bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of polar additives on charge transport in a molecularly doped polymer: Evaluation of disorder models
Authors: Young Ralph H. , Fitzgerald John J.
Published: July 2002

We have investigated the effect of small amounts of a highly polar additive, t-amylphthalonitrile (TAP), on the mobility of holes in polystyrene doped with tri-p-tolylamine. The mobility decreases rapidly and becomes more steeply dependent on electric field strength and temperature as the concentration of TAP is increased. The experimental results are compared with two current models. A ‘‘dipolar trap’’ model fails to reproduce the observed dependence of the mobility on TAP concentration. The Gaussian disorder model of Bässler and co-workers [Phys. Status Solidi 175, 15 (1993)] can fit the dependencies on field strength and temperature at each concentration, but the concentration dependencies of the fitting parameters are problematic.
Quantum dynamics of many-atom systems by the classically based separable potential (CSP) method: Calculations for I−(Ar)12 in full dimensionality
Authors: Jungwirth Pavel , Gerber R. Benny
Published: July 2002

A recently developed method for time-dependent quantum simulations of large systems on short time scales is applied to the dynamics following electron photodetachment from the clusters I−(Ar)2 and I−(Ar)12. The problem is treated in full dimensionality, incorporating all vibrational degrees of freedom, by the classically based separable potential (CSP) approach. This is essentially an approximate time-dependent quantization of classical dynamics: Classical molecular dynamics is used to generate effective, single mode separable time-dependent potentials for each degree of freedom. The quantum dynamics is then propagated separately for each mode, using the effective potentials that implicitly include effects such as energy transfer between the modes. In the current application of the CSP method we calculate properties relevant for the interpretation of spectroscopies, such as correlation functions of wave packets, as well as time-dependent atom–atom distribution functions, pertinent to future diffraction experiments using ultrafast pulses. The insight obtained from the quantum dynamics of these clusters is discussed. In particular, light is thrown on the differences in the dynamics associated with the system landing on the three different electronic surfaces of the neutral I(2P)⋅(Ar)n system.
Nonadiabatic corrections for coupled oscillators using Rayleigh–Schrödinger perturbation theory of very high orders
Authors: Špirko Vladimír , Čížek Jiří
Published: July 2002

Prospects for higher order perturbation theory in evaluating nonadiabatic corrections to the adiabatic energy levels are investigated by performing calculations on a series of two-dimensional anharmonically coupled oscillators. The convergence properties of the perturbation series are demonstrated for different harmonic frequencies and magnitudes of perturbation. It is found that the perturbation series corresponding to the adiabatic levels which are away from any intersections can accurately be summed, by means of the Padé summation technique, even in the case of ‘‘giant’’ couplings. The proposed ‘‘nondegenerate’’ perturbation theory procedure may also provide accurate results, under certain conditions, even in the case of intersecting energy levels. It fails to converge only in the regions around the crossing points. Elsewhere, it converges safely (especially when using high-accuracy arithmetics) and provides the basis for relatively accurate interpolation over the crossing regions.
Nonadiabatic corrections for coupled Morse oscillators using Hutson and Howard perturbation theory
Authors: Špirko V. , Čížek J , Skála L.
Published: July 2002

An adiabatic separation is applied to two coupled Morse oscillators. The resulting approximate energies and wavefunctions are corrected for nonadiabatic interactions by means of the perturbation theory approach of Hutson and Howard supplemented by the ‘‘Padé divergent series summation’’ technique. The convergence properties of the perturbation series are investigated as functions of the oscillator frequencies and coupling strengths varying over a wide range of values. The rate of convergency and accuracy of summability of the perturbation series depend strongly on the presence of accidental resonances among the adiabatic levels. For relatively well isolated levels, the series either converge strongly or can be summed very accurately for almost any strength of perturbation. In the case of close coincidence of more than two strongly coupled levels, the approach becomes unreliable. The convergency/summability problems faced in the ‘‘intermediate’’ cases of two ‘‘adiabatically crossing’’ levels appear to be curable by means of interpolating over the ‘‘near-degeneracy’’ regions.
The role of excluded volume in polyethylene intermolecular potentials
Authors: McCoy John D. , Mateas Saloman , Zorlu Meltem , Curro John G.
Published: July 2002

A number of common methylene–methylene intermolecular potentials are mapped onto effective hard monomer interactions. The potentials considered are of the united atom (UA), the anisotropic united atom (AUA), and the explicit atom (EA) types. The effective site diameter can be used as a means of comparison between these rather diverse potential functional forms. Although we have not attempted a complete survey of the literature, we find that there is a surprisingly wide range of hard site diameters predicted. The average diameter is 3.7 Å; the minimum, 3.4 Å; and the maximum, 3.9 Å. These are distressing findings in terms of predicting system properties such as the structure factor or the diffusion coefficient which sensitively depend upon excluded volume.
Long- and short-range interactions in the temperature dependent collisional excitation of the antisymmetric stretching CO2(001) level by highly vibrationally excited pyrazine
Authors: Michaels Chris A. , Mullin Amy S. , Flynn George W.
Published: July 2002

The relaxation of highly vibrationally excited pyrazine, C4H4N2, by collisions with CO2 that produce molecules in the vibrationally excited antisymmetric stretch state (0001) has been investigated using high resolution infrared transient absorption spectroscopy at a series of ambient cell temperatures. The vibrationally hot (Evib≊5 eV) pyrazine molecules are formed by 248 nm excimer laser pumping, followed by rapid radiationless decay to the ground electronic state. The nascent rotational and translational product state distributions of the vibrationally excited CO2 molecules are probed at short times following the excitation of pyrazine. The temperature dependence of this process, along with the CO2 product state distributions, strongly suggest that the vibrational excitation of CO2 occurs via two mechanisms. The vibrational energy transfer is dominated by a long-range attractive force interaction, which is accompanied by almost no rotational and translational excitation. However, the CO2(0001) product state distribution also reveals a smaller contribution from a short-range interaction that results in vibrational excitation accompanied by substantial rotational and translational excitation. The long-range interaction dominates scattering into low angular momentum (J) states while the short-range interaction is most important for molecules scattering into high J states. The implications of these results for our understanding of the relaxation of molecules with chemically significant amounts of vibrational energy are discussed.
Hot electron mediated photodesorption: A time-dependent approach applied to NO/Pt(111)
Authors: Harris S. M. , Holloway S. , Darling G. R.
Published: July 2002

Time-dependent quantum wave packets have been used in a model calculation to investigate the substrate-mediated photodesorption of a molecule from a metal surface. A ‘‘hot’’ electron, generated in the substrate by an absorbed photon, temporarily resonates in an unoccupied molecular orbital. This results in a new set of forces, and if the electron spends sufficient time in the resonance, then on returning to the electronic ground state the molecule will have acquired sufficient energy to desorb. Rather than modeling the excitation and relaxation steps independently, we treat the motion of the molecule and the hot electron on an equal footing. We have studied the dynamics on potential energy surfaces (PESs) explicitly including both the electronic and nuclear coordinates. PES parameters were chosen to model NO desorption from Pt where it has been suggested that the excited state is attractive. The desorption probability has been calculated as a function of hot electron energy and photon energy for different potential topologies. We show that observable desorption is possible for short resonance lifetimes (∼1 fs) and moderate excited state potential gradients. Also presented are the translational energy distributions of the desorbing molecules.
Calculation of the photodetachment spectrum of OHCl− using complex L2 functions
Authors: Mayrhofer Rudolph C. , Bowman Joel M.
Published: July 2002

The photodetachment spectrum of OHCl− is calculated using a complex L2 approach that was described and tested previously [R. Mayrhofer and J. M. Bowman, J. Chem. Phys. 100, 7229 (1994)]. The calculations are done using the ab initio potential of Koizumi et al. for the neutral system, and the results are compared with the experimental spectrum of the Neumark group, and a previous calculated spectrum, which also used the ab initio potential [M. J. Davis et al., J. Chem. Phys. 101, 4708 (1994)]. The present spectrum consists of two bands of closely spaced lines. These bands are assigned to OHCl quasibound states with zero and 1 quantum of OH stretching vibration. Within each band is a series of lines of varying width, but generally of the order of 10 meV, which are assigned to hindered-rotor states of the complex. These assignments confirm the ones made by Davis et al., who used a novel hierarchical analysis of the stick spectrum to make spectral assignments. The present spectrum is convoluted with a Gaussian function of width 10 meV to simulate the resolution of the experiment. This artificially broadened spectrum reproduces many of the features of the experimental spectrum, but is substantially narrower than the experimental one. Spectra for the excited Cl−–OH stretch, and also for small changes in the OHCl− equilibrium position are also presented.
Excited-state reaction pathways for s-cis buta-1,3-diene
Authors: Celani Paolo , Bernardi Fernando , Olivucci Massimo , Robb Michael A.
Published: July 2002

The topology and energetics of the potential energy surfaces associated with the 2A1 and 1B2 valence excited states of s-cis butadiene have been investigated via ab initio quantum chemical computations at a level of theory which includes dynamic correlation effects and extended basis sets. The results support a photochemical ring-closure mechanism involving 1B2 and 2A1 reaction/relaxation pathways that are disrotatory. The reaction path on the 2A1 surface begins at a 1B2/2A1 conical intersection and the ground state photoproducts are produced via radiationless decay at a second 2A1/1A1 conical intersection which has been documented in a previous publication. A local Cs equilibrium structure on 1B2 potential energy surface has been optimized using the complete active space-self-consistent field and configuration interaction singles methods. The 1B2/2A1 conical intersection is located near this Cs equilibrium structure and offers a rationalization of the experimentally observed femtosecond lifetime of this state. The observed preferential disrotatory stereochemistry appears to be simply determined by a difference in the energy barriers located along the 2A1 disrotatory and conrotatory paths. This finding is in contrast with the generally accepted notion that the stereochemistry is determined by a different rate of internal conversion at a ‘‘disrotatory’’ and ‘‘conrotatory’’ avoided crossing minima. Indeed, no avoided crossing can be located along the 2A1 paths.
Studies of C60-metal reactions in the laser-ablation plasma of C60/M2O3 (M=La, Y, Eu, Gd)
Authors: Huang Rongbin , Lu Wenyun , Yang Shihe
Published: July 2002

Reactions of excimer laser (XeCl, 308 nm) vaporized and excited fullerene C60 with La, Y, Eu, and Gd were carried out in mixtures of C60/La2O3, C60/Y2O3, C60/Eu2O3, and C60/Gd2O3. The reaction products M@C60, M@C60-2n and M@C60+2m (M=La, Y, Eu, and Gd) were identified by a reflectron type time-of-flight mass spectrometer (RTOFMS). The products were subjected to reactions with H2O, O2, and N2O in a pick-up source. The metallofullerenes were found to be nonreactive toward H2O, N2O, and O2. This gives support to the endohedral nature of the metallofullerenes. © 1995 American Institute of Physics.
On the equilibrium bond length of ammonia in the first excited singlet state
Authors: Stanton John F. , Kadagathur Narayani S.
Published: July 2002

The equilibrium bond distance in the Ã state of NH3 is investigated with the equation-of-motion coupled cluster method in the singles and doubles approximation (EOM-CCSD). In accord with a previous prediction [P. Rosmus et al., J. Chem. Phys. 86, 6677 (1987)], the equilibrium N–H distance is found to be considerably shorter than the 1.08 Å that is consistent with both dynamical simulations of the electronic spectrum and analysis of rotationally resolved spectra. With a basis set of 115 generally contracted Gaussian basis functions, the equilibrium bond distance is predicted to be 1.040 Å at the EOM-CCSD level. Further improvements in the theoretical treatment are not likely to change this result appreciably. It therefore appears that the true value of re is in the range 1.03–1.05 Å, and that further analysis of the Ã–X̃ photosystem is needed to resolve this disturbing discrepancy.
Proton interchange tunneling and internal rotation in HSH–NH3
Authors: Hilpert G. , Fraser G. T. , Suenram R. D. , Karyakin E. N.
Published: July 2002

An electric-resonance optothermal spectrometer and phase-locked backward-wave oscillators are used to investigate the b type, ΔK=±1, Δm=0 spectrum of the hydrogen-bonded HSH--NH3 and H34SH--NH3 complexes near 300 GHz. The spectrum is characterized by nearly free internal rotation of the NH3 subunit against the H2S, as initially concluded from Stark-effect measurements by Herbine et al. [J. Chem. Phys. 93, 5485 (1990)]. Transitions are observed for the K=1←0, m=0, A symmetry and the K=0←±1 and K=±2←±1, m=±1, Km≳0, E-symmetry subbands. The transitions are split into doublets with a 3:1 relative intensity ratio indicative of tunneling interchange of the two H2S protons. The observed selection rules, symmetric ↔ antisymmetric in the tunneling state, indicate that the tunneling motion reverses the sign of the molecular electric dipole moment component along the b inertial axis. The most likely interchange motion consists of a partial internal rotation of the H2S unit about its c inertial axis, through a bifurcated, doubly hydrogen-bonded transition state. The proton interchange tunneling splittings of 859–864 MHz vary little between K and m states, indicating that the interchange motion is only weakly coupled to the internal rotation. The barrier to proton interchange is determined to be 510(3) cm−1, which can be compared to the ∼700 cm−1 barrier estimated from the 57 MHz tunneling splittings associated with the H2O proton interchange in the related HOH--NH3 complex. The observation of dissociation of HSH--NH3 following excitation of the NH3 umbrella mode with a line-tunable CO2 laser places an upper bound of 992 cm−1 on the hydrogen-bond zero-point dissociation energy. The band origin for the umbrella vibration of 992.5(10) cm−1 is blueshifted by 43 cm−1 from the hypothetical inversion-free band origin of uncomplexed NH3. Previous studies have shown that the HOH--NH3 binding energy is greater than 1021 cm−1.
Photoabsorption of Kr+2 in the ultraviolet: Revisited
Authors: Jones R. B. , Tran H. C. , Eden J. G.
Published: July 2002

The photoabsorption spectrum of the Kr+2 ground electronic state (X 2Σ+u) has been measured in the ultraviolet (257–355 nm) by a fluorescence suppression technique. Peak absorption is recorded at ∼330 nm and the spectral width of the observed continuum is ∼60 nm (FWHM) which is ∼25% smaller than the value predicted by theory for a Kr+2(X) vibrational distribution thermalized at 300 K. Similar experiments with Ar/Kr mixtures: (1) reveal weak absorption attributed to ArKr+ peaking at ∼280 nm, and (2) suggest that the ArKr+ ion is rapidly converted to Kr+2 by a displacement reaction.
Photodissociation dynamics of NO2 at moderately high energy (λ=309.1 nm; Eavail=7222 cm−1)
Authors: Knepp Pamela T. , Terentis Andrew C. , Kable Scott H.
Published: July 2002

The dynamics of NO2 dissociation at 309.1 nm have been explored by examining the nascent distribution of NO rotational, vibrational, spin–orbit, and lambda-doublet states. The NO fragment is produced with a monotonically decreasing vibrational distribution over the energetically accessible vibrational states (υ=0–3), and nonstatistical rotational distributions within each vibrational manifold. The distribution within υ=0 and 1 is strongly peaked near J=25.5 with a fairly narrow spread, the distribution within υ=2 is fairly flat, terminating at the limit of available energy, and the υ=3 distribution is oscillatory, also terminating at the limit of available energy. The 2Π1/2 spin–orbit state is more strongly populated than the 2Π3/2 state by a factor of 1.9 for every vibrational state. The differences in lambda-doublet populations are, in general, minor; each Λ state being roughly equally populated, although oscillations are again evident. These results are discussed in relation to results at similar available energy at room temperature and in the free jet at different available energies. It is found that the results are intermediate between the previous data at low excess energy and at high available energy, the distributions showing aspects of both regimes. From the data it is inferred that the dissociation dynamics of NO2 vary continuously from a regime where phase space theory considerations with quantum overtones dominate the product state distributions to the regime where dynamics on the exit channel determine the distributions.
Photoion rotational distributions from near-threshold to deep in the continuum
Authors: Poliakoff E. D. , Choi Heung Cheun , Rao R. M. , Mihill A. G. , Kakar Sandeep , Wang Kwanghsi , McKoy V.
Published: July 2002

We present the first measurements of ion rotational distributions for photoionization over an extended range [0≤EK≤200 eV for N2 (2σ−1u) and 3≤EK≤125 eV for CO (4σ−1)]. The N2 ion rotational distributions are seen to change dramatically over this energy range, indicating that characteristically molecular behavior of the photoelectron persists far from ionization threshold. In addition, the N2 and CO results show a strikingly different dependence on energy. Although differences are expected due to the absence of a center of symmetry in CO, detailed calculations reveal that this behavior arises from the presence of Cooper minima in the 2σu→kσg continuum in the case of N2 and from an f-wave shape resonance in the 4σ→kσ channel in CO. Agreement between measured and calculated ion rotational distributions is excellent. The N2 results are also compared with electron bombardment ionization data. This comparison demonstrates that previous interpretations of electron bombardment data are prone to errors.
Spectroscopically determined Born–Oppenheimer and adiabatic surfaces for H3+, H2D+, D2H+, and D3+
Authors: Dinelli Bianca M. , Polyansky Oleg L. , Tennyson Jonathan
Published: July 2002

High resolution spectroscopic data for H3+, H2D+, D2H+, and D3+ is used to determine effective, mass-dependent potential energy surfaces for each isotopomers. These surfaces are expressed as a sum of the mass-independent Born–Oppenheimer (BO) potential and a mass dependent adiabatic correction. For H3+ and D3+ the adiabatic correction is a single surface of the same symmetry and functional form as the BO surface. For H2D+ and D2H+ a second, lower symmetry surface is required. Fits to all three surfaces were started from recent, high quality ab initio calculations. The standard deviations for fits using all the available data with J≤9 are 0.015 cm−1 for H3+, 0.010 cm−1 for H2D+ and D2H+ combined, and 0.015 cm−1 for D3+. These values are close to the intrinsic experimental error of much of the data and improve on the corresponding ab initio surfaces by at least an order of magnitude. The fits are very compact: nearly 1600 data are fitted by adjusting 36 constants and freezing 51 at their ab initio values.
Nonequilibrium solvent effects on the S
N2 reaction using a self-consistent reaction field continuum model based on multipole expansions
Authors: Ruiz-López M. F. , Rinaldi D. , Bertrán J.
Published: July 2002

A simple model has been developed that allows analysis of nonequilibrium solvent effects on chemical processes. It is based on the use of a self-consistent reaction field approach using a multipole development of the solvation energy and on the separation of the inertial and noninertial polarization of the solvent. The solute’s wave function is computed at the ab initio level. The main advantage with respect to previously reported models is that the inclusion of nonequilibrium or dynamic solvent effects are introduced through the definition of a single solvent coordinate which is related to the chemical system coordinates. Besides, inclusion of polarization effects is straightforward. Results are presented for the SN2 reaction F−+CH3F→FCH3+F−. The frozen-solvent hypothesis and the role of solvent fluctuations are discussed. It is shown that the climb to the transition barrier must be preceded by a convenient fluctuation of the solvent so that its inertial polarization component is suitable to solvate the transition state. Other solvent fluctuations, energetically less favorable, could decrease or even suppress the transition barrier. Nonequilibrium solvation effects on the value of the transmission coefficient are discussed. The methodology proposed in this work may be extended to the study of other rapid processes in solution such as proton transfers or electronic excitations.
Free jet IR spectroscopy of (32SF6)2 in the 10 μm region
Authors: Urban R.-D. , Takami M.
Published: July 2002

The rotation-vibration spectra of (32SF6)2 have been studied near the ν3 band of the 32SF6 monomer. The parallel band 14 cm−1 below the monomer band origin shows a well resolved J-structure, while the perpendicular band 8 cm−1 above the origin exhibits several Q-branch peaks as the only resolved strong lines. The structure of (32SF6)2 is consistent with a D2d symmetry from the intensity alternation and the existence of a first-order Coriolis interaction observed in the perpendicular band. The energy difference between the two bands is very close to the value calculated by a dipole–dipole and dipole-induced dipole interaction model, while the location of the two bands is blueshifted from the calculated values by about 2 cm−1. The possible influence of internal rotation is discussed.
Photoionization spectroscopy of Ag–rare gas van der Waals complexes
Authors: Brock L. R. , Duncan M. A.
Published: July 2002

Photoionization electronic spectroscopy is reported for the van der Waals complexes Ag–Ar, Ag–Kr, and Ag–Xe. Two band systems are observed for each complex correlating to the 2P1/2←2S and 2P3/2←2S atomic asymptotes. An additional weaker band system correlating to the 2D5/2←2S asymptote is also observed for Ag–Ar and Ag–Kr, but not for Ag–Xe. Extensive vibrational progressions are observed in each of these band systems indicating that there is a large change in bond distance between the ground and excited states. Isotopic analysis confirms that these spectra all have onsets at high vibrational quantum numbers, making it possible to probe the shape of the potentials near the dissociation limits. Hotbands are also observed providing ground state vibrational intervals. Vibrational constants and dissociation energies are obtained for the excited states and dissociation energies are obtained for the ground states of each complex. The excited states correlating to the 2P asymptote are significantly more strongly bound than the ground state for each complex, while the states correlating to 2D are extremely weakly bound with low vibrational frequencies. Dissociation energy trends are compared for the series of complexes and for corresponding spin–orbit states.
Structure and vibrations of phenol⋅CH3OH (CD3OD) in the electronic ground and excited state, revealed by spectral hole burning and dispersed fluorescence spectroscopy
Authors: Schmitt M. , Müller H. , Henrichs U. , Gerhards M. , Perl W. , Deusen Ch. , Kleinermanns K.
Published: July 2002

The intermolecular vibrations of phenol(CH3OH)1 and its deuterated isotopomer d-phenol(CD3OD)1 were examined by comparing the vibrational frequencies of the electronic ground and excited state with the results of ab initio normal mode calculations at the Hartree–Fock level, using the 4-31G* and 6-31G** basis sets. Full energy minimization showed a translinear structure similar to phenol(H2O)1 or to the water dimer. Dispersed fluorescence spectra have been recorded via excitation of the electronic cluster origin and several intermolecular vibrational transitions. The Franck–Condon intensity pattern allowed an assignment of the ground state vibrational frequencies to the excited state frequencies, which were examined by resonance enhanced multiphoton ionization and hole burning spectroscopy. The existence of another conformer that possibly absorbs in the region of interest was ruled out by hole burning spectroscopy of the phenol(CH3OH)1 cluster. A full assignment of all intermolecular vibrations of this hydrogen bonded cluster in the S0 state could be given for the first time on the basis of ab initio calculations and a combination of different spectroscopical methods.
Periodic orbits, bifurcation diagrams and the spectroscopy of C2H2 system
Authors: Prosmiti R. , Farantos S. C.
Published: July 2002

The principal families of periodic orbits that emerge from the stationary points of the six-dimensional potential energy surface of the C2H2 molecular system, as well as periodic orbits from saddle-node bifurcations, have been located and propagated for an energy range up to 36 500 cm−1 above the absolute minimum of the potential. The bifurcation diagrams of these periodic orbits reveal the regions of phase space where the dynamics are regular or chaotic (with soft or hard chaos) for acetylene, vinylidene, and the region over these two isomers. An association of the structure of phase space with spectroscopic findings is made by calculating Gutzwiller’s semiclassical trace formula and classical survival probability functions.
The molecular and electronic structure of s-tetrazine in the ground and first excited state: A theoretical investigation
Authors: Schütz Martin , Hutter Jürg , Lüthi Hans Peter
Published: July 2002

The ground- and first excited state of s-tetrazine arising from a π*←n excitation (1Ag,1B3u) have been studied using the complete active space (CASSCF) and the second order multiconfiguration perturbation theory (CASPT2) ab initio methods. The focus of this study is on the effect of the electronic excitation on the molecular structure and on those electronic properties which are important to model the solvatochromatic behavior of the molecule in polymer matrices as used in permanent hole burning experiments. Since the accurate computation of excited state molecular properties represents a major challenge for today’s numerical quantum chemistry, some technical aspects are also considered. The present study shows that the change in geometry upon electronic excitation is small. This is in partial contradiction with the experimental studies which however disagree among themselves [see K. K. Innes, I. G. Ross, and W. R. Moomaw, J. Mol. Spectrosc. 132, 492 (1988), and R. E. Smalley, L. Wharton, and D. H. Levi, ibid. 66, 375 (1977)]. This study also confirms that the first excited state equilibrium structure is of D2h symmetry. In an earlier theoretical study it was found that the D2h symmetry structure may represent a saddle point rather than a minimum on the excited state potential surface [see A. C. Scheiner and H. F. Schaefer III, J. Chem. Phys. 87, 3539 (1987)]. In the first excited state, we observe an increase of the mean polarizability of s-tetrazine along with an enhanced anisotropy. The change in the polarizability is almost exclusively in the ‘‘in-plane’’ components of the tensor; the polarizability in the vertical direction is nearly unchanged. This observation questions recent experimental results reported for this molecule [see S. Heitz, D. Weidnauer, and A. Hese, J. Chem. Phys. 95, 7952 (1991)].
Photodissociation of CBrCl3 at 193 nm by translational spectroscopy
Authors: Lee Y. R. , Yang Y. J. , Lin Y. Y. , Lin S. M.
Published: July 2002

The photodissociation of CBrCl3 at 193 nm has been studied by translational spectroscopy. Two major dissociation channels, (1) CBrCl3→CCl3+Br and (2) CBrCl3→CBrCl2+Cl, are detected with product translational energies of 17 and 22 kcal/mol, respectively. The relative yield of (1):(2) is calculated to be 7:3. The primary product, CBrCl2, which is internally excited, undergoes unimolecular decay to form the CCl2+Br products. From the derived values of the anisotropy parameter β, we conclude that these processes take place rapidly after excitation via an A1←A1 transition, with the transition moment aligned parallel to the threefold axis. Results obtained for these two primary pathways and other minor processes are discussed in terms of a simple direct dissociation mechanism.
Vibrational population dynamics of the HgI photofragment in ethanol solution
Authors: Pugliano Nick , Szarka Arpad Z. , Gnanakaran S. , Triechel Matt , Hochstrasser Robin M.
Published: July 2002

The vibrational population dynamics of HgI fragments in ethanol solution, resulting from the 320 nm photolysis of HgI2, are examined both experimentally and by a simulation. The experiments reveal an HgI population distribution which rapidly relaxes toward equilibrium. At the earliest times, the HgI exhibits vibrational coherent wave-packet motion that dephases with a time constant of ca. 1 ps. These data are used to gain insight into the character of the solvated potential energy curves. The population relaxation was adequately reproduced by master equations which were formulated to incorporate the HgI anharmonicity and a solvent frequency dependent friction. This treatment characterizes the spontaneous vibrational relaxation timescale for the n″=1→0 transition to be ca. 3 ps, and is used to identify the relaxation rate constants for all other HgI level pairs. The simulations estimate that the initial excess energy of HgI is centered at n″≂10 which corresponds to a total excess energy of ca. 1050 cm−1.
Quantum dynamics simulation with approximate eigenstates
Authors: Murphrey Tim H. , Rossky Peter J.
Published: July 2002

We present a new semiclassical formalism for nonadiabatic dynamics of a quantum subsystem interacting with an explicit bath. The method is based on a stationary phase approach to the bath and a variational principle for the quantum transition amplitudes, for quantum systems represented by approximate wave functions. A new expression for the force exerted on a classical bath by a quantum subsystem is derived which, in the adiabatic limit, reduces to the gradient of the expectation value of the energy. Our new methods for adiabatic and nonadiabatic dynamics are applied to a test problem of vibrational relaxation. For adiabatic dynamics, we find that our new algorithm produces results which converge faster, with increasing basis set size, than calculations performed with the Hellmann–Feynman force; for a limited basis set, our new algorithm gives results that are in better agreement with exact results. For nonadiabatic dynamics, we also find that, in comparison to an earlier algorithm, our new algorithm produces results which converge more rapidly with increasing basis set size. In addition, we find that our new algorithm is more robust with respect to the size of the time step than the earlier algorithm, a result of the implementation of a nuclear coordinate dependent basis.
Molecular orbital coefficients and transition dipoles of real polyenes
Authors: Kohler Bryan E. , Malysheva Lyuba I. , Onipko Alexander I.
Published: July 2002

A simple four configuration model that quantitatively reproduces all of the 11Bu and 21Ag state 0-0 energies that have been measured in high resolution spectroscopic experiments has been described previously. This model has been useful for explaining trends in the electronic properties of series of unsubstituted and substituted linear polyenes. While this model led to analytical expressions for the excitation energies, there were no closed form expressions for other quantities, such as the transition dipoles, that depend explicitly on the coefficients of the one-electron molecular orbitals. This paper derives exact expressions for the one-electron molecular orbital coefficients for an alternating chain as well as exact expressions for the transition dipole moments. This facilitates a detailed examination of the dependence of the transition dipole moments on the polyene length and alternation parameter which leads to an expression that accurately describes the dependence of the transition dipole moments on these chain parameters. The application of these expressions to an analytical analysis of nonlinear response in linear polyenes will be the subject of a subsequent paper.
The 2 3Πg and 3 3Πg states of 7Li2: Optical–optical double resonance spectroscopy and ab initio calculations
Authors: Yiannopoulou A. , Urbanski K. , Antonova S. , Lyyra A. M. , Li Li , An T. , Whang T. J. , Ji B. , Wang X. T. , Stwalley W. C. , Leininger T. , Jeung G.-H.
Published: July 2002

The (2p+2p) 2 3Πg and (2s+3p) 3 3Πg states of 7Li2 have been studied both experimentally and theoretically. Vibrational levels v=0–41 of the 2 3Πg state and v=6–10 of the 3 3Πg state have been observed by perturbation facilitated optical–optical double resonance (PFOODR) spectroscopy. Our ab initio calculations show that the 2 3Πg state, although dissociating into 2p+2p atomic limit, is a Rydberg state and strongly mixed with the (2s+3p) 3 3Πg and (2s+3d) 4 3Πg Rydberg states. Our theoretical calculations show good agreement with our experimental results.
Comparison of a fixed-charge and a polarizable water model
Authors: Mountain Raymond D.
Published: July 2002

Molecular dynamics simulations are used to examine two models for water. The first model is the fixed-charge model introduced by Stillinger and Rahman and the second model is the polarizable model developed by Dang. The site–site, intermolecular pair distribution functions and the hydrogen bond lifetimes are determined for three fluid states for which neutron-diffraction determined pair functions exist. The trends in the pair functions and the bond lifetimes with decreasing density and increasing temperature for both models are similar, with the fixed-charge model pair functions changing more slowly, and the bond lifetimes more rapidly than those for the polarizable model. For the temperatures and densities examined, the explicit inclusion of polarization in the interactions appears to have a relatively small effect on the pair functions.
An evaluation of methods designed to calculate energy levels in a selected range and application to a (one-dimensional) Morse oscillator and (three-dimensional) HCN/HNC
Authors: Roy Pierre-Nicholas , Carrington Tucker
Published: July 2002

In this paper we study three methods designed to calculate energy levels in a range of interest. The methods are applied to a one-dimensional (1-D) Morse oscillator and to HCN/HNC (in three-dimensions). Energy levels in the chosen range are computed using the filter-diagonalization method proposed by Neuhauser [J. Chem. Phys. 93, 2611 (1990)], a spectral transform Lanczos method, and a guided Lanczos method we suggest in this paper. In the guided Lanczos method convergence of the energy levels of interest is favored by choosing the Lanczos starting vector so that it has a substantial overlap only with eigenvectors of the eigenvalues in the chosen range. This biased starting vector is calculated from a solution of the time-dependent Schroedinger equation. Of the three methods the guided Lanczos is the most efficient for both the Morse oscillator and HCN/HNC. None of the methods designed to favor a chosen energy range are, however, (for the two problems we considered) as efficient as a straightforward Lanczos method (without an optimized starting vector).
Effects of solvation on chemical bonding: An electron-flow analysis
Authors: Cioslowski Jerzy , Martinov Martin
Published: July 2002

Effects of nonspecific solvation on chemical bonding, described with a simple self-consistent reaction field model, are rigorously analyzed in terms of electron flow and electronegativity equalization between two molecular fragments A and B. In most (but not all) systems AB, the energy-lowering rise in the dipole moment that accompanies solvation is the result of an enhanced charge transfer between A and B, the enhancement stemming from both the increased electronegativity difference ΔχAB and the decreased bond hardness κAB. In systems, such as H⋅Cl, H⋅CN, and CH3⋅CN, that ensue from interactions between charged closed-shell fragments (H++Cl−, H++CN−, CH+3+CN−, etc.) the energy-stabilizing effect of solvation is a trade-off between the energy lowering due to the enhanced charge-transfer component of bonding and destabilization due to diminished covalent bonding. On the other hand, interactions between electrically neutral fragments (NH3+SO3, etc.) produce systems, such as the zwitterion of sulfamic acid (+H3N⋅SO−3), in which charge-transfer and covalent components of bonding are strengthened in tandem by solvation. The aforementioned phenomena account for the experimentally observed solvation-induced changes in the A–B bonds, namely their lengthening (or even a complete dissociation) in the former systems and shortening in the latter ones.
Intermolecular versus intramolecular interactions in nuclear spin conversion: Experiments on 13CH3F–O2
Authors: Nagels B. , Schuurman M. , Chapovsky P. L. , Hermans L. J. F.
Published: July 2002

Ortho–para conversion for gaseous 13CH3F is measured in mixtures with O2. As collision partner, O2 is found to be 4 times less efficient for conversion that CH3F itself. This demonstrates that intramolecular rather than intermolecular magnetic interactions provide the main pathway leading to nuclear spin conversion for such molecules.
A stochastic theory of inhomogeneously broadened linewidths in solids
Authors: Zürcher Ulrich
Published: July 2002

We investigate spectral diffusion decay using a model for solids that consists of two-level-systems (TLSs) interacting via strain fields. For the case when the rate of TLS flips vanishes, we find algebraic decay of correlation functions of the local field. We show that properties of equilibrium fluctuations are in agreement with the hierarchical picture proposed by Basché and Moerner: TLSs far away produce fast fluctuations that are small in magnitude, and close TLSs produce large fluctuations that are less frequent.
The high resolution infrared spectroscopy of cyanogen di-N-oxide (ONCCNO)
Authors: Guo Bujin , Pasinszki Tibor , Westwood Nicholas P. C. , Bernath Peter F.
Published: July 2002

The high-resolution infrared absorption spectrum of the oxalodinitrile di-N-oxide (ONCCNO) molecule has been recorded in the gas phase with a Fourier transform spectrometer at a resolution of 0.003 cm−1. No previous high-resolution spectra have been recorded for this semistable palindromic molecule. On the basis of the 2:1 intensity alternation in the rotational lines caused by nitrogen nuclear spin statistics, the ONCCNO molecule appears to be linear. A quasilinear structure, however, cannot be ruled out at this stage of the analysis. The ν4 and ν5 fundamental modes at 2246.040 55(23) cm−1 and 1258.475 30(11) cm−1 have been analyzed to give ground state rotational constants of B0=0.042 202 10(96) cm−1 and D0=8.77(70)×10−10 cm−1. By fixing the CN and NO bond lengths to 1.1923 and 1.1730 Å, respectively, the C–C bond length was determined to be 1.3329 Å using the B0 value. This short C–C bond length is thus similar to that observed for a carbon–carbon double bond.
Solution of the associative mean spherical approximation for the shielded sticky point electrolyte model
Authors: Duda Yu. Ja. , Kalyuzhnyi Yu. V. , Holovko M. F.
Published: July 2002

An analytical solution of the two-density Ornstein–Zernike (OZ) equation with the associative mean spherical approximation (AMSA) closure is obtained for the shielded sticky point (SSP) electrolyte model. The model is presented by the dimerizing version of the restricted primitive electrolyte model with dimerization which occurs due to the site–site sticky interaction at distances less than the ionic hard-core diameter. The present version of the AMSA is an extension of the associative MSA proposed recently [M. Holovko and Yu. Kalyuzhnyi, Mol. Phys. 73, 1145 (1991)]. It is demonstrated that, in the limit of complete association, the present two-density OZ equation reduces to the Chandler–Silbey–Ladanyi equation. Predictions from the AMSA in this limit are compared with those obtained by Monte Carlo simulations.
Temporally two-dimensional femtosecond spectroscopy of binary mixture of CS2
Authors: Tominaga Keisuke , Yoshihara Keitaro
Published: July 2002

We have studied the inhomogeneity of the low-frequency modes of binary mixtures of CS2 with various cosolvents by the temporally two-dimensional spectroscopy with femtosecond pulses. The inhomogeneity in the underdamped mode is found to be decreased upon dilution for all the solvents investigated.
Equations-of-motion method for the spin–orbit coupling of aromatic molecules: Application to the phosphorescence lifetime of benzene
Authors: Ito Hirotoshi , Kameshima Hisamitu , Shibuya Tai-ichi
Published: July 2002

A phosphorescence theory for aromatic molecules is formulated in terms of the equations-of-motion method. The theory is applied to the INDO/S calculations on the lowest triplet radiative lifetime of benzene. All the calculations are performed within the spin-same-orbit interaction approximation. The random-phase approximations are found to give better results than the Tamm–Dancoff approximation (or the singly excited CI). The importance of the spin-other-orbit interactions contributing to the phosphorescence lifetime is discussed from the formula derived in an Appendix.
Cascading amplified spontaneous emission of NO Rydberg states
Authors: Ishii Juntarou , Uehara Kiyoji , Tsukiyama Koichi
Published: July 2002

Amplified spontaneous emission (ASE) from single rotational levels of the Rydberg states (3dσ,π)H 2Σ+, H′ 2Π(v=1), (4pσ)M 2Σ+(v=0), (4pπ)K 2Π(v=1), (4dσ,π)O 2Σ+, O′ 2Π(v=0), 4f(v=1), and (5sσ)S 2Σ+(v=0) of nitric oxide, populated through optical–optical double resonance excitation has been observed. The ultraviolet laser is fixed to a specific rotational component of the A 2Σ+(v′=0 and 1)←X 2Π3/2(v″=0) transitions of NO. When the second visible laser was introduced collinearly and the frequency was resonant to the transitions from the A 2Σ+ state to the higher Rydberg states, the highly directional ASE in the near infrared region was found to be generated along the excitation laser beams. ASE excitation spectra exhibit an excellent signal-to-noise ratio, demonstrating the usefulness of the laser-induced ASE as a novel spectroscopic technique for excited states of molecules. Dispersed ASE spectra revealed the cascading radiative decay from the initially populated levels down to the A 2Σ+ state. The rotational dependence of the ASE pattern as well as the effect of a perturbation between Rydberg and valence states were briefly discussed.
Diffusion-limited geminate recombination of O+O2 in solid xenon
Authors: Benderskii Alexander V. , Wight Charles A.
Published: July 2002

The thermally activated recombination reaction O+O2→O3 is observed in solid xenon matrices and in free-standing crystals of xenon at 14–25 K on the time scale 102–105 s. The reactants are prepared as spatially separated O...O2 pairs immobilized in solid Xe at 10 K by 266 nm photodissociation of O3 precursor molecules. The temperature dependence of the ozone recovery rate yields an activation energy for diffusion of O atoms in solid xenon of 2.0±0.5 kJ/mol. This value also represents an upper limit to the potential energy barrier to the O+O2 recombination reaction itself. In dilute samples (mole fraction of ozone less than 2×10−4) more than 90% of the initial O3 is recovered during the warming cycle. Only a small fraction of O atoms (<20%) escape geminate recombination with the partner oxygen molecule within the pair and react with other O2 molecules or O atoms. The experimental results are interpreted within the framework of a continuous diffusion model in which the initial spatial distribution of reactants is nonrandom.
Effective potential methods in variational treatments of electron-molecule collisions. I. Theoretical formulation
Authors: Rescigno T. N. , McCurdy C. W.
Published: July 2002

We investigate the use of current effective core potentials to simplify variational treatments of electron scattering by target molecules containing one or more heavy atoms. The nonlocal character of these potentials poses severe computational problems for general algebraic variational methods that do not rely on specific analytic schemes for computing matrix elements. We show that standard l-dependent pseudopotentials can be represented in a way that facilitates the numerical evaluation of the required collision integrals.
Effective potential methods in variational treatments of electron-molecule collisions. II. Application to HBr
Authors: Rescigno T. N.
Published: July 2002

We report the results of variational calculations on low energy e−+HBr collisions using the complex Kohn method. We compare the results of all-electron numerical calculations with those in which effective core potentials are used. We present total, differential, and momentum transfer cross sections for electronically elastic scattering, as well as dissociative excitation cross sections for the low-lying electronic states that dissociate to ground-state neutral atoms. We find excellent agreement between the all-electron and core-potential results for all processes considered.
Vibrational frequency shift of H2 in rare gas clusters and solutions: Comparison of semi-classical theory and experiment
Authors: de Souza Luís E. S. , Ben-Amotz Dor
Published: July 2002

A recently developed semi-classical statistical mechanical formulation [de Souza et al., J. Chem. Phys. 99, 9954 (1993)] is combined with accurate H2-rare gas potentials [Le Roy and Hutson, J. Chem. Phys. 86, 837 (1987)] to predict H2 vibrational frequency shifts in rare gas clusters and low density solutions. The results are compared with available experimental measurements as well as with predictions derived assuming a Lennard-Jones (LJ) atom–atom potential. The Le Roy–Hutson potential has a minimum cluster energy and maximum H2 bond softening in the linear atom–diatom geometry, in contrast to the T geometry predicted using the LJ potential. The Le Roy–Hutson potential also yields better agreement with experimental temperature and density dependent H2 frequency shifts. A classical approximation to the ground state frequency of H2-rare gas clusters is suggested which relates the probability density of the cluster configuration to the classical Boltzmann distribution at a temperature equal to the cluster zero point energy.