bluuebunny/crossref_metadata_2025 huggingface dataset:
A quantum chemical anaylsis of the time-resolved resonance Raman spectrum of 2,5-dimethyl–2,4-hexadiene in the T1 state
Authors: Negri Fabrizia , Orlandi Georgio , Langkilde Frans W. , Wilbrandt Robert
Published: July 2002

Theoretical calculations are presented on 1,3-butadiene and 2,5-dimethyl–2,4-hexadiene (tetramethyl–butadiene or TMB) in ground and excited triplet states. The T1 potential energy surfaces are calculated from extended self-consistent-field–linear combination of atomic orbits–molecular orbital–configuration interaction (SCF-LCAO-MO-CI) theory. Energy minima and equilibrium geometries are determined in T1. Frequencies and normal modes of vibration are calculated for planar geometries in S0 and T1 and for a geometry in T1 twisted 90° around one of the formal C■C double bonds. Energies of higher triplet levels are computed and oscillator strengths for the transitions from T1 to Tn are determined. The displacements in equilibrium geometries between the T1 and Tn levels corresponding to the strongest T1→Tn transitions are calculated and are used to estimate the intensities of the resonance Raman spectra in T1 under the assumption of a predominant Franck–Condon scattering mechanism. For TMB, the calculated resonance Raman spectra are compared with the experimentally observed one. Satisfactory agreement is found between the calculated and observed spectra. An assignment is obtained for the experimentally observed vibrational modes of TMB in T1. From this analysis, it is concluded that for TMB in T1, the main contribution to the observed resonance Raman spectrum is arising from molecules in the planar form.
Theoretical treatment of predissociation in the A 2Σ+, B 2Π, and C 2Σ+ states of HeH
Authors: Petsalakis I. D. , Theodorakopoulos G. , Buenker R. J.
Published: July 2002

Theoretical calculations have been carried out on the predissociation of the A 2Σ+ state of HeH by radial coupling to the ground state, X 2Σ+, of the B 2Π state by rotational coupling to X 2Σ+, and of the C 2Σ+ state by radial coupling to A 2Σ+ and by rotational coupling to the B 2Π state. The results are in good agreement with experimental data regarding the predissociation of the A 2Σ+ and C 2Σ+ states, while they also predict significant predissociation of the positive rotational levels of the B 2Π state.
Statistical structure of soluble conjugated polymers. II. Localization effects and electron self-trapping
Authors: Viallat Annie
Published: July 2002

We use a new approach we recently developed to deal with the properties of conjugated polymers in solution at finite temperature. Coupled electronic and conformational degrees of freedom of the chain are accounted for by introducing a configurational-dependent term in the electronic Hamiltonian. Fermionic properties are described by a Hückel Hamiltonian and a Monte Carlo simulation deals with the statistical conformational chain structure. The paper is focused on the localization properties of the π electrons located along the chain backbone. The localized versus extended character of the electronic states is measured upon variation of temperature. We further calculate the electronic density on the chain, 〈CiC+i〉, as carriers are added to the system through doping. Possibilities for self-trapping of the electrons arising from the coupling to the rotational modes are studied: local rigid regions containing additional electrons are predicted and are qualitatively described.
Frequency-dependent diffusion in a spherical cavity: The effects of domain structure on ionic conduction in polymer electrolytes
Authors: Druger S. D. , Ratner M. A. , Nitzan A. , Skinner D. W.
Published: July 2002

The effects of domain structure on the low-frequency conductivity response of a polymer electrolyte having low carrier concentration are investigated by modeling the domains as spheres. For zero leakage (no dc conductivity), the diffusion equation is solved exactly. The results are also extended approximately to the case of small but nonzero leakage by imposing physically reasonable approximate boundary conditions together with an ad hoc procedure for treating the diffusion in the less conductive exterior. Interaction between charge carriers in different domains is taken into account in the Maxwell–Garnet approximation and found to have only a small effect for physically reasonable parameter values. The predicted diffusive behavior is studied and the results are applied to examine the predicted behavior of the frequency-dependent conductivity.
Scattering from two-phase random media
Authors: Teubner Max
Published: July 2002

A unified exposition is given of the known exact result for the scattering from random two-phase isotropic media with a smooth interface. For the bulk–bulk scattering a new and simple derivation is given for the next to leading term (Porod–Kirste). The corresponding term for the film–film scattering is calculated. It is pointed out that from careful contrast matching experiments it may be possible to measure the average squared mean curvature 〈H2〉 and the average Gaussian curvature 〈K〉.
Effects of interchannel coupling on the photoionization cross sections of carbon dioxide
Authors: Lucchese Robert R.
Published: July 2002

The photoionization cross sections of CO2 leading to the first four electronic states of CO+2 have been computed including the effects of interchannel coupling. The results were obtained in the Tamm–Dancoff approximation using the Padé-approximant C̃-functional method to solve the resulting scattering equations. All of the required matrix elements have been computed using single-center expansions and numerical integration of the resulting radial functions. An alternative approach for computing products of single-center-expanded functions is presented where the functions are transformed into a coordinate representation, then the product is computed, and finally the product is transformed back into the angular momentum representation. The computational effort required in this approach depends on the second power of the number of partial waves in contrast to the third power dependence found in methods used previously. The photoionization cross sections are obtained in the mixed dipole representation which ensures that the Thomas–Reiche–Kuhn sum rule is satisfied. In the coupled-channel approximation, the shape resonance in the 4σg→kσu channel is found to remain at the same energy and have the same width as was found in earlier single-channel calculations.

Both the total cross section in the (4σg)−1 channel and the photoelectron asymmetry parameter are somewhat less affected by the resonance than in the single-channel approximation, but there is still a substantial disagreement with experimental data. The kσu shape resonance is found to modify the cross sections and asymmetry parameters in the other channels, with the largest effect being in the (3σu)−1 ionization channel. The full coupled-channel results, which include coupling among the 1πg→kπu,1πu→kπg,3σu→kσg, and 4σg→kσu channels, are found to significantly modify the cross section in the 1πg→kπu channel leading to good agreement between theory and experiment for the total ionization cross section in the (1πg)−1 channel. However, this coupling is found to significantly perturb the other channels, and in the case of the asymmetry parameters in the (3σu)−1 channel, this leads to relatively poor agreement with experimental data.
The influence of excited-state vibrations on fragment state distributions: The photodissociation of NOCl on T1(1 3A″)
Authors: Qian C. X. W. , Ogai A. , Iwata L. , Reisler H.
Published: July 2002

NO V,R distributions are reported following photodissociation of jet-cooled NOCl from selected vibrational levels of the T1(1 3A″) state. By varying the photolysis wavelength while monitoring selected rovibrational levels of NO, a photofragment yield spectrum showing the same diffuse vibrational structure as the absorption spectrum is obtained. NO rotational distributions are obtained at photolysis wavelengths corresponding to peaks in the absorption spectrum. We find that the NO stretching vibrations of T1 evolve adiabatically into NO vibrational excitations [i.e., excitation of v1 quanta of the T1 NO stretch yields predominantly NO(v″=v1) ]. The NO rotational distributions depend only on the number of T1 bending quanta, v3. The shapes of the distributions reflect the number of nodes in the bending wave functions, and similar rotational distributions are obtained following excitation of vibronic levels with equal number of ν3 quanta, but different number of ν1 quanta (v1=0–2).

We also find that the excited NO(2Π3/2) state is much more populated than the lower NO(2Π1/2) state, and the widths of the absorption features increase with increasing number of ν3 quanta, but decrease with increasing ν1 excitation. The results are explained in terms of a model in which the bending and NO stretch motions in the excited state are largely uncoupled. In order to explain the multimodal rotational distributions, we calculate separately the components of the NO rotational excitation that derive from the angular momentum inherent in the bending wave function and the angular anisotropy in the potential-energy surface. We find, using the momentum representation of the harmonic oscillator, that the rotational distributions map the bending wave functions and exhibit minima for v3>0. In addition, a unidirectional torque generated by the angular anisotropy in the potential causes shifts in the distributions calculated by the pure Franck–Condon model that are bending level dependent. The observation that the absorption linewidth decreases with increasing NO stretch excitation in the parent T1 state may be a manifestation of the energy mismatch between the frequency of the NO stretch in NOCl and free NO; the increased mismatch with increasing stretch quantum number results in slower dissociation.
Inert gas clusters of C6F+6: The evolution from isolated ion to solid matrix
Authors: Kung C.-Y. , Miller Terry A.
Published: July 2002

Simultaneous laser-induced fluorescence (LIF) spectra and time-of-flight mass spectra have been recorded for ionic clusters, C6F+6⋅Rn where R=He, Ne, and Ar. These spectra span the regime of clusters extending from the isolated ion to the ion located in the corresponding inert-gas matrix (except He). The conclusions of these studies include the following. Abundant clusters with n=1 and 2 exist in symmetrical forms with one atom above and below the benzene plane. Such configurations appear, however, to be evolutionary dead ends with respect to the ultimate matrix structure. Rather, the latter likely corresponds to several inert-gas atoms sharing more or less equally the cationic charge on each side of the ring. From our results, it may be speculated that most of the essential features of the matrix LIF spectra are obtained with the completion of what is roughly the first solvent shell in the cluster, 6–10 atoms, depending upon the inert gas.
Optimal control of selective vibrational excitation of harmonic molecules: Analytic solution and restricted forms for the optimal fields
Authors: Shi Shenghua , Rabitz Herschel
Published: July 2002

Analytic solutions of the optimal fields giving selective local excitation in harmonic molecules are presented, and calculated by a numerically stable algorithm. It is shown that the optimal fields can be decomposed into a finite number of monochromatic laser fields, with the following properties: (a) the number of component frequencies is equal to the number of normal modes of the molecule; (b) the component frequencies go to the molecular vibrational normal mode frequencies in the limit of low amplitude; (c) there is an inverse relationship between the amplitude of the fields (as controlled by the weighting factor for the field fluence term) and the time T at which the objective is reached; (d) there exists a limiting form for the optimal fields as the controlling time T→∞ (which had been observed empirically in previous work and now has a regorous mathematical basis). The intensity of the component laser fields, and thus the optimal field can be reduced to any desired level with a corresponding lengthening of the pulses. Thus by varying the design criteria one may determine a corresponding entire family of optimal fields with each member equivalently leading to the desired final local excitations. The optimization procedure clearly illustrates the trade off between optimal pulse length and amplitude. In order to try and achieve the control objectives with consideration of laboratory constraints on the laser fields a formalism is presented for designing the optimal fields with constrained functional forms. An illustration based on linear chain molecules shows that the objectives may be quite well achieved by using realistically constrained optimized fields.
Monte Carlo methods for accelerating barrier crossing: Anti-force-bias and variable step algorithms
Authors: Cao Jianshu , Berne B. J.
Published: July 2002

For computer simulations of systems in which particles must cross large potential energy barriers, slow convergence is a problem. Basically there are two very disparate time scales: one characterizing motion in the potential wells and one characterizing the rare jumps from one stable well to another. Multiple time scale problems like this sorely test computer resources, and stand in the way of progress on simulations of chain folding, glass transitions, nucleation phenomena, activated barrier crossing, and quantum tunneling processes. Here several new methods are developed and tested on classical and quantum barrier crossings in double well problems. These new methods, called the anti-force-bias and variable step methods, lead to much faster convergence than standard methods. Convergence is tested by studying the deviation in the mean of the cumulative spatial distribution function from the exact distribution function.
The binding energies of one and two water molecules to the first transition-row metal positive ions. II
Authors: Rosi Marzio , Bauschlicher Charles W.
Published: July 2002

The binding energy of H2O to transition-metal ions is determined not only by the electrostatic interaction, but by 4s4p and 3d4s hybridization and by 4s to 3d promotion on the metal. All of the M(H2O)+2 systems are linear except for Mn(H2O)+2 and Zn(H2O)+2, which we show to be bent with 7A1 and 2A1 ground states, respectively. The O–Mn–O bond angle is 94° and the O–Zn–O bond angle is 99°. These systems bend to allow 4s4p hybridization, which reduces the repulsion. For Mn+, the 3dn4s1–3dn+1 separation is too large to allow 3d4s hybridization or 4s to 3d promotion. For Zn+ the ground-state 3d104s1 occupation precludes 4s to 3d promotion or 3d4s hybridization.
Helium atom scattering from CO adsorbed at steps on Ni(001)
Authors: Berndt R. , Hinch B. J. , Toennies J. P. , Wöll Ch.
Published: July 2002

Diffraction of helium atoms from randomly distributed step edges on the otherwise smooth (001) surface of Ni has been observed. Measurements for different azimuths near the 〈100〉 direction indicate that the step edges are lined up perpendicular to the 〈100〉 direction. The effect of CO adsorption on both the amplitude of the diffraction oscillations and also on specular scattering has been studied. The in-plane diffraction oscillations from the steps and the specular peak intensity show a similar attenuation with CO adsorption. This is interpreted in terms of a simple model for the effect of adsorption on the step diffraction oscillations. With increasing CO adsorption, the step edge diffraction patterns are also found to be slightly shifted suggesting a continuous change in step edge shape with adsorption.
Reactive collision with excited states in a crossed beam experiment: O(1D)+H2(v)→OH(A 2Σ+)+H
Authors: Lebéhot A. , Drawin S. , Aguillon F. , Campargue R. , Chapuisat X.
Published: July 2002

At least for its most probable mechanisms, the reaction O(1D)+H2(X 1∑+g) →OH(A 2∑+)+H(1 2S) entirely takes place, from reagents to products, on electronically excited-state channels. Due to its endoergicity and to probable energy barriers (E*≊2.8 eV) encountered on these channels, the reaction can be produced in a crossed beam experiment only if the hydrogen molecule is excited on high vibrational levels (v≥5 or v≥7, according to the presence or the absence of energy barriers). This is obtained here by low-energy electron bombardment of the H2 molecular beam. The reaction is observed through the spontaneous fluorescence of the product OH. The measured spectrum corresponding to the 0–0 band of the A 2∑+→X 2Π transition is compared to simulated spectra, as obtained with a simple statistical model and with fitted rotational distribution for OH(A 2∑+,v=0): a broad rotational distribution and a strongly nonstatistical effect on the spin doublet populations are observed.
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o calculation of the stretching energies for the HF dimer
Authors: Bunker P. R. , Jensen Per , Karpfen Alfred , Kofranek Manfred , Lischka Hans
Published: July 2002

For the HF dimer we calculate the fundamental HF stretching vibration frequencies, and the fundamental and overtone frequencies of the intermolecular (HF–HF) stretching vibration, using an ab initio potential energy surface and the previously developed semirigid bender Hamiltonian. The ab initio surface used involves the addition of 459 nuclear geometry points to the 1061 reported in our earlier work. These extra points have been chosen to give more information on those parts of the surface that involve distortions of the HF bond lengths. We have fitted these 1520 points to an analytic expression, slightly modified from our previous work, that involves 39 adjustable parameters and one constrained parameter; the weighted standard deviation of the fit is 29.3 cm−1. To calculate the vibrational frequencies, and the tunneling splittings in these vibrationally excited states, we use the semirigid bender Hamiltonian to average over the trans-tunneling path. We also calculate from the ab initio surface the effect of the adiabatic corrections, for the HF stretching states, that arise from the separation of the tunneling mode. In the adiabatically corrected calculation we obtain ν1=3926 cm−1, and ν2=3875 cm−1, which are in good agreement with the experimental results (3930.9 and 3868.1 cm−1, respectively). We also predict ν4=146 cm−1, 2ν4=280 cm−1, and 3ν4=405 cm−1. The value obtained for ν4 enables us to explain the observed perturbation of the lower tunneling component of the K=4 ground state level as being due to interaction with the lower tunneling component of the ν4=1, K=3 level.
The rotational spectrum and nature of the heterodimer in trimethylammonium bromide vapor
Authors: Legon A. C. , Wallwork A. L. , Rego C. A.
Published: July 2002

The ground-state rotational spectra of three symmetric-top isotopomers (CH3)3 14N⋅⋅⋅H 79Br, (CH3)3 14N⋅⋅⋅H 81Br, and (CH3)3 14N⋅⋅⋅D 79Br of the heterodimer of trimethylamine and hydrogen bromide have been detected by pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectroscopic constants B0, DJ, DJK, χ(14N), and χ(Br) have been determined for each of the isotopomers and for (CH3)3 14N⋅⋅⋅H 81Br have the values 1161.6294(2) MHz, 0.148(5) kHz, 7.77(2) kHz, −2.883(7) MHz, and 99.645(7) MHz, respectively. A comparison of the 14N– and 81 Br–nuclear-quadrupole coupling constants χ(14N) and χ(Br) with those expected on the basis of a hydrogen-bonded model (CH3)3N⋅⋅⋅HBr and an ion-pair model (CH3)3NH+⋅⋅⋅Br− leads to the conclusion that in the heterodimer trimethylamine-hydrogen bromide there is a significant extent of proton transfer from HBr to (CH3)3N. The value of the intermolecular stretching force constant kσ=82(3) N m−1 determined from DJ is also compared with those expected for the limiting models of the dimer and is found to lie close to that associated with the ion-pair limit.
Sequential clustering reactions of SiD+3 with SiD4 and SiH+3 with SiH4: Another case of arrested growth of hydrogenated silicon particles
Authors: Mandich M. L. , Reents W. D. , Kolenbrander K. D.
Published: July 2002

Sequential clustering reactions of SiD+3 with SiD4 and SiH+3 with SiH4 are observed in the ion cell of a Fourier transform mass spectrometer. Clustering occurs either by addition of SiD2 or SiH2 accompanied by loss of D2 or H2, or by the formation and stabilization of the bimolecular adducts. All of the clustering reactions are highly inefficient and lead to bottleneck structures at small silicon cluster sizes containing two to four silicon atoms. Rates are measured for both the addition and association products for each step of the reaction. Back reaction rates are monitored via silicon-29 isotope exchange. Ab initio electronic structure calculations of the reaction pathways including intermediates, transition states and products have been performed by Raghavachari and are presented in his companion paper. The overall reaction mechanisms are similar for each reaction step. First an intermediate complex is formed between the ion and neutral which is strongly bound by a bridging deuterium or hydrogen atom.

Collisional stabilization of this complex leads to formation of the observed bimolecular adduct products. These bimolecular adducts do not react further with SiD4 (SiH4) on the time scale of our experiments. Elimination of D2 or H2 leading to the SiD2 (SiH2) addition products occurs via a thermoneutral transition state. Sequential growth by addition of SiD2 (SiH2) arrests at Si3D+7 (Si3H+7). Ab initio calculations find that this occurs because Si3D+7 (Si3H+7) assumes a highly stable cyclic structure. Phase space theoretical modeling of the experimentally measured reaction rates is performed to quantitatively test energies of the reaction intermediate complexes and transition states calculated by Raghavachari. Excellent agreement within 0.13 eV is obtained between the phase space and ab initio energies. Phase space derived kinetic isotope effects on the reaction rates of protiated and deuterated species also correspond well with experiment. Reaction rates at typical temperature and pressure conditions in silane plasmas are also calculated. These results strongly suggest that sequential clustering of SiH+3 with SiH4 does not lead to formation of the deleterious hydrogenated silicon dust observed in silane plasmas.
Rydberg-atom destruction in collisions with electron attaching targets at low-to-intermediate n
Authors: Zheng Z. , Ling X. , Smith K. A. , Dunning F. B.
Published: July 2002

Semiclassical model calculations of rate constants for Rydberg-atom destruction through electron transfer in collisions between K(nd) atoms and CF3I and SF6 are presented. The calculated rate constants are in good agreement with experimental data, but at low-to-intermediate values of n fall below those expected on the basis of the simple free-electron model. Reasons for this apparent discrepancy are discussed.
Nonlocal integral-equation approximations. II. Lennard-Jones fluids
Authors: Zhou Yaoqi , Stell George
Published: July 2002

The zeroth order (hydrostatic) nonlocal integral-equation approximation is applied here to Lennard-Jones (LJ) fluids. Systems of homogeneous LJ fluids are investigated, as well as LJ fluids near a hard wall, a model CO2 wall, and inside two model CO2 walls. The hydrostatic hypernetted chain (HHNC) approximation is shown to be better than both the Percus–Yevick and the hypernetted chain approximations when compared with computer simulations. The phenomena of solid wetting by liquid, solid wetting by gas, and capillary condensation are predicted by the HHNC approximation.
A molecular beam study of the one, two, and three photon photodissociation mechanism of the group VIB (Cr,Mo,W) hexacarbonyls at 248 nm
Authors: Venkataraman Bhawani , Hou Hui-qi , Zhang Zhuangjian , Chen Shanhua , Bandukwalla Gulnar , Vernon Matt
Published: July 2002

Photodissociation of the group VIB (Cr,Mo,W) hexacarbonyls has been studied at 248 nm using molecular beam photofragment spectroscopy. One, two and three photon processes have been observed. Analysis of the product velocity distributions shows that the photodissociation mechanism consists of sequential CO eliminations with the nth photon channel best described as the single photon photodissociation of the stable products of the n-1st photon channel. The product translational energy distribution for the first CO elimination step is quantitatively similar for all three hexacarbonyls and characteristic of a repulsive translational energy release. The product translational energy distributions of all subsequent CO elimination steps are accurately described by a simple, microcanonical model. Qualitative molecular orbital considerations suggest that the large product translational energy observed in the first CO elimination step results from a repulsive σ interaction between the closed shell CO ligand and an excited molecular orbital which has a significant admixture of metal (n+1)pz, (n+1)s and ndz2 orbitals. This repulsive interaction is absent in the remaining CO elimination steps because there are vacancies in the coordination shell along the z axis.
Models for bond distance dependent alkali dimer–rare gas potentials
Authors: Rubahn H.-G.
Published: July 2002

Analytic expressions for Li2–Rg and Na2–Rg electronic ground state potentials (Rg=He,Ne,Ar,Kr,Xe) that depend on all three Jacobian coordinates, atom–molecule distance R, bond length r, and orientation angle γ, are presented. The potentials are obtained by expanding the repulsive and attractive parts in a two-term Legendre expansion and connecting them via generalized damping functions as proposed by Tang and Toennies [J. Chem. Phys. 80, 3726 (1984)]. The bond distance dependence (req=5.051 a.u.≤r≤6.838 a.u. for Li2 and req=5.809 a.u.≤r≤7.607 a.u. for Na2) is introduced in the repulsive part via the r-dependent shift of the repulsive barrier and in the attractive part via the r dependence of the multipole polarizabilities and effective excitation energies. These potentials are shown to agree reasonably with ab initio data. The resulting values of potential well depth ε and equilibrium distance Rm are used to check the validity of recently proposed direct combining rules for r-dependent potentials.
Interaction of boron cluster ions with water: Single collision dynamics and sequential etching
Authors: Hintz Paul A. , Ruatta Stephen A. , Anderson Scott L.
Published: July 2002

Reactions of mass-selected, cooled, boron cluster ions (B+n, n=1–14) with water have been studied for collision energies from 0.1 to 6.0 eV. Most work was done with D2O, however isotope effects were examined for selected reactant cluster ions. For all size clusters there are exoergic product channels, which in most cases have no activation barriers. Cross sections are generally large, however there are fluctuations with cluster size in total reactivity, collision energy dependences, and in product distributions. For small cluster ions, there is a multitude of product channels. For clusters larger than B+6, the product distributions are dominated by a single channel: Bn−1D++DBO. Under multiple collision conditions, the primary products undergo a remarkable sequence of secondary ‘‘etching’’ reactions. As these occur, boron atoms are continuously replaced by hydrogen, and the intermediate products retain the composition: Bn−mH+m. This highly efficient chemistry appears to continue unchanged as the composition changes from pure boron to mostly hydrogen. Comparison of these results is made with boron cluster ion reactions with O2 and D2, as well as reactions with water of aluminum and silicon cluster ions. Some discussion is given of the thermochemistry for these reactions, and a possible problem with the thermochemical data in the BOD/DBO system is discussed.
Local electron momentum anisotropy in molecules
Authors: Anchell James L. , Harriman John E.
Published: July 2002

We introduce the Husimi second moment of momentum (SMM) tensor, which is a function of the position of an electron in a molecule. The major axis of the Husimi SMM tensor evaluated at a point q gives the most probable line of motion for an electron described by a Gaussian wave packet state centered at that point. We investigate two isoelectronic series: N2, NO+, CN−, CO, and HF, H2O, NH3, CH4. For molecules in the multiply bonded series we discover spatial regions in which electron motion is preferentially parallel or perpendicular to the bond axis. We also find a connection between these two regions and the σ and π symmetry contributions to the density. For molecules in the polyatomic series we observe two characteristic local momentum anisotropies. For electrons near a bond axis the preferred motion tends to be transverse to the bond axis, and for electrons near a plane defined by three atoms the preferred motion is normal to the plane. In all systems, the local anisotropy is typically on the order of 1% of the local isotropic component at the same position.
Electrostatic interactions in a solution of linear micelles
Authors: Odijk Theo
Published: July 2002

The interaction between charged linear micelles is taken into account via the first-order end contribution to the second virial coefficient. An asymptotic analysis of this term is given for finite lines in the Debye–Hückel approximation. The effective diameter introduced for infinite line charges also determines end effects to leading order. The size of linear micelles is a function of two ionic-strength dependent effects: one increasing with salt concentration, the other decreasing. There is a possibility of micellar growth with decreasing salt concentration at rather low ionic strength when the excluded-volume term starts to come into effect.
Adding configuration interaction to the time-dependent Hartree grid approximation
Authors: Campos-Martínez José , Coalson Rob D.
Published: July 2002

The time-dependent Hartree grid (TDHG) method is extended into an ab initio algorithm for obtaining exact quantum wave packet dynamics. The new algorithm employs a superposition of orthogonal zeroth order time-dependent basis functions generated from a single TDHG wave packet trajectory. The superposition coefficients are themselves time-dependent, and are responsible for mixing the basis functions in such a way as to represent exact solutions of the time-dependent Schrodinger equation. Evolution of the superposition coefficients is governed by a set of first-order linearly coupled ordinary differential equations. The couplings between coefficients are given by matrix elements of a naturally identified interaction potential taken between members of the zeroth order basis. In numerical tests involving computation of S-matrix elements for collinear inelastic atom–Morse oscillator scattering the method proves accurate, flexible and efficient, and appears to be easily extendable to more complicated systems.
Molecular dynamics simulations of diffusion of small molecules in polymers: Effect of chain length
Authors: Takeuchi Hisao
Published: July 2002

In order to investigate the influence of chain length on the diffusion of small molecules in polymers, molecular dynamics simulations have been carried out for two model systems. One is the short chain model which is composed of 30 n-alkane-like chains each having 20 segments. The other is the infinite length chain model, used as a model for polyethylene, which is composed of a noncyclic chain of 600 segments with no free ends. Self-diffusion coefficients of the small molecules in the two model systems are compared. It was found that the chains of shorter length facilitate faster diffusion of the small molecules as well as faster relaxation of internal rotations of the chains even for a fixed total amount of free volume. However, the self-diffusion coefficient of small molecules in the infinite length chain model was still larger than that obtained from experiment. Possible factors which give rise to the effect of chain length are discussed.
Localization in a Lennard-Jones fluid: The path-integral approach
Authors: Fan Yizhong , Miller Bruce N.
Published: July 2002

The equilibrium properties of a light particle (LP) in a dense fluid are investigated analytically and numerically. It is assumed that the fluid molecules interact via a Lennard-Jones 6,12 potential and that the LP is a rigid sphere. The path-integral RISM model of the LP developed by Chandler et al. is employed, extended to include the smooth intermolecular interaction, to investigate the quantum dispersion of the position of the LP and the LP-fluid radial distribution function, g(r). It is found that important changes in g(r) occur in a region of the liquid-vapor critical point of the fluid that are qualitatively similar to the properties of the ‘‘self-trapped’’ states that arise in the earlier density functional theories. It is demonstrated that the thermodynamic pressure and compressibility exert a competing influence on g(r), and evidence is presented that the usual understanding of localization in fluids has to be extended.
Desorption of vibrationally excited adsorbates in competition with relaxation: A quantal picture
Authors: Guan Y. , Muckerman J. T. , Uzer T.
Published: July 2002

The competition between desorption and relaxation of vibrationally excited CO adsorbed on a series of model surfaces is examined theoretically using a quantum mechanical description of the dynamics. This study complements that reported in the preceding paper which studied the classical mechanics of these processes. Quantitative differences between the quantal and classical results are seen in the rate constants for the various energy transfer processes. Moreover, qualitative differences are seen in the trend in the dynamics as the Debye frequency of the model surface is increased. The differences in the various rate constants in the quantal and classical calculations lead to an unusual ‘‘quantum effect’’ in which the trend in the energy flow with increasing Debye frequency is in different directions. Relaxation of the excited adsorbate is the dominant trend in the classical mechanics; thermal desorption of the excited adsorbate is the dominant trend in the quantal calculations.
Classical trajectory studies of the unimolecular decomposition of the 2-chloroethyl radical
Authors: Sewell Thomas D. , Thompson Donald L.
Published: July 2002

Classical trajectories have been employed in a study of the intramolecular dynamics and unimolecular decomposition of the 2-chloroethyl radical. A potential-energy surface was constructed by using the available experimental data and theoretical results. The following reaction channels were included in the study: ⋅CH2CH2Cl→CH2=CH2+⋅Cl, ⋅CH2CH2Cl→CH2=CHCl+⋅H. Mode-specific behavior was investigated by computing ensembles of trajectories for initial conditions (1) in which the normal-mode vibrations of the radical were assigned zero-point energies and a single C–H local stretch on the radical end of the system was excited, and (2) in which the normal modes were all excited so as to distribute the total energy uniformly throughout the radical. First-order rate coefficients were calculated both for the disappearance of the reactant and for the two chemically distinct reaction channels. The results do not indicate significant, if any, mode-specific effects. Energy transfer from and into local C–H stretching modes was studied. Relaxation of an initially excited C–H bond is observed to be irreversible and complete within about 0.6 ps.
Obtaining microhartree accuracy for two-electron systems with random-tempered Gaussian-type geminals
Authors: Alexander S. A. , Monkhorst H. J. , Roeland R. , Szalewicz K.
Published: July 2002

The ground state energies of the helium atom, H2 molecule, and the HeH+ and H+3 molecular ions are calculated, using the variational method and basis sets of explicitly correlated Gaussian-type geminals. These energies are accurate to about 1 μhartree for He and H2 , about 27 μhartrees for HeH+, and an estimated 10 μhartrees for H+3. This accuracy is comparable to that of the Hylleraas-CI method and for diatomics approaches that obtained with explicitly-correlated basis sets in elliptical coordinates.
Vibrational dynamics of the bifluoride ion. III. F–F (ν1) eigenstates and vibrational intensity calculations
Authors: Epa V. C. , Thorson W. R.
Published: July 2002

This paper concludes a theoretical study of vibrational dynamics in the bifluoride ion FHF−, which exhibits strongly anharmonic and coupled motions. Two previous papers have described an extended model potential surface for the system, developed a scheme for analysis based on a zero-order adiabatic separation of the proton bending and stretching motions (ν2,ν3) from the slower F–F symmetric-stretch motion (ν1), and presented results of accurate calculations of the adiabatic protonic eigenstates. Here the ν1 motion has been treated, in adiabatic approximation and also including nonadiabatic couplings in close-coupled calculations with up to three protonic states (channels). States of the system involving more than one quantum of protonic excitation (e.g., 2ν2, 2ν3 σg states; 3ν2, ν2+2ν3 πu states; ν3+2ν2, 3ν3 σu states) exhibit strong mixing at avoided crossings of protonic levels, and these effects are discussed in detail.

Dipole matrix elements and relative intensities for vibrational transitions have been computed with an electronic dipole moment function based on ab initio calculations for an extended range of geometries. Frequencies, relative IR intensities and other properties of interest are compared with high resolution spectroscopic data for the gas-phase free ion and with the IR absorption spectra of KHF2(s) and NaHF2(s). Errors in the ab initio potential surface yield fundamental frequencies ν2 and ν3 100–250 cm−1 higher than those observed in either the free ion or the crystalline solids, but these differences are consistent and an unambiguous assignment of essentially all transitions in the IR spectrum of KHF2 is made. Calculated relative intensities for stretching mode (ν3, σu symmetry) transitions agree well with those observed in both KHF2 [e.g., bands (ν3+nν1), (ν3+2ν2), (3ν3), etc.] and the free ion (ν3,ν3+ν1). Calculated intensities for bending mode (ν2, πu symmetry) transitions agree well with experiment for the ν2 fundamental in the free ion and KHF2(s), and for a πu transition in KHF2 which we assign to ν2+2ν3, but are far too small to explain the prominence of progression bands (ν2+nν1) and especially the strong overtone 3ν2 in the spectrum of KHF2(s). Intensity of the progression bands (ν2+nν1) in KHF2 can be explained by hydrogen bonding between adjacent FHF− ions; in NaHF2(s) where such interaction is absent, the band (ν2+ν1) is 50–100 times weaker, in agreement with calculations.

The relatively high intensity of the 3ν2 band, which also appears strongly in NaHF2(s), remains the major unexplained feature of the bifluoride spectrum in these solids. Suggestions are made for further experiments on the FHF− and FDF− systems which could test predictions of this dynamical analysis.
Vibrational dephasing in computer simulated molten LiNO3
Authors: Katō Toshiko , Machida Katsunosuke , Oobatake Motohisa , Hayashi Soichi
Published: July 2002

The vibrational dephasing of nitrate ions was studied in a molecular dynamics simulation of molten LiNO3, which included all degrees of freedom of vibrating nitrate ions. For the interionic interaction, a Coulomb pair potential with a Born-type repulsion was adopted as a standard potential, and the effect on vibrational dephasing of a potential well of varying depth between Li+ and O of NO−3 was studied. Vibrational correlation functions 〈Qi(0)Qi(t)〉 for the ν1 and ν2 modes of NO−3 were calculated and the vibrational spectra were obtained from their Fourier transforms. It was found that the vibrational correlation functions for the two modes decayed rapidly and the vibrational linewidths increased considerably as the well depth increased. Two simulations for the harmonic and the anharmonic intraionic potentials for NO stretching suggested that pure interionic interaction induced broadening dominated the band width of the ν1 mode in this melt, while vibrational anharmonicity coupled to the forces due to the environment did not play any important role. Results of the simulation were compared with the infrared and isotropic Raman band shapes in molten LiNO3. The assumed interionic potentials in the present simulation were found to result in two slow vibrational dephasing of the ν1 mode and too fast dephasing of the ν2 mode as compared with the spectroscopic results. The effect of vibration–rotation coupling on the vibrational spectra was found to be small in this system.
Extended Mulliken electron population analysis
Authors: Huzinaga S. , Sakai Y. , Miyoshi E. , Narita S.
Published: July 2002

The Mulliken electron population analysis has been a standard feature of computer output from the quantum mechanical molecular calculation. An extension of the original analysis is proposed here. It produces a point-charge model of a molecule that retains the same electric dipole moment as calculated with the molecular wave function. The analysis offers visually more interesting information than the original Mulliken analysis. The extension can be made easily by extracting and printing out some additional numerical data usually once computed but discarded after being processed in molecular calculations.
Calculation of the electronic spectrum for Ar–OH
Authors: Chakravarty C. , Clary D. C. , Esposti A. Degli , Werner H.-J.
Published: July 2002

We calculate the rovibrational structure for the electronic transition of the Ar–OH complex between the ground and first excited electronic states, which correlate asymptotically with Ar(1S0)+OH(X 2Π) and Ar(1S0)+OH(A 2Σ+), respectively. An ab initio potential energy surface is used and the rovibrational states are calculated using a basis set method which couples the electronic spin and orbital angular momentum of the diatomic fragment with the overall rotations and vibrations of the complex. The calculated spectrum is compared with experimental results. In the low-frequency region the spectrum is found to be well ordered and assignment of spectroscopic features in terms of bending and stretching quantum numbers is possible. Close to dissociation, bend–stretch coupling leads to highly mixed states for which such assignments are no longer possible.
Formation of O(3P
j) photofragments from the Hartley band photodissociation of ozone at 226 nm
Authors: Kinugawa Tohru , Sato Tetsuya , Arikawa Tatsuo , Matsumi Yutaka , Kawasaki Masahiro
Published: July 2002

The photodissociation of ozone at 226 nm is studied for O3→O2(X3 Σ−g)+O(2p3Pj) by probing O(3Pj) atomic photofragments with a resonance-enhanced multiphoton ionization method. Angular and kinetic energy distributions are determined by measuring time-of-flight spectra as a function of the angle between the polarization vector of the dissociation laser and the detector axis. The Doppler width of O(3Pj) photofragments is also measured. The translational energy distribution is well represented by assuming the formation of vibrationally excited O2 molecules with an average vibrational quantum number of 12. The anisotropy parameter β for the angular distribution is found to be 0.7±0.1. The predissociation dynamics from the photoprepared O3(1B2) state to the repulsive potential surface is discussed.
Geometries and energy separations of low-lying states of YNH and NYH
Authors: Das Kalyan K. , Balasubramanian K.
Published: July 2002

Complete active-space multiconfiguration self–consistent field followed by multireference configuration-interaction calculations are carried out on low-lying electronic states of YNH and NYH. We find the X 2Σ+ linear state of Y–N–H to be 55 kcal/mol more stable than the bent NYH and 59 kcal/mol more stable than the linear N–Y–H. Our calculations confirm the recent assignment of the first observed spectra generated by laser vaporization of Y metal + He/NH3. The theoretical dipole moment of the Y–N–H molecule (3.06 D) is in excellent agreement with an experimental value of 3.06 D obtained by Simard et al. The theoretical Y–N and N–H bond lengths are also in good agreement with the experimental results.
On the electronic structure and dynamical aspects of the predissociation of the A 2ΠΩ states of MgCl. A rigorous quantum mechanical treatment incorporating spin–orbit and derivative coupling effects
Authors: Parlant Gérard , Rostas Joëlle , Taieb Guy , Yarkony David R.
Published: July 2002

The nonadiabatic electronic structure and decay mechanisms of the spectroscopically analyzed A 2Π state of MgCl are studied using a unique combination of rigorous ab initio electronic structure and quantum dynamics techniques. The electronic structure treatment is based on ab initio multiconfiguration self-consistent field/first order and second-order configuration interaction wave functions [ΨaJ(r;R)] for the 1,2 2Π adiabatic electronic states. These wave functions are used to determine rigorous diabatic state wave functions using the derivative coupling matrix elements, gaJ,I(R)=〈ΨaJ(r;R) ‖(∂/∂R)ΨaI(r;R)〉r, and approximate diabatic state wave functions using a diabatization procedure based on diagonalizing the dipole moment operator suggested by Werner and Meyer [J. Chem. Phys. 74, 5802 (1981)]. Near its equilibrium geometry the A 2ΠΩ state is well characterized as a regular diabatic state corresponding to Mg+(2P)-Cl−(1S).

The higher vibrational levels of this state are significantly perturbed (predissociated) by the interaction with a second inverted, dissociative, diabatic state of the same symmetry corresponding to Mg0(1S)Cl0(2P). Because the fine structure splitting, E(2 2Π3/2)–E(2 2Π1/2), of the predissociating state is comparable to the vibrational spacing of the predissociated state, relativistic, spin–orbit, effects must be incorporated into the treatment of the predissociation. These relativistic effects are treated using the full microscopic Breit–Pauli spin–orbit (that is spin–orbit and spin–other–orbit contributions) operator. The coupled diabatic state representation incorporating relativistic effects is used as the basis for semiclassical and fully quantum mechanical treatments of the predissociation lifetimes and energy shifts of the A 2Π3/2,1/2 vibrational states. By correctly taking into account the mixing of the regular and inverted 1,2 2Π states the coupled state quantum scattering calculations are able to reproduce the observed ‘‘anomalous’’ dependence of the fine structure splitting factor Asov.
Far-infrared spectra and two-dimensional potential energy surface of silacyclopentane and its deuterated isotopomers
Authors: Colegrove Lloyd F. , Wells James C. , Laane J.
Published: July 2002

The far-infrared spectra of silacyclopentane and its 1-d1 and 1,1-d2 isotopomers have been recorded and analyzed. Spectral series corresponding to the bending and twisting transitions were observed. Bend-twist combination bands and bending overtone spectra were also detected. Kinetic energy (reciprocal reduced mass) expansions were calculated for the bending and twisting motions. These were used along with a five-term two-dimensional potential energy surface in the vibrational Hamiltonian in order to calculate the energy states. The basis sets were carefully generated to ensure that these levels were accurately calculated. The potential energy surface calculation does an excellent job of reproducing the 103 observed transition frequencies. The potential surface has energy minima at twist angles of 30°. The barrier to planarity is 2110±200 cm−1. The bent structure, which corresponds to a saddle point on the surface, has an energy about 1500 cm−1 above the twisted conformation.