bluuebunny/crossref_metadata_2025 huggingface dataset:
Model calculations of magnetic-field-induced perturbations and predissociations in 6Li7Li near dissociation
Authors: Uang Yea-Hwang , Ferrante Robert F. , Stwalley William C.
Published: February 2003

A model calculation of magnetic-field-induced perturbations and predissociations (scattering resonances) in 6Li7Li near dissociation is presented. The splitting of the 3Σ+u state by an external magnetic field yields field-dependent interactions (dominated by a curve crossing) between closely spaced, weakly bound high vibrational–rotational levels of the X 1Σ+g and 3Σ+u states near dissociation. Due to the symmetry of homonuclear molecules, there will be no such field-induced phenomena in the cases of 7Li2 and 6Li2. Since a bound–free–bound transition involving the 3Σ+u state of 7Li2 and high vibrational levels (v?36) in X 1Σ+g 6Li7Li and 7Li2 have recently been observed, experimental observation of these perturbations and predissociations should be feasible.
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o studies of structural features not easily amenable to experiment. 12. The molecular structure of bicyclo(2.1.0)pentane and the usefulness of a
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o geometries in interpreting microwave r
s-structure model uncertainties
Authors: Van Alsenoy C. , Scarsdale J. N. , Schäfer Lothar
Published: February 2003

The molecular structure of bicyclo(2.1.0)pentane was refined by standard single determinant ab initio procedures on the 4-21G level to interpret the relatively large model uncertainties of the microwave rs structure by S.N. Mathur, M.D. Harmony, and R.D. Suenram [J. Chem. Phys. 64, 4340 (1976)]. In order to provide estimates for rs−re (ab initio) corrections for C–C bonds, the structures of cyclopropane, n-propane, n-butane, and n-pentane were also refined in the same way. The calculated differences Δre between the C–C bond distances in the cyclopropane ring (0.026 Å) and in the cyclobutane ring (0.036 Å) of bicyclo(2.1.0)pentane were found in close agreement with the differences observed (Δrs; 0.029 and 0.037 Å, respectively). When estimates for the differences between rs and re (ab initio), derived from analogous sytems, were applied to the calculated C–C bond distances in the cyclopropane and in the cyclobutane ring of bicyclo(2.1.0)pentane, respectively, the calculated parameters were C1–C4 = 1.535 Å, C1–C5 = 1.509 Å, C1–C2 = 1.528 Å, and C2–C3 = 1.564 Å. The corresponding experimental values are 1.536(3), 1.507(4), 1.528(6), and 1.565(3) Å, respctively. Hence, the preferred conclusion of this study is that the trends in the experimental C–C bond distances of bicyclo(2.1.0)pentane very likely describe true structural features of this system, even though some of the individual parameters are unresolved due to experimental error limits. It is not unreasonable to assume that high qualtiy ab initio geometries may be generally of value in interpreting substitution structures with model dependent uncertainties which are not known exactly.
Magnetic circular dichroism spectra of alkaline earth metal atoms, dimers, and aggregates in noble gas matrices
Authors: Miller J. C. , Mowery R. L. , Krausz E. R. , Jacobs S. M. , Kim H. W. , Schatz P. N. , Andrews L.
Published: February 2003

The magnetic circular dichroism (MCD) of Mg, Ca, and Sr atoms, dimers, and higher aggregates have been studied after codeposition with noble gases at low temperatures. The1Σ+g→1Πu transition in each of the M2 species (M = Mg, Ca, Sr) occurring to the blue of the 1S→1P resonance transition, is unambiguously identified by measurement of the excited state magnetic moment. The distinct band at ∼30,000 cm−1 in magnesium samples is identified as Mg3, and the measured excited state magnetic moment favors the assignment, 1A1′→1E′, corresponding to an equilateral triangular (D3h) geometry. A broader band at ∼33 000 cm−1 in Ar is assigned to Mg4, and the very small excited state magnetic moment is consistent with the assignment, 1A1→1T2, of a tetrahedral species. In Ca/Ar, Ca/Kr, and Sr/Ar matrices, the 1S→1D atomic transition is seen with about 5% of the intensity of the corresponding 1S→1P transition. The accompanying MCD patterns unambiguously demonstrate the presence of two distinct sites for Ca atoms and three distinct states for Sr atoms. Furthermore, the fact that the 1S→1D ? terms are opposite in sign to those for 1S→1P together with a consideration of the probable structure of the noble gas lattices suggests that these sites have approximate D3h symmetry. It is clear that application of the MCD technique to systems trapped in matrices provides a rather unique means for characterizing the species present and can give considerable information about the matrix environment in which the species are located.
On the Chapman–Enskog solution method for mixtures
Authors: Eu Byung Chan
Published: February 2003

In the Chapman–Enskog solution method for the Boltzmann equations for mixtures the linear integral equations are separated into three independent components for diffusion, thermal conduction, and viscous (momentum) flow. It is shown that this procedure is not the most general one, but only an approximation, since the two vectorial components can be separated into two independent components only in an approximation that neglects the coupling between the two. An alternative procedure is described, which yields the independent separate equations in the Chapman–Enskog solution method as an approximation.
Theory of depolarized light scattering
Authors: Chappell Philip J. , Allen Michael P. , Hallem Robert I. , Kivelson Daniel
Published: February 2003

We have studied the VH depolarized light scattering spectrum of liquid triphenylphosphite over a wide range of temperature. At high temperature and low viscosity the Rytov doublet corresponding to shear-orientational modes is observed, while at low temperature and high viscosity weak side peaks corresponding to viscoelastic shear waves are seen. The fluctuations of the dielectric tensor ? which give rise to depolarized light scattering have been adequately described over the whole temperature range by a ’’three-variable’’ generalized hydrodynamic theory. In contrast with virtually all previous studies of VH spectra we use the independently measured shear viscosity as a known, rather than adjustable, parameter. As a result of our analysis we can express ?(t) as a linear combination of the molecular reorientation density ?(t) and the microscopic stress tensor ?(t), and we find that the intermolecular scattering represented by ?(t) is important at high as well as low temperature. We are also able to evaluate the autocorrelation function of ?(t) in the low-wave number, long-time limit as the sum of two exponential decays with comparable amplitudes. We include a comparative study of other theories.
Vibrational spectra and structure of fluorozirconate glasses
Authors: Almeida Rui M. , Mackenzie John D.
Published: February 2003

A series of binary fluorozirconate glasses have been prepared in the ZrF4–BaF2 system, containing between 52–74 mol % ZrF4. Their infrared and polarized Raman spectra are reported for the first time, down to 33 cm−1. The glass transition and crystallization temperatures were also measured. The vibrational modes have been assigned to different types of atomic motions in the glass network. The basic structure of the fluorozirconate glasses is proposed to consist of zigzag chains of ZrF6 octahedra, cross linked by Ba–F ionic bands. The interochtahedral Zr–F–Zr angle distribution was estimated to peak at ∼136°, based on the analysis of the two highest frequency Raman modes.
Proton relaxation and piezoelectricity in perchlorates
Authors: Svare I. , Fimland B. O.
Published: February 2003

Proton magnetic relaxation has been studied in powders of M(ClO4)2 ⋅ 6H2O, where M2+ = Mn2+, Fe2+, Co2+, Ni2+, Zn2+, and Cd2+ in order to gain information about crystal water motion. The pulse measurements also detect piezoelectricity which is discussed in relation to the numerous structural phase transitions that have been reported for this family of salts.
Collisional depolarization of state selected (J,MJ) BaOA 1Σ+ measured by optical–optical double resonance
Authors: Silvers Stuart J. , Gottscho Richard A. , Field Robert W.
Published: February 2003

The optical–optical double resonance (OODR) technique is used to investigate the change in magnetic quantum number (M) a state selected molecule undergoes on collision with other molecules. A first linearly polarized dye laser prepares A 1Σ+BaO(v = 1) in the J = 1, M = 0 sublevel. The extent of collisional transfer to other M sublevels of both J = 1 and J = 2 is then probed by a second polarized dye laser which induces fluorescence from the C 1Σ+ state. Elastic collisions (ΔJ = 0) between BaO (A 1Σ+) and CO2 are observed to change M from 0 to ±1 leaving J unchanged. The total elastic M-changing cross section is σΔMCO2 = 8.4±2.4 Å2. Inelastic collisions (ΔJ = +1’ which transfer molecules to j = 2 also cause M changes. with both Ar and CO2 as collision partners. M, the space-fixed projection of J, is found to be neither conserved nor randomized. Quantum atom–diatom collision models with quantization axis along the relative velocity vector are considered. Transition amplitudes in this system are evaluated using the l-dominant and CS approximations.
An EPR study of interlayer exchange coupling in the quasi-two-dimensional salts, (CnH2n+1NH3)2CuCl4, with n = 1, 2, and 3
Authors: Wong Raymond J. H. , Willett Roger D. , Drumheller John E.
Published: February 2003

The interlayer exchange coupling, J′, between magnetically inequivalent ions in adjacent layers has been studied by EPR in the quasi-two-dimensional salts of (CnH2n+1NH3)2CuCl4 where n = 1,2,3. The Cu2+ ions of the CuCl42− complexes in adjacent layers of these salts have slightly different g tensor orientations and, in the absence of J′, should give two separate EPR lines when the field does not lie in one of the crystallographic planes of symmetry. The interlayer coupling merges the lines so that a single line is observed whose linewidth becomes broadened at higher frequency. In (C3H2NH3)2CuCl4, J′ is small enough that the individual lines are resolved at 36 GHz. Assuming the g-tensor orientations are the same in each salt, this allows the ratio ‖J′/J‖ to be deduced from linewidth measurements at 9 and 36 GHz. The ratios are in good agreement with the results obtained from previous magnetic measurements [L. J. de Jongh and A. R. Miedema, Adv. Phys. 23, 1 (1979)].
Polarized Raman scattering of a binary liquid near the critical point
Authors: Wood Kurt A. , Strauss Herbert L.
Published: February 2003

Spontaneous Raman spectra have been obtained for three vibrational bands of the binary liquid mixture nitroethane, 3-methylpentane. Measurements for the one phase region at the critical concentration extend over a broad temperature range down to T−Tc = 0.008 °C. Over this range we have observed no critical anomaly in the vibrational bandwidth. The behavior, both near the critical point and far from it, is not consistent with the predictions of the fast modulation theories of pure dephasing which relate the bandwidth to the viscosity and other liquid properties. It is consistent with a variety of slow modulation limit predictions, but the measurements do not yet provide a definitive test of these theories.
A new, optically forbidden Rydberg series in O2 converging to the O+2 c 4Σ−u  limit
Authors: Dillon M. A. , Spence David
Published: February 2003

We have measured the angular dependence of inelastically scattered electrons in O2 in the energy-loss range 16 to 26 eV for incident electron energies between 75 and 400 eV, and for scattering angles between 2° and 12°. For high incident energy and low scattering angle our energy loss spectra correspond to the known optical absorption spectrum. At higher scattering angles, four new structures appear in our spectra at 21.85, 23.30, 23.80, and 24.06 eV. These four structures are the lowest members of the first optically forbidden Rydberg series observed to converge to the O+2 c 4Σ−u limit at 24.56 eV. The calculated quantum defects for these levels are about 0.75. This value, combined with angular scattering propensity rules, indicates that the new Rydberg states occur by promotion of an electron from the σu2s orbital to npσu orbitals, where n = 3,4,5,6. A consideration of the propensity rules for excitation of forbidden transitions by high energy electron impact suggest the term symbol of the new Rydberg states to be 3Σ−g.
Models of hydrocarbon product distributions in Fischer–Tropsch synthesis. I
Authors: Novak S. , Madon R. J. , Suhl H.
Published: February 2003

In Fischer–Tropsch synthesis the standard model for growth and termination of hydrocarbon chains on a catalytic surface is the Flory model, where growth proceeds by addition of a one-carbon intermediate and termination occurs by simple desorption. In this paper four different modifications of the Flory model are investigated. In addition to the Flory growth and termination mechanisms, these models include (a) growth via an independent two-carbon intermediate, (b) second order termination by combination of two chains on the surface with subsequent desorption, (c) same as (b) but with a fraction of the combined chains allowed to participate in growth on the surface, and (d) catalytic hydrocarbon cracking. Of the above mechanisms, the most interesting are (b) and (d), which result in an increase in the selectivity of the process over that predicted by the Flory model. For mechanism (d) this increase can be as great as a factor of 3. Mechanism (c) is of interest here because although (b) increases product selectivity, continued growth of product after combination tends to broaden the product weight distribution, thereby diminishing or even negating the effect of (b) alone. Thus, distributions that are broader than Flory distributions can result. Mechanism (a) produces oscillations in the product weight distribution, showing an increase in selectivity for ever other n, where n is the number of carbons in the hydrocarbon chain. With this paper we intend to develop a mathematical framework for expanding the Flory model to include additional reaction steps during CO hydrogenation. Although the qualitative results contained herein are to a large extent self-evident, it is hoped that the quantitative implications of these models will serve as a guide for interpreting experimental results and even perhaps for motivating future experimental work.
Lifetime of vibrational levels of the A 2Π and B 2Σ+ states of CO+
Authors: Arqueros F. , Campos J.
Published: February 2003

The radiative lifetimes of the A 2Π (v′ = 1–5) and B 2Σ+ (v′ = 0–2) states of CO+ have been measured by means of the delayed coincidence method. Excitation has been performed by a pulsed electron beam incident on CO. For the lifetime measurements of vibrational levels of the A 2Π state, particular attention has been paid to collisional quenching and electrostatic repulsion. The results of these measurements are 3.25±0.4 μs (v′ = 1), 3.04±0.17 μs (v′ = 2), 2.79±0.15 μs (v′ = 3), 2.56±0.15 μs (v′ = 4), and 2.38±0.16 (v′ = 5). For the B 2Σ+ state measurements, no pressure dependence over a range 1–40 mTorr has been observed; the lifetimes are found to be 53.8±0.8 ns (v′ = 0), 58.1±0.8 ns (v′ = 1), and 63.3±1.0 ns (v′ = 2).
Laser photodissociation of O3− by triple quadrupole mass spectrometry
Authors: Hiller J. F. , Vestal M. L.
Published: February 2003

Absolute cross sections for the production of both O− and O2− by photodissociation of O3− have been determined at intervals of 0.2 nm or less throughout the range from 380 to 650 nm. The results indicate that both the 2A2 and the 2A1 excited state are accessible in this range. Threshold energies and vibrational assignments are derived from the data. For the transition 2A2←2B1, T00 = 2.046±0.002 eV, υ1′ = 815±10 cm−1, υ2′ = 275±10 cm−1, υ1′′ = 975±10 cm−1, υ2′′ = 590±10 cm−1; for 2A1←2B1, T00 = 2.655 eV, υ1′ = 760±20 cm−1, υ2′ = 190±20 cm−1. The threshold for O2− production is interpreted to yield D(O–O2−)?2.41±0.01 eV, which together with other recent spectroscopic determinations of pertinent thermochemical quantities implies that D(02–O−)?1.388±0.013 eV and D(O2–O)?0.747±0.013. The latter value is in serious disagreement with the literature value of 1.05±0.02 eV determined calorimetrically but is in good agreement with results derived from recent spectroscopic measurements on the positive and negative ions of ozone.
Theoretical calculation of thermodynamic properties and melting curves for hydrogen and deuterium
Authors: Young David A. , Ross Marvin
Published: February 2003

Thermodynamic properties of solid H2 and D2 are computed from quasiharmonic lattice dynamics corrected by anharmonic terms. Liquid properties are computed from a modified hard-sphere variational perturbation theory with a quantum correction. In these models we use an intermolecular pair potential which has been fitted to high pressure solid data. The computed solid and liquid free energies are used to find the melting curves of H2 and D2 up to room temperature. Agreement between experiment and theory is good.
Rotational cooling in a supersonic expansion of ammonia
Authors: Snavely Deanne L. , Colson Steven D. , Wiberg Kenneth B.
Published: February 2003

Collisional selection rules are determined for ammonia in a cryopumped supersonic jet.(AIP)
Laser induced fluorescence of metal clusters produced by laser vaporization: Gas phase spectrum of Pb2
Authors: Bondybey V. E. , English J. H.
Published: February 2003

Laser vaporization coupled with laser induced fluorescence is studied for metal clusters. (AIP)
Microwave optical double resonance of X 1Σ+ of NaK
Authors: Wormsbecher Richard F. , Hessel M. M. , Lovas Frank J.
Published: February 2003

A microwave optical double resonance (MODR) study of the ground state X 1Σ+ is NaK is reported. The ν″ = 0 J = 7→8 and J = 8←9, and ν″4 J = 5←6 rotational transitions were observed as changes in the laser induced photoluminescence intensity with the Ar+ laser coincidences (12–0) band P(8) (4765 Å) and (’–4) band Q(5) (4965 Å), respectively, of the D 1Π–X 1Σ+ system of NaK. The improvement in sensitivity of the MODR technique over traditional microwave spectroscopy is discussed. Improved Dunham coefficients for the X 1Σ+ state are obtained by a weighted merged fit of the previous optical data with the three transitions obtained in the present work.
Vibrationally adiabatic distorted wave calculation for the rotationally excited reaction H+H2(v = 0, j)→H2(v′ = 0, j′)+H
Authors: Clary D. C. , Connor J. N. L.
Published: February 2003

Porter-Karplus potential energy surfaces are used to calculate differential cross sections.(AIP)
Scattering of Na 3 2P3/2 from Ar
Authors: Düren R. , Liedtke R.
Published: February 2003

Total differential cross section with a laser excited Na beam of thermal energy scattered from a secondary beam of argon measured.(AIP)
Long range transfer of positive charge between dopant molecules in a rigid glassy matrix
Authors: Miller John R. , Beitz James V.
Published: February 2003

Pulse radiolysis has been used to observe and measure the kinetics for intermolecular positive charge (hole) transfer from biphenyl+ or pyrene+ ions to TMPD molecules in rigid 2-chlorobutane glass at 77 K. These hole transfers occur over distances of about 17 Å at 10−6 s, increasing to about 34 Å at 102 s. The kinetic data are interpreted in terms of current theories which treat electron transfer processes as radiationless transitions. Estimates of the required electron exchange interactions based on the usual electron tunneling models can not explain the fast reactions observed, even when Coulombic effects on the ’’barrier’’ are considered. A superexchange model is proposed which involves interactions propagated by both negative and positive ion states of the solvent. This model adequately interprets the data in terms of a dominant role of the solvent positive ion states, and is also applicable to negative charge transfer in the condensed phase. In samples containing only one solute (biphenyl or pyrene), ion recombination with Cl− removed about one third of the positive ions of the solute between 10−6 and 102 s. The data on intermolecular hole transfer between two solutes must be corrected for the effects of ion recombination. The correction is simple and quantitative only when it is possible to observe decay of the reactants without substantial spectral overlap from the products. Because the effects of ion recombination on product growths are complex, it is not presently possible to use the growths to measure reliably the kinetics intermolecular positive charge transfer.
Electron scattering by CO2: Elastic scattering, rotational excitation, and excitation of the asymmetric stretch at 10 eV impact energy
Authors: Thirumalai Devarajan , Onda Kunizo , Truhlar Donald G.
Published: February 2003

Coupled-channels calculations based on an effective potential are presented for electron scattering by CO2 at 10 eV impact energy. The processes studied are pure elastic scattering, rotational excitation, and vibrational excitation of the asymmetric stretch; the vibrational excitation is always accompanied by rotational excitation. The quantities calculated are differential, partial, integral, and momentum transfer cross sections, both state to state and summed over final rotational states for a given final vibrational level. The effective potential is based on the INDOX2/1s method for the static and polarization potentials and the semiclassical exchange approximation for the exchange potential. There are no empirical parameters. The present calculations are compared to experiment and to previous calculations where available, and we also perform calculations with an altered polarization potential to further elucidate the reasons for the differences from one of the previous calculations. The agreement of the present results with the experimental rotationally summed, vibrationally inelastic differential cross section is excellent.
Differential scattering cross sections and the A 2Π potentials for the systems NaAr, NaKr, and NaXe
Authors: Düren R. , Gröger W. , Hasselbrink E. , Liedtke R.
Published: February 2003

For the systems Na(3 2P3/2)Ar, NaKr, and NaXe we have measured the total differential cross sections at thermal energies. All systems show a well resolved oscillation structure of the cross sections. For these data quantum mechanical calculations have been performed based on pseudopotentials (for NaAr), and calculations in the elastic WKB approximation using a Lennard-Jones (8,6) potential (for NaAr, NaKr, and NaXe). The results allow us to determine the interatomic potentials with high accuracy. A comparison is made by a detailed listing of experimental and theoretical results published up to now.
Collisional redistribution of vibrational energy in CO2-laser-excited benzene
Authors: Lyman John L. , Feldmann D. , Laukemper J. , Welge Karl H.
Published: February 2003

We have monitored changes in the population of benzene vibrational levels during and after irradiation with an intense CO2-laser pulse. Our method was to induce fluorescence from the first excited singlet state (1B2u) by absorption of tunable ultraviolet radiation. By varying the delay time between the infrared and ultraviolet pulses and by employing ultraviolet frequencies within many bands of the 1A1g–1B2u system, we measured the temporal evolution of the vibrational energy distribution over 12 benzene levels. We also used the technique to assign bands of the ultraviolet absorption spectrum that involve vibrational levels pumped by the infrared laser.
A method for nuclear spin statistics in molecular spectroscopy
Authors: Balasubramanian K.
Published: February 2003

Using spin projection operator methods, generating functions are developed for nuclear spin species. These operators also generate elegantly the irreducible respresentations spanned by a1b1 a2b2⋅⋅⋅atbt nuclear spin functions, where ai is the number of possible spin states of the bi nuclei of the same kind in the molecule. From these generating functions the statistical weights of the rovibronic levels of any polyatomic molecule can be obtained easily. The method is illustrated with 33SF6, 13C-triphenylene, and triphenylene with protons replaced by D. For 13C-triphenylene there are 1 073 741 824 nuclear spin functions from which we determined the statistical weights of the rovibronic levels A′1, A′2, E′, A″1, A″2, and E″ to be 178 940 928, 178 973 696, 357 913 600, 178 940 928, 178 973 696, and 357 913 600, respectively.
Wave vector dependence of the effective diffusion coefficient of Brownian particles
Authors: Fijnaut H. M.
Published: February 2003

On the basis of a density relaxation equation of Felderhof, the wave vector dependence of the effective diffusion coefficient is calculated for Brownian particles under the influence of thermodynamic and hydrodynamic interactions. The calculations are correct to first order in the density and show that in the large wave vector limit the diffusion coefficient has to be connected with self-diffusion. For three different model potentials (the hard sphere potential, the triangle potential, and the screened Coulomb potential), numerical results are given. It is shown that long range repulsion has a large effect on the effective diffusion coefficient especially at small values of the wave vector.
Reflectivity of a 5.8 kbar shock front in water
Authors: Harris Paul , Presles Henri Nöel
Published: February 2003

Theory and experiments are presented for reflection of a laser beam from a 5.8 kbar shock in water for both parallel and perpendicular (to the plane of incidence) optical polarizations. The theory is in closed form and valid in the nonlinear (large optical path length) region. Agreement between theory and experiment is obtained with a shock front thickness less than or equal to 4×10−6 cm.
Self-diffusion in compressed supercritical water
Authors: Lamb W. J. , Hoffman G. A. , Jonas J.
Published: February 2003

The self-diffusion coefficients D of compressed supercritical water have been measured as a function of pressure in the temperature range 400 to 700 °C using the NMR spin–echo technique. The experimental diffusion data were compared to theoretical predictions based on a dilute polar gas model using a Stockmayer potential for the evaluation of collision integrals and a temperature dependent hard sphere diameter. The empirical expression ρDαTn, where n = 0.76, fits the experimental data to within±10% over the entire density and temperature region studied. The value of the exponent n = 0.76 agrees favorably with the n values found for diffusion of other gases. The product ρD is density independent under isothermal conditions which indicates that two-body collisions dominate the diffusion behavior. This finding is in agreement with our earlier results for proton relaxation in compressed supercritical water which were analyzed using a binary collision approximation and a collision modulated spin–rotation interaction described by a single correlation function which is an exponential function of time. The hydrodynanic Stokes–Einstein equation appears to hold at densities above ρc. As expected, the diffusion data cannot be described in terms of a hard sphere model but an empirical fit to lnρD = (A/T)+B, where A and B are constants, represents the experimental data well over the range of temperatures and densities studied.
Translational and rotational friction in a rough sphere fluid
Authors: Lebenhaft Julian R. , Kapral Raymond
Published: February 2003

A microscopic derivation of the translational and rotational friction coefficients for a Browian particle in a dilute rough sphere fluid is presented. A projection operator method is used to couple the test particle’s motion to the collective fluid fields, and the resulting generalized Langevin equations are averaged over fluctuations to yield source hydrodynamic equations. After averaging over the surface and volume of the spherical Brownian particle, these equations are algebraically manipulated to give expressions for the force and torque exerted on the tagged particle by the surrounding fluid. The Stokes’ law relations, for partial stick boundary conditions, are obtained.
Fluctuations in optical activity: A probe of fast reactions using light scattering
Authors: Dewey T. G. , Turner Douglas H. , Sceats Mark G.
Published: February 2003

Theory is presented for light scattering from a liquid where there is a change in optical activity of the molecules upon chemical reaction. The results indicate that the difference spectrum for 90° scattering between right and left circularly polarized input is dominated by the reactive component through the cross term which couples fluctuations in the dielectric permittivity and the optical activity. The feasibility of the technique is illustrated by calculations for a unimolecular reaction.
The rotational and hyperfine spectrum of Ar–HF
Authors: Dixon T. A. , Joyner C. H. , Baiocchi F. A. , Klemperer W.
Published: February 2003

The radio frequency and microwave spectrum of Ar–HF has been remeasured by molecular beam electric resonance spectroscopy. Analysis of the data yields a revised value for the HF nulear spin–spin constant S, which in turn provides information about the vibrationally averaged geometry of the complex. Rotational and hyperfine constants and the dipole moment have also been measured for Ar–DF:               The average structures and estimated harmonic force constants are shown to be consistent with those observed for other Ar–HX complexes. Comparison of the two hyperfine constants for Ar–DF indicates that the average charge distribution around the deuterium is only weakly perturbed by the argon atom.
CO2–HF: A linear molecule
Authors: Baiocchi F. A. , Dixon T. A. , Joyner C. H. , Klemperer W.
Published: February 2003

The results of microwave and radio frequency spectroscopy of the weakly bound complexes of hydrogen fluoride with carbon dioxide and carbonyl sulfide are presented. The following spectroscopic constants are determined:                           A nearly linear hydrogen bonded equilibrium structure with an O–H bond length of ∼1.9 Å is consistent with all the experimental data. The stretching force constant, estimated from the distortion constant to be ks = 0.021 mdyne/Å for CO2–HF, appears anomalously small for such a short bond.
Laser-excited emission spectra of In atoms trapped in Kr and Xe matrices
Authors: Balling L. C. , Wright J. J.
Published: February 2003

The first measurements of the fluorescence spectra of In atoms trapped in Kr and Xe matrices are reported. The In atoms were trapped at 4 °K and the fluorescence was excited by a pulsed dye laser tuned to the matrix-isolated In absorption bands. The results are compared with the previously reported emission spectra of matrix-isolated Tl atoms.
Magnetic resonance study of Mo5+ in Ca1−xYxMoO4
Authors: Greenblatt M. , Strobel P. , Pifer J. H.
Published: February 2003

The ESR of MoO3−4 has been studied at 4.2 K in single crystals of Ca1−xYxMoO4 (x<0.01). The g values and Mo hyperfine constants are gx = 1.8925, gy = 1.8753, gz = 1.9780, Ax = 38.6×10−4 cm−1, Ay = 42.8×10−4 cm−1, and Az = 22.2×10−4 cm−1. The resonances show an isotropic superhyperfine splitting due to a nearby charge compensating yttrium ion. The ground state of the d1 electron is dz2 as expected for the MoO4 tetrahedron which is distorted to D2d symmetry by a c axis compression in this host. Crystal field parameters are calculated by fitting the ESR data to equations assuming xz mirror symmetry at the Mo5+ site.
Theoretical study of shape resonances in the partial photoionization cross sections for the b 4Σg− and B 2Σg− states of O2+
Authors: Raşeev G. , Lefebvre-Brion H. , Le Rouzo H. , Roche A. L.
Published: February 2003

Using the single-center static-exchange approximation, the 3σg photoionization cross section of O2 is calculated. The R-averaged results are obtained for the production of O+2 in the b 4Σ−g and B 2Σ−g states. Shape resonances, a few electron volts wide, are found at 3 and 2.5 eV from the threshold for these two states, respectively. We find reasonable agreement with the experimental cross sections for the B 2Σ−g state and with the β values for the b 4Σ−g state. For this last state, comparison between theory and experiment leads us to a possible interpretation of the data, but a definite answer can not be given without taking into account the autoionized Rydberg states.
Uniform semiclassical evaluation of Franck–Condon factors and inelastic atom–atom scattering amplitudes
Authors: Connor J. N. L.
Published: February 2003

The problem of obtaining uniform semiclassical approximations for Franck–Condon factors and inelastic atom–atom scattering amplitudes is considered. Starting from Langer’s uniform Airy approximation for the wave function and an Airy function representation of the inelastic S matrix element, it is shown how both these problems can be expressed in terms of a multidimensional oscillatory integral, the exponent of which possesses two coalescing saddle points. Using a general formula for the uniform asymptotic evaluation of this multidimensional integral, simple derivations are presented for the uniform semiclassical approximation to the Franck–Condon factor and inelastic scattering amplitude. Previous derivations are shown to be special cases of the more general derivations given here. The use of catastrophe theory for choosing the simplest and most convenient canonical form for the transformation of the exponent in the uniform asymptotic evaluation of multidimensional integrals is discussed.
Nitrogen and deuterium nuclear quadrupole resonance in lanthanum nicotinate dihydrate
Authors: Davidson M. M. , Edmonds D. T. , Mailer J. P. G.
Published: February 2003

Using nuclear double quadrupole resonance techniques the nuclear quadrupole resonance (NQR) spectra of the three inequivalent 14N sites and the four water 2D sites have been obtained at 77 K for lanthanum nicotinate dihydrate. The quadrupole coupling constants e2qQ/h in kHz and the anisotropy constant η are for nitrogen 4418 and 0.362, 4222 and 0.335, and 4220 and 0.327. For the deuterons they are 233.73 and 0.080, 177.47 and 0.153 for one water molecule and 219.73 and 0.098, 189.07 and 0.148 for the other. An attempt is made to extract structural data from these NQR results.
Two- and three-photon absorption of iodine molecules via dissociative states
Authors: Kasatani K. , Tanaka Y. , Shibuya K. , Kawasaki M. , Obi K. , Sato H. , Tanaka I.
Published: February 2003

Iodine vapor was irradiated by focused dye laser light in the range of 450–610 nm. Firstly, by irradiation of the laser light tuned near the dissociation limit of the B state (∼500 nm) emission bands were observed at 385, 342, 287, and 270 nm by two- or three-photon absorption. When the energy of laser light was above the dissociation limit of the B state, the emission intensity decreased drastically but was still observed. No effect of polarization of the laser light (circular or linear) was observed, indicating that the two-photon absorption is consecutive absorption of photons via dissociative states. Secondly, the absorption tuned far below the dissociation limit of the B state (550–600 nm) led to occurence of 342, 325, and 270 nm emission bands and IR emission at 1.3 μm originating from electronically excited iodine atoms I*(2P1/2). The excitation spectra of both UV and IR emission had the same threshold wavelength around 600 nm. The formation of the states responsible for the 325 and 270 nm bands is considered as three-photon absorption via the dissociative 0g+(1Σ) state that correlates to two I*(2P1/2) atoms.
An experimental investigation of rare gases pressure effects on the rovibrational line intensities of HCl
Authors: Piollet-Mariel Edmée , Boulet Christian , Levy Armand
Published: February 2003

A measurement method has been set up for the accurate determination of vibration–rotation line strengths. It has been applied to a careful analysis of the intensities of HCl lines pressurized by Ar or Xe. Several mixtures have been studied corresponding to pressures of the perturber ranging from 5 to 15 atm. It is shown that the line intensities S appear to vary linearly (within the accuracy of experimental measurements) with the density of the perturbing species. For each one of the investigated lines, a least squares fit allows one to retrieve the ’’standard’’ S0 value corresponding to pure HCl and excellent agreement with previous determinations is obtained. In addition, the rate of variation of S as a function of the density of the rare gas is determined and shown to be strongly m dependent.
Chemiluminescent ion–molecule reactions B++H2
Authors: Ottinger Ch. , Reichmuth J.
Published: February 2003

Emission spectra resulting from impact of low-energy (1–10 eVc.m.) B+ ions in a beam on an H2 target were measured. Numerous new bands of the BH+(A 2Π–X 2Σ+) transition were observed besides the previously known (0,0) and (1,1) bands. Also, at higher energy a new band system was discovered which is ascribed to the BH+(B′ 2Σ+–X 2Σ+) transition. It was identified by analogy with BeH and MgH. The results are discussed in terms of electronic state and molecular orbital correlation diagrams.
ESR spectra of matrix isolated potassium atom clusters
Authors: Thompson G. A. , Lindsay D. M.
Published: February 2003

ESR spectra assigned to the previously unobserved 39K3 molecule have been obtained by co-depositing atomic potassium with argon under conditions favorable to cluster formation. The ESR spectra show that the trimer is chemically bound, with predominantly s rather than p character. Approximately 95% of the 4s spin population resides equally on two 39K nuclei with less than 6% on the third atom. The trimer is assigned a symmetric linear or ’’obtuse angled’’ isosceles geometry with ground state symmetry 3Σ+u or 2B2. A second ESR spectrum, a pattern of 10 equally spaced hyperfine components centered close to the free electron g value, is indicative of a radical species containing three equivalent 39K nuclei each having an isotropic spin population of slightly less than 1/3. Plausible candidates for the carrier of this spectrum are K5 with a linear or ’’zig–zag’’ geometry, or a ’’pseudorotating’’ isomer of K3. ESR intensities show a pronounced temperature dependence. K3 spectra are significantly enhanced by warming to T∼19 K, but almost completely disappear at T∼25 K, where the 10 line spectrum is most intense.
ESR kinetics study of the decay of low-temperature radicals in glycine and β-alanine
Authors: Smith Clyde J. , Poole Charles P. , Farach Horacio A.
Published: February 2003

Monocrystals of glycine and β-alanine have been observed by electron spin resonance (ESR) after x-irradiation near 77 °K. The rate constants of the decay of one signal in each have been determined over the ranges 127 °–148 °K and 98 °–188 °K, respectively. Both obey first-order kinetics with activation energies of ∼7.0 and ∼2.6 kcal/mole, respectively, and pre-exponential factors of 6.4×108 and 15 Hz, respectively.
Infrared laser radiation effects on XeF2 interaction with silicon
Authors: Chuang T. J.
Published: February 2003

The presence of the laser radiation field on a silicon surface has been shown to influence the XeF2–silicon reaction rate. It is observed that the radiation enhancement in the surface reaction yield depends on the laser power, but is independent of the CO2 laser wavelength or the partial pressure of the active gas in the pressure range of 10−4–10−5 Torr. A model based on the variation of the sticking probability of XeF2 on Si as a function of fluorine surface coverage modified by the laser radiation is proposed to account for the experimentally determined characteristics of the gas–solid system. The results show that the laser-enhanced chemical process may not be due entirely to the thermal effect. Furthermore, the study provides a better understanding for the laser induced interaction between SF6 and silicon, and for the fluorine–silicon surface chemistry in general. The radiation effect by the infrared photons is also compared with those induced by energetic electrons and ions.
Pulsed laser stimulated field desorption of hydrogen from molybdenum
Authors: Kellogg G. L.
Published: February 2003

The recently developed pulsed laser atom probe has been used to investigate the adsorption and dissociation of molecular hydrogen in high electric fields. The results indicate that at temperatures of 60 K and fields of 2.0 V/Å and higher, hydrogen is field adsorbed on molybdenum surfaces in molecular form. The activation energy of desorption is found to depend on the square of the applied electric field, in agreement with an expression previously derived for noble gas atoms. The desorption mechanism is shown to be a two-step process consisting of thermal release followed by field ionization and/or dissociation above the surface at xc (the critical distance of field ionization). Values of xc are obtained for H+, H2+, and He+, and it is shown that the probability of molecular dissociation at a given field strength can be predicted from simple energetic considerations. An expression relating the number of field adsorbed molecules on a surface with N adsorption sites to various experimental parameters is derived from an empirical rate equation, and data from the present study are shown to be in good agreement with the theoretical predictions.
Infrared spectrum of solid hydrogen with high sensitivity spectrometers: Aspects of zero phonon transitions in solid para-hydrogen
Authors: Ivancic William , Balasubramanian T. K. , Gaines James R. , Rao K. Narahari
Published: February 2003

The infrared spectra of solid para-hydrogen are measured. The spectral resolution of 0.006 cm−1 was achieved at the infrared wavelengths reported. (AIP).
Energy redistribution observed in infrared multiphoton excited C2F5Cl
Authors: Hudgens Jeffrey W. , McDonald J. D.
Published: February 2003

The emission spectrum of infrared laser multiphoton C2F5Cl recorded under nearly collisionless conditions is shown. Emission from both unrelaxed discrete states and intramolecularly relaxed quasicontinuum levels are identified by comparison with thermally prepared C2F5Cl. The discrete states appear composed principally of ν4=1 levels indicating that rapid intramolecular energy redistribution begins at ν4=2,3 and state densities of ∼400/cm−1.
van der Waals molecules and the mechanism of dimer formation in jet-cooled CF3NO
Authors: DeKoven Benjamin M. , Levy Donald H.
Published: February 2003

The fluorescence spectra of CF3NO are reported. The relative intensity measurements in the emission spectra suggest that dimers or higher polymers of CF3NO are being formed in the supersonic expansion. (AIP).
The role of excitation in relaxation processes of non-Markovian nature
Authors: Grigolini Paolo
Published: February 2003

Quantum mechanical simulations of vibrational relaxation are commented upon. A non-markovian system is discussed. (AIP).
Experimental determination of the lowest excited Xe2 molecular states from VUV absorption spectra
Authors: Castex Marie-Claude
Published: February 2003

A quantitative analysis of absorption by Xe2 pairs in the wings of the two first resonant lines (1469.6 and 1295.6 Å) is presented as a function of pressure (P<760 Torr) and temperature (130 K<T<300 K). Using a quasistatic theory, absorption measurements provide valuable information on the lowest 0u+ and 1u excited states, the 0g+ ground state potential being known from literature. In the near wing region (‖Δν‖<100 cm−1) the shape of the line wings is used as a probe of the asymptotic −2C3/R3−C60/R6 (0u+) and +C3/R3−C61/R6 (1u) potentials assuming at large R a constant oscillator strength, C3 and C6 excited constants are determined. Furthermore the dependence of absorption with temperature is used to derive additional information about the upper states and also to put in evidence some variation of transition moments, at shorter internuclear distances (3.7 Å <R<4.6 Å). The potential curves experimentally derived are compared with ab initio calculated curves.
The terbium chloride–aluminum chloride vapor system. I. Absorption and excitation spectra
Authors: Caird J. A. , Carnall W. T. , Hessler Jan P. , Williams C. W.
Published: February 2003

The absorption spectrum of the vapor complex formed at elevated temperatures between TbCl3 and AlCl3 has been measured in the region 20 000–50 000 cm−1. Oscillator strengths of f–f absorption bands below 37 000 cm−1 were determined. Strong absorption due to opposite parity 4f75d states was observed in the 37 000 to 50 000 cm−1 region with a peak molar absorptivity of approximately 500 ℓ/mol cm. Significant additional absorption attributed to a molecular complex was also observed in this region. By measuring the excitation spectrum it was found that the molecular absorption does not appear to lead to fluorescence of the 5D4 state. In contrast, absorption by the 4f75d states does result in strong 5D4 fluorescence.
The terbium chloride–aluminum chloride vapor system. II. Fluorescence
Authors: Caird J. A. , Hessler Jan P. , Carnall W. T. , Williams C. W.
Published: February 2003

Measurements of the fluorescence spectra and fluorescence decay kinetics of the vapor complex formed at elevated temperatures between TbCl3 and AlCl3 have been made in the 350 to 700 nm wavelength range. The principal lines in the spectra were identified as emission from the 5D4, 5D3, and the 5G6 energy levels of the Tb3+ ion. The radiative lifetime of the 5D4 level at low temperatures was found to be 3.88 ms, and was used to determine the oscillator strengths of the 5D4→7FJ (J=0 through 6) transitions after their branching ratios were measured. The peak cross section for stimulated emission on the strong 5D4→7F5 transition was found to be 2.87×10−21 cm2 at λ=543 nm. A population inversion of 1018 cm−3 could produce a small signal gain of 30% per meter on this transition, indicating that laser emission may be possible at temperatures where sufficient vapor density can be obtained.
The theory of pulsed Fourier transform microwave spectroscopy carried out in a Fabry–Perot cavity: Static gas
Authors: Campbell E. J. , Buxton L. W. , Balle T. J. , Flygare W. H.
Published: February 2003

A semiclassical theory has been developed to describe pulsed Fourier transform microwave spectroscopy carried out in a Fabry–Perot cavity. A density matrix formalism is used to study the interaction of a two-level quantum system with a classical standing wave electric field, appropriate for the Fabry–Perot cavity. Equations describing the polarization of, and subsequent emission of radiation by arbitrary distributions of molecules in the cavity are derived. The specific problem of a static Maxwell–Boltzmann gas is studied in detail, both theoretically and experimentally. The static gas line shape in the power-broadened limit is described by an ordinary Doppler and pressure broadened envelope. Sensitivities of the ordinary waveguide cell and Fabry–Perot cavity pulsed Fourier transform spectrometers using static gas samples are compared.
S2–SO2 energy transfer studied by matrix isolation in solid argon
Authors: Cook Gary , Krogh Ole D.
Published: February 2003

Matrix samples of O2/OCS/Ar, SO2/OCS/Ar, and SO2/Ar were photolyzed with a Hg lamp over a wide range of sample concentrations. Emission spectra were recorded in both excitation and thermoluminescence with an optical multichannel analyzer. Infrared spectra of the same samples were recorded simultaneously with a PE 621 grating spectrometer. SO2 was observed in IR absorption, and SO2, S2, and S atoms were observed in UV–Vis emission. S2 fluorescence is dominant during photolysis before warmup, SO2 emission is dominant during warmup from 8 to 30 °K, and only S2 fluorescence is observed after warmup. In excitation S atom emission (1S→1D) is observed simultaneously with S2 fluorescence. These observations are explained in terms of an energetically coupled S2–SO2 complex involving rapid energy transfer between S2 (X 3Σg−↔B″ 3πu/B 3Σu−) and SO2(X̃ 1A1↔Ã 1B1). This same complex is also postulated to engage in energy transfer between S2(B′′ 3πu→b 1Σg) and S atoms (3P2→1S). The IR spectra offer an indication of a weak (S2–SO2) complex in form of a red shift of ν3 of 8 cm−1 compared to an SO2/Ar reference sample.