bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensitivity analysis of differential cross sections to the intermolecular potential
Authors: Eno Larry , Rabitz Herschel
Published: February 2003

This paper considers the sensitivity of both final state summed and state to state differential cross sections to the variation of parameters within a model intermolecular potential. In order to simplify the calculation of the cross sections and first order sensitivity coefficients (i.e., the partial derivative of cross sections with respect to potential parameters) attention is restricted to the scattering of an atom and rigid rotor. Furthermore, the collision dynamics are approximated by using the infinite order sudden (IOS) approximation. Particular emphasis is given to an examination of the sensitivity of angular features of the cross sections to potential parameter variations. This is facilitated by fitting the cross sections to functional forms which contain several adjustable parameters, each of which controls a particular feature. First order sensitivity coefficients are then used to derive quantitities which measure the sensitivity of a ’’feature parameter’’ with respect to the variation of a potential parameter. The first order sensitivities are also used to obtain so called derived sensitivity coefficients and, in particular, those which describe how the potential parameters are interrelated for a given set of cross section measurements. The behavior of these coefficients is examined as the angular range of the measurements is varied and as account is taken of the finite angular resolving power of molecular beam detectors. The results are used to determine the degree to which a set of differential cross section measurements is able to define various parameters of the assumed potential.
Vibrational deactivation of diatomic molecules by collisions with solid surfaces
Authors: Gerber R. B. , Beard L. H. , Kouri D. J.
Published: February 2003

A model is proposed for vibrational deexcitation of diatomic molecules by collisions with a solid surface. The expressions obtained are analyzed to yield insight into the collision dynamics and used to predict the rotational and translational energy distributions, and other properties of interest. The method is developed in the approximation of a stationary surface, and is closely related to a recent model for vibrational relaxation in atom–molecule collisions. From considerations based on the scales of the relevant energy spacings and coupling strengths applied to the vibrational, rotational, and diffraction states involved, the scattering equations are greatly simplified by several approximations. For a simple but realistic class of potentials, analytical expressions are obtained for the deactivation probabilities pertaining to all final translational–rotational channels. Using the expressions of the model, a detailed study is made of: (i) The rotational–translational energy distribution produced by the vibrational energy release, and its dependence on system parameters; (ii) isotope and collision-energy dependence of the deactivation probabilities; (iii) scaling properties of the transition probabilities with regard to ΔJ = J′−J, the change in rotational quantum number. The model is applied numerically to collisions of vibrationally excited H2, D2, T2, HD with a noncorrugated surface over a wide range of energies. The most striking feature of the model results is that a highly dominant fraction of the vibrational energy goes into molecular rotation, the main channel being an almost resonant V–R process in all cases.
Optical detrapping in solids
Authors: Morsink Jos B.W. , Wiersma Douwe A.
Published: February 2003

Energy transfer due to laser radiation between the lowest excited single state of pentacene and the lowest single exciton band in naphthalene is observed.(AIP)
An understanding of effective nuclear charges defined from homonuclear diatomic force constants
Authors: Ohwada Ken
Published: February 2003

Murrel’s effective nuclear charge model of a homonuclear diatomic molecule is further explained. The equations defining the effective nuclear charge are further explored.
Ideal gas thermodynamic properties of 1,4-dimethylbenzene
Authors: Draeger J. A. , Scott D. W.
Published: February 2003

Reliable thermodynamic properties of 1,4-dimethylbenzene in the ideal gas state have been recalculated. Selected values are compared with accurate experimental results. Free or very nearly free internal rotation of the methyl groups is deduced. (AIP)
Reply to a comment on ‘‘Reactions of Ar+ with various neutrals’’
Authors: Rakshit Asit B. , Warneck Peter
Published: February 2003

Lindinger et al’s2 comments on the author’s previously published study1 are discussed. In particular a possible falsification of data caused by high speed ions in the drift tube is considered. It is shown that the results obtained in the experiments could not be explained as being caused by the apparatus used for the experiments. (AIP)
Calculation of the polymer size exponent by direct perturbation expansion
Authors: Al-Noaimi G. F.
Published: February 2003

Without recourse to the field theory method of de Gennes it is shown how by evaluating the polymer end-to-end distance and the second virial coefficient perturbatively using the method of Fixman it is possible to calculate the size exponent ν correct to O(ε2), where 4-ε is the dimensionality of the system.
Rotational relaxation in free jet expansion for N2 from 300 to 1000 K
Authors: Yamazaki Satoshi , Taki Masahiro , Fujitani Yoshiyasu
Published: February 2003

The object of this study is to obtain information on the rotation–translation transition probability during N2–N2 collisions. Rotational relaxation for N2 in the free expansion flow is studied by TOF (time-of-flight) measurement with a molecular beam sampling mass filter system. Source temperatures were heated up to 1300 K by an electric heater. The terminal rotational temperatures for various source temperatures and pressures were determined from an energy balance equation in conjunction with the TOF data. Recently, Pritchard et al. have proposed that the transition probability from the ith to the jth rotational states decreases in proportion to some power of the energy difference between the states. This power law was fitted to experimental results for rotational relaxation in the free jet expansion. The results show that the state-to-state rotational relaxation rates vary as the inverse 3/2 power of the energy difference between the initial and final states. The rotational distributions in the jet expansion were also calculated by this power law. The results show a Boltzmann distribution for low j levels but not for high j levels.
The relationship of torsional flexibility to orientational correlation times: Linear and nonlinear variables
Authors: Evans Glenn T.
Published: February 2003

The orientational correlation times for the Rouse-like vector modes of three to eight bond torsionally flexble alkane chains are determined as a function of the rate of trans–gauche isomerization. An approximate expression is derived which relates τk the correlation time for the kth vector Rouse mode to the Kramers rate and to matrix elements of the linear and nonlinear variables. The predictions of the theory agree favorably with the correlation times calculated using Brownian dynamics although the correlation functions themselves are in unsatisfactory agreement.
A new equation of state for detonation products
Authors: Chirat R. , Pittion-Rossillon G.
Published: February 2003

The Weeks–Chandler–Andersen (WCA) model for liquids is simplified to calculate the thermodynamic properties of detonation products. Results are first compared with Monte Carlo (MC) calculations. The argon Hugoniot deduced from MC results is in good agreement with that of the model. Intermolecular potentials for H2O, N2, CH4, and CO2 are fitted with experimental Hugoniots. We propose a mixture model deduced from the Lee–Levesque model. This new mixture model allows us to calculate the Chapman–Jouguet pressure and velocity of PETN by solving the chemical equilibrium for ten different components. Good agreement with experiment is obtained without using any parameter other than those of intermolecular potentials. The CJ velocity of TNT and CJ temperature of NM agree with experimental data.
Investigation of a ferroelastic phase transition in NdP514 by EPR study of Gd3+ center
Authors: Barthou Carlos , Blanzat Bernard , Canny Bernard
Published: February 2003

The ferroelastic phase transition between P21/c and Pncm structure of GdxNd1−xP5O14 is analyzed by EPR spectra, and the dependence of the resonance spectrum is studied from 77 to 421 K. It is shown that the orientation of the principal axis of the classical D tensor is mainly related to the spatial symmetry of the crystal by a rotation angle, and its temperature dependence is analyzed using the Landau model of phase transitions. Alternatively, the critical exponent of the order parameter near the phase transition has been found to be β = 0.33.
Hole burning, softon–phonon scattering, and ultrafast dephasing of impurity electronic transitions in glasses
Authors: Hayes John M. , Stout Roland P. , Small Gerald J.
Published: February 2003

Solid state persistent hole burning data for impurity molecules embedded in glasses are presented which show that the pure dephasing associated with the impurity electronic transition is orders of magnitude faster than found in crystalline host media. This anomalously fast dephasing is explained in terms of a new theory which takes into account the two level systems structure of glasses and electron–softon–phonon scattering involving very low frequency phonons. As a result, the high temperature limit for the scattering where the dephasing frequency is linear in T occurs at temperatures of only a few K. The theory is used to gauge the width of the two level systems distribution function f(ε), where ε is the splitting between the zero-point levels of the two minima associated with a two level system.
Effect of pressure on the first singlet exciton in crystalline anthracene
Authors: Sonnenschein R. , Syassen K. , Otto A.
Published: February 2003

The first singlet exciton state of anthracene single crystals has been studied by optical reflection spectroscopy under hydrostatic pressures up to 30 kbar. The Davydov splittings of the 0–0, 0–1, and 0–2 vibrational bands increase much faster than expected on the basis of first order dipolar resonance interaction. The average pressure coefficients are 16.6, 13.6, and 9.0 cm−1/kbar for the 0–0, 0–1, and 0–2 bands, respectively. The pressure effect on the exciton shift is small compared to the strong pressure dependence of the Davydov splitting. The pressure induced shifts of the excitonic transition energies are discussed in terms of molecular exciton theory.
Chemiluminescent chemi-ionization: Ar*+Ca and the CaAr+ emission spectrum
Authors: Hartman Dennis C. , Winn John S.
Published: February 2003

A flowing afterglow chemiluminescence apparatus has been used to analyze visible fluorescence in the Ar*(3P 20)+Ca(1S0) reaction. The rate constants for production of Ca+(2P 3/20) and Ca+(2P 1/20) were measured to be 1.6×10−10 and 3.2×10−11 cm3 molecule−1 sec−1, respectively. These results demonstrate a transfer of the total electronic angular momentum polarization in Ar* to the excited ion levels. The molecular band spectrum of the associative ionization product CaAr+(A 2Π) was observed. Molecular fluorescence constituted 14% of the total fluorescence from all ion products. This spectrum was analyzed with a model (exp-Z4) potential, yielding, for the ground state X 2Σ+, Re = 2.8 Å, ωe″ = 87 cm−1, and De″ = 1000 cm−1, and, for the A 2Π state, Re = 2.6 Å, ωe′ = 200 cm−1, and De′ = 4900 cm−1. The nascent internal state distribution in CaAr+ is found to consist of a fairly narrow range of high vibrational levels.
Infrared spectra of 15NH3⋅H2O, 2 15NH3⋅H2O, and deuterated forms of ammonia hemihydrate at 90 °K
Authors: Bertie John E. , Morrison Mary M.
Published: February 2003

The infrared spectra of various deuterated samples of ammonia hemihydrate are reported with some infrared absorption frequencies of 2 15NH3⋅H2O and 15NH3⋅H2O. The spectra of the 15N-substituted samples confirm the previous general assignments, and reveal a third component of ν3(NH3) in NH3⋅H2O. The absorption by 2ND3⋅D2O, NDH2 isolated in 2NH3⋅H2O, and ND2H isolated in 2ND3⋅D2O, show, with the aid of normal coordinate calculations, that the primary splitting of the bands due to ν2 and ν3 of ammonia is multiple site splitting, due to the existence of two types of ammonia molecule in the hemihydrate. The Cs site symmetry of the ammonia molecules is revealed by the stretching vibrations of NH2D in 2NH3⋅H2O but not by the symmetric deformation vibrations of NH2D or ND2H. The stretching vibrations of NH2D in 2NH3⋅H2O at 90 °K also indicate that the type II ammonia molecules occupy both of the orientations which preserve the plane of symmetry. The uncoupled O–D stretching frequencies of HDO in 2NH3⋅H2O confirm the assignment of the two νOH(H2O) bands in the spectrum of 2NH3⋅H2O as largely due to site splitting. The low-frequency νOD(HDO) stretching band is very broad and the corresponding νOH(HDO) band is even broader, as has been seen previously for analogous bands in hexamethylenetetramine hexahydrate. Similarly, one set of isolated νND(NH2D) stretching bands is sharp while the corresponding νNH(ND2H) bands are very broad, as has also been reported previously for solid ammonia. The assignment to rotational vibrations of features below 850 cm−1 in 2NH3⋅H2O is confirmed, but no evidence indicates the degree of mixing of ammonia and water displacements in these vibrations.
UV transient absorptions in high pressure argon excited by relativistic electrons
Authors: Collier F. , Leblond J. B. , Hoffbeck F. , Cottin P.
Published: February 2003

Several new laser effects have been obtained by using electron beam pumped mixtures of a rare gas with another gas. Nevertheless, the laser action in those media appears to be very sensitive to the effect of a transient absorption which can be due to the rare gas itself. Also in this work we have made an experimental study of transient absorptions in the near UV (250–450 nm) for a high pressure of argon excited by relativistic electrons. Two different absorptions have been identified in the present work: (1) A ’’long time’’ absorption attributed to Ar2*(3Σu); the experimental value of its cross section has been found to be in satisfactory agreement with the theoretical one; (2) a ’’short time’’ absorption which exhibits a very broad spectral width, the origin of which is discussed.
Electron beam excited mixtures of O2 in argon. I. Spectroscopy
Authors: Keto J. W. , Hart C. F. , Kuo Chien-Yu
Published: February 2003

We have studied the production of O(1S0) in mixtures of oxygen and argon excited by an electron beam as a function of dopant density, total pressure, and electron beam current. For these conditions we have estimated the populations of O(3P) and O3 from the O(1S0) quenched lifetimes. We found significant production of O(1S0) by charge transfer from Ar+2 to O2 and O3 followed by dissociative recombination to O(1S0). We have measured an optimum quantum efficiency for this process of 11%. We discuss model calculations for the production of O(1S0), O(3P), and O3 which are in reasonable agreement with experiment.
The kinetic shear viscosity coefficient in a dilute, multicomponent hard sphere gas mixture
Authors: Eder O. J. , Lackner T. , Posch M.
Published: February 2003

Starting with the ’’successive uncorrelated binary collision model’’ the kinetic part of the shear viscosity is calculated for a multicomponent dilute hard sphere gas mixture defined by the parameters nα (number density), mα (mass), and σαα (hard sphere diameter). The concentration dependence of the shear viscosity in a multicomponent mixture is determined within the ’’one and two collision approximation.’’ It is shown that the semiempirical result for a multicomponent mixture can be obtained if one uses the concentration dependence calculated for the hard sphere system together with the experimentally determined or, for realistic potentials, calculated shear viscosities of the single components of the mixture.
Scattering of atoms by solid surfaces: A CCGM theory of diffraction by a one-dimensional stationary periodic wall
Authors: Goodman Frank O. , Scribani Luigi
Published: February 2003

The CCGM theory of elastic atom–surface scattering, proposed by Cabrera, Celli, Goodman, and Manson [Surf. Sci. 19, 67 (1970)], is applied to the now-popular corrugated wall model of the scattering. Instead of the original ’’hard’’ wall, a ’’softer’’ wall, with finite potential step height, is used. The CCGM soft-wall results are compared with corresponding exact hard-wall results, for corrugations of the sinusoidal type and of other types, for example those with nondifferentiable corrugation functions. It is concluded that the CCGM soft-wall results agree well with the exact hard-wall results provided that neither the dimensionless corrugation amplitude nor the dimensionless atom wave number is too large, although no explanation of the reason for this agreement is given. The results are important because a typical exact calculation may be far more time consuming than is a typical CCGM calculation, particularly for the ’’nastier’’ corrugation functions.
Energy of the A 1Δ state of ZrO
Authors: Hammer Philip D. , Davis Sumner P. , Zook Alma C.
Published: February 2003

The energy of the A 1Δ state of ZrO in the vapor phase is 5904.19 cm−1 above the ground state X 1Σ+. It was measured by laser-excited fluorescnce techniques.(AIP)
Direct inversion of high overtone collision broadened linewidths in the HCl–HCl system: Rotationally inelastic rates for highly vibrationally excited molecules
Authors: DePristo Andrew E. , BelBruno Joseph J. , Gelfand Jack , Rabitz Herschel
Published: February 2003

In this paper we present preliminary results for rotation–rotation inelastic collision rates for HCl molecules in vibrationally excited states up to v = 6 colliding with ground state HCl molecules. These were obtained by inverting the measured collision broadened linewidths of overtone vibration–rotation transitions up to the 6–0 overtone band. An energy corrected sudden scaling theory was used to reduce the number of independent parameters sufficiently so that the rates could be determined directly from the available experimental linewidths.
Role of impact parameter in branching reactions: Chemical accelerator studies of the reaction Xe++CH4→XeCH3++H
Authors: Miller G. D. , Strattan L. W. , Hierl P. M.
Published: February 2003

Integral reaction cross sections and product velocity distributions have been measured for the ion–molecule reaction Xe+(CH4,H)XeCH3+ over the relative reactant translational energy range of 0.7–5.5 eV by chemical accelerator techniques. The kinematic results indicate that reaction proceeds in a direct manner by a rebound mechanism over the energy range studied, suggesting that this substitution reaction occurs predominantly in small impact parameter collisions. This finding contrasts with the results obtained for the competing reaction, Xe+(CH4,CH3)XeH+, where the strong forward scattering of the XeH+ product indicates that H-atom abstraction occurs primarily in large impact parameter collisions.
Rate constants for formation of NO in vibrational levels v = 2 through 7 from the reaction N(4S)+O2→NO‡+O
Authors: Rahbee A. , Gibson J. J.
Published: February 2003

Vibration–rotation spectra of the Δv = 2 sequence of the nitric oxide formed by the chemiluminescent reaction N(4S)+O2→NO(X 2Π)+O have been obtained with a spectral resolution of 15 cm−1. Emission bands due to N2O were observed to occur in the same spectral region as the first overtone of NO. These were experimentally eliminated and the resulting NO spectra were used to derive rate constants for formation of NO in vibrational levels v = 2 through v = 7. In units of 10−19 cm3/sec, these room temperature rate constants are, respectively, 55±14, 57±9, 33±3, 24±4, 7±2, and 5±2. Of all the nitric oxide molecules formed in the reaction, only 18% are formed in levels v?2. In terms of energy, of the 1.39 eV exothermicity of the reaction, about 10% goes into vibrational energy in levels v?2.
Quantum topology. IV. Relation between the topological and energetic stabilities of molecular structures
Authors: Tal Yoram , Bader Richard F. W. , Nguyen-Dang T. Tung , Ojha M. , Anderson Steven G.
Published: February 2003

The relation between the structural stability of a molecular system as determined by the topological properties of its charge distribution and the energetic stability of the same system as determined by the properties of its potential energy hypersurface is studied. In general, it is found that one may associate a given molecular structure with an open neighborhood of an energetically stable geometry of the system. A change in molecular structure is an abrupt process, and examples are given in which the change in structure is found to occur in the immediate neighborhood of the transition state geometry. These observations suggest that topologically unstable structures correspond to energetically unstable geometries of a system. Such a correspondence can be rationalized in terms of the Hellmann–Feynman theorem which is shown to relate the gradients of the energy hypersurface to the gradient vector field of the charge density—the field whose instabilities determine the instabilities in molecular structure.
Theoretical studies on the structure of isobutane and the t
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r
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y-butyl radical
Authors: Yoshimine M. , Pacansky J.
Published: February 2003

A b initio SCF calculations are reported for the structure of isobutane and the tertiary-butyl radical. The calculation provides valuable information for the structure of the methyl groups in isobutane. For the tertiary-butyl radical, only one minimum is found on the ground state potential energy surface which corresponds to a nonplanar C3v geometry.
An SCF–CI study of the structures, inversion barriers, and inversion frequencies of SiH3, PH3+, and SH3++
Authors: Marynick Dennis S.
Published: February 2003

Large basis set SCF–CI calculations have been employed to determine the structures, inversion barriers, and inversion frequencies of SiH3, PH3+, and SH3++. All three species are nonplanar; however, the general trend is toward planarity as the positive charge increases. Values of the inversion barriers are 4.4 kcal/mol (SiH3), 2.9 kcal/mol (PH3+), and 0.5 kcal/mol (SH3++). Calculated frequencies of the vibrational transitions of the ν2 modes of these molecules are consistent with experiment for PH3+, but not for SiH3.
Theoretical calculation of shakeup intensities using Xα–SW wave functions
Authors: Tse John S. , Loubriel G.
Published: February 2003

The ground and 1s core hole state molecular wave functions of CH4, NH3, H2O, and HF obtained from Xα–SW calculations using the touching spheres (TS) and overlapping spheres (OS) approximations are used to calculate the intensity of shakeup satellites observed in their ls core level photoelectron spectra. The sudden approximation was assumed in the calculation. In case of TS Xα–SW wave functions, the one electron overlap integral inside the intersphere was calculated via Green’s theorem. For OS Xα–SW wave functions, the integration over the awkwardly shaped intersphere region was circumvented by distributing the intersphere charge into the atomic spheres according to the charge partition scheme suggested by Case and Karplus. Our results show that there are no significant differences between the shakeup energies calculated from the TS and OS approximations. However, shakeup intensities calculated from TS Xα–SW wave functions are more reliable and in better numerical agreement with experiment.
Molecular Rydberg transitions. XX. Vibronic doubling in alkyl bromides
Authors: Felps W. S. , Scott J. D. , Findley G. L. , McGlynn S. P.
Published: February 2003

A doubling of absorption bands occurs in certain transitions associated with first s- and p-Ryderg excitations in C2H5Br and C3H7Br. No such doubling occurs in the first d-Rydberg or second s-Rydberg excitation of C2H5Br. Furthermore, doubling is not evident in any Rydberg transition of CH3Br, CD3Br, or C2D5Br. The interpretation of this doubling phenomenon invokes vibronic coupling between Rydberg states of the same configuration. The active vibration is a C–H stretching mode ??3000 cm−1 and the presence of doubling is determined by coincidence (or near coincidence) of the intraconfigurational splitting and the frequency of the active vibrational mode.
Single vibronic level fluorescence from 1B3u pyrazine: The role of Fermi resonance and Duschinski rotation
Authors: McDonald Daniel B. , Rice Stuart A.
Published: February 2003

We report a study of the 1B3u←1Ag transition in pyrazine based on a combination of gas phase absorption and single vibronic level fluorescence spectra. Particular attention is paid to relative transition moments, especially where asymmetries exist between the intensities in the absorption and emission spectra. Band intensities and positions provide evidence for Fermi resonances and Duschinski rotations, but not for a symmetry change between the 1Ag and 1B3u states. Upper limits for displacements along several non-totally symmetric normal coordinates are set, and a few new vibrational assignments are made.
The rotational spectrum, H, 19F nuclear spin–nuclear spin coupling, D nuclear quadrupole coupling, and molecular geometry of a weakly bound dimer of carbon monoxide and hydrogen fluoride
Authors: Legon A. C. , Soper P. D. , Flygare W. H.
Published: February 2003

A dimer formed between carbon monoxide and hydrogen fluoride has been detected and identified in the gas phase through its rotational spectrum by using a pulsed Fourier transform microwave spectrometer equipped with a pulsed nozzle source of the dimers and a Fabry-Perot cavity. Rotational constants B0, centrifugal distortion constants DJ, deuterium nuclear quadrupole coupling constants χD, and the nuclear spin–nuclear spin coupling constants SHF and SDF for the vibrational ground state of each of the five isotopic species investigated are as follows (the errors in B0 and DJ are discussed in the text):                             These spectroscopic constants have been interpreted in terms of a linear equilbrium geometry in which the atoms are in the order OC⋅⋅⋅HF and in which the weak binding is therefore through a hydrogen bond to the carbon atom. Various quantities characterizing the intermolecular interaction potential have also been estimated from the above constants and are used with those similarly determined to make comparison both within the series OC⋅⋅⋅HX (X = F, Cl, and Br) and among the different series B⋅⋅⋅HX (B = Ar, Kr, OC; X = F, Cl, and Br).
A comparative study of the reaction dynamics of several potential energy surfaces of O(3P)+H2→OH+H. I
Authors: Schatz George C. , Wagner Albert F. , Walch Stephen P. , Bowman Joel M.
Published: February 2003

Two new potential energy surfaces for th O+H2→OH+H reaction are presented, and a detailed comparision of the saddle point properties and thermal rate constants of these and of six other O+H2 surfaces is made. The two new surfaces are (1) an extended BEBO surface and (2) a rotated-Morse-oscillator-spine (RMOS) fit to the accurate ab initio POLCI surface of Walch and Dunning. In the BEBO surface, an improved end atom repulsive potential is used which leads to a much more accurate barrier estimate (11.52 kcal/mol) than with the usual anti-Morse expression. The POLCI–RMOS surface is an essentially quantitative fit to the ab initio points, and has a barrier of 12.58 kcal/mole. The other O+H2 surfaces examined include the LEPS surface of Westenberg and de Haas (LEPS-WDH) and of Johnson and Winter (LEPS-JW), the diatomics-in-molecules (DIM) surface of Whitlock, Muckerman, and Fisher, the ab initio surface of Howard, McLean, and Lester (HML), and a fit to HML’s surface by Schinke and Lester (SL). For the LEPS-JW and SL surfaces, the quasiclassical trajectory (QCT) and Wigner corrected transition state theory (TST) rate constants are in excellent agreement with each other over the 300–2000 K range. There is, however, poor agreement between the QCT and TST rate constants for the DIM surface. This is apparently due to the more product-like location of the saddle point on that surface. Using both the QCT and TST results to make best estimates of the true O+H2 rate constants, we find that the LEPS-JW, DIM, and POLCI rate constants all agree with experiment within the experimental uncertainties. Although the treatment of multiple surface and spin-orbit effects does introduce some uncertainty into this analysis, the experimental uncertainties are large enough to enable agreement with experiment almost irrespective of which electronic weighting factor is used. While the LEPS-JW and POLCI surfaces have many similar features (both have ∼12.5 kcal/mol barriers), the DIM surface is quite different ( its barrier is 13.35 kcal/mol) and yet its differences compensate one another in the rate constant calculation so as to give agreement with experiment. Other comparisons with experiment indicate that the BEBO and LEPS-WDH surfaces have too low a barrier while the SL surface has too high a barrier. The normal mode stretch frequencies published by HML are surprisingly different from SL (and from those of the other surfaces), and this causes HML’s rate constants to be significantly higher then experiment even when SL’s are significantly lower.
IR multiphoton photochemistry of CF3Cl
Authors: Horwitz Alexander B. , Preses Jack M. , Weston Ralph E. , Flynn George W.
Published: February 2003

CF3Cl has been dissociated using the focused output of a CO2 TEA laser operating on the R(40) line of the 9.6 μm band. IR fluorescence has been observed for HF and HCl after irradiating mixtures of CF3Cl, HBr, and Ar, indicating the production of F as well as Cl. In addition, the laser-induced fluorescence spectrum of CF2 has been observed using a KrF laser (249 nm) to excite the CF2 Ã1B1←X̃1A1 transition. A two step dissociation mechanism in which CF3 and Cl are the primary products followed by the subsequent multiphoton absorption and dissociation of CF3 to produce CF2 and F is proposed. Evidence for secondary dissociation of CF3 has been demonstrated by observing CF2 in the infrared multiphoton dissociation of C2F6, which is known to produce CF3 at low fluence. Further evidence in support of a two-step dissociation mechanism is given by analysis of stable products, fluence studies, and RRKM calculations.
Deuteron quadrupole coupling in hydrogen bonded systems. IV. Deuteron quadrupole coupling in substituted phenols
Authors: Batchelder L. S. , Clymer J. , Ragle J. L.
Published: February 2003

The pure nuclear quadrupole spectrum of deuterium at oxygen in chlorinated phenols has been observed by level crossing double resonance with the ring protons. Observed coupling constants, ranging from 200 to 250 kHz, exhibit the effects of strong hydrogen bonding through their correlation with the intermolecular O–H⋅⋅⋅O bond lengths in those cases where structure data are available. This is interpreted below to indicate that a primary effect of chlorine substitution is the influence it exerts on intermolecular hydrogen bonding through modification of the barrier to hydroxyl group rotation. From an extrapolation of the observed distance dependence, one may obtain a coupling constant of ∼283 kHz for deuterium at the oxygen position in non-hydrogen-bonded phenol. An interpretation of these data is made using model calculations on phenol, vinyl alcohol, and chlorovinyl alcohol. Barriers to internal rotation, as well as the dependence of the deuterium quadrupole coupling constant on the orientation of the –OD bond with respect to the ring plane are reported using a standard STO-4/31G basis. A value of 299 kHz is obtained for the deuterium coupling constant in the gas phase by interpolation from STO-4/31G calculations and gas phase data for water, methanol, and formic acid. Calculation demonstrates that the coupling constant of deuterium is essentially independent of –OD twist angle in phenol, and that vinyl alcohol is an excellent model fragment for phenol insofar as deuterium field gradients are concerned. Chlorovinyl alcohol exhibits a substantially larger barrier to internal –OD rotation than phenol, and also shows a weak dependence of field gradient on twist angle. Since solid phenol and substituted phenols show substantial deviations of the aromatic ring and –OD group from coplanarity, one may rationalize trends in the coupling constants on the basis of a modification of the barrier to internal hydroxyl group rotation by chlorine substitution. Attempts were made to obtain spectra in methyl- and bromo-substituted phenols, but with the exception of 2,4-dimethylphenol, low field relaxation times were too short to permit their observation.
Far infrared spectra of strongly polar molecules in solid solution. I. Acetonitrile
Authors: Knözinger Erich , Leutloff Dieter
Published: February 2003

Strongly polar molecules such as acetone, nitromethane, and acetonitrile imbedded in an inert gas matrix give rise to characteristic absorption patterns below 150 cm−1. The bands observed in the case of acetonitrile are due to an activated phonon band, to two vibrations of a monomer molecule within the polarized cage of inert gas atoms, and to two intermolecular vibrations of an antiparallel dimer.
The influence of angular dependent intermolecular forces on vibrational spectra of solution phase molecules
Authors: McHale Jeanne L.
Published: February 2003

The zeroth, first, and second moments of the solution phase infrared, isotropic Raman, and anisotropic Raman bands of a totally symmetric mode are calculated. The existence of a strong orientationally dependent intermolecular potential is shown to lead to concentration dependent peak frequencies and bandwidths, as well as possible deviations from Beer’s law. Assumining a dominant transition dipole–transition dipole interaction, expressions for the explicit concentration dependence of the infrared, isotropic Raman, and anisotropic Raman first moments are derived and applied to the interpretation of the observed Raman spectra of polar molecules in the solution phase.
Perturbation theory of the electron correlation effects for atomic and molecular properties
Authors: Sadlej Andrzej J.
Published: February 2003

Two alternative perturbation approaches to the calculation of the correlation corrections to atomic and molecular properties are analyzed. One of them is based on the double-perturbation treatment of the external field and the correlation effects with reference to the Hartree–Fock (HF) Hamiltonian of the unperturbed system. This approach is equivalent to the calculation of correlation corrections to the results of the uncoupled Hartree–Fock (UCHF) perturbation scheme of Dalgarno. The other method consists of calculating the correlation corrections to the results of the coupled Hartree–Fock (CHF) perturbation theory. The diagrammatic analysis of the two perturbation methods reveals that in the case of the UCHF-based treatment the so-called correlation corrections involve both the self-consistency effects and the genuine correlation contributions. Since both these quantities follow from the correlation energy operator, it is proposed they be called the apparent and the true correlation effects, respectively. The structure of the CHF-based perturbation theory shows that the correlation corrections involve solely the true correlation effects. The relative role of the apparent and the true correlation contributions is analyzed for the UCHF-based theory by using the recent data of Itagaki and Saika. It is concluded that the true correlation effects can be expected to be much smaller than the apparent ones. It is proposed that a reliable estimate of the true perturbed energy can be obtained by adding the second-order correlation correction to the corresponding CHF result. As illustrated by the calculations of polarizabilities for He, Be, and Ne the correlation-corrected CHF values agree within a few percent with the best recommended data. The results of the diagrammatic analysis of the structure of the UCHF- and CHF-based perturbation theories are used to resolve some controversy concerning the cancellation of the higher-order self-consistency terms. It is explicitly shown that both theories contain all self-consistency contributions and that there is no cancellation of these terms. This permits one once again to conclude that the CHF-based perturbation theory of the correlation effects should be more efficient than the double-perturbation approach. The former corresponds to the HF level of accuracy for both the unperturbed and the perturbed system, while the latter satisfies this condition only in the absence of the external perturbation.
Molecular symmetry. III. Second derivatives of electronic energy with respect to nuclear coordinates
Authors: Takada Toshikazu , Dupuis Michel , King Harry F.
Published: February 2003

Symmetry methods employed in the ab initio polyatomic program HONDO are extended to the analytic computation of the energy Hessian matrix. A ’’skeleton’’ Hessian matrix is calculated from the unique blocks of electron repulsion integrals. The true Hessian matrix is generated by projecting the symmetric component out of the skeleton Hessian. The analysis is valid for many wave functions, including closed- or open-shell restricted and unrestricted Hartree–Fock wave functions, multiconfiguration Hartree–Fock wave functions, and configuration interaction wave functions. We also extend the use of translational invariance previously used for energy gradient calculations. To illustrate the method, we compare the computer time required for the two-electron contribution to the Hessian matrix of eclipsed ethane, using Pople’s 6-31G basis set and D3h symmetry and various subgroups of D3h. Computational times are roughly inversely proportional to the order of the point group.
Mössbauer studies on O2 and CO binding to the heme iron in myoglobin
Authors: Maeda Y. , Harami T. , Morita Y. , Trautwein A. , Gonser U.
Published: February 2003

The EFG tensors at the Fe atoms in myoglobin–O2 and –CO compounds are determined by Mössbauer measurements on single crystals and frozen solutions. In the O2 compound the quadrupole interaction (eQVẑẑ) is negative, the asymmetry parameter (η) is limited to the range of 0.3–0.4, and the direction of the largest EFG component (‖Vẑẑ‖) is most likely in the heme plane. In the CO compound eQVẑẑ is positive, η is limited to the range of 0.2–0.4, and the direction of ‖Vẑẑ‖ is probably perpendicular to the heme plane. These results are discused on the basis of structural analyses and MO calculations of these compounds.
Dipole reorientation of solute molecules dispersed in organic glasses
Authors: Crossley J. , Heravi A. , Walker S.
Published: February 2003

Dielectric loss curves (102–105 Hz) have been obtained for a variety of organic molecules dispersed in a six-ring polyphenyl ether over a range of temperatures below the glass transition. Characteristic broad loss curves were obtained for rigid molecules, such as nitrobenzene, and molecules, such as 1,4-dimethoxybenzene, which contain a rotatable polar group that can contribute to the dielectric absorption. Eyring activation enthalpies determined from the temperature dependence of the relaxation times for these systems are compared with earlier results using o-terphenyl and polystyrene glasses. The time scale of the group relaxation of a particular solute molecule in different organic glass solvents seems to be fairly independent of the nature of the solvent despite substantial differences in their glass transition temperature.
Viscometric functions for a simple fluid
Authors: Dufty James W. , Marchetti Maria Cristina
Published: February 2003

Time correlation function expressions for the viscometric functions to Burnett order are given and evaluated at low density for Maxwell molecules.
Isotropic Raman scattering for non-totally symmetric vibrations of correlated molecules with intrinsic optical anisotropy
Authors: Bancewicz Tadeusz , Kielich Stanisl/aw
Published: February 2003

The mechanism of isotropic Raman scattering for non-totally symmetric vibrations, forbidden in the absence of molecular correlations, is analyzed. It is shown that long-range molecular electric fields within the dipole–induced dipole model (DID) lead to isotropic Raman scattering in this case. By Racah algebra, the isotropic parts of the effective Raman polarizability and the intensity of scattered light are examined. The magnitude of this effect for the A2 vibration of the water molecule is estimated. It is shown that the order of this effect is the same as that of collision-induced depolarized Raman scattering for symmetric vibrations of optically isotropic molecules.
Energy pooling in laser CO2 multiphoton dissociation
Authors: Oref I.
Published: February 2003

Collision induced energy pooling in laser CO2 multiphoton dissociation is discussed. The number of molecules which are transported above the threshold energy for decomposition is calculated for two initial energy distributions. The effect of degrees of freedom and number of photons absorbed on the final internal energy distribution is reported. It is shown that collisional energy pooling does take place after the laser pulse and the number of molecules transported above a critical threshold depends on the initial energy distribution, degrees of freedom, and number of photons absorbed.
Absolute rate constant for the reaction of O(3P) with thiophene from 238 to 448 K
Authors: Lee J. H. , Tang I. N.
Published: February 2003

Interests in the gas-phase oxidation of organic sulfur compounds have become increasingly evident due to the important roles that these compounds may play in combustion processes, atmospheric chemistry, and photochemical air pollution. The rate constants for the reaction of O(3P) with thiophene (C4H4S) have been determined for the first time under pseudo-first-order reaction conditions, using the discharge flow–resonance fluorescence technique. The measured rate constants over a temperature reange 262–448 K are well represented by the Arrhenius expression k = (3.34±0.34)×10−11exp[−(1130±60)/RT] cm3 molecule−1 s−1. However, a discontinuity in the Arrhenius plot is noted around 262 K. The results are discussed in terms of different reaction pathways and compared with other compounds having similar molecular structures and various reactivities.
Tests of collinear quasiclassical trajectory transmission coefficient correction to transition state theory
Authors: Bowman Joel M. , Ju Guan-Zhi , Lee Ki Tung , Wagner Albert F. , Schatz George C.
Published: February 2003

We test the accuracy of a collinear quasiclassical trajectory transmission coefficient correction to conventional transition state theory. Comparisons are made between the so-modified transition state theory, conventional transition state theory, and previously reported three dimensional quasiclassical trajectory rate constants for several reactions. They are the O(3P)+H2(ν = 0), H2(ν = 1) reactions on three different potential energy surfaces, the F+H2(ν = 0) reaction on the LEPS surface of Muckerman (no. 5), and the H+H2(ν = 0) reaction on the Porter–Karplus surface. Although each of these systems has a collinear transition state, they span a wide variation in saddle point location and classical barrier height. We find that the collinear quasiclassical trajectory transmission coefficient very successfully corrects the conventional transition state rate constant even for the O(3P)+H2(ν = 1) reaction where the latter differs from the 3D quasiclassical one by two orders of magnitude.
Study of the chemiluminescent reaction between alkali dimers and oxygen atoms
Authors: Figger H. , Straubinger R. , Walther H.
Published: February 2003

The reaction of alkali dimers with oxygen atoms has been studied in a crossed beam experiment. Strong chemiluminescence of the reaction products was observed. It is shown that the luminescence was emitted by alkali atoms from the reaction M2+O→MO+M (M alkali atom). M can be excited up to the exoergicity of this reaction at least in the cases M = Cs and Na. For M = Cs, detailed rate constants for the excitation of the different excited states have been determined using both laser induced fluorescence and chemiluminescence. The rates decrease nearly exponentially as a function of the excitation energy. They partly follow the expectation of statistical theories. Absolute reaction cross sections have been determined for all of the reactions investigated. They agree partially with those predicted by the harpoon model.
Surface magnetic field/laser synergistic effects on the predissociation of adsorbed diatomic molecules
Authors: Bhattacharyya Dilip K. , Lam Kai-Shue , George Thomas F.
Published: February 2003

Synergistic effects of the surface magnetic field (SMF) and the laser on the predissociation of adsorbed diatomic molecules are studied theoretically. It is observed that the couplings between the laser-dressed and SMF-split molecular potentials create interference effects within the nuclear motion. These effects can cause enhancement or diminution in predissociation rate as compared to the analogous gas-phase laser-induced process. SMF/laser-induced predissociation rates for a few specific examples are derived using the semiclassical S-matrix formalism and results for the enchancement and diminution are discussed along with their dependence on laser power densities.
A
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o studies on polymers. V. All-t
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s-polyethylene
Authors: Karpfen Alfred
Published: February 2003

The ab initio crystal orbital method has been applied to study the electronic ground state of an infinite polyethylene chain in the all-trans conformation within the framework of the Hartree–Fock approximation. Gaussian basis sets of minimal and double zeta quality have been used to evaluate equilibrium geometry and longitudinal elastic modulus of this model system. A structure with rCC = 2.952 bohr, rCH = 2.082 bohr, ∢CCC = 112.2°, and ∢HCH = 107.4° has been found to be most stable and a longitudinal elastic modulus of 345 GPa is predicted. Basis set dependence and the influence of lattice sum truncations on the electronic band structure are thoroughly discussed. Calculations including polarization functions have subsequently been performed in order to obtain electronic band structure and density of states at a near Hartree–Fock limit quality.
Statistical mechanics of helical wormlike chains. XIII. Radius of gyration and moment of inertia tensor
Authors: Shimada Jiro , Nagasaka Kyosuke , Yamakawa Hiromi
Published: February 2003

Expressions for the moments of the radius of gyration and for the averages of the invariants of the inertia (gyration) tensor are derived for the helical wormlike chain by the use of the moments of its multivariate distribution function. The distribution function of the radius of gyration is constructed by the weighting function method on the basis of its moments. The moments of inertia tensor (its mean principal values) are evaluated approximately by replacing its three invariants by their averages. It is numerically shown that the distribution of the radius of gyration changes from a delta function to the well-known form in the coil limit as the contour length is increased from zero to infinity, its shape being much sharper than that of the distribution of the end-to-end distance. The results for the moments of inertia tensor lead to the conclusion that for the typical helical wormlike chain, its asymmetric shape in the coil limit persists down to relatively small contour length, and it never becomes spherically symmetric, its asymmetry being largest in the rod limit.
Madelung energy and theoretical zero-field splittings of (2:1) tetramethyltetraselenafulvalenium hexafluorophosphate [(TMTSF)2PF6]
Authors: Metzger Robert Melville
Published: February 2003

The Madelung energy of the organic superconductor (2:1) tetramethylselenafulvalenium hexafluorophosphate [(TMTSF)2PF6] is −236.5798 kJ/mol (−237.3152 kJ/mol if the PF6− ion rotates freely). Its theoretical fine-structure splitting parameters are D = 0.014 288 cm−1 and E = −0.000 557 cm−1 [nearest-neighbor (TMTSF+)2 dimer].(AIP)