bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoelectron spectroscopy of the nitrogen dimer (N2)2 and clusters (N2)n: N2 dimer revealed as the chromophore in photoionization of condensed nitrogen
Authors: Carnovale Frank , Peel J. Barrie , Rothwell Richard G.
Published: July 2002

The He i photoelectron spectra of gas-phase nitrogen dimer and nitrogen clusters have been measured in a pulsed cluster beam. The dimer (N2)2 is characterized by broad bands with vertical ionization energies which are 0.3±0.1 eV lower than for N2 monomer. The bands observed for a mixture of small clusters, estimated to be of average size N̄=10, are identical to the dimer bands except for further shifts of 0.3 eV to lower ionization energies. The clusters bandwidths and band shapes are virtually the same as measured for thin films of condensed N2, indicating that the nitrogen dimer (N2)2 is the ionization chromophore in each case. This offers support for Haberland’s hypothesis that ionization of any Mn cluster produces the ion M+2Mn−2 provided M is a closed-shell atom or molecule. The theory of electronic relaxation polarization of the dielectric medium, which explains the gas-to-solid ionization energy shifts, is modified for the case of finite clusters and to account for dimer ion formation.
High-frequency structural relaxation in supercooled liquids
Authors: Sridhar S. , Taborek P.
Published: July 2002

High-frequency structural relaxation in glass forming solutions of LiCl in water was studied using complex conductivity measurements in the frequency range 0.5 MHz to 32 GHz for temperatures between 300 and 160 K. The conductivity data show a low-frequency plateau, and a strong frequency dependence above a characteristic frequency. Both the low-frequency conductivity and the characteristic frequency decrease strongly with temperature, scaling approximately as the inverse of the viscosity, suggesting that hydrodynamic processes govern structural relaxation. The ionic conductivity can be related to the mechanical properties using the Stokes–Einstein relation. The frequency dependence cannot be understood in terms of a single viscoelastic relaxation time. A semiphenomenological version of the mode coupling theory of supercooled liquids, using the experimentally determined temperature dependence of the static viscosity as a parameter describes the frequency dependence of the data reasonably well.
Molecular solvent model for an electrical double layer: Reference hypernetted-chain (RHNC) results for solvent structure at a charged surface
Authors: Torrie G. M. , Kusalik P. G. , Patey G. N.
Published: July 2002

We report results of solving the full reference hypernetted-chain (RHNC) theory for a large, multiply charged macroion at infinite dilution in a solvent of hard spheres with point dipole and quadrupole moments chosen to represent liquid water. We obtain results for the restructuring of this model solvent next to the macroion surface for a range of surface charges and macroion sizes up to 30 solvent diameters. Although we are unable to solve the theory for larger particles, when this largest macroion is neutral we find a solvent orientational structure in the surface layer that is in good qualitative agreement with computer simulation results for water-like models at a planar surface. Our RHNC calculations show that this surface structure proves surprisingly resistant to the effect of surface charges as high as 17.5 μC/cm2, apparently because even such strong fields cannot compete with the still stronger intermolecular forces of water-like models. There is, nevertheless, strong oscillatory behavior in both the polarization density and the mean electrostatic potential and we discuss the implications of this for theories and models of the electrical double layer.
Inelastic helium scattering studies of the vibrational spectroscopy and dynamics of ordered Ar, Kr, and Xe multilayers physisorbed on Ag(111)
Authors: Gibson K. D. , Sibener S. J.
Published: July 2002

This is the second of three papers discussing our studies of overlayers of Ar, Kr, and Xe physisorbed on Ag(111). All of these rare gases form ordered structures, which are azimuthally aligned but translationally incommensurate with the Ag substrate. In this paper, we discuss experiments in which we utilized the angle resolved time of flight of inelastically scattered 18 MeV He atoms to examine the surface dynamics of multilayer rare gas films along the Γ̄–M̄ direction. This was done on a layer-by-layer basis for 2, 3, and ≥20 layers for each of the rare gases. Unlike the monolayers, the vibrational modes observed for the multilayers show dispersion across the surface Brillouin zone, the amount of dispersion increasing with the number of adsorbed layers. These results reveal in detail how the surface dynamical properties of a thin film evolve towards those of a thick crystal as a function of increasing dimension. Lattice dynamics calculations, which utilize realistic gas phase pair potentials, reproduce the experimentally observed phonon dispersion relations quite well. We also examine the inelastic scattering probabilities and linewidths of the transitions. One of the more notable results is that the inelastic scattering probabilities vary by at most a factor of 2–3 across the entire surface Brillouin zone. Isothermal desorption measurements for the Xe overlayers are also discussed. Like the monolayer, the bilayer and trilayer exhibit nearly zeroth order desorption until ∼90% of the top layer has desorbed, where the desorption kinetics become first order.
Surface diffusion of hydrogen and CO on Rh(111): Laser-induced thermal desorption studies
Authors: Seebauer E. G. , Kong A. C. F. , Schmidt L. D.
Published: July 2002

Surface diffusion of hydrogen, deuterium, and CO on Rh(111) has been investigated by laser-induced thermal desorption (LITD) and compared with previous results for these species on Pt(111) and on other metals. As the coverage θ of deuterium increases from 0.02 to 0.33, the preexponential factor D0 remains constant at 8×10−2 cm2/s, but the diffusion activation energy Ediff rises from 3.7 to 4.3 kcal/mol. Ediff for hydrogen is 0.6 kcal/mol lower than for deuterium, consistent with the difference in zero-point energy. For CO, Ediff =7 kcal/mol at all coverages, but D0 rises from 10−3 to 10−2 cm2/s between θ=0.01 and 0.40. Values of Ediff for these adsorbates vary by several orders of magnitude for surfaces on which heats of adsorption are essentially identical. These differences appear to correlate with differences in heats of adsorption in different binding states which form saddle point configurations in surface diffusion. Ediff is found to be nearly identical to the reaction activation energies for the CO and hydrogen oxidation reactions on Rh and on several other transition metal surfaces. This suggests that surface diffusion of the reducing agent may be the rate-limiting step in their bimolecular surface reactions.
Spectroscopy of tryptophan derivatives in supersonic expansions: Addition of solvent molecules
Authors: Sipior Jeffrey , Sulkes Mark
Published: July 2002

The addition of solvent molecules, primarily water and some alcohols, to isolated tryptophan derivative molecules has been carried out using supersonic free jet techniques. The derivatives studied include 3-indole acetic acid, 3-indole propionic acid, N-acetyltryptophan ethyl ester, tryptamine, and tryptophol. The primary spectroscopic method employed was laser induced fluorescence, with some individual bands also characterized by fluorescence lifetime measurements or dispersed emission spectra. Unlike solvent addition to indoles already studied, these tryptophan derivatives also offer polar addition sites on the 3-indole chain. Addition to these sites, further removed from the electronic transition, produces solvent shifts of the complex origins that are small compared to the red shifts observed in indoles; small blueshifts occur in some instances. Competition between binding at the 3-indole polar group and the indole moiety nitrogen sites is strongly unequal, with the polar 3-indole chain sites favored, especially for larger solvent molecules. In tryptamine, which was studied most extensively, a variety of –OH-bearing solvents were able to collapse the multiple origin bands, due to different conformers, to only one prominent solvent conformer feature. Similar though less pronounced effects were seen in trytophol. Growth of solvent bands was more indiscriminate for the other derivatives studied and was consistent with formation of complexes separately with each bare molecule conformer. The observation of a solvent induced conformation brings up the question of whether tryptophan itself may be ‘‘steered’’ predominantly to one conformation by solution interactions and, if so, whether this plays a role in the molecule’s fluorescence probe properties.
Some properties of the Husimi function
Authors: Harriman John E.
Published: July 2002

The Husimi function provides a phase-space view of quantum systems. This paper considers a number of its properties, including ways in which it can be expanded in terms of basis functions. A spectral or ‘‘natural’’ expansion and an expansion analogous to the Carlson–Keller expansion in terms of coordinate-density momentum-density products are considered, as is a method for separating the angular dependence of the momentum. There is a set of functions in phase space having the same overlap properties as the initial orbital basis in terms of which the charge density matrix is expressed. A Husimi matrix is defined and a scalar product in the space containing such matrices as elements is introduced. The connection with the vector space of density matrices is examined. The Husimi function is related to the Husimi matrix in a way analogous to the relationship between a density matrix and a density, but there is a major difference in that this map can always be inverted. For a harmonic oscillator basis the phase space basis functions, in terms of which the Husimi function is expressed, span a linear space but do not provide a complete set; their products provide a linearly independent set that is complete. It is suggested that similar behavior can be expected for other basis sets.
Intramolecular vibrational relaxation in the S state of s-tetrazine–X (X=Ar, Kr, Xe)
Authors: Weber Peter M. , Rice Stuart A.
Published: July 2002

A triple resonance experiment with fluorescence detection has been carried out to investigate the spectroscopy and intramolecular dynamics of the van der Waals molecules s-tetrazine–X (X=Ar, Kr, Xe) with vibrational energies from 1250 to 2210 cm−1 in the ground electronic state (S0). Vibrational band shifts in S0 van der Waals molecules are usually on the order of 1 cm−1, and most relaxation lifetimes are longer than 15 ns. Comparison with published data for intramolecular vibrational redistribution in the S1 electronic state indicates a strong influence of the electronic structure of the aromatic ring on the dissociation dynamics, in clear contradiction to statistical models which have been advanced previously. A perturbation theory treatment supports the existence of a correlation between vibrational band shifts and dissociation dynamics, and rationalizes qualitatively all the peculiar observations for this class of van der Waals molecules.
Interactions of low energy reactive ions with surfaces. II. Reactions of C+, O+, and CO+ ions with nickel oxide, carbide, and carbonyl
Authors: Kang Heon , Kasi Srinandan R. , Grizzi Oscar , Rabalais J. Wayne
Published: July 2002

Reactions of 5–200 eV C+, O+, and CO+ ions with nickel oxide (NiO), nickel carbide (NiC), and chemisorbed CO on nickel (CO/Ni) have been studied in an ultrahigh vacuum environment using the surface spectroscopic techniques of XPS, UPS, and AES. These low kinetic energy (Ek ) ions react with both the substrate Ni atoms as well as with the O, C, and CO adspecies, the latter reactions resulting in adsorbate chemical sputtering or desorption. Reaction probabilities PR and adsorbate desorption yields Y are determined for several different combinations of reactants and products. The reactions C+ + NiO and O+ + NiC result in O and C desorption, respectively, along with concurrent carbide and oxide formation. The O and C desorption yields are near unity for Ek <20 eV. The oxide desorption yield decreases with increasing Ek. This Ek dependence is contrasted with physical sputtering of NiO by Ne+ in the same Ek region. Recombination of C and O, inducing CO desorption, is asserted as the mechanism for these reactions. The reaction O+ + NiCO results in efficient depletion of surface CO, the results being consistent with recombination of O and CO followed by CO2 desorption. A Monte Carlo simulation is performed to model the C+ + NiO reaction. The results indicate that depletion of surface oxide is dominated by a chemical desorption mechanism for Ek ≲20 eV and that the physical sputtering mechanism becomes increasingly more important as Ek increases until it dominates for Ek ≳200 eV. The reactivity and mechanisms for reactive ion induced desorption are discussed and compared to thermal O2 and CO reactions with surfaces.
Simple models for the electronic structure of a molecule dissolved in a hard-sphere liquid
Authors: Dobrosavljević Vladimir , Henebry Charles W. , Stratt Richard M.
Published: July 2002

The electronic structure of a molecule in a liquid can be affected not only by the dielectric properties of the medium, but also by the volume that the solvent molecules exclude from the solute electrons. In order to examine the effects of such purely repulsive forces, we have chosen to study the behavior of a hydrogenic molecule in a liquid of hard spheres. Simple models are proposed for the two extremes of tightly bound and Rydberg-like electronic states, and the nature of the level shifts and line broadenings are calculated for each. In both cases, the behavior is controlled by the distribution of open spaces (cavities) in the liquid—something which is amenable to microscopic calculation with liquid theory. We note that the deviations from purely dielectric theories displayed by recent experiments on benzene in rare-gas liquids are consistent with the kinds of repulsive force effects we discuss.
Non-Arrhenius rate constants for nonadiabatic electron transfers: The role of quantum and solvent dynamics
Authors: Cukier R. I.
Published: July 2002

Nonadiabatic electron transfer rates are given at high temperature by an Arrhenius expression with an activation energy related to the free energy at the crossing point of the two potential surfaces. At lower temperatures the transition is no longer localized to the crossing point, and the dynamics around the crossing point become important. To investigate this non-Arrhenius behavior we use a linear crossing model to describe the potential surfaces near their crossing point, and a Fokker–Planck equation to describe the dynamics along the reaction coordinate. The linear crossing model permits the use of a semiclassical trajectory approach even when the energy is low compared with the energy of the crossing point. The Fokker–Planck model allows us to go continuously from ballistic to diffusive trajectories. When the forces arising from the potential surfaces are included in the dynamical equation, we find that the rate of transition between the surfaces is no longer obtained from an expression localized just to the crossing point; rather, a region of length μ along the reaction coordinate is involved. This region increases in width as the temperature decreases. As friction increases μ decreases, indicating that solvent effects suppress the non-Arrhenius nature of the rate expression. Eventually a minimum temperature Tmin is reached below which the linear crossing model fails to represent the correct surfaces over the range μ. We show that the linear model can represent the displaced oscillator surface model, commonly used in electron transfer theory, over a range l for the inverted (small origin shift) regime. Comparing l with μ then permits identification of a Tmin.
Interatomic potentials of A 3+ and B 31 states of HgHe, HgNe, and HgAr van der Waals complexes
Authors: Yamanouchi Kaoru , Isogai Shinji , Okunishi Misaki , Tsuchiya Soji
Published: July 2002

Rotational structures of A–X and B–X vibronic transitions of HgHe, HgNe, and HgAr van der Waals (vdW) complexes formed in supersonic free jets have been investigated. An analysis of the rotational contours shows that rotational structures for the six isotopic species, mHgHe, mHgNe, or mHgAr (m=204,202,201,200,199, and 198), are overlapped, and the observed isotopic splittings are utilized for the definite assignment of the vibrational quantum numbers in the A and B states. Based on the vibrational level spacings and the rotational constants, interatomic potentials for the A and B states of HgNe and HgAr are determined with good accuracy. In the case of the B state of the 199HgRg and 201HgRg (Rg=Ne or Ar), magnetic dipole hyperfine splittings are observed and analyzed.
A new potential energy surface for vibration–vibration coupling in HF–HF collisions. Formulation and quantal scattering calculations
Authors: Schwenke David W. , Truhlar Donald G.
Published: July 2002

We present new ab initio calculations of the HF–HF interaction potential for the case where both molecules are simultaneously displaced from their equilibrium internuclear distance. These and previous ab initio calculations are then fit to a new analytic representation which is designed to be efficient to evaluate and to provide an especially faithful account of the forces along the vibrational coordinates. We use the new potential for two sets of quantal scattering calculations for collisions in three dimensions with total angular momentum zero. First we test that the angular harmonic representation of the anisotropy is adequate by comparing quantal rigid rotator calculations to those carried out for potentials involving higher angular harmonics and for which the expansion in angular harmonics is systematically increased to convergence. Then we carry out large-scale quantal calculations of vibration–vibration energy transfer including the coupling of both sets of vibrational and rotational coordinates. These calculations indicate that significant rotational energy transfer accompanies the vibration-to-vibration energy transfer process.
A theoretical study of hydridocobalt carbonyls. II. Interdependence of geometry and electronic structure
Authors: Antolovic Danko , Davidson Ernest R.
Published: July 2002

The electronic structure of hydridocolbalt tri- and tetra-carbonyls was investigated by means of ab initio methods in two different Gaussian basis sets. Hartree–Fock, configuration-interaction, and MCSCF calculations were performed on a number of conformations and electronic states of both compounds. Pyramidal distortions of the symmetric C3v forms of HCo(CO)3 were investigated, and Jahn–Teller distortions of the triplet states were described at the MCSCF level of theory. The interdependence of correlation effects and molecular geometry was examined in both basis sets. It is concluded that dispersion forces play a large role in metal–ligand bonding and need to be included in the qualitative model.
The intermolecular potential of Ar–HCl: Determination from high-resolution spectroscopy
Authors: Hutson Jeremy M.
Published: July 2002

Two new intermolecular potentials for Ar–HCl are obtained by least-squares fitting to molecular beam microwave and far-infrared laser spectra of the Ar–HCl van der Waals complex. In agreement with previous potentials, the equilibrium geometry is found to be linear Ar–H–Cl, with a well depth around 175 cm−1. However, the far-infrared spectra allow the potential in the region of the linear Ar–Cl–H geometry to be determined as well, and a secondary minimum is found at this geometry, with a depth around 140 cm−1. The secondary minimum arises because the Ar atom can approach closer to the Cl atom at the linear geometry than at a T-shaped geometry. The fitted potential is used to calculate additional bound states of the Ar–HCl van der Waals complex, which have not yet been observed spectroscopically.
Dissociative scattering of 1.5–4.5 keV N+2 and N+ on gold and graphite surfaces
Authors: Sass C. S. , Rabalais J. W.
Published: July 2002

Scattering of molecular nitrogen ions in the 1.5–4.5 keV range from gold and graphite surfaces results in a small fraction of surviving molecules and molecular ions in addition to atoms and atomic ions resulting from dissociation. The kinetic energy (Ek ) distributions of scattered N+2 and N+ ions have been measured directly by means of an electrostatic sector analyzer (ESA) and the velocity distributions of the scattered N2 and N neutrals plus ions have been measured by time-of-flight (TOF) techniques. Scattered ion fractions were determined from the TOF measurements. The relative Ek distributions of the scattered atomic ions indicate that dissociation from excited repulsive electronic states which are populated during the collision dominate the mechanism, rather than purely vibrational or rotational excitation from the X 2Σ+g ground state of N+2 . The excited dissociative C 2Σ+u and D 2Πu states of N+2 are accessible by Franck–Condon transitions from the X2Σ+g state. The data are consistent with a mechanism in which these two dissociative states contribute their repulsive energy to the large relative Ek distributions of the scattered N+ ions. The electronic excitation occurs via electron promotion during the scattering collision through the Fano–Lichten mechanism.
Polar solvent relaxation: The mean spherical approximation approach
Authors: Nichols Albert L. , Calef Daniel F.
Published: July 2002

The use of the mean spherical approximation (MSA) in the study of dynamics of polar fluids is further explored in two ways. First, the recent result of Wolynes [J. Chem. Phys. 86, 5133 (1987)] showing that solvation dynamics can be extracted from the static solution of the MSA is further investigated. The solvation of a dipole in a dipolar fluid is calculated, and compared with an ion in a dipolar fluid. Both cases reduce to simple numerical quadrature. Second, the Smoluchowski–Vlasov equation (SVE) of Calef and Wolynes [J. Chem. Phys. 78, 4145 (1983)] is also reexamined. Using the analytic MSA results, a new set of relaxation times can be defined. In both sections, structural relaxation occurs with multiple relaxation times.
Quantum interference among competing unimolecular decay channels: Asymmetric S D2CO decay profiles
Authors: Polik William F. , Moore C. Bradley , Miller William H.
Published: July 2002

The dynamics of a state undergoing decay to a manifold of states coupled to a dissociative continuum is investigated in the weak coupling limit. The decay rate is found to be composed of terms symmetric and asymmetric in the relative energy difference between the initial state and the states in the manifold. The well-known symmetric terms arise from resonantly enhanced decay of the initial state through each state in the manifold to the continuum. The newly identified asymmetric terms arise from interfering couplings of the initial state to the continuum through different states in the manifold, i.e., from off-diagonal elements of the width matrix Γkk′ of the effective Hamiltonian describing dissociation of the states in the manifold. The general line shape derived here is used to fit asymmetric features in Stark level-crossing spectra of D2CO. Statistical properties of the width matrix are summarized, and the relation between diagonal and off-diagonal matrix element magnitudes is derived.
Symmetric stretch excitation of CH3 in the 193.3 nm photolysis of CH3I
Authors: Continetti R. E. , Balko B. A. , Lee Y. T.
Published: July 2002

New high resolution photofragment translational spectroscopy measurements on the 193.3 nm photolysis of CH3I reveal up to four quanta of ν1 C–H symmetric stretch excitation in the C–I bond fission channel. In addition these experiments show for the first time that C–H bond fission occurs at wavelengths longer than 185 nm with a quantum yield of ∼3%. The data yields upper bounds to the C–H bond dissociation energy in CH3I of 101±1 kcal/mol and for the C–I bond energy, 55.0±0.3 kcal/mol.
Q-branch line mixing in N2O: Effects of l-type doubling
Authors: Larrabee Strow L. , Pine Alan S.
Published: July 2002

Rotational collisional narrowing, or line mixing, has been observed in the Q branch of the ν2+ν3Π–Σ band of N2O near 2798 cm−1 using a difference-frequency spectrometer. Self-broadened spectra were recorded at pressures ranging from 20 to 747 Torr. The broadening coefficients, derived from the lower pressures before the lines significantly overlap, are in close agreement with prior measurements of P- and R-branch widths in Σ–Σ bands. At higher pressures where the Q-branch lines are blended, the band contours deviate from purely additive component line shapes, exhibiting stronger peak absorptions and weaker wings characteristic of line mixing. A simple rotational energy gap scaling law is used to model the off-diagonal relaxation matrix elements needed to calculate the observed collisional narrowing. Spectra calculated using several trial sets of collisional selection rules are presented. We find evidence for a parity conserving collisional selection rule and/or elastic-reorientation collisions.
Electromagnetic nuclear shielding tensors and their relation to other second-order properties: A study of the ammonia molecule
Authors: Lazzeretti P. , Zanasi R. , Bursi R.
Published: July 2002

The results of an accurate calculation of second-order properties of the ammonia molecule are reported, with particular attention to nuclear electromagnetic shielding tensors. These quantities enable one to evaluate the actual fields at the nuclei of a molecule perturbed by external radiation. The present theoretical study provides an extended numerical test on the mutual relationships among different properties. A theoretical scheme, based on force and torque gauges for the transition moments, has been applied to partition the molecular polarizabilities, the paramagnetic susceptibilities, and other properties into atomic terms transferable from molecule to molecule.
Further investigation of the dielectric normal mode process in undiluted c
i
s-polyisoprene with narrow distribution of molecular weight
Authors: Imanishi Yasuo , Adachi Keiichiro , Kotaka Tadao
Published: July 2002

Dielectric relaxations in undiluted cis-polyisoprene (cis-PI) with narrow molecular-weight distribution were investigated. The normal mode process due to fluctuation of the end-to-end distance and the segmental mode process due to the local segmental motions were observed. The average relaxation time τn for the normal mode process was insensitive to the polydispersity Mw/Mn, but the width of the loss curve reflecting the distribution of the relaxation times increased with Mw/Mn. The slope of the double logarithmic plot of τn against Mw changed at the characteristic molecular weight Mc from 2.0 in the range MwMc. It was found that although the half-width is nearly independent of Mw, the tail of the loss curve in the high frequency side broadens with increasing Mw. This indicates that by entanglement effects the distribution of the relaxation time for the normal mode process changes slightly. The segmental mode is found to be almost independent of the molecular weight and the polydispersity factor.
Kratzer oscillator functions as a diatomic molecule basis set
Authors: Secrest Don
Published: July 2002

The use of Kratzer oscillator functions as a basis set for calculations of diatomic molecule eigenfunctions is discussed. Exact expressions are given for integrals of these functions over general potential types.
Transient, collision-induced changes in polarizability for atoms interacting with linear, centrosymmetric molecules at long range
Authors: Hunt K. L. C. , Liang Y. Q. , Sethuraman S.
Published: July 2002

Transient changes in polarizability during collisions between atoms and molecules give rise to interaction-induced rototranslational Raman scattering: the scalar component of the collision-induced polarizability Δα00 accounts for isotropic scattering, while the second-rank component ΔαM2 accounts for collision-induced depolarized scattering. We have evaluated the changes in electronic polarizability due to interactions between an atom and a molecule of D∞h symmetry in fixed configurations, with nonoverlapping charge distributions. We have cast the resulting expressions into the symmetry-adapted form used in spectroscopic line shape analyses. Our results are complete to order R−6 in the atom–molecule separation R. To this order, the collision-induced change in polarizability of an atom and a D∞h molecule reflects not only dipole-induced–dipole (DID) interactions, but also molecular polarization due to the nonuniformity of the local field, polarization of the atom in the field due to higher multipoles induced in the molecule, hyperpolarization of the atom by the applied field and the quadrupolar field of the molecule, and dispersion. We have analyzed the dispersion contributions to the atom–molecule polarizability within our reaction-field model, which yields accurate integral expressions for the polarizability coefficients. For numerical work, we have also developed approximations in terms of static polarizabilities, γ hyperpolarizabilities, and dispersion energy coefficients. Estimated polarizability coefficients are tabulated for H, He, Ne, and Ar atoms interacting with H2 or N2 molecules. The mean change in polarizability Δᾱ, averaged over the orientations of the molecular axis and the vector between atomic and molecular centers, is determined by second-order DID interactions and dispersion. For the lighter pairs, dispersion terms are larger than second-order DID terms in Δᾱ. In both Δα00 and ΔαM2, first-order DID interactions dominate at long range; other interaction effects are smaller, but detectable. At long range, the largest deviations from the first-order DID results for Δα00 are

produced by dispersion terms for lighter species considered here and by second-order DID terms for the heavier species; in ΔαM2, the largest deviations from first-order DID results stem from the effects of field nonuniformity and higher multipole induction, for atoms interacting with N2.
Photoabsorption and photoemission of ozone in the Hartley band
Authors: Chasman David , Tannor David J. , Imre Dan G.
Published: July 2002

Theoretical calculations of ozone photoabsorption and photoemission in the Hartley band are presented. The potential energy surfaces of Sheppard and Walker [J. Chem. Phys. 78, 7191 (1983)] and of Barbe et al. [J. Mol. Spectrosc. 49, 171 (1974)] are used for the excited (1B2) and ground (1A1) states, respectively. In contrast with several recent studies, large amplitude motion in the symmetric and asymmetric stretch coordinates is explicitly included. Qualitative agreement is obtained with the experimental emission spectrum at 266 nm, although some discrepancies persists, using either the original Sheppard–Walker surface or various modifications thereof. Moreover, the calculations do not reproduce the experimentally observed structure atop the Hartley absorption band, eliminating some possibilities for the origin of this structure. The photofragmentation dynamics was computed by numerical integration of the time-dependent Schrödinger equation on a two-dimensional grid, and spectral observables were recovered via Fourier transform.
A stationary phase study of m
j rainbows in molecule-corrugated surface scattering
Authors: Mayne Howard R.
Published: July 2002

Using the stationary phase limit of the quantum mechanical full sudden S matrix for diatom-corrugated rigid surface scattering of Proctor, Kouri, and Gerber [J. Chem. Phys. 80, 3845 (1984)] we obtain expressions for the rotational actions j and mj of an inelastically scattered diatom. By integrating over all points on the lattice, we reduce these to functions of the polar angles θ and φ only. It is found that j is a strong function of θ, but almost independent of φ, whereas the reverse is true for mj. Both j(θ) and mj(φ) are continuous plots which exhibit extrema known to produce rainbow behavior in inelastic gas-phase scattering theory. We propose that this implies the existence of rainbows in the mj distribution, and show the dependence of these rainbows on various potential parameters, including corrugation, potential repulsion parameter, and lattice constant. The results explain earlier trajectory studies.
Resonance ionization spectroscopy of a new 1 1Δu←A 1Πu band system of C2
Authors: Goodwin Peter M. , Cool Terrill A.
Published: July 2002

Thirteen vibronic bands assigned to the two-photon 1 1Δu←A 1Πu transition, ν00=49 097±1 cm−1, have been observed by (2+2) resonance-enhanced multiphoton (REMPI) spectroscopy for laser wavelengths ranging from 370–480 nm. The measured term value Te=57 720±2 cm−1 of the previously unobserved 1 1Δu state is in good agreement with upper limits given by ab initio calculations. Additional spectroscopic constants measured for the 1 1Δu state are: D0=12 990 cm−1, ωe=1150±1 cm−1, ωexe=21.3±0.5 cm−1, Be=1.361±0.002 cm−1, αe=0.026±0.002 cm−1, and re=1.437±0.002 Å.
Percolation and connectivity of the attractive square-well fluid: Monte Carlo simulation study
Authors: Chiew Yee C. , Wang Y. H.
Published: July 2002

The percolation and clustering behaviors of a system of one-component attractive square-well hard-core fluid are studied through Monte Carlo simulation. The percolation densities of the square-well particles at different temperatures are determined for particles of different well widths. Comparison of the Monte Carlo data with the Percus–Yevick solution is made. The Percus–Yevick approximation is found to yield fairly good estimates of the percolation threshold except at low temperatures and high densities. The pair-connectedness functions at different temperatures and particle densities are also obtained. A new conditional probability of particle connectedness is defined and determined from this Monte Carlo study.
CH2I2 photodissociation: Emission spectrum at 355 nm
Authors: Zhang Jinzhong , Imre Dan G.
Published: July 2002

The emission spectrum from photodissociating CH2I2 excited at 355 nm is presented. Interpretation of the data is given in a time dependent picture. The progression on the CI2 symmetric stretch and even quanta in the antisymmetric stretch indicate initial motion during dissociation along the symmetric stretch coordinate and subsequent spreading in the antisymmetric stretch coordinate. The moderately strong bending fundamental suggests that the bond angle changes when the molecule is promoted from the ground to the excited state. Both dynamics and the geometry near the Franck–Condon region on the excited surface are discussed.
Rotational spectrum and structure of the linear HCN trimer
Authors: Ruoff R. S. , Emilsson T. , Klots T. D. , Chuang C. , Gutowsky H. S.
Published: July 2002

Microwave rotational spectra have been observed for 22 isotopic species of an HCN, hydrogen-bonded trimer with the pulsed nozzle, Fourier transform method using the Flygare/Balle Mark II spectrometer. The 14N nuclear quadrupole hyperfine structure was analyzed and the interaction constants and line centers determined. The line centers were fitted to obtain ground vibronic state rotational constants. For the normal isotopic species of (HCN)3, B0 was found to be 469.3073(1) MHz and DJ, 82.6(1) Hz. The quadrupole coupling constants χ(n) are −4.049(2), −4.251(2), and −4.375(1)MHz for n=1, 2, and 3, respectively, in HCN(1)HCN(2)HCN(3). The trimer has a linear or very near linear equilibrium structure. The B0’s are insensitive to the position and torsional oscillations of the central HCN but they determine the outer HCNs quite accurately. An isotopic substitution method gives R, the c.m. distance between the outer HCN’s, to be 8.790 Å in the 14–14–14 species. A slightly smaller value 8.788 Å is obtained from a fit of the B0’s which includes the effects of isotopic substitution on the H/D–C and C–N bond lengths in the monomer. The distance between c.m.(1) and c.m.(2) may be somewhat shorter (∼0.01 Å) than that between c.m.(2) and c.m.(3). The average c.m. separation in the trimer (4.395 Å) is halfway between that of the dimer (4.447 Å) which is known to be linear and the infinite linear chains in the solid (4.34 Å). It is shown that the smaller quadrupole coupling constants in the trimer compared to the monomer are caused by a combination of torsional and charge redistribution effects. The torsional vibrations have average angular displacements of 12.60° and 8.55° for HCN(1) and HCN(3). The charge redistribution effect upon χ in the trimer (6.5%) is about 1.8 times that in the HCN dimer. The dipole moment of the trimer was found to be 10.6 D, a value enhanced by 1.8 D over the vector sum of the three vibrating monomers (8.83 D), an enhancement about 1.7 times that of the dimer.
A local density-functional study of the electron density distribution in the H2O dimer
Authors: Krijn M. P. C. M. , Feil D.
Published: July 2002

Accurate local density-functional calculations of the electron density distribution in the H2O dimer are performed and, in order to distinguish intramolecular charge shifts from intermolecular charge transfer, analyzed in terms of an expansion in atom-centered multipole moments. The dependence on basis set and basis set superposition error of the electron density redistribution upon forming the hydrogen bonded complex has been examined. A model study reveals that only strong hydrogen bonds induce electron density redistributions large enough to be observable by means of x-ray diffraction.
The first absorption band for H2O: Interpretation of the absorption spectrum using time dependent pictures
Authors: Henriksen Niels E. , Zhang Jinzhong , Imre Dan G.
Published: July 2002

We examine the relation between photodissociation dynamics and the form of the total absorption spectrum for H2O in the first absorption band. Application of an exact time dependent formalism gives a direct and intuitive relation between molecular motion and spectral features. We show that the series of weak structures on top of the broad continuum is due to symmetric stretch motion in the excited state. The spacing between the structures is, essentially, given by the frequency associated with this motion. In addition, we present some excited state eigenfunctions, which provide a direct connection between the structured spectrum, the final product distributions, and the dynamics.
Rovibrational state mixing in the aldehyde C–H stretch fundamental region of acetaldehyde
Authors: Kim H. L. , Minton T. K. , Ruoff R. S. , Kulp T. J. , McDonald J. D.
Published: July 2002

We have studied rovibrational state mixing in acetaldehyde using infrared laser induced fluorescence. Molecules are isolated and cooled in supersonic molecular beams, and irradiated in the C–H stretch fundamental region with an infrared optical parametric oscillator. Spectral resolution is provided with either a circular variable filter machine or a cryogenic Michelson interferometer. We have found evidence of several strong Fermi resonances between the aldehyde C–H stretch and a few overtones and combinations of lower frequency modes. In addition, there is substantial random state mixing in this region as evidenced by the average experimental dilution factor of 0.2. The dependence of the dilution factor on the average J excited by the laser shows that the extent of state mixing scales linearly with J. We have observed from dispersed fluorescence spectra that random rotational coupling occurs between different Kp states. Our previous statistical coupling model has been applied to the interpretation of the data, and its applicability is discussed. For the model calculation, the methyl torsion is specially treated as a very anharmonic mode in the eumeration of the zeroth order bath states. The average coupling width derived from the model calculation is 0.35 cm−1. The relative energy content apportioned among vibrational modes in the molecule following excitation is measured and is successfully explained with the model.
Transport coefficients of dense fluids composed of globular molecules. Equilibrium molecular dynamics investigations using more-center Lennard-Jones potentials
Authors: Hoheisel C.
Published: July 2002

Equilibrium molecular dynamics calculations with constraints have been performed for model liquids SF6 and CF4. The computations were carried out with four- and six-center Lennard-Jones potentials and up to 2×105 integration steps. Shear, bulk viscosity and the thermal conductivity have been calculated with use of Green–Kubo relations in the formulation of ‘‘molecule variables.’’ Various thermodynamic states were investigated. For SF6, a detailed comparison with experimental data was possible. For CF4, the MD results could only be compared with experiment for one liquid state. For the latter liquid, a complementary comparison was performed using MD results obtained with a one-center Lennard-Jones potential. A limited test of the particle number dependence of the results is presented. Partial and total correlations functions are shown and discussed with respect to findings obtained for the one-center Lennard-Jones liquid.
Theoretical spectroscopy of the NO radical. II. Λ doubling in the ground X 2Π state and spin–orbit effects in the excited Π states
Authors: de Vivie Regina , Peyerimhoff Sigrid D.
Published: July 2002

Spin–orbit splittings of the a 4 Π and the 2Π states X, C, B, and L of the NO radical were calculated as a function of internuclear separation R using multireference configuration interaction wave functions and the potential curves presented in part I of this work. The resulting values averaged over vibrational levels, agree within a few wave numbers with the experimental data whenever available. Subsequently the R-dependent Λ splitting of the X2Π ground state is determined in a perturbation matrix procedure which is independent of Hund’s coupling cases taking into account 2Σ+, 2Σ−, 4Σ−, 4Σ+, 4Π and 2Δ states as possible perturbers. The resulting splitting (0.011 81 cm−1) of the first vibrational level of the 2Π1/2 component compares well with the experimental value of 0.011 88 cm−1. The analysis of the contributions of the various perturbers to the Λ splitting shows that the 2Σ+ states and the G2 Σ− state are dominant and determine the magnitude of the splitting. A possible change of the parity with R is indicated which also affects the magnitude of the splitting.
Vibrational effects in elastic rainbow scattering: K+HF(v=0), HF(v=1)
Authors: Hoffmeister M. , Schleysing R. , Stienkemeier F. , Loesch H. J.
Published: July 2002

We report laser correlated angular distributions of K atoms scattered off an HF nozzle beam which has been partially vibrationally excited to the v=1 state by modulated infrared laser radiation. Measurements have been performed at mean relative translational energies ranging from 0.25 to 0.82 eV. As a consequence of the preparation technique the distributions directly reflect differences between the nonreactive scattering off HF in the excited state and in the ground state (v=0). The data exhibit well resolved uncommon features which are rationalized assuming spherically symmetric potentials with different well depths ε0 and ε1 for K+HF (v=0) and K+HF (v=1), respectively. Adopting the value ε0=117 meV we find ε1 =151 meV. Employing a vibrationally adiabatic model, this finding is traced back qualitatively to the difference between the vibrational energies of HF as a free molecule and in the proximity of a K atom (at well distance). Furthermore, we report angular distributions of K scattered off unprepared HF molecules (v=0) measured at mean translational energies ranging from 0.13 to 0.64 eV. In the range 0.17 to 0.38 eV the data show clearly resolved rainbow structures from which the well depth ε0 of a spherically symmetric potential is deduced. The obtained value (ε0=117 meV) is roughly a factor of 5 larger than expected from the well depths of homologous systems. However, at the lowest translational energy achievable (0.13 eV) we find another faint rainbow which we associate with a shallow well of 26 meV depth. To rationalize these results we propose a double minimum potential for K+HF and attribute the shallow and deep well to interactions of K with the H and F side of the molecule, respectively.
Sideband optical–optical double resonance Zeeman spectroscopy of NiH: A new diagnostic for electronic and rotational assignment
Authors: Li Mingguang , Field Robert W.
Published: July 2002

We describe a one-laser optical–optical double resonance (OODR) scheme whereby sub-Doppler Zeeman splittings of individual rovibronic transitions are presented in a uniquely simple and diagnostically powerful format. Each rovibronic transition yields at most two Zeeman resonance features, each associated with the approximately M-independent (J,M+1)–(J,M − 1) Zeeman interval in either the upper or the lower state. Two laser beams, ωl and an acousto-optically shifted sideband at ωl + ωA0, copropagate through the sample. A sideband-OODR-Zeeman (SOODRZ) resonance results when a (J,M+1)–(J,M − 1) interval is Zeeman tuned through resonance with ωA0 . The SOODRZ effect, detected against a dark background in a magnetic rotation spectroscopy configuration, is illustrated for several lines of the NiH B 2 Δ5/2–X 2 Δ5/2 (1,0) band.
Multiphoton ionization of vibrationally hot nitric oxide produced in a pulsed supersonic glow discharge
Authors: Feigerle Charles S. , Miller John C.
Published: July 2002

Mass-resolved, resonant multiphoton ionization (MPI) spectroscopy has been used to identify and characterize transient species produced in a pulsed, supersonic glow discharge source. Vibrationally hot (up to v″=9), but rotationally cold nitric oxide is characterized by (1+1) MPI via the A 2Σ+ state and (2+1) MPI through the C 2Πr state. Nine A←X and six C←X hot bands are observed; only four of these have been previously characterized. Accidentally overlapping C and A state hot bands can be separately studied by using different order MPI schemes. Implications for several previous studies are discussed. Additionally, the 3P0,2 metastable rare gas atoms are readily formed and detected by MPI as are metal atoms sputtered from the electrodes.
Rotational branching ratios at low photoelectron energies in resonant enhanced multiphoton ionization of NO
Authors: Rudolph H. , McKoy V. , Dixit S. N.
Published: July 2002

We report calculated rotational branching ratios for very low energy (50 meV) photoelectrons resulting from (1+1′) resonant enhanced multiphoton ionization (REMPI) via the Ji =1/2, 3/2, 5/2, and 7/2 levels of the P11 branch of the A 2Σ+ (3sσ) state of NO. Even angular momentum transfer (ΔN≡N+−Ni) peaks are dominant in these rotational distributions, in agreement with the selection rule ΔN+l=odd. Angular momentum coupling in the photoelectron wave function arising from the molecular ion potential leads to smaller but appreciable ΔN=odd peaks. The calculated ΔN=0 to ΔN=+2 peak ratios show the same strong decrease when Ji increases from 1/2 to 3/2 as seen in the experimental zero-kinetic-energy (ZEKE) photoelectron spectra [Sander et al., Phys. Rev. A 36, 4543 (1987)], but do not show the rapid die-off of the ΔN≠0 peaks for higher Ji observed experimentally. The calculated trend in the ΔN=+2 vs ΔN=0 peaks could be understood on the basis of simple angular momentum transfer arguments. These same arguments indicate that this trend in the ΔN=0 and +2 peaks with increasing angular momentum is not generally expected in other branches. Spectra via the R21 ( J) branch are presented to support this assertion. We also present photoelectron angular distributions which show a strong dependence on ΔN reflecting the changing composition of the photoelectron wave function.