JCP Nameplate
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

You Tube Flickr Twitter iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue

22 Dec 1995

Volume 103, Issue 24, pp. 10413-10807

Page 1 of 2 Pages Next Page | Jump to Page

Experimental determination of the Compton profile of C60 through binary encounter electron spectroscopy

B. D. DePaola, R. Parameswaran, B. P. Walch, M. D. Troike, P. Richard, M. J. Puska, and R. M. Nieminen

J. Chem. Phys. 103, 10413 (1995); http://dx.doi.org/10.1063/1.469889 (4 pages) | Cited 3 times

Full Text: | Download PDF

Show Abstract
The method of 0° electron spectroscopy was used to study binary encounter electrons resulting from hard collisions between 1.5 MeV/u C6+ ions and the electrons in a C60 vapor target. The Compton profile of C60 was then extracted from the electron spectra using an impulse approximation treatment. The experimental results are in excellent agreement with theoretical Compton profiles of C60. The C60 Compton profile is compared with that of atomic carbon, as well as those for graphite and diamond. © 1995 American Institute of Physics.
Show PACS
34.50.-s Scattering of atoms and molecules
34.80.-i Electron and positron scattering
36.40.Mr Spectroscopy and geometrical structure of clusters

Rotational analysis of the threshold photoelectron spectra of room temperature and jet‐cooled CO2

Ralph T. Wiedmann, Michael G. White, Hélène Lefebvre‐Brion, and Claudina Cossart‐Magos

J. Chem. Phys. 103, 10417 (1995); http://dx.doi.org/10.1063/1.469890 (7 pages) | Cited 16 times

Full Text: | Download PDF

Show Abstract
The rotational structure associated with the math 2Πg (000) ground ionic state of CO+2 has been investigated by threshold photoelectron spectroscopy and semiempirical calculations based on the distribution of Rydberg state levels at n=2000. The calculations are in very good agreement with the rotationally resolved spectra for the math 2Πg,3/2 and math 2Πg,1/2 spin–orbit levels for both room temperature and supersonically cooled ground state CO2. Intensity anomalies are partly explained by decay mechanisms involving rotational and spin–orbit autoionization. © 1995 American Institute of Physics.
Show PACS
33.20.Sn Rotational analysis
33.60.+q Photoelectron spectra
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Interactions in undersaturated and supersaturated lysozyme solutions: Static and dynamic light scattering results

Martin Muschol and Franz Rosenberger

J. Chem. Phys. 103, 10424 (1995); http://dx.doi.org/10.1063/1.469891 (9 pages) | Cited 111 times

Full Text: | Download PDF

Show Abstract
We have performed multiangle static and dynamic light scattering studies of lysozyme solutions at pH=4.7. The Rayleigh ratio Rθ and the collective diffusion coefficient Dc were determined as function of both protein concentration cp and salt concentration cs with two different salts. At low salt concentrations, the scattering ratio Kcp/Rθ and diffusivity increased with protein concentration above the values for a monomeric, ideal solution. With increasing salt concentration this trend was eventually reversed. The hydrodynamic interactions of lysozyme in solution, extracted from the combination of static and dynamic scattering data, decreased significantly with increasing salt concentration. These observations reflect changes in protein interactions, in response to increased salt screening, from net repulsion to net attraction. Both salts had the same qualitative effect, but the quantitative behavior did not scale with the ionic strength of the solution. This indicates the presence of salt specific effects. At low protein concentrations, the slopes of Kcp/Rθ and Dc vs cp were obtained. The dependence of the slopes on ionic strength was modeled using a DLVO potential for colloidal interactions of two spheres, with the net protein charge Ze and Hamaker constant AH as fitting parameters. The model reproduces the observed variations with ionic strength quite well. Independent fits to the static and dynamic data, however, led to different values of the fitting parameters. These and other shortcomings suggest that colloidal interaction models alone are insufficient to explain protein interactions in solutions. © 1995 American Institute of Physics.
Show PACS
87.15.Nn
87.64.Bx Electron, neutron and x-ray diffraction and scattering

Spectroscopically determined Born–Oppenheimer and adiabatic surfaces for H3+, H2D+, D2H+, and D3+

Bianca M. Dinelli, Oleg L. Polyansky, and Jonathan Tennyson

J. Chem. Phys. 103, 10433 (1995); http://dx.doi.org/10.1063/1.469892 (6 pages) | Cited 22 times

Full Text: | Download PDF

Show Abstract
High resolution spectroscopic data for H3+, H2D+, D2H+, and D3+ is used to determine effective, mass‐dependent potential energy surfaces for each isotopomers. These surfaces are expressed as a sum of the mass‐independent Born–Oppenheimer (BO) potential and a mass dependent adiabatic correction. For H3+ and D3+ the adiabatic correction is a single surface of the same symmetry and functional form as the BO surface. For H2D+ and D2H+ a second, lower symmetry surface is required. Fits to all three surfaces were started from recent, high quality ab initio calculations. The standard deviations for fits using all the available data with J≤9 are 0.015 cm−1 for H3+, 0.010 cm−1 for H2D+ and D2H+ combined, and 0.015 cm−1 for D3+. These values are close to the intrinsic experimental error of much of the data and improve on the corresponding ab initio surfaces by at least an order of magnitude. The fits are very compact: nearly 1600 data are fitted by adjusting 36 constants and freezing 51 at their ab initio values. © 1995 American Institute of Physics.
Show PACS
31.30.Gs Hyperfine interactions and isotope effects
33.20.Ea Infrared spectra
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Infrared emission spectra from cryogenic proton‐irradiated helium gas

D. W. Tokaryk, G. R. Wagner, R. L. Brooks, and J. L. Hunt

J. Chem. Phys. 103, 10439 (1995); http://dx.doi.org/10.1063/1.469893 (6 pages) | Cited 2 times

Full Text: | Download PDF

Show Abstract
Spectra from proton‐beam irradiated helium gas, near 4.2 K, have been examined in the near infrared spectral region using a sensitive photomultiplier‐grating spectrometer combination (750–1000 nm) and a Fourier transform infrared spectrometer with an InGaAs detector (800–1800 nm). Most of the observed features can be assigned to known He2 transitions, and two bands, not previously observed (d 3Σ+u(v=4)→c 3Σ+g(v=3,4)) have been identified and analyzed. Some of the unidentified spectra have qualitative similarity to a set of visible emission lines tentatively assigned to an excimer–dimer (i.e., He4, two He2 excimers weakly bound together). These features, unlike the normal He2 spectra, demonstrate pronounced dependence on both the pressure and temperature of the sample. A comparison of the intensities of the singlet and triplet D(d)→C(c) transitions to the singlet and triplet C(c)→A(a) transitions is made. © 1995 American Institute of Physics.
Show PACS
33.20.Ea Infrared spectra
34.50.Gb Electronic excitation and ionization of molecules

Temperature dependence of diffusion of radical intermediates probed by the transient grating method

Koichi Okamoto, Masahide Terazima, and Noboru Hirota

J. Chem. Phys. 103, 10445 (1995); http://dx.doi.org/10.1063/1.469894 (8 pages) | Cited 13 times

Full Text: | Download PDF

Show Abstract
Diffusion processes of intermediate radicals created by the photoinduced hydrogen abstraction reactions of ketones, quinones, and N‐hetero aromatic molecules in ethanol and 2‐propanol are studied at various temperatures by using the transient grating (TG) method. The temperature dependences of the translational diffusion coefficients (D’s) of both the radicals and the parent molecules can be expressed by the Arrhenius relationship. The activation energies (ED) for diffusion of the radicals are larger than those of the parent molecules and the difference in ED depends on the molecular size. The different ED is explained in terms of the molecular volume dependence of ED; that is, larger molecular volumes of the radicals could be the cause of the larger ED. The larger apparent molecular volumes of the radicals are consistent with a model of microscopic aggregation of the surrounding molecules around the radical. © 1995 American Institute of Physics.
Show PACS
66.10.C- Diffusion and thermal diffusion
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

On the low lying excited states of methyl amine

D. P. Taylor and E. R. Bernstein

J. Chem. Phys. 103, 10453 (1995); http://dx.doi.org/10.1063/1.469895 (12 pages) | Cited 16 times

Full Text: | Download PDF

Show Abstract
Mass resolved excitation spectroscopy (MRES) and high level ab initio calculations are employed to explore the low lying excited states of methyl amine, CH3NH2. Both (1+1) and (2+2) MRES of CH3NH2 produce well resolved vibronic features in the energy region around 39 770 to 46 000 cm−1. A complete data set in this region for (2+2) MRES is presented for the isotopic series CH3NH2, CD3NH2, CH3ND2, and CD3ND2. Two apparent Franck–Condon progressions can be qualitatively characterized in these spectra. In order to identify the excited state vibrations active in these spectra and to identify the nature of the excited electronic state(s) accessed, a rather extensive set of ab initio calculations are undertaken. An open shell Hartree–Fock force constant calculation proves central to assigning the observed vibrations. Agreement between the predicted and observed vibrational frequencies provide the strongest evidence to date for a planar excited state C–NH2 geometry. Using combinations and overtones of only two vibrations, the amine wag and scissors modes, all the major features of the low energy region of the spectra can be assigned for all the isotopically substituted methyl amines. Ab initio calculations indicate that the lowest A′ excited state is an A′ 3s Rydberg and the lowest A″ excited state is a valence electronic state. An additional A′ 3s Rydberg state is also found in this region, which because of its geometry, can be implicated in the methyl hydrogen elimination photodissociation reaction of methyl amine. Complete active space self‐consistent field (CASSCF) calculations alone, and augmented by many body perturbation theory (MBPT), are also performed. The spectra are consistent with two excited electronic states in the 40 000 cm−1 region. This new characterization of the low energy absorption spectra, and the interpretation of the high energy region in terms of an addition electronic state, challenge the long held view of the nature of the methyl amine excited states. © 1995 American Institute of Physics.
Show PACS
31.15.A- Ab initio calculations
31.15.xr Self-consistent-field methods
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Femtosecond time‐resolved studies of coherent vibrational Raman scattering in large gas‐phase molecules

Carl C. Hayden and David W. Chandler

J. Chem. Phys. 103, 10465 (1995); http://dx.doi.org/10.1063/1.469896 (8 pages) | Cited 59 times

Full Text: | Download PDF

Show Abstract
Results are presented from femtosecond time‐resolved coherent Raman experiments in which we excite and monitor vibrational coherence in gas‐phase samples of benzene and 1,3,5‐hexatriene. Different physical mechanisms for coherence decay are seen in these two molecules. In benzene, where the Raman polarizability is largely isotropic, the Q branch of the vibrational Raman spectrum is the primary feature excited. Molecules in different rotational states have different Q‐branch transition frequencies due to vibration–rotation interaction. Thus, the macroscopic polarization that is observed in these experiments decays because it has many frequency components from molecules in different rotational states, and these frequency components go out of phase with each other. In 1,3,5‐hexatriene, the Raman excitation produces molecules in a coherent superposition of rotational states, through (O, P, R, and S branch) transitions that are strong due to the large anisotropy of the Raman polarizability. The coherent superposition of rotational states corresponds to initially spatially oriented, vibrationally excited, molecules that are freely rotating. The rotation of molecules away from the initial orientation is primarily responsible for the coherence decay in this case. These experiments produce large (∼10% efficiency) Raman shifted signals with modest excitation pulse energies (10 μJ) demonstrating the feasibility of this approach for a variety of gas phase studies. © 1995 American Institute of Physics.
Show PACS
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.20.Vq Vibration-rotation analysis

Vibrational wave packets in the C 1Πu state of Cs2: Two color pump–probe experiments

G. Rodriguez, P. C. John, and J. G. Eden

J. Chem. Phys. 103, 10473 (1995); http://dx.doi.org/10.1063/1.469897 (11 pages) | Cited 14 times

Full Text: | Download PDF

Show Abstract
Two color, pump–probe laser experiments on the ∼100 fs time scale have been applied to examining the dynamics of vibrational wave packets in the C 1Πu state of Cs2. Wave packets consisting of more than 20 C state vibrational levels are produced with an initial pulse having a central wavelength between ∼620 and 680 nm. The temporal history of the wave packet is inferred from the time and energy‐integrated photoelectron signal produced when the excited state is photoionized by a time‐delayed pulse centered at 605, 610, 615, 617, or 620 nm. Because of the difference in equilibrium internuclear separations for the Cs2(C) and Cs+2(X) states (ΔRe≊0.75 Å), wave packets are readily observed (signal‐to‐noise ratio ≳10) without the need to resort to mass selection techniques. Frequency analysis of the wave packet data shows a dominant (fundamental) component that decreases from 29 to ∼28.3 cm−1 as the pump wavelength is tuned from 627 to 641 nm. Other spectral modes at ∼23.5 and ∼34 cm−1 and a weaker term at twice the fundamental frequency are also observed and quantum mechanical calculations of the wavepacket motion are in accord with the experimental results. © 1995 American Institute of Physics.
Show PACS
33.20.Tp Vibrational analysis
33.60.+q Photoelectron spectra
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
07.60.-j Optical instruments and equipment

Diffraction mechanisms in gas‐phase laser induced grating spectroscopy of vibrational overtone transitions

Jon A. Booze, Donald E. Govoni, and F. Fleming Crim

J. Chem. Phys. 103, 10484 (1995); http://dx.doi.org/10.1063/1.469898 (8 pages) | Cited 9 times

Full Text: | Download PDF

Show Abstract
We have investigated the grating formation mechanism in laser‐induced grating spectroscopy by preparing transient gratings via excitation of O–H vibrational overtones in water vapor. In principle, our experiments are sensitive to three different mechanisms of diffraction: a density‐based phase grating originating from local thermalization of the vibrational overtone state, a population‐based phase grating caused by differences in ground and excited state polarizability volumes, and a population‐based amplitude grating that appears when the probe laser is coincident with an electronic transition of the overtone‐excited molecules. For water saturated air at 50–760 Torr, bulk acoustic responses originating from both collisional thermalization and from electrostriction dominate the diffraction efficiency. Measurement of the probe‐wavelength dependence of the diffraction efficiency at pressures of 18 Torr and below shows that the dominant signal originates from a phase grating and that contributions from the amplitude grating are relatively unimportant at all pressures. Analysis of the temporal evolution of the diffraction efficiency suggests that the thermalization mechanism dominates at 18 Torr, despite there being only one hard‐sphere collision on the time scale of the measurement. At 10 Torr, the temporal evolution of the diffraction signal begins to show evidence of a population based phase grating contribution as well. These conclusions are consistent with our measured thermalization rate constants for the vibrational overtone states and also with calculations of the effects of vibrational excitation on the molecular polarizability volume. © 1995 American Institute of Physics.
Show PACS
36.20.-r Macromolecules and polymer molecules
36.40.Ei Phase transitions in clusters

Vibronic activity in trans,trans‐1,3,5,7 octatetraene: The S0→S1 spectrum

Wybren Jan Buma and Francesco Zerbetto

J. Chem. Phys. 103, 10492 (1995); http://dx.doi.org/10.1063/1.469899 (10 pages) | Cited 18 times

Full Text: | Download PDF

Show Abstract
Various levels of configuration interaction are used to investigate the vibronic intensity pattern of the false origins of the 1 1Ag→2 1Ag transition of all‐trans octatetraene. The vibronically induced mixing of the Ag with the Bu states is best simulated when polarization, i.e., d, functions are added to the basis set of atomic orbitals. Normal mode rotation upon electronic excitation plays an important role in the intensity distribution of the bu false origins. The progressions of the totally symmetric modes built on the bu bands is satisfactorily simulated at the CASSCF/6‐31G∗ level. The calculations also show that the overtones of at least four out‐of‐plane modes should be present in the spectra whose assignment is tentatively proposed. Through comparison of the pure electronic intensities calculated for cis–trans octatetraene with the vibronically induced intensities of trans–trans octatetraene, it is found that the presence of a cis linkage induces a spectral perturbation similar to that of the most active bu mode. © 1995 American Institute of Physics.
Show PACS
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions

Internal dynamics contributions to the CH stretching overtone spectra of gaseous monohydrogenated nitromethane NO2CHD2

D. Cavagnat, L. Lespade, and C. Lapouge

J. Chem. Phys. 103, 10502 (1995); http://dx.doi.org/10.1063/1.469900 (11 pages) | Cited 14 times

Full Text: | Download PDF

Show Abstract
The methyl CH‐stretching overtone spectra of gaseous monohydrogenated nitromethane NO2CHD2 have been recorded with conventional near infrared spectroscopy in the ΔvCH=1 to 4 regions and by intracavity laser photoacoustic spectroscopy in the ΔvCH=5 and 6 regions. They all exhibit a complex structure with, at ΔvCH=1 and 2, a characteristic asymmetric top vibration–rotation profile which vanishes as vibrational energy increases. These spectra have been analyzed with a theoretical model which takes into account in the adiabatic approximation the coupling between the anharmonic CH stretch described by a Morse potential and the quasifree internal rotation of the methyl group. All the parameters of this model (the zero point energy, the CH stretch frequency, the expansion coefficients of the dipole moment function) and their variation with the internal rotation coordinate have been determined from HF/6‐31G∗∗ ab initio calculations. This simple calculation, which contains no adjustable parameters, successfully describes the relative intensity and frequency of each peak within a given overtone and accounts for the variation of the dipole moment function as the vibrational energy increases. Owing to the relative localization of the wave functions within the effective potential wells, the spectral features can be assigned to particular pseudoconformers. The outer bands correspond to rovibrational transitions associated with the parallel and perpendicular conformation of the CH bond versus the molecular plane, the central band is generated by ‘‘free rotor’’ rovibrational transitions. Fermi resonance phenomena lead to no sizeable IVR until the fifth overtone. The CH/CD interbond coupling shifts the overtone spectra toward high frequency and is responsible for some additional weaker features in the high overtone spectra (Δv=5 and 6). © 1995 American Institute of Physics.
Show PACS
31.15.A- Ab initio calculations
33.20.Ea Infrared spectra
33.20.Vq Vibration-rotation analysis

Double‐resonance spectroscopy of the high Rydberg states of HCO. I. A precise determination of the adiabatic ionization potential

Eric Mayer and Edward R. Grant

J. Chem. Phys. 103, 10513 (1995); http://dx.doi.org/10.1063/1.469901 (7 pages) | Cited 16 times

Full Text: | Download PDF

Show Abstract
We report the first spectroscopic observation of the high Rydberg states of HCO. Individual lines in a system of vibrationally autoionizing Rydberg series converging to the (010) state of HCO+ are rotationally labeled in a double‐resonance excitation scheme that uses resolved levels in the (010) A′ vibronic component of the 3pπ 2Π Rydberg state as intermediates. Observed high‐Rydberg structure extends from the adiabatic ionization threshold—which falls just below the principal quantum number of 12 in the vibrationally excited series—to the (010) vertical threshold. Elements of a single series extending from n=12 to 50, for which the total angular momentumless spin can be assigned as N=1, are extrapolated to obtain a vertical convergence limit with respect to the 3pπ 2Π(010)A′ N′=0 intermediate state of 20 296.9±0.3 cm−1. Referring this transition energy to the ground state, and subtracting the precisely known fundamental bending frequency of the cation, establishes the adiabatic ionization potential corresponding to the transition from HCO 2A′(000) J″=0, K″=0 to HCO+ J+=0 1Σ+(000). The result is 65 735.9±0.5 cm−1 or 8.150 22±0.000 06 eV. © 1995 American Institute of Physics.
Show PACS
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)

Counting levels within vibrational polyads: Generating function approach

D. A. Sadovskií and B. I. Zhilinskií

J. Chem. Phys. 103, 10520 (1995); http://dx.doi.org/10.1063/1.469836 (17 pages) | Cited 18 times

Full Text: | Download PDF

Show Abstract
Simple analytical formulas for the number of energy levels in the vibrational polyads are given. These formulas account for the resonances between the vibrational modes, and for the symmetry of the problem, so that the number of states of a particular symmetry type can be computed. The formulas are used to estimate the differential and integral densities of states from the minimum initial information about the molecule. Examples of the vibrational structure of triatomic molecules A3, tetrahedral molecules AB4, and linear molecules AB2 are considered. The analytical formulas are compared to the ab initio results for H3+ [J. R. Henderson et al., J. Chem. Phys. 98, 7191 (1993)]. © 1995 American Institute of Physics.
Show PACS
33.20.Tp Vibrational analysis

Study of correlation states of acetylene by synchrotron photoelectron spectroscopy

Maria Sabaye Moghaddam, S. J. Dejardins, A. D. O. Bawagan, K. H. Tan, Y. Wang, and E. R. Davidson

J. Chem. Phys. 103, 10537 (1995); http://dx.doi.org/10.1063/1.469837 (11 pages) | Cited 15 times

Full Text: | Download PDF

Show Abstract
The inner valence photoelectron spectra of acetylene (C2H2) and isotopically labeled acetylene (1,213C–C2H2) are obtained using high resolution synchrotron photoelectron spectroscopy. Four distinct correlation (satellite) peaks, consistent with previous x‐ray photoelectron spectroscopy measurements, are resolved. The photon energy dependence of the intensity ratios of these satellites to the 2σ−1g main peak is observed over a wide photon energy range (32–72 eV). Three of these satellites (26.6, 28.0, and 29.8 eV binding energy) exhibited constant photon energy dependence while the fourth satellite (31.2 eV binding energy) showed enhancement of intensity towards the threshold. The photon energy dependence of correlation (satellite) peak 4 can be explained in either of two ways: (1) Peak 4 is a dynamic correlation peak associated with the 2σ−1g ionization process or (2) peak 4 is an intrinsic correlation peak associated with the 3σ−1g ionization process. A multireference singles and doubles configuration interaction (MRSDCI‐ANO) calculation of the theoretical photoelectron inner valence spectrum using average natural orbitals indicates that the latter explanation (2) is more likely. Semiquantitative agreement (in terms of the peak positions and intensities) is also obtained between the experimental photoelectron spectrum and the MRSDCI(ANO) calculation. © 1995 American Institute of Physics.
Show PACS
31.15.vq Electron correlation calculations for polyatomic molecules
33.60.+q Photoelectron spectra

Ab initio calculations of anharmonic vibrational circular dichroism intensities of trans‐2,3‐dideuteriooxirane

Keld L. Bak, Ota Bludský, and Poul Jørgensen

J. Chem. Phys. 103, 10548 (1995); http://dx.doi.org/10.1063/1.469838 (8 pages) | Cited 12 times

Full Text: | Download PDF

Show Abstract
A priori theory is derived for anharmonic calculations of vibrational circular dichroism (VCD). The anharmonic VCD expression is gauge origin independent and reduce to the magnetic field perturbation theory expression in the double‐harmonic approximation. The theory has been implemented using second‐order contact transformations for the vibration problem. Zeroth, first, and diagonal second derivatives of the atomic axial tensor are needed at the molecular equilibrium geometry. Ab initio calculations have been carried out for trans‐2,3‐dideuteriooxirane using self consistent field theory for the atomic axial tensors and using second‐order Møller–Plesset theory for the atomic polar tensors and the force fields. The changes of the vibrational rotatory strengths from anharmonicities are small, and do not explain the previously observed large discrepancies between the double‐harmonic results and the experimental values for three out of the 15 vibrational modes. © 1995 American Institute of Physics.
Show PACS
31.15.A- Ab initio calculations
31.15.xr Self-consistent-field methods
33.55.+b Optical activity and dichroism

The predissociation dynamics of ammonia: A theoretical study

Tamar Seideman

J. Chem. Phys. 103, 10556 (1995); http://dx.doi.org/10.1063/1.469839 (10 pages) | Cited 11 times

Full Text: | Download PDF

Show Abstract
A quantum mechanical model of the ammonia predissociation dynamics is presented. The effects of an excited state barrier and well, a deep conical intersection between the ground and excited states, and strong angular dependence of the potential energy surfaces are explored. The predissociation rate is sensitive to both the vibrational (v2′) and the rotational (J′,K′) level of the initially excited metastable state. The product state distribution following excitation within the v2′=0 band reflects the shape of the ground bend resonance and is broad, extending to the energetic limit. The photofragment angular distributions following excitation of magnetic–rovibronic state‐selected parent molecules depend sensitively on the photon frequency. Their structure varies markedly with the internal state of the accompanying NH2 fragment. The results are traced to the complex excitation dynamics, which prepare a frequency‐dependent superposition of rotational states, and to the strong forces exerted on the dissociating system in the region of the conical intersection. © 1995 American Institute of Physics.
Show PACS
33.15.Fm Bond strengths, dissociation energies
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.80.Gj Diffuse spectra; predissociation, photodissociation
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

Calculation of elastic scattering cross sections of low‐energy electrons by PbH4 and SnH4

M. H. F. Bettega, A. P. P. Natalense, M. A. P. Lima, and L. G. Ferreira

J. Chem. Phys. 103, 10566 (1995); http://dx.doi.org/10.1063/1.469840 (5 pages) | Cited 17 times

Full Text: | Download PDF

Show Abstract
We report elastic integral, differential, and momentum transfer cross sections from 10 to 30 eV for electron scattering by SnH4 and PbH4, obtained using the Schwinger Multichannel Method with Pseudopotentials [M. H. F. Bettega, L. G. Ferreira, and M. A. P. Lima, Phys. Rev. A 47, 1111 (1993)]. With these molecules we close the series of XH4 molecules, with X=C, Si, Ge, Sn, Pb. We compare the present results with those obtained previously for CH4, SiH4, and GeH4. We find similarities in the cross sections for SiH4, GeH4, SnH4, and PbH4 and a distinctive behavior of CH4. We discuss the role of the center atom size in the scattering process. To our knowledge this is the first ab initio calculation of the SnH4 and PbH4 electron scattering cross sections. © 1995 American Institute of Physics.
Show PACS
34.80.Bm Elastic scattering
34.80.Gs Molecular excitation and ionization

Stability of the CH3Cl dication

D. Duflot, J‐M. Robbe, and J‐P. Flament

J. Chem. Phys. 103, 10571 (1995); http://dx.doi.org/10.1063/1.469841 (9 pages) | Cited 1 time

Full Text: | Download PDF

Show Abstract
The chloromethane cation and dication have been studied using the complete active space self‐consistent field method followed by a multireference perturbative configuration interaction. The 2E ground state of CH3Cl+ presents a weak Jahn–Teller distortion, the 2A′ and 2A″ components being separated by only 3.4 kcal/mol with very similar geometries. Both states are equilibrium structures. Contrary to previous calculations, the lowest singlet and triplet states of CH3Cl++ are calculated to be stable. While the 3A2 state keeps the neutral C3v symmetry, the 1E singlet state shows a large Jahn–Teller effect, with a splitting of 32.7 kcal/mol in favor of the 1A′ state, which is the ground state of the molecule. The planar 1A′ state of CH2ClH++ is found to be the most stable isomer, lying 41.4 kcal/mol below the corresponding state of CH3Cl++. The 3A″ state, which lies 22.59 kcal/mol above the 1A′ state, has a nonplanar Cs‐symmetry geometry. Finally, the CH3Cl++ (1A′)→CH2ClH++ (1A′) isomerization takes place via a C1‐symmetry transition state, with an energy barrier of 32.85 kcal/mol. © 1995 American Institute of Physics.
Show PACS
31.15.xr Self-consistent-field methods
31.30.Gs Hyperfine interactions and isotope effects

Comparison between molecular orbital and surface integral calculations of the exchange energy for the homonuclear dimer ions He+2, Li+2, and Be+2

T. C. Chang and K. T. Tang

J. Chem. Phys. 103, 10580 (1995); http://dx.doi.org/10.1063/1.469842 (9 pages) | Cited 6 times

Full Text: | Download PDF

Show Abstract
The exchange energy, defined as half of the energy splitting of the gerade and ungerade states of a molecular ion, is investigated by molecular orbital calculations and by the surface integral method. Numerical results of He+2, Li+2, and Be+2 are obtained through restricted Hartree–Fock, unrestricted Hartree–Fock and localized Heitler–London type calculations. The results of the surface integral method are analytical expressions which depend only on the ionization energy. While the approaches are completely different, the results are generally in good agreement. Discrepancies are highlighted with the hope of promoting further interplay of these complementary methods. © 1995 American Institute of Physics.
Show PACS
31.15.xr Self-consistent-field methods
34.70.+e Charge transfer

The dissociation energies of CH4 and C2H2 revisited

Harry Partridge and Charles W. Bauschlicher

J. Chem. Phys. 103, 10589 (1995); http://dx.doi.org/10.1063/1.469843 (8 pages) | Cited 18 times

Full Text: | Download PDF

Show Abstract
The bond dissociation energies of CH4, C2H2, and their fragments are investigated using basis set extrapolations and high levels of correlation. The computed bond dissociation energies (De) are accurate to within 0.2 kcal/mol. The agreement with the experimental (D0) values is excellent if we assume that the zero‐point energy of C2H is 9.18 kcal/mol. The effect of core (carbon 1s) correlation on the bond dissociation energies of C–H bonds is shown to vary from 0.2 to 0.7 kcal/mol and that for C–C bonds it varies from 0.4 to 2.2 kcal/mol. © 1995 American Institute of Physics.
Show PACS
31.15.vn Electron correlation calculations for diatomic molecules
33.15.Fm Bond strengths, dissociation energies

Molecular softness, hypersoftness, infrared absorption, and vibrational Raman scattering: New relations derived from nonlocal polarizability densities

P.‐H. Liu and K. L. C. Hunt

J. Chem. Phys. 103, 10597 (1995); http://dx.doi.org/10.1063/1.469844 (8 pages) | Cited 11 times

Full Text: | Download PDF

Show Abstract
This work rigorously relates electromagnetic properties and characteristics of molecular potential energy surfaces to the empirical concept of ‘‘softness,’’ used to categorize Lewis acids and bases, and to summarize observed patterns of reactivity. New equations are derived that connect infrared absorption intensities, vibrational force constants, intermolecular forces at first order, and linear electric‐field shielding tensors to softness kernels as defined in density functional theory. A generalization to nonlinear response—by introduction of the hypersoftness—leads to new equations in density‐functional terms for vibrational Raman band intensities, the cubic anharmonicities in molecular potential energy surfaces, intermolecular forces at second order, and nonlinear electric‐field shielding tensors. The analysis employs relations of the softness and hypersoftness to nonlocal polarizability and hyperpolarizability densities that represent the intramolecular distribution of response to inhomogeneous electric fields. © 1995 American Institute of Physics.
Show PACS
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
34.20.-b Interatomic and intermolecular potentials and forces, potential energy surfaces for collisions

A hybrid density functional study of the first‐row transition‐metal monocarbonyls

Carlo Adamo and Francesco Lelj

J. Chem. Phys. 103, 10605 (1995); http://dx.doi.org/10.1063/1.469845 (9 pages) | Cited 40 times

Full Text: | Download PDF

Show Abstract
The results of a systematic density functional study, carried out using a self‐consistent hybrid approach including exact exchange contribution, on the all monocarbonyls of first‐row transition metals, are reported. Geometries, harmonic wave numbers, and binding energies, obtained using both standard generalized gradient corrected and hybrid functionals, are compared with previous published theoretical data and the available experimental findings. It is shown that hybrid functionals give results close to highly correlated post Hartree–Fock approaches and which are sensibly different from those obtained by standard local, even gradient corrected, methods. A nice agreement has been also found between theoretical and experimental binding energies. A natural bond orbital analysis confirms the role of the π interaction in the metal‐carbonyl bond and gives an explanation to the preference for bent structures found in chromium and copper monocarbonyls. © 1995 American Institute of Physics.
Show PACS
31.15.E- Density-functional theory
31.15.xr Self-consistent-field methods
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

On the contribution of electron transfer reactions to the quenching of tryptophan fluorescence

Carla Goldman, Pedro G. Pascutti, Paulo Piquini, and Amando S. Ito

J. Chem. Phys. 103, 10614 (1995); http://dx.doi.org/10.1063/1.469846 (7 pages) | Cited 10 times

Full Text: | Download PDF

Show Abstract
We present a theoretical calculation of rates for excited state electron transfer (ET) reactions in zwitterionic tryptophan for each of its six rotameric conformers. Within the Born–Oppenheimer approximation, we calculate the electronic part of the rate, using the renormalized perturbation expansion (RPE) method. The vibrational part is extracted from experimental data, assuming that at neutral pH, the observed fluorescence decay profile is composed of two exponentials corresponding to two competing populations in the sample; one in which fluorescence is accompanied by ET and other that is not. Complementary data, namely, ionization potentials and charge distributions are obtained using a combination of classical molecular mechanics simulation to determine the geometry of the six rotamers, and semiempirical (INDO/S) molecular orbital calculation. Our results indicate that conformers perpχ2g− and antiχ2g− give the main contribution to ET in the time scale of fluorescence. © 1995 American Institute of Physics.
Show PACS
33.50.-j Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion)
87.15.Nn

Fukui function from a gradient expansion formula, and estimate of hardness and covalent radius for an atom

Pratim K. Chattaraj, Andrés Cedillo, and Robert G. Parr

J. Chem. Phys. 103, 10621 (1995); http://dx.doi.org/10.1063/1.469847 (6 pages) | Cited 36 times

Full Text: | Download PDF

Show Abstract
The Fukui function for a neutral atom is expressed as its LDA approximation plus a one‐parameter gradient correction, and the resultant formula is numerically tested. Expressing hardness as a density functional involving this Fukui function, global hardness values are determined for several atoms. Estimates also are made of the covalent radii of neutral atoms. Calculated Fukui functions exhibit characteristics similar to those reported in the literature. Calculated hardnesses compare favorably with experimental values, and predicted covalent radii are in agreement with existing theoretical values and experimental data. No information other than the electron densities of the neutral species enter in the calculations. An exact nuclear cusp condition on the Fukui function is derived. © 1995 American Institute of Physics.
Show PACS
31.15.xt Variational techniques
32.50.+d Fluorescence, phosphorescence (including quenching)
Page 1 of 2 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Go to AIP Home   © AIP Publishing LLC
close