shown to originate from four dynamically distinguishable reaction pathways. They may be broadly classified as electron-capture-induced dissociation

X. D. Zhou; A. K. Shukla; R. E. Tosh; J. H. Futrell

1997-01-01

206

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

207

Absolute cross sections and kinetic energy release distributions for electron impact ionization and dissociation of CD+  

NASA Astrophysics Data System (ADS)

Absolute cross sections for electron impact dissociative excitation and ionization of CD+ leading to the formation of ionic products (D+, C+, C2+ and C3+) are reported in the energy range from their respective thresholds to 2.5 keV. Around the maximum, cross sections are found to be (10.5 ± 1.0) × 10-17 cm2, (20.6 ± 3.5) × 10-17 cm2, (1.20 ± 0.11) × 10-17 cm2 and (8.2 ± 1.5) × 10-20 cm2 for D+, C+, C2+ and C3+, respectively. In the very low-energy region, dissociative excitation leading to the C+ formation dominates over the D+ one. The cross section for dissociative ionization (C+ + D+ formation) is found to be (6.9 ± 1.3) × 10-17 cm2 around 105 eV and the corresponding threshold energy is (22.1 ± 0.5) eV. The animated crossed-beams method is used and the analysis of ionic product velocity distributions allows the determination of the kinetic energy release distributions. They are seen to extend from 0 to 15 eV both for C+ and for D+, and up to 40 eV both for C2+ and for C3+. For singly charged products, the comparison of the present energy thresholds and kinetic energy release with published data allows the identification of states contributing to the observed processes. In particular, contributions from primary ions formed in the a3? metastable state are perceptible. At fixed electron energy, the cross sections for the various ionization channels are seen to reduce exponentially with the potential energy of each dissociated ion pair. Anisotropies are estimated to be in the range 8 ± 2% for both C+ and D+. The total CD+ single ionization cross section calculated by application of the Deutsch-Märk formalism is found to be in good agreement with experimental results.

Lecointre, J.; Cherkani-Hassani, S.; Belic, D. S.; Jureta, J. J.; Becker, K.; Deutsch, H.; Märk, T. D.; Probst, M.; Janev, R. K.; Defrance, P.

2007-06-01

208

Ion beam studies of the reactions of atomic cobalt ions with alkanes: determination of metal-hydrogen and metal-carbon bond energies and an examination of the mechanism by which transition metals cleave carbon-carbon bonds  

SciTech Connect

An ion beam apparatus is employed to study the reactions of singly charged cobalt positive ions with hydrogen and 17 alkanes. Reaction cross sections and product distributions as a function of kinetic energy are determined. Exothermic carbon-carbon bond cleavage reactions are observed for all alkanes but methane and ethane. A mechanism involving oxidative addition of C-C and C-H bonds to cobalt as a first step is demonstrated to account for all major reactions at all energies. Interpretation of several endothermic processes allows the extraction of thermochemical data. The bond dissociation energies obtained are D/sup 0/(Co/sup +/-H) = 52 +- 4 kcal/mol, D/sup 0/(Co-H) = 39 +- 6 kcal/mol, D/sup 0/(Co/sup +/-CH/sub 3/) = 61 +- 4 kcal/mol, and D/sup 0/(Co-CH/sub 3/) = 41 +- 10 kcal/mol.

Armentrout, P.B.; Beauchamp, J.L.

1981-02-25

209

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

210

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

NASA Astrophysics Data System (ADS)

Electron correlations in molecules can be divided in short range dynamical correlations, long range Van der Waals type interactions, and near degeneracy static correlations. In this work, we analyze for a one-dimensional model of a two-electron system how these three types of correlations can be incorporated in a simple wave function of restricted functional form consisting of an orbital product multiplied by a single correlation function f (r12) depending on the interelectronic distance r12. Since the three types of correlations mentioned lead to different signatures in terms of the natural orbital (NO) amplitudes in two-electron systems, we make an analysis of the wave function in terms of the NO amplitudes for a model system of a diatomic molecule. In our numerical implementation, we fully optimize the orbitals and the correlation function on a spatial grid without restrictions on their functional form. Due to this particular form of the wave function, we can prove that none of the amplitudes vanishes and moreover that it displays a distinct sign pattern and a series of avoided crossings as a function of the bond distance in agreement with the exact solution. This shows that the wave function ansatz correctly incorporates the long range Van der Waals interactions. We further show that the approximate wave function gives an excellent binding curve and is able to describe static correlations. We show that in order to do this the correlation function f (r12) needs to diverge for large r12 at large internuclear distances while for shorter bond distances it increases as a function of r12 to a maximum value after which it decays exponentially. We further give a physical interpretation of this behavior.

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

2014-05-01

211

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

NASA Astrophysics Data System (ADS)

The dissociation limits of isotopic water molecules are derived for the ground state. The equilibrium geometries, the vibrational frequencies, the force constants and the dissociation energies for the ground states of all isotopic water molecules under the dipole electric fields from -0.05 a.u. to 0.05 a.u. are calculated using B3P86/6-311++G(3df,3pf). The results show that when the dipole electric fields change from -0.05 a.u. to 0.05 a.u., the bond length of H—O increases whereas the bond angle of H—O—H decreases because of the charge transfer induced by the applied dipole electric field. The vibrational frequencies and the force constants of isotopic water molecules change under the influence of the strong external torque. The dissociation energies increase when the dipole electric fields change from -0.05 a.u. to 0.05 a.u. and the increased dissociation energies are in the order of H2O, HDO, HTO, D2O, DTO, and T2O under the same external electric fields.

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

2011-06-01

212

Mass spectrometry study and infrared spectroscopy of the complex between camphor and the two enantiomers of protonated alanine: the role of higher-energy conformers in the enantioselectivity of the dissociation rate constants.  

PubMed

The properties of the protonated complexes built from S camphor and R or S alanine were studied in a Paul ion trap at room temperature by collision-induced dissociation (CID) and infrared multiple-photon dissociation spectroscopy (IRMPD), as well as molecular dynamics and ab initio calculations. While the two diastereomer complexes display very similar vibrational spectra in the fingerprint region, in line with similar structures, and almost identical calculated binding energies, their collision-induced dissociation rates are different. Comparison of the IRMPD results to computed spectra shows that the SS and SR complexes both contain protonated alanine strongly hydrogen-bonded to the keto group of camphor. The floppiness of this structure around the NH?...O=C hydrogen bond results in a complex potential energy surface showing multiple minima. Calculating the dissociation rate constant within the frame of the transition state theory shows that the fragmentation rate larger for the heterochiral SR complex than the homochiral SS complex can be explained in terms of two almost isoenergetic low-energy conformers in the latter that are not present for the former. PMID:23740577

Sen, Ananya; Le Barbu-Debus, Katia; Scuderi, Debora; Zehnacker-Rentien, Anne

2013-08-01

213

Hydrogen bond energy of the water dimer  

SciTech Connect

Large scale ab initio molecular orbital calculations on the binding energy of the water dimer have been performed. These calculations extend the previous correlation consistent basis set work to include larger basis sets (up to 574 functions), and core/valence correlation effects have now been included. The present work confirms the earlier estimate of -4.9 kcal/mol as the MP2(FC) basis set limit. Core/valence correlation effects are found to increase the binding energy by nearly 0.05 kcal/mol. The best estimate of the electronic binding energy of the water dimer is -5.0{+-}0.1 kcal/mol. Correcting this value for zero-point and temperature effects yields the value {Delta}H(375)=-3.2{+-}0.1 kcal/mol. This value is within the error limits of the best experimental estimate of -3.6{+-}0.5 kcal/mol with the calculations favoring the lower end of the experimental energy range. It should be useful to adopt the present estimate in empirical and semiempirical model potentials. 39 refs., 1 fig., 3 tabs.

Feyereisen, M.W. [Cray Research, Inc., Eagen, MN (United States)] [Cray Research, Inc., Eagen, MN (United States); Feller, D. [Pacific Northwest Lab., Richland, WA (United States)] [Pacific Northwest Lab., Richland, WA (United States); Dixon, D.A. [Du Pont Central Research and Development, Wilmington, DE (United States)] [Du Pont Central Research and Development, Wilmington, DE (United States)

1996-02-22

214

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

215

Storing Renewable Energy in Chemical Bonds  

ScienceCinema

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

Helm, Monte; Bullock, Morris

2014-06-13

216

Activation of Peptide Ions by Blackbody Radiation: Factors That Lead to Dissociation Kinetics in the Rapid Energy Exchange Limit  

PubMed Central

Unimolecular rate constants for blackbody infrared radiative dissociation (BIRD) were calculated for the model protonated peptide (AlaGly)n (n = 2–32) using a variety of dissociation parameters. Combinations of dissociation threshold energies ranging from 0.8 to 1.7 eV and transition entropies corresponding to Arrhenius preexponential factors ranging from very “tight” (A? = 109.9 s?1) to “loose” (A? = 1016.8 s?1) were selected to represent dissociation parameters within the experimental temperature range (300–520 K) and kinetic window (kuni = 0.001–0.20 s?1) typically used in the BIRD experiment. Arrhenius parameters were determined from the temperature dependence of these values and compared to those in the rapid energy exchange (REX) limit. In this limit, the internal energy of a population of ions is given by a Boltzmann distribution, and kinetics are the same as those in the traditional high-pressure limit. For a dissociation process to be in this limit, the rate of photon exchange between an ion and the vacuum chamber walls must be significantly greater than the dissociation rate. Kinetics rapidly approach the REX limit either as the molecular size or threshold dissociation energy increases or as the transition-state entropy or experimental temperature decreases. Under typical experimental conditions, peptide ions larger than 1.6 kDa should be in the REX limit. Smaller ions may also be in the REX limit depending on the value of the threshold dissociation energy and transition-state entropy. Either modeling or information about the dissociation mechanism must be known in order to confirm REX limit kinetics for these smaller ions. Three principal factors that lead to the size dependence of REX limit kinetics are identified. With increasing molecular size, rates of radiative absorption and emission increase, internal energy distributions become relatively narrower, and the microcanonical dissociation rate constants increase more slowly over the energy distribution of ions. Guidelines established here should make BIRD an even more reliable method to obtain information about dissociation energetics and mechanisms for intermediate size molecules.

Price, William D.

2005-01-01

217

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

218

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

219

The kinetic energy change on covalent bond formation  

PubMed Central

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

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

1981-01-01

220

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

221

Ionization energy of tert-butyl-d{sub 9} alcohol and the appearance energy of protonated acetone: a nonequilibrium dissociation  

SciTech Connect

In the present photoionization study of tert-butyl alcohol, the parent ion of the deuterated isotopomer [(CD{sub 3}){sub 3}-COH] was observed and an ionization energy (IE) of 9.82{+-}0.02 eV was derived from a step-function threshold at 126.25 nm. The appearance energies (AE`s) of (CD{sub 3}){sub 2}COH{sup +} and (CH{sub 3}){sub 2}COH{sup +} were also determined. From these results, the IE of undeuterated tert-butyl alcohol (which was not observed) was estimated. The difference between the IE and the derived AE{sub 0} implies an upper limit for the barrier to dissociation of (CH{sub 3}){sub 3}COH{sup +}. A recent evaluation of the proton affinity of acetone was employed to derive a value for {Delta}{sub f}H{degree}{sub 0}[(CH{sub 3}){sub 2}COH{sup +}] and, thence, the enthalpy of reaction; and from this, an upper limit for the reverse barrier of the dissociation was obtained. RRKM calculations were performed by using the energies derived from the experimental (and estimated) values. For excitation energies >= 0.2 eV above threshold, RRKM calculations yield large rate coefficients for dissociation. Also, the kinetic energy release (KER) was calculated for various models of the dissociation complex. The calculated KER`s are consistent with experimental values when it is assumed that only 5 of the 38 vibrational modes of the transition state are active in the randomization of internal energy. 34 refs., 6 figs., 1 tab.

Tardy, D.C. [Univ. of Iowa, Iowa City, IA (United States)] [Univ. of Iowa, Iowa City, IA (United States); Kuo, S.C.; Zhang, Z.; Klemm, R.B. [Brookhaven National Lab., Upton, NY (United States)] [Brookhaven National Lab., Upton, NY (United States)

1996-05-16

222

Energy-sensitive imaging detector applied to the dissociative recombination of D2H+  

NASA Astrophysics Data System (ADS)

We report on an energy-sensitive imaging detector for studying the fragmentation of polyatomic molecules in the dissociative recombination of fast molecular ions with electrons. The system is based on a large area (10×10 cm2) position-sensitive, double-sided Si-strip detector with 128 horizontal and 128 vertical strips, whose pulse height information is read out individually. The setup allows us to uniquely identify fragment masses and is thus capable of measuring branching ratios between different fragmentation channels, kinetic energy releases, and breakup geometries as a function of the relative ion-electron energy. The properties of the detection system, which has been installed at the Test Storage Ring (TSR) facility of the Max-Planck Institute for Nuclear Physics in Heidelberg, is illustrated by an investigation of the dissociative recombination of the deuterated triatomic hydrogen cation D2H+. A huge isotope effect is observed when comparing the relative branching ratio between the D2 + H and the HD + D channel; the ratio 2B(D2 + H)/B(HD + D), which is measured to be 1.27±0.05 at relative electron-ion energies around 0 eV, is found to increase to 3.7±0.5 at ~5 eV.

Buhr, H.; Mendes, M. B.; Novotný, O.; Schwalm, D.; Berg, M. H.; Bing, D.; Heber, O.; Krantz, C.; Orlov, D. A.; Rappaport, M. L.; Sorg, T.; Stützel, J.; Varju, J.; Wolf, A.; Zajfman, D.

2010-06-01

223

Lithium and transition metal ions enable low energy collision-induced dissociation of polyglycols in electrospray ionization mass spectrometry  

Microsoft Academic Search

Electrospray ionization tandem mass spectrometry has the potential to be widely used as a tool for polymer structural characterization.\\u000a However, the backbones or molecular chains of many industrial polymers including functional polyglycols are often difficult\\u000a to dissociate in tandem mass spectrometers using low energy collision-induced dissociation (CID). We present a method that\\u000a uses Li+ and transition metal ions such as

Rui Chen; Liang Li

2001-01-01

224

Absolute cross sections and kinetic energy release distributions for electron-impact dissociative excitation and ionization of NeD+  

Microsoft Academic Search

Absolute cross sections for electron impact dissociative excitation and ionization of NeD+ leading to the formation of singly and multiply charged products (D+, Ne+, Ne2+ and Ne3+) are reported, in the energy range from their respective thresholds to 2.5 keV. The animated crossed-beams method is used. For singly charged fragments, absolute cross sections are obtained separately for dissociative excitation and

J. Lecointre; J. J. Jureta; J. B. A. Mitchell; V. Ngassam; A. E. Orel; P. Defrance

2008-01-01

225

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

226

Studies of two-center three-electron S...S bonds in [n-Pr{sub 2}S...Sn-Pr{sub 2}]{sup +} and [i-Pr{sub 2}S...Si-Pr{sub 2}]{sup +}: Thermochemistry of adduct formation and MS/MS metastable and collision-induced dissociation spectra of the adducts  

SciTech Connect

Gas-phase ion-molecule association reactions of n-propyl sulfide radical cation ([n-Pr{sub 2}S]{sup +}) with n-propyl sulfide (n-Pr{sub 2}S) were studied by equilibrium methods in CO{sub 2} bath gas to investigate the bond energy of the 2c-3e bond. The 2c-3e S...S bond enthalpy in [n-Pr{sub 2}S...Sn-Pr{sub 2}]{sup +} was determined to be 119 kJ/mol at 507 K. This results in a scaled S...S bond energy of 123 kJ/mol. The S...S bond enthalpy in the i-propyl sulfide dimer cation ([i-Pr{sub 2}S...Si-Pr{sub 2}]{sup +}) could not be determined due to a fragmentation reaction, the loss of an i-propyl group. MS/MS metastable and collision-induced dissociation experiments were carried out to determine metastable fragmentation pathways and to aid in structure analysis. The results are consistent with association products containing 2c-3e bonds; statistical unimolecular metastable fragmentation of the association adduct, [i-Pr{sub 2}S...Si-Pr{sub 2}]{sup +}, confirms the loss of the i-propyl group, which prevented the equilibrium experiments. 21 refs., 11 figs., 1 tab.

James, M.A.; Illies, A.J. [Auburn Univ., AL (United States)] [Auburn Univ., AL (United States)

1996-09-26

227

Guided ion beam studies of the reactions of Co n+ (n=1-18) with N2: Cobalt cluster mononitride and dinitride bond energies.  

PubMed

The reactions of Co n+ (n=1-18) with N2 are measured as a function of kinetic energy over a range of 0-15 eV in a guided ion beam tandem mass spectrometer. A variety of Co m +, Co m N+, and Co m N2+ (mdissociation dominating the products for all clusters. Bond dissociation energies for both cobalt cluster nitrides and dinitrides are derived from threshold analysis of the energy dependence of the endothermic reactions using several different approaches. These values show only a mild dependence on cluster size over the range studied, although the Co13+-N bond energy is relatively weak. The bond energies of Co n+-N for larger clusters suggest that a reasonable value for the desorption energy of atomic nitrogen from bulk phase cobalt is 6.3+/-0.2 eV, which is somewhat lower than the only available value in the literature, an estimate based on the enthalpy of formation of bulk cobalt nitride. The trends in the cobalt nitride thermochemistry are also compared to previously determined metal-metal bond energies, D 0(Co n+-Co), and to D 0(Fe n+ -N). Implications for catalytic ammonia production using cobalt versus iron are discussed. PMID:18500871

Liu, Fuyi; Li, Ming; Tan, Lin; Armentrout, P B

2008-05-21

228

Molecular dynamics study on the free energy profile for dissociation of ADP from N-terminal domain of Hsp90  

NASA Astrophysics Data System (ADS)

The free energy profile for dissociation of ADP from Hsp90 was calculated as a function of the distance r between the centers of mass of Hsp90 and ADP by using molecular dynamics simulations and the thermodynamic integration method. The free energy profile is defined as the difference from a reference state. We found that the free energy reaches a minimum at r = 0.8 nm and that the mean force at r = 1.0 nm was considerably difference-dependent on the trajectories. Our results suggest that Met98 blocks the dissociation pathway of ADP at r = 1.0 nm.

Kawaguchi, Kazutomo; Saito, Hiroaki; Okazaki, Susumu; Nagao, Hidemi

2013-11-01

229

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

NASA Technical Reports Server (NTRS)

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

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

1976-01-01

230

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

231

Dissociation Energy for C{sub 2} Loss from Fullerene Cations in a Storage Ring  

SciTech Connect

We have stored positively charged fullerene ions C{sub n}{sup +} (n even, from 48 to 70 and 76), C{sub 60}{sup 2+} and C{sub 70}{sup 2+} in an electrostatic storage ring and have measured the rate of emission of neutral fragments as a function of time. In the time range of the measurements, 50 {mu}s to a few milliseconds, the rate decreases strongly due to radiative cooling of the molecules. Using the cooling rate predicted from a dielectric model, we have extracted the dissociation energies for C{sub 2} loss from the measurements. As expected, the energies are largest for the 'magic' fullerenes, C{sub 50}, C{sub 60}, and C{sub 70}, and the value of 9.8{+-}0.1 eV for C{sub 2} loss from C{sub 60}{sup +} is in reasonable agreement with theory and with other recent experiments.

Tomita, S.; Andersen, J. U.; Gottrup, C.; Hvelplund, P.; Pedersen, U. V.

2001-08-13

232

Intramolecular hydrogen bonding as reflected in the deuterium isotope effects on carbon-13 chemical shifts. Correlation with hydrogen bond energies  

SciTech Connect

The carbon-13 resonances of atoms bearing phenolic or enolic hydroxyl groups, that are engaged in intramolecular hydrogen bonds, experience large (/sup 2/..delta.. may exceed 1 ppm) upfield deuterium isotope effects. The magnitude of the two-bond isotope effect, /sup 2/..delta.., correlates with the hydrogen bond energy as obtained from the hydroxyl proton chemical shift. In the conjugated systems investigated in this work, the isotope effects extend over several (up to six) chemical bonds. The signs and magnitudes of the long-range isotope effects are related to molecular structure.

Reuben, J.

1986-04-16

233

The Fe-CO bond energy in myoglobin: a QM/MM study of the effect of tertiary structure.  

PubMed

The Fe-CO bond dissociation energy (BDE) in myoglobin (Mb) has been calculated with B3LYP quantum mechanics/molecular mechanics methods for 22 different Mb conformations, generated from molecular dynamics simulations. Our average BDE of 8.1 kcal/mol agrees well with experiment and shows that Mb weakens the Fe-CO bond by 5.8 kcal/mol; the calculations provide detailed atomistic insight into the origin of this effect. BDEs for Mb conformations with the R carbonmonoxy tertiary structure are on average 2.6 kcal/mol larger than those with the T deoxy tertiary structure, suggesting two functionally distinct allosteric states. This allostery is partly explained by the reduction in distal cavity steric crowding as Mb moves from its T to R tertiary structure. PMID:16387767

Strickland, Nikki; Mulholland, Adrian J; Harvey, Jeremy N

2006-02-15

234

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

235

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

NASA Astrophysics Data System (ADS)

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 CH3+ and C5H3+ 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.

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

2011-10-01

236

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

PubMed

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

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

2006-11-01

237

Bond Length and Local Energy Density Property Connections for Non-transition- Metal-Oxide-Bonded Interactions  

SciTech Connect

For a variety of molecules and Earth materials, the theoretical local kinetic energy density, G(rc), increases and the local potential energy density, V(rc), decreases as the MO bond lengths (M = first and second row metal atoms) decrease and electron density, ?(rc), is localized at the bond critical points, rc. Despite claims that the ratio, G(rc)/?(rc), classifies bonded interactions as shared covalent when less than unity and closed shell ionic when greater than unity, the ratio was found to increase from 0.5 to 2.5 a.u. as the local electronic energy density H(rc) = G(rc) + V(rc) decreases and becomes progressively more negative. In any event, the ratio is indicated to be a measure of the character for a given M-O bond, the greater the ratio, the larger the value of ?(rc), the smaller the coordination number of the M atom and the more covalent the bond. H(rc)/?(rc) vs. G(rc)/?(rc) scatter diagrams categorize the M-O bond data into domains with the H(rc)/?(rc) ratio tending to increase as the electronegativity of the M atoms increase. Estimated values of G(rc) and V(rc), using an expression based on gradient corrected electron gas theory, are in good agreement with theoretical values, particularly for bonded interactions involving second row M atoms. The agreement is poorer for the more covalent C-O and N-O bonds.

Gibbs, Gerald V.; Spackman, M. A.; Jayatilaka, Dylan; Rosso, Kevin M.; Cox, David F.

2006-11-09

238

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

239

Electron energy-dependent product state distributions in the dissociative recombination of O{sub 2}{sup +}  

SciTech Connect

We present product state distributions and quantum yields from the dissociative recombination reaction of O{sub 2}{sup +} in its electronic and vibrational ground states as a function of electron collision energy between 0 and 300 meV. The experiments have been performed in the heavy-ion storage ring, CRYRING, and use a cold hollow-cathode discharge source for the production of cold molecular oxygen ions. The branching fractions over the different dissociation limits show distinct oscillations while the resulting product quantum yields are largely independent of electron collision energy above 40 meV. The branching results are well reproduced assuming an isotropic dissociation process, in contrast with recent theoretical predictions.

Petrignani, Annemieke; Hellberg, Fredrik; Thomas, Richard D.; Larsson, Mats; Cosby, Philip C.; Zande, Wim J. van der [FOM Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ, Amsterdam (Netherlands); Molecular Physics, Stockholm University, AlbaNova University Centre, SE-106 91 Stockholm (Sweden); Molecular Physics Laboratory, SRI International, Menlo Park, California 94025 (United States); Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 1, 6525 ED Nijmegen (Netherlands)

2005-06-15

240

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

NASA Astrophysics Data System (ADS)

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 of a proton from the side chain of a tyrosine molecule, as a realistic model system. We compute a free energy difference, using umbrella integration, from the average restraint force as a function of O^--H^+ distance as the proton is transferred from the side-chain to nearby water molecules to form H3O^+. We use a combination of periodic QM calculations using DFT and force-mixing QM/MM simulations implemented in QUIP and CP2K. The pure QM calculations are used for reference values and for determining appropriate restraint conditions for the free energy calculations. The force-mixing QM/MM method, which gives accurate forces throughout the system, is used to evaluate free energies for comparison with experiment. We extrapolate the free energy for the initial transfer of the proton to the bulk solvated proton regime by analytically computing electrostatic and entropy contributions.

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

2011-03-01

241

Measuring the energy landscape of complex bonds using AFM  

NASA Astrophysics Data System (ADS)

We measured rupture force of a complex bond of two interacting proteins with atomic force microscopy. Proteins of interest were active and latent Matrix metalloproteinases (MMPs), type 2 and 9, and their tissue inhibitors TIMP1 and TIMP2. Measurements show that the rupture force depends on the pulling speed; it ranges from 30 pN to 150 pN at pulling speeds 30nm/s to 48000nm/s. Analyzing data using an extended theory enabled us to understand the mechanism of MMP-TIMP interaction; we determined all physical parameters that form the landscape energy of the interaction, in addition to the life time of the bond and its length. Moreover, we used the pulling experiment to study the interaction of TIMP2 with the receptor MT1-MMP on the surface of living cells.

Mayyas, Essa; Hoffmann, Peter; Runyan, Lindsay

2009-03-01

242

Collision-Induced Dissociation of No(+) And O2(+) At Low Kinetic Energies: Effects of Internal Ionic Excitation.  

National Technical Information Service (NTIS)

The reactions resulting in dissociation of NO(+) and O2(+) upon impact with various atoms and molecules have been investigated in a double mass spectrometer of in-line geometry in the reactant ion kinetic energy range below 50 eV. Cross sections measured ...

T. O. Tiernan R. E. Marcotte

1970-01-01

243

Electrospray ionization with low-energy collisionally activated dissociation tandem mass spectrometry of glycerophospholipids: Mechanisms of fragmentation and structural characterization  

Microsoft Academic Search

This review describes the use of low-energy collisionally activated dissociation (CAD) with both tandem quadrupole and ion-trap mass spectrometry toward structural characterization of glycerophospholipids (GPLs), including classes of glycerophosphocholine, glycerophosphoethanolamine, glycerophosphoserine, glycerophosphoglycerol glycerophosphoinositol and glycerophosphatidic acid, as well as their lyso-, plasmanyl-, and plasmenylphospholipid subclasses. The mechanisms underlying the fragmentation processes leading to structural characterization of GPLs in various ion

Fong-Fu Hsu; J. Turk

2009-01-01

244

Dislocation Dissociation Strongly Influences on Frank—Read Source Nucleation and Microplasticy of Materials with Low Stacking Fault Energy  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

245

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

246

Structures and bond energies of the noble gas complexes NgBeO (Ng?Ar, Kr, Xe)  

NASA Astrophysics Data System (ADS)

The geometries, vibrational frequencies and Ng?BeO bond dissociation energies are calculated for the title compounds using quantum chemical methods. The electronic structure of the molecules is investigated with the help of the topological analysis of the electron density distribution. At the MP4 level of theory using effective core potentials for the noble gases and large valence basis sets (quadruple-zeta for Ng, triple-zeta for Be and O, three d and one f type polarization functions), the bond strengths D 0 are predicted after correcting for the BSSE to be 12.6 for XeBeO, 9.3 for KrBeO and 6.7 kcal mol -1 for ArBeO. The Ng?BeO bond of ArBeO and KrBeO is caused by induced dipole interactions, but the Xe?BeO bond has small covalent contributions. The shift of the BeO stretching frequency towards higher wave numbers upon formation of the noble gas complexes is in agreement with the observed blue-shift of the compounds.

Veldkamp, A.; Frenking, G.

1994-08-01

247

Structures and bond energies of the noble gas complexes NgBeO (Ng?Ar, Kr, Xe)  

NASA Astrophysics Data System (ADS)

The geometries, vibrational frequencies and Ng?BeO bond dissociation energies are calculated for the title compounds using quantum chemical methods. The electronic structure of the molecules is investigated with the help of the topological analysis of the electron density distribution. At the MP4 level of theory using effective core potentials for the noble gases and large valence basis sets (quadruple-zeta for Ng, triple-zeta for Be and O, three d and one f type polarization functions), the bond strengths D0 are predicted after correcting for the BSSE to be 12.6 for XeBeO, 9.3 for KrBeO and 6.7 kcal mol -1 for ArBeO. The Ng?BeO bond of ArBeO and KrBeO is caused by induced dipole interactions, but the Xe?BeO bond has small covalent contributions. The shift of the BeO stretching frequency towards higher wave numbers upon formation of the noble gas complexes is in agreement with the observed blue-shift of the compounds.

Veldkamp, A.; Frenking, G.

1994-08-01

248

Relative Proton Affinities from Kinetic Energy Release Distributions for Dissociation of Proton-Bound Dimers: 2. Diamines as a Test Case  

SciTech Connect

Dissociation of proton-bound dimers containing diamines is often characterized by a substantial entropy difference between the two competing reaction channels. Kinetic energy release distributions (KERDs) upon dissociation of diamine-containing dimers are utilized along with Finite Heat Bath theory analysis to obtain relative proton affinities of monomeric species composing the dimer. When dissociation of a proton-bound dimer is not associated with reverse activation barrier our method provides reliable relative energetics and dynamics.

Hache, John J.; Futrell, Jean H.; Laskin, Julia

2004-04-15

249

Presolvated low energy electron attachment to peptide methyl esters in aqueous solution: C-O bond cleavage at 77 K.  

PubMed

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

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

2013-03-14

250

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

PubMed Central

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

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

2013-01-01

251

Dissociation of Disulfide-Intact Somatostatin Ions: The Roles of Ion Type and Dissociation Method  

PubMed Central

The dissociation chemistry of somatostatin-14 was examined using various tandem mass spectrometry techniques including low energy beam type and ion trap CID of protonated and deprotonated forms of the peptide, CID of peptide-gold complexes, and 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 CH2-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. Electron transfer dissociation 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? bond can be cleaved following a single electron transfer reaction.

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

2011-01-01

252

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

253

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

254

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

255

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

PubMed

A scheme to produce accurate full-dimensional coupled diabatic potential energy surfaces including dissociative regions and suitable for dynamical calculations is proposed. The scheme is successfully applied to model the two-sheeted surface of the (2)E(?) state of the NO3 radical. An accurate potential energy surface for the [Formula: see text] 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 [Formula: see text] and the photo-electron detachment spectrum of [Formula: see text] leading to the neutral radical in the (2)E(?) state by full dimensional multi-surface wave-packet propagation for NO3 performed using the Multi-Configuration Time Dependent Hartree method. The achieved agreement of the simulations with available experimental data demonstrates the power of the proposed scheme and the high quality of the obtained potential energy surfaces. PMID:24929376

Eisfeld, Wolfgang; Vieuxmaire, Olivier; Viel, Alexandra

2014-06-14

256

Thermal dissociation of cesium dimers  

Microsoft Academic Search

A simple method of thermal dissociation of alkali metal dimers has been developed, in particular, the thermal dissociation of cesium dimers has been realized. The experimental dependence of the relative dimer density on temperature in superheated cesium vapor has been obtained. A simple method for the determination of alkali metal dimer dissociation energy has been proposed and its value for

D. H. Sarkisyan; A. S. Sarkisyan; A. K. Yalanusyan

1998-01-01

257

Collision-induced dissociation of niobium cluster ions: Transition metal cluster binding energies  

SciTech Connect

The cross sections for collision-induced dissociation (CID) of Nb{sub n}{sup +} (n = 2-6) with Xe are presented. Experiments are conducted on a recently constructed guided ion beam mass spectrometer, which produces intense beams of thermalized, mass-selected, niobium cluster ions. Nb{sub n}{sup +} are observed to fission to all possible ionic fragments and the largest possible neutral fragments at collision energies < 10 eV. Evidence is presented for loss of multiple Nb atoms from the cluster at energies higher than 10 eV. This fragmentation pattern differs markedly from that previously observed for small iron cluster ions. CID thresholds are used to derive D{degree}(Nb{sub n{minus}1}{sup +}-Nb) for n = 2-6, along with D{degree}(Nb{sub m}) and ionization potentials (IPs) of Nb{sub m} for m = 2 and 3. By using known IPs, D{degree}(Nb{sub n}) for n = 4,5 and 6 are also obtained. Nb{sub 2}{sup +} is found to be the most strongly bound cluster ion, D{degree}(Nb{sup +}-Nb) = 6.15 {plus minus} 0.15, and Nb{sub 3}{sup +} is the most weakly bound cluster ion, D{degree} (Nb{sub 2}{sup +}-Nb) = 4.60 {plus minus} 0.15 eV.

Loh, S.K. (Univ. of California, Berkeley (USA)); Lian, Li; Armentrout, P.B. (Univ. of Utah, Salt Lake City (USA))

1989-04-26

258

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

ERIC Educational Resources Information Center

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

Cooper, Melanie M.; Klymkowsky, Michael W.

2013-01-01

259

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

Microsoft Academic Search

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

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

2008-01-01

260

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

261

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

262

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

263

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

264

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

265

Intrinsic errors in several ab initio methods. The dissociation energy of N{sub 2}  

SciTech Connect

Using sequences of correlation consistent basis sets, complete basis set (CBS) limits for the dissociation energy D{sub c} of N{sub 2} have been estimated for a variety of commonly used electron correlation methods. After extrapolation to the CBS limit, the difference between theory and experiment corresponds to the error intrinsic to the chosen theoretical method. Correlated wave functions (valence electrons correlated only) for which intrinsic errors have been estimated include internally contracted multireference configuration interaction (CMRCI), singles and doubles coupled cluster theory with and without perturbative triple excitations [CCSD, CCSD(T)], and second-, third-, and fourth-order Moller-Plesset perturbation theory (MP2, MP3, MP4). For CMRCI and CCSD(T), D{sub c} converges smoothly from below the experimental value and yields the smallest intrinsic errors, -0.8 and -1.6 kcal/mol, respectively. In contrast, for MP2 and MP4, D{sub c} exhibits fortuitously good agreement with experiment for small basis sets but leads to CBS limits that are 11.6 and 3.4 kcal/mol larger than experiment, respectively. Correlation of the 1s core electrons is predicted to yield intrinsic errors of less than 1 kcal/mol for CMRCI and CCSD(T), while those for MP2 and MP4 increase still further. 38 refs., 1 fig., 1 tab.

Peterson, K.A. [Washington State Univ., Richland, WA (United States)]|[Pacific Northwest Lab., Richland, WA (United States); Dunning, T.H. Jr. [Pacific Northwest Lab., Richland, WA (United States)

1995-03-23

266

Low-energy collisionally activated dissociation of pentose-borate complexes  

NASA Astrophysics Data System (ADS)

Pentose-borate 1:1 complexes were generated in the ESI source of a triple quadrupole and ion trap mass spectrometer by electrospray ionization of Na2B4O7 and pentose (arabinose, lyxose, ribose, xylose) 2:1 solution in CH3CN/H2O. The study of their low-energy collisionally activated dissociation (CAD) demonstrated that ribose and lyxose are preferentially complexed at the C2-C3 cis-diol function whereas arabinose and xylose are esterified at the C1-C2 hydroxyl groups. No evidence was found of the stronger affinity for ribose to borate. The ribose probiotic rule can be explained by considering its peculiar capability, among the investigated pentoses, to almost totally complex the borate anion at the C2-C3 hydroxyl group, thus enabling the subsequent stages of nucleotide assembly, such as phosphorylation and linkage to the nucleobases. Finally, the differences observed in the pentose-borate complex CAD spectra can be used for the mass spectrometric discrimination of isomeric pentoses in complex mixtures.

Pepi, Federico; Garzoli, Stefania; Tata, Alessandra; Giacomello, Pierluigi

2010-01-01

267

Metal cation dependence of interactions with amino acids: bond energies of Rb+ to Gly, Ser, Thr, and Pro.  

PubMed

The interactions of rubidium cations with the four amino acids (AA), glycine (Gly), serine (Ser), threonine (Thr), and proline (Pro), are examined in detail. Experimentally, the bond energies are determined using threshold collision-induced dissociation of the Rb(+)(AA) complexes 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 reactant ions, and multiple ion-molecule collisions. 0 K bond energies of 108.9 +/- 7.0, 115.7 +/- 4.9, 122.1 +/- 4.6, and 125.2 +/- 4.5 kJ/mol are determined for complexes of Rb(+) with Gly, Ser, Thr, and Pro, respectively. Quantum chemical calculations are conducted at the B3LYP, B3P86, and MP2(full) levels of theory with geometries and zero point energies calculated at the B3LYP level using both HW*/6-311+G(2d,2p) and Def2TZVP basis sets. Results obtained using the former basis sets are systematically low compared to the experimental bond energies, whereas the latter basis sets show good agreement. For Rb(+)(Gly), the ground state conformer has the rubidium ion binding to the carbonyl group of the carboxylic acid, and a similar geometry is found for Rb(+)(Pro) except the secondary nitrogen accepts the carboxylic acid hydrogen to form the zwitterionic structure. Both Rb(+)(Ser) and Rb(+)(Thr) are found to have tridentate binding at the B3LYP and MP2(full) levels, whereas the B3P86 slightly prefers binding Rb(+) at the carboxylic acid. Comparison of these results to those for the lighter alkali ions provides insight into the trends in binding affinities and structures associated with metal cation variations. PMID:20184306

Bowman, Vanessa N; Heaton, Amy L; Armentrout, P B

2010-03-25

268

Characterization of the thermosonic wire bonding technique. [Combination of ultrasonic energy and thermocompression  

Microsoft Academic Search

This study was designed to evaluate the combination of ultrasonic energy and thermocompression techniques with regard to the bond response of thin film substrate metallization and thick film discrete component terminations. The object was to determine not only the quality of thermosonic gold wire bonds and the performance of these bonds when subjected to thermal environmental tests, but also to

D. R. Johnson; E. L. Chavez

1976-01-01

269

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

270

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

271

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

272

Dynamics on the HOCO potential energy surface studied by dissociative photodetachment of HOCO{sup -} and DOCO{sup -}  

SciTech Connect

An experimental study of the dissociative photodetachment (DPD) dynamics of HOCO{sup -} and DOCO{sup -} at a photon energy of 3.21 eV has been carried out to probe the potential energy surface of the HOCO free radical and the dynamics of the OH+CO{yields}H+CO{sub 2} reaction. These photoelectron-photofragment coincidence experiments allow the identification of photodetachment processes leading to the production of stable HOCO free radicals and both the H+CO{sub 2} and OH+CO dissociation channels on the neutral surface. Isotopic substitution by deuterium in the parent ion is observed to reduce the product branching ratio for the D+CO{sub 2} channel, consistent with tunneling playing a role in this dissociation pathway. Other isotope effects on the detailed partitioning of kinetic energy between photoelectrons and photofragments are also discussed. The results are compared to recent theoretical predictions of this DPD process, and evidence for the involvement of vibrationally excited HOCO{sup -} anions is discussed.

Lu, Zhou; Hu, Qichi; Oakman, Jonathan E.; Continetti, Robert E. [Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0340 (United States)

2007-05-21

273

Absolute cross-sections and kinetic-energy-release distributions for electron-impact ionization and dissociation of CD{3/+}  

NASA Astrophysics Data System (ADS)

Absolute cross-sections have been measured for electron-impact dissociative excitation and ionization of CD3+ / {left( {CH3+ } right)} leading to formation of singly-charged fragments (CD{2/+}, CH+, C+, H{2/+} and D+). The animated crossed-beams method is applied in the energy range from the reaction threshold up to 2.5 keV. The maximum cross-sections are found to be (14.0±1.0)×10-17 cm2, (6.5± 0.7)×10-17 cm2, (3.3± 0.3)×10-17 cm2, (1.1±0.1)×10-17 cm2 and (14.0± 1.3)×10-17 cm2 for CD{2/+}, CH+, C+, H{2/+} and D+, respectively. Individual contributions for dissociative excitation and dissociative ionization are determined for each product as they are indispensable for plasma modelling, diagnostics and data analysis in fusion experiments. Conforming to the scheme recently used in the CD{4/+} study, the cross-sections are presented in analytic forms suitable for their implementation in plasma simulation codes. Kinetic-energy-release distributions are determined for each product at selected electron energies.

Lecointre, J.; Belic, D. S.; Jureta, J. J.; Janev, R. K.; Defrance, P.

2009-12-01

274

Absolute cross-sections and kinetic-energy-release distributions for electron-impact ionization and dissociation of CD{2/+}  

NASA Astrophysics Data System (ADS)

Absolute cross-sections have been measured for electron-impact dissociative excitation and ionization of CD{2/+} leading to formation of CD{2/2+}, CD+, C+, D{2/+} and D+. The animated crossed-beams method is applied in the energy range from the reaction threshold up to 2.5 keV. The maximum total cross-sections are found to be (1.2±0.1)×10-17 cm2, (6.1±0.7)×10-17 cm2, (6.4±0.7)×10-17 cm2, (26.3±3.8)×10-19 cm2 and (14.9±1.4)×10-17 cm2 for CD{2/2+}, CD+, C+, D{2/+} and D+ respectively. Individual contributions for dissociative excitation and dissociative ionization are determined for each singly-charged product, which are of significant interest in fusion plasma edge modelling and diagnostics. Conforming to the scheme recently applied in the CD{4/+} and in the CD{3/+} articles, the cross-sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. Kinetic-energy-release distributions are determined for each ionic fragment at selected electron energies.

Lecointre, J.; Belic, D. S.; Jureta, J. J.; Janev, R. K.; Defrance, P.

2009-12-01

275

High-energy collision induced dissociation of biomolecules: MALDI-TOF/RTOF mass spectrometry in comparison to tandem sector mass spectrometry.  

PubMed

MALDI in combination with high-energy collision-induced dissociation (CID) performed by tandem time-of-flight mass spectrometry (TOF/RTOF) is a relatively new technology for the structural analysis of various classes of biomolecules as e.g., peptides, carbohydrates, glycoconjugate drugs and lipids. Fragmentation mechanisms for these classes of compounds as well as corresponding fragment ion nomenclatures based mainly on data from tandem magnetic sector mass spectrometers are summarized in this article. The major instrumental differences between the present commercially available TOF/RTOFs are compiled (e.g., ion gate, gas-collision cell, type of reflectron, etc.). Whereas peptides have been investigated by MALDI-TOF/RTOF and their CID spectra are well understood, other classes of compounds (e.g., carbohydrates or lipids) are far less well investigated. By comparing data from two different MALDI-TOF/RTOF-instruments, it becomes evident that as they are operated at rather different collision energies for CID (1 versus 20 keV) strong differences in corresponding CID spectra for the same analyte are observed, causing problems with library searches in databases as e.g., abundant peptide side-chain fragmentations mainly occurring in the 8 to 20 keV collision regime are not considered. In contrast, differences in CID spectra of carbohydrates among different TOF/RTOF instruments are less clear-cut, because the required collision energy is spread across a wide range. Especially, carbohydrate cross-ring cleavages require less collision energy in the keV-range than the corresponding peptide side-chain fragmentations. Some of these carbohydrate cross-ring fragmentations are even observed by very low energy CID (< 1 eV fragmentation amplitude). Similar observations can also be made for glycoconjugates (e.g., the drug tylosin A). The lipid class triacylglycerol needs rather high collision energies for dissociating carbon-carbon bonds based upon classical charge-remote fragmentation mechanisms. Comparison of high-energy CID-data of ESI generated triacylglycerol precursors with CID spectra from MALDI generated precursors shows different mechanisms for charge-remote fragmentations. MALDI-TOF/RTOF-instruments operated in the elevated high-energy CID mode exhibit a strong potential in structural analysis of natural and synthetic biomolecules with information often not obtainable by low energy CID. PMID:19199883

Pittenauer, Ernst; Allmaier, Günter

2009-02-01

276

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

SciTech Connect

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

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

2006-02-28

277

Angular and energy distribution of fragment ions in dissociative double photoionization of acetylene molecules at 39 eV  

SciTech Connect

The two-body dissociation reactions of the dication, C{sub 2}H{sub 2}{sup 2+}, produced by 39.0 eV double photoionization of acetylene molecules, have been studied by coupling photoelectron-photoion-photoion coincidence and ion imaging techniques. The results provide the kinetic energy and angular distributions of product ions. The analysis of the results indicates that the dissociation leading to C{sub 2}H{sup +}+H{sup +} products occurs through a metastable dication with a lifetime of 108 {+-} 22 ns, and a kinetic energy release (KER) distribution exhibiting a maximum at {approx}4.3 eV with a full width at half maximum (FWHM) of about 60%. The reaction leading to CH{sub 2}{sup +}+C{sup +} occurs in a time shorter than the typical rotational period of the acetylene molecules (of the order of 10{sup -12} s). The KER distribution of product ions for this reaction, exhibits a maximum at {approx}4.5 eV with a FWHM of about 28%. The symmetric dissociation, leading to CH{sup +} + CH{sup +}, exhibits a KER distribution with a maximum at {approx}5.2 eV with a FWHM of 44%. For the first two reactions the angular distributions of ion products also indicate that the double photoionization of acetylene occurs when the neutral molecule is mainly oriented perpendicularly to the light polarization vector.

Alagia, M. [IOM CNR Laboratorio TASC, I-34012 Trieste (Italy); Callegari, C.; Richter, R. [Sincrotrone Trieste, Area Science Park, 34149 Basovizza, Trieste (Italy); Candori, P.; Falcinelli, S.; Vecchiocattivi, F. [Dipartimento di Ingegneria Civile ed Ambientale, 06125 Perugia (Italy); Pirani, F. [Dipartimento di Chimica dell'Universita di Perugia, 06123 Perugia (Italy); Stranges, S. [IOM CNR Laboratorio TASC, I-34012 Trieste (Italy); Dipartimento di Chimica, Universita di Roma ''La Sapienza'', 00185 Roma (Italy)

2012-05-28

278

Strong photon energy dependence of the photocatalytic dissociation rate of methanol on TiO2(110).  

PubMed

Photocatalytic dissociation of methanol (CH3OH) on a TiO2(110) surface has been studied by temperature programmed desorption (TPD) at 355 and 266 nm. Primary dissociation products, CH2O and H atoms, have been detected. The dependence of the reactant and product TPD signals on irradiation time has been measured, allowing the photocatalytic reaction rate of CH3OH at both wavelengths to be directly determined. The initial dissociation rate of CH3OH at 266 nm is nearly 2 orders of magnitude faster than that at 355 nm, suggesting that CH3OH photocatalysis is strongly dependent on photon energy. This experimental result raises doubt about the widely accepted photocatalysis model on TiO2, which assumes that the excess potential energy of charge carriers is lost to the lattice via strong coupling with phonon modes by very fast thermalization and the reaction of the adsorbate is thus only dependent on the number of electron-hole pairs created by photoexcitation. PMID:24299197

Xu, Chenbiao; Xu, Chengbiao; Yang, Wenshao; Ren, Zefeng; Dai, Dongxu; Guo, Qing; Minton, Timothy K; Yang, Xueming

2013-12-18

279

Near-infrared fluorescence energy transfer imaging of nanoparticle accumulation and dissociation kinetics in tumor-bearing mice.  

PubMed

In the current study we show the dissociation and tumor accumulation dynamics of dual-labeled near-infrared quantum dot core self-assembled lipidic nanoparticles (SALNPs) in a mouse model upon intravenous administration. Using advanced in vivo fluorescence energy transfer imaging techniques, we observed swift exchange with plasma protein components in the blood and progressive SALNP dissociation and subsequent trafficking of individual SALNP components following tumor accumulation. Our results suggest that upon intravenous administration SALNPs quickly transform, which may affect their functionality. The presented technology provides a modular in vivo tool to visualize SALNP behavior in real time and may contribute to improving the therapeutic outcome or molecular imaging signature of SALNPs. PMID:24134041

Zhao, Yiming; van Rooy, Inge; Hak, Sjoerd; Fay, Francois; Tang, Jun; Davies, Catharina de Lange; Skobe, Mihaela; Fisher, Edward Allen; Radu, Aurelian; Fayad, Zahi A; de Mello Donegá, Celso; Meijerink, Andries; Mulder, Willem J M

2013-11-26

280

Ionic dissociation of methanesulfonic acid in small water clusters  

NASA Astrophysics Data System (ADS)

Ionic dissociation of methanesulfonic acid (MSA) in the aqueous environment is studied by density functional theory and ab initio calculations of the water clusters MSA-(H 2O) n, n = 1-5. Molecular structures and stabilities are discussed based on the calculated stable conformers and relative energies. The clusters with up to three water molecules ( n = 1-3) are dominated by strong hydrogen bond interactions. With a minimum of n = 4, MSA is dissociated as a result of proton transfer from MSA to H 2O. All of the clusters are shown thermodynamically stable in the gas phase with respect to separate monomers.

Li, Shujin; Qian, Wei; Tao, Fu-Ming

2007-04-01

281

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

282

Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion  

SciTech Connect

The dissociative recombination (DR) of {sup 3}He {sup 4}He{sup +} has been investigated at the heavy-ion Test Storage Ring (TSR) in Heidelberg by observing neutral products from electron-ion collisions in a merged beams configuration at relative energies from near-zero (thermal electron energy about 10 meV) up to 40 eV. After storage and electron cooling for 35 s, an effective DR rate coefficient at near-zero energy of 3x10{sup -9} cm{sup 3}s{sup -1} is found. The temporal evolution of the neutral product rates and fragment imaging spectra reveals that the populations of vibrational levels in the stored ion beam are nonthermal with fractions of {approx}0.1-1 % in excited levels up to at least v=4, having a significant effect on the observed DR signals. With a pump-probe-type technique using DR fragment imaging while switching the properties of the electron beam, the vibrational excitation of the ions is found to originate mostly from ion collisions with the residual gas. Also, the temporal evolution of the DR signals suggests that a strong electron induced rotational cooling occurs in the vibrational ground state, reaching a rotational temperature near or below 300 K. From the absolute rate coefficient and the shape of the fragment imaging spectrum observed under stationary conditions, the DR rate coefficient from the vibrational ground state is determined; converted to a thermal electron gas at 300 K it amounts to (3.3{+-}0.9)x10{sup -10} cm{sup 3}s{sup -1}. The corresponding branching ratios from v=0 to the atomic final states are found to be (3.7{+-}1.2) % for 1s2s {sup 3}S,(37.4{+-}4.0) % for 1s2s {sup 1}S,(58.6{+-}5.2) % for 1s2p {sup 3}P, and (2.9{+-}3.0) % for 1s2p {sup 1}P. A DR rate coefficient in the range of 2x10{sup -7} cm{sup 3}s{sup -1} or above is inferred for vibrational levels v=3 and higher. As a function of the collision energy, the measured DR rate coefficient displays a structure around 0.2 eV. At higher energies, it has one smooth peak around 7.3 eV and a highly structured appearance at 15-40 eV. The small size of the observed effective DR rate coefficient at near-zero energy indicates that the electron induced rotational cooling is due to inelastic electron-ion collisions and not due to selective depletion of rotational levels by DR.

Pedersen, H.B.; Buhr, H.; Altevogt, S.; Andrianarijaona, V.; Kreckel, H.; Lammich, L.; Schwalm, D.; Wolf, A. [Max-Planck-Institut fuer Kernphysik, D-69117 Heidelberg (Germany); Ruette, N. de; Staicu-Casagrande, E.M.; Urbain, X. [Departement de Physique, Universite Catholique de Louvain, B-1348, Louvain-la-Neuve (Belgium); Strasser, D. [Department of Particle Physics, Weizmann Institute of Science, Rehovot 76100 (Israel); Zajfman, D. [Max-Planck-Institut fuer Kernphysik, D-69117 Heidelberg (Germany); Department of Particle Physics, Weizmann Institute of Science, Rehovot 76100 (Israel)

2005-07-15

283

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

Microsoft Academic Search

the HOCO free radical and the dynamics of the OH + CO ? H+CO 2 reaction. These photoelectron-photofragment coincidence experiments allow the identification of photodetachment processes leading to the production of stable HOCO free radicals and both the H + CO2 and OH + CO dissociation channels on the neutral surface. Isotopic substitution by deuterium in the parent ion is

Zhou Lu; Qichi Hu; Jonathan E. Oakman; Robert E. Continettia

284

Middle School Chemistry: Energy Levels, Electrons, and Ionic Bonding  

NSDL National Science Digital Library

This multimedia lesson for Grades 7-8 features six animations, one video, and a hands-on lab to explore the process of ionic bonding. Learners can visualize what happens when positive and negative ions attract each other and form a bond, build 2D and 3D models, and perform a hands-on activity to observe sodium chloride crystals and relate their shape to the molecular model. Editor's Note: Ionic bonding occurs when electrons are transferred between atoms through electrostatic attraction between two oppositely charged ions. Covalent bonding occurs when electrons are shared between atoms. The processes are quite different. This module very effectively explores the atomic processes that underlie ionic bonding.

Galvan, Patti; Kessler, Jim

2011-08-17

285

Absolute cross sections and kinetic energy release distributions for electron-impact ionization and dissociation of CD+ 4  

NASA Astrophysics Data System (ADS)

Absolute cross sections for electron-impact dissociative excitation and ionization of CD+ 4 leading to formation of ionic products (CD2+ 4, CD+ 3, CD+ 2, CD+, C+, D+ 3, D+ 2, and D+) have been measured. The animated crossed-beams method is applied in the energy range from the reaction threshold up to 2.5 keV. Around 100 eV, the maximum cross sections are found to be (3.8±0.2) ×10-19 cm2, (10.8 ± 1.5) × 10^{-17} cm2, (7.1±0.8) ×10-17 cm2, (9.0±0.8) × 10-17 cm2 and (3.7±0.4) ×10-17 cm2 for the heavy carbonaceous ions CD2+ 4, CD+ 3, CD+ 2, CD+ and C+ respectively. For the light fragments, D+ 3, D+ 2, and D+, the cross sections around the maximum are found to be (5.0±0.6) ×10-19 cm2, (1.7± 0.2) ×10-17 cm2 and (10.6±1.0) ×10-17 cm2, respectively. The cross sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. The analysis of ionic product velocity distributions allows determination of the kinetic energy release distributions which are seen to extend from 0 to 9 eV for heavy fragments, and up to 14 eV for light ones. The comparison of present energy thresholds and kinetic energy release with available published data gives information about states contributing to the observed processes. Individual contributions for dissociative excitation and dissociative ionization are determined for each detected product. A complete database including cross sections and energies is compiled for use in fusion application.

Lecointre, J.; Belic, D. S.; Jureta, J. J.; Janev, R.; Defrance, P.

2008-12-01

286

Structures, energies and bonding in neutral and charged Li microclusters.  

PubMed

Structural and chemical properties of charged and neutral Lithium microclusters are investigated for [Formula: see text]. A total of 18 quantum conformational spaces are randomly walked to produce candidate structures for local minima. Very rich potential energy surfaces are produced, with the largest structural complexity predicted for anionic clusters. Analysis of the electron charge distributions using the quantum theory of atoms in molecules (QTAIM) predicts major stabilizing roles of Non-nuclear attractors (NNAs) via NNA···Li interactions with virtually no direct Li···Li interactions, except in the least stable configurations. A transition in behavior for clusters containing more than seven nuclei is observed by using the recently introduced quantum topology to determine in a quantum mechanically consistent fashion the number of spatial dimensions each cluster has. We experiment with a novel scheme for extracting persistent structural motifs with increase in cluster size. The new structural motifs correlate well with the energetic stability, particularly in highlighting the least stable structures. Quantifying the degree of covalent character in Lithium bonding independently agrees with the observation in the transition in cluster behavior for lithium clusters containing more than seven nuclei. Good correlation with available experimental data is obtained for all properties reported in this work. PMID:22538507

Yepes, Diana; Kirk, Steven Robert; Jenkins, Samantha; Restrepo, Albeiro

2012-09-01

287

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

288

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

PubMed Central

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

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

2010-01-01

289

Dissociation Chemistry of Hydrogen-Deficient Radical Peptide Anions  

NASA Astrophysics Data System (ADS)

The fragmentation chemistry of anionic deprotonated hydrogen-deficient radical peptides is investigated. Homolytic photodissociation of carbon-iodine bonds with 266 nm light is used to generate the radical species, which are subsequently subjected to collisional activation to induce further dissociation. The charges do not play a central role in the fragmentation chemistry; hence deprotonated peptides that fragment via radical directed dissociation do so via mechanisms which have been reported previously for protonated peptides. However, charge polarity does influence the overall fragmentation of the peptide. For example, the absence of mobile protons favors radical directed dissociation for singly deprotonated peptides. Similarly, a favorable dissociation mechanism initiated at the N-terminus is more notable for anionic peptides where the N-terminus is not protonated (which inhibits the mechanism). In addition, collisional activation of the anionic peptides containing carbon-iodine bonds leads to homolytic cleavage and generation of the radical species, which is not observed for protonated peptides presumably due to competition from lower energy dissociation channels. Finally, for multiply deprotonated radical peptides, electron detachment becomes a competitive channel both during the initial photoactivation and following subsequent collisional activation of the radical. Possible mechanisms that might account for this novel collision-induced electron detachment are discussed.

Moore, Benjamin; Sun, Qingyu; Hsu, Julie C.; Lee, Albert H.; Yoo, Gene C.; Ly, Tony; Julian, Ryan R.

2012-03-01

290

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

291

DIFFRACTION DISSOCIATION - 50 YEARS LATER.  

SciTech Connect

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

WHITE, S.N.

2005-04-27

292

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

293

Threshold collision-induced dissociation of Sr2+(H2O)x complexes (x=1-6): An experimental and theoretical investigation of the complete inner shell hydration energies of Sr2+  

NASA Astrophysics Data System (ADS)

The sequential bond energies of Sr2+(H2O)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 Sr2+(H2O)x complexes, where x=6-9. Smaller Sr2+(H2O)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 Sr2+(H2O) complex to Sr2+(H2O)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 Sr2+, we also present an in-depth theoretical study on the energetics of the Sr2+(H2O)x systems by employing several levels of theory with multiple effective core potentials for Sr and different basis sets for the water molecules.

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

2010-01-01

294

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

295

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

296

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

297

Kinetic-energy release in the dissociative capture-ionization of CO molecules by 97MeV Ar14+ ions  

Microsoft Academic Search

The dissociation of COQ+ molecular ions (Q=4 to 9) produced in multiply ionizing collisions accompanied by the transfer of an electron to the projectile has been studied using time-of-flight techniques. Analysis of the coincident-ion-pair flight-time-difference distributions yielded average values of the kinetic-energy releases for the various dissociation reactions. These values were found to be as much as a factor of

R. L. Watson; G. Sampoll; V. Horvat; O. Heber

1996-01-01

298

CO dissociation on iron nanoparticles: Size and geometry effects  

NASA Astrophysics Data System (ADS)

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

Melander, Marko; Latsa, Ville; Laasonen, Kari

2013-10-01

299

Photodissociation of CO3(-) - Product kinetic energy measurements as a probe of excited state potential surfaces and dissociation dynamics  

NASA Astrophysics Data System (ADS)

The process of the photodissociation of CO3(-) into O(-) + CO2 is studied at photon energy of 2.41, 2.50, 2.54, 2.60, and 2.71 eV. The photon energy dependence of the average photofragment kinetic energies shows that photodissociation at these energies does not proceed by a direct dissociation process on a repulsive potential surface or by a statistical vibrational predissociation process on a bound surface. It is found that ground state CO3(-) has a planar D(3h) geometry and 2(A-prime)2 electronic symmetry. The results suggest that the photodissociation of CO3(-) occurs via the interaction of bound and repulsive excited potential surfaces.

Snodgrass, Joseph T.; Roehl, Coleen M.; van Koppen, Petra A. M.; Palke, William E.; Bowers, Michael T.

1990-05-01

300

Absolute cross-sections and kinetic energy release distributions for electron-impact dissociation of D+3  

Microsoft Academic Search

Absolute cross-sections for electron-impact dissociation of D+3 leading to the formation of D+ and D+2 products have been measured by applying the animated electron-ion beam method in the energy range from the respective thresholds up to 2.5 keV. The maximum total cross-sections are observed to be (13.9 ± 1.1) × 10-17 cm2 and (8.2 ± 0.1) × 10-17 cm2 (around

J. Lecointre; M. O. Abdellahi El Ghazaly; J. J. Jureta; D. S. Belic; X. Urbain; P. Defrance

2009-01-01

301

Absolute cross sections and kinetic energy release distributions forelectron-impact ionization and dissociation of CD + 4  

Microsoft Academic Search

Absolute cross sections for electron-impact dissociative excitation and\\u000a ionization of CD+\\u000a 4 leading to formation of ionic products (CD2+\\u000a 4, CD+\\u000a 3, CD+\\u000a 2, CD+, C+, D+\\u000a 3, D+\\u000a 2, and D+) have been measured. The animated crossed-beams\\u000a method is applied in the energy range from the reaction threshold up to 2.5 keV. Around 100 eV, the maximum cross sections\\u000a are found

J. Lecointre; D. S. Belic; J. J. Jureta; R. Janev; P. Defrance

2008-01-01

302

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

303

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

PubMed

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

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

2012-03-21

304

Studies on high-energy collision-induced dissociation of endogenous cannabinoids: 2-arachidonoylglycerol and n-arachidonoylethanolamide in FAB-mass spectrometry.  

PubMed

Analysis of 2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamide (anandamide) via alkali or alkaline earth metal-adduct high-energy collision-induced dissociation (CID) in fast-atom bombardment (FAB) ionization-mass spectrometry (MS) is described. The CID-MS/MS of the [2-AG+Li](+) or [2-AG+Na](+) ion undergoes charge-remote fragmentation (CRF), which is useful for the determination of the double-bond positions in the hydrocarbon chain, while the CID-MS/MS of the [2-AG-H+Cat](+) (Cat = Mg(2+), Ca(2+), Ba(2+)) ion provides an abundant fragment ion of the cationized arachidonic acid species, which is derived from cleaving the ester bond via a McLafferty-type rearrangement in addition to structurally informative CRF ions in small amounts. On the other hand, the CID-MS/MS spectra of anandamide cationized with both alkali metal (Li(+) or Na(+)) and alkaline earth metal (Mg(2+), Ca(2+), or Ba(2+)) show CRF patterns: the spectra obtained in lithium or sodium adduct are more clearly visible than those in magnesium, calcium, or barium adduct. The McLafferty rearrangement is not observed with metal-adduct anandamide. The characteristics in each mass spectrum are useful for the detection of these endogenous ligands. m-Nitrobenzyl alcohol (m-NBA) is the most suitable matrix. A lithium-adduct [2-AG+Li](+) or [anandamide+Li](+) ion is observed to be the most abundant in each mass spectrum, since the affinity of lithium for m-NBA is lower than that for other matrices examined. PMID:16837740

Kasai, Hiroko F; Tsubuki, Masayoshi; Honda, Toshio

2006-07-01

305

Direct-dynamics VTST study of hydrogen or deuterium abstraction and C-C bond formation or dissociation in the reactions of CH3 + CH4, CH3 + CD4, CH3D + CD3, CH3CH3 + H, and CH3CD3 + D  

NASA Astrophysics Data System (ADS)

Direct-dynamics variational transition-state theory calculations are studied at the MPWB1K/6-311++G(d,p) level for the four parts of reactions. The first part is hydrogen or deuterium abstraction in the reactions of CH3 + CH4, CH3 + CD4, and CH3D + CH3. The second part involves C-C bond formation in these reactions. The third one is the reactions of CH3CH3 + H and CH3CD3 + D to form of H2, HD, and D2. The last one is the dissociation of C-C bonds in the last group of reactions. The ground-state vibrational adiabatic potential is plotted for all channels. We have carried out direct-dynamics calculations of the rate constants, including multidimensional tunneling in the temperature range T = 200-2200 K. The results of CVT/?OMT rate constants were in good agreement with the experimental data which were available for some reactions. Small-curvature tunneling and Large-curvature tunneling with the LCG4 version were used to include the quantum effects in calculation of the rate constants. To try to find the region of formation and dissociation of bounds we have also reported the variations of harmonic vibrational frequencies along the reaction path. The thermally averaged transmission probability (P(E)exp (-?E/RT)) and representative tunneling energy at 298 K are reported for the reactions in which tunneling is important. We have calculated kinetic isotope effect which shows tunneling and vibrational contributions are noticeable to determine the rate constant. Nonlinear least-squares fitting is used to calculate rate constant expressions in the temperature range 200-2200 K. These expressions revealed that pre-exponential factor includes two parts; the first part is a constant number which is important at low temperatures while the second part is temperature dependent which is significant at high temperatures.

Ramazani, Shapour

2013-05-01

306

Renner-Teller effect on dissociative electron attachment to carbon dioxide  

NASA Astrophysics Data System (ADS)

Stereodynamics of dissociative electron attachment to CO2 is investigated using O- anion velocity imaging experiments. Here 2?g as a Feshbach resonant state of CO2- is confirmed to play a role in the dissociation CO2- ? CO(1?+) + O-(2P) around 8.0 eV. At the lower energy, 7.7 eV, two split states of 2?g due to the Renner-Teller effect are found to couple with the dissociation path; while above this energy, at 8.2 and 8.7 eV, the coupling between the dissociation and the C-O bond stretching becomes predominant. The evolutions of the potential energy surface around this Feshbach resonant state result in the dramatically different angular distributions of the O- momentum.

Wu, Bin; Xia, Lei; Wang, Yong-Feng; Li, Hong-Kai; Zeng, Xian-Jin; Tian, Shan Xi

2012-05-01

307

A bond-bond description of the intermolecular interaction energy: the case of the weakly bound acetylene-hydrogen complex.  

PubMed

A new semiempirical potential energy surface (PES) for the acetylene-hydrogen system has been derived by using the recently introduced bond-bond methodology. The proposed PES, expressed in an analytic form suitable for molecular dynamics simulations, involves a limited number of parameters, each one having a physical meaning and allowing the accurate description of the system also in the less stable configurations. The analysis of novel integral cross sections data, measured with nearly effusive molecular beams, combined with that of available pressure broadening coefficients of isotropic Raman lines at 143 K and IR lines at 173 and 295 K of C(2)H(2) in H(2), provides a test of the reliability of the proposed PES and suggests also some refinements. An extensive comparison with a recent ab initio potential is also exploited. PMID:19842658

Thibault, F; Cappelletti, D; Pirani, F; Bartolomei, M

2009-12-31

308

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.

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

2013-01-01

309

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

NASA Astrophysics Data System (ADS)

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

Wang, Yimin; Bowman, Joel M.

2011-10-01

310

Toward a general mechanism of electron capture dissociation.  

PubMed

The effects of positive charge on the properties of ammonium and amide radicals were investigated by ab initio and density functional theory calculations with the goal of elucidating the energetics of electron capture dissociation (ECD) of multiply charged peptide ions. The electronic properties of the amide group in N-methylacetamide (NMA) are greatly affected by the presence of a remote charge in the form of a point charge, methylammonium, or guanidinium cations. The common effect of the remote charge is an increase of the electron affinity of the amide group, resulting in exothermic electron capture. The N-Calpha bond dissociation and transition state energies in charge-stabilized NMA anions are 20-50 kJ mol(-1) greater than in the hydrogen atom adduct. The zwitterions formed by electron capture have proton affinities that were calculated as 1030-1350 kJ mol(-1), and are sufficiently basic for the amide carbonyl to exothermically abstract a proton from the ammonium, guanidinium and imidazolium groups in protonated lysine, arginine, and histidine residues, respectively. A new mechanism is proposed for ECD of multiply charged peptide and protein cations in which the electron enters a charge-stabilized electronic state delocalized over the amide group, which is a superbase that abstracts a proton from a sterically proximate amino acid residue to form a labile aminoketyl radical that dissociates by N-Calpha bond cleavage. This mechanism explains the low selectivity of N-Calpha bond dissociations induced by electron capture, and is applicable to dissociations of peptide ions in which the charge carriers are metal ions or quaternary ammonium groups. The new amide superbase and the previously proposed mechanisms of ECD can be uniformly viewed as being triggered by intramolecular proton transfer in charge-reduced amide cation-radicals. In contrast, remote charge affects N-H bond dissociation in weakly bound ground electronic states of hypervalent ammonium radicals, as represented by methylammonium, CH3NH3*, but has a negligible effect on the N-H bond dissociation in the strongly bound excited electronic states. This refutes previous speculations that loss of "hot hydrogen" can occur from an excited state of an ammonium radical. PMID:15694771

Syrstad, Erik A; Turecek, Frantisek

2005-02-01

311

Esters Dissociatively Adsorb on Alumina.  

National Technical Information Service (NTIS)

Inelastic electron tunneling spectra for esters of the form RCOOR' show that these compounds dissociate on alumina and only the RCOO ion bonds to the surface. For phenethyl benzoate, ethyl-d5 benozate, benzyl-d7 benzoate, the benzoate ion is symmetrically...

A. Bayman P. K. Hansma L. H. Gale

1983-01-01

312

Tests of the RPBE, revPBE, ?-HCTHhyb, ?B97X-D, and MOHLYP density functional approximations and 29 others against representative databases for diverse bond energies and barrier heights in catalysis  

NASA Astrophysics Data System (ADS)

Thirty four density functional approximations are tested against two diverse databases, one with 18 bond energies and one with 24 barriers. These two databases are chosen to include bond energies and barrier heights which are relevant to catalysis, and in particular the bond energy database includes metal-metal bonds, metal-ligand bonds, alkyl bond dissociation energies, and atomization energies of small main group molecules. Two revised versions of the Perdew-Burke-Ernzerhof (PBE) functional, namely the RPBE and revPBE functionals, widely used for catalysis, do improve the performance of PBE against the two diverse databases, but give worse results than B3LYP (which denotes the combination of Becke's 3-parameter hybrid treatment with Lee-Yang-Parr correlation functional). Our results show that the Minnesota functionals, M05, M06, and M06-L give the best performance for the two diverse databases, which suggests that they deserve more attention for applications to catalysis. We also obtain notably good performance with the ?-HCTHhyb, ?B97X-D, and MOHLYP functional (where MOHLYP denotes the combination of the OptX exchange functional as modified by Schultz, Zhao, and Truhlar with half of the LYP correlation functional).

Yang, Ke; Zheng, Jingjing; Zhao, Yan; Truhlar, Donald G.

2010-04-01

313

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

PubMed

A classification of the hydrogen fluoride H-F-bonded interactions comprising a large number of molecules has been proposed by Espinosa et al. [J. Chem. Phys. 117, 5529 (2002)] based on the ratio /Vr(c)/ / Gr(c) where /Vr(c)/ is the magnitude of the local potential-energy density and Gr(c) is the local kinetic-energy density, each evaluated at a bond critical point r(c). A calculation of the ratio for the M-O bonded interactions comprising a relatively large number of oxide molecules and earth materials, together with the constraints imposed by the values of inverted Delta2rho r(c) and the local electronic energy density, Hr(c) = Gr(c) + Vr(c), in the H-F study, yielded practically the same classification for the oxides. This is true despite the different trends that hold between the bond critical point and local energy density properties with the bond lengths displayed by the H-F and M-O bonded interactions. On the basis of the ratio, Li-O, Na-O, and Mg-O bonded interactions classify as closed-shell ionic bonds, Be-O, Al-O, Si-O, B-O, and P-O interactions classify as bonds of intermediate character with the covalent character increasing from Be-O to P-O. N-O interactions classify as shared covalent bonds. C-O and S-O bonded interactions classify as both intermediate and covalent bonded interactions. The C-O double- and triple-bonded interactions classify as intermediate-bonded interactions, each with a substantial component of covalent character and the C-O single-bonded interaction classifies as a covalent bond whereas their local electronic energy density values indicate that they are each covalent bonded interactions. The ratios for the Be-O, Al-O, and Si-O bonded interactions indicate that they have a substantial component of ionic character despite their classification as bonds of intermediate character. The trend between the ratio and the character of the bonded interactions is consistent with trends expected from electronegativity considerations. The ratio increases as the net charges and the coordination numbers for the atoms for several Ni-sulfides decrease. On the contrary, the ratio for the Si-O bonded interactions for the orthosilicate, forsterite, Mg2SiO4, and the high-pressure silica polymorph, stishovite, decreases as the observed net atomic charges and the coordination numbers of Si and O increase in value. The ratio for the Ni-Ni bonded interactions for the Ni-sulfides and bulk Ni metal indicate that the interactions are intermediate in character with a substantial component of ionic character. PMID:16512733

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

2006-02-28

314

Regiospecific coordination of tert-butylfulleride ion and 1,4-dicyclopropyltropylium ion. Synthesis of a dialkyldihydrofullerene having a heterolytically dissociative carbon-carbon {sigma} bond  

SciTech Connect

The high electron affinity of fullerene (C{sub 60}) suggests that this important structure is a framework of highly stabilized carbanions. Recent studies of the controlled addition of organolithium and Grignard reagents to C{sub 60} demonstrated the formation of monosubstituted fulleride ions (RC{sub 60}{sup {minus}}) in high yields. Their regiospecific protonation to form 1-R-1,2-dihydrofullerenes as thermodynamically-controlled products has suggested that stepwise introduction of two different alkyl groups into distinct positions of the C{sub 60} framework can be achieved by using RC{sub 60}{sup {minus}} as a nucleophile. The reported high stability of t-BuC{sub 60}{sup {minus}} (1{sup {minus}}) toward electrophiles prompted the authors to synthesize new ionically-dissociative hydrocarbons by the carbocation-carbanion coordination of 1{sup {minus}} and highly stabilized hydrocarbon cations. Here, the authors report the synthesis of a disubstituted dihydro-fullerene 3 in isomerically pure form by the reaction of tert-butylfulleride ion (1{sup {minus}}), generated by deprotonation of t-BuC{sub 60}H, with 1,4-dicyclopropyltropylium ion (2{sup +}) and its reversible heterolysis to regenerate 1{sup {minus}} and 2{sup +} in highly polar solvents.

Toshikazu Kitagawa; Toru Tanaka; Yuki Takata [Kyoto Univ., (Japan)] [and others

1995-03-24

315

Dissociation of diatomic gases  

NASA Technical Reports Server (NTRS)

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

Hansen, C. F.

1991-01-01

316

Comparing femtosecond multiphoton dissociative ionization of tetrathiafulvene with imaging photoelectron photoion coincidence spectroscopy.  

PubMed

In this paper we describe femtosecond photoionization and the imaging photoelectron photoion coincidence spectroscopy of tetrathiafulvene, TTF. Femtosecond photoionization of TTF results in the absorption of up to twelve 808 nm photons leading to ion internal energies up to 12.1 eV as deduced from the photoelectron spectrum. Within this internal energy a variety of dissociation channels are accessible. In order to disentangle the complex ionic dissociation, we utilized the imaging photoelectron photoion coincidence (iPEPICO) technique. Above the dissociation threshold, iPEPICO results show that the molecular ion (m/z = 204) dissociates into seven product ions, six of which compete in a 1.0 eV internal energy window and are formed with the same appearance energy. Ab initio calculations are reported on the possible fragment ion structures of five dissociation channels as well as trajectories showing the loss of C2H2 and C2H2S from high internal energy TTF cations. A three-channel dissociation model is used to fit the PEPICO data in which two dissociation channels are treated as simple dissociations (one with a reverse barrier), while the rest involve a shared barrier. The two lower energy dissociation channels, m/z = 146 and the channel leading to m/z = 178, 171, 159, 140, and 127, have E0 values of 2.77 ± 0.10 and 2.38 ± 0.10 eV, respectively, and are characterized by ?S(‡)(600 K) values of -9 ± 6 and 1 ± 6 J K(-1) mol(-1), respectively. Competing with them at higher internal energy is the cleavage of the central bond to form the m/z = 102 fragment ion, with an E0 value of 3.65 ± 0.10 eV and ?S(‡)(600 K) = 83 ± 10 J K(-1) mol(-1). PMID:23463913

Mayer, Paul M; Staedter, David; Blanchet, Valerie; Hemberger, Patrick; Bodi, Andras

2013-04-01

317

APCI low energy collision-induced dissociation fragmentation of protonated ortho silicates: mclafferty or ion-neutral complex rearrangement?  

PubMed

The fragmentation mechanism of tetraethyl ortho silicate and tetrapropyl ortho silicate was studied to determine if the consecutive alkene losses observed in their MS/MS daughter ion spectra were produced via a McLafferty rearrangement or by ion-neutral rearrangement mechanisms. The experiments were carried out using atmospheric pressure chemical ionization and low energy collision-induced dissociation. Deuterium labeling of the ?-position provided evidence mat the rearrangement mechanism of the successive alkene losses proceeds predominantly via the ion-neutral complex mechanism. Because the energies imparted to the ions in this experiment are of the same order of magnitude as solution phase reactions, this mechanism may shed light on the formation of silica gels (e.g., aerogels) in that similar structures have been proposed as reaction intermediates in the polymerization of SiO2. PMID:24222622

Kenny, D V; Olesik, S V

1994-06-01

318

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

PubMed

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

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

2014-07-01

319

Binding Energies of Proton-Bound Dimers of Imidazole and n-Acetylalanine Methyl Ester Obtained by Blackbody Infrared Radiative Dissociation  

PubMed Central

The dissociation kinetics of protonated n-acetyl-L-alanine methyl ester dimer (AcAlaMEd), imidazole dimer, and their cross dimer were measured using blackbody infrared radiative dissociation (BIRD). Master equation modeling of these data was used to extract threshold dissociation energies (Eo) for the dimers. Values of 1.18 ± 0.06, 1.11 ± 0.04, and 1.12 ± 0.08 eV were obtained for AcAlaMEd, imidazole dimer, and the cross dimer, respectively. Assuming that the reverse activation barrier for dissociation of the ion–molecule complex is negligible, the value of Eo can be compared to the dissociation enthalpy (?Hd°) from HPMS data. The Eo values obtained for the imidazole dimer and the cross dimer are in agreement with HPMS values; the value for AcAlaMEd is somewhat lower. Radiative rate constants used in the master equation modeling were determined using transition dipole moments calculated at the semiempirical (AM1) level for all dimers and compared to ab initio (RHF/3-21G*) calculations where possible. To reproduce the experimentally measured dissociation rates using master equation modeling, it was necessary to multiply semiempirical transition dipole moments by a factor between 2 and 3. Values for transition dipole moments from the ab initio calculations could be used for two of the dimers but appear to be too low for AcAlaMEd. These results demonstrate that BIRD, in combination with master equation modeling, can be used to determine threshold dissociation energies for intermediate size ions that are in neither the truncated Boltzmann nor the rapid energy exchange limit.

Jockusch, Rebecca A.; Williams*, Evan R.

2005-01-01

320

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

PubMed

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

Uddin, M; Coombe, D

2014-03-20

321

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

PubMed

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

Jacobsen, Heiko

2009-06-01

322

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

SciTech Connect

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

Borisov, Oleg V.(ASSOC WESTERN UNIVERSITY) [ASSOC WESTERN UNIVERSITY; Goshe, Michael B.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB); Conrads, Thomas P.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB); Rakov, Vsevolod S.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB); Veenstra, Timothy D.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB); Smith, Richard D.(BATTELLE (PACIFIC NW LAB)) [BATTELLE (PACIFIC NW LAB)

2002-05-15

323

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

Microsoft Academic Search

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

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

1969-01-01

324

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

PubMed

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

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

2013-02-14

325

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

326

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

NASA Astrophysics Data System (ADS)

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

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

2004-05-01

327

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

PubMed Central

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

Li, Yilei; Zhu, Zhencai; Chen, Guoan

2014-01-01

328

Electrospray Ionization with Low-energy Collisionally Activated Dissociation Tandem Mass Spectrometry of Glycerophospholipids: Mechanisms of Fragmentation and Structural Characterization  

PubMed Central

This review describes the use of low-energy collisionally activated dissociation (CAD) with both tandem quadrupole and ion-trap mass spectrometry toward to structural characterization of glycerophospholipids (GPLs), including classes of glycerophosphocholine, glycerophosphoethanolamine, glycerophosphoserine, glycerophosphoglycerol glycerophosphoinositol and glycerophosphatidic acid, as well as their lyso-, plasmanyl-, and plasmenylphospholipid subclasses.. The mechanisms underlying the fragmentation processes leading to structural characterization of GPLs in various ion forms desorbed by electrospray ionization in the positive-ion and negative-ion modes are also discussed. The tandem mass spectrometric approaches afford the identification of the polar head group, the fatty acid substituents and the location of the radyl groups on the glycerol backbone of all the GPLs.

Hsu, Fong-Fu; Turk, J.

2009-01-01

329

Absolute cross-sections and kinetic-energy-release distributions for electron-impact ionization and dissociation of CD 2 +  

Microsoft Academic Search

Absolute cross-sections have been measured for electron-impact dissociative\\u000a excitation and ionization of CD2+ leading to\\u000a formation of CD22+, CD+, C+,\\u000a D2+ and D+. The animated crossed-beams method\\u000a is applied in the energy range from the reaction threshold up to 2.5 keV.\\u000a The maximum total cross-sections are found to be (1.2±0.1)×10-17 cm2, (6.1±0.7)×10-17 cm2, (6.4±0.7)×10-17 cm2, (26.3±3.8)×10-19 cm2 and (14.9±1.4)×10-17 cm2 for\\u000a CD22+, CD+, C+,\\u000a D2+

J. Lecointre; D. S. Belic; J. J. Jureta; R. K. Janev; P. Defrance

2009-01-01

330

Absolute cross-sections and kinetic-energy-release distributions for electron-impact ionization and dissociation of CD 3 +  

Microsoft Academic Search

Absolute cross-sections have been measured for electron-impact dissociative excitation and ionization of leading to formation of singly-charged fragments (CD2+, CH+, C+,\\u000a H2+ and D+). The animated crossed-beams method is applied in the energy range from the reaction threshold up to 2.5 keV. The maximum\\u000a cross-sections are found to be (14.0±1.0)×10-17 cm2, (6.5± 0.7)×10-17 cm2, (3.3± 0.3)×10-17 cm2, (1.1±0.1)×10-17 cm2 and (14.0± 1.3)×10-17 cm2 for CD2+, CH+,

J. Lecointre; D. S. Belic; J. J. Jureta; R. K. Janev; P. Defrance

2009-01-01

331

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

SciTech Connect

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

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

2013-01-15

332

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

PubMed Central

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

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

2008-01-01

333

Dynamics of rotational energy release for dissociation of singlet ketene and the singlet/triplet branching ratio  

SciTech Connect

The rotational energy release in the dissociation of ketene along its singlet potential energy surface is observed and compared with various statistical and dynamical theories. Rotational distributions for CO(XO{sup 1}{Sigma}{sup +})({upsilon}=1) are measured from the threshold for production of CH{sub 2}(aO{sup 1}A{sub 1})(0,0,0) + CO(XO{sup 1}{Sigma}{sup +})({upsilon}=1) to 1720 cm{sup -1} above. At low energies (<200 cm{sup -1}), phase space theory (PST) matches the observed distributions. At 357 and 490 cm{sup -1}, PST, constrained by the measured state distributions of the methylene fragment, provides a good fit. For E > 1107 cm{sup -1}, the constrained PST matches the average rotational energy observed but gives distributions which are broader than observed. This contrasts with the {sup 1}CH{sub 2} fragment rotations which become progressively colder than PST as energy increases from 200 cm{sup -1} above the threshold. The CO({upsilon}=1) rotational distributions for E > 357 cm{sup -1} contain no measurable product from triplet channel fragmentation. They can be compared with the previously determined CO(v=0) rotational distributions in order to partition the yield between singlet and triplet channels and recalculate the singlet yield. This yield is found to be at the upper limit of the range previously reported. 32 refs., 10 figs., 2 tabs.

Wade, E.A.; Clauberg, H.; Kim, S.K.; Mellinger, A.; Moore, C. B. [Lawrence Berkeley National Lab., CA (United States)] [Lawrence Berkeley National Lab., CA (United States); [Univ. of California, Berkeley, CA (United States)

1997-01-23

334

Neutral and ionic metal-hydrogen and metal-carbon bond energies: Reactions of Co sup + , Ni sup + , and Cu sup + with ethane, propane, methylpropane, and dimethylpropane  

SciTech Connect

The reactions of Co{sup +}, Ni{sup +}, and Cu{sup +} with a series of alkanes are examined by guided ion beam mass spectrometry. The emphasis of this study is on C-H and C-C bond cleavage channels from which bond dissociation energies for M-H, M-CH{sub 3}, and M{sup +}-CH{sub 3} are derived from the endothermic reaction thresholds. For these three bond energies, we find values (in kilocalories per mole) of 46 {plus minus} 3, 46 {plus minus} 3, and 49.1 {plus minus} 3.5, respectively, for M = Co; 58 {plus minus} 3, 55 {plus minus} 3, and 45.0 {plus minus} 2.4, respectively, for M = Ni; 61 {plus minus} 4, 58 {plus minus} 2, 29.7 {plus minus} 1.7, respectively, for M = Cu. Trends in the thermochemistry of these species and M{sup +}-H are briefly discussed. The reactivity of Cu{sup +}, which has not been previously studied, is compared with that for other transition-metal ions. Also, unusual features in the reactivity of Co{sup +} and Ni{sup +} that have not previously been commented on are discussed.

Georgiadis, R. (Univ. of California, Berkeley (USA)); Fisher, E.R.; Armentrout, P.B. (Univ. of Utah, Salt Lake City (USA))

1989-06-07

335

Guided ion-beam studies of the reactions of Co(n)+ (n=2-20) with O2: cobalt cluster-oxide and -dioxide bond energies.  

PubMed

The kinetic-energy dependence for the reactions of Co(n)+ (n=2-20) with O2 is measured as a function of kinetic energy over a range of 0 to 10 eV in a guided ion-beam tandem mass spectrometer. A variety of Co(m)+, Co(m)O+, and Co(m)O2+ (m < or = n) product ions is observed, with the dioxide cluster ions dominating the products for all larger clusters. Reaction efficiencies of Co(n)+ cations with O2 are near unity for all but the dimer. Bond dissociation energies for both cobalt cluster oxides and dioxides are derived from threshold analysis of the energy dependence of the endothermic reactions using several different methods. These values show little dependence on cluster size for clusters larger than three atoms. The trends in this thermochemistry and the stabilities of oxygenated cobalt clusters are discussed. The bond energies of Co(n)+-O for larger clusters are found to be very close to the value for desorption of atomic oxygen from bulk-phase cobalt. Rate constants for O2 chemisorption on the cationic clusters are compared with results from previous work on cationic, anionic, and neutral cobalt clusters. PMID:16122305

Liu, Fuyi; Li, Feng-Xia; Armentrout, P B

2005-08-01

336

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

337

A translational energy spectrometer to probe interatomic potentials: Dissociation dynamics of CO 2 + ions  

Microsoft Academic Search

A new ion translational energy spectrometer has been developed to carry out low-energy, gas-phase ion-molecule collision experiments\\u000a which aim to probe molecular potential energy surfaces. The collisional technique employed relates small changes in the kinetic\\u000a energy of a projectile ion after it has undergone collision with a static neutral atom\\/molecule to changes in the overall\\u000a potential energy of the collision

M. Krishnamurthy; U T Raheja; D. Mathur

1993-01-01

338

Ultraviolet Bonding of PFPE With Carbon Overcoat: Surface Energy and Spreading  

Microsoft Academic Search

Ultraviolet (UV) irradiation effects on the functional perfluoropolyether (PFPE), i.e., Ztetraol films, were investigated by studying the bonded film thickness as well as the surface energy of PFPE lubricated media using Lifshitz-van der Waals and Lewis acid\\/base (LW\\/AB) theory. It was found that short-time UV irradiation enhanced the bonding of Ztetraol film with ion beam deposited carbon overcoat, which is

Haigang Chen; Pil Seung Chung; Myung S. Jhon

2008-01-01

339

Dissociative electron attachment and vibrational excitation of H{sub 2} by low-energy electrons: Calculations based on an improved nonlocal resonance model  

SciTech Connect

An improved nonlocal resonance model proposed by Cizek, Horacek, and Domcke [J. Phys. B 31, 2571 (1998)] is used for the calculation of cross sections of electron dissociative attachment and vibrational excitation of molecular hydrogen by the impact of low-energy electrons in the range of {sup 2}{sigma}{sub u}{sup +} resonance. The model is based on ab initio data and takes full account of the nonlocality of the effective potential for the nuclear motion. The dissociative attachment cross sections and rate constants are calculated for all target states (v,J) of relevance and compared with other theoretical and experimental data. It is found that the present dissociative attachment cross section calculated under the conditions of the experiment carried out by Schulz and Asundi reproduces the larger of the two values proposed by them, i.e.-2.8x10{sup -21} cm{sup 2}. A detailed discussion of the dissociative attachment cross section as a function of the vibrational and rotational target states is given. Very narrow peaks, with a width of 1 meV, are observed in the dissociative attachment cross section for large values of the orbital quantum number J. These structures are interpreted as shape resonances in H{sup -}+H collision dynamics. It is shown that for large values of J rotational excitation of the hydrogen molecule enhances the dissociative attachment more efficiently than vibrational excitation. The largest dissociative attachment cross section of 28.3x10{sup -16} cm{sup 2} is obtained for v=1 and J=29. The process of vibrational excitation will be discussed in a separate paper.

Horacek, J.; Cizek, M.; Houfek, K.; Kolorenc, P.; Domcke, W. [Institute of Theoretical Physics, Charles University, Prague (Czech Republic); Department of Chemistry, Technical University of Munich, D-85747 Garching (Germany)

2004-11-01

340

Metal cation dependence of interactions with amino acids: bond energies of Rb+ and Cs+ to Met, Phe, Tyr, and Trp.  

PubMed

The interactions of rubidium and cesium cations with four amino acids (AA) including methionine (Met), phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp) are examined in detail. Experimentally, the bond dissociation energies (BDEs) are determined using threshold collision-induced dissociation of the Rb(+)(AA) and Cs(+)(AA) complexes 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. 0 K BDEs of 121.0 ± 7.0 (102.8 ± 6.6), 123.8 ± 7.2 (112.9 ± 5.5), 125.8 ± 7.4 (115.6 ± 6.9), and 138.1 ± 7.5 (125.0 ± 6.8) kJ/mol are determined for complexes of Rb(+) (Cs(+)) with Met, Phe, Tyr, and Trp, respectively. Quantum chemical calculations are conducted at the B3LYP, MP2(full), and M06 levels of theory with geometries and zero point energies calculated at the B3LYP level using def2-TZVPPD basis sets. Results obtained using all three levels show good agreement with experiment, with B3LYP values being systematically low and MP2(full) and M06 values being systematically high. At 0 and 298 K, theory predicts the ground-state conformers for M(+)(Met) either have tridentate binding of the metal cation to the carbonyl, amino, and sulfur groups (MP2 and M06) or to both oxygens of a zwitterionic conformation (B3LYP). At 298 K, binding to the carboxylic acid group and the sulfur also becomes competitive. For the aromatic amino acids at 0 K, most levels of theory favor tridentate binding of the metal ions to the backbone carbonyl and amino groups along with the ?-cloud of the ring, whereas for Rb(+)(Trp) and Cs(+)(AA), B3LYP theory favors binding to only the carbonyl and ring groups. At 298 K, B3LYP favors the latter binding mode for all three Rb(+)(aromatic AA) complexes. Comparison of these results to those for the smaller alkali cations provides insight into the trends in binding affinities and structures associated with metal cation variations. PMID:23514190

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

2013-04-11

341

Electronic Structure of the First Row Hydrides. III. Predissociation by Rotation in the A^1 II State and the Dissociation Energy of BH  

Microsoft Academic Search

The potential energy curve of the A ^1II state of BH is determined by combining spectroscopic results with theoretical calculations. The dissociation energy D_0(BH) is found to be 3.39±0.04 eV. The calculation employing the intra-atomic correlation correction (but not the ab initio orbital calculation) leads to a potential energy curve with a maximum as well as a mmimum in agreement

A. C. Hurley

1961-01-01

342

Dissociation of chloride from ortho-, meta- and para-chloromethylphenoxides  

NASA Astrophysics Data System (ADS)

The enthalpy of formation of m-quinomethane has been determined by energy-resolved collision-induced dissociation measurements involving chloro-substituted phenoxide ions. The chloride affinity of m-quinomethane is measured to be 202 ± 9 kJ/mol, whereas the chloride affinities of o- and p-quinomethane are both 57 ± 5 kJ/mol. The difference in the chloride affinities reflects the difference in the stabilities of the Kekule and non-Kekule structures. Combination of the dissociation energy of the meta-isomer with the gas-phase acidity of 3-(chloromethyl)phenol, measured by using the kinetic method to be 1432 ± 6 kJ/mol, results in an enthalpy of formation of 166 ± 13 kJ/mol for the m-quinomethane diradical. The measured value agrees with that predicted by bond additivity. The low bond dissociation energies for the o- and p-isomers, along with electronic structure calculations, suggest that the corresponding chlorine-substituted ions are best described as halide/diradical complexes.

Chacko, Silvi A.; Wenthold, Paul G.

2007-11-01

343

Ionic fragmentation of a CH4 molecule induced by 10-keV electrons: Kinetic-energy-release distributions and dissociation mechanisms  

NASA Astrophysics Data System (ADS)

The dynamics of ionic fragmentation of CH4 molecules under impact of 10-keV electrons has been studied. The technique of recoil ion momentum spectroscopy is employed to obtain information about the kinetic energy release and the dissociation mechanisms of different pathways arising from the fragmentation of a CH4 dication. The results show that there are altogether eight dissociation pathways that arise from the complete and the incomplete Coulomb explosions of the CH42+ molecular ions. The kinetic energy release for these pathways is compared with earlier data from the literature for the impact of different charged particles, photons, and their impact energies. The present results indicate that mostly the lower electronic states of CH42+ are involved for the observed dissociation channels. Also, the dissociation mechanisms associated with these channels are suggested and discussed. Further, we have also estimated the relative ion intensities of different channels of fragmentation of CH4 dication produced under impact of considered energy of electrons.

Singh, Raj; Bhatt, Pragya; Yadav, Namita; Shanker, R.

2013-06-01

344

H2 dissociation over NbO: the first step toward hydrogenation of Mg.  

PubMed

Niobium-based oxide nanoparticles have proven to be catalytically effective toward hydrogenation of Mg where H2 dissociation over the niobium-oxides is considered to be a crucial reaction step. However, the role of niobium oxides toward H2 dissociation still remains unclear as to what atomic configurations are responsible for the catalytic activity. H2 dissociation over different surface planes of Nb, NbO, and Nb2O5 as well as small NbO clusters is performed by using a density functional theory. The calculations reveal that H2 dissociation, adsorption energy, and the bond type between H and surfaces (clusters) depend on the atomic configurations of Nb and O. In particular, H2 adsorption on NbO(111) is enhanced by O atoms without forming O-H bond where the bond type of H and surface is found to be an electron pairing. Thus, NbO(111) could not only be a effective catalyst but also potentially prevent the formation of MgO during the hydrogenation of Mg. The results should be helpful in developing and tailoring the efficient catalyst toward H2 dissociation and hydrogenation of Mg. PMID:23980657

Takahashi, Keisuke; Isobe, Shigehito; Ohnuki, Somei

2013-09-24

345

Electron-impact dissociation of carbon monoxide  

NASA Astrophysics Data System (ADS)

The electron-impact dissociation of CO to form C and O atoms is observed in a crossed beam experiment at electron energies between the dissociation threshold (14 eV) and 198.5 eV. The center-of-mass energy released in the dissociation of individual molecules is explicitly measured using a position and time sensitive detector for the correlated neutral fragments. The observed energy release distribution is found to be highly structured, reflecting electron-impact excitation to Rydberg states converging to CO(+) (X 2Sigma/+/) which predissociate to ground state atoms. Little or no dissociation is observed from states above the first ionization limit. Total electron impact dissociation cross sections, exclusive of dissociative ionization contributions, and partial cross sections for the dissociative excitation of specific CO electronic states are presented.

Cosby, P. C.

1993-05-01

346

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

SciTech Connect

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

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

2005-09-01

347

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

NASA Astrophysics Data System (ADS)

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

Hayakawa, Shigeo; Tsujinaka, Taiga; Fujihara, Akimasa

2012-11-01

348

Guided ion beam studies of the reactions of Co{sub n}{sup +} (n=1-18) with N{sub 2}: Cobalt cluster mononitride and dinitride bond energies  

SciTech Connect

The reactions of Co{sub n}{sup +} (n=1-18) with N{sub 2} are measured as a function of kinetic energy over a range of 0-15 eV in a guided ion beam tandem mass spectrometer. A variety of Co{sub m}{sup +}, Co{sub m}N{sup +}, and Co{sub m}N{sub 2}{sup +} (m{<=}n) product ions are observed, all in endothermic processes, with collision-induced dissociation dominating the products for all clusters. Bond dissociation energies for both cobalt cluster nitrides and dinitrides are derived from threshold analysis of the energy dependence of the endothermic reactions using several different approaches. These values show only a mild dependence on cluster size over the range studied, although the Co{sub 13}{sup +}-N bond energy is relatively weak. The bond energies of Co{sub n}{sup +}-N for larger clusters suggest that a reasonable value for the desorption energy of atomic nitrogen from bulk phase cobalt is 6.3{+-}0.2 eV, which is somewhat lower than the only available value in the literature, an estimate based on the enthalpy of formation of bulk cobalt nitride. The trends in the cobalt nitride thermochemistry are also compared to previously determined metal-metal bond energies, D{sub 0}(Co{sub n}{sup +}-Co), and to D{sub 0}(Fe{sub n}{sup +}-N). Implications for catalytic ammonia production using cobalt versus iron are discussed.

Liu Fuyi; Li Ming; Tan Lin; Armentrout, P. B. [Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States)

2008-05-21

349

Guided ion beam studies of the reactions of group 3 metal ions (Sc{sup +}, Y{sup +}, La{sup +}, and Lu{sup +}) with silane. Metal silicon bond energies  

SciTech Connect

Guided ion beam techniques are used to measure cross sections as a function of kinetic energy for the reactions of the group 3 metal ions, Sc{sup +}, Y{sup +}, La{sup +} and Lu{sup +} with silane. In all four systems, products include the metal hydride and dihydride cations, as well as metal silicon species, MSiH{sub x}{sup +} (x = 0-3). The general mechanistic details of these reactions may be understood in terms of an insertion of the metal center into the Si-H bond of silane. The subsequently formed intermediate then decomposes to yield the observed products. The energy dependences of the cross sections are analyzed to yield 0 K bond dissociation energies of the various metal silicon species. The present results are compared to those previously reported by Sunderlin and Armentrout for reactions of the group 3 metal ions with methane.

Kickel, B.L.; Armentrout, B.

1993-12-01

350

Dissociation of the Tubulin Dimer Is Extremely Slow, Thermodynamically Very Unfavorable, and Reversible in the Absence of an Energy Source  

PubMed Central

The finding that exchange of tubulin subunits between tubulin dimers (?-? + ???? ? ??? + ???) does not occur in the absence of protein cofactors and GTP hydrolysis conflicts with the assumption that pure tubulin dimer and monomer are in rapid equilibrium. This assumption underlies the many physical chemical measurements of the Kd for dimer dissociation. To resolve this discrepancy we used surface plasmon resonance to determine the rate constant for dimer dissociation. The half-time for dissociation was ?9.6 h with tubulin-GTP, 2.4 h with tubulin-GDP, and 1.3 h in the absence of nucleotide. A Kd equal to 10?11 M was calculated from the measured rate for dissociation and an estimated rate for association. Dimer dissociation was found to be reversible, and dimer formation does not require GTP hydrolysis or folding information from protein cofactors, because 0.2 ?M tubulin-GDP incubated for 20 h was eluted as dimer when analyzed by size exclusion chromatography. Because 20 h corresponds to eight half-times for dissociation, only monomer would be present if dissociation were an irreversible reaction and if dimer formation required GTP or protein cofactors. Additional evidence for a 10?11 M Kd was obtained from gel exclusion chromatography studies of 0.02–2 nM tubulin-GDP. The slow dissociation of the tubulin dimer suggests that protein tubulin cofactors function to catalyze dimer dissociation, rather than dimer assembly. Assuming N-site-GTP dissociation is from monomer, our results agree with the 16-h half-time for N-site GTP in vitro and 33 h half-life for tubulin N-site-GTP in CHO cells.

Caplow, Michael; Fee, Lanette

2002-01-01

351

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

National Technical Information Service (NTIS)

Clean renewable energy bonds (CREBs) present a low-cost opportunity for public entities to issue bonds to finance renewable energy projects. The federal government lowers the cost of debt by providing a tax credit to the bondholder in lieu of interest pay...

C. Kreycik J. Couglin

2009-01-01

352

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

353

Single-molecule measurements of dissociation rates and energy landscapes of binary trans snare complexes in parallel versus antiparallel orientation.  

PubMed

Interactions between synaptobrevin 2 (Sb2) and syntaxin 1A (Sx1A) can be readily isolated and studied with the use of force spectroscopy single-molecule measurements. We studied interactions between Sx1A and Sb2 in two different orientations (parallel and antiparallel) using four different terminus configurations of these proteins. Force-loading experiments indicated that protein pairs in any configuration/orientation are zippered. We measured the extension and force for disassembly of these interactions, calculated the spontaneous dissociation lifetimes, and determined their free energies, enthalpies, and entropies. Although the free energies were very similar for all four configurations (?28 k(B)T (Eyring model) and ?20 k(B)T (Kramers model)), the enthalpy changes of binary Sx1A-Sb2 interactions varied between 24.7 k(B)T and 33.1 k(B)T. This variation is consistent with the conformation changes that occur during disassembly of the various protein terminus configurations, as verified by alterations in the extension. The parallel interactions appear to be energetically somewhat advantageous over antiparallel configurations/orientation, especially when the N-termini of Sx1A-Sb2 are left to interact freely. PMID:22004738

Liu, Wei; Montana, Vedrana; Parpura, Vladimir; Mohideen, U

2011-10-19

354

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

NASA Astrophysics Data System (ADS)

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.

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

2014-04-01

355

Single-Molecule Measurements of Dissociation Rates and Energy Landscapes of Binary trans SNARE Complexes in Parallel versus Antiparallel Orientation  

PubMed Central

Interactions between synaptobrevin 2 (Sb2) and syntaxin 1A (Sx1A) can be readily isolated and studied with the use of force spectroscopy single-molecule measurements. We studied interactions between Sx1A and Sb2 in two different orientations (parallel and antiparallel) using four different terminus configurations of these proteins. Force-loading experiments indicated that protein pairs in any configuration/orientation are zippered. We measured the extension and force for disassembly of these interactions, calculated the spontaneous dissociation lifetimes, and determined their free energies, enthalpies, and entropies. Although the free energies were very similar for all four configurations (?28 kBT (Eyring model) and ?20 kBT (Kramers model)), the enthalpy changes of binary Sx1A-Sb2 interactions varied between 24.7 kBT and 33.1 kBT. This variation is consistent with the conformation changes that occur during disassembly of the various protein terminus configurations, as verified by alterations in the extension. The parallel interactions appear to be energetically somewhat advantageous over antiparallel configurations/orientation, especially when the N-termini of Sx1A-Sb2 are left to interact freely.

Liu, Wei; Montana, Vedrana; Parpura, Vladimir; Mohideen, U.

2011-01-01

356

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.

Young, Elizabeth R.; Rosenthal, Joel

2013-01-01

357

A theoretical investigation of methane dissociation on Rh(111)  

NASA Astrophysics Data System (ADS)

Methane dissociation (CH 4 ? CH x + (4 - x) H ? C + 4H) over a cluster model of the Rh(111) surface has been investigated using a quasi-relativistic density functional method. The main aim is to evaluate the dissociation energies which may determine catalytic activity of the metal in the partial oxidation of methane to syngas. Dissociative adsorption of methane can be initiated on the Rh surface. However, the abstraction of H from CH 4 to produce gas-phase CH n3,g radical is energetically unfavorable. This would explain the absence of C 2 products. The presence of adsorbed oxygen at an on-top site promotes methane dehydrogenation while that at a hollow site exerts the opposite effect. All calculated dissociation energies of CH x,s are compatible with those obtained with the bond-order conservation Morse-potential approach. The combination and desorption of surface species, which are critical to the formation of syngas, are also discussed.

Au, Chak Tong; Liao, Meng-Sheng; Ng, Ching Fai

1997-03-01

358

A new visualization scheme of chemical energy density and bonds in molecules.  

PubMed

Covalent bond describes electron pairing in between a pair of atoms and molecules. The space is partitioned in mutually disjoint regions by using a new concept of the electronic drop region R(D), atmosphere region R(A), and the interface S (Tachibana in J Chem Phys 115:3497-3518, 2001). The covalent bond formation is then characterized by a new concept of the spindle structure. The spindle structure is a geometrical object of a region where principal electronic stress is positive along a line of principal axis of the electronic stress that connects a pair of the R(D)s of atoms and molecules. A new energy density partitioning scheme is obtained using the Rigged quantum electrodynamics (QED). The spindle structure of the stress tensor of chemical bond has been disclosed in the course of the covalent bond formation. The chemical energy density visualization scheme is applied to demonstrate the spindle structures of chemical bonds in H2, C2H6, C2H4 and C2H2 systems. [Figure: see text]. Field theory of the energy density. PMID:15889293

Tachibana, Akitomo

2005-09-01

359

Relative cross-sections and kinetic energy release values in dissociative negative ion formation by successive single-electron transfer from alkali metal targets  

Microsoft Academic Search

Positive ions formed from C2H2 were collided with Cs, K and Na targets in the kiloelectronvolt energy range. The dissociative negative ion formations of C-2 and C2H- ions from C2H+2 ions and C-2 ions from C2H+ ions with an alkali metal target were determined to be double-collision processes using the target density dependence. By considering the reaction energies and comparing

S. Hayakawa

1992-01-01

360

Gas-phase photodissociation of FeCH/sub 2//sup +/ and CoCH/sub 2//sup +/: determination of the carbide, carbyne, and carbene bond energies  

SciTech Connect

Photodissociation of MCH/sub 2//sup +/ (M = Fe, Co) is observed to yield three products M/sup +/, MC/sup +/, and MCH/sup +/. This result is in contrast to the low-energy collision-induced dissociation of MCH/sub 2//sup +/, which yields M/sup +/ exclusively. From the photoappearance thresholds of the products, the following bond energies are assigned: D/sup 0/(Co/sup +/-CH/sub 2/) = 84 +/- 5 kcal/mol, D/sup 0/(Co/sup +/-CH) = 100 +/- 7 kcal/mol, D/sup 0/(Co/sup +/-C) = 90 +/- 7 kcal/mol, D/sup 0/(Fe/sup +/-CH/sub 2/) = 82 +/- 5 kcal/mol, D/sup 0/(Fe/sup +/-CH) = 101 +/- 7kcal/mol, and D/sup 0/(Fe/sup +/-C) = 94 +/- 7 kcal/mol. Compared to the results of an earlier ion-beam study, the Co/sup +/-CH/sub 2/ bond energy reported here is in excellent agreement while the Fe/sup +/-CH/sub 2/ value is significantly lower.

Hettich, R.L.; Freiser, B.S.

1986-05-14

361

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

SciTech Connect

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

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

1988-01-15

362

The [Re, O 8] + potential energy surface: fourier transform ion cyclotron resonance collision induced dissociation studies and density functional calculations 1 1 Dedicated to Professor Michael T. Bowers on the occasion of his 60th birthday  

Microsoft Academic Search

As potential model systems for organometallic oxidation reaction, ions of the composition [Re, On]+, n = 2–6, 8, are produced using a standard laser vaporization source and examined by Fourier transform ion cyclotron resonance collision induced dissociation mass spectrometry. Energy resolved collision induced dissociation (CID) in combination with density functional theory calculations is used to characterize the species and extract

Martin Beyer; Christian Berg; Stefan Joos; Uwe Achatz; Wolfgang Hieringer; Gereon Niedner-Schatteburg; Vladimir E. Bondybey

1999-01-01

363

Comparison of laser-induced dissociation and high-energy collision-induced dissociation using matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI-TOF/TOF) for peptide and protein identification.  

PubMed

The fragmentation of peptides under laser-induced dissociation (LID) as well as high-energy collision-induced dissociation (CID) conditions has been investigated. The effect of the different fragmentation mechanisms on the formation of specific fragment ion types and the usability of the resulting spectra, e.g. for high-throughput protein identification, has been evaluated. Also, basic investigations on the influence of the matrix, as well as laser fluence, on the fragment ion formation and the consequences in the spectral appearance are discussed. The preconditions for obtaining 'pure' CID spectra on matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI-TOF/TOF) instruments are evaluated and discussed as well as the differences between LID and CID in the resulting fragment ion types. While containing a wealth of information due to additional fragment ions in comparison with LID, CID spectra are significantly more complex than LID spectra and, due to different fragmentation patterns, the CID spectra are of limited use for protein identification, even under optimized parameter settings, due to significantly lower scores for the individual spectra. Conditions for optimal results regarding protein identification using MALDI-TOF/TOF instruments have been evaluated. For database searches using tandem mass spectrometric data, the use of LID as fragmentation technique in combination with parameter settings supporting the use of internal fragment ions turned out to yield the optimal results. PMID:15378722

Macht, Marcus; Asperger, Arndt; Deininger, Sören-Oliver

2004-01-01

364

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

Microsoft Academic Search

The primary objective of this study is to develop a more accurate research and design tool than those in the currently available literature for active constrained layer damping treatments applied in bending. A five layer beam finite element model is presented that includes bonding layer strain energy and extends current finite element models for Euler-Bernoulli beams with segmented active constrained

Peter F. Cento; Grzegorz Kawiecki

2001-01-01

365

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

366

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

PubMed

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

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

2014-03-25

367

Collision-Induced Dissociation and Theoretical Studies of Ag+(methanol)(n) , n= 1 - 4  

SciTech Connect

Collision-induced dissociations of the Ag+(methanol)n complexes for n= 1 - 4 are studied using kinetic energy dependent guided ion beam tandem mass spectrometry. In all cases, the primary products are endothermic loss of an intact neutral ligand from the complex. The cross section thresholds are interpreted to yield 0 and 298 K bond dissociation energies (BDEs) after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and unimolecular decay rates. These values are compared with theoretical values obtained using high level ab initio calculations. Generally good agreement is found except for the third ligand. The nature of the bonding in these complexes and their BDEs are examined in detail. Although the effect is not as dramatic as in singly or doubly ligated copper complexes, 5s-4ds hybridization found in the Ag+(methanol)n complexes, n= 1 and 2, enhances the BDEs.

Koizumi, Hideya (Utah, Univ Of); Larsen, Melissa (Utah, Univ Of); Armentrout, Peter B. (U of Utah); Feller, David F. (BATTELLE (PACIFIC NW LAB))

2003-04-24

368

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

369

Dissociation of H-related defect complex in InP using high energy light ions  

SciTech Connect

High energy light ion irradiation has been used to anneal H-related defect complexes and to modify the electronic properties of semi-insulating InP (SI-InP). Raman and infrared spectroscopic measurements have been used to investigate the annihilation of native defects in SI-InP irradiated with 85 MeV C. Irradiation resulted in a decrease in sample resistivity by four orders of magnitudes and a change in the type of conductivity. The Raman spectroscopic results indicate an improvement in the InP sample due to irradiation up to an optimum fluence. The role of high electronic energy loss in defect annealing, which includes modification of the electrical properties and crystal structure of irradiated SI-InP, is discussed.

Kabiraj, D. [Inter-University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067 (India); Roy, A. [Department of Physics, Indian Institute of Technology, Kharagpur 721302 (India); Pivin, J. C. [CSNSM, IN2P3-CNRS, Batiment 108, F-91405 Orsay Campus (France); Ghosh, Subhasis [School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067 (India)

2008-08-01

370

Kinetic Energy Release in the Dissociation of Some Simple Molecular Ions. Water and Hydrogen Sulfide  

Microsoft Academic Search

The technique of ion kinetic energy spectroscopy has been applied to a study of S+. formation from H2S+. and O+. formation from H2O+.. Unimolecular formation of S+. occurs by predissociation of the first excited state via the repulsive 4A2 state of H2S+.. Above the classical crossover region this reaction proceeds rapidly on the mass spectrometer time scale but tunneling through

E. G. Jones; J. H. Beynon; R. G. Cooks

1972-01-01

371

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

372

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

373

Suppression and dissociation  

Microsoft Academic Search

The present study examined the connection between susppression and dissociation. Fifty-four normal subjects completed the White Bear Suppression Inventory and the Dissociative Experiences Scale. Results showed that suppression and dissociation were significantly correlated. Furthermore, both suppression and dissociation correlated positively with less adaptive defense categories as indexed by the Defense Style Questionnaire: suppression was found to be related to immature

Peter Muris; Harald Merckelbach

1997-01-01

374

Gold-catalyzed C(sp(3))-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

2014-07-01

375

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

376

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

377

Structure, energy, vibrational spectrum, and Bader's analysis of ?···H hydrogen bonds and H(-?)···H(+?) dihydrogen bonds.  

PubMed

In this paper, the intermolecular structural study asserted by the vibrational analysis in the stretch frequencies of hydrogen bonds (?···H) and dihydrogen bonds (H(-?)···H(+?)) have definitively been revisited by means of calculations carried out by Density Functional Theory (DFT) and topological parameters derived from the classic treatise of the Quantum Theory of Atoms in Molecules (QTAIM). As a matter of fact the ?···H hydrogen bond is formed between the hydrofluoric acid and the C?C bond of the acetylene, but the QTAIM calculations revealed a distortion in this interaction due to the formation of the ternary complex C(2)H(2)···2(HF). Although the ? bonds of ethylene (C(2)H(4)), propylene (C(2)H(3)(CH(3))), and t-butylene (C(2)H(2)(CH(3))(2)) are considered proton acceptors, two hydrogen-bond types--?···H and C···H--can be observed. Over and above the analysis of the ? hydrogen bonds, theoretical arguments also were used to discuss the red-shifts in the stretch frequencies of the binary dihydrogen complexes formed by BeH(2)···HX with X = F, Cl, CN, and CCH. Although a vibrational blue-shift in the stretch frequency of the H-C bond of HCF(3) due to the formation of the BeH(2)···HCF(3) dihydrogen complex was obtained, unmistakable red-shifts were detected in LiH···HCF(3), MgH(2)···HCF(3), and NaH···HCF(3). Moreover, the alkali-halogen bonds were identified in relation to the formation of the trimolecular systems NaH···2(HCF(3)) and NaH···2(HCCl(3)). At last, theoretical calculations and QTAIM molecular integrations were used to study a novel class of dihydrogen-bonded complexes (mC(2)H(5)(+)···nMgH(2) with m = 1 or 2 and n = 1 or 2) based in the insight that MgH(2) can bind with the non-localized hydrogen H(+?) of the ethyl cation (C(2)H(5)(+)). In an overview, QTAIM calculations were applied to evaluate the molecular topography, charge density, as well as to interpret the shifted frequencies either to red or blue caused by the formation of the hydrogen bonds and dihydrogen bonds. PMID:23138158

de Oliveira, Boaz Galdino

2013-01-01

378

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

PubMed

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

Cao, Zheng; Bowie, James U

2014-05-01

379

Determination of carbide, carbyne, and carbene bond energies by gas-phase photodissociation of RhCH/sub 2//sup +/, NbCH/sub 2//sup +/, and LaCH/sub 2//sup +/  

SciTech Connect

Three photoproducts, MCH/sup +/, MC/sup +/, and M/sup +/ are observed in the photodissociation of MCH/sub 2//sup +/ (M = Rh, Nb, and La). In contrast, the low-energy collision-induced dissociation of RhCH/sub 2//sup +/ and NbCH/sub 2//sup +/ yields MC/sup +/ and M/sup +/ whereas LaCH/sub 2//sup +/ produces only La/sup +/. Each photodissociation spectrum reveals two peaks: 240 nm (sigma = 0.06 A/sup 2/) and 280 nm for RhCH/sub 2//sup +/, 240 nm (sigma = 0.20 A/sup 2/) and 390 nm for NbCH/sub 2//sup +/, and 260 nm (sigma = 0.19 A/sup 2/) and 320 nm for LaCH/sub 2//sup +/. Photoappearance thresholds for the products yield bond energies for M/sup +/-CH/sub 2/, M/sup +/-CH, and m/sup +/-C for each metal ion. Ionization potentials for RhC, NbC, and LaC are calculated on the basis of D/sup 0/(M-C) and D/sup 0/(M/sup +/-C). Plots of metal-ion ligand bond energies vs. bond energies for corresponding carbon analogs show linear correlation and allow bond order predictions to be made for the metal complexes.

Hettich, R.L.; Freiser, B.S.

1987-06-10

380

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

381

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

PubMed

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

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

2013-04-01

382

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

383

Influence of nitrogroups positions in molecules of various classes of explosives on results of quantum-chemical calculation of dissociation energy  

Microsoft Academic Search

Results of quantum-chemical calculation of dissociation energies of nitrogroups in molecules of various classes of explosives such as aliphatic and aromatic nitrocompounds (C-NO2), aliphatic, heterocyclic (N-NO2) and aromatic (C-NO2, N-NO2) amines, nitrates of spirits (O-NO2) are presented. Molecules more than thirty explosives, from nitromethane to octogen and PETN are examined. Calculations were carried out with the use of the Gaussian

Vladimir Golubev

2005-01-01

384

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

385

Guided ion beam studies of the reactions of Cr{sub n}{sup +} (n=1{endash}18) with CO{sub 2}: Chromium cluster oxide bond energies  

SciTech Connect

The kinetic energy dependence of the reactions of Cr{sub n}{sup +} (n=1{endash}18) with CO{sub 2} are studied in a guided ion beam mass spectrometer. The primary product ions are Cr{sub n}O{sup +}, which then decompose by sequential loss of chromium atoms as the kinetic energy is increased. Simple collision-induced dissociation to form the Cr{sub n{minus}1}{sup +} product ions is also observed. Large cluster ions, n{ge}9, form the Cr{sub n}CO{sub 2}{sup +} adduct at low kinetic energies. For many cluster sizes, the cross section for the primary reaction, Cr{sub n}{sup +}+CO{sub 2}{r_arrow}Cr{sub n}O{sup +}+CO, exhibits an interesting bimodal energy behavior that is discussed in some detail. Cr{sub n}{sup +}{endash}O bond energies are measured and found to compare well with measurements obtained from guided ion beam studies of the Cr{sub n}{sup +}+O{sub 2} systems. The trends in this thermochemistry are discussed and compared to bulk phase oxidation values. {copyright} {ital 1998 American Institute of Physics.}

Griffin, J.B.; Armentrout, P.B. [Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States)] [Department of Chemistry, University of Utah, Salt Lake City, Utah 84112 (United States)

1998-05-01

386

Physical and chemical transformations of highly compressed carbon dioxide at bond energies.  

PubMed

Carbon dioxide exhibits a richness of high-pressure polymorphs with a great diversity in intermolecular interaction, chemical bonding, and crystal structures. It ranges from typical molecular solids to fully extended covalent solids with crystal structures similar to those of SiO2. These extended solids of carbon dioxide are fundamentally new materials exhibiting interesting optical nonlinearity, low compressibility and high energy density. Furthermore, the large disparity in chemical bonding between the extended network and molecular structures results in a broad metastability domain for these phases to room temperature and almost to ambient pressure and thereby offers enhanced opportunities for novel materials developments. Broadly speaking, these molecular-to-non-molecular transitions occur due to electron delocalization manifested as a rapid increase in electron kinetic energy at high density. The detailed mechanisms, however, are more complex with phase metastabilities, path-dependent phases and phase boundaries, and large lattice strains and structural distortions - all of which are controlled by well beyond thermodynamic constraints to chemical kinetics associated with the governing phases and transitions. As a result, the equilibrium phase boundary is difficult to locate precisely (experimentally or theoretically) and is often obscured by the presence of metastable phases (ordered or disordered). This paper will review the pressure-induced transformations observed in highly compressed carbon dioxide and present chemistry perspectives on those molecular-to-non-molecular transformations that can be applied to other low-Z molecular solids at Mbar pressures where the compression energy rivals the chemical bond energies. PMID:23615853

Yoo, Choong-Shik

2013-06-01

387

Quantum enhancement of vibrational predissociation near the dissociation threshold  

SciTech Connect

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.

Cote, R. [Physics Department, University of Connecticut, Storrs, Connecticut 06269-3046 (United States); Dashevskaya, E.I. [Department of Chemistry, Technion-Israel Institute of Technology, Haifa, 32000 (Israel); Nikitin, E.E. [Department of Chemistry, Technion-Israel Institute of Technology, Haifa, 32000 (Israel); Institut fuer Physikalische Chemie der Universitaet Goettingen, Tammannstrasse 6, D-37077 Goettingen (Germany); Troe, J. [Institut fuer Physikalische Chemie der Universitaet Goettingen, Tammannstrasse 6, D-37077 Goettingen (Germany)

2004-01-01

388

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

SciTech Connect

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

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