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1

Hydrocarbon bond dissociation energies  

SciTech Connect

The best available values for homolytic bond dissociation energies (BDEs) of various classes of neutral compounds are considered in this review. (BDEs in ionic species is a legitimate subject that is touched on briefly and could easily be included in a longer review. The same can be said for heterolytic BDEs, which are not reviewed as such, although some of the ionic thermochemical data discussed yield values for these processes.) The major emphasis is on hydrocarbons and their nitrogen, oxygen, sulfur, halogen, and silicon-containing derivations, but limited data for inorganic molecules are included. The focus is particularly on prototypical radicals whose heats of formation, formerly thought to be well in hand, have recently been called into serious question. The intent is to include all the major types of sigma bonds, if not all specific cases where known or estimatable heats of formation allow bond dissociation energies to be generated. This review attempts to acknowledge all the standard techniques for measuring BDEs in polyatomic molecules and to offer critical analysis of selected portions of the literature. This leaves values that the authors recommend as the most likely to be correct at the time of this writing. 246 references, 9 tables.

McMillen, D.F.; Golden, D.M.

1982-01-01

2

Bond dissociation energy of astrophysically important molecules.  

NASA Astrophysics Data System (ADS)

The bond dissociation energies for astrophysically important diatomic molecules have been estimated based on the derived relation DAB = DAB+32.058??, where DAB = (DAADBB)1/2, ?? represents Pauling electronegativity difference (?A-?B). Based on the formula suggested by Reddy et al. bond energies are estimated. These values are in reasonably good agreement with the available literature values. The bond energies estimated with the present relation give an error of 12.6%. The corresponding error associated with Pauling's equation is 37.2%.

Reddy, R. R.; Ahammed, Y. N.; Gopal, K. R.; Anjaneyulu, S.

1999-03-01

3

CH and NH bond dissociation energies of small aromatic hydrocarbons  

Microsoft Academic Search

A survey of computational methods was undertaken to calculate the homolytic bond dissociation energies (BDEs) of the C-H and N-H bonds in monocyclic aromatic molecules that are representative of the functionalities present in coal. These include six-membered rings (benzene, pyridine, pyridazine, pyrimidine, pyrazine) and five-membered rings (furan, thiophene, pyrrole, oxazole). By comparison of the calculated C-H BDEs with the available

Cynthia Barckholtz; Timothy A. Barckholtz; Christopher M. Hadad

1999-01-01

4

A C-C bonded phenoxyl radical dimer with a zero bond dissociation free energy.  

PubMed

The 2,6-di-tert-butyl-4-methoxyphenoxyl radical is shown to dimerize in solution and in the solid state. The X-ray crystal structure of the dimer, the first for a para-coupled phenoxyl radical, revealed a bond length of 1.6055(23) for the C4-C4a bond. This is significantly longer than typical C-C bonds. Solution equilibrium studies using both optical and IR spectroscopies showed that the Keq for dissociation is 1.3 0.2 M at 20 C, indicating a C-C bond dissociation free energy of -0.15 0.1 kcal mol(-1). Van't Hoff analysis gave an exceptionally small bond dissociation enthalpy (BDE) of 6.1 0.5 kcal mol(-1). To our knowledge, this is the smallest BDE measured for a C-C bond. This very weak bond shows a large deviation from the correlation of C-C bond lengths and strengths, but the computed force constant follows Badger's rule. PMID:23952108

Wittman, Jessica M; Hayoun, Rebecca; Kaminsky, Werner; Coggins, Michael K; Mayer, James M

2013-08-23

5

Bond dissociation energies in second-row compounds.  

PubMed

Heats of formation at 0 and 298 K are predicted for PF3, PF5, PF3O, SF2, SF4, SF6, SF2O, SF2O2, and SF4O 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 SF6 molecule to give the unstable SF5 radical is 2.8 times the BDE needed for the removal of one fluorine ligand from the unstable SF5 radical to give the stable closed-shell SF4 molecule. Similarly, the BDE for the removal of one fluorine ligand from the stable closed-shell PF3O molecule to give the unstable PF2O radical is higher than the BDE needed to remove the oxygen atom to give the stable closed-shell PF3 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. PMID:18351757

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

2008-03-20

6

Splitting multiple bonds: A comparison of methodologies on the accuracy of bond dissociation energies.  

PubMed

A benchmarking of different quantum chemical methodologies for the splitting of multiply bonded systems is presented, with an emphasis on quantitative reproduction of experimentally determined dissociation energies. New benchmark full configuration interaction (FCI) calculations are presented for nitrogen and acetylene, and comparisons are made between various methods with both the FCI results and with experiment in an effort to understand qualitatively and quantitatively how well these different methods cope with the bond-breaking process. It is found that the multireference methods fare well, but are sometimes slowly convergent with respect to the size of the basis set, and in particular the angular momenta of the polarization functions. Single-reference (SR) wavefunction-based methods perform poorly against full CI, while CCSD(T) is reasonably accurate for comparison with experiment. Density functional theory with hybrid functionals have very quick basis-set convergence, and offer reliable estimates of bond dissociation energies. Spin-restricted SR wavefunctions are found to be poor for such systems, while unrestricted wavefunctions give reasonably good energies, but with severe spin contamination. 2013 Wiley Periodicals, Inc. PMID:24037810

Robinson, David

2013-09-13

7

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

8

Bond dissociation energy of the phenol O sbnd H bond from ab initio calculations  

NASA Astrophysics Data System (ADS)

The phenol O sbnd H bond dissociation energy (BDE) is currently disputed, despite its importance in combustion chemistry and in the reactions of antioxidants such as vitamin E. We have studied this BDE using the computational methods G3, G3B3 and CBS-APNO, with bond-isodesmic work reactions. These calculations yield a BDE of 89.0 1.0 kcal mol -1, which supports other recent calculations [B.J. Costa Cabral, S. Canuto, Chem. Phys. Lett. 406 (2005) 300]. From our BDE we determine the enthalpy of formation of the phenoxy radical to be 13.9 1.0 kcal mol -1. Comparison of the phenol C sbnd H BDE with the vinyl alcohol H sbnd CH dbnd CHOH BDE reveals the bond in phenol to be around 3 kcal mol -1 stronger than that in vinyl alcohol. Replacement of a H atom with the OH group on benzene or ethylene strengthens the C sbnd H bonds on adjacent carbons by 3 to 4 kcal mol -1.

da Silva, Gabriel; Chen, Chiung-Chu; Bozzelli, Joseph W.

2006-06-01

9

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

Microsoft Academic Search

The equilibrium acidities (pKAHs) and the oxidation potentials of the conjugate anions (Eox(A?)s) were determined in dimethyl sulfoxide (DMSO) for eight ketones of the structure GCOCH3 and twenty of the structure RCOCH2G, (where R= alkyl, phenyl and G= alkyl, aryl). The homolytic bond dissociation energies (BDEs) for the acidic C H bonds of the ketones were estimated using the equation,

Mikhail S. Alnajjar; Xian-Man Zhang; Gerald J. Gleicher; Scott V. Truksa; James A. Franz

2002-01-01

10

Prediction of RH Homolytic Bond Dissociation Energies from Gas-Phase IR Data on ?CH Values  

Microsoft Academic Search

The main goal of this work is the application of ?CH IR frequencies of gaseous R-H molecules to thermochemistry of carbon-centered Rfree radicals. For the first time the variable ??CH (in R-H molecules) per 1 kcal mol -1 in bond dissociation energies are suggested: 9 cm -1 for alkanes, 11 cm -1 for C-H bond in alkenes, 12 cm -1

Aleksander Golovin; Dmitry Ponomarev; Viatcheslav Takhistov

2004-01-01

11

Designing new free-radical reducing reagents: Theoretical study on SiH bond dissociation energies of organic silanes  

Microsoft Academic Search

Bond dissociation energies of a series of substituted silanes were studied with the density functional theory methods. The performances of six different density functional methods including B3LYP, B3P86, BH&HLYP, B1LYP, PBE1KCIS, and TPSSLYP1W were examined for the prediction of SiH bond dissociation energies. The results showed that B3P86 was the most accurate theoretical procedure among these six DFT methods. Using

Hua-Jing Wang; Yao Fu

2009-01-01

12

Evaluation of NH bond dissociation energies in some amides using ab initio and density functional methods  

Microsoft Academic Search

The performance of ab initio and DFT methods in the evaluation of NH bond dissociation energies of formamide, N-methyl formamide, urea, and acetamide molecules has been analyzed. Both restricted and unrestricted HF and MP2 fail to provide reliable results because of unreliable spin localization of the radical. The composite methods G3, G2MP2, and CBS-Q, however, provide fairly accurate bond dissociation

D. Kaur; Rupinder Preet Kaur

2005-01-01

13

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

NASA Astrophysics Data System (ADS)

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

Zeng, Hui; Zhao, Jun; Xiao, Xun

2013-02-01

14

The C-H bond dissociation energy of furan: Photoelectron spectroscopy of the furanide anion  

NASA Astrophysics Data System (ADS)

Using photoelectron spectroscopy, we interrogate the cyclic furanide anion (C4H3O-) to determine the electron affinity and vibrational structure of the neutral furanyl radical and the term energy of its first excited electronic state. We present the 364-nm photoelectron spectrum of the furanide anion and measure the electron affinity of the X~2A' ground state of the ?-furanyl radical to be 1.853(4) eV. A Franck-Condon analysis of the well-resolved spectrum allows determination of the harmonic frequencies of three of the most active vibrational modes upon X~2A' <-- X~1A' photodetachment: 855(25), 1064(25), and 1307(40) cm-1. These modes are ring deformation vibrations, consistent with the intuitive picture of furanide anion photodetachment, where the excess electron is strongly localized on the ?-carbon atom. In addition, the A~2A'' excited state of the ?-furanyl radical is observed 0.68(7) eV higher in energy than the X~2A' ground state. Through a thermochemical cycle involving the known gas-phase acidity of furan, the electron affinity of the furanyl radical yields the first experimental determination of the C-H? bond dissociation energy of furan (DH298(C4H3O-H?)): 119.8(2) kcal mol-1.

Vogelhuber, Kristen M.; Wren, Scott W.; Sheps, Leonid; Lineberger, W. Carl

2011-02-01

15

Determination of bond dissociation energies by threshold ion-pair production spectroscopy: An improved D0(HCl)  

Microsoft Academic Search

A recently developed form of threshold ionization spectroscopy has been used to determine the bond energy for HCl to spectroscopic accuracy (0.8 cm?1). This method is based on excitation to highly vibrationally excited ion-pair states using single-photon transitions from the ground state of HCl. These metastable Rydberg-like states were selectively detected using electricfield induced dissociation. By systematically varying the electric

J. D. D. Martin; J. W. Hepburn

1998-01-01

16

Determination of bond dissociation energies by threshold ion-pair production spectroscopy: An improved D0(HCl)  

Microsoft Academic Search

A recently developed form of threshold ionization spectroscopy has been used to determine the bond energy for HCl to spectroscopic accuracy (+\\/-0.8 cm-1). This method is based on excitation to highly vibrationally excited ion-pair states using single-photon transitions from the ground state of HCl. These metastable Rydberg-like states were selectively detected using electricfield induced dissociation. By systematically varying the electric

J. D. D. Martin; J. W. Hepburn

1998-01-01

17

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

SciTech Connect

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

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

2004-07-19

18

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

PubMed Central

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

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

2009-01-01

19

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

NASA Astrophysics Data System (ADS)

The highest frequency hydrogen bond fundamental of formic acid dimer, ?24 (Bu), 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 Bu 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 D0 = 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.

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

2012-04-01

20

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

PubMed

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 kcalmol(-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 kcalmol(-1) to 0.15 and 0.18 kcalmol(-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 kcalmol(-1). This study shows that DFT-SOFM-RBFNN is an efficient and highly accurate method for Y-NO homolysis BDE. The method may be used as a tool to design new NO carrier molecules. PMID:22942689

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

2012-06-28

21

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 kcalmol?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 kcalmol?1 to 0.15 and 0.18 kcalmol?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 kcalmol?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

22

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)

1998-06-01

23

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

24

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

PubMed

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

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

2007-11-01

25

The CH bond dissociation enthalpies of haloethers and its correlation with the activation energies for hydrogen abstraction by OH radical: A DFT study  

Microsoft Academic Search

The CH bond dissociation enthalpies for 12 haloether molecules were computed from the results of density functional theory calculations using B3LYP exchange-correlation functional in conjunction with two basis sets, such as 6-311G(d,p) and 6-311++G(2d,p). The trend in reactivity towards hydrogen abstraction by OH radical has been discussed in the light of the CH bond dissociation enthalpies. Good correlation has been

Asit K. Chandra; Tadafumi Uchimaru

2001-01-01

26

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

SciTech Connect

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

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

2010-08-26

27

Electron capture dissociation of the disulfide bond--a quantum chemical model study  

NASA Astrophysics Data System (ADS)

Four possible mechanism for ECD of disulfide bonds have been assessed using quantum chemical methods (B3LYP, G2, CASSCF and QCISD). For protonated peptides and proteins interacting with zero-energy electrons, the two most likely mechanisms appear to be either spontaneous dissociation of the S---S bond upon impact of a slowly moving free hydrogen or induced by uptake of a nascent hydrogen radical initially in close contact through a hydrogen bond.

Uggerud, Einar

2004-05-01

28

The energie of dissociation of Hg2  

Microsoft Academic Search

A new measurement of the energy of dissociation of Hg2 was made under conditions to avoid some possible errors in previous determinations. The value obtained was 00710,002 volts in agreement with previous measurements. It is pointed out that this is the dissociation energy for an average rotational energy about equal to the dissociation energy. The dissociation energy for a non

J. G. Winans; M. P. Heitz

1952-01-01

29

The energie of dissociation of Hg 2  

Microsoft Academic Search

A new measurement of the energy of dissociation of Hg2 was made under conditions to avoid some possible errors in previous determinations. The value obtained was 00710,002 volts in agreement with previous measurements. It is pointed out that this is the dissociation energy for an average rotational energy about equal to the dissociation energy. The dissociation energy for a non

J. G. Winans; M. P. Heitz

1952-01-01

30

Density functional theory and ab initio study of bond dissociation energy for peroxonitrous acid and peroxyacetyl nitrate  

Microsoft Academic Search

Geometries and energies of two nitro peroxides, HOONO2 and CH3COOONO2 are calculated by two common ab initio (ROHF and MP2), local (SVWN), four hybrid (BHandH, BHandHLYP, Becke3LYP, and Becke3P86) and two non-local (BLYP and BP86) density functional theory (DFT) methods. In all calculations standard GAUSSIAN-type basis sets [6-31+G(d) and 6-311++G(3df,3pd)] are used. Based on the comparison of computed and experimental

Branko S. Jursic

1996-01-01

31

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

SciTech Connect

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

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

1999-05-01

32

Reliability theory for receptor-ligand bond dissociation  

NASA Astrophysics Data System (ADS)

Cell adhesion in the presence of hydrodynamic forces is a critical factor in inflammation, cancer metastasis, and blood clotting. A number of assays have recently been developed to apply forces to small numbers of the receptor-ligand bonds responsible for adhesion. Examples include assays using hydrodynamic shear in flow chambers or elastic probe deflection assays such as the atomic force microscope or the biomembrane force probe. One wishes to use the data on the time distribution of dissociation from these assays to derive information on the force dependence of reaction rates, an important determinant of cell adhesive behavior. The dissociation process can be described using the theory developed for reliability engineering of electronic components and networks. We use this framework along with the Bell model for the reverse reaction rate (kr=kr0 exp[r0 f/kT], where f is the applied force and kr0 and r0 are Bell model parameters) to write closed form expressions for the probability distribution of break-up with multiple independent or interacting bonds. These expressions show that the average lifetime of n bonds scales with the nth harmonic number multiplied by the lifetime of a single bond. Results from calculation and simulations are used to describe the effect of experimental procedures in forced unbinding assays on the estimation of parameters for the force dependence of reverse reaction rates.

Tees, David F. J.; Woodward, John T.; Hammer, David A.

2001-05-01

33

Accurate O-H bond dissociation energy differences of hydroxylamines determined by EPR spectroscopy: computational insight into stereoelectronic effects on BDEs and EPR spectral parameters.  

PubMed

Differences in O-H bond dissociation enthalpies (?BDEs) between the hydroxylamine of (15)N-labeled TEMPONE and 10 N,N-di-tert-alkyl hydroxylamines were determined by EPR. These ?BDEs, together with the g and a(N) values of the derived nitroxide radicals, are discussed in relation to various geometric, intramolecular dipole/dipole, and steric effects and in relation to the results from DFT calculations. We find that dipole/dipole interactions are the dominant factors in dictating a(N) values and O-H BDEs in all of these structurally similar nitroxides and hydroxylamines, respectively. The importance of including the Boltzmann distribution of conformations for each nitroxide in the a(N) calculations is emphasized. PMID:21182264

Billone, Paul S; Johnson, Paul A; Lin, Shuqiong; Scaiano, J C; DiLabio, Gino A; Ingold, K U

2010-12-23

34

The Badger-Bauer Rule Revisited: Correlation of Proper Blue Frequency Shifts in the OC Hydrogen Acceptor with Morphed Hydrogen Bond Dissociation Energies in OC-HX (X = F, Cl, Br, I, CN, CCH).  

PubMed

Potential morphing has been applied to the investigation of proper blue frequency shifts, ??0 in CO, the hydrogen acceptor complexing in the hydrogen bonded series OC-HX (X= F, Cl, Br, I, CN, CCH). Linear correlations of morphed hydrogen bonded ground dissociation energies D0 with experimentally determined ??0 free from matrix and solvent effects demonstrate consistency with original tenets of the Badger-Bauer rule (J. Chem. Phys. 1937, 5, 839-51). A model is developed that provides a basis for explaining the observed linear correlations in the range of systems studied. Furthermore, the generated calibration curve enables prediction of dissociation energies for other related but different complexes. The latter include D0 for H2O-CO, H2S-CO, and CH3OH-CO which are predicted by interpolation and found to be 355(13), 171(11), and 377(14) cm(-1) respectively from available experimentally determined proton acceptor shifts. Results from this study will also be discussed in relation to investigations in which CO has been used as a probe of heme protein active sites. PMID:23895042

Rivera-Rivera, Luis A; McElmurry, Blake A; Scott, Kevin W; Lucchese, Robert R; Bevan, John W

2013-08-20

35

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

PubMed Central

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

Hutchins, Patrick M.; Murphy, Robert C.

2013-01-01

36

Peroxide bond driven dissociation of hydroperoxy-cholesterol esters following collision induced dissociation.  

PubMed

Oxidative modification of polyunsaturated fatty acids, which occurs through enzymatic and nonenzymatic processes, is typically initiated by the attachment of molecular oxygen to an unsaturated fatty acyl chain forming a lipid hydroperoxide (LOOH). Enzymatic pathways are critical for cellular homeostasis but aberrant lipid peroxidation has been implicated in important pathologies. Analysis of primary oxidation products such as hydroperoxides has proven to be challenging for a variety of reasons. While negative ion electrospray ionization has been used for the specific detection of some LOOH species, hydroperoxide dehydration in the ion source has been a significant drawback. Here we describe positive ion electrospray ionization of ammoniated 13-hydroperoxy-9Z, 11E-octadecadienoyl cholesterol and 9-hydroperoxy-10E, 12Z-octadecadienoyl cholesterol, [M + NH(4)](+), following normal phase high-pressure liquid-chromatography. Dehydration in the ion source was not prevalent and the ammoniated molecular ion was the major species observed. Collisionally induced dissociation of the two positional isomers yielded unique product ion spectra resulting from carbon-carbon cleavages along their acyl chains. Further investigation of this behavior revealed that complex collision induced dissociations were initiated by scission of the hydroperoxide bond that drove subsequent acyl chain cleavages. Interestingly, some of the product ions retained the ammonium nitrogen through the formation of covalent carbon-nitrogen or oxygen-nitrogen bonds. These studies were carried out using hydroperoxy-octadecadienoate cholesteryl esters as model compounds, however the observed mechanisms of [LOOH + NH(4)](+) ionization and dissociation are likely applicable to the analysis of other lipid hydroperoxides and may serve as the basis for selective LOOH detection as well as aid in the identification of unknown lipid hydroperoxides. PMID:21472521

Hutchins, Patrick M; Murphy, Robert C

2011-03-26

37

Formation, structure and bond dissociation thresholds of gas-phase vanadium oxide cluster ions  

NASA Astrophysics Data System (ADS)

The formation and structure of gas-phase vanadium oxide cluster anions are examined using a guided ion beam mass spectrometer coupled with a laser vaporization source. The dominant peaks in the anion total mass distribution correspond to clusters having stoichiometries of the form (VO2)n(VO3)m(O2)q-. Collision-induced dissociation studies of the vanadium oxide species V2O4-6-, V3O6-9-, V4O8-10-, V5O11-13-, V6O13-15-, and V7O16-18- indicate that VO2, VO3, and V2O5 units are the main building blocks of these clusters. There are many similarities between the anion mass distribution and that of the cation distribution studied previously. The principal difference is a shift to higher oxygen content by one additional oxygen atom for the stoichiometric anions (VxOy-) as compared to the cations with the same number of vanadium atoms, which is attributed to the extra pair of electrons of the anionic species. The oxygen-rich clusters, VxOy(O2)-, are shown to more tightly adsorb molecular oxygen than those of the corresponding cationic clusters. In addition, the bond dissociation thresholds for the vanadium oxide clusters ?E(V+-O)=6.09+/-0.28 eV, ?E(OV+-O)=3.51+/-0.36 eV, and ?E(O2V--O)=5.43+/-0.31 eV are determined from the energy-dependent collision-induced dissociation cross sections with Xe as the collision partner. To the best of our knowledge, this is the first bond dissociation energy reported for the breaking of the V-O bond of a vanadium oxide anion.

Bell, R. C.; Zemski, K. A.; Justes, D. R.; Castleman, A. W.

2001-01-01

38

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

39

The nature of electron correlation in a dissociating bond  

NASA Astrophysics Data System (ADS)

We have constructed the unrestricted Hartree-Fock (UHF), restricted Hartree-Fock (RHF), and full configuration interaction (FCI) position and momentum intracules and holes for H...H at bond lengths R from 1 to 10 bohrs. We trace the recently discovered inversion of the UHF position hole at intermediate R to over-localization of the spin-orbitals, and support this by a correlation energy component analysis. The RHF and UHF momentum holes are found to be more complicated; however their features are explained through decomposition of electron correlation effects. The UHF momentum hole is also found to invert and exhibits interesting behavior at large R. The RHF (but not UHF) and FCI momentum intracules exhibit Young-type interference patterns related to recent double photoionization experiments. Our analyses yield the most comprehensive picture to date of the behavior of the electrons during homolytic bond fission.

Hollett, Joshua W.; McKemmish, Laura K.; Gill, Peter M. W.

2011-06-01

40

The nature of electron correlation in a dissociating bond.  

PubMed

We have constructed the unrestricted Hartree-Fock (UHF), restricted Hartree-Fock (RHF), and full configuration interaction (FCI) position and momentum intracules and holes for HH at bond lengths R from 1 to 10 bohrs. We trace the recently discovered inversion of the UHF position hole at intermediate R to over-localization of the spin-orbitals, and support this by a correlation energy component analysis. The RHF and UHF momentum holes are found to be more complicated; however their features are explained through decomposition of electron correlation effects. The UHF momentum hole is also found to invert and exhibits interesting behavior at large R. The RHF (but not UHF) and FCI momentum intracules exhibit Young-type interference patterns related to recent double photoionization experiments. Our analyses yield the most comprehensive picture to date of the behavior of the electrons during homolytic bond fission. PMID:21682503

Hollett, Joshua W; McKemmish, Laura K; Gill, Peter M W

2011-06-14

41

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

PubMed

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

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

2004-09-01

42

Reconfiguration and dissociation of bonded hydrogen in silicon by energetic ions  

NASA Astrophysics Data System (ADS)

We report in situ infrared measurements of ion-induced reconfiguration and dissociation of bonded hydrogen associated with various defects in silicon at low temperatures. Defect-associated Si-H complexes were prepared by low-temperature proton implantation in silicon followed by room-temperature annealing. As a result of subsequent low-temperature He3 ion irradiation, we observed (1) ion-induced dissociation of Si-H complexes, (2) a notable difference in the dissociation rate of interstitial- and vacancy-type defects, and, unexpectedly, (3) the growth of bond-centered hydrogen, which is generally observed in association with low-temperature proton implantation. These findings provide insight into the mechanisms responsible for the dissociation of hydrogen bonds in silicon and thus have important implications for bond-selective nanoscale engineering and the long-term reliability of state-of-the-art silicon semiconductor and photovoltaic devices.

Nageswara Rao, S. V. S.; Dixit, S. K.; Lpke, G.; Tolk, N. H.; Feldman, L. C.

2011-01-01

43

Reconfiguration and dissociation of bonded hydrogen in silicon by energetic ions  

SciTech Connect

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

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

2011-01-15

44

Chemically distinct transition states govern rapid dissociation of single L-selectin bonds under force  

PubMed Central

Carbohydrateprotein bonds interrupt the rapid flow of leukocytes in the circulation by initiation of rolling and tethering at vessel walls. The cell surface carbohydrate ligands are glycosylated proteins like the mucin P-selectin glycoprotein ligand-1 (PSGL-1), which bind ubiquitously to the family of E-, P-, and L-selectin proteins in membranes of leukocytes and endothelium. The current view is that carbohydrateselectin bonds dissociate a few times per second, and the unbinding rate increases weakly with force. However, such studies have provided little insight into how numerous hydrogen bonds, a Ca2+ metal ion bond, and other interactions contribute to the mechanical strength of these attachments. Decorating a force probe with very dilute ligands and controlling touch to achieve rare single-bond events, we have varied the unbinding rates of carbohydrateselectin bonds by detachment with ramps of force/time from 10 to 100,000 pN/sec. Testing PSGL-1, its outer 19 aa (19FT), and sialyl LewisX (sLeX) against L-selectin in vitro on glass microspheres and in situ on neutrophils, we found that the unbinding rates followed the same dependence on force and increased by nearly 1,000-fold as rupture forces rose from a few to ?200 pN. Plotted on a logarithmic scale of loading rate, the rupture forces reveal two prominent energy barriers along the unbinding pathway. Strengths above 75 pN arise from rapid detachment (<0.01 sec) impeded by an inner barrier that requires a Ca2+ bond between a single sLeX and the lectin domain. Strengths below 75 pN occur under slow detachment (>0.01 sec) impeded by the outer barrier, which appears to involve an array of weak (putatively hydrogen) bonds.

Evans, Evan; Leung, Andrew; Hammer, Dan; Simon, Scott

2001-01-01

45

Structure, energetics, and dissociation of Si-H bonds at dangling bonds in silicon  

Microsoft Academic Search

We investigate the interaction of hydrogen with dangling bonds in bulk silicon, using first-principles pseudopotential-density-functional calculations. Two geometries are employed: the first is that of a hydrogenated vacancy; the second geometry allows investigation of an isolated dangling bond and minimizes any H-H interactions. The effect of H-H repulsion is quantified. We find that the energy required to remove the hydrogen

Chris G. van de Walle

1994-01-01

46

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

PubMed

The ionization energy (IE) of CoC and the 0 K bond dissociation energies (D0) and the heats of formation at 0 K (?Hf0) and 298 K (?Hf298) for CoC and CoC(+) are predicted by the wavefunction based coupled-cluster theory with single, double, triple and quadruple excitations (CCSDTQ) and complete basis set (CBS) approach. The CCSDTQ?CBS calculations presented here involve the approximation to the CBS limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy, high-order correlation, core-valence (CV) electronic, spin-orbit coupling, and scalar relativistic effect corrections. The present calculations provide the correct symmetry, (1)?(+), for the ground state of CoC(+). The CCSDTQ?CBS IE(CoC) = 7.740 eV is found in good agreement with the experimental IE value of 7.73467 0.00007 eV, determined in a two-color laser photoion and pulsed field ionization-photoelectron study. This work together with the previous experimental and theoretical investigations support the conclusion that the CCSDTQ?CBS method is capable of providing reliable IE predictions for 3d-transition metal carbides, such as FeC, CoC, and NiC. Among the single-reference based coupled-cluster methods and multi-reference configuration interaction (MRCI) approach, the CCSDTQ and MRCI methods give the best predictions to the harmonic frequencies ?e (?e (+)) = 956 (992) and 976 (1004) cm(-1) and the bond lengths re (re (+)) = 1.560 (1.528) and 1.550 (1.522) A?, respectively, for CoC (CoC(+)) in comparison with the experimental values. The CCSDTQ?CBS calculations give the prediction of D0(Co(+)-C) - D0(Co-C) = 0.175 eV, which is also consistent with the experimental determination of 0.14630 0.00014 eV. The theoretical results show that the CV and valence-valence electronic correlations beyond CCSD(T) wavefunction and the relativistic effect make significant contributions to the calculated thermochemical properties of CoC?CoC(+). For the experimental D0 and ?H(o) f0 values of CoC?CoC(+), which are not known experimentally, we recommend the following CCSDTQ?CBS predictions: ?H(o) f0(CoC) = 775.7 kJ?mol and ?H(o) f0(CoC(+)) = 1522.5 kJ?mol, ?H(o) f298(CoC) = 779.2 kJ?mol and ?H(o) 298(CoC(+)) = 1526.0 kJ?mol. PMID:23485289

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

2013-03-01

47

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

ERIC Educational Resources Information Center

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

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

2008-01-01

48

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

PubMed

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

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

2009-12-31

49

Low energy electron induced dissociation in condensed diallyl disulfide  

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

50

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

51

Competitive bond rupture in the photodissociation of bromoacetyl chloride and 2- and 3-bromopropionyl chloride: adiabatic versus diabatic dissociation.  

PubMed

Competitive bond dissociation mechanisms for bromoacetyl chloride and 2- and 3-bromopropionyl chloride following the (1) [n(O)??*(C=O)] transition at 234-235 nm are investigated. Branching ratios for C?Br/C?Cl bond fission are found by using the (2+1) resonance-enhanced multiphoton ionization (REMPI) technique coupled with velocity ion imaging. The fragment branching ratios depend mainly on the dissociation pathways and the distances between the orbitals of Br and the C=O chromophore. C?Cl bond fission is anticipated to follow an adiabatic potential surface for a strong diabatic coupling between the n(O)?*(C=O) and np (Cl)?*(C?Cl) bands. In contrast, C?Br bond fission is subject to much weaker coupling between n(O)?*(C=O) and np (Br)?*(C?Br). Thus, a diabatic pathway is preferred for bromoacetyl chloride and 2-bromopropionyl chloride, which leads to excited-state products. For 3-bromopropionyl chloride, the available energy is not high enough to reach the excited-state products such that C?Br bond fission must proceed through an adiabatic pathway with severe suppression by nonadiabatic coupling. The fragment translational energies and anisotropy parameters for the three molecules are also analyzed and appropriately interpreted. PMID:23400968

Hsu, Ming-Yi; Tsai, Po-Yu; Wei, Zheng-Rong; Chao, Meng-Hsuan; Zhang, Bing; Kasai, Toshio; Lin, King-Chuen

2013-02-10

52

Carbonhydrogen bond dissociation enthalpies in ethers: a theoretical study  

Microsoft Academic Search

Density functional theory calculations based on different representations of the exchange-correlation functional (BLYP, B3LYP, B3PW91, mPW1PW91, B1LYP, BHandHLYP, BHandH, and B3P86) were carried out to predict CH bond dissociation enthalpies in selected ethers (dimethyl ether, tetrahydrofuran (thf), and 1,4-dioxane), and some related molecules. Comparison with available experimental information shows that bond dissociation enthalpies are accurately predicted by several functionals when

Filipe Agapito; Benedito J. Costa Cabral; Jos A. Martinho Simes

2005-01-01

53

Effect of loading conditions on the dissociation behaviour of catch bond clusters  

PubMed Central

Under increasing tensile load, the lifetime of a single catch bond counterintuitively increases up to a maximum and then decreases exponentially like a slip bond. So far, the characteristics of single catch bond dissociation have been extensively studied. However, it remains unclear how a cluster of catch bonds behaves under tensile load. We perform computational analysis on the following models to examine the characteristics of clustered catch bonds: (i) clusters of catch bonds with equal load sharing, (ii) clusters of catch bonds with linear load sharing, and (iii) clusters of catch bonds in micropipette-manipulated cell detachment. We focus on the differences between the slip and catch bond clusters, identifying the critical factors for exhibiting the characteristics of catch bond mechanism for the multiple-bond system. Our computation reveals that for a multiple-bond cluster, the catch bond behaviour could only manifest itself under relatively uniform loading conditions and at certain stages of decohesion, explaining the difficulties in observing the catch bond mechanism under real biological conditions.

Sun, L.; Cheng, Q. H.; Gao, H. J.; Zhang, Y. W.

2012-01-01

54

Early stages of water/hydroxyl phase generation at transition metal surfaces--synergetic adsorption and O-H bond dissociation assistance.  

PubMed

The dissociation of water is a key elementary step in many processes. From density functional theory, we show on several transition metal surfaces (Ru, Co, Rh, Ir, Ni, Pd and Pt) that water prefers to chemisorb as a H-bonded dimer, one molecule being chemisorbed by the O atom, but the second one developing only a weak interaction with the surface. Counterintuitively, the molecule in the dimer that shows the smallest activation energy for O-H dissociation is the one interacting weakly with the surface. The H-bonded dimer provides a clear synergy for its chemisorption and assists the dissociation of the H-bond acceptor water molecule. Two different classes of O-H activation pathways are clearly identified with a linear activation energy-reaction energy relationship, of Brnstedt-Evans-Polanyi type. PMID:23052096

Michel, Carine; Gltl, Florian; Sautet, Philippe

2012-10-10

55

Probing hydrogen bond energies by mass spectrometry.  

PubMed

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

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

2013-04-12

56

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

PubMed Central

We have studied the principles that govern the formation and dissociation of an adhesive bond between a cell moving in shear flow and a substrate and tested different theories of how force affects bond dissociation. Viscosity relates the kinematics of fluid movement (shear rate, units of time?1) to shear stress (units of force/area, the product of shear rate and viscosity). At different medium viscosities, the formation of receptorligand bonds between a cell in the flowstream and P-selectin on the vessel wall showed a similar efficiency as a function of shear rate but not of shear stress. Therefore, bond formation was a function of shear rate and hence of the kinematics of receptor and ligand movement. By contrast, the kinetics of bond dissociation was a function of shear stress and hence of force on the bond. The different requirements for bond formation and dissociation allowed dissociation kinetics to be measured at higher forces on the bond by increasing medium viscosity. Data over an extended range of forces on the bond therefore could be collected that enabled five different proposed equations, relating force to bond dissociation, to be compared for fit to experimental data. The relationship proposed by Bell [Bell, G. I. (1978) Science 200, 618627] fit the data significantly the best and also predicted an off-rate in the absence of force that best matched an independent measurement [Mehta, P., Cummings, R. D. & McEver, R. P. (1998) J. Biol. Chem. 273, 3250632513].

Chen, Shuqi; Springer, Timothy A.

2001-01-01

57

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 152 eV, and the irradiated ions further dissociated into SF3+ at 502 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

58

Preferential cleavage of SS and CS bonds in electron detachment dissociation and infrared multiphoton dissociation of disulfide-linked peptide anions  

NASA Astrophysics Data System (ADS)

Disulfide bonds generally show only limited cleavage in positive ion mode collision activated dissociation (CAD). However, it has been demonstrated that a reverse situation exists in negative ion mode in which preferential SS and CS bond cleavage occurs. Here, we show that electron detachment dissociation (EDD) and infrared multiphoton dissociation (IRMPD) of peptide anions containing disulfide linkages also result in preferential cleavage of SS and CS bonds. Resulting products are mainly radical ions in EDD whereas IRMPD produces even-electron product ions, as expected, thereby supporting different disulfide cleavage mechanisms for these two fragmentation processes. We also show that, in EDD, the presence of tryptophan can result in abundant side chain loss (129 Da), which effectively can compete with disulfide bond cleavage.

Kalli, Anastasia; Hkansson, Kristina

2007-05-01

59

Femtosecond real time dynamics of hydrogen bond dissociation in photoexcited adeninewater clusters  

Microsoft Academic Search

Direct dissociation of hydrogen bonds in photoexcited adeninewater clusters was observed in real time by femtosecond pumpprobe transient ionization time-of-flight mass spectrometry. When hydrated clusters of adenine were excited by femtosecond laser pulse at 262 nm, they lost all of the solvent molecules in ca. 200 fs, regardless of the number of the water molecules attached. It is suggested that

Hyuk Kang; Kang Taek Lee; Seong Keun Kim

2002-01-01

60

Pressure-Induced Molecular Dissociation and Metallization in Hydrogen-Bonded H2S Solid  

Microsoft Academic Search

Infrared spectra at high pressure and room temperature reveal that molecular dissociation and metallization occur in solid H2S near 46 and 96 GPa, respectively. The disappearance of SH stretching bands in the 2300-2500 cm-1 region and simultaneous appearance of a lattice vibrational mode around 1300 cm-1 signal the molecular dissociation. At higher pressures, a low-energy electronic absorption band develops and

M. Sakashita; H. Yamawaki; H. Fujihisa; K. Aoki; S. Sasaki; H. Shimizu

1997-01-01

61

The Significance of Chemical Bond Energies  

Microsoft Academic Search

In view of recently reported departures from bond additivity of chemical energies of formation, a purely empirical study has been made of the significance of chemical bond energies. If one assumes that the energy of formation is made up of bond energies and interaction energies between the bonds as well, it is shown that both of these two types of

C. T. Zahn

1934-01-01

62

Bond energy analysis revisited and designed toward a rigorous methodology  

NASA Astrophysics Data System (ADS)

The present study theoretically revisits and numerically assesses two-body energy decomposition schemes including a newly proposed one. The new decomposition scheme is designed to make the equilibrium bond distance equivalent with the minimum point of bond energies. Although the other decomposition schemes generally predict the wrong order of the C-C bond strengths of C2H2, C2H4, and C2H6, the new decomposition scheme is capable of reproducing the C-C bond strengths. Numerical assessment on a training set of molecules demonstrates that the present scheme exhibits a stronger correlation with bond dissociation energies than the other decomposition schemes do, which suggests that the new decomposition scheme is a reliable and powerful analysis methodology.

Nakai, Hiromi; Ohashi, Hideaki; Imamura, Yutaka; Kikuchi, Yasuaki

2011-09-01

63

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-Labb, Alejandro; Clark, Tim; Politzer, Peter

2008-12-04

64

Dissociation energy of the ground state of NaH  

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

65

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

Microsoft Academic Search

Final product states of Ne2<\\/sub>+<\\/sup> 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<\\/i> metastable states to higher Rydbcrg

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

1998-01-01

66

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

NASA Astrophysics Data System (ADS)

Ions produced by crossed-beam collisions of pulsed monoenergetic electrons and supersonic expansion molecules have been analysed by time-of-flight mass spectroscopy (TOF-MS) in order to determine the appearance potentials, absolute total, dissociative and parent ionization cross sections and nascent ion kinetic energy distributions. The electron impact study was conducted at incident electron energies up to 100 eV on the parent CH2F2 molecule (and Ar/CH2F2 mixtures), a fluoromethane where the CH2F+ ion is produced at higher yields (1:18) than the parent molecule ion, CH2F2+. TOF-MS band profiles analysis has enabled us to determine the ions' nascent kinetic energy distributions, information that combined with the dissociative ionization appearance potentials, calculated molecular orbital energies and orbital bond characters, leads to improved identification of the electron impact dissociative channels.

Torres, I.; Martnez, R.; Snchez Rayo, M. N.; Castao, F.

2000-09-01

67

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

SciTech Connect

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

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

2011-01-01

68

Vibrational Population Depletion in Thermal Dissociation for Nonequilibrium Energy Distribution  

NASA Astrophysics Data System (ADS)

The generalized depletion equations, considering state-to-state kinetics of dissociating Nitrogen, are solved to predict the extent of vibrational depletion in the temperature range of 3000-10000 K. For the case of dissociation from the last vibrational quantum level, depletion of vibrational population is high. Vibration-translation (V-T) energy transfers make a major contribution to depletion whereas the effect of vibration-vibration (V-V) exchanges is minor. The dissociation rates predicted using the vibration-dissociation coupling model are significantly lower than the Park's rates and helps explain the restricted success of the Park's dissociation model in certain temperature ranges of hypersonic flow past a blunt body. Underprediction of shock-standoff distance of 17% by Park dissociation model for a Mach 11.18 flow past a blunt body is predicted well by the present model.

Josyula, Eswar; Bailey, William F.

2003-05-01

69

DIATOMIC MOLECULES OF ASTROPHYSICAL INTEREST: IONIZATION POTENTIALS AND DISSOCIATION ENERGIES  

Microsoft Academic Search

A critical analysis was made of the ionization potentials and ; dissociation energies of 148 diatomic molecules and molecular ions that have ; astrophysical significance. This summary provides useful data for the ; calculation of molecular abundances and for discussions of dissociation ; equllibria and ionization processes. It also points out the great need for ; further experimental and theoretical

P. G. Wilkinson

1963-01-01

70

Calculation of bond energies in diatomic molecules  

Microsoft Academic Search

An extrapolation method is proposed for an approximative evaluation of covalent bonding powers of some elements from their electronegativity values. Using these values in the bond energy equation, obtained from the principle of electronegativity equalization [3], bond energies can be calculated with an accuracy, comparable with the one, obtained by Evans and Huheey [1], who included an electrostatic attraction energy

G. VAN HOOYDONK

1971-01-01

71

Cleavage of Multiple Disulfide Bonds in Insulin via Gold Cationization and Collision-induced Dissociation  

PubMed Central

Intact bovine insulin, with its two chains linked via two disulfide linkages, has been used as a model system to study the incorporation of one or more gold cations as means for facilitating the cleavage of multiple disulfide bonds in a tandem mass spectrometry experiment. Gas-phase ion/ion reactions involving Au(I)Cl2? or Au(III)Cl4? were used to incorporate either one or two gold cations into multiply-protonated insulin cations, followed by ion trap collision-induced dissociation (CID) of the products. The incorporation of a single gold cation followed by CID showed little evidence for disulfide bond cleavage. Rather, the CID spectra were similar to those acquired for the same charge state with only excess protons present. However, the incorporation of two gold cations, regardless of oxidation state, resulted in efficient cleavage of the disulfide bonds connecting the two chains of insulin. Furthermore, ion trap CID of the insulin complexes containing two gold cations showed more sequence information compared to the complexes containing only one gold cation or no gold cations. The partitioning of the gold cations between the two chains upon CID proved to be largely asymmetric, as both gold cations tended to stay together. There appeared to be a slight preference for both gold cations to partition into the B-chain. However, the relatively low contribution from single chain ions with only one gold ion suggests a degree of cooperativity in the overall mechanism for separation of the two chains.

Mentinova, Marija; McLuckey, Scott A.

2011-01-01

72

Energy transport via coordination bonds  

NASA Astrophysics Data System (ADS)

Vibrational energy transport in transition metal complexes involves stages where energy crosses relatively weak coordination bonds between a coordinated metal atom and the ligands. Understanding the energy transport rules on a molecular level is fundamentally important; it is also essential in relation to a recently proposed structural method, the relaxation-assisted two-dimensional infrared (RA 2DIR) technique, where the vibrational population transport time across the molecule of interest is linked to the transport distance. In this study we report on the energy transport across coordination bonds in tetraethylammonium bis(maleonitriledithiolate)iron(III)nitrosyl complex, studied using dual-frequency RA 2DIR spectroscopy. Three mode pairs, C?N and N=O, N=O and C?N, and N=O and C-C, were interrogated. All three cross-peaks show substantial amplification due to vibrational energy transport from the initially excited mode toward the ``probed'' mode, including a record amplification of 27-fold observed for the C?N/N=O cross-peak. A ninefold amplification measured for the N=O/C?N cross-peak, where the ``probed'' CN mode has higher frequency than the initially excited NO, proves unequivocally that the excitation of the ``probed'' mode via energy transport is not essential for observing stronger cross-peaks and that lower frequency modes serve as the energy accepting modes. A simple modeling of the energy transport is presented highlighting the role of a spatial overlap of the interacting modes. The observed strong cross-peak amplifications and a correlation between the energy transport time and the intermode distance, the distance between atom pairs on which vibrational excitations predominantly reside, demonstrate an applicability of the RA 2DIR method for structural interrogation of transition metal complexes.

Kasyanenko, Valeriy M.; Lin, Zhiwei; Rubtsov, Grigory I.; Donahue, James P.; Rubtsov, Igor V.

2009-10-01

73

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

74

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

75

Defining the Disulfide Bonds of Insulin-like Growth Factor-binding Protein-5 by Tandem Mass Spectrometry with Electron Transfer Dissociation and Collision-induced Dissociation*  

PubMed Central

The six high-affinity insulin-like growth factor-binding proteins (IGFBPs) comprise a conserved family of secreted molecules that modulate IGF actions by regulating their half-life and access to signaling receptors, and also exert biological effects that are independent of IGF binding. IGFBPs are composed of cysteine-rich amino- (N-) and carboxyl- (C-) terminal domains, along with a cysteine-poor central linker segment. IGFBP-5 is the most conserved IGFBP, and contains 18 cysteines, but only 2 of 9 putative disulfide bonds have been mapped to date. Using a mass spectrometry (MS)-based strategy combining sequential electron transfer dissociation (ETD) and collision-induced dissociation (CID) steps, in which ETD fragmentation preferentially induces cleavage of disulfide bonds, and CID provides exact disulfide linkage assignments between liberated peptides, we now have definitively mapped 5 disulfide bonds in IGFBP-5. In addition, in conjunction with ab initio molecular modeling we are able to assign the other 4 disulfide linkages to within a GCGCCXXC motif that is conserved in five IGFBPs. Because of the nature of ETD fragmentation MS experiments were performed without chemical reduction of IGFBP-5. Our results not only establish a disulfide bond map of IGFBP-5 but also define a general approach that takes advantage of the specificity of ETD and the scalability of tandem MS, and the predictive power of ab initio molecular modeling to characterize unknown disulfide linkages in proteins.

Nili, Mahta; Mukherjee, Aditi; Shinde, Ujwal; David, Larry; Rotwein, Peter

2012-01-01

76

Competing dissociation of and bond formation between CH3CHOH+ and .CH2CH3 formed by bimolecular processes  

NASA Astrophysics Data System (ADS)

The C4H10O.+ potential energy surface was accessed at several energies through different ion/molecule reactions. Reaction of CH3CH.+3 with CH3CHO and CH3CHO.+ with CH3CH3 gave predominantly CH3CHOH+ +. CH2CH3 and small amounts of CH3CH2CHOH+ +. CH3. CH3CH.+3 also produced a small amount of CH3CHO+CH3 +. CH3 upon reaction with CH3CHO. CH2 = CHOH. + did not react with CH3CH3. CH3CH2OH. + reacted CH2 = CH2 and CH2 = CH.+2 with CH3CH2OH to produce CH3CH2OH+2 and CH3CHOH+, but only the second pair of reactants produced detectable C3H7O+ ions. CH3CH2CHO.++CH4 produced only CH3CH2CHOH+. In all of the reactions examined, initial proton or H-transfer was much more often followed by simple dissociation than by CC bond formation or multiple H-transfers. This contrasts with the metastable decompositions of ionized 2-butanol, in which elimination of ethane and methane through the complexes [CH3CHOH+.CH2CH3] and [CH3CH2CHOH+.CH3] are important processes. This contrast is attributed to the ion/molecule reactions taking place in a higher energy regime than the metastable decompositions.

Ahmed, Mohammed S.; Giam, C. S.; McAdoo, David J.

1994-01-01

77

Dissociation energy of the ground state of NaH  

SciTech Connect

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

Huang, Hsien-Yu; Lu, Tsai-Lien; Whang, Thou-Jen [Department of Chemistry, National Cheng-Kung University, Tainan 70101, Taiwan (China); Chang, Yung-Yung; Tsai, Chin-Chun [Department of Physics, National Cheng-Kung University, Tainan 70101, Taiwan (China)

2010-07-28

78

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

PubMed

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

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

2013-09-10

79

Solvation of copper ions by acetone. Structures and sequential binding energies of Cu + (acetone) x , x = 14 from collision-induced dissociation and theoretical studies  

Microsoft Academic Search

Collision-induced dissociation of Cu+(acetone)\\u000a x\\u000a , x = 14, with Xe is studied as a function of kinetic energy using guided ion beam mass spectrometry. In all cases, the primary\\u000a and lowest energy dissociation channel observed is endothermic loss of one acetone molecule. The primary cross section thresholds\\u000a are interpreted to yield 0 and 298 K bond energies after accounting

Y. Chu; Z. Yang; M. T. Rodgers

2002-01-01

80

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

Microsoft Academic Search

Disulfide bonds are a post-translational modification (PTM) that can be scrambled or shuffled to non-native bonds during recombinant\\u000a expression, sample handling, or sample purification. Currently, mapping of disulfide bonds is not easy because of various\\u000a sample requirements and data analysis difficulties. One step towards facilitating this difficult work is developing a better\\u000a understanding of how disulfide-bonded peptides fragment during collision

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

2011-01-01

81

Hydrogen bonding Part 67. Thermodynamic study of the dissociation of tri- i-pentylammonium chloride and bromide monohydrates  

Microsoft Academic Search

Tri-i-pentylammonium bromide and chloride form very stable, highly crystalline monohydrates which contain planar C2h (H2OX?)2 clusters in which two water molecules mutually bridge two halide ions. Each halide ion in turn accepts an N?H?? hydrogen bond from cation to give a dimeric unit in which each cluster is sandwiched between two large cations. The enthalpy of dissociation of these monohydrates

Kenneth M. Harmon; Stacee H. Gill; Julie A. Giera

1998-01-01

82

Ab initio study of the energy hypersurface of uneven sulfuranes. Dissociation of HCl from Cl-SH(OH)Cl  

Microsoft Academic Search

The MP2\\/6-311G(d) level of theory has been applied to answer the question of how the geometry and total energy changes with respect to lengthening of the S-Cl bond in Cl-SH(OH)-Cl. The results predict that the title compound would readily dissociate forming HCl and Cl-S(H)O. The dissociation energy is calculated at the G2(MP2) and CCSD(T)\\/6-311G(d) levels of theory with zero-point and

Gabor I. Csonka; Michel Loos; Arpad Kucsman; Imre G. Csizmadia

1994-01-01

83

Critical re-evaluation of the O-H bond dissociation enthalpy in phenol.  

PubMed

The gas-phase O-H bond dissociation enthalpy, BDE, in phenol provides an essential benchmark for calibrating the O-H BDEs of other phenols, data which aids our understanding of the reactivities of phenols, such as their relevant antioxidant activities. In a recent review, the O-H BDE for phenol was presented as 90 +/- 3 kcal mol(-1) (Acc. Chem. Res. 2003, 36, 255-263). Due to the large margin of error, such a parameter cannot be used for dynamic interpretations nor can it be used as an anchor point in the development of more advanced computational models. We have reevaluated the existing experimental gas-phase data (thermolyses and ion chemistry). The large errors and variations in thermodynamic parameters associated with the gas-phase ion chemistry methods produce inconsistent results, but the thermolytic data has afforded a value of 87.0 +/- 0.5 kcal mol(-1). Next, the effect of solvent has been carefully scrutinized in four liquid-phase methods for measuring the O-H BDE in phenol: photoacoustic calorimetry, one-electron potential measurements, an electrochemical cycle, and radical equilibrium electron paramagnetic resonance (REqEPR). The enthalpic effect due to solvation, by, e.g., water, could be rigorously accounted for by means of an empirical model and the difference in hydrogen bond interactions of the solvent with phenol and the phenoxyl radical. For the REqEPR method, a second correction is required since the calibration standard, the O-H BDE in 2,4,6-tri-tert-butylphenol, had to be revised. From the gas-phase thermolysis data and three liquid-phase techniques (excluding the electrochemical cycle method), the present analysis yields a gas-phase BDE of 86.7 +/- 0.7 kcal mol(-1). The O-H BDE was also estimated by state-of-the-art computational approaches (G3, CBS-APNO, and CBS-QB3) providing a range from 86.4 to 87.7 kcal mol(-1). We therefore recommend that in the future, and until further refinement is possible, the gas-phase O-H BDE in phenol should be presented as 86.7 +/- 0.7 kcal mol(-1). PMID:16833571

Mulder, Peter; Korth, Hans-Gert; Pratt, Derek A; DiLabio, Gino A; Valgimigli, Luca; Pedulli, G F; Ingold, K U

2005-03-24

84

Strength of Hydrogen Bond Network Takes Crucial Roles in the Dissociation Process of Inhibitors from the HIV-1 Protease Binding Pocket  

PubMed Central

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

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

2011-01-01

85

?? bond energy from the Nijmegen potentials  

NASA Astrophysics Data System (ADS)

The ?? bond energy ? B?? in ?? hypernuclei is obtained from a G -matrix calculation which includes the coupling between the ?? , ?N , and ?? channels, as well as the effect of Pauli blocking to all orders. The Nijmegen NSC97e model is used as bare baryon-baryon interaction in the strangeness S=-2 sector. The ?? - ?N coupling increases substantially the bond energy with respect to the uncoupled ?? case. However, the additional incorporation of the ?? channel, which couples simultaneously to ?? and ?N states, has a surprisingly drastic effect and reduces the bond energy down to a value closer to that obtained in an uncoupled calculation. We find that a complete treatment of Pauli blocking reduces the repulsive effect on the bond energy to about half of what was claimed before.

Vidaa, I.; Ramos, A.; Polls, A.

2004-08-01

86

Activation Energies for Dissociation of Double Strand Oligonucleotide Anions: Evidence for Watson-Crick Base Pairing in Vacuo  

PubMed Central

The dissociation kinetics of a series of complementary and noncomplementary DNA duplexes, (TGCA)23?, (CCGG)23?, (AATTAAT)23?, (CCGGCCG)23?, A7T73?, A7A73?, T7T73?, and A7C73? were investigated using blackbody infrared radiative dissociation in a Fourier transform mass spectrometer. From the temperature dependence of the unimolecular dissociation rate constants, Arrhenius activation parameters in the zero-pressure limit are obtained. Activation energies range from 1.2 to 1.7 eV, and preexponential factors range from 1013 to 1019 s?1. Dissociation of the duplexes results in cleavage of the noncovalent bonds and/or cleavage of covalent bonds leading to loss of a neutral nucleobase followed by backbone cleavage producing sequence-specific (a base) and w ions. Four pieces of evidence are presented which indicate that WatsonCrick (WC) base pairing is preserved in complementary DNA duplexes in the gas phase: i. the activation energy for dissociation of the complementary dimer, A7T73?, to the single strands is significantly higher than that for the related noncomplementary A7A73? and T7T73? dimers, indicating a stronger interaction between strands with a specific base sequence, ii. extensive loss of neutral adenine occurs for A7A73? and A7C73? but not for A7T73? consistent with this process being shut down by WC hydrogen bonding, iii. a correlation is observed between the measured activation energy for dissociation to single strands and the dimerization enthalpy (??Hd) in solution, and iv. molecular dynamics carried out at 300 and 400 K indicate that WC base pairing is preserved for A7T73? duplex, although the helical structure is essentially lost. In combination, these results provide strong evidence that WC base pairing can exist in the complete absence of solvent.

Schnier, Paul D.; Klassen, John S.; Strittmatter, Eric F.; Williams*, Evan R.

2005-01-01

87

A 'universal' B3LYP-based method for gas-phase molecular properties: bond dissociation enthalpy, ionization potential, electron and proton affinity and gas-phase acidity  

NASA Astrophysics Data System (ADS)

The paper describes a density functional theory methodology using the B3LYP functional, with small correction terms introduced for open shell doublet states and closed-shell anions. The procedure is based on a B3LYP/6-31G(d) geometry optimization and frequency determination, followed by (RO)B3LYP/6-311 + G(2d,2p) single point energy calculations. Using a correction term of +8.368 kJ mol-1 for (doublet) radicals and + 4.184 kJ mol-1 for (closed shell) anions, close agreement is obtained with experiment (i.e. within 10 kJ mol-1) for a series of molecular properties. These include bond dissociation enthalpies for X-H, where X = functional groups containing C, N, O, F, S, and X-Y, where X and Y are binary combinations of the same five heavy atoms plus Si and Cl, ionization potentials, electron and proton affinities, and gas-phase acidities. Using locally dense basis sets the approach can be extended to bond dissociation enthalpy calculations of large molecules with only a small increase in error. Using the same approach and popular solvation models allows a good starting point for reaction properties in solution. The approach is termed 'niversal' because by applying these corrections there is no need to change functionals and/or basis sets to obtain accurate results for different molecular properties, unlike some of the work reported previously.

Wright, J. S.; Rowley, C. N.; Chepelev, L. L.

88

The physical origin of large covalent-ionic resonance energies in some two-electron bonds.  

PubMed

This study uses valence bond (VB) theory to analyze in detail the previously established finding that alongside the two classical bond families of covalent and ionic bonds, which describe the electron-pair bond, there exists a distinct class of charge-shift bonds (CS-bonds) in which the fluctuation of the electron pair density plays a dominant role. Such bonds are characterized by weak binding, or even a repulsive, covalent component, and by a large covalent-ionic resonance energy RE(cs) that is responsible for the major part, or even for the totality, of the bonding energy. In the present work, the nature of CS-bonding and its fundamental mechanisms are analyzed in detail by means of a VB study of some typical homonuclear bonds (H-H, H3C-CH3, H2N-NH2, HO-OH, F-F, and Cl-Cl), ranging from classical-covalent to fully charge-shift bonds. It is shown that CS-bonding is characterized by a covalent dissociation curve with a shallow minimum situated at long interatomic distances, or even a fully repulsive covalent curve. As the atoms that are involved in the bond are taken from left to right or from bottom to top of the periodic table, the weakening effect of the adjacent bonds or lone pairs increases, while at the same time the reduced resonance integral, that couples the covalent and ionic forms, increases. As a consequence, the weakening of the covalent interaction is gradually compensated by a strengthening of CS-bonding. The large RE(cs) quantity of CS-bonds is shown to be an outcome of the mechanism necessary to establish equilibrium and optimum bonding during bond formation. It is shown that the shrinkage of the orbitals in the covalent structure lowers the potential energy, V, but excessively raises the kinetic energy, T, thereby tipping the virial ratio off-balance. Subsequent addition of the ionic structures lowers T while having a lesser effect on V, thus restoring the requisite virial ratio (T/-V = 1/2). Generalizing to typically classical covalent bonds, like H-H or C-C bonds, the mechanism by which the virial ratio is obeyed during bond formation is primarily orbital shrinkage, and therefore the charge-shift resonance energy has only a small corrective effect. On the other hand, for bonds bearing adjacent lone pairs and/or involving electronegative atoms, like F-F or Cl-Cl, the formation of the bond corresponds to a large increase of kinetic energy, which must be compensated for by a large participation or covalent-ionic mixing. PMID:17328432

Hiberty, Philippe C; Ramozzi, Romain; Song, Lingchun; Wu, Wei; Shaik, Sason

2007-01-01

89

Adhesive bonding using variable frequency microwave energy  

DOEpatents

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

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

1998-08-25

90

Adhesive bonding using variable frequency microwave energy  

DOEpatents

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

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

1998-09-08

91

Heats of Dissociation of Carbon-Hydrogen Bonds in Methane and Its Radicals  

Microsoft Academic Search

The evidence pertaining to the heat of sublimation of graphite is summarized, with the conclusion that the value of 170.6 kcal. per mole is the most probable. This figure is consistent with a value of 393 kcal. for the heat of removing the four hydrogen atoms from methane, the assignment of the heats of the successive dissociations being as follows:

K. J. Laidler; E. J. Casey

1949-01-01

92

Dissociation of N 2 triple bond: a reduced multireference CCSD study  

Microsoft Academic Search

The reduced multireference (RMR) coupled cluster method with singles and doubles is applied to the dissociation of the ground state of the nitrogen molecule. It is shown that even with a relatively modest highly truncated reference space one obtains an accurate potential over a wide range of internuclear separations.

Xiangzhu Li; Josef Paldus

1998-01-01

93

Evaluation of noncovalent interactions between peptides and polyether compounds via energy-variable collisionally activated dissociation  

Microsoft Academic Search

Energy-variable collisionally activated dissociation (CAD) was used to analyze noncovalent interactions of protonated peptide\\/polyether\\u000a complexes in a quadrupole ion trap complexes were formed with a series of four polyether host molecules and thirteen peptide\\u000a molecules. Comparison of dissociation thresholds revealed correlations between the gas-phase basicities of the peptides and\\u000a polyether molecules and the onset of dissociation. The dissociation thresholds of

Matthew C. Crowe; Jennifer S. Brodbelt

2003-01-01

94

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

95

Excitation and multiple dissociation of projectiles at intermediate energy  

SciTech Connect

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

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

1989-04-01

96

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

Microsoft Academic Search

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

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

2004-01-01

97

Bond Energies in Models of the Schrock Metathesis Catalyst  

SciTech Connect

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

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

2011-06-02

98

Formation, structure and bond dissociation thresholds of gas-phase vanadium oxide cluster ions  

Microsoft Academic Search

The formation and structure of gas-phase vanadium oxide cluster anions are examined using a guided ion beam mass spectrometer coupled with a laser vaporization source. The dominant peaks in the anion total mass distribution correspond to clusters having stoichiometries of the form (VO2)n(VO3)m(O2)q-. Collision-induced dissociation studies of the vanadium oxide species V2O4-6-, V3O6-9-, V4O8-10-, V5O11-13-, V6O13-15-, and V7O16-18- indicate that

R. C. Bell; K. A. Zemski; D. R. Justes; A. W. Castleman

2001-01-01

99

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

NASA Astrophysics Data System (ADS)

Optimal control theory is used to design a laser pulse for the multiphoton dissociation of the Fe-CO bond in the CO-heme compounds. The study uses a hexacoordinated iron-porphyrin-imidazole-CO complex in its ground electronic state as a model for CO liganded to the heme group. The potential energy and dipole moment surfaces for the interaction of the CO ligand with the heme group are calculated using density functional theory. Optimal control theory, combined with a time-dependent quantum dynamical treatment of the laser-molecule interaction, is then used to design a laser pulse capable of efficiently dissociating the CO-heme complex model. The genetic algorithm method is used within the mathematical framework of optimal control theory to perform the optimization process. This method provides good control over the parameters of the laser pulse, allowing optimized pulses with simple time and frequency structures to be designed. The dependence of photodissociation yield on the choice of initial vibrational state and of initial laser field parameters is also investigated. The current work uses a reduced dimensionality model in which only the Fe-C and C-O stretching coordinates are explicitly taken into account in the time-dependent quantum dynamical calculations. The limitations arising from this are discussed in Sec. IV.

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

2010-11-01

100

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

101

Effect of ring substitution on the S-H bond dissociation enthalpies of thiophenols. An experimental and computational study.  

PubMed

There are conflicting reports on the origin of the effect of Y substituents on the S-H bond dissociation enthalpies (BDEs) in 4-Y-substituted thiophenols, 4-YC(6)H(4)S-H. The differences in S-H BDEs, [4-YC(6)H(4)S-H] - [C(6)H(5)S-H], are known as the total (de)stabilization enthalpies, TSEs, where TSE = RSE - MSE, i.e., the radical (de)stabilization enthalpy minus the molecule (de)stabilization enthalpy. The effects of 4-Y substituents on the S-H BDEs in thiophenols and on the S-C BDEs in phenyl thioethers are expected to be almost identical. Some S-C TSEs were therefore derived from the rates of homolyses of a few 4-Y-substituted phenyl benzyl sulfides, 4-YC(6)H(4)S-CH(2)C(6)H(5), in the hydrogen donor solvent 9,10-dihydroanthracene. These TSEs were found to be -3.6 +/- 0.5 (Y = NH(2)), -1.8 +/- 0.5 (CH(3)O), 0 (H), and 0.7 +/- 0.5 (CN) kcal mol(-1). The MSEs of 4-YC(6)H(4)SCH(2)C(6)H(5) have also been derived from the results of combustion calorimetry, Calvet-drop calorimetry, and computational chemistry (B3LYP/6-311+G(d,p)). The MSEs of these thioethers were -0.6 +/- 1.1 (NH(2)), -0.4 +/- 1.1 (CH(3)O), 0 (H), -0.3 +/- 1.3 (CN), and -0.8 +/- 1.5 (COCH(3)) kcal mol(-1). Although all the enthalpic data are rather small, it is concluded that the TSEs in 4-YC(6)H(4)SH are largely governed by the RSEs, a somewhat surprising conclusion in view of the experimental fact that the unpaired electron in C(6)H(5)S(*) is mainly localized on the S. The TSEs, RSEs, and MSEs have also been computed for a much larger series of 4-YC(6)H(4)SH and 4-YC(6)H(4)SCH(3) compounds by using a B3P86 methology and have further confirmed that the S-H/S-CH(3) TSEs are dominated by the RSEs. Good linear correlations were obtained for TSE = rho(+)sigma(p)(+)(Y), with rho(+) (kcal mol(-1)) = 3.5 (S-H) and 3.9 (S-CH(3)). It is also concluded that the SH substituent is a rather strong electron donor with a sigma(p)(+)(SH) of -0.60, and that the literature value of -0.03 is in error. In addition, the SH rotational barriers in 4-YC(6)H(4)SH have been computed and it has been found that for strong electron donating (ED) Ys, such as NH(2), the lowest energy conformer has the S-H bond oriented perpendicular to the aromatic ring plane. In this orientation the SH becomes an electron withdrawing (EW) group. Thus, although the OH group in phenols is always in-plane and ED irrespective of the nature of the 4-Y substituent, in thiophenols the SH switches from being an ED group with EW and weak ED 4-Ys, to being an EW group for strong ED 4-Ys. PMID:16898699

Mulder, Peter; Mozenson, Olga; Lin, Shuqiong; Bernardes, Carlos E S; Minas da Piedade, Manuel E; Santos, Ana Filipa L O M; Ribeiro da Silva, Manuel A V; Dilabio, Gino A; Korth, Hans-Gert; Ingold, K U

2006-08-17

102

Formation, structure and bond dissociation thresholds of gas-phase vanadium oxide cluster ions  

Microsoft Academic Search

The formation and structure of gas-phase vanadium oxide cluster anions are examined using a guided ion beam mass spectrometer coupled with a laser vaporization source. The dominant peaks in the anion total mass distribution correspond to clusters having stoichiometries of the form (VO2)n(VO3)m(O2)q?. Collision-induced dissociation studies of the vanadium oxide species V2O46?,V3O69?,V4O810?,V5O1113?,V6O1315?, and V7O1618? indicate that VO2,VO3, and V2O5 units

R. C. Bell; K. A. Zemski; D. R. Justes

2001-01-01

103

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

104

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

PubMed

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

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

2013-09-25

105

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

PubMed Central

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

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

2013-01-01

106

Energy Dissipation during Rupture of Adhesive Bonds  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations were used to study energy-dissipation mechanisms during the rupture of a thin adhesive bond formed by short chain molecules. The degree of dissipation and its velocity dependence varied with the state of the film. When the adhesive was in a liquid phase, dissipation was caused by viscous loss. In glassy films, dissipation occurred during a sequence of rapid structural rearrangements. Roughly equal amounts of energy were dissipated in each of three types of rapid motion: cavitation, plastic yield, and bridge rupture. These mechanisms have similarities to nucleation, plastic flow, and crazing in commercial polymeric adhesives.

Baljon, Arlette R. C.; Robbins, Mark O.

1996-01-01

107

Force-dependent bond dissociation govern rolling of HL-60 cells through E-selectin.  

PubMed

E-selectin-mediated rolling on vascular surface of circulating leukocyte on vascular surface is a key initial event during inflammatory response and lymphocyte homing. This event depends not only on the specific interactions of adhesive molecules but also on the hemodynamics of blood flow. Little is still understood about whether wall shear stress or shear rate regulates the rolling. With flow chamber techniques, we here measured the effects of transport, shear stress and cell deformation on rolling of both unfixed and fixed HL-60 cells on E-selectin either in the absence or in the presence of 3% Ficoll in medium at various wall shear stresses from 0.05 to 0.7 dyn/cm(2). The results demonstrated a triphasic force-dependent rolling, that is, as increasing of force, the rolling would be accelerated firstly, then followed a decelerating phase occurred at the initial shear threshold of about 0.1 dyn/cm(2), and lastly returned to an accelerating process starting at the optimal shear threshold of 0.35 dyn/cm(2) approximately. The catch bond regime was completely reflected to rolling behaviors, such as tether lifetime, cell stop time and rolling velocity, meaning that the dominant factor to govern rolling is force. The initial shear threshold might be the minimum level of wall shear stress to sustain a stationary rolling, and the optimal shear threshold would make rolling to the most stable and regular. These findings strongly elucidate the catch bond mechanism for flow-enhanced rolling through E-selectin since longer bond lifetimes led to slower and stabler rolling. PMID:22659166

Li, Quhuan; Fang, Ying; Ding, Xiaoru; Wu, Jianhua

2012-05-30

108

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

NASA Astrophysics Data System (ADS)

We present a detailed study of the potential energy surfaces of the water dication correlating asymptotically with O(3P) and O(1D). Using ab initio multireference configuration interaction method, we computed a large ensemble of data, which was used to generate a fit of each potential energy surface for bending angles ?>=80 degrees and OH distances ROH>=1.0 a.u. The fit is used to investigate the dissociation dynamics along each potential energy surface for several initial geometries corresponding to Franck-Condon transition from neutral or singly ionized water molecule. For each case, we determine the dissociation channels and we compute the kinetic energy release and angular momentum distribution of the final arrangements. Among the eight potential energy surfaces investigated here, only the lowest triplet and the three lowest singlet can lead to the formation of bound residual fragment. The dissociation of HOD2+ presents a strong preference for OH rather than OD bond breakage. It is characterized by the isotopic ratio, defined as the number of OD+ over the number of OH+ residual fragments. This ratio depends strongly on the shape of each potential energy surface and on the initial conditions.

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

2009-07-01

109

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

110

Fragmentation of intra-peptide and inter-peptide disulfide bonds of proteolytic peptides by nanoESI collision-induced dissociation.  

PubMed

Characterisation and identification of disulfide bridges is an important aspect of structural elucidation of proteins. Covalent cysteine-cysteine contacts within the protein give rise to stabilisation of the native tertiary structure of the molecules. Bottom-up identification and sequencing of proteins by mass spectrometry most frequently involves reductive cleavage and alkylation of disulfide links followed by enzymatic digestion. However, when using this approach, information on cysteine-cysteine contacts within the protein is lost. Mass spectrometric characterisation of peptides containing intra-chain disulfides is a challenging analytical task, because peptide bonds within the disulfide loop are believed to be resistant to fragmentation. In this contribution we show recent results on the fragmentation of intra and inter-peptide disulfide bonds of proteolytic peptides by nano electrospray ionisation collision-induced dissociation (nanoESI CID). Disulfide bridge-containing peptides obtained from proteolytic digests were submitted to low-energy nanoESI CID using a quadrupole time-of-flight (Q-TOF) instrument as a mass analyser. Fragmentation of the gaseous peptide ions gave rise to a set of b and y-type fragment ions which enabled derivation of the sequence of the amino acids located outside the disulfide loop. Surprisingly, careful examination of the fragment-ion spectra of peptide ions comprising an intramolecular disulfide bridge revealed the presence of low-abundance fragment ions formed by the cleavage of peptide bonds within the disulfide loop. These fragmentations are preceded by proton-induced asymmetric cleavage of the disulfide bridge giving rise to a modified cysteine containing a disulfohydryl substituent and a dehydroalanine residue on the C-S cleavage site. PMID:18663433

Mormann, Michael; Eble, Johannes; Schwppe, Christian; Mesters, Rolf M; Berdel, Wolfgang E; Peter-Katalini?, Jasna; Pohlentz, Gottfried

2008-07-29

111

IR multiple photon dissociation of C2HCl3: Molecular elimination vs bond fission and efficient dissociation of the C2Cl2 producta)  

Microsoft Academic Search

The primary step in the IR multiple photon dissociation (IRMPD) of C2HCl3 is molecular elimination of HCl, even with laser fluences as high as 102 J cm?2. A large amount of atomic chlorine derives from the secondary photolysis of the vibrationally excited C2Cl2 produced concomitantly with HCl in the molecular elimination step. This C2Cl2 is dissociated very efficiently ([Cl]\\/[HCl]=0.60.2), since

J. F. Caballero; C. Wittig

1983-01-01

112

Zero kinetic energy photoelectron spectroscopy of tryptamine and the dissociation pathway of the singly hydrated cation cluster  

NASA Astrophysics Data System (ADS)

The relative ionization energies of tryptamine conformations are determined by zero kinetic energy photoelectron spectroscopy and photoionization efficiency measurements. The relative cationic conformational stabilities are compared to the published results for the neutral molecule. In the cation, the interaction strength changes significantly between amino group and either the phenyl or the pyrrole moiety of the indole chromophore where most of the positive charge is located, leading to different conformational structures and relative conformer energies in the cation. In particular, the measured adiabatic ionization potential of isomer B is 60 928 +/- 5 cm-1, at least 400 cm-1 higher than any of the 6 other tryptamine isomers which all have ionization potentials within 200 cm-1 of each other. In addition to the monomer, measurements were made on the A conformer of the tryptamine+-H2O complex including the ionization threshold and cation dissociation energy measured using a threshold photoionization fragmentation method. The water cluster exhibits an unexpectedly high ionization potential of 60 307 +/- 100 cm-1, close to the conformer A monomer of 60 320 +/- 100 cm-1. It also exhibits surprisingly low dissociation energy of 1750 +/- 150 cm-1 compared to other H-bonding involved cation-H2O complexes which are typically several thousands of wavenumbers higher. Quantum chemical calculations indicate that upon ionization the structure of the parent molecule in the water complex remains mostly unchanged due to the rigid intermolecular double hydrogen bonded water molecule bridging the monomer backbone and its side chain thus leading to the high ionization potential in the water cluster. The surprisingly low dissociation energy measured in the cationic water complex is attributed to the formation of a much more stable structural isomer H+ in the exit channel.

Gu, Quanli; Knee, J. L.

2012-09-01

113

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

SciTech Connect

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

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

2010-11-09

114

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

115

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

SciTech Connect

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

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

2012-10-24

116

A complete look at the multi-channel dissociation of propenal photoexcited at 193 nm: branching ratios and distributions of kinetic energy.  

PubMed

We observed fifteen photofragments upon photolysis of propenal (acrolein, CH(2)CHCHO) at 193 nm using photofragment translational spectroscopy and selective vacuum-ultraviolet (VUV) photoionization. All the photoproducts arise from nine primary and two secondary dissociation pathways. We measured distributions of kinetic energy of products and determined branching ratios of dissociation channels. Dissociation to CH(2)CHCO + H and CH(2)CH + HCO are two major primary channels with equivalent branching ratios of 33%. The CH(2)CHCO fragment spontaneously decomposes to CH(2)CH + CO. A proportion of primary products CH(2)CH from the fission of bond C-C of propenal further decompose to CHCH + H but secondary dissociation HCO ? H + CO is negligibly small. Binary dissociation to CH(2)CH(2) (or CH(3)CH) + CO and concerted three-body dissociation to C(2)H(2) + CO + H(2) have equivalent branching ratios of 14%-15%. The other channels have individual branching ratios of ?1%. The production of HCCO + CH(3) indicates the formation of intermediate methyl ketene (CH(3)CHCO) and the production of CH(2)CCH + OH and CH(2)CC + H(2)O indicate the formation of intermediate hydroxyl propadiene (CH(2)CCHOH) from isomerization of propenal. Distributions of kinetic energy release and dissociation mechanisms are discussed. This work provides a complete look and profound insight into the multi-channel dissociation mechanisms of propenal. The combination of a molecular beam apparatus and synchrotron VUV ionization allowed us to untangle the complex mechanisms of nine primary and two secondary dissociation channels. PMID:21423979

Chaudhuri, Chanchal; Lee, Shih-Huang

2011-03-21

117

Low-energy behavior of exothermic dissociative electron attachment  

Microsoft Academic Search

We discuss two models for electron attachment to molecules: the Vogt-Wannier model for capture into a polarization well and the resonance model for dissociative attachment. The Vogt-Wannier model is generalized for the case of a target with a permanent dipole moment, and results are presented for dissociative attachment to CH3I. It is shown that the resonance theory should incorporate in

Ilya I. Fabrikant; Hartmut Hotop

2001-01-01

118

Thermochemical studies on 3-methyl-quinoxaline-2-carboxamide-1,4-dioxide derivatives: enthalpies of formation and of N-O bond dissociation.  

PubMed

The standard molar enthalpies of formation of the 3-methyl-N-R-2-quinoxalinecarboxamide-1,4-dioxides (R = H, phenyl, 2-tolyl) in the gas phase were derived using the values for the enthalpies of combustion of the crystalline compounds, measured by static bomb combustion calorimetry, and for the enthalpies of sublimation, measured by Knudsen effusion, at T = 298.15 K. These values have also been used to calibrate a computational procedure that has been employed to estimate the gas-phase enthalpies of formation of the corresponding 3-methyl-N-R-2-quinoxalinecarboxamides and also to compute the first, second, and mean N-O bond dissociation enthalpies in the gas phase. It is found that the size of the substituent almost does not influence the computed N-O bond dissociation enthalpies; the maximum enthalpic difference is approximately 5 kJ.mol-1. PMID:17274651

Gomes, Jos R B; Sousa, Emanuel A; Gomes, Paula; Vale, Nuno; Gonalves, Jorge M; Pandey, Siddharth; Acree, William E; Ribeiro da Silva, Maria D M C

2007-02-03

119

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

NASA Astrophysics Data System (ADS)

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 (ECID) and collision-induced charge separation dissociation (CICSD). Detailed analysis of the kinetic energy lost by CS2+2 ions in forming product ions shows that S+ fragments originating from ECID are produced from ground state dications, whereas CS+ fragments originate predominantly from an excited state, probably the first or second electronically excited state of CS2+2. Two energetically distinct CICSD processes which result in pairwise formation of CS+ and S+ have been characterized, with recoil kinetic energies of 3.4 eV and 4.1 eV and nearly zero energy transfer from translation into internal modes. The lowest energy set has the same energy release as the unimolecular metastable decay process for electron-impact-generated CS2+2 ions, suggesting that the activation step involves mainly those ions that are internally excited near the dissociation threshold prior to collisional activation. It is proposed that the low kinetic energy release mechanism is "relaxed", proceeding on the minimum energy pathway from reactants to products, whereas the higher kinetic energy release mechanism is a "sudden" dissociation in which decomposition occurs from a surface in which one of the bond distances is "frozen" at or near its equilibrium position and decomposition occurs very rapidly. These experimental observations are supported by ab initio quantum chemical calculations which rationalize quantitatively the energetic consequences of following relaxed and sudden reaction paths. The minor products S+2 and C+ are also formed by ECID and CICSD processes, but were in too low abundance to be fully characterized.

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

1997-01-01

120

SACM/CT Study of Product Energy Distributions in the Dissociation of n- Propylbenzene Cations.  

National Technical Information Service (NTIS)

The distribution of translational, rotational, and vibrational energy in the fragments (benzylium ions and ethyl radicals) of the dissociation of n-proplybenzene cations has been determined by statistical adiabatic channel model/classical trajectory (SACM...

J. Troe V. G. Ushakov A. A. Viggiano

2005-01-01

121

Low temperature silicon direct bonding for application in micromechanics: bonding energies for different combinations of oxides  

Microsoft Academic Search

Plain or structured hydrophillic silicon wafers covered with native oxide or with thermally grown oxide layers have been directly bonded at room temperature; afterwards, the samples were annealed at 100C to 400C. There is a significant difference in the observed bonding energy depending on the wafer pairing chosen. If one or both wafers are covered with a native oxide layer,

Gertrud Kruter; Andreas Schumacher; Ulrich Gsele

1998-01-01

122

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

Microsoft Academic Search

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

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

2009-01-01

123

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 Brnsted-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

2012-10-24

124

Lifetime and kinetic energy release of metastable dications dissociation  

NASA Astrophysics Data System (ADS)

A new method for the determination of dynamical features of the molecular dication dissociation processes, following the single photon double ionization, investigated by time-of-flight mass spectrometry technique has been developed. The method is based on an extension of the generalized simulated annealing statistical methodology, previously applied in other fields. Here it is described and applied, as an example, to the case of the dissociation of the CO22+ dication giving CO+ + O+ ion fragments. The results are consistent with previous determination of the metastable lifetime of the dication, but the analysis also provides additional information about the dynamics of the reaction.

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

2012-04-01

125

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

PubMed

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

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

2013-07-09

126

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

127

Hydrogen bond energy of CH sub 3 CN-HCl by FTIR photometry  

SciTech Connect

The temperature dependence of an IR absorption band of CH{sub 3}CN-HCl is characterized by FTIR photometry. The heat of dimer formation at 41{degree}C obtained from this data, {Delta}H{sub D} = {minus}13.8 {plus minus} 1.2 kJ/mol, is used to calculate the equilibrium hydrogen bond dissociation energy, D{sub e} = 21.8 {plus minus} 1.7 kJ/mol. These results are compared with recent ab initio theoretical calculations and empirical estimates based on centrifugal distortion parameters.

Ballard, L.; Henderson, G. (Eastern Illinois Univ., Charleston (USA))

1991-01-24

128

On the dissociation energy of positively charged species  

NASA Astrophysics Data System (ADS)

The effect of positive ionization of diatomic molecules and solid univalent metals on their bond strength is considered with special emphasis on some concomitant paradoxes. Counter-intuitively, it is suggested that partial removal of bonding electrons may stabilize the system under consideration.

Batsanov, Stepan S.

2013-03-01

129

Determination of dissociative fragment-adsorbate interaction energy during chemisorption of the diatomic molecule HCl on Si(100)  

NASA Astrophysics Data System (ADS)

This study investigates the surface chemistry and the ordering characteristics of coadsorbed hydrogen and chlorine atoms, generated by the exposure of the Si(100) surface to gas-phase HCl molecules at various substrate temperatures, by scanning tunneling microscopy (STM), core-level photoemission spectroscopy, and Monte Carlo simulation. Experimental results show that saturation exposure to HCl causes all surface dangling bonds to be terminated by the two fragments H and Cl atoms and that the number of H-terminated sites exceeds that of Cl-terminated ones by more than 10%. This finding suggests that, in addition to the dominant dissociative chemisorption, atomically selective chemisorption or atom abstraction occurs. STM images reveal that some Cl-terminated sites form patches with a local 22 structure at 110 K and that the degree of ordering is reduced as the substrate temperature increases. Results of Monte Carlo simulations demonstrate the importance of including dissociative fragment-adsorbate interactions during the random adsorption of diatomic molecules. Comparing the correlations between Cl-terminated sites identified from STM images and those predicted by simulation reveals two effective interaction energies of 8.52.0 and 3.52.0meV between a dissociative fragment Cl atom and a nearest neighboring Cl adsorbates in the same dimer row and in the adjacent row, respectively.

Hsieh, Ming-Feng; Cheng, Jen-Yin; Yang, Jenq-Cheng; Lin, Deng-Sung; Morgenstern, Karina; Pai, Woei-Wu

2010-01-01

130

Free energy profiles for H+ conduction along hydrogen-bonded chains of water molecules.  

PubMed Central

The molecular mechanism for proton conduction along hydrogen-bonded chains, or "proton wires," is studied with free energy simulations. The complete transport of a charge along a proton wire requires two complementary processes: 1) translocation of an excess proton (propagation of an ionic defect), and 2) reorientation of the hydrogen-bonded chain (propagation of a bonding defect). The potential of mean force profile for these two steps is computed in model systems comprising a single-file chain of nine dissociable and polarizable water molecules represented by the PM6 model of Stillinger and co-workers. Results of molecular dynamics simulations with umbrella sampling indicate that the unprotonated chain is preferably polarized, and that the inversion of its total dipole moment involves an activation free energy of 8 kcal/mol. In contrast, the rapid translocation of an excess H+ across a chain extending between two spherical solvent droplets is an activationless process. These results suggest that the propagation of a bonding defect constitutes a limiting step for the passage of several protons along single-file chains of water molecules, whereas the ionic translocation may be fast enough to occur within the lifetime of transient hydrogen-bonded water chains in biological membranes.

Pomes, R; Roux, B

1998-01-01

131

Inelastic processes in e --HCl collisions in the energy range including the dissociation threshold  

SciTech Connect

Inelastic processes in low-energy collisions of electrons with HCl molecules are considered. We present results of calculations of vibrational excitation cross sections from the ground state and vibrationally excited states, dissociative attachment cross sections, and electron-impact dissociation cross sections near threshold. Our approach is based on the resonance {ital R}-matrix theory with the quasiclassical treatment of the nuclear motion. We use a rigorous procedure for the inclusion of the vibrational continuum. This allows for calculations of the cross sections in the energy range including dissociation threshold. The results for the dissociation cross sections are analyzed from the point of view of the threshold law for the three-particle break-up process.

Fabrikant, I.I.; Kalin, S.A.; Kazansky, A.K. (Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska (USA))

1991-10-01

132

Ab initio study of dissociative attachment of low-energy electrons to F  

Microsoft Academic Search

Adiabatic-nuclei resonance theory has been applied to the study of dissociative attachment of low-energy electrons to F. Stieltjes moment theory was used to derive fixed-nuclei electronic resonance parameters from large scale configuration-interaction calculations on F and F⁻. Dissociative attachment cross sections are reported for the four lowest vibrational levels of F and compared to available experimental data.

A. U. Hazi; A. E. Orel; T. N. Rescigno

1981-01-01

133

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 ) and O I (1302 and 1152 ) 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

134

Inelastic processes in e-HCl collisions in the energy range including the dissociation threshold  

Microsoft Academic Search

Inelastic processes in low-energy collisions of electrons with HCl molecules are considered. We present results of calculations of vibrational excitation cross sections from the ground state and vibrationally excited states, dissociative attachment cross sections, and electron-impact dissociation cross sections near threshold. Our approach is based on the resonance R-matrix theory with the quasiclassical treatment of the nuclear motion. We use

I. I. Fabrikant; S. A. Kalin; A. K. Kazansky

1991-01-01

135

Nonstatistical bond breaking in the multiphoton ionization/dissociation of [Fe(CO)5]mArn clusters  

NASA Astrophysics Data System (ADS)

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

Bililign, S.; Feigerle, C. S.; Miller, John C.; Velegrakis, M.

1998-04-01

136

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

SciTech Connect

Recently, water monomer dissociation energies from neutral water clusters were estimated from the measured appearance energies resulting from vacuum ultraviolet photoionization. The monomer dissociation energies of neutral water clusters were determined via a thermodynamic cycle, which encompassed the experimentally measured appearance energies of the photoionized water clusters and the previously reported dissociation energies of protonated water clusters. A key approximation was assumed - that the relaxation energy for the process ! (H2O)n + "(H2O)n -1H+ +OH is zero. We will show that the relaxation energies are large and thus cannot be neglected. Thus, the neutral water cluster monomer dissociation energies cannot be determined directly from the measured ionization potentials since they are themselves involved in the thermodynamic cycle. This work was supported by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences, US Department of Energy. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy. Computer resources were provided by the Office of Science, US Department of Energy.

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

2008-03-06

137

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+)= 1.260.02 eV.

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

1998-02-28

138

Electron-capture induced dissociation of doubly charged dipeptides: on the neutral losses and N-C? bond cleavages.  

PubMed

Electron capture by doubly charged peptide cations leads to neutral losses in addition to N-C(?) bond cleavages that give c and z fragments. In this work we discuss the influence of amino acid sequence on hydrogen versus ammonia loss and the propensity for subsequent partial side-chain cleavage after ammonia loss to give w fragment ions. Experiments were done on two series of doubly protonated dipeptides, [XK+2H](2+) and [XR+2H](2+), where X is one of the twenty common amino acid residues, excluding aspartic acid (D), and K and R are lysine and arginine, respectively. While it was previously established that NH(3) is lost exclusively from the N-terminal ammonium group and not from side-chain ammonium groups, we find here that ammonia can be lost from guanidinium radicals as well. The ratio between H loss and NH(3) loss reveals some information on internal ionic hydrogen bonds and peptide conformation since proton sharing between the N-terminal ammonium group and a basic side chain decreases the probability for NH(3) loss due to a lower recombination energy and as a result reduced capture probability. The abundance of w ions was found to correlate with the reaction energy for their formation; highest yield was found for CK and lowest for AK and HK. The survival rate of charge-reduced species was higher for XR than for XK, which is likely linked to the formation of long-lived C(?) radicals in the latter case. The probability for N-C(?) bond cleavage is smaller on average for XR than for XK which indicates that hydrogen transfer from the ?-ammonium radical to the amide group triggers some of the cleavages, or is a result of the different distances between the amide group and the charges in XR and XK. Finally, our data support the previous concept that charge partitioning between c and z fragments can be explained by competition between the two fragments for the proton. PMID:21826349

Jensen, Camilla Skinnerup; Wyer, Jean Ann; Houmller, Jrgen; Hvelplund, Preben; Nielsen, Steen Brndsted

2011-08-08

139

Dissociation energies of gold clusters Au{sub N}{sup +}, N=7-27  

SciTech Connect

Unimolecular decay rates and monomer-dimer branching ratios of gold clusters Au{sub N}{sup +} (N=7-27) have been measured as a function of excitation energy in photodissociation experiments on size-selected clusters stored in a Penning trap. Part of the data set has previously been used to extract model-free values of dissociation energies [Vogel et al., Phys. Rev. Lett. 87, 013401 (2001)]. Other parts of the data set do not allow this analysis. We use these data to extract tentative dissociation energies, based on the systematics of deviations between an Arrhenius analysis and the model-free values. The observed systematics also allows an estimate of the true frequency factor which often is much higher than the Arrhenius value but in good agreement with the expected detailed balance value. The data are also reanalyzed including radiative cooling which may explain part of the discrepancy between model-free and Arrhenius dissociation-energy values.

Hansen, K.; Herlert, A.; Schweikhard, L.; Vogel, M. [Department of Physics, Goeteborg University, SE-412 96 Goeteborg (Sweden); Institut fuer Physik, Ernst-Moritz-Arndt-Universitaet, D-17487 Greifswald (Germany); Institut fuer Physik, Johannes-Gutenberg-Universitaet, D-55099 Mainz (Germany)

2006-06-15

140

Surface-induced reactions and dissociations of small acetone, acetonitrile and ethanol cluster ions: competitive chemical reactions, dissociation mechanisms and determination of dissociation energy  

NASA Astrophysics Data System (ADS)

Using a recently commissioned tandem mass spectrometer system, BESTOF, we have carried out systematic investigations (using also deuterated molecules) on the interaction of various molecular cluster ions (including stoichiometric acetone and acetonitrile cluster ions and protonated ethanol cluster ions) with a hydrocarbon-covered stainless steel surface. Besides observing competitive chemical reactions for the stoichiometric cluster ions driven by the energy transfer in the surface collision (intra-cluster reactions versus surface H-atom pick-up reactions), we were able to see clear evidence that unimolecular dissociation kinetics determines the production of the observed decay patterns in collision energy-resolved mass spectra (CERMS). From characteristic shifts in these CERMS we can deduce corresponding binding energies, i.e., {D}((CD3CN)2+ - CD3CN) = 0.66 eV, {D}((C2H5OH)2H+ - C2H5OH) = 0.95 eV, and for the protonated dimer {D}((C2H5OH)H+ - C2H5OH) = 1.6 eV. The first value is in good agreement with values currently calculated using the B3LYP (Becke-Lee-Yang-Parr) density functional and the 6-311G(d, p) basis set, the latter values are in good agreement with values derived earlier from thermochemical data. Moreover, in the case of the protonated ethanol cluster ion, it is possible to arrive at a single (universal) breakdown graph for the trimer composed of data derived from monomer, dimer and trimer CERMS. This can be achieved by renormalizing the energy scale in the CERMS for the monomer, dimer and trimer ions (taking into account the conversion from translational to internal energy and assuming that the clusters behave like a statistical ensemble with the corresponding degrees of freedom).

Mair, C.; Fedor, J.; Lezius, M.; Scheier, P.; Probst, M.; Herman, Z.; Mrk, T. D.

2003-01-01

141

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

142

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

SciTech Connect

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

Rezayat, T.; Shukla, A.

2004-01-01

143

Municipal bond financing of solar energy facilities  

SciTech Connect

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 the Internal Revenue Code of 1954, as amended, to the issuance of municipal bonds for solar facility financing is examined also. Five bond laws of five representative states are examined and whether the eight types of solar facilities under consideration could be financed under such law is discussed. The application of the general legal principle is illustrated. Three hypothetical situations are set forth and common legal issues to be confronted by city officials in proposing such financing are discussed. These issues will be raised in most financings, but the purpose is to examine the common context in which they are raised. It is concluded that if it can be shown that the purpose of the solar facilities to be financed is to benefit the public, all legal obstacles to the use of municipal financing of solar facilities can be substantially overcome.

White, S.S.

1979-12-01

144

Measurement of bonding energy in an anhydrous nitrogen atmosphere and its application to silicon direct bonding technology  

NASA Astrophysics Data System (ADS)

Bonding energy represents an important parameter for direct bonding applications as well as for the elaboration of physical mechanisms at bonding interfaces. Measurement of bonding energy using double cantilever beam (DCB) under prescribed displacement is the most used technique thanks to its simplicity. The measurements are typically done in standard atmosphere with relative humidity above 30%. Therefore, the obtained bonding energies are strongly impacted by the water stress corrosion at the bonding interfaces. This paper presents measurements of bonding energies of directly bonded silicon wafers under anhydrous nitrogen conditions in order to prevent the water stress corrosion effect. It is shown that the measurements under anhydrous nitrogen conditions (less than 0.2 ppm of water in nitrogen) lead to high stable debonding lengths under static load and to higher bonding energies compared to the values measured under standard ambient conditions. Moreover, the bonding energies of Si/SiO2 or SiO2/SiO2 bonding interfaces are measured overall the classical post bond annealing temperature range. These new results allow to revisit the reported bonding mechanisms and to highlight physical and chemical phenomena in the absence of stress corrosion effect.

Fournel, F.; Continni, L.; Morales, C.; Da Fonseca, J.; Moriceau, H.; Rieutord, F.; Barthelemy, A.; Radu, I.

2012-05-01

145

Decay pathways and dissociation energies of copper clusters, Cun+ (2<=n<=25), Cun2+ (15<=n<=25)  

Microsoft Academic Search

The fragmentation pathways and dissociation energies of copper cluster cations, Cun+ and Cun2+, are determined by multiple-collision induced dissociation. For singly charged clusters, an odd-even staggering is observed throughout the investigated size range, 2<=n<=25, where the odd-size clusters have a higher dissociation energy than the average value of their even-size neighbors. The odd-even effect decreases with increasing cluster size. In

S. Krckeberg; L. Schweikhard; J. Ziegler; G. Dietrich; K. Ltzenkirchen; C. Walther

2001-01-01

146

Dissociative Electron Attachment to chloroacetylene  

NASA Astrophysics Data System (ADS)

The production of two fragments with ? symmetry from electron-impact dissociation of C2H2, which has only a low lying &*circ; resonance at equilibrium geometry, has been explained by the existence of interactions with &*circ; resonances at bent geometries. We are investigating the presence of such multidimensional effects in the dissociative attachment of chloroacetylene (C2HCl). We have performed electron scattering calculations using the Complex Kohn variational method to determine the resonance energies and widths of the chloroacetylene resonances as a function of both the Cl--C2H bond distance as well as the variation with C-C stretch and bend. We will discuss our results and our prediction of the dissociation dynamics in comparison to the findings for for C2H2. This work was supported by the U.S. DOE Office of Basic Energy Sciences, Division of Chemical Sciences and the National Science Foundation, PHY-05-55401.

Ngassam, V.; Orel, A. E.

2007-06-01

147

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

148

Electron impact excitation of methane: determination of appearance energies for dissociation products  

NASA Astrophysics Data System (ADS)

In this work, we present an experimental study of dissociative excitation of CH4 utilizing a crossed electron molecular beam experiment. Methane was excited by nearly monochromatic electrons generated by a trochoidal electron monochromator. The dissociative products were identified on the basis of the emission spectra in the ultraviolet-visible (UV/VIS) spectral range. The excitation functions were recorded as the function of the electron energy for different emission bands of the fragments (Balmer series for H: n = 3,49?2, and moreover, CH: A2??X2?, CH: B2?-? X2?, CH: C2?+? X2?, CH+: B1?? A1?, and CI: 2p3s 1Po1?2p2 1S0). From the experimental data we have determined the threshold energies for excitation of particular fragments. Present experimental results indicate that the threshold energies for some dissociative excitation channels could be lower by 1-2 eV in comparison to earlier studies and indicate that different dissociative processes may be operative at the threshold than assumed in the former studies.

Danko, M.; Orszagh, J.; ?urian, M.; Ko?iek, J.; Daxner, M.; Zttl, S.; Maljkovi?, J. B.; Fedor, J.; Scheier, P.; Denifl, S.; Matej?k, .

2013-02-01

149

High-energy diffraction dissociation of K0L into exclusive final states  

Microsoft Academic Search

We have observed diffraction dissociation of K0L mesons with a carbon target into the exclusive final states K0Spi+pi-, K0Somega, and K0Sphi. The diffraction production cross section for these states is not strongly dependent on the incident energy, varying at most by 30% between 75 and 150 GeV. The mass distributions do not change appreciably as a function of laboratory energy.

M. J. Lamm; J. E. Wiss; P. Avery; J. Butler; G. Gladding; M. C. Goodman; T. O'halloran; J. J. Russell; A. Wattenberg; J. Busenitz; P. Callahan; C. Olszewski; M. Binkley; J. P. Cumalat; I. Gaines; M. Gormley; J. Peoples; D. Harding; M. S. Atiya; E. P. Hartouni; S. D. Holmes; B. C. Knapp; W. Lee; R. Seto; W. Wisniewski

1987-01-01

150

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

Microsoft Academic Search

The dissociative recombination (DR) of He3He+4 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

H. B. Pedersen; H. Buhr; S. Altevogt; V. Andrianarijaona; H. Kreckel; L. Lammich; N. de Ruette; E. M. Staicu-Casagrande; D. Schwalm; D. Strasser; X. Urbain; D. Zajfman; A. Wolf

2005-01-01

151

Carbon-Hydrogen Bond Strengths in Methane  

Microsoft Academic Search

Earlier formulas for the electron-pair bonding energies of methane, and radicals derivable from methane, are combined with recent data on the energy levels of the carbon atom, the heat of sublimation of carbon, the energy for removal of the first hydrogen, and the dissociation energy of CH to obtain the energies of CH3 and CH2. A consistent set of values

H. H. Voge

1948-01-01

152

Density Functional Study on Relative Energies, Structures, and Bonding of Low-lying Electronic States of Lutetium Dimer  

NASA Astrophysics Data System (ADS)

Low-lying electronic states of the lutetium dimer (Lu2) were studied based on density functional theory (DFT) using ten different density functionals together with three different relativistic effective core pseudopotentials (RECPs). Relative state energies, equilibrium bond lengths, vibrational frequencies, and ground-state dissociation energies were evaluated. It was found that the ground state is a triplet state irrespective of the type of functional and RECP used. This result is in contrast with a previous DFT calculation which gave a singlet ground state for Lu2. By comparing with the high-level ab initio and available experimental results, it is evident that the hybrid-GGA functionals combined with the Stuttgart small-core RECP yield the best overall agreement for the properties under study. The effects of Hartree-Fock exchange in B3LYP functional on the calculated bond length and dissociation energy of the ground state were examined, and rationalized in terms of 5d participation in Lu-Lu covalent bonding.

Xia, Qiong-qiong; Xiao, Wei; Zhang, Yong-fan; Ning, Li-xin; Cui, Zhi-feng

2009-08-01

153

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

154

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

155

Improving collision induced dissociation (CID), high energy collision dissociation (HCD), and electron transfer dissociation (ETD) fourier transform MS/MS degradome-peptidome identifications using high accuracy mass information.  

PubMed

MS dissociation methods, including collision induced dissociation (CID), high energy collision dissociation (HCD), and electron transfer dissociation (ETD), can each contribute distinct peptidome identifications using conventional peptide identification methods (Shen et al. J. Proteome Res. 2011), but such samples still pose significant informatics challenges. In this work, we explored utilization of high accuracy fragment ion mass measurements, in this case provided by Fourier transform MS/MS, to improve peptidome peptide data set size and consistency relative to conventional descriptive and probabilistic scoring methods. For example, we identified 20-40% more peptides than SEQUEST, Mascot, and MS_GF scoring methods using high accuracy fragment ion information and the same false discovery rate (FDR) from CID, HCD, and ETD spectra. Identified species covered >90% of the collective identifications obtained using various conventional peptide identification methods, which significantly addresses the common issue of different data analysis methods generating different peptide data sets. Choice of peptide dissociation and high-precision measurement-based identification methods presently available for degradomic-peptidomic analyses needs to be based on the coverage and confidence (or specificity) afforded by the method, as well as practical issues (e.g., throughput). By using accurate fragment information, >1000 peptidome components can be identified from a single human blood plasma analysis with low peptide-level FDRs (e.g., 0.6%), providing an improved basis for investigating potential disease-related peptidome components. PMID:22054047

Shen, Yufeng; Toli?, Nikola; Purvine, Samuel O; Smith, Richard D

2011-12-01

156

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

Microsoft Academic Search

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

I. Torres; R. Martnez; M. N. Snchez Rayo; F. Castao

2000-01-01

157

Topology maps of bond descriptors based on the kinetic energy density and the essence of chemical bonding.  

PubMed

Analysis of the kinetic energy density within a molecule identifies patterns in its electronic structure that are intuitively linked to familiar concepts of chemical bonding. The function ?(r), termed localized-orbital locator and based on the positive-definite kinetic energy density ?+, is employed to characterize classes of covalent bonds in terms of its full topology of all critical points of rank three. Not only does ?(r) reveal patterns in chemical bonding, it also discloses features and the influence of extended electronic cores. Gradient paths define the extension of the valence space around an atomic centre; they separate various core level regions from bonding domains, and partition molecules in sensible bonded subunits. Location and ?(r)-values of critical points add a quantitative aspect to the bond characterization; profiles of unconventional chemical linkages such as charge-shift bonds emerge in a natural way. PMID:23450168

Jacobsen, Heiko

2013-04-14

158

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 4593.150.03 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

159

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

160

Hydrogen bond energy of the water dimer  

Microsoft Academic Search

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

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

1996-01-01

161

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

NASA Astrophysics Data System (ADS)

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

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

2004-04-01

162

Dissociation energy of the water dimer from quantum Monte Carlo calculations  

Microsoft Academic Search

We report a study of the electronic dissociation energy of the water dimer using quantum Monte Carlo techniques. We have performed variational quantum Monte Carlo and diffusion quantum Monte Carlo (DMC) calculations of the electronic ground state of the water monomer and dimer using all-electron and pseudopotential approaches. We have used Slater-Jastrow trial wave functions with B3LYP type single-particle orbitals,

I. G. Gurtubay; R. J. Needs

2007-01-01

163

Measuring internal energy deposition in collisional activation using hydrated ion nanocalorimetry to obtain peptide dissociation energies and entropies  

Microsoft Academic Search

The internal energy deposited in both on- and off-resonance collisional activation in Fourier transform ion cyclotron resonance\\u000a mass spectrometry is measured with ion nanocalorimetry and is used to obtain information about the dissociation energy and\\u000a entropy of a protonated peptide. Activation of Na+(H2O)30 results in sequential loss of water molecules, and the internal energy of the activated ion can be

Maria Demireva; Evan R. Williams

2010-01-01

164

The chemical bond in external electric fields: Energies, geometries, and vibrational Stark shifts of diatomic molecules  

NASA Astrophysics Data System (ADS)

It is shown that the response of molecular properties of diatomics such as the total energy, the bond length, and the vibrational Stark shift to an external homogenous electric field (EF) can be predicted from field-free observable properties such as the equilibrium bond length, the bond dissociation energy, the polarizability and dipole moment functions, and the vibrational frequency. Delley [J. Mol. Struct.: THEOCHEM 434, 229 (1998)] suggested to approximate the potential energy surface under an EF by a Morse function augmented with a EF term proportional to the internuclear separation. In this work, this term is replaced by the expression of the field-induced energy change which yields a field-perturbed Morse potential that tends to a constant asymptotic limit when the EF term itself become proportional to the sum of the polarizabilities of the separated atoms. The model is validated by comparison with direct calculations on nine diatomics, five homo-nuclear (H2, N2, O2, F2, and Cl2) and four hetero-nuclear (HF, HCl, CO, and NO), covering a range and combinations of dipole moments and polarizabilities. Calculations were conducted at the quadratic configuration interaction with single and double excitations (QCISD) and density functional theory (DFT)-B3LYP levels of theory using the 6-311++G(3df,2pd) basis set. All results agree closely at the two levels of theory except for the Stark effect of NO which is not correctly predicted by QCISD calculations as further calculations, including at the coupled cluster with single and double excitation (CCSD) level of theory, demonstrate.

Sowlati-Hashjin, Shahin; Matta, Chrif F.

2013-10-01

165

Energy transfer, scattering and dissociation in ion atom collisions: CO2+/Ar  

NASA Astrophysics Data System (ADS)

Collision-induced dissociation (CID) and nondissociative scattering of CO2+ ions following collision with a supersonic molecular beam of argon has been studied at low collision energies by crossed-beam tandem mass spectrometry. The center-of-mass (c.m.) velocity contour diagram at 23.8 eV collision energy showed that the scattering of CO2+ ions have two energetically distinct components: elastic collisions at smaller angles in which momentum exchange apparently involves Ar/O repulsive interactions and inelastic collisions at larger angles in which internally excited CO2+ ions recoil from the two-body CO2+/Ar c.m. The most probable energy transfer in the inelastic process is 4.8+/-0.5 eV, just below the lowest dissociation threshold. The CID processes at the same collision energy leading to fragment ions, CO+ and O+, show similar characteristics. CID occurs via both spectator knock-out and two-body collisions that result into two distinct scattering patterns. The energy transfers for the two pathways for O+ fragment ions are 4.7+/-0.5 eV for knock-out collisions and 7.6+/-0.5 eV for the two-body inelastic recoil collision mechanism. It is suggested that CID for O+ via the latter process must involve an electronic state higher than the C state and proceed via curve crossing. Energy transfers for CO+ fragment ions via the two corresponding processes are 5.7+/-0.5 eV and 7.6+/-0.5 eV, respectively, clearly suggesting similar mechanisms for energy transfer and dissociation for this CID process also. It is suggested that the bent geometry of the CO2+ ions may be an important factor in promoting two distinct mechanisms.

Tosh, Ronald E.; Shukla, Anil K.; Futrell, Jean H.

2001-02-01

166

Activation energies for gas-phase dissociations of multiply charged ions from electrospay ionization mass spectrometry  

SciTech Connect

The reactions of multiply protonated melittin molecular ions of various charge states produced from an electrospray ionization source have been studied. The flow of ions entrained in gas through a heated metal capillary inlet serves as a reaction vessel for gas-phase measurements of molecular ion reaction rates using mass spectrometry. Activation energies for the unimolecular dissociation reactions are calculated from the temperature dependence of the reaction kinetics. The differences in activation energies for the reactions of the different charge states are attributed to the destabilizing effect of Coulombic repulsion for high charged ions. 18 refs., 3 figs., 1 tab.

Busman, M.; Rockwood, A.L.; Smith, R.D. [Pacific Northwest Lab., Richland, WA (United States)

1992-03-19

167

Evaluation of the Rh((II))-Rh((II)) Bond Dissociation Enthalpy for [(TMTAA)Rh]2 by (1)H NMR T2 Measurements: Application in Determining the Rh-C(O)- BDE in [(TMTAA)Rh]2C?O.  

PubMed

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

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

2013-09-04

168

Bonding energies and long-range order in the trialuminides  

SciTech Connect

The degree of long-range order in the trialuminides is determined by X-ray powder diffraction techniques. Long-range order exists to their melting points. For the binary trialuminides Al{sub 3}Ti, Al{sub 73}Ti{sub 27}, and Al{sub 3}Sc, the degree of long-range order is nearly perfect and is a measure of the lack of mixing of the aluminum atoms onto the sublattice occupied by either Ti or Sc. A calculation of the bond energy between neighboring pairs of atoms from the ordering (melting) temperature is made following the Bragg-Williams mean field theory approach. These bond energies compare favorably with more sophisticated calculations. Bond energies are found to be larger than the energy difference between the crystal structure forms DO{sub 22}, Ll{sub 2}, and DO{sub 23}, and therefore, more relevant to understanding the mechanical and chemical behavior of the trialuminides. Ordering or melting temperatures of these intermetallics reflect the strong Al-metal near-neighbor pair potentials and may provide insights to their brittle properties. 11 refs., 2 figs., 2 tabs.

Sparks, C.J.; Specht, E.D.; Ice, G.E.; Zschack, P.; Schneibel, J.

1990-01-01

169

Coulomb energy determination of a single Si dangling bond.  

PubMed

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

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

2010-11-24

170

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

SciTech Connect

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

Ghosh, Prasenjit [Abdus Salam International Centre for Theoretical Physics (ICTP), Strada Costiera 11, I-34151 Trieste (Italy); Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur PO, Bangalore 560 064 (India); Pushpa, Raghani; Gironcoli, Stefano de [Scuola Internazionale Superiore di Study Avanzati (SISSA), Via Beirut 2/4, I-34151 Trieste (Italy); Narasimhan, Shobhana [Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur PO, Bangalore 560 064 (India)

2009-12-15

171

Bond energies of nitrogen and phosphorous hydrides and fluorides  

SciTech Connect

Recent measurements of bond energies in the N-H/sub n/ and P-H/sub n/ systems by photoionization mass spectrometry are compared with modern ab initio calculations and a semi-empirical theory. Good agreement is noted, providing confirmation for the level of accuracy of the ab initio calculations, and for the essential corrections of the semi-empirical parametrization. However, the N-F/sub n/ and P-F/sub n/ systems, also measured, are currently beyond the capabilities of such high quality ab initio calculations, and the trends observed in the bond energies indicate that other parametrizations are necessary in the semi-empirical approach. 20 refs., 8 figs.

Berkowitz, J.; Gibson, S.T.; Greene, J.P.; Neskovic, O.M.; Ruscic, B.

1985-01-01

172

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

NASA Astrophysics Data System (ADS)

We report absolute dissociative electron attachment (DEA) and dissociative ionization (DI) cross sections for electron scattering from the focused electron beam induced deposition (FEBID) precursor Co(CO)3NO in the incident electron energy range from 0 to 140 eV. We find that DEA leads mainly to single carbonyl loss with a maximum cross section of 4.1 10-16 cm2, while fragmentation through DI results mainly in the formation of the bare metal cation Co+ with a maximum cross section close to 4.6 10-16 cm2 at 70 eV. Though DEA proceeds in a narrow incident electron energy range, this energy range is found to overlap significantly with the expected energy distribution of secondary electrons (SEs) produced in FEBID. The DI process, on the other hand, is operative over a much wider energy range, but the overlap with the expected SE energy distribution, though significant, is found to be mainly in the threshold region of the individual DI processes.

Engmann, Sarah; Stano, Michal; Papp, Peter; Brunger, Michael J.; Matej?k, tefan; Inglfsson, Oddur

2013-01-01

173

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

174

Thermochemistry of 2-amino-3-quinoxalinecarbonitrile-1,4-dioxide. Evaluation of the mean dissociation enthalpy of the (N-O) bond.  

PubMed

The standard enthalpy of formation of the 2-amino-3-quinoxalinecarbonitrile-1,4-dioxide compound in the gas-phase was derived from the enthalpies of combustion of the crystalline solid measured by static bomb combustion calorimetry and its enthalpy of sublimation determined by Knudsen mass-loss effusion at T= 298.15 K. This value is (383.8 +/- 5.4) kJ mol(-1) and was subsequently combined with the experimental gas-phase enthalpy of formation of atomic oxygen and with the computed gas-phase enthalpy of formation of 2-amino-3-quinoxalinecarbonitrile, (382.0 +/- 6.3) kJ mol(-1), in order to estimate the mean (N-O) bond dissociation enthalpy in the gas-phase of 2-amino-3-quinoxalinecarbonitrile-1,4-dioxide. The result obtained is (248.3 +/- 8.3) kJ mol(-1), which is in excellent agreement with the B3LYP/6-311+G(2d,2p)//B3LYP/6-31G(d) computed value. PMID:15326531

Ribeiro da Silva, Maria D M C; Gomes, Jose R B; Goncalves, Jorge M; Sousa, Emanuel A; Pandey, Siddharth; Acree, William E

2004-08-10

175

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

176

Excitation energies of dissociating H2: A problematic case for the adiabatic approximation of time-dependent density functional theory  

NASA Astrophysics Data System (ADS)

Time-dependent density functional theory (TDDFT) is applied for calculation of the excitation energies of the dissociating H2 molecule. The standard TDDFT method of adiabatic local density approximation (ALDA) totally fails to reproduce the potential curve for the lowest excited singlet 1?u+ state of H2. Analysis of the eigenvalue problem for the excitation energies as well as direct derivation of the exchange-correlation (xc) kernel fxc(r,r',?) shows that ALDA fails due to breakdown of its simple spatially local approximation for the kernel. The analysis indicates a complex structure of the function fxc(r,r',?), which is revealed in a different behavior of the various matrix elements K1c,1cxc (between the highest occupied Kohn-Sham molecular orbital ?1 and virtual MOs ?c) as a function of the bond distance R(H-H). The effect of nonlocality of fxc(r,r') is modeled by using different expressions for the corresponding matrix elements of different orbitals. Asymptotically corrected ALDA (ALDA-AC) expressions for the matrix elements K12,12xc(??) are proposed, while for other matrix elements the standard ALDA expressions are retained. This approach provides substantial improvement over the standard ALDA. In particular, the ALDA-AC curve for the lowest singlet excitation qualitatively reproduces the shape of the exact curve. It displays a minimum and approaches a relatively large positive energy at large R(H-H). ALDA-AC also produces a substantial improvement for the calculated lowest triplet excitation, which is known to suffer from the triplet instability problem of the restricted KS ground state. Failure of the ALDA for the excitation energies is related to the failure of the local density as well as generalized gradient approximations to reproduce correctly the polarizability of dissociating H2. The expression for the response function ? is derived to show the origin of the field-counteracting term in the xc potential, which is lacking in the local density and generalized gradient approximations and which is required to obtain a correct polarizability.

Gritsenko, O. V.; van Gisbergen, S. J. A.; Grling, A.; Baerends, E. J.

2000-11-01

177

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

Microsoft Academic Search

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

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

1992-01-01

178

Nuclear quantum effect on the dissociation energies of cationic hydrogen clusters  

Microsoft Academic Search

Ab initio path integral molecular dynamics based on MP2\\/cc-pVTZ method has been carried out for a series of small hydrogen cluster cations, H3+,H5+,H7+ and H9+. Our dissociation enthalpy for the reaction H3+(H2)n?H3+(H2)n?1+H2 is found to be 5.4, 2.1, and 3.2kcal\\/mol, respectively, which are slightly smaller than the corresponding experimental values. It is found that energies of quantum zero-point vibration and

Masataka Sugimoto; Motoyuki Shiga; Masanori Tachikawa

2011-01-01

179

High energy collision-induced dissociation (CID) product ion spectra of isomeric polyhydroxy sugars  

NASA Astrophysics Data System (ADS)

High energy (4 keV) collision-induced dissociation (CID) product ion spectra have been obtained for a series of isomeric sugar molecules of close structural similarity. The reproducibility of the approach has been established and the spectra shown to have significant differences. These differences have been rationalised in terms of conventional mass spectrometric fragmentation rules. The data have also been subjected to analysis using chemometric methods, which require no specialist mass spectrometric input. The resulting classification of the data shows good agreement with the conventional interpretation approach.

Scrivens, James H.; Jackson, Anthony T.; Jennings, Keith R.; Jennings, Richard C. K.; Everall, Neil J.

2003-12-01

180

Metal-Olefin Bond Energies in M(CO)5(C2H4-nCln) M = Cr, Mo, W; n = 0-4: Electron-Withdrawing Olefins Do Not Increase the Bond Strength  

NASA Astrophysics Data System (ADS)

Metal-olefin bond dissociation enthalpies have been calculated for the series of complexes M(CO)5(C2H4-nCln), M = Cr, Mo, W; n = 0-4 using density functional theory. Experimental values of the bond enthalpies have been measured for M(CO)5(C2H4-nCln) M = Cr, Mo, W; n = 2 (vinyl chloride), 3, and 4 using laser photoacoustic calorimetry in n-hexane solution. Experimental and calculated values indicate that the trend in metal-olefin bond energies is opposite to the electron-withdrawing ability of the olefin, which is counter to expectations based on the Dewar-Chatt-Duncanson model for metal-olefin bonding. An in-depth analysis of the metal-olefin interaction using a bond energy decomposition scheme implies that the observed and calculated decreasing trend is influenced by the increase in steric interactions and olefin reorganizational energy which is concomitant to the increase of the number of electron-withdrawing halogen atoms.

Schlappi, Darin N.; Cedeo, David L.

2009-08-01

181

Thermochemical properties of methyl-substituted cyclic alkyl ethers and radicals for oxiranes, oxetanes, and oxolanes: C-H bond dissociation enthalpy trends with ring size and ether site.  

PubMed

Cyclic ethers are an important product from the gas-phase reactions of hydrocarbon radicals with molecular oxygen in the atmospheric chemistry of diolefins and in low to moderate temperature combustion and oxidation reaction systems. They are also important in organic synthesis. Structures, and fundamental thermochemical parameters-enthalpy (?H(f,298)), entropy (S(298)), and heat capacity (C(p)(T))-have been calculated for a series of cyclic alkyl ethers and their carbon centered radicals. Enthalpies of formation (?H(f,298)) are determined at the B3LYP/6-31G(d,p), B3LYP/6-31G(2d,2p), and CBS-QB3 levels using several work reactions for each species. Entropy (S) and heat capacity (C(p)(T)) values from vibration, translational, and external rotational contributions are calculated using the rigid-rotor-harmonic-oscillator approximation based on the vibration frequencies and structures obtained from the density functional studies. Contributions from the internal methyl rotors are substituted for torsion frequencies. Calculated enthalpies of formation for a series of 12 cyclic ethers and methyl substituted cyclic ethers are in good agreement with available literature values. C-H bond dissociation enthalpies are reported for 28 carbon sites of 3 to 5 member ring cyclic ethers for use in understanding effects of the ring and the ether oxygen on kinetics and stability. Trends in carbon-hydrogen bond energies for the ring and methyl substituents relative to ring size and to distance from the ether group are described. PMID:23194387

Auzmendi-Murua, Itsaso; Charaya, Sumit; Bozzelli, Joseph W

2013-01-02

182

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

Microsoft Academic Search

The recent syntheses of several new elements (including the recent reports of elements 116 and 118), coupled with the controversy surrounding the naming of elements 104--109, have stimulated a great interest in the chemistry of the transactinide elements. This contribution addresses hypothetical hexacarbonyl complex of seaborgium (Sg, element 106), which is predicted to be a 6d-block transition element with six

Clinton S. Nash; Bruce E. Bursten

1999-01-01

183

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

PubMed

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

Lu, Tian; Chen, Feiwu

2013-04-02

184

Importance of hindered rotations and other anharmonic effects in the thermal dissociation of small unsaturated molecules: Application to HCN.  

National Technical Information Service (NTIS)

A standard low-pressure limit RRKM rate constant is shown to significantly underestimate measured thermal dissociation rates for C(sub 2)H(sub 2) and HCN if the correct value of the bond dissociation energy is used. An explanation for this discrepancy is ...

A. F. Wagner J. H. Kiefer S. S. Kumaran

1992-01-01

185

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

NASA Astrophysics Data System (ADS)

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

Lombardi, Erminio; Jansen, Laurens

1986-05-01

186

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

187

Dissociative Tendencies and Dissociative Disorders  

Microsoft Academic Search

Although dissociative disorders are relatively rare, dissociative experiences are rather common in everyday life. Dissociative tendencies appear to be modestly related to other dimensions of personality, such as hypnotizability, absorption, fantasy proneness, and some facets of openness to experience. These dispositional variables may constitute diatheses, or risk factors, for dissociative psychopathology, but more complex models relating personality to psychopathology may

John F. Kihlstrom; Martha L. Glisky; Michael J. Angiulo

1994-01-01

188

Combining High-energy C-trap Dissociation and Electron Transfer Dissociation for Protein O-GlcNAc Modification Site Assignment  

PubMed Central

Mass spectrometry-based studies of proteins that are post-translationally modified by O-linked ?-N-acetylglucosamine (O-GlcNAc) are challenged in effectively identifying the sites of modification while simultaneously sequencing the peptides. Here we tested the hypothesis that a combination of high-energy C-trap dissociation (HCD) and electron transfer dissociation (ETD) could specifically target the O-GlcNAc modified peptides and elucidate the amino acid sequence while preserving the attached GlcNAc residue for accurate site assignment. By taking advantage of the recently characterized O-GlcNAc-specific IgG monoclonal antibodies and the combination of HCD and ETD fragmentation techniques, O-GlcNAc modified proteins were enriched from HEK293T cells and subsequently characterized using the LTQ Orbitrap Velos ETD (Thermo Fisher Scientific) mass spectrometer. In our dataset, 83 sites of O-GlcNAc modification are reported with high confidence confirming that the HCD/ETD combined approach is amenable to the detection and site assignment of O-GlcNAc modified peptides. Realizing HCD triggered ETD fragmentation on a linear ion trap/Orbitrap platform for more in-depth analysis and application of this technique to other post-translationally modified proteins are currently underway. Furthermore, this report illustrates that the O-GlcNAc transferase appears to demonstrate promiscuity with regards to the hydroxyl-containing amino acid modified in short stretches of primary sequence of the glycosylated polypeptides.

Zhao, Peng; Viner, Rosa; Teo, Chin Fen; Boons, Geert-Jan; Horn, David; Wells, Lance

2011-01-01

189

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

SciTech Connect

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

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

2009-10-14

190

Scapulothoracic dissociation: An emerging high-energy trauma in medical literature  

PubMed Central

Scapulothoracic dissociation (STD) is a devastating consequence of high-energy trauma sustained by the shoulder girdle that can easily result in rapid mortality. Since described by Oreck et al. in 1984, STD has been reported in a handful of journals and individual case series, though is still considered a rare occurrence in the context of shoulder injuries. In this report, we examine the case of a 25-year-old female involved in a high-speed rollover auto accident. Unique to this case was the discovery of a completely transected axillary artery and vein with intracorporeal bleeding and complete avulsion of the ipsilateral brachial plexus requiring immediate ligation of the vessels followed by interval above-elbow-amputation and later glenohumeral disarticulation.

McCague, Andrew; Schulte, Adam; Davis, Joseph Vivian

2012-01-01

191

Unambiguous Phosphosite Localization using Electron-Transfer/Higher-Energy Collision Dissociation (EThcD)  

PubMed Central

We recently introduced a novel scheme combining electron-transfer and higher-energy collision dissociation (termed EThcD), for improved peptide ion fragmentation and identification. We reasoned that phosphosite localization, one of the major hurdles in high-throughput phosphoproteomics, could also highly benefit from the generation of such EThcD spectra. Here, we systematically assessed the impact on phosphosite localization utilizing EThcD in comparison to methods employing either ETD or HCD, respectively, using a defined synthetic phosphopeptide mixture and also using a larger data set of Ti4+-IMAC enriched phosphopeptides from a tryptic human cell line digest. In combination with a modified version of phosphoRS, we observed that in the majority of cases EThcD generated richer and more confidently identified spectra, resulting in superior phosphosite localization scores. Our data demonstrates the distinctive potential of EThcD for PTM localization, also beyond protein phosphorylation.

2013-01-01

192

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

NASA Astrophysics Data System (ADS)

The dissociation energy (D0) of CN is determined to be 7.650.06 eV. This corresponds to ?Hf(CN) = 105.31.5 kcal per mole. This result is obtained not only from extensive ab inition 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 for NO, C2, and N2. The lifetime of the ?arcmin = 0 level of the violet (B2?+ ? X2?+) system has been completed to be 62.4 ns. Lifetimes for the red (A2? ? X2?+) system decrease with increasing ?arcmin, which is consistent both with recent experiment and calculations.

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

1988-09-01

193

High-energy collision-induced dissociation of [M+Na]+ ions desorbed by fast atom bombardment of ceramides isolated from the starfish Distolasterias nipon.  

PubMed

Ten ceramides and four cerebrosides were extracted from the starfish Distolasterias nipon by solvent extraction, silica gel column chromatography and reversed-phase high-performance liquid chromatography. Structural identification was conducted using tandem mass spectrometry of monosodiated ions desorbed by fast atom bombardment. The complete structures of four cerebrosides were determined by a previously reported method. The high-energy collision-induced dissociation (CID) spectral characteristics of ceramides with various structures depend on the number and positions of double bonds on both the N-acyl and sphingoid chains, the presence of a hydroxyl group or a double bond at the C-4 position of the sphingoid chain and the presence of an ?-hydroxy group on the N-acyl chain. The high-energy CID of the monosodiated ion, [M+Na](+), of each ceramide molecular species generated abundant ions, providing information on the composition of the fatty acyl chains and sphingoid long-chain bases. Each homologous ion series along the fatty acyl group and aliphatic chain of the sphingoid base was used for locating the double-bond positions of both chains and hydroxyl groups on the sphingoid base chain. The double-bond positions were also confirmed by the m/z values of abundant allylic even- and odd-electron ions, and the intensity ratio of the T ion peak relative to the O ion peak. This technique could determine the complete structures of ceramides and cerebrosides in an extract mixture and has great potential for determining other sphingolipids isolated from various biological sources. PMID:23378088

Yoo, Ji Sun; Park, Taeseong; Bang, Geul; Lee, Chulhyun; Rho, Jung-Rae; Kim, Young Hwan

2013-02-01

194

Bond energy effects on strength, cooperativity and robustness of molecular structures.  

PubMed

A fundamental challenge in engineering biologically inspired materials and systems is the identification of molecular structures that define fundamental building blocks. Here, we report a systematic study of the effect of the energy of chemical bonds on the mechanical properties of molecular structures, specifically, their strength and robustness. By considering a simple model system of an assembly of bonds in a cluster, we demonstrate that weak bonding, as found for example in H-bonds, results in a highly cooperative behaviour where clusters of bonds operate synergistically to form relatively strong molecular clusters. The cooperative effect of bonding results in an enhanced robustness since the drop of strength owing to the loss of a bond in a larger cluster only results in a marginal reduction of the strength. Strong bonding, as found in covalent interactions such as disulphide bonds or in the backbone of proteins, results in a larger mechanical strength. However, the ability for bonds to interact cooperatively is lost, and, as a result, the overall robustness is lower since the mechanical strength hinges on individual bonds rather than a cluster of bonds. The systematic analysis presented here provides general insight into the interplay of bond energy, robustness and other geometric parameters such as bond spacing. We conclude our analysis with a correlation of structural data of natural protein structures, which confirms the conclusions derived from our study. PMID:23050078

Chou, Chia-Ching; Buehler, Markus J

2011-07-27

195

Bond energy effects on strength, cooperativity and robustness of molecular structures  

PubMed Central

A fundamental challenge in engineering biologically inspired materials and systems is the identification of molecular structures that define fundamental building blocks. Here, we report a systematic study of the effect of the energy of chemical bonds on the mechanical properties of molecular structures, specifically, their strength and robustness. By considering a simple model system of an assembly of bonds in a cluster, we demonstrate that weak bonding, as found for example in H-bonds, results in a highly cooperative behaviour where clusters of bonds operate synergistically to form relatively strong molecular clusters. The cooperative effect of bonding results in an enhanced robustness since the drop of strength owing to the loss of a bond in a larger cluster only results in a marginal reduction of the strength. Strong bonding, as found in covalent interactions such as disulphide bonds or in the backbone of proteins, results in a larger mechanical strength. However, the ability for bonds to interact cooperatively is lost, and, as a result, the overall robustness is lower since the mechanical strength hinges on individual bonds rather than a cluster of bonds. The systematic analysis presented here provides general insight into the interplay of bond energy, robustness and other geometric parameters such as bond spacing. We conclude our analysis with a correlation of structural data of natural protein structures, which confirms the conclusions derived from our study.

Chou, Chia-Ching; Buehler, Markus J.

2011-01-01

196

Using dissociation energies to predict observability of b- and y- peaks in mass spectra of short peptides  

PubMed Central

RATIONALE Peptide identification reliability can be improved by excluding from analysis those m/z peaks of candidate peptides, which can not be observed in practice due to various physical, chemical or thermodynamic considerations. We propose using dissociation energies (as opposed to proton affinities) as a predictor of observability of different m/z peaks in spectra of short peptides. METHODS Experiment Mass spectra of tetrapeptides AAAA, AAFA, AAVA, AFAA, AVAA, AFFA, AVVA have been measured in the CID activation mode on a grid of activation times 0.05 to 100 ms and normalized collision energy 10 to 35 %. Computations Lowest energy geometries and vibrational spectra were calculated for the precursor ions and their charged and neutral fragments using DFT at the TPSS/6-31G(d,p) level. Dissociation energies were calculated for all fragmentation channels leading to b? or y? fragments. RESULTS It is demonstrated that m/z peaks observed in the mass spectra correspond to the fragmentation channels with the lowest dissociation energies. Using 50 kcal/mol as the cut off value of dissociation energy, it was predicted that 28 out of 42 possible peaks in the b? and y? series of the seven tetrapeptides cab be observed in mass spectra. In the experiments, 26 b? or y? peaks were observed, all of which are among the 28 predicted ones. CONCLUSIONS The use of dissociation energies generalizes the use of proton affinities for semi-quantitative predictions of relative intensities of different m/z peaks of short peptides. Further advances in this direction will pave the way for reliable quantitative predictions and, hence, for a significant improvement in robustness and accuracy of peptide and protein identification tools.

Obolensky, O. I.; Wu, Wells W.; Shen, R.-F.; Yu, Yi-Kuo

2012-01-01

197

Ultraslow dissociation of the H{sub 2}{sup +} molecular ion via two-color ultrafast laser pulses  

SciTech Connect

We report a mode of dissociative ionization in an intense two-color laser field. When bond softened by the superposition of 800 and 400 nm ultrafast laser pulses in a narrow intensity range, H{sub 2}{sup +} molecular ions experience ultraslow dissociation. This near-zero kinetic-energy release is supported by theoretical simulations and two-color field-dressed adiabatic potential curves. Furthermore, we show that the shift to lower energy of a known bond-softened peak can be explained by the influence of a two-color field-induced potential well. Such ultraslow dissociation can facilitate ultrafast time-resolved spectroscopy of molecules.

Moser, B.; Gibson, G. N. [Department of Physics, University of Connecticut, Storrs, Connecticut 06269 (United States)

2009-10-15

198

Classification of zero-energy resonances by dissociation of Feshbach molecules  

SciTech Connect

We study the dissociation of Feshbach molecules by a magnetic field sweep across a zero-energy resonance. In the limit of an instantaneous magnetic field change, the distribution of atomic kinetic energy can have a peak indicating dominance of the molecular closed-channel spin configuration over the entrance channel. The extent of this dominance influences physical properties such as stability with respect to collisions, and so the readily measurable presence or absence of the corresponding peak provides a practical method of classifying zero-energy resonances. Currently achievable ramp speeds, e.g., those demonstrated by Duerr et al. [Phys. Rev. A 70, 031601 (2005)], are fast enough to provide magnetic field changes that may be interpreted as instantaneous. We study the transition from sudden magnetic field changes to asymptotically wide, linear ramps. In the latter limit, the predicted form of the atomic kinetic energy distribution is independent of the specific implementation of the two-body physics, provided that the near-resonant scattering properties are properly accounted for.

Hanna, Thomas M.; Goral, Krzysztof; Koehler, Thorsten [Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU (United Kingdom); Witkowska, Emilia [Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU (United Kingdom); Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, 02-668 Warsaw (Poland)

2006-08-15

199

Photosensitized dissociation of di-tert-butyl peroxide. Energy transfer to a repulsive excited state  

SciTech Connect

Energy transfer from a variety of aromatic hydrocarbons and ketones to di-tert-butyl peroxide has been examined by using nanosecond laser flash photolysis techniques. Triplet energy transfer to the peroxide leads to its efficient cleavage into two tert-butoxy radicals. Representative rate constants for triplet quenching in benzene at 25/sup 0/C are 7.9 x 10/sup 6/, 3.4 x 10/sup 6/, and 7.0 x 10/sup 4/M/sup -1/s/sup -1/ for p-methoxypropiophenone, benzophenone, and benz(a)anthracene, respectively. The rate of transfer for p-methoxypropiophenone (E/sub T/ = 72.5 kcal/mol) is approximately temperature independent; for lower energy sensitizers ca. 0.17 kcal/mol activation energy is required for each kilocalorie per mole decrease in triplet energy. No evidence indicating exciplex intermediacy was found. A model for energy transfer to a repulsive state of the peroxide is proposed in which no activation energy is required if the sensitizer meets the energy requirements at the 0-0 equilibrium distance. For sensitizers of lower triplet energy, energy transfer to a repulsive state is proposed to occur from a thermally activated ground state having a greater than equilibrium oxygen-oxygen bond length. The same mechanism may apply in other systems where the acceptor lacks low-lying excited states. A few rate constants for the quenching of singlet sensitizers have also been determined by using fluorescence techniques.

Scaiano, J.C.; Wubbels, G.G.

1981-02-11

200

Determination of the activation energy for unimolecular dissociation of a non-covalent gas-phase peptide: Substrate complex by infrared multiphoton dissociation fourier transform ion cyclotron resonance mass spectrometry  

Microsoft Academic Search

The activation energy for the unimolecular dissociation of a non-covalent supramolecular complex between an Artificial Cationic\\u000a Receptor A ([Gua-Val-Val-Val-Amide]+, in which Gua is guanidiniocarbonyl pyrrole) and an Anionic Tetrapeptide B ([N-Acetyl-Val-Val-Ile-Ala]?) has been determined by measurement of the dissociation rate constant as a function of infrared CO2 laser power density. Singly-charged quasimolecular [A+B+H]+ ions are isolated, stored in a Fourier

Mathias Schfer; Carsten Schmuck; Martin Heil; Helen J. Cooper; Christopher L. Hendrickson; Michael J. Chalmers; Alan G. Marshall

2003-01-01

201

Dissociative Disorders  

MedlinePLUS

... trauma and help keep difficult memories at bay. Treatment for dissociative disorders may include psychotherapy, hypnosis and medication. ... epilepsy. Treatments and drugs Psychotherapy is the primary treatment for dissociative disorders. This form of therapy, also known ...

202

Ab initio calculation of the potential energy surface for the dissociation of H2 on the sulfur-covered Pd(100) surface  

Microsoft Academic Search

The presence of sulfur atoms on the Pd(100) surface is known to hinder the dissociative adsorption of hydrogen. Using density-functional theory and the full-potential linear augmented plane-wave method, we investigate the potential energy surface (PES) of the dissociative adsorption of H2 on the sulfur covered Pd(100) surface. The PES is changed significantly compared to the dissociation on the clean Pd(100)

C. M. Wei; A. Gro; M. Scheffler

1998-01-01

203

"Surface-Induced Dissociation of Acetone Cations from Self-Assembled Monolayer Surface of Flourinated Alkyl Thiol on Au (111) Substrate at Low Collision Energies"  

SciTech Connect

We have studied the dissociation of acetone molecular cations to acetyl cations following collision with a monolayer surface of fluorinated alkyl thiol (FC12) self-assembled on Au (111) substrate at 13, 25.2 and 49.6 eV kinetic energies. Three energetically distinct dissociation processes contribute to total dissociation in this energy range. At all energies there is a common dissociation pathway involving loss of nearly all of the parent ions kinetic energy in the collision process. Fragment ions resulting from this dissociation mechanism are scattered over a wide range of angles. The second pathway, observed at 25.2 and 49.6 eV kinetic energy is delayed dissociation of collisionally excited acetone cations after only a small fraction of the ions kinetic energy is lost in the collision process. Fragment ions resulting from this unique dynamics feature are scattered close to the surface parallel. These dissociations take place after the excited ions have passed through the collision region and the energy analyzer and prior to their entering the mass analyzer. At 49.6 eV kinetic energy, a small intensity fragment ion peak appears at intermediate kinetic energy spectra between the low energy loss and the highly inelastic scattering peaks.

Shukla, Anil K. (BATTELLE (PACIFIC NW LAB)); Futrell, Jean H. (BATTELLE (PACIFIC NW LAB))

2003-08-15

204

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

Microsoft Academic Search

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

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

1994-01-01

205

A new look at the ylidic bond in phosphorus ylides and related compounds: energy decomposition analysis combined with a domain-averaged fermi hole analysis.  

PubMed

Geometries and bond dissociation energies of the ylide compounds H2CPH3, H2CPMe3, H2CPF3, (BH2)2CPH3, H2CNH3, H2CAsH3, H2SiPH3, and (BH2)2SiPH3 have been calculated using ab initio (MP2, CBS-QB3) and DFT (B3LYP, BP86) methods. The nature of the ylidic bond R2E1-E2X3 was investigated with an energy decomposition analysis and with the domain-averaged Fermi hole (DAFH) analysis. The results of the latter method indicate that the peculiar features of the ylidic bond can be understood in terms of donor-acceptor interactions between closed-shell R2E1 and E2X3 fragments. The DAFH analysis clearly shows that there are two bonding contributions to the ylidic bond. The strength of the donor and acceptor contributions to the attractive orbital interactions can be estimated from the energy decomposition analysis (EDA) calculations, which give also the contributions of the electrostatic attraction and the Pauli repulsion of the chemical bonding. The EDA and DAFH results clearly show that the orbital interactions take place through the singlet ground state of the R2E1 fragment where the donor orbital of E1 yields pi-type back-donation while the E2X3 lone-pair orbital yields sigma-type bonding. Both bonds are polarized toward E2X3 when E2 = P, while the sigma-type bonding remains more polarized at E2X3 when E2 = N, As. This shows that the phosphorus ylides exhibit a particular bonding situation which is clearly different from that of the nitrogen and arsenic homologues. With ylides built around a P-C linkage, the pi-acceptor strength of phosphorus and the sigma-acceptor strength at carbon contribute to a double bond which is enhanced by electrostatic contributions. The strength of the sigma and pi components and the electrostatic attraction are then fine-tuned by the substituents at C and P, which yields a peculiar type of carbon-phosphorus bonding. The EDA data reveal that the relative strength of the ylidic bond may be determined not only by the R2E1 --> E2X3 pi back-donation, but also by the electrostatic contribution to the bonding. The calculations of the R2E1-E2X3 bond dissociation energy using ab initio methods predict that the order of the bond strength is H2C-PMe3 > H2C-PF3 > H2C-PH3 > (BH2)2C-PH3 > H2C-AsH3 > H2C-NH3 approximately H2Si-PH3 approximately (BH2)2Si-PH3. The DFT methods predict a similar trend, but they underestimate the bond strength of (BH2)2CPH3. PMID:17388399

Calhorda, Maria Jos; Krapp, Andreas; Frenking, Gernot

2007-03-24

206

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

NASA Astrophysics Data System (ADS)

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. A 5 1726). Kinetic energy release (KER) distributions have been extracted from momentum analysis of the released protons and deuterons at selected impact energies. A model calculation has been performed to interpret the different spectra. Below 100 eV, the distributions exhibit a sharp peak in the range 0-1 eV that is attributed to the dissociative excitation of high vibrational levels to the 2psgru repulsive state in the vicinity of their outer turning point. This observation is consistent with the measured vibrational population extending up to v = 13, as confirmed by the appearance threshold of the dissociative ionization (DI) channel. The KER distributions exhibit a second contribution peaking between 1 and 5 eV, resulting from the admixture of the (1ssgrg rarr 2psgru), (1ssgrg rarr 2ppgru) and (1ssgrg rarr 2ssgrg) electronic transitions. A distinctive hump is also present around 9 eV, that coincides both with the maximum of the DI contribution, and with the high-energy shoulder of the 2ppgru and 2ssgrg contributions. The present measurements are in qualitative agreement with the previous results of Caudano and Delfosse, and are fairly well reproduced by our first-order model.

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

2004-06-01

207

Energy expression of the chemical bond between atoms in metal oxides  

Microsoft Academic Search

The chemical bond between atoms in metal oxides is expressed in an energy scale. Total energy is partitioned into the atomic energy densities of constituent elements in the metal oxide, using energy density analysis. The atomization energies, ?EM for metal atom and ?EO for O atom, are then evaluated by subtracting the atomic energy densities from the energy of the

Yoshifumi Shinzato; Yuki Saito; Masahito Yoshino; Hiroshi Yukawa; Masahiko Morinaga; Takeshi Baba; Hiromi Nakai

2011-01-01

208

Experimental and computational thermochemical study of sulfur-containing amino acids: L-cysteine, L-cystine, and L-cysteine-derived radicals. S-S, S-H, and C-S bond dissociation enthalpies.  

PubMed

This paper reports an experimental and theoretical study of the standard (p(degrees) = 0.1 MPa) molar enthalpies of formation at T = 298.15 K of the sulfur-containing amino acids l-cysteine [CAS 52-90-4] and l-cystine [CAS 56-89-3]. The standard (p(degrees) = 0.1 MPa) molar enthalpies of formation of crystalline l-cysteine and l-cystine were calculated from the standard molar energies of combustion, in oxygen, to yield CO2(g) and H2SO4.115H2O, measured by rotating-bomb combustion calorimetry at T = 298.15 K. The vapor pressures of l-cysteine were measured as function of temperature by the Knudsen effusion mass-loss technique. The standard molar enthalpy of sublimation, at T = 298.15 K, was derived from the Clausius-Clapeyron equation. The experimental values were used to calculate the standard (p(degrees) = 0.1 MPa) enthalpy of formation of l-cysteine in the gaseous phase, DeltafH(degrees)m(g) = -382.6 +/- 1.8 kJ x mol-1. Due to the low vapor pressures of l-cystine and since this compound decomposes at the temperature range required for a possible sublimation, it was not possible to determine its enthalpy of sublimation. Standard ab initio molecular orbital calculations at the G3(MP2)//B3LYP and/or G3 levels were performed. Enthalpies of formation, using atomization and isodesmic reactions, were calculated and compared with experimental data. A value of -755 +/- 10 kJ x mol-1 was estimated for the enthalpy of formation of cystine. Detailed inspections of the molecular and electronic structures of the compounds studied were carried out. Finally, bond dissociation enthalpies (BDE) of S-H, S-S, and C-S bonds, and enthalpies of formation of l-cysteine-derived radicals, were also computed. PMID:20734495

Roux, Maria Victoria; Foces-Foces, Concepcin; Notario, Rafael; da Silva, Manuel A V Ribeiro; da Silva, Maria das Dores M C Ribeiro; Santos, Ana Filipa L O M; Juaristi, Eusebio

2010-08-19

209

Influence of confinement on hydrogen bond energy. The case of the FHNCH dimer.  

PubMed

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

Jab?o?ski, Miros?aw; Sol, Miquel

2010-09-23

210

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

211

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

NASA Astrophysics Data System (ADS)

A rovibrational collisional model is developed to study energy transfer and dissociation of N2(1?g+) molecules interacting with N(4Su) atoms in an ideal isochoric and isothermal chemical reactor. The system examined is a mixture of molecular nitrogen and a small amount of atomic nitrogen. This mixture, initially at room temperature, is heated by several thousands of degrees Kelvin, driving the system toward a strong non-equilibrium condition. The evolution of the population densities of each individual rovibrational level is explicitly determined via the numerical solution of the master equation for temperatures ranging from 5000 to 50 000 K. The reaction rate coefficients are taken from an ab initio database developed at NASA Ames Research Center. The macroscopic relaxation times, energy transfer rates, and dissociation rate coefficients are extracted from the solution of the master equation. The computed rotational-translational (RT) and vibrational-translational (VT) relaxation times are different at low heat bath temperatures (e.g., RT is about two orders of magnitude faster than VT at T = 5000 K), but they converge to a common limiting value at high temperature. This is contrary to the conventional interpretation of thermal relaxation in which translational and rotational relaxation timescales are assumed comparable with vibrational relaxation being considerable slower. Thus, this assumption is questionable under high temperature non-equilibrium conditions. The exchange reaction plays a very significant role in determining the dynamics of the population densities. The macroscopic energy transfer and dissociation rates are found to be slower when exchange processes are neglected. A macroscopic dissociation rate coefficient based on the quasi-stationary distribution, exhibits excellent agreement with experimental data of Appleton et al. [J. Chem. Phys. 48, 599-608 (1968)]. However, at higher temperatures, only about 50% of dissociation is found to take place under quasi-stationary state conditions. This suggest the necessity of explicitly including some rovibrational levels, when solving a global kinetic rate equation.

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

2013-01-01

212

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

Microsoft Academic Search

Calculations of rate constants for the process of dissociative attachment of low-energy electrons to hydrogen halides HCl, HBr, and HI and for the reverse process of associative detachment based on the nonlocal reso- nance model are reported. The calculated data are of importance for the modeling of plasma processes, environmental chemistry, etc. The calculated dissociative attachment rate constants are found

Karel Houfek; Martin ?ek; Ji? Hor?ek

2002-01-01

213

Hydrogen-bonding contributions to the lattice energy of salts for second harmonic generation  

Microsoft Academic Search

The lattice energies of a series of organic dihydrogenphosphate salts capable of second harmonic generation (SHG) have been calculated. These calculations, coupled with empirical data, indicate that a minimum of 2025% of the lattice energy arises from hydrogen-bond interactions. Hydrogen bonding is shown to be a strong enough force to have a profound effect on the overall packing and crystal

Christer B. Aakery; Kenneth R. Seddon; Maurice Leslie

1992-01-01

214

Photoinduced charge-transfer dissociation of hydrogen halides on silver and potassium  

SciTech Connect

The photodissociation of HCl(ad) and HI(ad) on Xe/Ag(111) and Xe/K/Ag(111) surfaces at 248, 308, and 350 nm has been studied by measuring the time-of-flight spectra of H atoms recoiling from the surface. In each case, HCl(ad) and HI(ad), the lower work function metal gave photodissociation out to much longer wavelengths, indicative of a charge-transfer mechanism. For HCl(ad) on Xe/K/Ag(111) the photoinduced charge-transfer dissociation occurred at photon energies well below the bond dissociation energy, ruling out direct dissociation of the adsorbate.

Dixon-Warren, S.J.; Polanyi, J.C.; Stanners, C.D.; Xu, G.Q. (Univ. of Toronto, Ontario (Canada))

1990-07-26

215

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

SciTech Connect

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

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

2011-03-15

216

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

217

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 NNALi interactions with virtually no direct LiLi 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

2012-04-27

218

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

NASA Astrophysics Data System (ADS)

The dissociative recombination (DR) of He3He+4 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 310-9cm3s-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 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 (3.30.9)10-10cm3s-1 . The corresponding branching ratios from v=0 to the atomic final states are found to be (3.71.2)% for 1s2sS3,(37.44.0)% for 1s2sS1,(58.65.2)% for 1s2pP3 , and (2.93.0)% for 1s2pP1 . A DR rate coefficient in the range of 210-7cm3s-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.; de Ruette, N.; Staicu-Casagrande, E. M.; Schwalm, D.; Strasser, D.; Urbain, X.; Zajfman, D.; Wolf, A.

2005-07-01

219

Chemical control through dissociative electron attachment - A study on pentafluorotoluene, pentafluoroaniline and pentafluorophenol  

NASA Astrophysics Data System (ADS)

In a combined experimental and theoretical study on dissociative electron attachment (DEA) to pentafluorotoluene, pentafluoroaniline and pentafluorophenol in the energy range 0-3 eV we reveal the role of rearrangement and hydrogen bonded intermediates in the DEA process and show that HF formation can be used to enable otherwise inaccessible, efficient low energy DEA processes.

marsson, Benedikt; Bjarnason, Elas H.; Inglfsson, Oddur; Haughey, Sean; Field, Thomas A.

2012-06-01

220

Chapter 12 New Expression of the Chemical Bond in Hydrides Using Atomization Energies  

Microsoft Academic Search

Atomization energy diagram is proposed for analyzing the chemical bond in the hydrides including perovskite-type hydrides, metal hydrides and complex hydrides. The atomization energies of hydrogen and metal atoms in them are evaluated theoretically by the energy density analysis (EDA) of the total energy, and used for the construction of the atomization energy diagram. Every hydride can be located on

Yoshifumi Shinzato; Hiroshi Yukawa; Masahiko Morinaga; Takeshi Baba; Hiromi Nakai

2008-01-01

221

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 (14.01.0)10-17 cm2, (6.5 0.7)10-17 cm2, (3.3 0.3)10-17 cm2, (1.10.1)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

222

Conformational stability of disulfide bonds in redox processes  

NASA Astrophysics Data System (ADS)

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

Houe-Levin, C.; Bergs, J.

2008-10-01

223

The trouble with chemical energy: why understanding bond energies requires an interdisciplinary systems approach.  

PubMed

Helping students understand "chemical energy" is notoriously difficult. Many hold inconsistent ideas about what energy is, how and why it changes during the course of a chemical reaction, and how these changes are related to bond energies and reaction dynamics. There are (at least) three major sources for this problem: 1) the way biologists talk about chemical energy (which is also the way we talk about energy in everyday life); 2) the macroscopic approach to energy concepts that is common in physics and physical sciences; and 3) the failure of chemistry courses to explicitly link molecular with macroscopic energy ideas. From a constructivist perspective, it is unlikely that students can, without a coherent understanding of such a central concept, attain a robust and accurate understanding of new concepts. However, changes are on the horizon, guided by the increasing understanding that difficult concepts require coherent, well-designed learning progressions and the new National Research Council Framework for K-12 Science Education. We provide supporting evidence for our assertions and suggestions for an interdisciplinary learning progression designed to better approach the concept of bond energies, a first step in an understanding chemical energy and behavior of reaction systems that is central to biological systems. PMID:23737636

Cooper, Melanie M; Klymkowsky, Michael W

2013-01-01

224

Dissociating Damage  

Microsoft Academic Search

Dissociation is a defense often mobilized against the pain and helplessness engendered by traumatic experiences such as rape, incest, and combat. This use of dissociation is different from the traditional understanding of defense mechanisms in that it provides protection from immediate experiences rather than unconscious memories or wishes. However, the price paid for this defense is subsequent fragmentation manifested by

David Spiegel

1986-01-01

225

Broken-Bond Rule for the Surface Energies of FCC Metals  

NASA Astrophysics Data System (ADS)

Using two different full-potential ab initio techniques we introduce a very simple rule based on the number of broken first-neighbor bonds to determine the surface energies of the noble metals and fcc transition metals . When a bond is broken, the rearrangement of the electronic charge for these metals does not lead to a significant change of the remaining bonds. Thus the energy needed to break a bond is independent of the surface orientation, so that the anisotropy of the surface energies is determined by the number of broken nearest-neighbors bonds. While this rule is well obeyed for the fcc noble ans transition metals, significant deviations occur for the fcc sp-metals. This novel finding can lead to the development of simple models to describe the energetics of a surface like step and kink formation, crystal growth, alloy formation, equilibrium shape of mesoscopic crystallites and surface faceting.

Galanakis, Iosif; Bihlmayer, Gustav; Papanikolaou, Nikolaos; Zeller, Rudi; Bluegel, Stefan; Dederichs, Peter H.

2002-03-01

226

Evaluation of Intrinsic Binding Energy from a Hydrogen Bonding Group in an Enzyme Inhibitor  

Microsoft Academic Search

This and two accompanying reports describe the intrinsic binding energy derived from a single hydrogen bond between an inhibitor and an enzyme. The results were obtained by comparing matched pairs of inhibitors of the zinc endopeptidase thermolysin that bind to the enzyme in an essentially identical manner but differ in the presence or absence of a specific hydrogen bond. This

Paul A. Bartlett; Charles K. Marlowe

1987-01-01

227

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

228

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

NASA Astrophysics Data System (ADS)

The two-body dissociation reactions of the dication, C2H22+, 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 C2H++H+ products occurs through a metastable dication with a lifetime of 108 +/- 22 ns, and a kinetic energy release (KER) distribution exhibiting a maximum at ~4.3 eV with a full width at half maximum (FWHM) of about 60%. The reaction leading to CH2++C+ occurs in a time shorter than the typical rotational period of the acetylene molecules (of the order of 10-12 s). The KER distribution of product ions for this reaction, exhibits a maximum at ~4.5 eV with a FWHM of about 28%. The symmetric dissociation, leading to CH+ + CH+, exhibits a KER distribution with a maximum at ~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.; Callegari, C.; Candori, P.; Falcinelli, S.; Pirani, F.; Richter, R.; Stranges, S.; Vecchiocattivi, F.

2012-05-01

229

Molecular dynamics mass spectrometric study of the collision-induced dissociation of CS2+ ions at low and intermediate collision energies  

NASA Astrophysics Data System (ADS)

The dynamics of the collision-induced dissociation of CS2+ molecular ions to CS and S+ fragment ions has been investigated using a crossed-beam tandem hybrid mass spectrometer at collision energies ranging from near threshold to 34.5 eV in the center-of-mass (CM) reference frame. The results show that small impact parameter impulsive collisions are involved in the collisional activation process, resulting in extensive scattering of fragment ions with intensity maxima at non-zero angles. The dissociation of CS2+ to S+ proceeds via a mechanism mainly involving the transfer of the minimum amount of energy required to dissociate the parent ion into S+ (4S) and CS (X1 [Sigma]+) at all collision energies. However, the mechanism for the formation of CS+ depends strongly on the collision energy. Energy transfer is very efficient for this process and a large fraction of the CM collision energy is converted to internal excitation of the colliding CS2+ ions up to a maximum of nearly 16 eV (at 34.5 eV collision energy). At the lowest collision energy we have investigated, 6.5 eV, the lowest energy reaction path to form CS+ (X2 [Sigma]+) and S (3P) is followed exclusively. However, as the collision energy is increased, several additional dissociation channels contribute towards the total dissociation. These results are rationalized by the efficient electronic excitation of the colliding CS2+ ions at these collision energies.

Shukla, A. K.; Tosh, R. E.; Chen, Y. B.; Futrell, J. H.

1995-08-01

230

Dissociative Electron Attachment to HCN, HCCH and HCCCN  

NASA Astrophysics Data System (ADS)

Studies of polyatomic molecules show that more than one degree of freedom comes into play in the dissociative process of certain molecules upon low-energy electron collision. In many of these cases, bond breaking may only proceed if the initial symmetry of the target molecule is distorted. We have performed a multi-dimensional computational treatment of the dissociative electron attachment (DEA) to three polyatomic systems, HCN, HCCH, and HCCCN below 10 eV and compared their nuclear motion and dissociation cross section. We further investigated the isotope effect in the case of HCN and HCCH. We have adopted the same computational approach in the study of these systems. This approach consists of time-dependent wavepacket propagation where the Hamiltonian operator involves the multi-dimensional complex potential energy surfaces (PESs) of the resonant anion.

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

2011-07-01

231

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

232

The Dissociation Energy of NiO and Vaporization and Sublimation Enthalpies of Ni.  

National Technical Information Service (NTIS)

Mass spectrometric studies in the temperature range 1700 to 2000 K showed that NiO(s) undergoes dissociation to both liquid and solid elemental Ni and O2, and to NiO(g) to a much lesser extent. It was determined that the partial pressure of O2 is approxim...

M. Farber R. D. ivastava

1974-01-01

233

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

234

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

235

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

PubMed

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

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

2004-08-01

236

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

Microsoft Academic Search

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 |V(rc)|\\/G(rc) where |V(rc)| is the magnitude of the local potential-energy density and G(rc) is the local kinetic-energy density, each evaluated at a bond critical point rc. A calculation of

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

2006-01-01

237

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

Microsoft Academic Search

A classification of the hydrogen fluoride HF-bonded interactions comprising a large number of molecules has been proposed by Espinosa &etal; [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-energy density, each evaluated at a bond critical point rc. A calculation of the

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

2006-01-01

238

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

Microsoft Academic Search

molecules has been proposed by Espinosa et al. J. Chem. Phys. 117, 5529 2002 based on the ratio Vrc\\/Grc where Vrc is the magnitude of the local potential-energy density and Grc is the local kinetic-energy density, each evaluated at a bond critical point rc. A calculation of the ratio for the M-O bonded interactions comprising a relatively large number of

G. V. Gibbsa; T. D. Crawford; N. L. Ross

239

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.  

PubMed

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. PMID:23697416

Ramazani, Shapour

2013-05-21

240

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

2009-04-22

241

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

242

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

SciTech Connect

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

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

2010-06-15

243

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

244

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

NASA Astrophysics Data System (ADS)

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

Houfek, K.; ?ek, M.; Hor?ek, J.

2002-01-01

245

Energy-selective reaction of the hydrogen-passivated Si surface with carbon tetrafluoride via dissociative electron attachment  

NASA Astrophysics Data System (ADS)

We report the partial fluorination of a H-passivated, sputtered Si(111) surface at 35 K induced by irradiating a physisorbed carbon tetrafluoride overlayer with 2-13 eV electrons. The reaction cross section depends strongly on the energy of incoming electrons with a threshold at 4.0 eV and a clear resonance peak at 6.0 eV having a maximum value of 4.810-17 cm2, which is attributed to dissociative electron attachment (DEA) to CF4. Our study demonstrates the energetic selectivity of DEA for chemically modifying a semiconductor surface.

di, W.; Rowntree, P.; Sanche, L.

1995-12-01

246

Identification of the strongest bonds in chemistry.  

PubMed

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

Kalescky, Robert; Kraka, Elfi; Cremer, Dieter

2013-08-30

247

Energy density analysis of the chemical bond between atoms in perovskite-type hydrides  

Microsoft Academic Search

Atomization energy diagram is proposed for analyzing the chemical bond in the perovskite-type hydrides such as M1MgH3 (M1=Na, K, Rb), RbCaH3, CaNiH3 and SrPdH3. The atomization energies of hydrogen and metal atoms in the hydrides are evaluated theoretically by the energy density analysis (EDA) of the total energy, and used for the construction of the atomization energy diagram. Every hydride

Yoshifumi Shinzato; Hiroshi Yukawa; Masahiko Morinaga; Takeshi Baba; Hiromi Nakai

2007-01-01

248

Evaluation of the surface bonding energy of an InP membrane bonded oxide-free to Si using instrumented nanoindentation  

NASA Astrophysics Data System (ADS)

Instrumented nanoindentation is used in conjunction with scanning transmission electron microscopy to evaluate the mechanical resistance at the bonding interface of a 450 nm thick InP membrane bonded oxide-free to Si. Indentation using a Berkovich tip is shown to cause the planes in InP to rotate by as much as 16. The shear stress resulting from this rotation causes the InP membrane to buckle, forming a debonded blister around the indented zone. The geometry of this blister is used to compute the surface bond energy of InP bonded oxide-free to Si. An average surface bonding energy of 585 mJ m-2 is reported.

Pantzas, Konstantinos; Patriarche, Gilles; Le Bourhis, Eric; Troadec, David; Itawi, Ahmad; Beaudoin, Grgoire; Sagnes, Isabelle; Talneau, Anne

2013-08-01

249

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

PubMed

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

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

2013-09-05

250

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

PubMed

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

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

2013-10-08

251

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

NASA Astrophysics Data System (ADS)

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

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

1997-01-01

252

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

253

Strong-field dissociation dynamics  

SciTech Connect

The strong-field dissociation behavior of diatomic molecules is examined under two distinctive physical scenarios. In the first scenario, the dissociation of the isolated hydrogen and deuterium molecular ions is discussed. The dynamics of above-threshold dissociation (ATD) are investigated over a wide range of green and infrared intensities and compared to a dressed-state model. The second situation arises when strong-field neutral dissociation is followed by ionization of the atomic fragments. The study results in a direct measure of the atomic fragment's ac-Stark shift by observing the intensity-dependent shifts in the electron or nuclear fragment kinetic energy. 8 figs., 14 refs.

DiMauro, L.F.; Yang, Baorui.

1993-01-01

254

Strong-field dissociation dynamics  

SciTech Connect

The strong-field dissociation behavior of diatomic molecules is examined under two distinctive physical scenarios. In the first scenario, the dissociation of the isolated hydrogen and deuterium molecular ions is discussed. The dynamics of above-threshold dissociation (ATD) are investigated over a wide range of green and infrared intensities and compared to a dressed-state model. The second situation arises when strong-field neutral dissociation is followed by ionization of the atomic fragments. The study results in a direct measure of the atomic fragment`s ac-Stark shift by observing the intensity-dependent shifts in the electron or nuclear fragment kinetic energy. 8 figs., 14 refs.

DiMauro, L.F.; Yang, Baorui

1993-02-01

255

Energy Considerations Show that Low-Barrier Hydrogen Bonds do not Offer a Catalytic Advantage over Ordinary Hydrogen Bonds  

Microsoft Academic Search

Low-barrier hydrogen bonds have recently been proposed as a major factor in enzyme catalysis. Here we evaluate the feasibility of transition state (TS) stabilization by low-barrier hydrogen bonds in enzymes. Our analysis focuses on the facts that (i) a low-barrier hydrogen bond is less stable than a regular hydrogen bond in water, (ii) TSs are more stable in the enzyme

Arieh Warshel; Arno Papazyan

1996-01-01

256

Competing pathways in the infrared multiphoton dissociation of hexafluoropropene  

SciTech Connect

The infrared multiphoton dissociation of hexafluoropropene was studied by photofragment translational spectroscopy. Two primary channels and one secondary channel were identified. The predominant primary channel produces CF{sub 3}CF or C{sub 2}F{sub 4} and CF{sub 2}, with the heavier species undergoing further dissociation to two CF{sub 2} fragments. A number of dissociation mechanisms are proposed for the elimination of CF{sub 2}, including direct cleavage of the carbon-carbon double bond. In the second primary channel, a simple bond rupture reaction produces CF{sub 3} and C{sub 2}F{sub 3}. As expected, the translational energy distribution for this channel peaks near zero, indicating no exit barrier is present. The activation energy for this simple bond rupture is estimated to be 100-105 kcal/mol. The branching ratio, [CF{sub 2}]/[CF{sub 3}], between the two primary pathways is 4.0 {+-} 1.0. 38 refs., 7 figs., 1 tab.

Longfellow, C.A.; Smoliar, L.A.; Lee, Y.T. [Lawrence Berkeley Lab., CA (United States)]|[Univ. of California, Berkeley, CA (United States); Lee, Y.R.; Yeh, C.Y.; Lin, S.M. [Inst. of Atomic and Molecular Sciences, Taipei (Taiwan, Province of China)

1997-01-23

257

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

2013-04-01

258

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

259

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

SciTech Connect

The authors use transient absorption spectroscopy to monitor the ionization and dissociation products following two-photon excitation of pure liquid water. The primary decay mechanism changes from dissociation at an excitation energy of 8.3 eV to ionization at 12.4 eV. The two channels occur with similar yield for an excitation energy of 9.3 eV. For the lowest excitation energy, the transient absorption at 267 nm probes the geminate recombination kinetics of the H and OH fragments, providing a window on the dissociation dynamics. Modeling the OH geminate recombination indicates that the dissociating H atoms have enough kinetic energy to escape the solvent cage and one or two additional solvent shells. The average initial separation of H and OH fragments is 0.7{+-}0.2 nm. Our observation suggests that the hydrogen bonding environment does not prevent direct dissociation of an O-H bond in the excited state. We discuss the implications of our measurement for the excited state dynamics of liquid water and explore the role of those dynamics in the ionization mechanism at low excitation energies.

Elles, Christopher G.; Shkrob, Ilya A.; Crowell, Robert A.; Bradforth, Stephen E. [Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Department of Chemistry, University of Southern California, Los Angeles, California 90089 (United States)

2007-04-28

260

Frictional effects of interface bonding energy in blister testing  

Microsoft Academic Search

Blister tests are used to investigate the size effect on the critical energy release rate for the onset of debonding of interfaces between commercial tape and plain steel. The measured data display a size effect if the interfacial friction is not taken into account. A proportional displacement model is thus proposed to simultaneously evaluate the critical energy release rate and

M Zheng; Y. J Su; L. Q Chen; T. Y Zhang

1999-01-01

261

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

PubMed Central

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

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

2008-01-01

262

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

PubMed Central

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

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

2013-01-01

263

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

PubMed

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

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

2012-12-31

264

Energetics and Dynamics of Fragmentation of Protonated Leucine Enkephalin from Time-and Energy-Resolved Surface-Induced Dissociation Studies  

SciTech Connect

Dissociation of singly protonated leucine enkephalin (YGGFL) 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 seven primary dissociation channels were deduced from modeling the time- and energy-resolved fragmentation efficiency curves for different fragment ions using an RRKM based approach developed in our laboratory. The following threshold energies and activation entropies were determined in this study: E0=1.20 eV and ?S=-20 e.u.1 (MH+?b5); E0=1.14 eV and ?S=-14.7 e.u. (MH+?b4); E0=1.42 eV and ?S=-2.5 e.u. (MH+?b3); E0=1.30 eV and ?S=-4.1 e.u. (MH+?a4); E0=1.37 eV and ?S=-5.2 e.u. (MH+?y ions); E0=1.50 eV and ?S=1.6 e.u. (MH+?internal fragments); E0=1.62 eV and ?S=5.2 e.u. (MH+?F). Comparison with Arrhenius activation energies reported in the literature demonstrated for the first time the reversal of the order of activation energies as compared to threshold energies for dissociation.

Laskin, Julia

2006-07-13

265

Energy partitioning in the collision-free multiphoton dissociation of molecules: Energy of ? CF2 from CF2HCl, CF2Br2, and CF2Cl2  

Microsoft Academic Search

We have developed a simple laser-excited fluorescence method to determine the translational energy of the nascent products of infrared multiphoton dissociations, and have applied this method to the measurement of the average translational energy ET of the ? 1A1 CF2 radicals formed from the collision-free dissociation of CF2HCl, CF2Br2, and CF2Cl2 by CO2 TEA laser pulses. The initially formed CF2

John C. Stephenson; David S. King

1978-01-01

266

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

2013-09-11

267

Potential energy surfaces for CH bond cleavage reactions  

SciTech Connect

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

Harding, L.B.

1996-12-31

268

Low-energy conformers of pamidronate and their intramolecular hydrogen bonds: a DFT and QTAIM study.  

PubMed

Extensive DFT and ab initio calculations were performed to characterize the conformational space of pamidronate, a typical pharmaceutical for bone diseases. Mono-, di- and tri-protic states of molecule, relevant for physiological pH range, were investigated for both canonical and zwitterionic tautomers. Semiempirical PM6 method were used for prescreening of the single bond rotamers followed by geometry optimizations at the B3LYP/6-31++G(d,p) and B3LYP/6-311++G(d,p) levels. For numerous identified low energy conformers the final electronic energies were determined at the MP2/6-311++G(2df,2p) level and corrected for thermal effects at B3LYP level. Solvation effects were also considered via the COSMO and C-PCM implicit models. Reasonable agreement was found between bond lengths and angle values in comparison with X-ray crystal structures. Relative equilibrium populations of different conformers were determined from molecular partition functions and the role of electronic, vibrational and rotational degrees of freedom on the stability of conformers were analyzed. For no level of theory is a zwitterionic structure stable in the gas-phase while solvation makes them available depending on the protonation state. Geometrically identified intramolecular hydrogen bonds were analyzed by QTAIM approach. All conformers exhibit strong inter-phosphonate hydrogen bonds and in most of them the alkyl-amine side chain is folded on the P-C-P backbone for further hydrogen bond formation. PMID:22940874

Arabieh, Masoud; Karimi-Jafari, Mohammad Hossein; Ghannadi-Maragheh, Mohammad

2012-09-02

269

Orbital Energy Spectra of Electrons in Chemisorption Bonds: O, S, Se on Ni(100)  

Microsoft Academic Search

This work presents the first experimental determinations of orbital energy spectra of electrons in chemisorption bonds. Our method, ion neutralization spectroscopy, determines a transition density function which is essentially the local density of states in the surface region of the solid. For the particular surface formed by chemisorption of the chalcogens in ordered, surface-crystalline arrays on Ni(100), the local density

H. D. Hagstrum; G. E. Becker

1971-01-01

270

Energy-loss near-edge structure changes with bond length in carbon systems  

NASA Astrophysics Data System (ADS)

We show that when the graphene planes of graphite are uniformly expanded, thereby increasing the C?C bond length to 1.7 , the ?* edge onset of the energy-loss near-edge structure (ELNES) spectrum shifts to lower energies by almost 5eV , meanwhile the ?* edge shifts by less than 0.2eV . The shift of the ?* edge demonstrates that for bond lengths which are typical of some carbon systems such as amorphous carbon, it is possible to find ?* features in the ELNES spectra at energies as low as 286-288eV . Calculations on 64-atom amorphous carbon (a-C) and amorphous carbon nitride model structures characterized by a wide range of bond lengths confirm this. Most of the sp2/sp3 quantification techniques that are available overlook this issue of ?* contamination of the ?* region and assume that all features within this energy range are entirely of ?* origin. We show that the effect of bond length variation on the ?* spectrum of graphite and a-C is minor, thereby supporting the reliability of the former spectrum for sp2/sp3 quantification purposes, as was recently demonstrated [see J. T. Titantah and D. Lamoen, Phys. Rev. B 70, 075115 (2004)].

Titantah, J. T.; Lamoen, D.

2005-11-01

271

Hydrophobic bond energy of non-polar molecules: Application to ? -ionone and 11- cis retinal  

Microsoft Academic Search

A method for calculating the hydrophobic bond energy (HPE) of a nonpolar molecule at room temperature was presented by assuming that the whole HPE is the sum of HPE of each group or atom composing the molecule. This method was applied to ?-ionone and 11-cis retinal and those HPE's were found to be considerable. Some comparison of the present method

T. Kakitani; H. Kakitani; S. Yomosa

1980-01-01

272

Palladium nanoparticles with high energy facets as a key factor in dissociating O2 in the solvent-free selective oxidation of alcohols.  

PubMed

Palladium (Pd) nanocatalysts with high energy facets {110} supported on flower-like hydroxyapatite (F-HAP) were successfully prepared. Based on the experimental data and theoretical calculations, it was found that the O2 dissociation on Pd {110} facets could be key to the performance of Pd nanoparticles in the solvent-free selective oxidation of alcohols. PMID:23770710

Wang, Feifei; Lu, Zhansheng; Yang, Lin; Zhang, Yanxing; Tang, Qinghu; Guo, Yuming; Ma, Xiaoming; Yang, Zongxian

2013-07-28

273

Density functional theory with approximate kinetic energy functionals applied to hydrogen bonds  

Microsoft Academic Search

Applicability of the approximate kinetic energy functionals to study hydrogen-bonded systems by means of the formalism of KohnSham equations with constrained electron density (KSCED) [Cortona, Phys. Rev. B 44, 8454 (1991); Wesołowski and Warshel, J. Phys. Chem. 97, 8050 (1993); Wesołowski and Weber, Chem. Phys. Lett. 248, 71 (1996)] is analyzed. In the KSCED formalism, the ground-state energy of a

Tomasz Adam Wesolowski

1997-01-01

274

Dissociative Recombination of CH4+  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

275

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 CH--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 LiHHCF(3), MgH(2)HCF(3), and NaHHCF(3). Moreover, the alkali-halogen bonds were identified in relation to the formation of the trimolecular systems NaH2(HCF(3)) and NaH2(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

2012-11-09

276

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

PubMed

The double bond photoisomerization of fulvene has been studied with quantum dynamics calculations using the multi-configuration time-dependent Hartree method. Fulvene is a test case to develop optical control strategies based on the knowledge of the excited state decay mechanism. The decay takes place on a time scale of several hundred femtoseconds, and the potential energy surface is centered around a conical intersection seam between the ground and excited state. The competition between unreactive decay and photoisomerization depends on the region of the seam accessed during the decay. The dynamics are carried out on a four-dimensional model surface, parametrized from complete active space self-consistent field calculations, that captures the main features of the seam (energy and locus of the seam and associated branching space vectors). Wave packet propagations initiated by single laser pulses of 5-25 fs duration and 1.85-4 eV excitation energy show the principal characteristics of the first 150 fs of the photodynamics. Initially, the excitation energy is transferred to a bond stretching mode that leads the wave packet to the seam, inducing the regeneration of the reactant. The photoisomerization starts after the vibrational energy has flowed from the bond stretching to the torsional mode. In our propagations, intramolecular energy redistribution (IVR) is accelerated for higher excess energies along the bond stretch mode. Thus, the competition between unreactive decay and isomerization depends on the rate of IVR between the bond stretch and torsion coordinates, which in turn depends on the excitation energy. These results set the ground for the development of future optical control strategies. PMID:21992301

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

2011-10-01

277

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

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

2013-04-01

278

Analyzing angular distributions for two-step dissociation mechanisms in velocity map imaging.  

PubMed

Increasingly, velocity map imaging is becoming the method of choice to study photoinduced molecular dissociation processes. This paper introduces an algorithm to analyze the measured net speed, P(vnet), and angular, ?(vnet), distributions of the products from a two-step dissociation mechanism, where the first step but not the second is induced by absorption of linearly polarized laser light. Typically, this might be the photodissociation of a C-X bond (X = halogen or other atom) to produce an atom and a momentum-matched radical that has enough internal energy to subsequently dissociate (without the absorption of an additional photon). It is this second step, the dissociation of the unstable radicals, that one wishes to study, but the measured net velocity of the final products is the vector sum of the velocity imparted to the radical in the primary photodissociation (which is determined by taking data on the momentum-matched atomic cophotofragment) and the additional velocity vector imparted in the subsequent dissociation of the unstable radical. The algorithm allows one to determine, from the forward-convolution fitting of the net velocity distribution, the distribution of velocity vectors imparted in the second step of the mechanism. One can thus deduce the secondary velocity distribution, characterized by a speed distribution P(v1,2) and an angular distribution I(?2), where ?2 is the angle between the dissociating radical's velocity vector and the additional velocity vector imparted to the product detected from the subsequent dissociation of the radical. PMID:23464815

Straus, Daniel B; Butler, Lynne M; Alligood, Bridget W; Butler, Laurie J

2013-03-06

279

Geometrical structures and probable dissociation channels of CrPm+ (m=2, 4, 6, 8) clusters  

NASA Astrophysics Data System (ADS)

A density functional theory study on the geometrical structures and probable dissociation channels of CrPm+ (m=2, 4, 6, 8) clusters has been performed. Our results reveal that the tetrahedral P4 structure and linear P2 structure are two stable units in CrPm+ clusters relatively. The lowest energy structures of CrPm+ clusters are constructed by bonding Cr with P4 unit or P2 unit. The bond between Cr and P4 unit or P2 unit is much weaker than the bond between P atoms in P4 or P2 unit. The most probable dissociation channel for CrP8+ cluster is the detachment of P4 unit or P2 unit. Our conclusions are consistent with the previous laser photodissociation experiments.

Kuang, Xiangjun; Wang, Xinqiang; Liu, Gaobin

2010-08-01

280

[Dissociative disorders].  

PubMed

There are problems with dissociative and conversion disorders with respect to classification, diagnosis, and therapeutic strategies which can only be understood in the historic context of hysteria. Even current diagnostic systems such as the DSM-IV and ICD-10 differ in the classification of such disorders. High prevalence rates ranging from 3% in the general population to 30% in clinical samples underscore their clinical relevance, and traumatic experiences play a major role in the pathogenesis. High rates of comorbid psychiatric disorders, the tendency to chronicity, and concepts of somatization (particularly in patients with conversion disorders) complicate psychotherapeutic approaches. Depending on the treatment goals, both psychodynamic and cognitive-behavioral methods can be applied, supplemented by specific techniques from trauma therapy, e.g. EMDR. PMID:15976921

Freyberger, H J; Spitzer, C

2005-07-01

281

Real-Time Evolution of the Valence Electronic Structure in a Dissociating Molecule  

SciTech Connect

Time-resolved valence band photoelectron spectroscopy with a temporal resolution of 135 fs is used to map the entire occupied valence electronic structure of photoexcited gas-phase Br{sub 2} molecules during dissociation. The observed shifting and mixing of valence energy levels defines a transition period where the system appears to be intermediate between atoms and molecules. The surprisingly short bond breaking or dissociation time is determined by monitoring in real time how the photoelectron multiplet structure of the free atom arises from the valence states of the photoexcited molecule.

Wernet, Ph.; Godehusen, K.; Gaudin, J.; Schwarzkopf, O.; Eberhardt, W. [Helmholtz-Zentrum Berlin, Albert-Einstein-Strasse 15, D-12489 Berlin (Germany); Odelius, M. [FYSIKUM, Stockholm University, AlbaNova, S-106 91 Stockholm (Sweden)

2009-07-03

282

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

PubMed

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

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

2013-01-28

283

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

PubMed

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

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

2011-10-07

284

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

Microsoft Academic Search

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

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

2012-01-01

285

The existence of an intramolecular C?H?O hydrogen bond in creatine and carbamoyl sarcosine  

NASA Astrophysics Data System (ADS)

The theory of atoms in molecules demonstrates the existence of an intramolecular hydrogen bond between a methyl group and a negatively charged oxygen in the biomolecules creatine and its competitive inhibitor carbamoyl sarcosine. In addition to the topological evidence, other properties of the charge density are in quantitative agreement with those previously found for intermolecular hydrogen bonding. It is suggested that this hydrogen bond provides a prestabilization of the hydrolysis product sarcosine. The analysis of the charge density presented here and its correlation with properties of a hydrogen bond, including its dissociation energy, can be applied to experimentally determined charge distributions.

Popelier, P. L. A.; Bader, R. F. W.

1992-02-01

286

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, Sren-Oliver

2004-01-01

287

Radical cascades in electron transfer dissociation (ETD) - implications for characterizing peptide disulfide regio-isomers.  

PubMed

Direct characterization of peptides with multiple disulfide bonds by mass spectrometry is highly desirable. In this study, electron transfer dissociation (ETD) of peptide disulfide regio-isomers was studied using model peptides containing two intrachain disulfide bonds. ETD provided rich sequence information (c/z ions) even for the backbone region under the coverage of two disulfide bonds. This behavior presented an analytical advantage over low energy collision-induced dissociation (CID) of protonated intact peptide ions, which produced very limited sequence (b/y) ions. Mechanistic studies suggested that the formation of c/z ions under the two disulfide bond covered region resulted from an initial N-C? bond cleavage, followed by radical cascades to cleave multiple disulfide bonds. The ETD spectra of the disulfide regio-isomers produced similar product ions due to radical cascades; while the relative intensities of the product ions varied, to a certain degree, which could be helpful in distinguishing isomers with overlapping disulfide bonds. PMID:24061148

Tan, Lei; Durand, Kirt L; Ma, Xiaoxiao; Xia, Yu

2013-10-15

288

Autocatalytic Water Dissociation on Cu(110) at Near Ambient Conditions  

SciTech Connect

Autocatalytic dissociation of water on the Cu(110) metal surface is demonstrated on the basis of 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.

Andersson, K.; Ketteler, G.; Bluhm, H.; Yamamoto, S.; Ogasawara, H.; Pettersson, L.G.M.; Salmeron, M.; Nilsson, A.; /SLAC, SSRL /Stockholm U. /LBL, Berkeley /UC, Berkeley

2009-04-30

289

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

290

Bond energy and electronic structure in M-bis-terpyridine complexes (M=Os, Co and Ru)  

NASA Astrophysics Data System (ADS)

We investigate the nature of bond energy and electronic structure of M-bis-terpyridine complexes (M = Os, Co and Ru) using Hartree Fock and DFT calculations. The nature of bond energy is analyzed using a Morokuma Kitaura decomposition. DFT results are compared with the Hartree Fock leading to the conclusion that charge transfer and polarization effects are responsible for the bond energy of the complexes. Also we point out the fact that the electronic configuration of the metallic atom plays a dominant role in the charge transfer process.

Morari, C.

2008-03-01

291

Amide-to-E-olefin versus amide-to-ester backbone H-bond perturbations: Evaluating the O-O repulsion for extracting H-bond energies.  

PubMed

Both amide-to-ester and amide-to-E-olefin backbone amide mutation methods were employed to perturb the same H-bond (formed by the NH of F23 and the CO of R14) in the Pin WW domain. Comparison of the thermodynamic folding energies of the ester mutant and the E-olefin mutant, accounting for the transfer free energy differences measured on relevant model compounds, yielded an estimated value of 0.3 kcal/mol for the O-O repulsion term (DeltaGO-Orep) in a beta-sheet context. The value of DeltaGO-Orep enabled us to calculate the intrinsic F23-R14 H-bond free energy to be 1.3 kcal/mol. PMID:17165703

Fu, Yanwen; Gao, Jianmin; Bieschke, Jan; Dendle, Maria A; Kelly, Jeffery W

2006-12-20

292

Associative detachment, dissociative attachment, and vibrational excitation of HCl by low-energy electrons  

Microsoft Academic Search

An improved nonlocal resonance model for electron-HCl collisions is constructed. The model takes account of the dependence of the dipole-modified threshold exponent on the internuclear distance. The long-range part of the HCl- potential-energy function has been determined from the most accurate ab initio calculations which are available. Only the s-wave component of the electronic continuum wave function is taken into

M. CZek; J. Horcek; W. Domcke

1999-01-01

293

Rearrangement and dissociative processes in the [C3H6O]+. potential energy surface. Radical cations with the CCCO frame: a model system  

NASA Astrophysics Data System (ADS)

The complete potential energy profile associated with the isomerization of ionized enol, [CH3CHCHOH]+, 1; distonic ion, [CH2CH2CHOH]+, 2; ionized propanal, [CH3CH2CHO]+, 3; ionized ally alcohol, [CH2CHCH2OH]+, 4; and their dissociation into C2H5CO+ + H., 5 has been constructed by means of molecular orbital calculations at the MP2/6-311 + G**//MP2/6-31G* + ZPE level. Investigated reactions were: 1,2-, 1,3- and 1,4-hydrogen migrations, 1,2-HCOH migration 2 [right arrow over left arrow] 2' and the sigmatropic 1,3-OH shift, 4 [right arrow over left arrow] 4'. It is found that the energy-determining step of the overall process 1 --> 2 --> 3 --> 5 is the 1,4-hydrogen atom migration 2 --> 3. Another illustration of the key role played by the distonic species 2 is provided by the calculation of a very low critical energy for its degenerate isomerization 2 [right arrow over left arrow] 2'. A rationalization of the experimental findings concerning the dissociation energetics and the metastable dissociations of 1-4 is given by RRKM calculations on the ab initio potential energy surface.

Bouchoux, G.; Luna, A.; Tortajada, J.

1997-11-01

294

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

PubMed Central

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

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

2013-01-01

295

Benchmark of density functional theory methods on the prediction of bond energies and bond distances of noble-gas containing molecules  

NASA Astrophysics Data System (ADS)

We have tested three pure density functional theory (DFT) functionals, BLYP, MPWPW91, MPWB95, and ten hybrid DFT functionals, B3LYP, B3P86, B98, MPW1B95, MPW1PW91, BMK, M05-2X, M06-2X, B2GP-PLYP, and DSD-BLYP with a series of commonly used basis sets on the performance of predicting the bond energies and bond distances of 31 small neutral noble-gas containing molecules. The reference structures were obtained using the CCSD(T)/aug-cc-pVTZ theory and the reference energies were based on the calculation at the CCSD(T)/CBS level. While in general the hybrid functionals performed significantly better than the pure functionals, our tests showed a range of performance by these hybrid functionals. For the bond energies, the MPW1B95/6-311+G(2df,2pd), BMK/aug-cc-pVTZ, B2GP-PLYP/aug-cc-pVTZ, and DSD-BLYP/aug-cc-pVTZ methods stood out with mean unsigned errors of 2.0-2.3 kcal/mol per molecule. For the bond distances, the MPW1B95/6-311+G(2df,2pd), MPW1PW91/6-311+G(2df,2pd), and B3P86/6-311+G(2df,2pd), DSD-BLYP/6-311+G(2df,2pd), and DSD-BLYP/aug-cc-pVTZ methods stood out with mean unsigned errors of 0.008-0.013 A? per bond. The current study showed that a careful selection of DFT functionals is very important in the study of noble-gas chemistry, and the most recommended methods are MPW1B95/6-311+G(2df,2pd) and DSD-BLYP/aug-cc-pVTZ.

Lai, Tai-Yuan; Yang, Chun-Yu; Lin, Hsiao-Jing; Yang, Chang-Yu; Hu, Wei-Ping

2011-06-01

296

Prediction of Reliable Metal-PH? Bond Energies for Ni, Pd, and Pt in the 0 and +2 Oxidation States  

SciTech Connect

Phosphine-based catalysts play an important role in many metal-catalyzed carbon-carbon bond formation reactions yet reliable values of their bond energies are not available. We have been studying homogeneous catalysts consisting of a phosphine bonded to a Pt, Pd, or Ni. High level electronic structure calculations at the CCSD(T)/complete basis set level were used to predict the M-PH? bond energy (BE) for the 0 and +2 oxidation states for M=Ni, Pd, and Pt. The calculated bond energies can then be used, for example, in the design of new catalyst systems. A wide range of exchange-correlation functionals were also evaluated to assess the performance of density functional theory (DFT) for these important bond energies. None of the DFT functionals were able to predict all of the M-PH3 bond energies to within 5 kcal/mol, and the best functionals were generalized gradient approximation functionals in contrast to the usual hybrid functionals often employed for main group thermochemistry.

Craciun, Raluca; Vincent, Andrew J.; Shaughnessy, Kevin H.; Dixon, David A.

2010-06-21

297

Vibrational Feshbach resonances in dissociative electron attachment to uracil  

NASA Astrophysics Data System (ADS)

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

Gallup, Gordon A.; Fabrikant, Ilya I.

2011-01-01

298

Free energy decomposition analysis of bonding and nonbonding interactions in solution  

NASA Astrophysics Data System (ADS)

A free energy decomposition analysis algorithm for bonding and nonbonding interactions in various solvated environments, named energy decomposition analysis-polarizable continuum model (EDA-PCM), is implemented based on the localized molecular orbital-energy decomposition analysis (LMO-EDA) method, which is recently developed for interaction analysis in gas phase [P. F. Su and H. Li, J. Chem. Phys. 130, 074109 (2009)]. For single determinant wave functions, the EDA-PCM method divides the interaction energy into electrostatic, exchange, repulsion, polarization, desolvation, and dispersion terms. In the EDA-PCM scheme, the homogeneous solvated environment can be treated by the integral equation formulation of PCM (IEFPCM) or conductor-like polarizable continuum model (CPCM) method, while the heterogeneous solvated environment is handled by the Het-CPCM method. The EDA-PCM is able to obtain physically meaningful interaction analysis in different dielectric environments along the whole potential energy surfaces. Test calculations by MP2 and DFT functionals with homogeneous and heterogeneous solvation, involving hydrogen bonding, vdW interaction, metal-ligand binding, cation-?, and ionic interaction, show the robustness and adaptability of the EDA-PCM method. The computational results stress the importance of solvation effects to the intermolecular interactions in solvated environments.

Su, Peifeng; Liu, Hui; Wu, Wei

2012-07-01

299

Free energy decomposition analysis of bonding and nonbonding interactions in solution.  

PubMed

A free energy decomposition analysis algorithm for bonding and nonbonding interactions in various solvated environments, named energy decomposition analysis-polarizable continuum model (EDA-PCM), is implemented based on the localized molecular orbital-energy decomposition analysis (LMO-EDA) method, which is recently developed for interaction analysis in gas phase [P. F. Su and H. Li, J. Chem. Phys. 130, 074109 (2009)]. For single determinant wave functions, the EDA-PCM method divides the interaction energy into electrostatic, exchange, repulsion, polarization, desolvation, and dispersion terms. In the EDA-PCM scheme, the homogeneous solvated environment can be treated by the integral equation formulation of PCM (IEFPCM) or conductor-like polarizable continuum model (CPCM) method, while the heterogeneous solvated environment is handled by the Het-CPCM method. The EDA-PCM is able to obtain physically meaningful interaction analysis in different dielectric environments along the whole potential energy surfaces. Test calculations by MP2 and DFT functionals with homogeneous and heterogeneous solvation, involving hydrogen bonding, vdW interaction, metal-ligand binding, cation-?, and ionic interaction, show the robustness and adaptability of the EDA-PCM method. The computational results stress the importance of solvation effects to the intermolecular interactions in solvated environments. PMID:22830687

Su, Peifeng; Liu, Hui; Wu, Wei

2012-07-21

300

Dissociation of PH3 and AsH3 on Ge(100)(2x1) Surface  

NASA Astrophysics Data System (ADS)

The most stable structures for the dissociation of phosphine and arsine on Ge(100)(2x1) surface have been investigated by relative total energy calculations based on Density Functional Theory. It has been found that the thermodynamically preferred structures in the dissociation path of phosphine and arsine are the same; PH2 and AsH2 products prefer to be on a single Ge dimer bond, but PH and AsH prefer to be between the adjacent Ge dimers. According to the optimization calculations, the dissociation path started with the adsorption of PH3(AsH3) on the electron deficient side of the Ge dimer bond is ended with the formation of P-P (As-As) dimers parallel to the dimers of Ge.

Katircio?lu, ?enay

301

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

Microsoft Academic Search

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

Fong-Fu Hsu; John Turk

2001-01-01

302

Minimum energy spin crossings for an O-O bond formation reaction  

NASA Astrophysics Data System (ADS)

The O-O bond formation reaction in the synthetic O 2 formation catalyst, [(terpy)(H 2O)Mn IV(?-O) 2Mn III(H 2O)(terpy)] 3+ (terpy = 2,2':6,2?-terpyridine), goes through a transition between two spin surfaces. Using DFT with the B3LYP functional, three different minimum energy crossing points have been located for this redox reaction. The system is predicted to perform the spin crossing close to (+0.1 kcal/mol) the low-spin Mn III-OOH product and this transition does not significantly affect the kinetics. The location of spin crossings in this system is relevant for discussions of O-O bond formation in the oxygen evolving complex of photosystem II.

Lundberg, Marcus; Siegbahn, Per E. M.

2005-01-01

303

Local bond length variations in boron-doped nanocrystalline diamond measured by spatially resolved electron energy-loss spectroscopy  

NASA Astrophysics Data System (ADS)

Variations in local bond length and coordination in boron-doped nanocrystalline diamond (NCD) films have been studied through changes in the fine structure of boron and carbon K-edges in electron energy-loss spectra, acquired in a scanning transmission electron microscope. The presence of high concentrations of B in pristine diamond regions and enrichment of B at defects in single NCD grains is demonstrated. Local bond length variations are evidenced through an energy shift of the carbon 1s --> ?* edge at B-rich defective regions within single diamond grains, indicating an expansion of the diamond bond length at sites with local high B content.

Lu, Ying-Gang; Turner, Stuart; Verbeeck, Johan; Janssens, Stoffel D.; Haenen, Ken; Van Tendeloo, Gustaaf

2013-07-01

304

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

305

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

SciTech Connect

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

Zohrabi, M.; McKenna, J.; Gaire, B.; Johnson, Nora G.; Carnes, K. D.; De, S.; Bocharova, I. A.; Magrakvelidze, M.; Ray, D.; Litvinyuk, I. V.; Cocke, C. L.; Ben-Itzhak, I. [J. R. Macdonald Laboratory, Physics Department, Kansas State University, Manhattan, Kansas 66506 (United States)

2011-05-15

306

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

SciTech Connect

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

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

2002-12-01

307

Chemical bonding in 1-(chlorodimethylstannylmethyl)-2-piperidone and its Si and Ge analogues. General trends and O ? M (M = Si, Ge, Sn) coordination bond energy  

NASA Astrophysics Data System (ADS)

Experimental and computational charge density study in the crystal and isolated molecule of 1-(chlorodimethylstannylmethyl)-2-piperidone containing pentacoordinated Sn atom was carried out. Quantum chemical calculations were performed out for Si and Ge analogues of the title compound. Also the calculations were carried out for its Ge and Si analogues. The O ? Sn coordination bond was found to be a weak interaction with mostly ionic character. The integration of electron density over atomic basins with the subsequent computation of atomic charges allowed to estimate the amount of the electron density transferred from the 2-piperidone ligand to the Me2SnCl moiety. The energy of the O ? Sn coordination bond estimated from the strengthening potential was in good agreement with the values obtained from the topological analysis of the charge density.

Korlyukov, Alexander A.; Lyssenko, Konstantin A.; Baukov, Yuri I.; Bylikin, Sergey Yu.

2013-11-01

308

Reaction of phenols with the 2,2-diphenyl-1-picrylhydrazyl radical. Kinetics and DFT calculations applied to determine ArO-H bond dissociation enthalpies and reaction mechanism.  

PubMed

The formal H-atom abstraction by the 2,2-diphenyl-1-picrylhydrazyl (dpph(*)) radical from 27 phenols and two unsaturated hydrocarbons has been investigated by a combination of kinetic measurements in apolar solvents and density functional theory (DFT). The computed minimum energy structure of dpph(*) shows that the access to its divalent N is strongly hindered by an ortho H atom on each of the phenyl rings and by the o-NO(2) groups of the picryl ring. Remarkably small Arrhenius pre-exponential factors for the phenols [range (1.3-19) x 10(5) M(-1) s(-1)] are attributed to steric effects. Indeed, the entropy barrier accounts for up to ca. 70% of the free-energy barrier to reaction. Nevertheless, rate differences for different phenols are largely due to differences in the activation energy, E(a,1) (range 2 to 10 kcal/mol). In phenols, electronic effects of the substituents and intramolecular H-bonds have a large influence on the activation energies and on the ArO-H BDEs. There is a linear Evans-Polanyi relationship between E(a,1) and the ArO-H BDEs: E(a,1)/kcal x mol(-1) = 0.918 BDE(ArO-H)/kcal x mol(-1) - 70.273. The proportionality constant, 0.918, is large and implies a "late" or "product-like" transition state (TS), a conclusion that is congruent with the small deuterium kinetic isotope effects (range 1.3-3.3). This Evans-Polanyi relationship, though questionable on theoretical grounds, has profitably been used to estimate several ArO-H BDEs. Experimental ArO-H BDEs are generally in good agreement with the DFT calculations. Significant deviations between experimental and DFT calculated ArO-H BDEs were found, however, when an intramolecular H-bond to the O(*) center was present in the phenoxyl radical, e.g., in ortho semiquinone radicals. In these cases, the coupled cluster with single and double excitations correlated wave function technique with complete basis set extrapolation gave excellent results. The TSs for the reactions of dpph(*) with phenol, 3- and 4-methoxyphenol, and 1,4-cyclohexadiene were also computed. Surprisingly, these TS structures for the phenols show that the reactions cannot be described as occurring exclusively by either a HAT or a PCET mechanism, while with 1,4-cyclohexadiene the PCET character in the reaction coordinate is much better defined and shows a strong pi-pi stacking interaction between the incipient cyclohexadienyl radical and a phenyl ring of the dpph(*) radical. PMID:18991378

Foti, Mario C; Daquino, Carmelo; Mackie, Iain D; DiLabio, Gino A; Ingold, K U

2008-12-01

309

Energy as Money, Chemical Bonding as Business, and Negative ?H and ?G as Investment  

NASA Astrophysics Data System (ADS)

A simple analogy is suggested illustrating the thermodynamic sign convention and the significance of the negative sign of ?H and ?G on spontaneity for general or introductory chemistry students. Enthalpy or energy is associated with money, and atoms or molecules are referred to as people. The suggested metaphor for ?H is net profit or investment into the surroundings; positive ?S is viewed as internal investment into the system. Hence, ?G is similar to gross profit in business; its dependence on temperature is illustrated by the reversal of the market trends for high-tech companies in 2000. The analogy is further expanded to illustrate the significance of ionic lattice enthalpy, the positive sign of atomic ionization energies, and chemical bond enthalpies.

Kozliak, Evguenii I.

2002-12-01

310

Contributions of water transfer energy to protein-ligand association and dissociation barriers: Watermap analysis of a series of p38? MAP kinase inhibitors.  

PubMed

In our previous work, we proposed that desolvation and resolvation of the binding sites of proteins can serve as the slowest steps during ligand association and dissociation, respectively, and tested this hypothesis on two protein-ligand systems with known binding kinetics behavior. In the present work, we test this hypothesis on another kinetically-determined protein-ligand system-that of p38? and eight Type II BIRB 796 inhibitor analogs. The kon values among the inhibitor analogs are narrowly distributed (10(4) ? kon ? 10(5) M(-1) s(-1) ), suggesting a common rate-determining step, whereas the koff values are widely distributed (10(-1) ? koff ? 10(-6) s(-1) ), suggesting a spectrum of rate-determining steps. We calculated the solvation properties of the DFG-out protein conformation using an explicit solvent molecular dynamics simulation and thermodynamic analysis method implemented in WaterMap to predict the enthalpic and entropic costs of water transfer to and from bulk solvent incurred upon association and dissociation of each inhibitor. The results suggest that the rate-determining step for association consists of the transfer of a common set of enthalpically favorable solvating water molecules from the binding site to bulk solvent. The rate-determining step for inhibitor dissociation consists of the transfer of water from bulk solvent to specific binding site positions that are unfavorably solvated in the apo protein, and evacuated during ligand association. Different sets of unfavorable solvation are evacuated by each ligand, and the observed dissociation barriers are qualitatively consistent with the calculated solvation free energies of those sets. PMID:23468227

Pearlstein, Robert A; Sherman, Woody; Abel, Robert

2013-07-02

311

Electron energy-loss study of bonding in amorphous silicon-carbon alloy films prepared with hydrogen dilution  

Microsoft Academic Search

Electron energy-loss spectroscopy was used to study the nature of chemical bonding in a-Si1?xCx:H films produced by rf glow discharge decomposition of SiH4\\/CH4 mixtures with hydrogen dilution. The low-loss region, the Si L edge, and the C K edge were studied. It was found that near stoichiometric films have a high degree of Si to C bonding and that substoichiometric

D. R. McKenzie; J. Bruley; G. B. Smith

1988-01-01

312

The energy and geometric characteristics of the transition state in reactions of RO 2 with carbonyl compound CH bonds  

Microsoft Academic Search

The energy and geometry of the transition state in reactions of the ethyl peroxyl radical with ethane, ethanol (its ? and\\u000a ? C-H bonds), acetone, butanone-2, and acetaldehyde were calculated by the density functional theory method. In all these\\u000a reactions (except EtO2\\/ + ethanol ? C-H bond), the CHO reaction center has an almost linear configuration (? = 176

A. F. Shestakov; E. T. Denisov; N. S. Emelyanova; T. G. Denisova

2009-01-01

313

The energy and geometric characteristics of the transition state in reactions of RO{2\\/} with carbonyl compound CH bonds  

Microsoft Academic Search

The energy and geometry of the transition state in reactions of the ethyl peroxyl radical with ethane, ethanol (its alpha and beta C-H bonds), acetone, butanone-2, and acetaldehyde were calculated by the density functional theory method. In all these reactions (except EtO2\\/ + ethanol alpha C-H bond), the C...H...O reaction center has an almost linear configuration (phi = 176

A. F. Shestakov; E. T. Denisov; N. S. Emel'Yanova; T. G. Denisova

2009-01-01

314

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

PubMed

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

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

2012-01-01

315

Subliminal processes, dissociation and the 'I'  

Microsoft Academic Search

The study of unconscious processes leads to the hypothesis of the limit of consciousness, which involves two main kinds of psychic activity. The first represents psychic contents which are subliminal for their low energy, the second subliminal contents which are inaccessible to consciousness because they are dissociated in the subliminal region. Dissociation is a concept introduced by Pierre Janet for

Petr Bob

2003-01-01

316

Dissociation and dissociative phase transition in dense hydrogen  

SciTech Connect

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

Khomkin, A. L., E-mail: alhomkin@mail.ru; Shumikhin, A. S., E-mail: shum_ac@mail.ru [Russian Academy of Sciences, Joint Institute for High Temperatures (Russian Federation)

2012-01-15

317

J/? Dissociation and Adler's Theorem  

NASA Astrophysics Data System (ADS)

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

Bourque, Alex; Gale, Charles; Haglin, Kevin L.

318

The Two-Pathway Model of the Biological Catch-Bond as a Limit of the Allosteric Model  

Microsoft Academic Search

Catch-binding is a counterintuitive phenomenon in which the lifetime of a receptor\\/ligand bond increases when a force is applied to break the bond. Several mechanisms have been proposed to rationalize catch-binding. In the two-pathway model, the force drives the system away from its native dissociation pathway into an alternative pathway involving a higher energy barrier. Here, we analyze an allosteric

Eugenia Prezhdo

2011-01-01

319

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

NASA Astrophysics Data System (ADS)

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

Whaley, Shawn D.

320

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

SciTech Connect

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

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

2005-08-08

321

Energies and bonding in manganese phosphides. Annual progress report, July 1, 1979-June 30, 1980  

SciTech Connect

Manganese monophosphide and other first row transition metal phosphides have been studied by x-ray photoelectron spectroscopy in collaboration with colleagues at Ames Laboratory. Electron binding energies of both valence-conduction band and core level electrons show an evolution of metallic behavior in the series ScP, TiP, VP, MnP, FeP, and in the series FeP, Fe/sub 2/P, Fe/sub 3/P. Phosphorus dissociation pressure measurements on MnP lead to: 4MnP/sub (s)/ = 2Mn/sub 2/P/sub (s)/ + P/sub 2//sub (g)/, ..delta..H/sup 0//sub 298/ /sub 15//sub R/ = 35.1 +- 1.0 kK when the data are treated by the third law method using estimated entropies. Combination of this result with published data yields: ..delta..H/sup 0//sub f/ /sub 298/ /sub 15/(MnP) = -12.5 +- 0.6 kK which is in satisfactory agreement with the published value: ..delta..H/sup 0//sub f/ /sub 298/ /sub 15/ = -11.6 kK. The apparently low value of the atomization enthalpy of MnP is confirmed and is attributed to a high valence state preparation energy. A study of the congruent vaporization of Mn/sub 2/P has been initiated. Apparatus for solid state galvanic cell measurements on metal phosphide systems has been fabricated and assembled. Studies are proceeding on a high pressure synthesis of MnP/sub 3/.

Myers, C.E.; Jung, E.D.; Simpson, D.J.; Patterson, E.L.; Melzer, J.I.

1980-03-01

322

Quantum entanglement and the dissociation process of diatomic molecules  

NASA Astrophysics Data System (ADS)

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

Esquivel, Rodolfo O.; Flores-Gallegos, Nelson; Molina-Espritu, Moyocoyani; Plastino, A. R.; Angulo, Juan Carlos; Antoln, Juan; Dehesa, Jess S.

2011-09-01

323

Somatoform Dissociation in Depersonalization Disorder  

Microsoft Academic Search

Along with psychoform dissociation, somatoform dissociation has been put forth as a core aspect of dissociative states, possibly as reliable as psychoform dissociation in the screening for dissociative disorders. The goal of this study was to investigate the prominence and correlates of somatoform dissociation in one of the major Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev.)

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

2008-01-01

324

Dissociative Electron Attachment to Hydrocarbons. A Laboratory Study  

NASA Astrophysics Data System (ADS)

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

Szymanska, E.; Mason, N. J.

2011-05-01

325

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

PubMed

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

Jacob, Timo; Goddard, William A

2004-08-01

326

Variable photon energy photoelectron spectroscopic studies of covalent bonding in 3d/sup 10/ transition-metal compounds  

SciTech Connect

Variable photon energy photoelectron spectroscopy (PES) is used to determine the valence band electronic structure and to study the covalent bonding properties of three tetrahedral, 3d/sup 10/ transition-metal complexes with /sigma/-donor, /pi/-donor ligands: ZnO, ZnCl/sub 4//sup 2/minus//, and CuCl. PES data obtained over the photon energy range of 16.7-1486.6 eV show dramatic intensity changes of valence band features that are caused by changes in photoionization cross sections and resonance effects at the metal 3p absorption edge. Intensity changes with photon energy allow detailed assignments of spectra to be made by using molecular orbital theory. Analyses of the peak intensities and binding energies provide a measure of the covalent bonding. Larger ZnO 3d band splitting relative to that for ZnCl/sub 4//sup 2/minus// indicates greater ligand field strength (10Dq) for the oxide ligands, which arises from the stronger /sigma/-bonding interactions of the Zn/sup 2+/ 3d with the O/sup 2/-2p orbitals. The increased effective nuclear charge on Zn/sup 2+/ shifts the d levels below the ligand levels, making them bonding and reversing the sign of the tetrahedral 10Dq value. This greater effective nuclear charge on Zn/sup 2+/ also significantly lowers the energy of the empty metal 4s and 4p levels, resulting in greater covalent stabilization of the ligand bonding levels in ZnCl/sub 4//sup 2/minus// than in CuCl. The relative contributions of ionic and covalent bonding in ZnCl/sub 2/ and CuCl are examined and related to the much greater thermodynamic stability of Zn/sup 2+/ complexes with donor ligands. 74 references, 13 figures, 5 tables.

Didziulis, S.V.; Cohen, S.L.; Butcher, K.D.; Solomon, E.I.

1988-06-29

327

Endgroup-assisted siloxane bond cleavage in the gas phase.  

PubMed

Unimolecular dissociation of H(2)N(CH(2))(3)SiOSi(CH(2))(3)NH(3)(+) generates SiC(5)H(16)NO(+) and SiC(5)H(14)N(+). The formation of SiC(5)H(16)NO(+) involves dissociation of a Si[bond]O bond and formation of an O[bond]H bond through rearrangement. The fragmentation mechanism was investigated utilizing ab initio calculations and Fourier transform ion cyclotron resonance (FTICR) mass spectrometry in combination with hydrogen/deuterium (H/D) exchange reactions. Sustained off-resonance irradiation collision-induced dissociation (SORI-CID) studies of the fully deuterated ion D(2)N(CH(2))(3)SiOSi(CH(2))(3)ND(3)(+) provided convincing evidence for a backbiting mechanism which involves hydrogen transfer from the terminal amine group to the oxygen to form a silanol-containing species. Theoretical calculations indicated decomposition of H(2)N(CH(2))(3)SiOSi(CH(2))(3)NH(3)(+) through a backbiting mechanism is the lowest energy decomposition channel, compared with other alternative routes. Two mechanisms were proposed for the fragmentation process which leads to the siloxane bond cleavage and the SORI-CID results of partially deuterated precursor ions suggest both mechanisms should be operative. Rearrangement to yield a silanol-containing product ion requires end groups possessing a labile hydrogen atom. Decomposition of disiloxane ions with end groups lacking labile hydrogen atoms yielded product ions from direct bond cleavages. PMID:12954172

Chen, Huiping

2003-09-01

328

Hydrogen dissociation on high-temperature tungsten  

Microsoft Academic Search

H2 dissociation on polycrystalline tungsten is measured from 1700 to 3000K using the filament temperature (T) change and a normalized H-atom density at the chamber surface. The dissociation probability per H2 filament collision (Pdiss) saturates at 0.40 at high T and has a 2.250.05eV apparent activation energy when Pdiss?1. This activation energy is consistent with prior data and models, but

Wengang Zheng; Alan Gallagher

2006-01-01

329

Determination of bond ionicity using low-energy D[sup +] scattering  

SciTech Connect

We report on the systematic investigation of neutralization of low-energy D[sup +] ions scattered from 17 ionic-compound surfaces with particular emphasis on the relation between the neutralization probability of D[sup +] and the ionicity of the surface atomic bonds. The D[sup +] ions tend to survive neutralization provided that the target atom is completely ionized, whereas almost complete neutralization results if the target has covalent or metallic orbital hybridization with the ligand. The D[sup +] spectra from nitrates, sulfates, and carbonates of Na and K, as well as K[sub 2]SiO[sub 3], exhibit surface peaks of D[sup +] surviving neutralization for both cations and oxygen, indicating large ionicity in the alkali-metal--oxygen bond. Rather exceptional is Na[sub 2]SiO[sub 3], for which a relatively small ionicity is concluded from the absence of surface peaks. For the alkaline-earth compounds, ionicity decreases in going to the light elements as evidenced by the decrease of the surface-peak intensity. The occurrence of charge-exchange relaxation between cations and anions of NiSO[sub 4] and CuSO[sub 4] results in large neutralization probability of D[sup +], while the closed-shell structures of Ag[sup +] (4[ital d][sup 10]) and Pb[sup 2+] (6[ital s][sup 2]) in AgNO[sub 3] and Pb(NO[sub 3])[sub 2], respectively, suppress neutralization to some extent so that the appreciable surface peaks appear.

Souda, R.; Hayami, W.; Aizawa, T.; Ishizawa, Y. (National Institute for Research in Inorganic Materials, 1-1 Namiki, Tsukuba, Ibaraki 305 (Japan))

1994-07-15

330

Theoretical study of the binding energy and bonding of benzene to the Ni (111), (100), and (110) surfaces  

SciTech Connect

The atomic superposition electron delocalization molecular orbital (ASED-MO) method has been applied to a study of the favored bonding sites for benzene adsorbed on the (111), (100), and (110) crystal faces of nickel metal. The different faces were represented in the calculations by clusters, which contained 30 nickel atoms. By using the same size clusters and parameters, it was possible to compare the results among the three different crystal faces. The most favored (highest binding energy) sites for the benzene ring parallel to the surface were found to be the highest coordination site for the (111) and (100) planes and the atop site for the (110) plane. These results are compared with both experimental and other theoretical calculations on these crystal planes. In addition, the bonding of the benzene to the Ni surfaces has been investigated by using [open quotes]bonding plots[close quotes], which are graphical representations of the Mulliken population matrix. By use of these bonding plots, a picture of the bonding of the benzene to the nickel surface is developed and an explanation for the increase of the binding energy with increased cluster size is discussed. 28 refs., 5 figs., 3 tabs.

Grimm, F.A. (Univ. of Tennessee, Knoxville (United States) Oak Ridge National Lab., TN (United States)); Huntley, D.R. (Oak Ridge National Lab., TN (United States))

1993-04-15

331

Excited Carriers Relaxation and Hydrogen Dissociation on Hydrogenated Graphene: A Theory  

NASA Astrophysics Data System (ADS)

Using ab initio molecular dynamics coupled with time-dependent density functional theory (TDDFT), we show that the energy transfer of photo-excited carriers into atomic kinetic energy on hydrogenated graphene depends sensitively on the surface H coverage. Here, the energy transfer rate plays a crucial role in the determination of the H dissociation dynamics from graphene. In the low density ``isolated'' hydrogen atom limit, the energy transfer is significantly suppressed 80 fs after the excitation. Thus, it is difficult to dissociate hydrogen due to the faster energy dissipation from H into carbon backbone, despite that initially the H kinetic energy had increased to around 1.5 eV and the C-H bondlength had starched to 2.4 . In sharp contrast, at the high-density graphane limit, an efficient energy transfer channel is established when the C-H bondlength exceeds 1.4 . A fraction of the H readily dissociates within 15 fs. This is because ionized H forms a charged layer that expels, and as such accelerates the H ions with higher initial thermal velocities flying away. Our study thus reveals the importance of performing TDDFT calculations for excited carrier dynamics as from the widely adopted ground-state or constrained DFT dynamics one would expect the C-H bonds in graphane to be significantly stronger, due to full surface passivation, than that of isolated H.

Bang, Junhyeok; Sun, Y. Y.; West, D.; Zhang, S. B.; Meng, S.; Wang, Z. G.; Gao, F.

2012-02-01

332

Dissociation of dicarboxylate and disulfonate dianions  

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

333

Tetramethylthiuram monosulfide and tetramethylthiuram disulfide: heats of formation by rotating-bomb calorimetry; the SS thermochemical bond energy  

Microsoft Academic Search

The heats of combustion and formation were determined for tetramethylthiuram monosulfide (bis-(dimethylthiocarbamoyl) sulfide) and tetramethylthiuram disulfide (bis-(dimethylthiocarbamoyl) disulfide). The S-S thermochemical bond energy in tetramethylthiuram disulfide was shown to be about the same as in normal alkane disulfides and in S. Rotating-bomb combustion calorimetry was found satisfactory for compounds that contain both sulfur and nitrogen.

W. D. Good; J. L. Lacina; J. P. McCullough

1961-01-01

334

Partial dissociation of water on Ru(0001)  

NASA Astrophysics Data System (ADS)

It is hard to overstate the importance of water-surface interactions in real-world phenomena. They govern aqueous heterogeneous chemistry, flow through nanoscale channels, adhesion and brittle fracture in humid environments, a host of biological and geophysical phenomena, condensation in the upper atmosphere, ... a virtually endless list. Current theory can accelerate our understanding of hydration effects by helping us discern the arrangement of the first water molecules deposited on a surface, a template for what follows. Here, based on Density Functional Theory total energy calculations, I offer a novel interpretation of Held & Menzel's Low Energy Electron Diffraction analysis of water adsorption on Ru(0001).(G. Held, D. Menzel, Surf. Sci. 316, 92(1994).) Initial water deposition on this moderately reactive precious-metal surface has been thought to produce an ice-like bilayer. However, the calculations show that the observed wetting layer cannot be formed of undissociated water molecules. An energetically-favorable alternative, consistent with the remarkable finding^1 that the wetting layer's oxygen atoms are nearly coplanar, is a half-dissociated monolayer wherein water molecules and hydroxyl fragments are hydrogen-bonded in a hexagonal structure and hydrogen atoms bind directly to the metal.

Feibelman, Peter J.

2002-03-01

335

Dissociation and Dissociative Identity Disorder: Treatment Guidelines and Cautions  

Microsoft Academic Search

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

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

336

Contemporary concepts of dissociation.  

PubMed

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

Avdibegovi?, Esmina

2012-10-01

337

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

PubMed

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

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

2010-04-01

338

Solvent dependent competition between fluorescence resonance energy transfer and through bond energy transfer in rhodamine appended hexaphenylbenzene derivatives for sensing of Hg(2+) ions.  

PubMed

Hexaphenylbenzene (HPB) derivatives 5 and 7 having rhodamine B moieties have been designed and synthesized, and have been shown to display solvent dependent. Fluorescence resonance energy transfer (FRET) and through bond energy transfer (TBET) in the presence of Hg(2+) ions among the various cations (Cu(2+), Pb(2+), Zn(2+), Ni(2+), Cd(2+), Ag(+), Ba(2+), Mg(2+), K(+), Na(+), and Li(+)) have been tested. Derivative 5 displays quite high through bond energy transfer efficiency in the presence of Hg(2+) ions in methanol whereas derivative 7 exhibits better FRET efficiency in the presence of Hg(2+) ions in THF and CH(3)CN than derivative 5. PMID:23385981

Bhalla, Vandana; Vij, Varun; Tejpal, Ruchi; Singh, Gopal; Kumar, Manoj

2013-04-01

339

Dissociative versus molecular adsorption of phenol on Si(100)21 : A first-principles calculation  

NASA Astrophysics Data System (ADS)

We investigated the competitive adsorption of a bifunctional molecule, phenol, on Si(100)21 by ab initio calculations. We performed geometry optimizations of phenol adsorbed either molecularly or dissociatively, on five possible sites (top, bridge, valley bridge, cave, and pedestal), in the low coverage regime. We found that the dissociative adsorption of phenol on top of a silicon dimer is the most favorable adsorption configuration. In the group of dissociative adsorption the phenol initially placed on the bridge or the valley-bridge sites ends up as a toplike local minima. The pedestal and cave sites remain as low-adsorption energy open sites. In the group of molecular adsorption, a higher adsorption energy is associated to the adsorption through an addition reaction and loss of the aromatic character (bridge, valley-bridge, and pedestal sites). Standard butterfly or diagonal butterfly are the corresponding optimized geometries. Retention of aromatic character and lower adsorption energy are associated to the adsorption on the top and cave sites. The ordering of adsorption sites according to the adsorption energy shows a mixture of the dissociative and the molecular sites. In the case of adsorption on the top site, the adsorption energies after a rotation of the phenoxy fragment along the bonding axis and hydrogen migration on the surface are very similar. The bend of the phenoxy fragment on the surface, instead, is not favored (the adsorption energy is 1.004eV lower compared to the vertical position). Different electron density maps were calculated for different adsorption sites and modes. Finally, we investigated the possibility that molecularly adsorbed phenol behaves as a precursor for the dissociative one by nudged elastic band calculations. We found a barrier of the same order of magnitude of the thermodynamic energy at room temperature for the conversion of the valley-bridge molecular into the top dissociative site.

Carbone, Marilena; Meloni, Simone; Caminiti, Ruggero

2007-08-01

340

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

PubMed

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

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

2013-02-01

341

Zero kinetic energy photoelectron (ZEKE) spectroscopy of the heterotrimer phenol-water-argon: Interaction between a hydrogen bond and a van der Waals bond  

Microsoft Academic Search

The heterotrimer phenol -water- Ar, a complex containing two different types of intermolecular bonds a van der Waals bond and a hydrogen bond has been studied in a supersonic jet with various spectroscopic techniques. The two-photon, two-color (1 + 1?) resonance-enhanced multiphoton ionization (REMPI) spectrum of the S1 state shows striking differences compared to the spectrum of the

Otto Dopfer; Markus Melf; Klaus Mller-Dethlefs

1996-01-01

342

Evaluation of Front-end Higher Energy Collision-Induced Dissociation on a Bench-top Dual Pressure Linear Ion Trap Mass Spectrometer for Shotgun Proteomics  

PubMed Central

We report the implementation of front-end higher energy collision induced dissociation (fHCD) on a bench-top dual pressure linear ion trap. Software and hardware modifications were employed, described in detail vide-infra, to allow isolated ions to undergo collisions with ambient gas molecules in an intermediate multipole (q00) of the instrument. Results comparing the performance of fHCD and resonance excitation collision induced dissociation (RE-CID) in terms of injection time, total number of scans, efficiency, mass measurement accuracy (MMA), unique peptide identifications, and spectral quality of labile modified peptides are presented. fHCD is approximately 23% as efficient as RE-CID and, depending on the search algorithm, it identifies 6.6% more or 15% less peptides (q<0.01) from a soluble whole-cell lysate (Caenorhabditis elegans) than RE-CID using Mascot or Sequest search algorithms, respectively. fHCD offers a clear advantage for the analysis of phosphorylated and glycosylated (O-GlcNAc) peptides as the average cross-correlation score (XCorr) for spectra using fHCD was statistically greater (p<0.05) than for spectra collected using RE-CID.

Bereman, Michael S.; Canterbury, Jesse D.; Egertson, Jarrett D.; Horner, Julie; Remes, Philip M.; Schwartz, Jae; Zabrouskov, Vlad; MacCoss, Michael J.

2011-01-01

343

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

PubMed

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

Cern, Jir; Hobza, Pavel

2009-11-13

344

Potential energy surface and unimolecular dynamics of stretched n-butane.  

PubMed

The potential energy surface (PES) and unimolecular reaction dynamics of stretched n-butane are investigated, as a model for a stretched "normal" alkane or straight chain polymer. The nature of the PES for stretched n-butane depends on the extent of stretching. If it is less than that required to reach the inflection points in the C[Single Bond]C stretch potentials and the C[Single Bond]C torsions are considered free rotors, there is only one potential energy minimum, with each bond elongated. However, for stretching past these inflection points, the PES has three minima and each has one bond longer than the other two, i.e., C[Single Bond]C[Single Bond]C[Single Bond]C, C[Single Bond]C[Single Bond]C[Single Bond]C, and C[Single Bond]C[Single Bond]C[Single Bond]C. There are three transition states (TSs) connecting these minima. A linear alkane, consisting of n carbon atoms and stretched past its C[Single Bond]C inflection points, has (n-1) minima and (n-1)(n-2)2 TSs connecting them. For stretching less than that required to reach the C[Single Bond]C inflection points, the only unimolecular pathways are dissociations to form the C+C[Single Bond]C[Single Bond]C, C[Single Bond]C+C[Single Bond]C, and C[Single Bond]C[Single Bond]C+C products. However, with stretching past the C[Single Bond]C inflection points, isomerizations between the three potential energy minima may also occur. The relative importance of isomerization versus dissociation depends on the relative size of their barriers. For slight stretching past the C[Single Bond]C inflection points, the isomerization barriers are much lower than those for dissociation and relaxation between the minima is much faster than dissociation. Thus, the molecule samples these minima randomly during its dissociation, with a density of states that comprises the complete PES. With extensive stretching past the inflection points, isomerizations between the potential energy minima do not occur and only dissociation for the excited minima occurs, e.g., C[Single Bond]C[Single Bond]C[Single Bond]C-->C+C[Single Bond]C[Single Bond]C. For intermediate stretching past the C[Single Bond]C inflection points, the rates for the isomerization and dissociation pathways are competitive and both must be considered in modeling the dissociation kinetics. Microcanonical chemical dynamics simulations are performed to study the unimolecular kinetics of n-butane in three stretched configurations: Stretched less than the C[Single Bond]C inflection point; stretched slightly beyond the C[Single Bond]C inflection point; and stretched significantly beyond the C[Single Bond]C inflection point. The resulting unimolecular dynamics were found to be in excellent agreement with RRKM theory. Frequency nu factors, determined by fitting the trajectory unimolecular rate constants to the classical harmonic RRKM rate constant expression, depend upon the extent of stretching and vary from 1.0 x 10(12)-8.4 x 10(16) s(-1). For a molecule with a large number of vibrational degrees of freedom and high excess energy, it is shown that the classical harmonic RRKM and classical harmonic transition state theory rate constants, k(E) and k(T), are equivalent. PMID:19044880

Lourderaj, Upakarasamy; McAfee, Jason L; Hase, William L

2008-09-01

345

Ultraviolet photolysis of adenine: Dissociation via the 1??* state  

NASA Astrophysics Data System (ADS)

High resolution total kinetic energy release (TKER) spectra of the H atom fragments resulting from photodissociation of jet-cooled adenine molecules at 17 wavelengths in the range 280>?phot>214 nm are reported. TKER spectra obtained at ?phot>233 nm display broad, isotropic profiles that peak at low TKER (~1800 cm-1) and are largely insensitive to the choice of excitation wavelength. The bulk of these products is attributed to unintended multiphoton dissociation processes. TKER spectra recorded at ?phot<=233 nm display additional fast structure, which is attributed to N9-H bond fission on the 1??* potential energy surface (PES). Analysis of the kinetic energies and recoil anisotropies of the H atoms responsible for the fast structure suggests excitation to two 1??* excited states (the 1La and 1Bb states) at ?phot~230 nm, both of which dissociate to yield H atoms together with ground state adeninyl fragments by radiationless transfer through conical intersections with the 1??* PES. Parallels with the photochemistry exhibited by other, smaller heteroaromatics (pyrrole, imidazole, phenol, etc.) are highlighted, as are inconsistencies between the present conclusions and those reached in two other recent studies of excited state adenine molecules.

Nix, Michael G. D.; Devine, Adam L.; Cronin, Brd; Ashfold, Michael N. R.

2007-03-01

346

Force History Dependence of Receptor-Ligand Dissociation  

Microsoft Academic Search

Receptor-ligand bonds that mediate cell adhesion are often subjected to forces that regulate their dissociation via modulating off-rates. Off-rates control how long receptor-ligand bonds last and how much force they withstand. One should therefore be able to determine off-rates from either bond lifetime or unbinding force measurements. However, substantial discrepancies exist between the force dependence of off-rates derived from the

Bryan T. Marshall; Krishna K. Sarangapani; Jizhong Lou; Rodger P. McEver; Cheng Zhu

2005-01-01

347

Communications: Photoinitiated bond dissociation of bromoiodomethane in solution: Comparison of one-photon and two-photon excitations and the formation of iso-CH(2)Br-I and iso-CH(2)I-Br.  

PubMed

Broadband UV-visible femtosecond transient absorption spectroscopy was used to monitor the excited state photochemistry of CH(2)BrI following one-photon excitation at 266 or 271 nm and two-photon excitation at 395 or 405 nm in 2-butanol. The results for one-photon excitation agree with earlier studies in acetonitrile, showing clear formation of iso-CH(2)Br-I following cleavage of the C-I bond. In contrast, two-photon excitation at 395 nm results in the appearance of a blueshifted photoproduct absorption band assigned to formation of iso-CH(2)I-Br following cleavage of the C-Br bond. The results are discussed in the context of prior experimental and theoretical work and the prospects for optical control of bond cleavage. PMID:20405978

Tang, Kuo-Chun; Peng, Jian; Spears, Kenneth G; Sension, Roseanne J

2010-04-14

348

Communications: Photoinitiated bond dissociation of bromoiodomethane in solution: Comparison of one-photon and two-photon excitations and the formation of iso-CH2Br-I and iso-CH2I-Br  

NASA Astrophysics Data System (ADS)

Broadband UV-visible femtosecond transient absorption spectroscopy was used to monitor the excited state photochemistry of CH2BrI following one-photon excitation at 266 or 271 nm and two-photon excitation at 395 or 405 nm in 2-butanol. The results for one-photon excitation agree with earlier studies in acetonitrile, showing clear formation of iso-CH2Br-I following cleavage of the C-I bond. In contrast, two-photon excitation at 395 nm results in the appearance of a blueshifted photoproduct absorption band assigned to formation of iso-CH2I-Br following cleavage of the C-Br bond. The results are discussed in the context of prior experimental and theoretical work and the prospects for optical control of bond cleavage.

Tang, Kuo-Chun; Peng, Jian; Spears, Kenneth G.; Sension, Roseanne J.

2010-04-01

349

Direct observation of the primary and secondary C-Br bond cleavages from the 1,2-dibromopropane photodissociation at 234 and 265 nm using the velocity map ion imaging technique.  

PubMed

Photodissociation dynamics of 1,2-dibromopropane has been investigated at 234 and 265 nm by using the velocity map ion imaging method. At both pump energies, a single Gaussian-shaped speed distribution is observed for the Br*((2)P(1/2)) fragment, whereas at least three velocity components are found to be existent for the Br((2)P(3/2)) product. The secondary C-Br bond cleavage of the bromopropyl radical which is energized from the ultrafast primary C-Br bond rupture should be responsible for the multicomponent translational energy distribution at the low kinetic energy region of Br((2)P(3/2)). The recoil anisotropy parameter (beta) of the fragment from the primary C-Br bond dissociation is measured to be 0.53 (0.49) and 1.26 (1.73) for Br((2)P(3/2)) and Br*((2)P(1/2)), respectively, at 234 (265) nm. The beta value of Br((2)P(3/2)) from the secondary C-Br bond dissociation event at 265 nm is found to be 0.87, reflecting the fact that the corresponding Br((2)P(3/2)) fragment carried the initial vector component of the bromopropyl radical produced from the primary bond dissociation event. Density functional theory has been used to calculate energetics involved both in the primary and in the secondary C-Br bond dissociation dynamics. PMID:18665578

Lee, Kyoung-Seok; Yeon, Ki Young; Jung, Kyung-Hoon; Kim, Sang Kyu

2008-07-30

350

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

PubMed

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

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

2011-02-25

351

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

PubMed

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

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

2009-06-10

352

Modeling energy transfer to copper wire for bonding in an inert environment  

Microsoft Academic Search

Copper wire ball bonding has gained popularity in the last few years due to its economic advantage and superior electrical performance. However, because of copper's reactive nature to oxygen, free air ball formation for copper bonding is more crucial than in the gold wire process. To create a free air ball (FAB), the wire bonder uses an electronic flame-off (EFO)

Hong Meng Ho; J. Tan; Yee Chen Tan; Boon Hoe Toh; P. Xavier

2005-01-01

353

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

354

Determination of dissociative fragment-adsorbate interaction energy during chemisorption of the diatomic molecule HCl on Si(100)  

Microsoft Academic Search

This study investigates the surface chemistry and the ordering characteristics of coadsorbed hydrogen and chlorine atoms, generated by the exposure of the Si(100) surface to gas-phase HCl molecules at various substrate temperatures, by scanning tunneling microscopy (STM), core-level photoemission spectroscopy, and Monte Carlo simulation. Experimental results show that saturation exposure to HCl causes all surface dangling bonds to be terminated

Ming-Feng Hsieh; Jen-Yin Cheng; Jenq-Cheng Yang; Deng-Sung Lin; Karina Morgenstern; Woei-Wu Pai

2010-01-01

355

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

356

Dissociation of copper(II) ternary complexes containing cystine.  

PubMed

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

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

2010-06-10

357

Rapid bond rearrangement in core-excited molecular water.  

PubMed

The angular anisotropy of fragments created in the dissociation of core-electron excited water molecules is studied to probe the correlation between fragmentation channels, kinematics and molecular geometry. We present fragment kinetic measurements for water molecules where the inner-shell oxygen electron is excited to the unoccupied 4a1 and 2b2 valence molecular orbitals. The kinematics of individual fragmentation channels are measured using fully three-dimensional momentum imaging of fragments. The results show that the geometry of the molecule and the kinetic energy of fragments are strongly coupled in the atomisation process. In addition we identify a fragmentation process arising from bond rearrangement evidenced by the H2(+)-O(+) ion pair which is accessible for resonant excitation of the 1s electron. In all of the two-body fragmentation processes the dissociation takes place along the potential-energy surface, while atomisation reveals both dissociation along the potential surface and Coulomb explosion. The angular distribution of fragments suggests that the bond rearrangement is very rapid; likely on a sub 10 fs time scale. PMID:24121279

Laksman, Joakim; Mnsson, Erik P; Sankari, Anna; Colin, Denis; Gisselbrecht, Mathieu; Sorensen, Stacey L

2013-10-23

358

Identification of c-Type Heme-Containing Peptides Using Non-Activated IMAC Resin Enrichment and Higher-Energy Collisional Dissociation  

SciTech Connect

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

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

2011-10-01

359

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

PubMed

Background: Localized singlet diradicals are in general quite short-lived intermediates in processes involving homolytic bond-cleavage and formation reactions. In the past decade, long-lived singlet diradicals have been reported in cyclic systems such as cyclobutane-1,3-diyls and cyclopentane-1,3-diyls. Experimental investigation of the chemistry of singlet diradicals has become possible. The present study explores the substituents and the effect of their substitution pattern at the C(1)-C(3) positions on the lifetime of singlet octahydropentalene-1,3-diyls to understand the role of the substituents on the reactivity of the localized singlet diradicals. Results: A series of singlet 2,2-dialkoxy-1,3-diaryloctahydropentalene-1,3-diyls DR were generated in the photochemical denitrogenation of the corresponding azoalkanes AZ. The ring-closed products CP, i.e., 3,3-dialkoxy-2,4-diphenyltricyclo[3.3.0.0(2,4)]octanes, were quantitatively obtained in the denitrogenation reaction. The first-order decay process (k = 1/?) was observed for the fate of the singlet diradicals DR (?max ? 580-590 nm). The activation parameters, ?H () and ?S (), for the ring-closing reaction (?-bond formation process) were determined by the temperature-dependent change of the lifetime. The energy barrier was found to be largely dependent upon the substituents Ar and Ar'. The singlet diradical DRf (Ar = 3,5-dimethoxyphenyl, OCH2Ar' = OCH2(3,5-dimethoxyphenyl)) was the longest-lived, ?293 = 5394 59 ns, among the diradicals studied here. The lifetime of the parent diradical DR (Ar = Ph, OCH2Ar' = OCH3) was 299 2 ns at 293 K. Conclusion: The lifetimes of the singlet 1,3-diyls are found to be largely dependent on the substituent pattern of Ar and Ar' at the C(1)-C(3) positions. Both the enthalpy and entropy effect were found to play crucial roles in increasing the lifetime. PMID:23766808

Ye, Jianhuai; Fujiwara, Yoshihisa; Abe, Manabu

2013-05-14

360

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

PubMed

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

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

2011-04-14

361

Theoretical and computational studies of dissociative recombination of trihydrogen with low kinetic energy electrons: Time-independent and time-dependent approach  

NASA Astrophysics Data System (ADS)

Dissociative recombination of molecular ions by collisions with electrons is a reactive collision, in which the electronic kinetic energy is transferred to the excitation of the molecule that, then, dissociates. The goals of this dissertation was (1) to improve existing approaches in theory of DR of triatomic ions in the time-independent framework developed in recent years by Kokoouline and Greene, and (2) to develop a time-dependent theoretical framework for DR treatment based on quantum defect theory. The theoretical method developed by Kokoouline and Greene is based on multichannel quantum defect theory and accounts for the major non-Born-Oppenheimer Jahn-Teller interaction between electronic and vibrational motions of the molecule. The study of this dissertation is partially based on this method but improved, extended, and systematically applied in the framework of my thesis. This dissertation presents the calculated DR rate coefficient for H+3 within the time-independent framework and the description of the method used to obtain the (qualitative) flux with time-dependent method. The time-independent results show good agreement with experimental data from storage ring experiments. The DR rate coefficients for ortho- and para- H+3 were calculated separately and show a significant difference at very low electronic energies; a result that agrees with recent storage ring experiments. Also, it is discussed results for other isotopologues of H+3 (H2D+, D2H+, and D+3 ) and the results for vibrationally-excited initial states of H+3 . It was found that the DR rate coefficients for vibrationally-excited initial states are larger than the rates for the ion initially in the ground vibrational state. At the end, this dissertation discuss the time-dependent calculations done with a diatomic model system.

Santos, Samantha Fonseca Dos

362

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

SciTech Connect

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

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

1997-11-01

363

Dissociation of methane on different transition metals  

Microsoft Academic Search

Dissociation of methane on different transition metals M (M=Ru, Ir, Rh, Ni, Pd, Pt, Cu, Ag, Au) has been investigated using a quasi-relativistic density-functional method. Reaction enthalpies for the steps involved are determined. The activation energies have been estimated using the analytic BOC-MP formula. The transition metals, Ru, Rh, , Pt are shown to exhibit high activity in the dissociation

Meng-Sheng Liao; Qian-Er Zhang

1998-01-01

364

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

SciTech Connect

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

Kreycik, C.; Couglin, J.

2009-12-01

365

Prediction of distinct surface segregation effects due to coordination-dependent bond-energy variations in alloy nanoclusters  

NASA Astrophysics Data System (ADS)

The first implementation of a recently introduced method based on the extraction of the coordination dependence of surface bond-energy variations (CBEV) from density-functional theory (DFT) computed pure-metal surface-energy anisotropy is reported. In particular, polynomial functions fitted to DFT data computed previously for Pt, Pd, and Rh are used as input energetics for statistical-mechanical computations of Pt-Pd 923-atom cuboctahedron-cluster compositional structures (and Pt-Rh(111) as a test case) using the free-energy concentration expansion method (FCEM). The major findings concern the roles of preferential strengthening of intrasurface and surface-subsurface interlayer bonds leading to quite unique segregation characteristics: (i) strong Pt segregation at certain (111) surface sites of the Pt-Pd clusters, accompanied, at relatively high overall Pt composition, by weaker Pt segregation forming Pt-Pd ordered (100) structure, whereas Pd segregates mainly at the edge and vertex sites; (ii) dominant Pd subsurface segregation. The high computation efficiency of the CBEV/FCEM approach allows the determination of the complete temperature dependence of atomic-exchange processes among surface sites, as well as between subsurface and deeper sites, reflected in the corresponding configurational heat-capacity curves. Compared to other approaches, the high transparency of this method helps to elucidate the origin of the distinct bond-energy-variation effects on site-specific segregation in alloy nanoclusters.

Rubinovich, Leonid; Polak, Micha

2009-07-01

366

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

PubMed

Stalke's dilemma, stating that different chemical interpretations are obtained when one and the same density is interpreted either by means of natural bond orbital (NBO) and subsequent natural resonance theory (NRT) application or by the quantum theory of atoms in molecules (QTAIM), is reinvestigated. It is shown that within the framework of QTAIM, the question as to whether for a given molecule two atoms are bonded or not is only meaningful in the context of a well-defined reference geometry. The localized-orbital-locator (LOL) is applied to map out patterns in covalent bonding interaction, and produces results that are consistent for a variety of reference geometries. Furthermore, LOL interpretations are in accord with NBO/NRT, and assist in an interpretation in terms of covalent bonding. PMID:19090572

Jacobsen, Heiko

2009-05-01

367

Electrochemistry of Au(II) and Au(III) pincer complexes: determination of the Au(II)-Au(II) bond energy.  

PubMed

The bond energy of the unsupported Au-Au bond in the Au(ii) dimer [(C(?)N(?)C)Au]2 and the difference between Au(III)-OH and Au(III)-H bond enthalpies have been determined experimentally by electrochemical methods, with Au-OH and Au-H complexes showing unexpected differences in their reduction pathways, supported by DFT modelling. PMID:24051607

Dann, Thomas; Ro?ca, Drago?-Adrian; Wright, Joseph A; Wildgoose, Gregory G; Bochmann, Manfred

2013-10-01

368

Effect of the character of homo- and heteronuclear chemical bond on the intermolecular interaction energy and properties of halogens and hydrogen halides  

Microsoft Academic Search

The effect of the chemical bond character (the degrees of covalence C\\u000a c, metallicity C\\u000a m, and ionicity C\\u000a i) on the bond rigidity and the components of the van der Waals intermolecular interaction have been shown for halogens and\\u000a hydrogen halides as an example. The force constant is determined by the chemical bond character. The intermolecular interaction\\u000a energy of

O. S. Sirotkin; R. O. Sirotkin; P. B. Shibaev

2011-01-01

369

Gas-Phase Peptide Sulfinyl Radical Ions: Formation and Unimolecular Dissociation  

NASA Astrophysics Data System (ADS)

A variety of peptide sulfinyl radical (RSO) ions with a well-defined radical site at the cysteine side chain were formed at atmospheric pressure (AP), sampled into a mass spectrometer, and investigated via collision-induced dissociation (CID). The radical ion formation was based on AP reactions between oxidative radicals and peptide ions containing single inter-chain disulfide bond or free thiol group generated from nanoelectrospray ionization (nanoESI). The radical induced reactions allowed large flexibility in forming peptide radical ions independent of ion polarity (protonated or deprotonated) or charge state (singly or multiply charged). More than 20 peptide sulfinyl radical ions in either positive or negative ion mode were subjected to low energy collisional activation on a triple-quadrupole/linear ion trap mass spectrometer. The competition between radical- and charge-directed fragmentation pathways was largely affected by the presence of mobile protons. For peptide sulfinyl radical ions with reduced proton mobility (i.e., singly protonated, containing basic amino acid residues), loss of 62 Da (CH2SO), a radical-initiated dissociation channel, was dominant. For systems with mobile protons, this channel was suppressed, while charge-directed amide bond cleavages were preferred. The polarity of charge was found to significantly alter the radical-initiated dissociation channels, which might be related to the difference in stability of the product ions in different ion charge polarities.

Tan, Lei; Xia, Yu

2012-11-01

370

Critical surface energy of composite cement containing MDP (10-methacryloyloxydecyl dihydrogen phosphate) and chemical bonding to hydroxyapatite.  

PubMed

Self-adhesive composite cements are increasingly used for cementing inlays/onlays, intraradicular posts, crowns and laminate veneers. Wider clinical acceptance is driven by simpler and faster handling procedures, much like observed for self-etching adhesives. 10-Methacryloyloxydecyl dihydrogen phosphate (MDP) is a bi-functional monomer incorporated as the reactive ingredient in a contemporary self-adhesive cement. We have examined the surface free energy parameters of this cement and studied the mode of action of the cement on dentine substrate by contact angle measurements to determine the critical surface energy of the cement. Retention of the infrared absorption bands characteristic of the acrylate moieties on the surface of hydroxyapatite particles suggests that MDP contributes to the overall bonding to dentine by forming ionic chemical bonds with surface calcium ions in dentine crystalites. PMID:21310107

Dabsie, Firas; Grgoire, Genevive; Sharrock, Patrick

2011-02-10

371

Inferring modules of functionally interacting proteins using the Bond Energy Algorithm  

PubMed Central

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

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

2008-01-01

372

Dissociative recombination of HCl^+  

NASA Astrophysics Data System (ADS)

Recently, the molecular ion HCl^+ has been observed in the interstellar medium. There is little information available about the cross sections for creation and destruction of this ion. Therefore, we have begun calculations to predict the dissociative recombination cross section and the final state distribution of atomic states produced in the dissociation. The relevant electronic states are calculated ab initio by combining electron scattering calculations using complex Kohn variational method to obtain resonance positions and autoionization widths and multi-reference configuration interaction calculations to construct the ion and Rydberg states. The direct dissociation recombination cross section is obtained by using wave packets propagating on the resonant states.

Larson, sa; Fonseca Dos Santos, Samantha; Orel, Ann E.

2012-06-01

373

Dissociative recombination study of Na{sup +}(D{sub 2}O) in a storage ring  

SciTech Connect

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

Zhaunerchyk, Vitali; Ehlerding, Anneli; Geppert, Wolf D.; Hellberg, Fredrik; Thomas, Richard D.; Larsson, Mats; Viggiano, Albert A.; Arnold, Susan T.; Oesterdahl, Fabian; Hlavenka, Peter [Department of Physics, Albanova, Stockholm University, SE-106 91 Stockholm (Sweden); Air Force Research Laboratory, Space Vehicles Directorate, 29 Randolph Road, Hanscom AFB, Massachusetts 01731 (United States); Department of Physics, Albanova, Royal Institute of Technology, SE-106 91 Stockholm (Sweden); Department of Electronics and Vacuum Physics, Faculty of Mathematics and Physics, Charles University Prague V Holesovickach 2, Prague 8 (Czech Republic)

2004-12-01

374

UV and 532 nm Photo-Dissociation of 2-Nitrotoluene: Observation of Electronically-Excited NO; Emission from Carbon (I); N2-NO Energy Transfer; and Stabilization of 2-Nitrotoluene-Ar Clusters  

NASA Astrophysics Data System (ADS)

2-nitrotoluene is a taggant used in explosive compounds and also often used as a simulant for nitro-based high explosives. Various spectroscopic techniques focus on the detection of vibrationally excited NO as an indicator for the presence of explosives. We report on the photo-dissociation of 2-nitrotoluene using UV and 532 nm wavelengths. We not only observe vibrationally excited NO in its electronic ground state, but also vibrationally excited NO in its electronic excited state. The photo-dissociation of 2-nitrotoluene leads to the formation of atomic carbon and its emission, overlapping the NO emission, is observed. Energy transfer from laser-excited nitrogen to NO leads to NO emission with long lifetimes. Argon atoms stabilize 2-nitrotoluene molecules and delay their photo-dissociation.

Diez-y-Riega, H.; Eilers, H.

2012-07-01

375

Mass-Spectrometric Studies of Bonding in the Group IIA Fluorides  

Microsoft Academic Search

A mass spectrometer was used to study high-temperature gaseous equilibria of the type M(g) + MF2(g) = 2MF(g), where M = Mg, Sr, and Ba. The heat of this reaction gives directly the difference between bond dissociation energies D (MF ?F) ? D (M ?F). Results obtained for the above equilibrium were ?H298 = 25.6, 2.1, and ?6.7 kcal (all

D. L. Hildenbrand

1968-01-01

376

Electron impact dissociation of molecular ions  

NASA Astrophysics Data System (ADS)

The ORNL Electron-Ion Crossed Beams Experiment is used to determine absolute cross sections for electron-impact dissociation of molecular ions. Investigations have been carried out on DCO^+, CH3^+ , and N2D^+ cations, considered as amongst those species playing important roles in such diverse areas as laboratory plasmas, astrophysics, and thermonuclear fusion. The obtained results on dissociation of DCO^+ resulting in CO^+ fragments are discussed in light of the energy levels and photo-dissociation cross section of HCO^+ predicted by ab initio multi-reference configuration interaction calculations [Koch et al, 1995 Ber. Bunsenges Phys. Chem. 99 (3) 393]. Preliminary results on CH3^+ are compared to the measurements of Lecointre et al [XXIV ICPEAC, Rosario, Argentina, 20 - 26 July 2005; (Poster Session)]. Results for dissociation of N2D^+ producing ND^+ are also presented.

Bahati, E. M.; Fogle, M. R.; Vane, C. R.; Bannister, M. E.; Zhaunerchyk, V.; Thomas, R. D.

2006-05-01

377

Gas-Phase Dissociation Pathways of Multiply Charged Peptide Clusters  

PubMed Central

Numerous studies of cluster formation and dissociation have been conducted to determine properties of matter in the transition from the condensed phase to the gas phase using materials as diverse as atomic nuclei, noble gasses, metal clusters, and amino acids. Here, electrospray ionization is used to extend the study of cluster dissociation to peptides including leucine enkephalin with 719 monomer units and 25 protons, and somatostatin with 5 monomer units and 4 protons under conditions where its intramolecular disulfide bond is either oxidized or reduced. Evaporation of neutral monomers and charge separation by cluster fission are the competing dissociation pathways of both peptides. The dominant fission product for all leucine enkephalin clusters studied is a proton-bound dimer, presumably due to the high gas-phase stability of this species. The branching ratio of the fission and evaporation processes for leucine enkephalin clusters appears to be determined by the value of z2/n for the cluster where z is the charge and n the number of monomer units in the cluster. Clusters with low and high values of z2/n dissociate primarily by evaporation and cluster fission respectively, with a sharp transition between dissociation primarily by evaporation and primarily by fission measured at a z2/n value of ~0.5. The dependence of the dissociation pathway of a cluster on z2/n is similar to the dissociation of atomic nuclei and multiply charged metal clusters indicating that leucine enkephalin peptide clusters exist in a state that is more disordered, and possibly fluid, rather than highly structured in the dissociative transition state. The branching ratio, but not the dissociation pathway of [somatostatin5 + 4H]4+ is altered by the reduction of its internal disulfide bond indicating that monomer conformational flexibility plays a role in peptide cluster dissociation.

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

2005-01-01

378

Dissociated Prismatic Dislocation Loops.  

National Technical Information Service (NTIS)

Transmission electron microscopy observations on heterogeneous precipitation in dilute aluminum-base silver alloys tend to support a previously proposed model for dissociated prismatic dislocation loops. During the initial stage of precipitation, the perf...

A. K. Eikum

1968-01-01

379

Adiabatic and nonadiabatic dissociation of ethyl radical  

NASA Astrophysics Data System (ADS)

Direct ab initio molecular dynamics using the trajectory surface hopping method with Tully's fewest switches simulates the photodissociation dynamics of ethyl radical, C2H5, following electronic excitation to the A~-state. Nonadiabatic dissociation dominates and produces ground state ethylene and fast hydrogen atoms with an anisotropic angular distribution. Surface hopping also generates hot ground state ethyl radicals followed ultimately by unimolecular dissociation to C2H4+H. The calculated excited state lifetime and the product recoil energy distribution obtained from an ensemble of trajectories are consistent with previous experiments and suggest that a strictly nonadiabatic mechanism can account for nonradiative decay. This process is in competition with adiabatic dissociation producing electronically excited state ethylene and H, a dissociation channel that has not yet been experimentally observed. The branching ratio between adiabatic and nonadiabatic dissociation pathways depends sensitively on the quality of the potential energy surfaces. At the multireference configuration interaction with singles and doubles level of theory, 15% of all trajectories dissociate adiabatically.

Hostettler, Jonas M.; Bach, Andreas; Chen, Peter

2009-01-01

380

Dissociative identity disorder  

Microsoft Academic Search

The research literature on dissociative identity disorder is smaller than that on many other Axis I and II disorders. Despite\\u000a its smaller quantity, however, this literature contains a number of themes and developments of interest to the mental health\\u000a field as a whole. These themes or topic areas will likely be the focus of research on dissociative identity disorder over

Colin A. Ross

2006-01-01

381

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

PubMed

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

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

2011-09-05

382

Kinetics of thermal unimolecular dissociation by ambient infrared radiation  

SciTech Connect

The truncated Boltzmann distribution is used for interpreting the Arrhenius activation energy to obtain an estimate of the ion dissociation energy. This is used to show that the experimental observation of infrared radiation-induced thermal dissociation of ions on a time scale is inevitable at pressures below the limit of collisional interference. 25 refs., 10 figs.

Dunbar, R.C. [Case Western Reserve Univ., Cleveland, OH (United States)

1994-09-01

383

Experimental determination of the HO-Br bond energy and its relevance to the stratospheric and tropospheric ozone cycles  

SciTech Connect

The HO-Br bond energy (and consequently the heat of formation of HOBr) has been determined experimentally for the first time. HOBr can be photolyzed in the stratosphere to form Br and OH, both of which can react with ozone, and destroy it. Previous calculations modeling stratospheric reactions have assumed a lower stability than that found in the current research. The stability of HOBr was determined by measuring the threshold for formation of Br{sup +} from this molecule, using photoionization mass spectrometry. Their work was supported by the Division of Chemical Sciences, Office of Basic Energy Sciences.

Ruscic, B.; Berkowitz, J.

1996-02-01

384

Multiphoton dissociation of SF6 by a molecular beam method  

NASA Astrophysics Data System (ADS)

The dynamics of infrared multiphoton excitation and dissociation of SF6 has been investigated under collision-free conditions by a crossed laser-molecular beam method. In order to understand the excitation mechanism and to elucidate the requirements of laser intensity and energy fluence, a series of experiments have been carried out to measure the dissociation yield dependences on energy fluence, vibrational temperature of SF6, the pulse duration of the CO2 laser, and the frequency in both one and two laser experiments. Translational energy distributions of the primary dissociation product SF5, measured by time-of-flight and angular distributions and the dissociation lifetime of excited SF6 as inferred from the observation of secondary dissociation of SF5 into SF4 and F during the laser pulse suggest that the dynamics of dissociation of excited molecules is dominated by complete energy randomization and rapid intramolecular energy transfer and can be adequately described by RRKM theory. An improved phenomenological model including the initial intensity dependent excitation, a rate equation describing the absorption and stimulated emission of single photons, and the unimolecular dissociation of excited molecules is constructed based on available experimental results. Our studies show that although the energy fluence of the laser determines the dissociation yield of molecules in the quasicontinuum, the role played by the intensity of the laser in multiphoton dissociation is more significant than just that of overcoming the intensity dependent absorption in the lowest levels. Once molecules are excited beyond the dissociation energy, the average level of excitation of the dissociating molecules will be significantly influenced by the laser intensity for a given energy fluence when the rate of decomposition starts to compete with the rate of up-excitation.

Schulz, P. A.; Sudb, Aa. S.; Grant, E. R.; Shen, Y. R.; Lee, Y. T.

1980-05-01

385

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

SciTech Connect

Electron attachment to clusters of N{sub 2}O in the energy range of 0-4 eV yields the ionic complexes [(N{sub 2}O){sub n}O]{sup -}, [(N{sub 2}O){sub n}NO]{sup -}, and (N{sub 2}O){sub n}{sup -} . The shape of the ion yields of the three homologous series differs substantially reflecting the different formation mechanisms. While the generation of [(N{sub 2}O){sub n}O]{sup -} can be assigned to dissociative electron attachment (DEA) of an individual N{sub 2}O molecule in the target cluster, the formation of [(N{sub 2}O){sub n}NO]{sup -} is interpreted via a sequence of ion molecule reactions involving the formation of O{sup -} via DEA in the first step. The nondecomposed complexes (N{sub 2}O){sub n}{sup -} are preferentially formed at very low energies (below 0.5 eV) as a result of intramolecular stabilization of a diffuse molecular anion at low energy. The ion yields of [(N{sub 2}O){sub n}O]{sup -} and (N{sub 2}O){sub n}{sup -} versus electron energy show sharp peaks at the threshold region, which can be assigned to vibrational Feshbach resonances mediated by the diffuse anion state as already observed in an ultrahigh resolution electron attachment study of N{sub 2}O clusters [E. Leber, S. Barsotti, J. Boemmels, J. M. Weber, I. I. Fabrikant, M.-W. Ruf, and H. Hotop, Chem. Phys. Lett. 325, 345 (2000)].

Vizcaino, Violaine; Denifl, Stephan; Maerk, Tilmann D.; Scheier, Paul [Institut fuer Ionenphysik und Angewandte Physik, Leopold Franzens-Universitaet Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria); Illenberger, Eugen [Institut fuer Chemie und Biochemie-Physikalische und Theoretische Chemie, Freie Universitaet Berlin, Takustrasse 3, D-14195 Berlin (Germany)

2010-10-21

386

Thermal dissociation of gaseous bradykinin ions  

SciTech Connect

Singly, doubly, and triply charged bradykinin ions have been dissociated thermally in a quadrupole ion trap operated with a bath gas comprised principally of helium at 1 mTorr. Dissociation rates as a function of bath gas temperature were measured along with product ion spectra. Studies were conducted to show that dissociation rates were independent of ion storage conditions and bath gas pressure. These studies indicate that good approximations to true Arrhenius parameters could be determined from Arrhenius plots using the bath gas temperature as a measure of the internal energy distribution of the parent ion population. Arrhenius parameters derived in this work agree with those reported recently using blackbody-induced radiative dissociation for the singly and doubly charged ions within experimental error. The spectrum of dissociation products were also very similar, reflecting the equivalency of the two methods for deriving Arrhenius parameters. Arrhenius parameters for the triply charged ion (E{sub a} = 0.79 {+-} 0.03 eV; log A = 9.3 {+-} 0.36 s{sup {minus}1}) are reported for the first time. Comparison of the Arrhenius parameters for the doubly and triply charged parent ions, along with dissociation reactions of the ions formed via water loss from the two parent ions indicate that water loss reactions from doubly protonated bradykinin and from triply protonated bradykinin proceed via distinctly different mechanisms.

Butcher, D.J.; Asano, K.G.; Goeringer, D.E.; McLuckey, S.A.

1999-10-28

387

Ionic dissociation of NaCl on frozen water  

Microsoft Academic Search

Low-energy reactive ion scattering (RIS) experiments show that NaCl dissociates almost completely on condensed ice surfaces prepared on Ru(001) even at 100 K forming solvated ions. NaCl by itself does not dissociate on a Ru(001) substrate; however, submonolayer coverages of water sets-in dissociation. Na+ ions thus created are immobile such that they do not migrate across one water bilayer (BL)

Seong-Chan Park; T. Pradeep; H. Kang

2000-01-01

388

Imaging the molecular dynamics of dissociative electron attachment to water  

SciTech Connect

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

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

2009-10-19

389

Bond- and Site-Selective Loss of H{sup -} from Pyrimidine Bases  

SciTech Connect

Electron attachment to gas phase thymine and uracil leads to H{sup -} loss within a broad and structured feature in the energy range between about 5 and 12 eV consisting of 4 overlapping resonances. By using thymine and uracil methylated at the N1 and N3 positions, respectively, and taking into account recent results from partly deuterated thymine, we find that by tuning the electron energy, H{sup -} loss turns out to be not only bond selective, i.e., (C-H) versus (N-H) bonds, but also site selective (N1 versus N3 site). Such a bond and site selectivity by energy has not been observed before in dissociative electron attachment. Implications for the mechanism of strand breaks observed in plasmid DNA are considered.

Ptasinska, Sylwia; Denifl, Stephan; Grill, Verena; Maerk, Tilmann D.; Illenberger, Eugen; Scheier, Paul [Institut fuer Ionenphysik and Center of Molecular Biosciences Innsbruck, Leopold Franzens Universitaet Innsbruck, Technikerstrasse 25, A-6020 Innsbruck (Austria)

2005-08-26

390

Isotope separation by photoselective dissociative electron capture  

DOEpatents

Disclosed is a method of separating isotopes based on photoselective electron capture dissociation of molecules having an electron capture cross section dependence on the vibrational state of the molecule. A molecular isotope source material is irradiated to selectively excite those molecules containing a desired isotope to a predetermined vibrational state having associated therewith an electron capture energy region substantially non-overlapping with the electron capture energy ranges associated with the lowest vibration states of the molecules. The isotope source is also subjected to electrons having an energy corresponding to the non-overlapping electron capture region whereby the selectively excited molecules preferentially capture electrons and dissociate into negative ions and neutrals. The desired isotope may be in the negative ion product or in the neutral product depending upon the mechanism of dissociation of the particular isotope source used. The dissociation product enriched in the desired isotope is then separated from the reaction system by conventional means. Specifically, [sup 235]UF[sub 6] is separated from a UF[sub 6] mixture by selective excitation followed by dissociative electron capture into [sup 235]UF[sub 5]- and F. 2 figs.

Stevens, C.G.

1978-08-29

391

A diabatic state model for donor-hydrogen vibrational frequency shifts in hydrogen bonded complexes  

NASA Astrophysics Data System (ADS)

A simple diabatic two-state Hamiltonian is considered which describes hydrogen bonding and proton transfer between a donor (D) and an acceptor (A), including different classes of bonds (weak, low-barrier, and strong). The independent variables are the distance R and the difference in proton affinity &z.epsi; between the donor and acceptor. With only two free parameters the model Hamiltonian gives a quantitative description of experimental data from a wide range of molecular complexes exhibiting correlations between R and &z.epsi; and binding energies, D-H bond lengths, and the frequencies of D-H stretch and bend vibrations. The UV photo-dissociation of strong H-bonded complexes via an excited electronic state with an exalted vibrational frequency is predicted.

McKenzie, Ross H.

2012-05-01

392

Bond Breaking and Bond Formation: How Electron Correlation is Captured in Many-Body Perturbation Theory and Density-Functional Theory  

NASA Astrophysics Data System (ADS)

For the paradigmatic case of H2 dissociation, we compare state-of-the-art many-body perturbation theory in the GW approximation and density-functional theory in the exact-exchange plus random-phase approximation (RPA) for the correlation energy. For an unbiased comparison and to prevent spurious starting point effects, both approaches are iterated to full self-consistency (i.e., sc-RPA and sc-GW). The exchange-correlation diagrams in both approaches are topologically identical, but in sc-RPA they are evaluated with noninteracting and in sc-GW with interacting Green functions. This has a profound consequence for the dissociation region, where sc-RPA is superior to sc-GW. We argue that for a given diagrammatic expansion, sc-RPA outperforms sc-GW when it comes to bond breaking. We attribute this to the difference in the correlation energy rather than the treatment of the kinetic energy.

Caruso, Fabio; Rohr, Daniel R.; Hellgren, Maria; Ren, Xinguo; Rinke, Patrick; Rubio, Angel; Scheffler, Matthias

2013-04-01

393

Classical trajectory studies of the molecular dissociation dynamics of formaldehyde - H2CO yield H2 + CO  

NASA Astrophysics Data System (ADS)

Classical trajectory calculations have been carried out to simulate the unimolecular decomposition of formaldehyde in the ground electronic state (S0). Global potential-energy surfaces were constructed using the empirical valence-bond (EVB) approach. Two sets of ab initio input were used to characterize two different EVB potential-energy surfaces, and trajectory calculations using one of these gives excellent agreement with experimental data for the product-state distributions of H2 and CO. The trajectory study of vector correlations with prompt dissociation of the parent molecule provides understanding of the dissociation dynamics in the molecular frame. From comparison with some of the experimental results and information from a few ab initio calculations, some improvements for the current potential surfaces are suggested.

Chang, Yan-Tyng; Minichino, Camilla; Miller, William H.

1992-03-01

394

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

NASA Astrophysics Data System (ADS)

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

Fantner, Georg E.

2005-03-01

395

Matrix-Assisted Laser Desorption/Ionisation - High-Energy Collision-Induced Dissociation of Steroids: Analysis of Oxysterols in Rat Brain  

PubMed Central

Neutral steroids have traditionally been analysed by gas chromatography mass spectrometry (GC-MS) after necessary derivatisation reactions. However, GC-MS is unsuitable for the analysis of many conjugated steroids and those with unsuspected functional groups. Here we describe an alternative analytical method specifically designed for the analysis of oxosteroids and those with a 3?-hydroxy-?5 or 5?-hydrogen-3?-hydroxy structure. Steroids were derivatised with Girard P (GP) hydrazine to give GP hydrazones which are charged species and readily analysed by matrix-assisted laser desorption/ionization mass spectrometry. The resulting [M]+ ions were then subjected to high-energy collision-induced dissociation on a tandem time-of-flight instrument. The product-ion spectra give structurally informative fragment-ion patterns. The sensitivity of the analytical method is such that steroids structures can be determined from low pg (low fmole) amounts of sample. The utility of the method has been demonstrated by the analysis of oxysterols extracted from rat brain.

Wang, Yuqin; Hornshaw, Martin; Alvelius, Gunvor; Bodin, Karl; Liu, Suya; Sjovall, Jan; Griffiths, William J.

2008-01-01

396

Effect of the reducing-terminal substituents on the high energy collision-induced dissociation matrix-assisted laser desorption/ionization mass spectra of oligosaccharides.  

PubMed

High-energy collision-induced dissociation (CID) matrix-assisted laser desorption/ionization mass spectra of N-linked oligosaccharides bearing different, commonly encountered, reducing terminal modifications (hydroxyl, 2-aminobenzamide, asparagine and a tetrapeptide) were recorded on a magnetic sector instrument equipped with an orthogonal-acceleration time-of-flight (OA-TOF) analyser. All the compounds formed abundant molecular (MNa+) and fragment ions, the latter corresponding to glycosidic and cross-ring cleavages as well as to internal fragment ions, all of which provided much insight into the oligosaccharide structure. The nature of the modification considerably influenced the CID behaviour. The strongest and most complete series of glycosidic cleavage ions (mainly Y and B--Domon and Costello nomenclature) was formed by the underivatized oligosaccharide whereas most cross-ring fragment ions, diagnostic of linkage, were found in the spectra of the glycopeptides. A-type cross-ring cleavage ions were particularly abundant in the spectrum of the asparagine derivative. Reductive amination using 2-aminobenzamide resulted in an opened reducing-terminal sugar ring and suppression of the cross-ring fragment ions carrying information associated with that ring. This information was present in the spectra of the free carbohydrate and the peptide derivatives. PMID:8914337

Kster, B; Naven, T J; Harvey, D J

1996-01-01

397

Diode laser measurements of CD{sub 3} quantum yields and internal energy for the dissociation of dimethyl sulfoxide-d{sub 6}  

SciTech Connect

Infrared diode laser absorption spectroscopy has been used to measure the CD{sub 3} radical photoproducts formed in the 193 and 222 nm photodissociation of dimethyl sulfoxide-d{sub 6}. Quantum yields of CD{sub 3} have been determined to be 1.4{plus_minus}0.1 at 193 nm and 1.2{plus_minus}0.2 at 222 nm, compared to 2.0 for acetone-d{sub 6} at 193 nm. An analysis of transient waveforms reflecting the vibrational relaxation and radical recombination kinetics also yields an estimate of the nascent CD{sub 3} vibrational energy content by determining the fraction of total CD{sub 3} initially produced in the vibrationless state. The nascent CD{sub 3} population in the vibrational ground state decreases in order for the following photodissociation systems: CD{sub 3}I at 248 nm, DMSO-d{sub 6} at 193 and 222 nm and acetone-d{sub 6} at 193 nm. The DMSO results are in good agreement with recent photofragment translational spectroscopy results and support a stepwise mechanism for the dissociation of DMSO at both wavelengths. {copyright} {ital 1997 American Institute of Physics.}

Rudolph, R.N.; North, S.W.; Hall, G.E.; Sears, T.J. [Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States)

1997-01-01

398

First-order correction for bond energy applied to polar molecules: Alkali halides, alkali cyanides, LiCH3, and CH3F  

NASA Astrophysics Data System (ADS)

The ionic bond in molecules containing an electropositive moiety and an electronegative moiety originates from a coupling between the ionic and the covalent contributions. Some representative cases in the example of LiF, LiCl, NaF, NaCl, KF, KCl, LiCH3, CH3F, LiCN, NaCN and KCN are calculated by ab initio and density functional methods. The resulting bond energy can be improved a posteriori by a recently proposed first-order method using the dipole moment or the effective charge. For the ab initio calculations, this method brings about a systematic improvement of the bond energy with respect to the experimental value. While the density functional method gives qualitatively mixed results, application of this first-order method generally improves the bond energy.

Lee, Dong-Ki; Lee, Yoon Sup; Hagebaum-Reignier, D.; Jeung, Gwang-Hi

2006-09-01

399

a vibrationally-adiabatic impulsive dissociation model  

NASA Astrophysics Data System (ADS)

The final fragment energy distribution in fast photodissociation reactions is often close to an impulsive limit since there is little time for intramolecular vibrational relaxation to occur. The computer program implements a new vibrationally-adiabatic impulsive dissociation model [K.F. Lim, in: IQEC '96 Technical Digest (Optical Soc. of America, 1996), paper WL 117], in which holonomic constraints are used to decouple vibrations from the dissociation reaction coordinate. Final photofragment vibrational, translational, and rotational energies and the associated angular momentum quantum numbers are calculated. The "soft" impulsive dissociation model of Busch and Wilson (J. Chem. Phys. 56 (1972) 3626) is included for comparison. The FORTRAN 77 code has been tested on a DEC ALPHA 300 workstation computer, a Fujitsu VP supercomputer, and a Solbourne 5e computer (with 3 cpu's).

Lim, Kieran F.

1996-09-01

400

Hot exciton dissociation in polymer solar cells  

NASA Astrophysics Data System (ADS)

The standard picture of photovoltaic conversion in all-organic bulk heterojunction solar cells predicts that the initial excitation dissociates at the donor/acceptor interface after thermalization. Accordingly, on above-gap excitation, the excess photon energy is quickly lost by internal dissipation. Here we directly target the interfacial physics of an efficient low-bandgap polymer/PC60BM system. Exciton splitting occurs within the first 50?fs, creating both interfacial charge transfer states (CTSs) and polaron species. On high-energy excitation, higher-lying singlet states convert into hot interfacial CTSs that effectively contribute to free-polaron generation. We rationalize these findings in terms of a higher degree of delocalization of the hot CTSs with respect to the relaxed ones, which enhances the probability of charge dissociation in the first 200?fs. Thus, the hot CTS dissociation produces an overall increase in the charge generation yield.

Grancini, G.; Maiuri, M.; Fazzi, D.; Petrozza, A.; Egelhaaf, H.-J.; Brida, D.; Cerullo, G.; Lanzani, G.

2013-01-01

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