bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactions of ground-state and metastable O2+ ions with He, O2, N2, and CO2 at thermal energies
Authors: Johnsen Rainer , Biondi Manfred A.
Published: February 2003

Evidence is presented that some previous studies of reactions of O2+ ions with various atoms and molecules referred to ion samples composed in part of ions in metastable (1D and/or 1S) states. This finding resolves the 3 orders of magnitude discrepancy between previous experimental and calculated rate coefficients for the O2+(3P)+He charge transfer process. Using a drift tube to distinguish, via arrival time differences, ground-state O2+(3P) and metastable ions, a rate coefficient of (3.5±1.5)×10−11 cm3/sec is obtained for the reaction, in good agreement with that obtained from ab initio theoretical calculations. Previous conclusions concerning reactions of O2+ with O2 and N2, however, remain valid since the difference in reactivity of ground-state and metastable O2+ ions appears to be negligible in this case. The rate coefficient for the reaction O2++CO2 has been determined to be (2±0.5)×10−9 cm3/sec for ions either in the ground-state or in metastable states.
A complete determination of vibrational energy transfer pathways in CH2D2 for states below 3000 cm−1: A laser induced fluorescence study
Authors: Moser Mark , Apkarian V. A. , Weitz Eric
Published: February 2003

Vibrational energy transfer processes in dideuteromethane were studied using a variety of complementary, laser induced fluorescence techniques. The time evolution of population in all infrared active fundamentals, except ν4 and ν7, were monitored following three different initial conditions: excess population in ν7, excess population in a 2000 cm−1 state, and simultaneous excess population in ν4 and a 2000 cm−1 state. These initial perturbations were achieved by irradiating the molecule with the R(22), P(24), and P(38) lines of the 9.6μ CO2 laser band. Experiments were performed on pure CH2D2, CH2D2 rare gas, and CH2D2–O2 mixtures in order to elucidate the vibrational equilibration pathways in the parent molecule. The experimental studies afforded a complete map of the energy transfer pathways between the fundamentals and yielded rate constant for some specific V–V steps. The validity of these conclusions were confirmed by numerical modeling of the system. Theoretical calculations based on the Sharma and Brau, and Schwartz, Slawsky, and Herzfeld formulations were performed to conclude that V–V processes in CH2D2 are governed almost exclusively by hard core collisions.
Ultraviolet laser photolysis: Primary photochemistry of Fe(CO)5 in PF3
Authors: Nathanson Gilbert , Gitlin Barbara , Rosan Alan M. , Yardley James T.
Published: February 2003

We have studied the photolysis of mixtures of Fe(CO)5 and PF3 with a KrF laser operating at 248 nm. The product yields of Fe(CO)2(PF3)3, Fe(CO)3(PF3)2, and Fe(CO)4PF3 have been measured as a function of laser fluence and mixture composition. A simple kinetic model appears to explain semiquantitatively the observed dependence of product yield upon mixture composition. This model has allowed us to determine that the primary photochemical yields at 248 nm for the fragments Fe(CO)2, Fe(CO)3, and Fe(CO)4 over the fluence range 0.1–200 mJ/cm2 are 0.55, 0.35, and 0.10, respectively, independent of laser fluence. This fragmentation results from a simple one-photon absorption process. We have found that CO ligands are exchanged readily in collisions of the above fragments with Fe(CO)5, with a bimolecular rate constant relative to that for trapping by PF3 of kM/kT=4. We have also found that these primary photofragments react with Fe(CO)5 to form unobserved products with a rate constant (relative to that for trapping by PF3) of kQ/kT=7.
Temperature dependence as a probe of intramolecular relaxation in the infrared multiphoton excitation of CF2Cl2
Authors: Chou Jim-Son J. , Grant Edward R.
Published: February 2003

Systematic variations have been seen as a function of temperature and irradiation frequency in the multiphoton dissociative product yields for CF2Cl2. Thermal shifts in the small signal absorption spectrum do not account for the observed effects, which are attributed instead to an interference between initial thermal vibrational excitation and laser pumping through the anharmonic bottle neck. A simple stochastic classical model for the excitation of an active oscillator coupled to an intramolecular heat bath is developed to explain our results. Temperature dependence in this model comes from the dependence of the dephasing rate in the driven system on the initial energy of the heat bath. Comparison of the model with experiment yields good agreement with characteristic times for our derived dephasing parameter of 0.1 nsec at 300 °K and 2 psec at 500 °K. It is predicted that under certain conditions of irradiation frequency and pressure, enhanced relaxation will lead to increased primary isotope separation efficiency at elevated temperatures.
Jet-cooled naphthalene. II. Single vibronic level fluorescence spectra
Authors: Beck S. M. , Hopkins J. B. , Powers D. E. , Smalley R. E.
Published: February 2003

Single vibronic level fluorescence spectra have been measured for naphthalene cooled in a supersonic free jet. Ten spectra in all have been recorded, the excitation energies ranging from 0 to 4029 cm−1 above the 1B3u(ππ*)←1Ag origin. These results reveal extensive intramolecular vibrational redistribution (IVR) occurring in the absence of collision on a time scale much faster than fluorescence even at vibrational energies as low as 2570 cm−1. Comparison of the observed spectra with model calculations shows that this IVR process involves most of the harmonic overtone/combination basis states of overall b1g symmetry having energies within the absorption line profile.
Absorption and emission of 2,12-dimethyltridecahexaene
Authors: Auerbach Roy A. , Christensen Ronald L. , Granville Mark F. , Kohler Bryan E.
Published: February 2003

We have obtained well resolved optical spectra of a simple, methyl substituted hexaene at 4.2 K. These spectra provide detailed information on the vibronic levels associated with the ground (1 1Ag) and first excited (2 1Ag) singlet electronic states. The strongest vibronic feature, due to a totally symmetric CC double bond stretch, shifts from 1576 cm−1 in the 1 1Ag state to 1779 cm−1 in the 2 1Ag state. This shift, not accounted for by current theoretical descriptions of polyene electronic states at the crude adiabatic level, may be rationalized as a manifestation of vibronic coupling between the ground and first excited singlet states.
Vibrational relaxation and the statistics of triplet states and matrix elements in methylglyoxal
Authors: Gurnick M. , Chaiken J. , McDonald J. D.
Published: February 2003

Quantum beat spectroscopy is presently the only direct probe of intramolecular couplings and spacings between individual highly exicted states of polyatomic molecules with state densities of the order of 1000 states per wave number. We have applied this method to methylglyoxal in an attempt to discover if there are preferred pathways of intramolecular energy flow and if it is possible, in this and similar molecules, to localize energy in particular bonds. The method has enough resolution to allow observation of hyperfine splittings of excited triplet states as well as states which are different vibrationally excited triplet states. Consequently, the vibrational coupling and spacing trends are slightly obscured. However, our data indicate that there are no selection rules for intersystem crossing other than rigorous conservation laws and a requirement for conserving nuclear spin states. The dependence on the initial rotational angular momentum N is evidently not important at all at low N but might be useful at high N.
Crystal field effects on the vibronic properties of the Jahn–Teller unstable S1 state of zinc porphin
Authors: Canters G. W.
Published: February 2003

The spacings in the vibrational progression associated with a Jahn–Teller (JT) active normal coordinate in the S1 state of a metalloporphin (MeP) and the intensities and polarizations of the corresponding S1–S0 optical transitions have been calculated as a function of the b1g and b2g strain components (δ1 and δ2 respectively) of the crystal field. The numerical results obtained for the specific case of zinc porphin (ZnP) demonstrate that the vibronic spacing and the optical properties are noticeably affected by the b2g strain component of the crystal field. From previous experimental data on ZnP in the so-called A site of n-octane (n-C8) and n-decane (n-C10) it is deduced that δ2<15 cm−1 (n-C8) and <10 cm−1 (n-C10)≪δ1. A preliminary analysis of the experimental data on ZnP in anthracene demonstrates that here the reverse situation may obtain, i.e., that δ1≪δ2.
An EPR study of the dichlorofluoromethyl radical and other chlorinated radicals in irradiated dichlorofluoroacetamide single crystals
Authors: Wang Han-Ching , Pace M. Dale , Kispert Lowell D.
Published: February 2003

An electron paramagnetic resonance (EPR) study of the ⋅CCl2F radical trapped in dichlorofluoroacetamide single crystals irradiated with x-rays at 77 K and later warmed to 173 K is reported. At 173 K, the two α-chlorine couplings are equivalent, indicating that the ⋅CCl2F radical is rotating about an axis of symmetry. The fluorine-19 and chlorine-35 hyperfine couplings are found to be Az=193, Ax=28, Ay=30 G and Az=22.5, Ax=5.0, Ay=5.0 G, respectively. Two molecular forms of the ⋅CClFCONH2 radical were also observed. Comparing the crystal structure derived bond directions of the parent molecule to those of the coupling constants indicates that ⋅CCl2F rotates about an axis approximately parallel to the original C–C bond direction while considerable reorientation occurs following chlorine loss to form ⋅CClFCONH2.
Ultraviolet absorption and photoelectron spectra of the oximes and O-methyloximes of a series of polyenic Schiff bases. Relation to visual pigments
Authors: Dupuis P. , Roberge R. , Sandorfy C. , Vocelle D.
Published: February 2003

The HeI photoelectron and ultraviolet absorption spectra of the oximes and O-methyloximes of a series of conjugated Schiff bases have been determined. The importance of the low ionization potentials of these compounds is stressed, especially in connection with the chromophore of visual pigments. The location of the (π,π*), (n,π*), and lowest Rydberg bands in the UV spectra is discussed.
A pseudopotential study of the iron-series transition metal hydrides
Authors: Das G.
Published: February 2003

Using a modified Phillips–Kleinman pseudopotential method, the nature of binding in the iron-series transition metal hydrides is studied. While no (or limited types of) atomic correlation terms are considered, the wave functions contain all important molecular correlation effects. The spectroscopic constants derived theoretically agree well in all cases with those available experimentally. The agreement with some previous theoretical results, however, is poor.
On the application of MCSCF models for the calculation of spectroscopic constants for several low lying states of O2+
Authors: Ruttink Paul J. A. , van Lenthe Joop H.
Published: February 2003

The behavior of multiconfiguration self-consistent field (MCSCF) and restricted configuration interaction (CI) wave functions are investigated for the case of a homonuclear positive diatomic, i.e., O2+. Both molecular orbital (MO) and orthogonalized valence bond (VB) models are used. In the MO model the normal symmetry restrictions (D∞h) are imposed on the orbital while these are lifted in the VB model, thus permitting a more correct behavior on dissociation. Using He2+ as a prototype system, the customary partitioning of the MO configuration set into subsets corresponding to proper dissociation, molecular extra correlation, and atomic correlation is examined. It is shown that when the orbitals are optimized this partitioning is no longer valid, i.e., atomic correlation cannot be excluded. For O2+ the proper dissociation function in the MO model is rather unwieldy. This arises because allowance must be made for the difference between the atomic orbitals of O and O+. We therefore use, as our starting point in the configuration selection procedure, the much simpler base wave function which corresponds to a correct dissociation limit in a minimal basis set. The VB model does not suffer from these difficulties. However, due to the absence of symmetry restrictions, there is a symmetry breakdown in the VB calculation in the range 1.5<R<2.5 Å caused by a transition from D∞h symmetry in the equilibrium conformation to effective C∞v symmetry for R = ∞. Using a double zeta + polarization basis, satisfactory results were obtained for the spectroscopic constants of four of the five lowest lying states. viz., 2Πg, 4Πu, 2Πu, and 2Φu, via MO–MCSCF calculations using the base wave function augmented by all valence shell (2p) configurations of the correct symmetry. For the 4Πu and for the 4Σg− state (for which poor results were obtained in the MO model) VB–CI calculations were also performed. In these calculations all single excitations from a reference state consisting of the proper dissociation function and all valence shell (2p) C∞v configurations were included, leading to satisfactory agreement with experimental data.
Deuterium NMR and molecular ordering in the cholesteryl alkanoates mesophases
Authors: Luz Z. , Poupko R. , Samulski E. T.
Published: February 2003

Deuterium NMR of the smectic, cholesteric, and the blue phases of two members of the cholesteryl alkanoate series, viz. cholesteryl nonanoate and cholesteryl myristate, are reported. Deuterium spectra of probe molecules dissolved in these liquid crystals are also discussed. The measurements were made at 63 kG (42 MHz). At this high field both the smectic and cholesteric phases can be fully or partially aligned with the director oriented predominantly perpendicular to the magnetic field. The results provide information on the order parameter in the various phases and on the ordering process of the helical axis. It is found that the smectic mesophase forms well oriented domains, but that the cholesteric phase consists of two types of domains: (i) uniformly oriented domains with the helical axis parallel to the magnetic field and (ii) randomly oriented domains apparently with focal conic texture. The relative abundance of the two types of domains depends on the thermal history of the sample and other parameters. The spectral line shapes of the randomly oriented cholesteric samples depend on the molecular diffusion rate and on the cholesteric pitch length. A theory of the magnetic resonance line shape due to reorientational diffusion of the director about the cholesteric pitch axis is presented and used for the quantitative interpretation of the experimental results.
Linewidth and viscosity of isobutyric acid—deuterium oxide mixtures of critical composition above and below the phase separation temperature
Authors: Kalbskof B. , Woerman D. , Chu B. , Gulari Erdogan
Published: February 2003

Linewidth and visocity measurement covering the single phase and two phase region were made. Comparison of the data with the mode–mode coupling results of Kawasaki show good agreement with no adjustable parameters. In the one phase region measurements of autocorrelation functions indicate small deviations from a single exponential when ‖T −Tc‖?0.05 °C. The shear viscosity exponent φ was found to be 0.077±0.002, somewhat larger than the theoretical estimates.
Explicit expression for the relaxation spectrum of a system of reacting polymers
Authors: Kjaer Knud Hindhede
Published: February 2003

An explicit expression for the relaxation spectrum of the polymerization reaction An+Am?An+m where all (the chemically dependent) reactions are supposed to have identical thermodynamic and kinetic parameters, is given. The suprising result is that the relaxation spectrum for an infinity of reactions can be described exactly by only one relaxation time. The total eigenvalue spectrum and the corresponding eigenvectors for the model are also found. A perturbation of the model, in which one rate constant differs from the others leads to a relaxation spectrum which can be described with the use of at most two relaxation times.
Vibrational analysis of phase III of poly (vinylidene fluoride)
Authors: Bachmann M. A. , Koenig J. L.
Published: February 2003

Normal coordinate calculations have been performed for an isolated chain having the conformation of phase III of poly (vinylidene fluoride). A valence force field, which was refined from phase I and phase II data, was transferred to the phase III chain calculation. The agreement between the calculated and observed spectra of phase III was good, and approximate normal mode assignments for most of the phase III bands were made. The geometric dependence of calculated frequencies and potential energy distribution for the phase I and phase II chain conformations were also studied.
Coordination chemistry of metal surfaces: Chemisorption of PF3
Authors: Nitschké F. , Ertl G. , Küppers J.
Published: February 2003

The electronic and thermal properties of PF3 bonded to surfaces of Cr, Fe, Ni, Cu, Ru, Pd, Ir, and Pt were investigated by means of ultraviolet photoelectron spectroscopy (UPS), electron energy loss sectroscopy, LEED, and thermal desorption. Bond formation can be described in terms of coupling of the highest occupied ligand orbital (σ-donor 8a1) to metallic s states and of ’’back donation’’ of metallic d electrons into the lowest empty ligand orbital (π-acceptor 7e). The observed lowering of the ionization potential of the 8a1 level exhibits close similarities with the properties of the corresponding zero-valent mononuclear complex compounds, indicating that in this case the chemisorption bond has to be considered as an essentially local phenomenon. The agreement is best with the fcc metals Ni, Pd, Ir, and Pt, whereas larger variations (as well as a dependence on the crystallographic orientation of the surface) were found with the bcc metals Cr and Fe. Ordered 2×2 overlayers observed with Ni(111) and Pd(111) surfaces are interpreted in terms of a simple structure model based on the van der Waals diameter of PF3 and on linear bond formation. Thermal desorption takes place at temperatures which are very close to those observed for CO, indicating very similar bond strengths for both ligands. Thermal decomposition of PF3 (which obviously needs several metal atoms and is therefore not observed with mononuclear complexes) was found to dominate with Cr and Fe surfaces. Although the σ-donor coupling is rather pronounced with the system PF3Cu(110) in this case thermal desorption already takes place around 200 K. This low thermal stability is presumably the reason why so far no mononuclear Cu–PF3 complex could be prepared.
Spectroscopy and photokinetics of chromium (III) in glass
Authors: Andrews L. J. , Lempicki A. , McCollum B. C.
Published: February 2003

The optical absorption, emission, emission lifetime, and absolute quantum efficiency have been measured for chromium (III) in a wide variety of oxide and fluoride glasses. In all cases, the room temperature emission is dominated by inhomogeneously broadened 4T2 fluorescence, and the relaxation of this level is shown to be primarily nonradiative. Multiphonon emission to lattice modes, concentration quenching, and quenching by hydroxyl moieties is shown not to be of significance in this relaxation at low doping levels. Instead, it is proposed that the radiationless process involves primarily local modes associated with the CrX6 cluster and is sensitive to site symmetry.
Infrared matrix isolation studies on the t-butyl radical
Authors: Pacansky J. , Chang J. S.
Published: February 2003

The infrared spectrum of the t-butyl radical isolated in an argon matrix was obtained by gas phase pyrolysis of azoisobutane and 2-nitrosoisobutane. The infrared spectrum is consistent with a C3v structure for the radical. The data obtained from the matrix isolation studies were used to reassess the ΔH°f,300 for the radical.
State selected ion–molecule reactions by a TESICO technique. II. Separation of the reactant spin–orbit states in the reaction Ar+(2P3/2, 2P1/2)+H2(D2)→ArH+(ArD+)+H(D)
Authors: Tanaka Kenichiro , Durup Jean , Kato Tatsuhisa , Koyano Inosuke
Published: February 2003

Cross sections for the atomic rearrangement reaction Ar++H2(D2)→ArH+(ArD+)+H(D) [Reaction (1)] and the charge transfer reaction Ar++H2(D2)→Ar+H+2(D+2) [Reaction (2)] have been determined for each of the Ar+ spin–orbit states (2P3/2 and 2P1/2) separately in the collision energy range from 0.05 to 0.5 eV (c.m.), utilizing the threshold electron–secondary ion coincidence (TESICO) technique which we developed recently. It has been found that the cross sections of Reaction (1) are larger for the 2P1/2 excited state than for the 2P3/2 ground state by a factor of 1.5 (with H2) and 1.3 (with D2), regardless of the collision energy in the range studied. The cross sections for both the H2 and D2 reactions show an approximately E−1/2.5 collision energy dependence which is somewhat milder than that expected from the simple Langevin theory. The cross sections of Reaction (2) have been found to be about seven times larger for the 2P1/2 state than for the 2P3/2 state with H2, whereas these are almost the same for both states with D2. The charge transfer cross sections are almost independent of the collision energy in the same energy range as above. A simple reaction model has been developed and a calculation of cross sections has been performed based on it, with a result which satisfactorily explains the essential features of the experimental results.
Interpretation of ES, CS, and IOS approximations within a translational–internal coupling scheme. IV. ES and IOS molecule–molecule cross sections
Authors: Snider R. F. , Parvatiyar M. G.
Published: February 2003

Properties of energy sudden and infinite order sudden translational–internal reduced S matrices are given for general molecule–molecule collisions. Formal similarities with the distorted wave Born approximation are discussed. Structural simplifications of energy dependent and kinetic cross sections associated with making the ES approximation are described. Conceptual difficulties associated with applying the ES and IOS approximations to kinetic processes dominated by energetically inelastic collisions are pointed out.
Enhanced isotope separation in CF2Cl2 by infrared multiphoton dissociation at elevated temperatures
Authors: Chou Jim-Son J. , Grant Edward R.
Published: February 2003

Isotopic specificity in the infrared multiphoton dissociation of CF2Cl2 has been found to be significantly enhanced by irradiation at elevated temperatures. We have observed the extent of this effect to depend sensitively on laser wavelength. Frequencies to the blue of the ν8 fundamental at 927 cm−1 produce a systematic pattern of varying enhancements, while increased temperatures for irradiation to the red of ν1 at 1120 cm−1 destroy isotopic specificity evident at room temperature. We explain these results by introducing a pumping-frequency specific temperature dependence for the rate of multiphoton excitation, such that, in the bulk gas phase, isotopically selective, temperature dependent pumping competes with collisional scrambling to yield a temperature dependent selectivity. We show that a simple kinetic model, incorporating the quantitative expression of this temperature dependence developed in earlier work, adequately accounts for our observations.
Kinetics study of a condensed detonating explosive
Authors: Bdzil John B. , Engelke Ray , Christenson David A.
Published: February 2003

We discuss a method for determining chemical–kinetic parameters for condensed explosive materials under the extreme pressure and temperature conditions of detonation. It utilizes theoretical results obtained from the Euler equations of fluid mechanics and experimental detonation data, which consist of steady-state shock shapes and detonation velocities measured as a function of charge size. We determine Arrhenius parameters for detonating commercial-grade nitromethane. The sensitivity of the method to various uncertainties in the input is tested. Results for the Arrhenius activation energy (EA = 92±23 kcal/mole) and vibrational factor [log10 k(sec−1) = 18±2] are larger than the gas phase values. These results are compared with those of other workers.
Energy derivatives for configuration interaction wave functions
Authors: Dupuis M.
Published: February 2003

Equations providing the first and second derivatives of a configuration interaction (CI) energy with respect to an external parameter are provided. We assume no restriction on the form of the CI expansion built from molecular orbitals obtained in a multiconfiguration Hartree–Fock (MCHF) calculation. Also, the coupled perturbed multiconfiguration Hartree-Fock formalism is presented for a general MCHF wave function and provides the first order and second order changes of the molecular orbital expansion coefficients with respect to an external parameter.
On the core binding energies of ions:  The 3d levels of I− and Cs+
Authors: Mathews R. D. , Key R. J. , Sur A. , Ewig C. S. , Banna M. S.
Published: February 2003

The 3d5/2 binding energies of cesium and iodine in gaseous CsI have been measured by x-ray photoelectron spectroscopy. The values obtained are 732.3±0.1 eV for Cs and 623.6±0.2 eV for I. A simple electrostatic model is used to compute ionic and atomic 3d5/2 binding energies from the CsI measurements. We have also obtained these energies by relativistic Dirac–Fock calculations. Comparison is made with analogous nonrelativistic results and with experiment.
Theory of magnetic linear dichroism. Application to matrix-isolated atomic transitions
Authors: Kreglewski Marek , Vala Martin
Published: February 2003

A general theory for magnetic linear dichroism (MLD) is presented. The derivation uses a perturbation approach together with the rigid shift approximation and includes terms in the Boltzmann population of the ground state and in the band shape function which are proportional to the square of the magnetic field strength. A six term expression for the MLD is obtained. The different terms result from the Zeeman splitting of the ground and/or excited states, the population redistribution of the ground state, or the intermixing of electronic states. Expressions for each of the six terms are given. They are functions of the electric dipole transition moments polarized parallel and perpendicular to the magnetic field and of the magnetic moments of the ground and/or excited states. Estimates are made of their relative importance for conditions of possible experimental importance. Computer simulations of the MLD band shapes for diamagnetic and paramagnetic species as a function of bandwidth and temperature are given. The effects of the varying contribution of the zeroth, first, and second derivatives of the assumed Gaussian band shape function are illustrated. The application of the method of moments to the quantitative analysis of an MLD spectrum is also discussed. Finally, the present theory is applied to atomic spectroscopy, e.g., atoms isolated in matrices. It is shown that the results of an MLD experiment combined with the results of a magnetic circular dichroism (MCD) experiment should provide an unambiguous assignment of the total angular momentum of excited electronic states in atoms.
Optical spectra and Zeeman effect for Er3+ in LuPO4 and HfSiO4
Authors: Hayhurst T. , Shalimoff G. , Edelstein N. , Boatner L. A. , Abraham M. M.
Published: February 2003

The absorption spectra of Er3+ diluted in LuPO4 and HfSiO4 crystals have been measured from 6000 to 28 000 cm−1 at liquid He and N2 temperatures. Zeeman spectra were obtained in the visible region. The transitions were assigned and fitted to a semiempirical Hamiltonian with ten adjustable parameters. Satisfactory fits were obtained including reasonable agreement between calculated and measured g values.
Time-domain measurements of pressure-induced frequency shifts in methyl chloride and ethylene oxide
Authors: Hom Richard C. , Coy Stephen L.
Published: February 2003

Pressure-induced rotational frequency shifts at microwave frequencies have been measured in the time domain. The computerized technique involves using the Stark effect to move molecules into resonance with an incident microwave field. The heterodyned emission decay signals can then be fitted for the frequency and relaxation time. Measurements are reported for the three J = 0–1 hyperfine transitons of CH3 35Cl and three ethylene oxide transitions 211–202, 321–330, and 431–422.
Electronic band-shape calculations in ammonia
Authors: Avouris Phaedon , Rossi A. R. , Albrecht A. C.
Published: February 2003

The vibronic nature of the lowest energy electronic absorption and of the lowest energy photoelectron spectrum of NH3 are investigated theoretically. Two-dimensional Franck–Condon factor calculations are performed and theoretical spectra are constructed including the effect of vibronic linewidth. The comparison of the experimental with theoretical spectra, computed under various assumptions, leads to several conclusions. The conspicuous continuum underlying the ?←? transition is seen to arise from the overlapping tails of vibronic line shapes. There is no need to attribute the continuum to a second electronic transition. The ν1, N–H stretching mode, is excited in both the electronic absorption and photoelectron spectrum. The ? state of NH3 may be able to support two quanta of ν1. The planar NH3+ ion has a N–H bond longer than in the ground state NH3 by about 0.06 Å.
Statistical treatment of EPR data: The spectrum of IO2 in KIO2F2 single crystals
Authors: Atherton N. M. , Morton J. R. , Preston K. F. , Strach S. J.
Published: February 2003

The EPR spctrum in γ-irradiated KIO2F2 crystals has been reinvestigated. Originally thought to be due to IO2F−, the spectrum has been reanalyzed and reassigned to the radical IO2. Improved principal values for the g factor and the 127I hyperfine and quadrupole interactions were obtained by the statistical technique of minimizing χ2 for measurements made with H0 parallel to the crystal axes.
The transient current in a one-dimensional molecular crystal with traps
Authors: Scher H. , Wu C. H.
Published: February 2003

The transient current, due to the hopping transport of a carrier in a one-dimensional molecular crystal, in the presence of a random distribution of traps and an arbitrary value of external electric field, is determined exactly. The trapping time as a function of electric field is derived from the current decay curves. It is shown that the current ∝exp(−At1/2) for all t at low fields. This is in agreement with the simple kinetic approach to one-dimensional trapping and not with more recent sophisticated approaches. The current decays asymptotically as exp(−Bt) for high field.
Inhibition of chemical reactions by a strong laser field
Authors: Kulander K. C. , Orel A. E.
Published: February 2003

Collinar model systems are described for reactions in a Stong laser field. H+H2 reaction and Li+FH reaction are discussed. The reaction probability is calculated in both cases. (AIP)
The specific concentration dependence of the proton magnetic resonance chemical shift in the system acetic acid–water
Authors: Kimtys L. , Balevičius V.
Published: February 2003

The proton magnetic resonance chemical shift of the averaged signal of water and carboxyl group of acetic acid has been studied as a function of concentration and found no anomaly in the region of 20 wt.% water. However, the difference between experimentally measured chemical shift and average of the chemical shifts of water and acid indicates the specific association occurring at about 15 wt.% of water.
Role of attractive forces in determining the relaxation behavior of polymeric systems
Authors: Bruns W. , Bansal R.
Published: February 2003

The static and dynamic properties of a model polymre chain immersed in a solvent are studied by computer molecuar dynamics techniques. The effect of the attractive part of the Lennard-Jones potential, on the dynamic properties of polymeric chains is studied. Autocorrelation functions are calculated.(AIP)
Comment on ‘‘The reactivity dependence of the recombination probability’’
Authors: Waldenstro/m S. , Naqvi K. Razi , Mork K. J.
Published: February 2003

The author’s previous work2 is reexamined. Especially the definition of diffusion controlled reaction. It is argued that the author’s definition of diffusion-controlled reactions is substantially different from that of Pedersen1. (AIP)
Electronic absorption spectra of biphenyl as studied by multiphoton ionization–supersonic beam technique
Authors: Murakami Jun-ichi , Ito Mitsuo , Kaya Koji
Published: February 2003

The vibrational structure of biphenyl is studied by observing the multiphoton ionization spectra due to radiation from a dye (coumarin 540) laser.(AIP)
Application of dimensional regularization to single chain polymer static properties: Conformational space renormalization of polymers. III
Authors: Oono Y. , Ohta T. , Freed Karl F.
Published: February 2003

A dimensional regularization approach to the renormalization group treatment of polymer excluded volume is formulated in chain conformation space where monomers are specified by their spatial positions and their positions along the chain and the polymers may be taken to be monodisperse. The method utilizes basic scale invariance considerations. First, it is recognized that long wavelength macroscopic descriptions must be well defined in the limit that the minimum atomic or molecular scale Λ is set to zero. Secondly, the microscopic theory is independent of the conveniently chosen macroscopic scale of length κ. The freedom of choice of κ is exploited along with the assumed renormalizability of the theory to provide the renormalization group equations which directly imply the universal scaling laws for macroscopic properties. The renormalizability of the model implies the existence of the general relations between the basic macroparameters, such as chain length, excluded volume, etc., and their microscopic counterparts in the microscopic model for the system. These macro–micro relations are defined through the condition that macroscopic quantities be well defined for polymer chains for any spatial dimensionality. The method is illustrated by calculating the end vector distribution function for all values of end vectors R. The evaluation of this distribution function currently requires the use of expansions in ε = 4−d. In this case our distribution reduces to known limits for R→0 or ∞. Subsequent papers will present calculations of the polymer coherent scattering function, the monomer spatial distribution function, and concentration dependent properties.
The internal energy distribution of atom-recombination product N2 desorbing from polycrystalline Fe
Authors: Thorman R. P. , Bernasek S. L.
Published: February 2003

The vibrational and rotational energies of recombination product nitrogen molecules desorbing from a polycrystalline iron surface were measured. The internal energy of the product gas was determined by electron beam induced fluoresence and surface composition was monitored by soft x-ray appearance potential spectroscopy. For clean iron with surface temperature ranging from 1086 to 1390 K, the vibrational temperature remained relatively constant, within the error limits, at a temperature slightly above that of the surface. Vibrational temperatures significantly higher than the surface temperature were found for sulfur contaminated surfaces. A rotational temperature of 400±30 K was observed for both the clean and sulfur covered surfaces between 1086 and 1239 K. A model incorporating surface imposed steric constraints causing the low rotational energies and potential barriers to reaction affecting vibrational energies is proposed.
CN(X 2Σ+) vibrational population inversion from the C+N2O→CN+NO reaction at 300 K
Authors: Costes M. , Dorthe G. , Caubet Ph.
Published: February 2003

The rotational and vibrational populations of CN(X 2Σ+) produced by the reaction O(3P)+N2O(X 1Σ+)→CN(X 2Σ+)+NO(X 2Π) in H+CHBr3+N2O diffusion flames were probed by laser induced fluorescence. Rotational populations were thermalized at 300 K. The vibrational population was found to exhibit a maximum for v′′ = 4.
Growth of structurally different oxide layers of the same stoichiometry on metals by multispecies diffusion
Authors: Fromhold A. T.
Published: February 2003

The growth of structurally different oxide layers on metals is investigated. The possibility is discussed that there may be an interior reactions zone for new oxide formation. (AIP)
TOF analysis of an optically pumped metastable neon beam
Authors: Kroon J. P. C. , Beijerinck H. C. W. , Verster N. F.
Published: February 2003

Optical pumping of a Ne beam is reported. The flight source used was single mode, frequency stabilized dye laser. The light beam and the atomic beam were crossed at right angles. The optical pumping was investigated by mearusing the fluorescence, and the metastable atoms were detected by secondary electron emission fraom a steel surface.(AIP)
A Monte Carlo method for large reaction–diffusion systems
Authors: Hanusse P. , Blanché A.
Published: February 2003

We present a Monte Carlo algorithm which is specially designed for studying the stochastic behavior of large reaction–diffusion systems. We compare its performance and results to those obtained by a standard method for a solvable model system for which we calculate the mean concentration, the variance, and the spatial autocorrelation function of concentration.
A study of the reactions Ca(1S,3P, and 1D)+N2O under single-collision conditions and at higher pressures: Chemiluminescence cross sections, photon yields, and collisional energy transfer in CaO* by N2O
Authors: Irvin John A. , Dagdigian Paul J.
Published: February 2003

A study of the chemiluminescence under single-collision conditions of the reactions of the ground state (4s2 1S) and the two metastable (4s4p 3P0 and 4s3d 1D) of atomic calcium with N2O is presented. An earlier study of Ca(3P0)+N2O from this laboratory [P. J. Dagdigian, Chem. Phys. Lett. 55, 239 (1978)] is corrected, and the spectral region investigated is extended into the near infrared (to 890 nm). Chemiluminescence cross sections and photon yields for production of various CaO* band systems are reported for each of the reactant states. In addition, a novel beam–gas scattering technique, which uses a very small Ca beam collimator and sharply focused detection optics, has been employed to measure the yield of short-lived CaO* (mostly A 1Σ+) emission in the Ca(3P0)+N2O reaction up to 0.3 Torr N2O pressure. The observed increase in yield with pressure is indicative of collisional energy transfer between excited CaO* states produced reactively. The present results are compared and contrasted with similar observations on the well-studied Ba(1S)+N2O reaction.
Resonance energy transfer in LiH(A 1Σ)
Authors: Ibbs K. G. , Wine P. H. , Chung K. J. , Melton L. A.
Published: February 2003

Measurement of the rates of quenching of specific vibrational–rotational levels of LiH(A 1Σ) by Li(2 2S) show very strongly resonant behavior, including distinct resonance with P and R branch transitions. These are interpreted in terms of resonant energy transfer to form LiH(X 1Σ) and Li(2 2P). Semiclassical calculations confirm this mechanism.
On a few points concerning the vacuum-ultraviolet photolysis of NH3
Authors: Xuan C. Nguyen , Di Stefano G. , Lenzi M. , Margani A.
Published: February 2003

Some aspects of the vacuum-ultraviolet photolysis of NH3 have been revised on the basis of new experimental results: (a) A normalized fluorescence excitation spectrum of the NH2(Ã 2A1) has an apparent energy threshold at 193±1 nm corresponding to the excitation of the 6–7th levels of the ν2′ mode of NH3 (Ã 1A2″). (b) A new value for the energy threshold of the formation of NH(c 1π) is 126±1 nm, corresponding to a ΔHf(NH)≲94±2 kcal mol−1. (c) The radiative lifetime of the (b 1Σt) state of NH has been redetermined and a value ≳2×10−3 s probably around 6×10−3 s has been obtained.
Hyperfine potential energy curves of the heteronuclear diatomics HD, DT, and HT in an external magnetic field
Authors: Uang Yea-Hwang , Ferrante Robert F. , Stwalley William C.
Published: February 2003

Hyperfine interaction potential energy curves between two different ground state isotopic hydrogen atoms (H, D, or T) in the presence of an external magnetic field are constructed. It is found that the interaction between two isotopic hydrogen atoms is noncentral if relativistic effects are included. The eigenfunctions are expressed in terms of the basis set consisting of electronic and nuclear quantum numbers ‖ms1, mIa; mS2, mIb≳. Unlike the zero-field case with degenerate potential curves, there are 24 and 16 distinct curves for the systems H–D (or D–T) and H–T, respectively. Sample results are given for a magnetic field of B = 100 000 G, in particular. Interesting features at the true crossings and the avoided crossings between those potential curves will be described. With these accurately calculated potential curves, the accurate study of inelastic spin-exchange scattering between two different spin-polarized atoms (H↑, D↑, or T↑) can now be carried out.
Analytic representation of the dipole oscillator-strength distribution
Authors: Dillon Michael A. , Inokuti Mitio
Published: February 2003

It is possible to represent an essential factor of the dipole oscillator-strength distribution for a single-electron continuum in terms of a compact expression involving a polynomial of several degrees in a suitable variable. The factor, which may be called the reduced oscillator-strength distribution, is defined in terms of the radial dipole matrix element with respect to the final-state wave function normalized in an energy-independent way near the origin. The key variable is g = ε/(ε+I), where ε is the kinetic energy of the ejected electron and I is the ionization threshold energy. The structure of the analytic representation has been identified through a study of the analytic properties of the dipole matrix element as a function of ε. For illustration, H, He, Li, and Na atoms are treated explicitly. Implications of our results to molecules and multichannel cases are also indicated. The present findings will be especially useful for interpolation and extrapolation of experimental data.
The modified moment method, irreversible thermodynamics, and the nonlinear viscosity of a dense fluid
Authors: Eu Byung Chan
Published: February 2003

The extended Gibbs relation is derived for dense fluids in a nonequilibrium state from the kinetic equation for dense fluids proposed in a previous paper. The method used for derivation is basically the same as that used in the case of dilute (ideal) gases described by the Boltzmann equation. The extended Gibbs relation derived is, as it should be, in the same form as for ideal gases, but the evolution equations for macroscopic variables involved contain contributions due to molecular interactions. This derivation together with that of the corresponding relation for ideal gases previously reported provides us with a mathematical basis to study irreversible thermodynamics for systems at any nonequilibrium state without making the assumption of local equilibrium. The non-Newtonian viscosity is also studied for a dense fluid with the stationary solution of the evolution equation for stress tensor and viscosity formulas are obtained as extensions of the formulas for ideal gases reported previously.
Resonance Raman scattering of semiquinone radical anions
Authors: Tripathi G. N. R.
Published: February 2003

The time resolved electronic absorption spectra of p-benzosemiquinone (PBSQ) and 2,5-di-t-butyl-p-benzosemiquinone (DTBSQ) radical anions are obtained in pulse radiolysis. The same radicals have been generated chemically in a flow system. The Raman spectra are excited by tuning a pulsed dye laser in the electronic absorption region. Time adjusted gate electronics have been used for the temporal resolution of the Raman spectra from fluorescence. The resonance effect has been utilized to record the Raman spectra of unstable semiquinone radical anions, 10−3–10−4 M in concentration. The observed Raman spectra and excitation profile are interpreted to assign the electronic and the vibrational transitions in the radicals. The semiquinone radical anions are fairly stable on photoirradiation above 330 nm.
On the overtone-combination spectra of XY2 molecules
Authors: Stannard Paul R. , Elert Mark L. , Gelbart William M.
Published: February 2003

It is well known that overtone and combination features in the infrared spectra of YXY molecules arise from several different effects: (1) anharmonicity in the individual stretch and bend motions; (2) nonlinear dependence of the electronic-ground-state dipole moment (μ) on the stretch and bend displacements (r, ?, and ϑ); and (3) coupling of stretches and bend via nonseparable terms in the many-dimensional potential energy (V). In order to unambiguously sort out these contributions it is necessary to know the r, ?, and ϑ dependence of both μ and V from which follow the vibrational eigenstates, line positions, and oscillator strengths. In this paper we discuss general criteria for separability of the nuclear potential energy with respect to stretch and bend motions. Preference for ’’local’’ versus ’’normal’’ coordinates is shown to derive from the atomic mass differences and bonding types. The infrared spectrum of the HOH molecule is treated in detail, since a great deal of information is already available concerning its V (r, ?, ϑ) and μ (r, ?, ϑ). First we obtain the vibrational eigenstates and use them to study the breakdown of separability with increasing energy. Then we compare the relative intensities of neighboring overtone and combination states and account for them in terms of ’’electrical’’ (μ) and ’’vibrational’’ (V) anharmonicity.
Classical trajectory models for electronically nonadiabatic collision processes: A classical valence bond model for electronic degrees of freedom
Authors: Miller William H. , Orel Ann E.
Published: February 2003

A classical interpretation of the Dirac–Van Vleck spin version of valence bond theory is used to obtain a classical model for electronic degrees of freedom within the valence bond framework. The approach is illustrated by deriving the explicit forms of the classical Hamiltonians, involving electronic and heavy particle degrees of freedom, for the H–H2, F–H2, and O–H2 systems. It is also shown how the initial conditions for both electronic and heavy particle degrees of freedom are chosen to carry out a classical trajectory simulation of collision processes. The attractive feature of this model is that it is as easily applicable to electronically nonadiabatic processes as it is to adiabatic ones.
A perturbation solution of the Smoluchowski equation in the weak potential region
Authors: Sibani Paolo , Pedersen J. Boiden
Published: February 2003

A general perturbation method for solving the Smoluchowski equation with an arbitary but weak potential is presented. The perturbation scheme has a predictable applicability and accuracy and yields both the scavenging free rate of recombination R(t), its Laplace transform ?(s), and the full probability distribution. The uniform convergence of the perturbation series depends on the ’’strength’’ of the potential, a quantity which is uniquely defined by a convergence criterion. However, the method is applicable to most potentials, for sufficiently small times. Also derived are expressions which give upper bounds to the perturbation error. A derived ’’pseudoinfinite nth order’’ perturbation expression improves the accuracy of the perturbation calculation in cases where the convergence is slow; for those cases it gives an accuracy corresponding to an (n+1)th order perturbation calculation but requires calculation of nth order quantities only. The method is applied to a Coulomb and a shielded Coulomb potential and closed form expressions are obtained for the first order quantities.