bluuebunny/crossref_metadata_2025 huggingface dataset:
Penning ionization electron spectroscopy of CO and Fe(CO)5. Study of electronic structure of Fe(CO)5 from electron distribution of individual molecular orbitals
Authors: Harada Y. , Ohno K. , Mutoh H.
Published: February 2003

The He* Penning ionization electron spectra (PIES) and He I UV photoelectron spectra (UPS) of CO and Fe(CO)5 were measured. The relative intensity of the bands in PIES was shown to give information on the spatial electron distribution of individual molecular orbitals. On the basis of the information together with the results of the population analysis, most of the bands in the UPS of Fe(CO)5 were assigned. The usefulness of PIES in the study of stereochemistry was indicated.
Molecular dynamics in intense laser fields. I. One-dimensional systems in infrared radiation
Authors: Nguyen-Dang T. Tung , Bandrauk André D.
Published: February 2003

The Bloch–Nordsieck transformation of quantum electrodynamics is applied to the molecular Hamiltonian in order to include explicitly radiative corrections in molecular dynamics. General coupled equations are obtained for all field strengths. In the adiabatic limit, we obtain dressed potential surfaces which undergo radiative distortions relative to the field free potentials. Analytic expressions are obtained for these radiative effects in the presence of intense IR laser fields for harmonic, Morse, and double well potentials. These effects are shown to be important at field intensities greater than 1012 W/cm2 and may be interpreted as generalized field induced Lamb shifts.
The existence of straight-line paths, invariant vectors, and invariant tensors characterizing nonequilibrium state distributions during chemical reactions
Authors: Lim Carmay , Truhlar Donald G.
Published: February 2003

We have deduced the existence of straight-line reaction paths for various reaction systems. The general conditions for their existence in isomerization systems, dissociation–recombination reactions, and bimolecular reactions are discussed. We have also derived the invariant quantity that characterizes the internal-state distributions of either reactants or products when the phenomenological rate constant is steady. An invariant vector is obtained for first-order reactions, and an invariant tensor is obtained for second-order reactions. Analytic expressions for these invariant quantities are given for several cases. The application and usefulness of an invariant vector is illustrated for an example reaction by using it to calculate the internal-state population distributions at any time during the forward or reverse reactions from the internal-state distributions at any one time during either. These calculations check satisfactorily against the distributions obtained by numerical solution of the master equation.
Selective vibronic excitation of singlet oxygen–furan reactions in cryogenic matrices
Authors: Frei Heinz , Pimentel George C.
Published: February 2003

The reactions of 2,5-dimethylfuran (DMF), 2-methylfuran (MF), and furan with molecular oxygen to form endoperoxides have been induced in Ar and O2 matrices at 12 K with selective vibronic excitation of O2 using near infrared light. Reaction was induced through excitation of the 1Δg(v′=0, v′=1) and 1Σg+(v′=0, v′=1) O2 states near 8000 and 13 100 cm−1, respectively, as well as by the (1Δg, 1Δg) simultaneous transitions of (O2)2 at 15 900 and 17 300 cm−1. The 1Δg ← 3Σg− vibronic progression in solid O2 was recorded by FTIR spectroscopy, whereas members of the 1Σg+ ← 3Σg− and (1Δg, 1Δg) ← (3Σg−, 3Σg−) progressions in Ar matrices were located by ‘‘reaction excitation’’ spectroscopy. The DMF+O2 reaction is a single photon process, apparently with unit quantum yield, for all vibronic levels excited. For MF+O2(1Δg, v′=0) and furan +O2(1Δg, v′=0), quantum yields were high, ∼0.6 and 0.4, respectively, but the reservoirs of reactive pairs were 10–20 times smaller than for DMF+O2. The furan+O2 reaction rate showed an 18O2 isotope effect 0.78±0.15, which can be interpreted in terms of quantum mechanical tunneling on the lowest singlet hypersurface. The IR matrix spectra of DMF endoperoxide and its peroxidic 18O counterpart are reported, and a partial vibrational assignment for this intermediate is given. The endoperoxide vibration that absorbs at 815.7 cm−1 is dominated by the bridge O–O stretching motion.
Strong hot Raman transitions ensuing via quadratic Jahn–Teller interactions
Authors: Scharf B. , Band Yehuda B.
Published: February 2003

The theory for vibronic Raman transitions within the split manifold of excited vibrational levels of quadratically Jahn–Teller active modes in molecules with D6h symmetry is presented. The spectroscopic pattern, depolarization ratios and excitation profiles for all possible intermediate states are elaborated. These hot Raman transitions are marked by exceptionally high polarizabilities comparable in magnitude to those of Rayleigh transitions. Despite the attenuation by the Boltzmann factor these Raman transitions are expected to be one of the prominent features in the vibrational Raman spectrum of Jahn–Teller active states.
Intramolecular vibrational energy transfer in methyl formate
Authors: Stewart G. M. , Ensminger Mark D. , Kulp T. J. , Ruoff R. S. , McDonald J. D.
Published: February 2003

Intramolecular vibrational energy transfer in isolated gas phase molecules of methyl formate has been studied by spectrally resolving the IR laser induced fluorescence from C–H stretch fundamentals, combination bands, and overtones in the region from 2900 to 3500 cm−1. By comparing the experimentally observed relative energy content of the IR active modes with that calculated from a statistical model it is concluded that complete randomization of the energy initially deposited in the zeroth order optically excited state occurs. However, due to the finite density of vibrations, that statistical distribution differs clearly from a thermal distribution. Both the model and experiment agree that different optically excited states deposit different amounts of energy in the carbonyl stretching mode at 1754 cm−1. We also observe a rotational state dependence of vibrational energy transfer in the 2939 cm−1 band. The experiments are performed by exciting a molecule cooled in a nozzle expansion with light from an infrared optical parametric oscillator. The fluorescence spectra are recorded with a cryogenic Michelson interferometer.
Vibrational relaxation of highly excited diatomics. V. The V–V channel in HF(v)+HF(0) collisions
Authors: Dzelzkalns L. S. , Kaufman F.
Published: February 2003

The V–V fraction in HF self-relaxation is determined in fast-flow infrared chemiluminescence experiments through the consistent accounting of all HF(v) populations in partially relaxed mixtures. The v-level specific, fractional V–V probabilities fv are measured for v=2 and 3 using the F+H2 and F+CH4 generating reactions, and estimates are obtained for v=4 to 7 using F+HBr and H+F2 data. A consistent set of fv’s is 0.55±0.10, 0.30±0.10, 0.15±0.10, and zero for v=2, 3, 4, and 5 to 7, respectively. These values are compared with one recent laser measurement for v=2 and with the theoretical predictions of semiclassical trajectory calculations.
The infrared multiphoton excitation and photochemistry of DN3
Authors: Simpson T. B. , Mazur E. , Lehmann Kevin K. , Burak I. , Bloembergen N.
Published: February 2003

Multiphoton excitation and dissociation of DN3 by short CO2 laser pulses is shown to be a collisionless process. The characteristic features of this multiphoton process are systematically studied. The average number of photons absorbed per DN3 molecule and the absolute dissociation yield show a strong dependence on the peak laser intensity. Resonantly enhanced coherent multiphoton excitation, rather than stepwise incoherent excitation, is suggested. The primary dissociation products of DN3 are ND[1Δ] and N2. Formation of vibrationally excited ND[1Δ] intermediates is suggested. The reactions of ND[1Δ] with DN3 lead to chemiluminescent signals originating from the formation of electronically excited ND2[2A1] and ND[3Π]. Formation of the ND[3Π] intermediate is attributed to a reaction of ND[1Δ] and vibrationally excited DN*3 molecules: ND[1Δ]+DN*3→ND[3Π]+ND[3Σ−]+N2.
Exact Thomas–Fermi method for kinetic energy and other averages of Compton profile for atomic closed shells in a bare Coulomb field
Authors: March N. H.
Published: February 2003

For the model of closed electron shells in a bare Coulomb potential energy −Z/r, the mth moment of the momentum p for 𝒩 closed shells is calculated as             which is valid in the range −3<m<5. For the reduced range −3<m<3, it is shown that (i) can be written in terms of an integral over a finite domain, which is then interpreted as an r-space representation of the moments of momentum. For an arbitrary number 𝒩 of closed shells, the total kinetic energy T can then be written exactly in the form           where         and μ is determined by normalization of ρsemiclassical to the total number of electrons N. The quantity ck(N) in Eq. (ii) depends on N through             Other moments 〈p〉 and 〈p−1〉 are briefly discussed, as well as the relevance of these bare Coulomb field results to the true situation in atomic ions with screened Coulomb potentials and especially to moments of the Compton profile.
The ground and excited states of PtH and PtH+ by relativistic ab initio electronic structure calculations: A model study for hydrogen chemisorption on platinum surfaces and related photoemission properties
Authors: Wang S. W. , Pitzer Kenneth S.
Published: February 2003

Relativistic electronic structure calculations for the ground and excited states of PtH and PtH+ are performed using first a spin-averaged relativistic effective core potential (AREP) at the self-consistent field (SCF) level and later incorporating the spin dependence at the configuration interaction (CI) level. These calculations lead to several conclusions: (1) Both the 6s and 5d orbitals of Pt interact strongly with the H orbitals, clearly indicating that the bonding involves both 6s and 5d electrons. (2) Correlation energies contribute significantly to the PtH binding energy but have little effect on the force constant. (3) The polarization functions centered on H are much more important than those centered on Pt in affecting the binding energy. (4) The two lowest states 2Δ5/2 and 2Σ1/2 are calculated to have almost exactly the same energy; either may be the lower one. The lowest 3/2 state is mixed 2(π+Δ)3/2 and lies a little higher in energy. (5) Both the first ionization potential and the ionization energy of the H-like level agree reasonably well with the experimental data. Finally, the absolute binding energy of PtH is 2.45 eV, to be compared with the experimental value of 3.44 eV. The discrepancy is due to our computational limitations.
Relationships between atomic chemical potentials, electrostatic potentials, and covalent radii
Authors: Politzer Peter , Parr Robert G. , Murphy Danny R.
Published: February 2003

The chemical potential μ of a many-electron system equals its total electrostatic potential V(r) at any point r at which δT/δρ =−δ(εX+εC)/δρ, where ρ is the electronic density and T, εX, and εC are, respectively, the kinetic, exchange, and correlation energy functionals. The Thomas–Fermi–Dirac theory predicts that this relationship is satisfied at all points at which ρ=0.008 72. This prediction has been tested for 25 ground-state atoms and has been found to give unsatisfactory results; the values of V(r) at the points in question are not in good agreement with μ, as approximated by −0.5(I+A), I and A being the atomic ionization potentials and electron affinities. However, an investigation of the radial distances rμ at which V(r) does equal μ shows that these are very close to the standard covalent radii of the atoms. (This supports an early electronegativity formulation by Gordy.) It is also shown that there is a very good correlation between μ and VQ, the electrostatic potential created at rμ by the nuclear and electronic charge within this radial distance from the nucleus. VQ is therefore a direct measure of the electronic rearranging power of the atom in the formation of chemical bonds. This further demonstrates the special significance of rμ with regard to the bonding properties of the atom.
Homogeneous nucleation and growth of ice from solutions. TTT curves, the nucleation rate, and the stable glass criterion
Authors: MacFarlane D. R. , Kadiyala R. K. , Angell C. A.
Published: February 2003

Using water-in-oil emulsion samples to avoid, for the most part, heterogeneous nucleation, the crystallization of ice from a series of aqueous LiCl solutions has been studied isothermally, using differential calorimetry to monitor the process through the release of the heat of crystallization. The classical form of the time–temperature transformation TTT curve has thereby been directly observed for the first time for cystallizing supercooled liquids, and its movement with concentration changes has been determined. The conditions of observation are such that each ∼3 μ diameter droplet is multiply nucleated during the time of observation. At temperatures well above the ‘‘nose’’ of the TTT curve, where multiple nucleation does not occur, a new phenomenon—in which the rate of crystallization increases with increasing temperature of observation—is encountered. It seems probable that this is due to some heterogeneous process perhaps involving a reaction at the water–oil–surfactant interface to account for the positive temperature coefficient. The results in the homogeneously nucleated region correlate well with the much longer time scale studies reported recently on the basis of time-dependent conductivity measurements. Using approximate diffusivity data for water in this system, the combined crystallization data can be analyzed to yield nucleation rates which are in reasonable agreement with the results of recent small angle neutron scattering studies on this system.
The equilibrium statistical mechanics of cooperative intramolecular behavior in molecules with coupled conformational/electronic transitions
Authors: Stratt Richard M. , Smithline Shepard J.
Published: February 2003

Molecules, such as conjugated polymers, whose electronic structure is significantly altered by conformational changes can be shown to have cooperative conformational transitions. In an isolated polymer, this long ranged cooperativity can be analyzed by representing the polymer as a one-dimensional gas of simple conformational defects that interact with a nearest-neighbor attraction. For a condensed phase, it is suggested that the same analysis remains valid but that the relevant defects become more complex. The resulting ‘‘thermodynamics’’ of the defects, along with their predicted spatial distribution, have experimental consequences for the UV/visible and Raman spectra of conjugated polymers— some aspects of which are discussed.
A simple new way to help speed up Monte Carlo convergence rates: Energy-scaled displacement Monte Carlo
Authors: Goldman Saul
Published: February 2003

A method we call energy-scaled displacement Monte Carlo (ESDMC) whose purpose is to improve sampling efficiency and thereby speed up convergence rates in Monte Carlo calculations is presented. The method involves scaling the maximum displacement a particle may make on a trial move to the particle’s configurational energy. The scaling is such that on the average, the most stable particles make the smallest moves and the most energetic particles the largest moves. The method is compared to Metropolis Monte Carlo (MMC) and Force Bias Monte Carlo of (FBMC) by applying all three methods to a dense Lennard-Jones fluid at two temperatures, and to hot ST2 water. The functions monitored as the Markov chains developed were, for the Lennard-Jones case: melting, radial distribution functions, internal energies, and heat capacities. For hot ST2 water, we monitored energies and heat capacities. The results suggest that ESDMC samples configuration space more efficiently than either MMC or FBMC in these systems for the biasing parameters used here. The benefit from using ESDMC seemed greatest for the Lennard-Jones systems.
Calculated ground-state structures of 13-molecule clusters of carbon dioxide, methane, benzene, cyclohexane, and naphthalene
Authors: van de Waal B. W.
Published: February 2003

The ground-state structures of 13-molecule clusters of carbon dioxide, methane, benzene, cyclohexane, and naphthalene have been calculated by potential energy minimization, employing -12-6-1 nonbonded atom–atom potential functions. In addition, seven-molecule clusters were calculated for carbon dioxide and benzene. In all cases, noncrystallographic pentagonal motifs were found to stabilize the structures. The coordination polyhedra of the 13-molecule clusters are close to regular icosahedra, much the same as has been reported earlier for noble-gas clusters. The factors, determining the ability of the clusters to adopt this conformation, are discussed.
Deuterium NMR of biaxial discotic liquid crystals
Authors: Goldfarb D. , Poupko R. , Luz Z. , Zimmermann H.
Published: February 2003

Deuterium NMR spectra of deuterated probe molecules dissolved in several discotic liquid crystals possessing biaxial mesophases are reported. The spectra exhibit typical features characteristic of biaxial phases. This is particularly manifested through the asymmetry parameter of the average quadrupole tensor. The effect is demonstrated on two types of biaxial discotic phases: (i) a rectangular Drd mesophase which appears in homologs of triphenylenehexa-n-alkanoates; and (ii) a tilted Dt mesophase which occurs in homologs of benzenehexa-n-alkanoates. The theory relating to the motional constants in biaxial phases and the asymmetry parameter of the quadrupole tensor (and other tensorial properties) is reviewed, and applied to some specific examples.
The series expansion for the concentration dependence of relaxation times for dilute polymer solutions
Authors: Muthukumar M.
Published: February 2003

We have applied our earlier cluster theory of polymer solution viscosity to calculate the concentration (c) dependence of the polymer relaxation times for θ solutions in the steady state limit. It is shown that the concentration dependences of the polymer mode relaxation times are of the form τμ=τ0μ[1+0.5450cAμ−1/2+0.2865Ac +0.2862c2A2μ−1/2+0.8636A2c2+ ⋅⋅⋅ ], μ is the polymer mode index, τ0μ is the infinite dilution lifetime, and A is a positive constant. A value of 0.6949 is obtained for the Higgins coefficient under θ conditions.
Nonreentrant and reentrant nematic liquid crystals under high pressure: A volumetric study
Authors: Johnson Cynthia S. , Collings Peter J.
Published: February 2003

The results of volumetric measurements under high pressure near three different phase transitions in heptyloxyazoxybenzene (70AB), a nonreentrant nematic liquid crystal, and octyloxycyanobiphenol (80CB), a reentrant nematic liquid crystal, are reported. Volume changes at the isotropic–nematic transition in these two liquid crystals are similar at low pressure, but behave differently at high pressure. Volume changes at the nonreentrant nematic–smectic C transition are an order of magnitude larger than at the reentrant nematic–smectic A transition. The volume dependence along these two nematic–smectic coexistence curves also reveals the stronger role played by attractive forces in these transitions as compared to the isotropic–nematic transition. Finally, these data do not support a previously reported nematic–smectic C-solid triple point in 70AB.
Observation of a metastable state of SO+2 by ion photodissociation spectroscopy
Authors: Thomas Timothy F. , Dale Fred , Paulson John F.
Published: February 2003

The photodissociation spectrum (PDS) of SO+2 for the process  SO+2+hν→SO++O is presented for the range 4900–5120 Å. The Ã 2 A2 state of SO2+ is proposed as the absorbing species and the results of a preliminary analysis of the well-defined vibrational structure in the PDS are given. The lifetime of this state is measured to be ∼25 μs. It is proposed that metastable absorption may be a significant contributor to the threshold region of PDS in general and the examples of O+3 and CO−3 are cited.
Rotational spectroscopic constants and structure of the mercury–hydrogen chloride van der Waals complex
Authors: Campbell E. J. , Shea J. A.
Published: February 2003

High resolution rotational spectra for nine isotopic species of a weakly bound 1:1 gas phase complex formed between mercury and hydrogen chloride have been measured using pulsed Fourier transform microwave spectroscopy carried out in a Fabry–Perot cavity. For 202Hg H35Cl we obtain: B̄0=998.006 4 (2), DJ=0.003 697 (1), and χaa (35Cl=−40.350(94), and for 202Hg H37Cl: B̄0=953.046 9 (8), DJ=0.003 375 (6), and χaa (37Cl=−31.894(400), in units of MHz. The proton is found to be between the two heavy atoms. The heavy atom separation in mercury–hydrogen chloride is 4.097 Å, giving a van der Waals radius for mercury of approximately 1.99 Å.
Multiple-collision rotational rainbow effect in molecule-surface scattering
Authors: Elber Ron , Gerber Robert B.
Published: February 2003

Classical calculations of molecular scattering from smooth surfaces show that multiple rainbow spikes in the rotational intensities may occur where the peaks correspond, respectively, to single, double, etc. collisions of the molecule with the repulsive potential. Unlike single collision rainbows, this effect may cause multiple peaks even for homonuclear diatomics.
Study of the dissociative ionization of nitrogen and oxygen by coincidence measurements
Authors: Feldmeier F. , Durchholz H. , Hofmann A.
Published: February 2003

The ion pair production has been studied for the gases N2 and O2, excited by 400 eV electrons. For the detection of the ions, a channel electron multiplier and a quadrupole mass spectrometer were operated in coincidence. The ion energy was measured by the time-of-flight method. We found groups of ion pairs with kinetic energies of 7.8, 10.6, and 15.0 eV for nitrogen and of 7.6, 10.6, and 16.8 eV for oxygen. From our data, we conclude that about half of all ions with kinetic energies higher than 2 eV originate from ion pair production. The process N3+2→N2++N+ was observed. The N+ energy distribution starting at about 8 eV passes through a broad maximum at about 16 eV.
FTIR spectra of water–hydrogen fluoride complexes in solid argon. Evidence for inversion doubling in the HF librational modes of H2O– –HF
Authors: Andrews Lester , Johnson Gary L.
Published: February 2003

Co-condensation of dilute Ar/HF and Ar/H2O samples at 12 K produces a number of sharp new infrared absorptions. The major species, which exhibits a strong 3554.7 cm−1 band and two quartets beginning at 753.1 and 635.6 cm−1, is identified as H2O– –HF. Isotopic substitution in the base submolecule changes the splitting in the latter multiplets and provides evidence for inversion doubling of the H–F librational modes in the H2O– –HF complex. The reverse complex HF– –HOH, identified at 3915.5 cm−1, exhibits a stronger interaction when HOH is replaced by DOD. Two H–F stretching fundamentals, which show small D2O shifts, increased markedly on sample warming and are assigned to the 1:2 complex H2O– –HF– –HF with an open structure.
Analysis of observables in diagonally polarized light scattering experiments
Authors: McClain W. M. , Harris Robert A.
Published: February 2003

We analyze the polarization of light scattered from an ensemble of stationary, randomly oriented molecules of arbitrary size, for ‘‘diagonally’’ polarized incident light (linearly polarized at ±45° to the scattering plane). The results are expressed in terms of the ‘‘diagonal modulation,’’ the change in scattered intensity when the incident polarization switches from +45° to −45°. We use the exact nonrelativistic operators for the interaction of light and matter, and we use no wave function approximations. The diagonal modulation is expressed as a superposition of four independent observables, which may be separated by polarization filters in the observation channel. Three of these are found to posses interesting characteristics after the classical orientation average is taken: (a) they vanish when the damping constants of the molecule are set to zero; and (b) they vanish in the limit of a dipolar scattering tensor. This analysis therefore suggests experiments in which combinations of damping constants and higher transition multipoles might be directly observed.
Long range behavior of the gerade states near the 2P3/2+ 2P3/2 iodine dissociation limit by laser-induced-fluorescence Fourier-transform spectroscopy
Authors: Martin F. , Churassy S. , Bacis R. , Field R. W. , Vergès J.
Published: February 2003

The near infrared LIF–FTS spectra from the I2 B 0u+ state, excited by an argon ion laser and recorded by a high resolution Fourier-transform spectrometer, contain information about perturbations between the gerade states converging to the I2→2I(2P3/2) dissociation limit. The observed perturbation interactions are sampled at internuclear distances near 5 Å and are interpreted in a separated atom (I2=Ia+Ib; ψI2=φaφb; φa=‖ ja=3/2, ma〉) basis set. Near r=5 Å the X 0g+ and a′ 0g+ states are found to have predominant ma=−mb=±1/2 and ma=−mb=±3/2 character, respectively, but with slight ‖m‖=1/2∼‖m‖=3/2 mixing. In this pure ‖m‖ basis, S=sa+sb and Jatomic=ja+jb are not well defined, but in the limit of complete ‖m‖=1/2∼‖m‖= 3/2 mixing, S and Jatomic are well defined. The behavior of three gerade states (X 0g+, a′ 0g+, a 1g) at large internuclear distance has been analyzed using the long range theory of LeRoy and Bernstein. The results are in fair agreement with theoretical predictions, and give a direct and precise determination of the X state well depth, D00=12 440.083±0.145 cm−1.
Vibrational-rotational deexcitation of HF in collision with He
Authors: Bieniek Ronald J.
Published: February 2003

State-to-state cross sections are reported for vibrational-rotational transitions for HF in collisions with He, at collisional energies of 0.5 and 1.0 eV. These were computed within the infinite-order sudden (IOS) approximation using adiabatic, distorted-wave techniques. Values are tabulated for the vibrational-rotational deexcitation sequences (v, j) → (v–1, 0), with v=1, 2, 3, 4 and j=0 – 40. These quenching cross sections can be used in conjunction with IOS factorization formulas to compute VRT cross sections for final rotational states other than jf=0. In addition to IOS results, vibrational quenching cross sections were computed using the much more simple breathing-sphere technique. The breathing-sphere results compare favorably to the more accurate IOS results, particularly as to energy dependence. This suggests a simple method of utilizing known quenching cross sections to predict values for different vibrational levels and/or collisional energies.
Reduced dimensionality quantum rate constants for the D+H2(v=0) and D+H2(v=1) reactions on the LSTH surface
Authors: Bowman Joel M. , Lee Ki Tung , Walker Robert B.
Published: February 2003

Collinear exact quantum reaction probabilities for the D+H2(v=0) and D+H2(v=1) reactions were calculated using the ab initio surface of Liu and Siegbahn (as fit by Truhlar and Horowitz) with an adiabatic treatment of the ground state bend. These probabilities are used to obtain approximate three-dimensional thermal rate constants which are compared with experiment and other calculations.
Chemiluminescent reactions of fluorine and chlorine atoms with bromine azide
Authors: Coombe R. D. , Lam C. H.-T.
Published: February 2003

Chemiluminescence from the reactions of fluorine and chlorine atoms with BrN3 has been observed in a discharge-flow apparatus. The F+BrN3 reaction produces electronically excited BrF(B 3Π0+) in low vibrational levels (v≤2), as well as excited NBr(b 1Σ+). The only emission observed from the Cl+BrN3 reaction is the b 1Σ+→X 3Σ− transition in NBr. The data are consistent with mechanisms involving attack of the halogen atoms on the nitrogen chain of the azide. The vibrational excitation of the emitting products suggests the heat of formation of BrN3 to be 131±2 kcal mol−1.
Low-frequency Raman scattering from vitreous and molten B2O3
Authors: Walrafen G. E. , Hokmabadi M. S. , Krishnan P. N. , Guha S. , Munro R. G.
Published: February 2003

Integrated Raman intensities of bands between ∼0–900 cm−1 have been obtained for molten B2O3 from 288–906 °C. Emphasis was placed on the highly depolarized low-frequency contour (adjoining the exciting line) which is intense, broad, skewed to high frequencies, and displays a weak, broad, shoulder centered between ∼100–150 cm−1. The total integrated contour intensity from 0–300 cm−1, as well as the peak intensity, obey the one-phonon Bose–Einstein (BE) relation within 6%. The integrated intensity of the polarized 800 cm−1 boroxol ring (B3O6) line, however, decreases with temperature rise, in quantitative agreement with previous work [J. Chem. Phys. 72, 113 (1980)], and correction using neutron scattering results yields a ΔH° value of 5.0 kcal/mol ring rupture. The low-frequency contour probably involves nonsymmetric collective modes of very large assemblies, cages, or rings, as well as librations of B3O6 groups (∼100–150 cm−1), and the fact that the BE distribution is obeyed at temperatures for which B3O6 ring rupture is important indicates that such large temporal aggregates are involved that whether BO3 triangles or B3O6 rings are present may be nearly irrelevant. The peak frequency of the BE corrected low-frequency contour was also observed to be constant, ∼50 cm−1, from −265 to ∼200 °C, but it falls rapidly near TG≊280 °C, and then reaches a ∼27 cm−1 limit above 400 °C. This suggests that the force constants of the low-frequency modes decrease upon melting because the anharmonicity increases due to the increased melt free volume produced by boroxol ring rupture. However, most features of the low-frequency Raman data, including depolarization, may be explained in equivalent terms of ultrasonic modes and viscoelastic stress wave theory.
Subpicosecond relaxation study of malachite green using a three-laser frequency-domain technique
Authors: Trebino Rick , Siegman A. E.
Published: February 2003

We report measurements of the ground-state-recovery dynamics of malachite green in water, made using a new three-laser tunable-induced-grating technique. We observe a recovery consistent with either the sum of two decaying exponentials (0.78±0.10 and 7.4±3.0 ps) or with a uniform range of exponentials (0.34±0.04 to 7.2±3.0 ps). Our three-frequency induced-grating method provides a new and useful approach for studying picosecond and femtosecond atomic and molecular processes, working in the frequency rather than the time domain.
The effect of isotopic substitution on the collisional quenching of vibronically excited CO+
Authors: Katayama D. H. , Welsh J. A.
Published: February 2003

Rovibronic levels of the A 2Πi state for 12C16O+ and 13C16O+ have been selectively excited by a pulsed, tunable dye laser and their time resolved fluorescence obtained as a function of helium pressure. These ions are formed by reaction of neutral carbon monoxide with helium metastable atoms created in a dc discharge. Since 13CO+ has essentially the same potential energy curves as 12CO+, but differs primarily in its vibrational energy spacings, this experiment accentuates the role, in the collisional deactivation process, of the high lying ground state vibrational levels which are adjacent to the laser populated vibronic levels of the A 2Πi state. Quenching rates are determined for the v′=0, 1, and 2 levels which have relatively insignificant isotope shifts of a few wave numbers for the two isotopes. The difference in rates for the two isotopic ions demonstrates the importance of the positions for the high lying v″=10 and 11 ground state levels which have large isotope shifts of hundreds of wave numbers. A discussion of the deactivation process is given in terms of perturbations, Franck–Condon factors, energy gaps, and other considerations.
ESR spectrum of ClO (2Π3/2) isolated in a CO2 matrix
Authors: Trainer M. , Helten M. , Knapska D.
Published: February 2003

Upon isolation of ClO in a CO2 matrix at 10 K, a highly anisotropic ESR spectrum is observed which is attributed to ClO. This might be the first observation of a neutral radical with a 2Π ground state in a nonpolar matrix. Some of the structure discernible on the spectrum at 10 K may be related to ClO at different trapping sites. After annealing the sample at T≳45 K, the radical concentration diminishes and the g⊥ peak of the most prominent site splits into four peaks which may correspond to the hyperfine splitting of ClO. The spectrum can be explained by the following g and A tensors, gx=1.889, gy=1.899, gz=2.66 and Ax=111 MHz, Ay≤20 MHz, Az≤55 MHz. In a simple crystal field model these values are compared with molecular parameters of ClO deduced from gas phase spectra.
Lifetime measurements of the B 3Πg state of N2 using laser excitation
Authors: Eyler E. E. , Pipkin F. M.
Published: February 2003

A chopped cw dye laser has been used to excite selected levels of the B 3Πg state of N2 in a molecular beam of A 3Σu+ state metastables. Laser-induced fluorescence was observed from the vibrational levels v=5 through v=12, and a photomultiplier was used in conjunction with a microcomputer system to perform time-resolved detection of the decay light. The lifetimes have been measured to an accuracy of about 3%. They show a smooth decline from 5.87 μs for v=5 to 4.11 μs for v=12. No dependence on rotational level was observed, and no contributions to the B state decay were found from intrasystem cascading of the form B→W 3Δu→B→A 3Σu+.
Thermal electron attachment to van der Waals molecules (O2 ⋅ C2H6)
Authors: Toriumi Minoru , Hatano Yoshihiko
Published: February 2003

Using microwave conductivity technique with pulse radiolysis, thermal electron attachment in O2–C2H6 mixtures is studied at various temperatures (−120–100 °C) and C2H6 densities (7×1017–3×1019 molecules cm−3). van der Waals (vdW) molecules (O2 ⋅ M) (M; a third-body molecule C2H6) are clearly shown to contribute to electron attachment even at low densities of M. A large rate constant value for the initial electron attachment to vdW molecules, k5=(1.9+1.0−0.6 ×10−4(1/T)3/2 exp[−(3.5±0.6)×102/T]cm3 s−1, where T is the absolute temperature, is elucidated by a smaller resonance energy (30±5) meV as compared with that of an isolated oxygen molecule and by a larger resonance width of (O2 ⋅C2H6), (4.5+2.5−1.5)×10−4 eV. A dissociative electron attachment to vdW molecules is negligible in the vdW molecule mechanism.
Path integral solutions for Fokker–Planck conditional propagators in nonequilibrium systems: Catastrophic divergences of the Onsager–Machlup–Laplace approximation
Authors: Hunt Paul M. , Hunt Katharine L. C. , Ross John
Published: February 2003

When the conditional propagator for a single-variable Fokker–Planck equation is represented in functional path integral form, it separates into a path-independent thermodynamic factor and a reversible, time-dependent kinetic factor. The validity of the Onsager–Machlup–Laplace (OML) approximation to the conditional propagator is determined solely by the mechanical potential associated with the kinetic factor. The OML approximation is exact if the underlying mechanical force is linear; Hongler’s model exemplifies a class of nonlinear Fokker–Planck equations that are solved exactly by the OML approximation, because the nonlinearity is confined to the thermodynamic factor. Contrary to earlier suggestions, neither the existence of turning points in the mean paths nor limited information content of the path of least thermodynamic action indicates the breakdown of the OML approximation. When classical paths on the mechanical potential surface coalesce, however, the OML approximation breaks down catastrophically. Divergences analogous to the classical catastrophes of scattering theory are found for extremal path durations; these extremal times must exist whenever the underlying mechanical potential surface possesses two or more nonidentical maxima. Path coalescence and the consequent divergence of the OML approximation are illustrated for a system with the deterministic kinetics of the Schlögl model and constant probability diffusion coefficient. Catastrophic divergences of the OML approximation may be predicted and classified by generalization of similar problems found in the stationary phase approximation of semiclassical scattering theory; additionally, methods of semiclassical collision theory suggest approaches for eliminating erroneous divergences of the conditional propagator for nonequilibrium thermodynamic systems.
Models for the hydrogen atom confined within crystalline quartz
Authors: Goshen S. , Friedman M. , Thieberger R. , Weil J. A.
Published: February 2003

Simple cylindrical models of a hydrogen atom confined in crystalline quartz are considered. The isotropic and anisotropic components of the hyperfine splitting are evaluated by solving numerically the appropriate two-dimensional Schrödinger equation, utilizing an adaptation of a finite element package previously described. The results show good agreement with electron paramagnetic resonance data, and given an estimate of d-orbital admixture in the H-atom ground state orbital.
Variational cellular method for polyatomic molecules: SiH4
Authors: Machado Wanda V. M. , Ferreira Luiz G. , De Siqueira Manoel L.
Published: February 2003

We review the variational cellular method for polyatomic systems and discuss some of its most interesting features. This method may be as fast as the multiple scattering method but is free from the defects of the muffin-tin potential and charge density. Thus it is a method very attractive for large systems such as solids and large molecules, and capable of giving calculated results with a degree of precision at least as good as those of Hartree–Fock calculations. The method is applied to SiH4, where we explore its capabilities with excellent results.
Uniform semiclassical theory of avoided crossings
Authors: Uzer T. , Noid D. W. , Marcus R. A.
Published: February 2003

Avoided crossings influence spectra and intramolecular redistribution of energy. A semiclassical theory of these avoided crossings shows that when primitive semiclassical eigenvalues are plotted vs a parameter in the Hamiltonian they cross instead of avoiding each other. The trajectories for each are connected by a classically forbidden path. To obtain the avoided crossing behavior, a uniform semiclassical theory of avoided crossings is presented in this article for the case where that behavior is generated by a classical resonance. A low order perturbation theory expression is used as the basis for a functional form for the treatment. The parameters in the expression are evaluated from canonical invariants (phase integrals) obtained from classical trajectory data. The results are compared with quantum mechanical results for the splitting, and reasonable agreement is obtained. Other advantages of the uniform method are described.
Theoretical results for dielectric and structural properties of aqueous electrolytes. The influence of ion size and charge
Authors: Kusalik P. G. , Patey G. N.
Published: February 2003

The present paper describes a theoretical investigation of aqueous electrolytes in the infinite dilution limit. The linearized hypernetted chain theory is applied to solutions of hard spherical ions in a waterlike solvent at 25 °C and the properties of solution are studied as a function of ion size and charge. We examine both dynamical and equilibrium contributions to the apparent ‘‘dielectric constant’’ of solution and compare with previous theoretical calculations as well as with experimental measurements. Ion–solvent correlation functions and ion–ion potentials of mean force for several common electrolytes are also presented and discussed.
Investigation of the conformational change in triphenylmethane dyes via polarization spectroscopy
Authors: Saikan S. , Sei J.
Published: February 2003

Internal conversion process in triphenylmethane dyes caused by the conformational change has been investigated using polarization spectroscopy. The relaxation times of these dyes in water–glycerol mixture were found to vary with solvent viscosity according to a η2/3 viscosity dependence at below 50 cP. Besides, it was observed that for all of the six triphenylmethane dyes investigated here, the relaxation times vary according to the size of the phenyl ring para-substituent.
Determination of the 14N quadrupole coupling tensor and the 13C chemical shielding tensors in a single crystal of l-serine monohydrate
Authors: Naito A. , Ganapathy S. , Raghunathan P. , McDowell C. A.
Published: February 2003

The 14N quadrupole coupling tensor for the NH3+ nitrogen nucleus in a single crystal of l-serine monohydrate was completely determined. The quadrupole coupling constant, and the asymmetry parameter, were evaluated to be e2Qq/h=1.069 MHz and η=0.214 at room temperature by measuring the angular variation of the proton-enhanced 14N NMR spectra about the three experimental axes. It was found that the direction of the largest principal value of the 14N quadrupole coupling tensor is at an angle of 3.5° to the direction of the C–N bond. The sign of the 14N quadrupole coupling constant was determined to be positive by analyzing the 13C–14N dipolar splitting pattern in the 13C NMR signal of the Cα carbon. The 13C chemical shielding tensors for three chemically different carbon nuclei, namely COO−, Cα, and Cβ were determined and assigned to the molecule in the unit cell by inspecting the 13C–14N dipolar interaction rather than relying only on the local symmetry. The most shielded direction of the COO− carbon is perpendicular to the O–C–O plane, and the least shielded direction is parallel to the Cα–C bond direction. It was found that the most shielded direction for the Cβ carbon is almost parallel to the Cβ–O bond direction.
IR-induced photorotamerization of allyl alcohol in low-temperature matrices and ab initio calculations
Authors: Aspiala A. , Lotta T. , Murto J. , Räsänen M.
Published: February 2003

The infrared regions νOH, τOH, and 950–900 cm−1 of allyl alcohol (2-propen-l-ol) were studied in low-temperature Ar, Kr, Xe, N2, and CO matrices. A fast IR-induced process and a similar slow dark process were found. It is concluded that the photoprocess is a rotamerization (obviously Cg→Gg′), since the process was similar in all five matrix media and also for other allyl compounds. The photoprocess was found to obey the first order rate law. Radiation from 9000 to below 2600 cm−1 was found to be active in initiating the process, especially the radiation corresponding to the νOH and methylenic νCH2 regions. The process is very fast in xenon. A possible mechanism for the process is discussed. To aid the interpretation of the results, ab initio calculations were carried out. All five conformers of allyl alcohol were optimized on the 4-31G level, and the corresponding semirigid potential energy curves of the torsional coordinates were constructed. Some calculations were carried out also on the 6-31G**, MP/4-31G, and CID/4-31G levels, using the 4-31G geometries. These calculations indicated that the conformers Gg′ and Cg are the lowest-energy species of quite similar energies.
Radiative and predissociative lifetimes of the V′=0 level of the A 2Σ+ state of SH and SD from chemical and spectroscopic studies
Authors: Friedl Randall R. , Brune Wm. H. , Anderson James G.
Published: February 2003

Predissociation is observed to occur throughout the V′=0 level of the A 2Σ+ states of SH and SD, based upon laser-induced fluorescence measurements obtained in conjunction with knowledge of the absolute concentrations of both radicals via chemical titration in a fast flow reactor in the pressure range 1–5 Torr. By comparison of results with those obtained in the same system for OH, a radical for which both the kinetics and spectroscopy are well defined, predissociative and radiative lifetimes are calculated to be 3 and 820 ns for SH; 260 and 730 ns for SD.
Nonlinear resonances and vibrational energy flow in model hydrocarbon chains
Authors: Hutchinson John S. , Reinhardt William P. , Hynes James T.
Published: February 2003

Intramolecular energy transfer in hydrocarbons is modeled with an anharmonic HC bond coupled to a chain of harmonically coupled carbon atoms. The HC stretch is initially excited to various vibrational states and the flow of energy from the HC bond is observed. It is found that, at sufficiently high excitation, vibrational energy flow is irreversible and occurs on a time scale of roughly 100 fs, independent of chain length. This corresponds very well to experimentally observed spectral bandwidths. By analyzing the motion in a set of natural dynamical modes, it is shown that this energy transfer is due to sequential nonlinear resonances in the chain. Analytic modeling of the mode–mode couplings then provides a simple approximate description of the energy transfer process.
Vibrational distributions of AlF(a 3Π) produced by crossed-beam collisions of Al and F2 at two kinetic energies
Authors: Ishikawa Toshiaki , Parson J. M.
Published: February 2003

Chemiluminescent spectra of AlF(a 3Π) produced in the reaction of Al with an F2 nozzle beam are reported at two different nozzle temperatures. From spectral simulations treating AlF(a 3Π) in the intermediate case between Hund’s cases (a) and (b), it is found that the peak position of the derived vibrational distribution is shifted to a higher vibrational state for the higher temperature case. Both vibrational distributions give linear surprisal plots with nearly the same highly negative slope. In order to explain the shift of the vibrational distribution, a collinear model calculation for multiple nonadiabatic processes is proposed.
Excited state dynamics of NO3
Authors: Nelson H. H. , Pasternack Louise , McDonald J. R.
Published: February 2003

The fluorescence decay of NO3 excited to vibronic levels between the origin at 661.9 and ∼606 nm is measured and found to be nonexponential. An exponential fit to the long-lived portion of the decay gives an apparent, collision-free lifetime of 340±20 μs. Electronic quenching rates have been measured for a variety of collision partners including He, N2, O2, C3H8, and HNO3. Our results are interpreted in terms of the Douglas effect, i.e., an extensive coupling of excited electronic levels with nonemissive vibronic levels of the ground electronic state. This coupling is likely responsible for the anomalously long lifetime and the apparent diffuseness of the absorption spectrum.
Raman intensities of Fermi diads. I. Overtones in resonance with nondegenerate fundamentals
Authors: Montero S.
Published: February 2003

Expressions for the vibrational transition moments of the molecular polarizability involved in Fermi resonances of the type 2νs:νr (qs=single, doubly, or triply degenerate mode; qr=nondegenerate mode) are reported as a function of the observed splittings ‖X‖ and of the cubic force constant krss. Fermi resonances in H2O, CO2, CH4, and CD4 are interpreted in terms of bond polarizability parameters.
Inner-valence shell photoionization of Ar2, Ar3, Kr2, and Kr3
Authors: White M. G. , Grover J. R.
Published: February 2003

The inner-valence shell photoionization spectra (420<λ<500 Å) of Ar2, Ar3, Kr2, and Kr3 have been obtained with a molecular beam apparatus using synchrotron radiation from the VUV storage ring at the National Synchrotron Light Source. The photoionization spectra exhibit regular series of window resonances which are closely associated with the ms→np Rydberg series in atomic Ar(m=3) and Kr(m=4). Vertical ionization potentials of the lowest ionic state in the molecular ms regions were obtained by series extrapolation and these were used to estimate the well depths in the Franck–Condon region and dissociation energies. Assignments of the observed Rydberg transitions were made by analogy with similar excitations in He2 and the group II and II B metal dimers. For Ar+2 and Kr+2, the observed structure is tentatively assigned to 1u (1Πu) and O+u (1Σu+) states which correlate with the ‘‘promoted’’ ndπg and ndσg series. Plausible assignments for the trimer spectra are also discussed.