bluuebunny/crossref_metadata_2025 huggingface dataset:
Product state and kinetic energy distributions in the ultraviolet photodissociation of the NO–Ar van der Waals molecule
Authors: King David S.
Published: July 2002

The internal state and kinetic energy distributions of the X̃ NO fragments formed from the ultraviolet photodissociation of the NO–Ar van der Waals species were obtained by laser-excited fluorescence techniques. The initially excited Ã NO–Ar rapidly dissociates to form X̃ NO with little rotational excitation, with vibrational excitation determined by a Franck–Condon process, with a cos2 θ angular flux distribution (θ defined relative to the direction of polarization of the pump laser), and with a speed v∼4.4×105 cm/s.
Dual Lanczos vector space. I. A formal and numerical framework for the theoretical investigation of relaxation processes
Authors: Wassam W. A.
Published: July 2002

We lay down the mathematical foundations of a matrix formulation of relaxation processes that places no symmetry restrictions on the Liouville operator appearing in the relevant linear equation of motion for the density distribution function or density operator. Adopting a dual Lanczos vector space, we construct a ‘‘global’’ dual Lanczos transformation scheme that may be utilized to facilitate spectral density and transient behavior calculations. It is shown that the basis vectors adopted in the Mori projection operator method correspond to the results obtained in a restricted global dual Lanczos transformation scheme limited to reversible systems, i.e., systems described by a Hermitian Liouville operator. Since the present approach places no symmetry restrictions on the Liouville operator, we are able to provide a mathematical framework that can handle relaxation processes in both reversible and irreversible systems.
Improved canonical and microcanonical variational transition state theory calculations for a polyatomic reaction: OH+H2→H2O+H
Authors: Isaacson Alan D. , Sund Mark T. , Rai Sachchida N. , Truhlar Donald G.
Published: July 2002

We have applied improved canonical and microcanonical variational transition state theories to the calculation of the rate constants for the polyatomic reaction OH+H2→H2O+H over the temperature range 200–2400 K using the Schatz–Elgersma fit to the Walch–Dunning ab initio potential energy surface. The results are compared to canonical variational transition state theory calculations that employed the same potential energy surface and to experiment. We find that the new results, which are in good agreement with experiment, differ very slightly from those obtained with canonical variational theory. One explanation for this agreement is that the microcanonical variational transition states have a rather weak energy dependence and lie within 0.04a0 of the ground-state adiabatic barrier maximum. We also find that quantum mechanical effects and the inclusion of reaction-path curvature are important at lower temperatures, and that the transition state theory treatment of this reaction breaks down for temperatures higher than about 2400 K.
A Green’s function and configuration interaction investigation on the doubly ionized states of H2O
Authors: Tarantelli F. , Tarantelli A. , Sgamellotti A. , Schirmer J. , Cederbaum L. S.
Published: July 2002

A recently developed Green’s function method for the calculation of molecular doubly ionized states is presented. Calculations of the dicationic states of water have been carried out, employing a number of different basis sets. For comparison, several configuration interaction calculations including multireference treatments have also been performed, complementing those available in the literature. The Green’s function approach is very efficient computationally and size-consistent, therefore it appears very promising in view of its applicability to larger molecular systems.
On the thermodynamic curvature of nonequilibrium gases
Authors: Casas-Vazquez J. , Jou D.
Published: July 2002

We compute the Gaussian curvature of the thermodynamic metric defined by the second derivatives of the entropy for a nonequilibrium heat-conducting dilute gas of rigid spheres. It is seen that the presence of the heat flux increases the thermodynamic curvature.
Investigation of the spatially isotropic component of the laterally averaged molecular hydrogen/Ag(111) physisorption potential
Authors: Yu Chien-fan , Whaley K. Birgitta , Hogg C. S. , Sibener S. J.
Published: July 2002

A comprehensive study of the spatially isotropic component of the laterally averaged molecular hydrogen/Ag(111) physisorption potential is presented. Diffractive selective adsorption scattering resonances for rotationally state-selected H2 and D2 on Ag(111) have been mapped out as a function of incident polar angle for several crystal azimuths and beam energies. These resonances have been used to determine the bound eigenvalues, and subsequently the shape, of the potential well. Best fit Lennard-Jones, Morse, variable exponent, and exponential-3 potentials having well depths of ∼32 meV are derived from the data. These measurements are supported by rotationally inelastic scattering measurements for HD and exact close-coupled quantum scattering calculations. Debye–Waller attenuation measurements are also presented for H2, D2, and HD. The ability to detect these diffractively coupled resonances on a closest-packed metallic surface, i.e., a surface of extremely low corrugation, suggests that such measurements can be carried out on a much wider class of surfaces than previously envisioned.
Flowing afterglow infrared chemiluminescence studies of vibrational energy disposal in the ion–molecule reactions F−+HBr,DBr→HF,DF+Br−
Authors: Langford Andrew O. , Bierbaum Veronica M. , Leone Stephen R.
Published: July 2002

Product vibrational state distributions for the ion–molecule reactions F−+HBr,DBr→HF(v≤4), DF (v≤6)+Br− are determined using the flowing afterglow infrared chemiluminescence technique. The nascent distributions are (0.09±0.04)v=1: (0.29±0.04)v=2: (0.34±0.04)v=3: (0.28±0.04)v=4 for the HF product, and (0.05±0.04)v=1: (0.12±0.04)v=2: (0.16±0.04)v=3: (0.25±0.04)v=4: (0.22±0.04)v=5: (0.20±0.04)v=6 for the DF product. The fractions of the available energy deposited in product vibration are 0.60±0.04 and 0.63±0.05 for the proton transfer and deuteron transfer reactions, respectively. A surprisal analysis suggests that less than 5% of the product molecules are formed in v=0. The HF distribution is somewhat hotter than that reported previously, while the DF distribution is measured for the first time. Both distributions are remarkably similar to those reported for the analogous neutral processes, which suggests that direct collisions dominate the reactive encounters despite the presence of a deep attractive well in the potential surface for the ion–molecule reactions.
Autoionization in N2O as measured by angle-resolved photoelectron spectroscopy
Authors: Carlson Thomas A. , Svensson W. Agneta , Krause Manfred O. , Whitley Timothy A. , Grimm Frederick A.
Published: July 2002

Angle-resolved photoelectron spectroscopy has been carried out on N2O as a function of photon energy from 13.5 to 20.5 eV using monochromatized synchrotron radiation. The purpose of these studies has been to investigate autoionization, and most of the data have been collected under conditions of constant ionic state. Six resonances are discussed in detail: the first four that form a portion of several Rydberg series leading to the A 2Σ+ ionic state and the first two window resonances leading to the C 2Σ+ state. Data have been taken as a function of the final state vibrational band and as a function of angle between the ejected photoelectron and polarization vector. In particular, the correlation between the integrated angular intensity and its angular distribution parameter, β, has been measured as a function of photon energy over the resonances. The nature of these results and importance to the understanding of autoionization in molecules is discussed.
The direct ultraviolet absorption spectrum of the 1Σg+ → 1B2(1Σu+) transition of jet-cooled 13C32S2 and 12C34S2
Authors: Roebber J. L. , Vaida V.
Published: July 2002

The absorption spectra of isotopically substituted carbon disulfide, i.e., 13C32S2 and 12C34S2, cooled in supersonic expansion are reported here and compared with the spectrum of the natural isotope. Cooling these samples eliminated spectral congestion due to inhomogeneous factors and yielded measurements of frequencies and isotopic shifts of bands of 13C32S2 and 12C34S2 relative to 12C32S2. The spectrum obtained is interpreted to reflect a transition from a linear ground state to a bent excited state up to ∼49 000 cm−1 and to a quasilinear excited state above this energy.
Formation of negative cluster ions of CO2, OCS, and CS2 produced by electron transfer from high-Rydberg rare gas atoms
Authors: Kondow Tamotsu , Mitsuke Koichiro
Published: July 2002

A novel method of the collisional ionization by using high-Rydberg atoms is applied to van der Waals clusters of CO2, OCS,and CS2. This method is found to be useful for gentle production of negative cluster ions and provides information on the vertical electron affinities of the clusters and relaxation involved in the ionization.
Coherent Raman and infrared spectroscopy of HCN complexes in free jet expansions and in equilibrium samples
Authors: Maroncelli M. , Hopkins G. A. , Nibler J. W. , Dyke T. R.
Published: July 2002

Small hydrogen bonded complexes of HCN and DCN have been examined in the gas phase using FTIR and photoacoustic Raman spectroscopy (PARS). Four distinct bands are seen and assigned to CN stretching modes of the HCN dimer (D) and trimer (T). Previous microwave studies have shown the HCN dimer to be linear and analysis of the IR trimer band shape unambiguously demonstrates that the HCN trimer is also linear. The pressure dependent intensity of the observed transitions yields IR and Raman cross sections relative to the monomer of: (σD/σM)IR =30±10, (σT‘/σM)IR =500±200, (σD/σM)Ram =0.5±0.1, (σT/σM)Ram =3.3±0.7. The dramatic enhancements seen in the IR cross sections are due to small but significant (∼2×) changes in the CH bond dipole derivative. CARS spectroscopy has been used to examine the complexes formed in supersonic expansions of pure HCN (DCN) and HCN diluted in Ar and He carriers. Due to the cooling and collision-free conditions in the jet, this method yields higher effective resolution than is possible with equilibrium samples. The added ability to ‘‘tune’’ the size of complexes by varying expansion conditions has allowed us to observe a number of other modes in HCN and DCN dimer and trimer as well as in higher polymers. These data have been used to partially refine a harmonic valence force field for the stretching modes of the dimer and trimer complexes.
One-electron diatomics in momentum space. I. Implication of first iterated solutions for the ground state
Authors: Koga Toshikatsu
Published: July 2002

For one-electron diatomic systems, an iterative solution of the momentum-space Schrödinger equation is examined using the Fock transformation which enables us to expand the kernel of the integral equation by the four-dimensional spherical harmonics. Starting from the united atom (UA) and simple LCAO approximations, first iterated solutions are derived and their properties are analyzed. The corresponding approximate energy eigenvalues are also obtained as a function of the internuclear distance R. The result from the LCAO starting function is found to be reliable semiquantitatively: in the range of 0≤R≤20, the maximum errors of the ground-state electronic energy are 4.7% and 1.7%, respectively, for the H+2 and HeH2+ systems, when compared with the exact values.
Excitation energy transport and reversible trapping in aromatic vinylpolymers: Transient long-time behavior of a dissociative monomer–excimer system. A deterministic kinetic treatment
Authors: Weixelbaumer Wolf-Dieter , Bürbaumer Josef , Kauffmann Harald F.
Published: July 2002

A deterministic kinetic analysis has been presented in an attempt to model the δ-pulse dynamics of a monomer–excimer pair in presence of energy migration and detrapping. Because of the reversibility of the system and the formal treatment of excitation energy transport by means of a time-dependent rate function k(t), the linear first order equations of evolution are coupled and consist of nonautonomous coefficients. The formalism involves a linear, affine transform technique for decoupling the simultaneous rate equations. This procedure leads to nonlinear, but decoupled first-order Riccati equations which have been further transformed to yield a second-order differential equation with time-dependent coefficients. For k(t)=b+Ct−1/2, the present study develops approximate WKB solutions to the transient δ-pulse response behavior of the system under the condition of weak coupling. The limitation of this approach have been tested towards numerical computer results. The WKB solutions are well behaved at relatively long times and, thus, prove useful for providing the typical asymptotic behavior of a polychromophoric monomer–excimer system in which transport and trapping will proceed via a quasi-one-dimensional pathway. The physics of this treatment has been discussed on the basis of energy-dispersive hopping processes along the chromophor array of aromatic polymer with typical, diagonal disorder. The analytical solutions, however, might have more general significance, presumably, with respect to forthcoming, subnanosecond reconvolution procedures in the transient fluoresence analysis of dilute aromatic vinylpolymers.
Spectroscopic identification of the lowest rotation-vibration levels of the (2pσ)2 F 1Σ+g state of the H2 molecule
Authors: Senn P. , Quadrelli P. , Dressler K. , Herzberg G.
Published: July 2002

Many lines in the infrared emission spectrum of the hydrogen molecule are still unidentified. We report here the identification of a number of such lines corresponding to transitions from the lowest two vibrational levels, v=0 and v=1, of the (2pσ)2 F 1∑+g state of H2. Intensity distributions observed in the bands of the F 1∑+g−B 1∑+u system are consistent with theory. New or more accurate rotational term values are also found for the v=2–4 levels of the F state, and molecular constants are reported. The rotation-vibration structure of the F state (v=0–4; J=0–5) is in good agreement with accurate ab initio calculations which include the effects of tunneling in the double-minimum potential function of the EF state as well as nonadiabatic effects.
Intramolecular vibrational relaxation of a polyatomic in the solid state. II. HC14N and HC15N in Ar, Kr, and Xe
Authors: Abbate Alison D. , Moore C. Bradley
Published: July 2002

The vibrational relaxation of HC14N and HC15N isolated in Ar, Kr, and Xe matrices was studied by laser-excited vibrational fluorescence. Complete sets of rate constants for the unimolecular relaxation of ν3 excitation through the ν1 and ν2 manifolds were obtained for HCN/Xe. At low temperatures the (1,00,0) level is a metastable trap and at increased temperatures detrapping shifts the relaxation route from the ν1 to the ν2 manifold. Dipole–dipole hopping of ν3 and ν2 quanta was observed and treated quantitatively with Förster theory. The temperature dependence of rates indicates that the vibrational energy is transferred to a local guest mode. The increase in rate, kXe<kKr<kAr, with steepness of repulsive potential and with vibrational frequency in the matrix shows that relaxation is caused by a repulsive interaction between guest and matrix. Gas phase theory is adapted to model hard ‘‘collisions’’ with the matrix cage; it indicates that translation rather than rotation is the accepting mode. The success of this model in treating the dependence of rate on vibrational energy and quantum number change suggests that it will be useful for predicting relaxation mechanisms and rates in other systems.
Phenomenological theory of multiply reentrant solubility
Authors: Goldstein Raymond E.
Published: July 2002

A phenomenological approach to the theory of complex phase diagrams in binary liquid mixtures is developed. The random-mixing Flory–Huggins free energy expression is modified by the generalization of local pairwise energies to the corresponding free energies which, for systems with specific interactions such as hydrogen bonds, are described in terms of multiple-level partition functions. The temperature-dependent effective interactions in recent lattice models for these systems appear as special cases of this more general result. While characteristic asymmetries of various interactional correlation functions evaluated in the coexisting phases are found to parallel those of the interactions themselves, the symmetry of the phase diagram is not affected by such interactions, in contrast to the results of decorated-lattice calculations. A heuristic explanation of this is given, supporting a recent suggestion that the description of interaction-driven asymmetric coexistence curves requires an enlarged space of statistical variables which includes density fluctuations.
Electron affinity of SF6 and perfluoromethylcyclohexane. The unusual kinetics of electron transfer reactions A−+B=A+B−, where A=SF6 or perfluorinated cyclo-alkanes
Authors: Grimsrud E. P. , Chowdhury S. , Kebarle P.
Published: July 2002

Measurements of the equilibria (1): A−+B=A+B− with a pulsed electron high pressure mass spectrometer lead to ΔG01, ΔH01, and ΔS01. Equilibria involving SF6 as A and perfluoromethylcyclohexane C7F14 provide electron affinities E.A.(SF6)=1.05±0.1 eV and E.A.(C7F14)=1.06±0.15 eV. The kinetics of reactions (1) involving the above two compounds were studied. The rate constants kf for SF−6 +B=SF6+B− were found to increase with exothermicity of the reaction. The temperature dependence for kf was determined. B compounds leading to high exothermicities were associated with kf at the collision limit and essentially no temperature dependence. B of progressively lower electron affinity led to kf below the collision limit and negative temperature dependence, while B with the lowest E.A. but still leading to exothermic reaction produced lowest kf with positive temperature dependence. A model is provided explaining the above behavior. The known large change of geometry between SF−6 and SF6 introduces an internal barrier in the reaction coordinate for the reactions (1) involving SF6.
On the computation of two surface properties by coordinate-space propagator techniques
Authors: Coalson Rob D.
Published: July 2002

The time-dependent two-surface formalism (used to calculate electronic absorption spectra, Raman excitation profiles, etc.) is recast so as to enable the employment of recently developed coordinate space propagator techniques in the computation of the relevant time kernels. Two classes of propagator methods are discussed in connection with the two-surface problem: matrix multiplication of discretized short-time propagators and Monte Carlo path integration. As a nontrivial test case, the matrix multiplication procedure is successfully utilized to extract a high resolution finite temperature electronic absorption spectrum involving displaced one-dimensional Morse wells.
On the theory of interaction between chemical reaction and viscous flow in dilute gases
Authors: Popielawski Jan
Published: July 2002

The Boltzmann equation modified for the case of the chemical reaction: A+A=B+C is solved by the Chapman–Enskog perturbation method up to the third order (Burnett) approximation. This approximation is applied to the calculation of the contribution of the chemical reaction to the viscosity coefficient. Numerical calculations are performed with the use of the model of chemically reacting hard spheres. It is pointed out that this contribution can be quite important for values of the mean kinetic energy of the system, as indicated by kBT, close to the activation energy of the chemical reaction.
Screening in semirigid polymer systems
Authors: Ten Bosch A. , Sixou P.
Published: July 2002

An expression for screening of the effective monomer interactions in semirigid polymer systems is developed. Anisotropic interactions dependent on monomer orientation are taken into account in an expansion of the bare potential in spherical harmonics. Using the method of Gaussian random fields previously applied to simple flexible polymers, the equation for the screened potential is given as an expansion in the density correlation functions of the effective chain. The effect of the polymer interactions on the persistence length and end-to-end distance of worm-like chains is calculated and shown to be small.
Inelastic collisions of CaCl(X 2Σ+) with Ar: A collaborative theoretical and experimental study
Authors: Alexander Millard H. , Davis Stephen L. , Dagdigian Paul J.
Published: July 2002

We investigate rotationally inelastic cross sections of CaCl(X 2Σ+) with Ar at a collision energy of 0.24 eV. Theoretical cross sections, determined by coupled states calculations based on an electron-gas description of the potential surface, are compared with experimental cross sections, determined in a molecular beam apparatus involving initial state selection by an electric quadrupole field and final state detection by laser-induced fluorescence. The agreement between theoretical and experimental cross sections is excellent, except for the e → e transitions with ΔN=even, which suggests a residual inaccuracy in the theoretical description of the second Legendre moment of the anisotropy in the potential. Both the theoretical and experimental cross sections clearly confirm a propensity toward conservation of the spectroscopic e/ f label. The sets of experimental and theoretical cross sections can be well fit by the sudden scaling relation, although the entire set of base cross sections can not be well represented by a simple power law.
On the non-Markovian theory of activated rate processes in the small friction limit
Authors: Dygas M. M. , Matkowsky B. J. , Schuss Z.
Published: July 2002

The motion of a particle in a one-dimensional potential well under the effect of thermal noise and damping plays an important role in modeling many physical and chemical phenomena. The problem of interest is to determine the escape rate κ from the well. The generalized Langevin equation, describing this motion, is examined in the asymptotic limit of the small friction. A limiting backward Kolmogorov operator in the energy variable is derived by averaging on constant energy contours, and then employed to calculate explicit analytical expressions for the activation rate κ.
Nascent product excitations in unimolecular reactions: The separate statistical ensembles method
Authors: Wittig C. , Nadler I. , Reisler H. , Noble M. , Catanzarite J. , Radhakrishnan G.
Published: July 2002

The unimolecular reaction of a vibrationally excited molecule having low rotational excitation often leads to nascent products in which the vibrational degrees of freedom appear ‘‘hotter’’ than the rotation, translation (R,T) degrees of freedom. We show that this can derive from parent vibrations being ‘‘hot’’ while parent rotations remain ‘‘cold,’’ since the parentage of product vibration is parent vibration, while product R,T excitations are obtained from parent vibration as well as rotation. Calculations are performed for reactions having loose transition states and no reverse barriers, in which an ensemble of 3N–6 degrees of freedom are used to equilibrate parent vibrations, thereby providing a statistical distribution of product vibrational excitations. For each set of product vibrational states, all R,T excitations are then apportioned statistically using the phase space theory of unimolecular reactions (PST). The results indicate that for those energies above reaction threshold (E‡) which exceed the lowest product vibrational energies, product vibrations are more excited than with PST, while product R,T excitations are less than with PST. These differences increase with E‡, and rotational distributions obtained using the separate statistical ensembles (SSE) method peak at low N″ relative to PST. When product vibrations are energetically inaccessible, SSE and PST are identical. The calculations are compared to nascent distributions from the unimolecular dissociation of monoenergetic NCNO, and the agreement is excellent.
Compound clusters. II. Intermetallics and phosphides
Authors: Martin T. P.
Published: July 2002

Compound clusters composed of two metallic elements have been produced by allowing the elements to react in the vapor phase. The composition of the clusters could be varied by changing the relative partial pressures of the two vapors. Mass spectrometry indicates that clusters with certain well defined compositions are particularly stable. For example, in the Cs–Sn system, mass peaks corresponding to (Cs3Sn2)+, (Cs3Sn5)+, (Cs5Sn4)+, and (Cs5Sn9)+ are unusually strong. Other metallic systems discussed are Pb–Cs, Pb–In, Pb–Sr, Pb–In, and In–Cs. In another series of experiments each of these elemental metallic vapors was allowed to react with phosphorus vapor. In this way the relative stability of the various phosphide clusters could be tested. For example, (Cs4P7)+ and (Cs3P4)+ are shown to be particularly stable. The probable structures of some of the intermetallic and phosphide clusters are presented.
Dynamics of excitation transfer in solution: Short range reactive and caging effects
Authors: Sipp B. , Voltz R.
Published: July 2002

In this paper, we analyze the kinetics of excitation transfer when short-range effects due to an additional reactive interaction (exchange) and to solvent cage perturbations of the relative molecular motion are introduced. We show that the short-range solvent caging influence on the observable transfer length can be brought to direct observation only in reactive systems undergoing fast molecular motion (slow reaction limit). In contrast, considering resonant electronic excitation transfer, a strong exchange mechanism (slow diffusion regime) is required to optimize its efficiency in the competition with the long-range dipolar potential. In this case, we show how to measure the range and the frequency factor of the exchange interaction, which are usually unknown parameters.
Non-Arrhenius rate constants in complex reaction systems
Authors: Gorensek M. B. , Kostin M. D.
Published: July 2002

Explicit analytical expressions for the rate constants have been derived which take into account the distortion of the Maxwellian caused by chemical reactions. In contrast to simple systems involving a single chemical reaction, where the rate constant is usually not affected much by the distortion, the analytical expressions show how in complex reaction systems the frequency factors of the rate constants for the reactions with the higher threshold energies may be substantially less than the Arrhenius values. The validity of the analytical expressions is verified by comparison with exact numerical solutions.
Analytic computation of energy derivatives. Relationships among partial derivatives of a variationally determined function
Authors: King Harry F. , Komornicki Andrew
Published: July 2002

This paper considers three functions of several variables, W(r,x), λ(r), and E(r), related by E(r)=W[r,λ(r)] and the condition that W(r,x) be stationary with respect to variations of x when x=λ. Formulas are presented which relate coefficients in the Taylor series expansions of these three functions. We call λ the response function. Partial derivatives of the response function are obtained by solution of a recursive system of linear equations. Solution through order n yields derivatives of E through order 2n+1. This analysis extends Pulay’s demonstration of the applicability of Wigner’s 2n+1 rule to partial derivatives in coupled perturbation theory. A four-term second derivative formula is shown to be numerically more stable than the usual two-term formula. We refute previous claims in the literature that energy derivatives are stationary properties of the wave function.
Quantitative VUV spectroscopy of Cl2
Authors: Lee L. C. , Suto Masako , Tang K. Y.
Published: July 2002

The photoabsorption and fluorescence cross sections of Cl2 were measured in the 105–145 nm region using synchrotron radiation as a light source. The oscillator strengths for the major absorption bands were calculated from the measured absorption cross sections. The measured oscillator strengths for the 2 3Πu and 2 1Πu←X 1Σ+g transitions agree quite well with the theoretical values. The absorption spectrum was analyzed in accord with the excited electronic states calculated by Peyerimhoff and Buenker (1981). The Rydberg series converging to the first and second ionization potentials were classified. The vibrational levels of the 2 1Σ+u ionic state were determined up to v′=15 from the fluorescence excitation spectrum. It was observed that a band with peak at 108.3 nm produces VUV fluorescence, but it produces UV fluorescence only by a collisional excitation process.
A direct inverse transform for resonance Raman scattering
Authors: Cable J. R. , Albrecht A. C.
Published: July 2002

A direct inverse transform procedure is presented that can efficiently determine the resonant absorption band (ABS) responsible for an experimental Raman excitation profile (REP). In this technique, an integral Hilbert transform is directly evaluated, to reveal the phase of the complex function, which, at the magnitude squared level, represents the measurable REP. Once this complex REP function is known, the complex linear electrical susceptibility is readily calculated and hence the spectrum of any property derivable from it can be determined. The inverse transform is first demonstrated on a model REP to produce the corresponding ABS. It is then applied to several experimental REPs in resonance with the S4 transition in azulene. Finally it is linked with the conventional ‘‘forward’’ transform to show how the REP of one mode may be used to predict REPs of other vibrational modes. This linked procedure is tested using published REP data for the S1 transition in azulene.
Aluminum clusters: Magnetic properties
Authors: Cox D. M. , Trevor D. J. , Whetten R. L. , Rohlfing E. A. , Kaldor A.
Published: July 2002

We report the first measurement of the magnetic moments of gas phase aluminum clusters ranging in size from 2 to 25 atoms. Aluminum clusters are produced by pulsed laser vaporization of an aluminum rod inside the throat of a high pressure pulsed nozzle. The highly collimated cluster beam is passed through a Stern–Gerlach magnet and the deflected beam is analyzed by spatially resolved photoionization time-of-flight mass spectrometry. Aluminum clusters less than nine atoms in size are found to have magnetic moments generally consistent with those predicted from spin and orbital moments of the ground electronic states. As expected, a general trend toward reduced magnetic moment per atom with increasing cluster size is observed.
Dynamics of helical worm-like chains. VIII. Higher-order subspace approximations to dielectric and magnetic relaxation and fluorescence depolarization for flexible chains
Authors: Yamakawa Hiromi , Yoshizaki Takenao , Fujii Motoharu
Published: July 2002

Following the general scheme developed in the preceding paper (paper VII), dielectric and magnetic relaxation and fluorescence depolarization for flexible chain polymers in dilute solution are reinvestigated on the basis of the discrete helical worm-like chain in the higher-order subspace approximation. A comparison of theory with experiment is made with respect to the dielectric correlation time τD, the spin-lattice relaxation time T1, the spin–spin relaxation time T2, the nuclear Overhauser enhancement (NOE), the fluorescence emission anisotropy r(t), the average fluorescence anisotropy r̄, and the fluorescence correlation time τF. It is found that there is agreement between the diameters of the chains determined from these dynamic properties and those from chemical structures, better than in the previous crude subspace approximation, indicating that the theory is remarkably improved in the present approximation. The magnetic correlation time τM is in general not an observable, and therefore an empirical equation to be used for its determination from the observed T1 is constructed. It is then found that there is good correlation between the dynamic chain stiffness τX/τ0X and the static chain stiffness λ−1, where τ0X is the correlation time of the isolated subbody (monomer unit) with X=D, M, and F; τX/τ0X is a monotonically increasing function of λ−1 nearly independent of X as far as perpendicular dipoles are concerned. An explanation of this result is given. However, the dependence of τX on temperature cannot be explained very satisfactorily.
Deexcitation time shortening for the electronic states of trapped oxygen by matrix doping. I. Theoretical aspects
Authors: Girardet Claude , Maillard Daniel , Fournier Janine
Published: July 2002

The shortening of the 1S level lifetime of a rare gas trapped oxygen atom is interpreted according to the following scheme: a perturber disturbs the Oh ideal environment around the oxygen atom and induces a transition dipole moment for the 1S → 1D normally quadrupolar transition. We choose to represent the perturber by a foreign rare gas atom also trapped in the matrix since (i) the rare gas–rare gas interaction potential is generally of good quality and (ii) double doping experiments are easily performed. The distortion induced by the perturber is calculated at any lattice point of the crystal in the framework of the Green static functions. The energies of the level correlating with 1S and of the five levels correlating with 1D are determined together with the transition dipole elements. The bar spectrum is then reconstructed and the lifetime of the 1S level calculated, as a function of the oxygen-perturber distance.
Nonlinear dynamics of vibration–rotation interactions: Rigid bender H2O
Authors: Frederick John H. , McClelland Gary M.
Published: July 2002

A classical nonlinear dynamics analysis of intramolecular vibration–rotation interaction is presented. The system studied is a water molecule which is allowed to rotate in three dimensions and bend, but angular momentum conservation is used to reduce the problem to two degrees of freedom. A classical perturbation theory treatment is developed which accurately treats first order corrections to the dynamical frequencies and which provides a qualitative picture of the role of nonlinear resonances in the onset of vibration–rotation chaos. Additionally, a classical trajectory study of the high j, high E regime provides information about the onset of chaos. The relationship of this work to an earlier trajectory study and a comparison of the results to those found for coupled oscillator systems are discussed.
The classical mechanics of vibrational predissociation: A model based study of phase space structure and its influence on fragmentation rates
Authors: Gray Stephen K. , Rice Stuart A. , Noid D. W.
Published: July 2002

The classical dynamics pertinent to van der Waals molecule vibrational predissociation of a T-shaped model for HeI2(B) is examined. An interesting phase space structure involving nonlinear resonances and stochastic motion is found. For low initial vibrational excitations of the I2 partner of the vdW complex the relevant part of phase space is dominated by quasiperiodic motion indicating a purely quantal mode of decay (‘‘dynamical tunneling’’), but for higher initial vibrational excitations van der Waals molecule predissociation is a classically allowed process. Classically determined rates of decay agree to within a factor of 3 with the rates calculated from quantum mechanics.
On the physical origin of propensity rules in collisions involving molecules in 2Σ electronic states
Authors: Alexander Millard H. , Smedley Jane E. , Corey Gregory C.
Published: July 2002

A general quantum treatment of the collision dynamics of 2S+1Σ-state diatomic molecules is developed, with particular emphasis given to the physical origin of the collisional propensity for conservation of the e/f molecular symmetry label. State-resolved integral cross sections are expressed as a weighted sum of tensor opacities which are related to the probability that a collision will reorient the nuclear rotational angular momentum vector. Previous derivations of the propensity rules for collisions of 2S+1Σ-state diatomic molecules were restricted to the sudden or Born approximations. Here a general derivation is developed that is free of dynamical approximations, and that clearly establishes the direct connection between the observed propensity for the conservation of the e/f molecular symmetry and the collisional propensity for the conservation of the orientation of the nuclear rotational angular momentum vector. A power-law model suggested by previous semiempirical fits to cross sections for 1Σ+-state molecules is extended to open-shell molecules. This simple model allows us to predict semiquantitatively the degree to which the e/f symmetry index is conserved without performing a full dynamical calculation.
Depolarized differential Rayleigh light scattering (DDRLS) by uncorrelated molecules with degenerate electronic states
Authors: Woźniak S. , Zawodny R.
Published: July 2002

A detailed analysis of DDRLS is performed for arbitrary scattering angle θ and all molecular symmetries. Different quantum mechanisms are shown to be responsible for the effect at θ=π/2 and θ≠π/2. For one magnetic point group, the DDRLS is described by c tensors only (i.e., by tensors asymmetric with respect to time inversion), whereas for 13 other magnetic point groups—by i tensors (symmetric with respect to time inversion); in the remaining magnetic point groups it is dependent on i tensors as well as c tensors, or does not exist altogether. Equations are derived permitting, by way of DDRLS measurements, the determination of the tensor components G and A for seven magnetic point groups. For molecules with an isotropic electromagnetic polarizability tensor G a simple relation between the DDRLS and the angle of rotation of the light polarization plane in the effect of natural optical activity is established.
Excitation of molecular rotation by periodic microwave pulses. A testing ground for Anderson localization
Authors: Blümel R. , Fishman S. , Smilansky U.
Published: July 2002

We study the excitation of molecular rotation by microwave pulses of duration σ which occur periodically with frequency ω. We analyze the molecular dynamics both classically and quantum mechanically and consider situations where the coupling of the field to the molecule is strong. In both approaches, the angular momentum transmitted to the molecule is confined to a finite band of width ≊1/σ. But, while the classical dynamics displays chaotic features, the quantum treatment distinguishes clearly between two regimes. Resonance excitation occurs when ω is rationally related to the basic rotation frequency ω0. Off resonance (ω/ω0 irrational), the probability to transfer angular momentum to the molecule is small and the underlying mechanism for this effect is analogous to the Anderson model of localization in a one-dimensional random lattice with a finite number of sites. We show that the conditions required by our analysis can be achieved with, e.g., PbTe or CsI molecules and conventional field strengths and we propose this system as an experimental testing ground for the Anderson localization mechanism.
Ultraviolet resonance Raman scattering of azulene: A test of transform theory
Authors: Cable J. R. , Albrecht A. C.
Published: July 2002

Raman excitation profiles (REPs) from a highly excited state in azulene are presented for several vibrational modes. These include four fundamentals, a combination, and an overtone. Experimental REPs are compared to transform theory predictions which are based on the observable absorption spectrum (ABS) of the resonant electronic state. Though both the REPs and the ABS are multimode in nature, the transform provides a single mode link between the two and allows for extraction of excited state parameters on a mode by mode basis. For several modes, excited state frequencies and Franck–Condon coupling constants are estimated. Observed discrepancies between experiment and transform for other modes raise questions as to the applicability of the ‘‘standard assumptions’’ on which the transform is based to all of the vibrational modes in this electronic state. The strongly enhanced Raman scattering also allows depolarization ratios to be determined for all the azulene symmetric ring vibrations and directly confirms previous symmetry assignments.
Average wave function method for gas–surface scattering
Authors: Singh Harjinder , Dacol Dalcio K. , Rabitz Herschel
Published: July 2002

The average wave function method (AWM) is applied to scattering of a gas off a solid surface. The formalism is developed for both periodic as well as disordered surfaces. For an ordered lattice an explicit relation is derived for the Bragg peaks along with a numerical illustration. Numerical results are presented for atomic clusters on a flat hard wall with a Gaussian-like potential at each atomic scattering site. The effect of relative lateral displacement of two clusters upon the scattering pattern is shown. The ability of AWM to accommodate disorder through statistical averaging over cluster configurations is illustrated. Enhanced uniform backscattering is observed with increasing roughness on the surface.
Semiempirical treatment of the benzophenone molecule as a function of twist angle
Authors: Weitzel K.-M. , Bässler H.
Published: July 2002

The benzophenone molecule has been treated in MNDO, MNDOC, and MINDO/3 approximation as a function of the twist angle α of the phenyl rings. Calculated were (i) the energies of S0 and T1 state, (ii) delocalization of the n and π* orbitals involved in the 3nπ* state, (iii) net atomic charges,(iv) the force constants of the C=O vibration in the S0 and T1 state, respectively, (v) vertical transition energies for T1←S0 and S1←S0, and (vi) the position of upper triplet states. The results are discussed in relation to the spectroscopic properties of the T1 state of a vitreous benzophenone phase. It is concluded that diagonal disorder is due to a significant fluctuation of α causing both a spread of the site energies of the glass-forming molecules and a variation of spin-orbit coupling.
Density functional theory of bound states of positrons in negative ions
Authors: Harrison Joseph G.
Published: July 2002

Bound states of a single positron and a negative ion are studied in the self-interaction-corrected local spin density approximation (SIC-LSDA). The calculations do not include electron–electron or electron–positron correlation effects. The results are found to be in good agreement with restricted Hartree–Fock calculations. Implications for future work including correlation effects are discussed.
Delayed ionization following resonant photon absorption and intracluster electron transfer
Authors: Dao P. D. , Castleman A. W.
Published: July 2002

Ionization of clusters comprised of paraxylene (PX) bound to NH3 and N(CH3)3 is studied following the absorption of photons through the perturbed S1 state of PX. In the case of PX ⋅ NH3 where the ionization potential of PX (8.445 eV) lies below that of NH3 (10.16 eV), ionization of the cluster near the ionization threshold of PX leads to the formation of the cluster ion (PX  ⋅  NH3)+. By contrast, for clusters of PX ⋅ N(CH3)3 where the ionization potential of N(CH3)3 (7.82 eV) lies below that of PX, resonance absorption through high Rydberg states of PX below its I.P. leads to the production of N(CH3)+3 and H+⋅N(CH3)3, but no parent cluster ions. In this case, following photon absorption the ionization and formation of N(CH3)+3 is substantially delayed for times ranging from 160–200 ns, the longer values being obtained at lower photon energies.
Semiclassical quantization of the vibration-rotation problem
Authors: Frederick John H. , McClelland Gary M.
Published: July 2002

A semiclassical quantization of rigid bender H2O with a single bending vibration coupled to three dimensional rotation is presented. Angular momentum conservation reduces this problem to two degrees of freedom. An efficient new algorithm is developed for EBK semiclassical quantization in two dimensions, and a tunneling approximation used to generate asymmetry splitting. This technique reproduces to within 1% the level shifts due to vibration-rotation interaction for j=3,10 and nv from 0 to 3 and is successful where the usual approximate quantum (centrifugal distortion) treatment of these interactions fails.
Resonance Raman overtone intensity calculations of a matrix-isolated I2 molecule by the symmetrized split operator fast Fourier transform method
Authors: Kono H. , Lin S. H.
Published: July 2002

Resonance Raman overtone progressions of I2 in an Ar crystal are computed using the time dependent formula of Raman scattering which has been known to possess distinct computational advantages over the Kramers–Heisenberg–Dirac sum-over-states method, especially when treating condensed phase systems. The symmetrized split operator fast Fourier transform method, which provides a simple and accurate algorithm, is applied to computing the time evolution of the vibrational wave packet involved in the time dependent formula. Our calculated result based on Heller’s time dependent formula is in qualitative agreement with the experimental one of Grzybowski and Andrews, but there are some discrepancies between them (for example, the overtone enhancement with the 530.9 nm excitation is not so strong as the experimental one). Those discrepancies are ascribed to the adopted assumption that the line shape for a vibronic transition is a Lorentzian and it is independent of the vibrational level in the excited electronic state. The use of an incident frequency dependent line shape proves to resolve the disagreements to a great extent, which implies that to obtain perfect agreement one needs to explicitly deal with the motion of the trapped molecule and its neighboring host atoms.
State selected ion–molecule reactions by a TESICO technique. X. O+2(v)+CH4
Authors: Tanaka Kenichiro , Kato Tatsuhisa , Koyano Inosuke
Published: July 2002

Vibrational state selected (relative) reaction cross sections have been determined for v=0–3 of the O+2 ion, for each of the three product channels of the reaction O+2(v)+CH4, viz. O+2(v)+CH4→CH3O+2+H (1) →CH+3+HO2 (2) →CH+4+O2 , (3) using the TESICO (threshold electron–secondary ion coincidence) technique. At a fixed collision energy of 0.27 eV, it has been found that the cross section of exoergic channel (1) increases most prominently with increasing vibrational quantum number v in the range v=0–2, but decreasees sharply in going from v=2 to v=3. The cross sections of endoergic channels (2) and (3) also increase with increasing v but their rates of increase are much smaller than that of channel (1) in the range v=0–2. When v is increased to 3, however, charge transfer channel (3) is enhanced dramatically and the CH+4 ion becomes the most abundant product ion. The cross section of channel (2) also increases more sharply in going from v=2 to v=3 than in the range v=0–2, but the CH+3 ion still remains the least abundant of the three product ions. As a result of these variations in the individual cross sections, the overall cross section for the O+2+CH4 reaction increases monotonically with increasing v throughout the range studied (v=0–3). The results are compared with that of the collision energy dependence as obtained in drift and flow-drift experiments and the implications are discussed in conjunction with the structure of the CH3O+2 ion and the relevant potential energy surfaces.