bluuebunny/crossref_metadata_2025 huggingface dataset:
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o CI calculation of the radiationless transition of the 1(nπ) state of formaldehyde
Authors: van Dijk J. M. F. , Kemper M. J. H. , Kerp J. H. M. , Buck H. M.
Published: February 2003

This paper reports an ab initio CI calculation of the radiationless decay of the formaldehyde 1A2 state. First we derive quantitative conditions, which a basis set must satisfy if it is to be used for describing radiationless decay. We checked these conditions for the formaldehyde molecule and found them to be satisfied for the adiabatic Born–Oppenheimer set used in the calculation. We then derive a general equation for the coupling elements resulting from this basis set. With the method used, rotational coupling could be treated completely equivalent with vibrational coupling; this rotational coupling turned out to be not important in formaldehyde however. The coupling elements for D2CO are a factor 10 smaller than the corresponding ones in H2CO. The results of the calculation show, that the internal conversion in formaldehyde is an example of the so-called resonance case. Therefore the decay cannot be described by the model proposed by Yeung and Moore, where S1→S0 internal conversion is the rate determining step in the photodissociation. Finally, we discuss the applicability of the ’’golden rule’’ in describing radiationless decay.
A quadratic valence force field for diborane
Authors: Blom C. E. , Müller A.
Published: February 2003

The complete GVFF of diborane has been determined from ab initio (4-31G) energies. The scale factor method has been applied to adjust seven scale factors on 62 experimental frequencies. The average difference between calculated and experimental wavenumbers amounted to 10.4 cm−1 or 0.71%. Calculated second order Coriolis coupling constants were in agreement with experimental values. The force constants of diborane, expressed in local symmetry coordinates, show resemblance to those of ethene: The signs of all comparable interaction force constants in diborane and ethylene are the same.
Systematics of EPR spectra of Gd3+ in rare-earth trinitrate hexahydrate hosts
Authors: Misra Sushil K. , Mikolajczak P.
Published: February 2003

Electron paramagnetic resonance spectra of the Gd3+ ion in various rare-earth trinitrate hexahydrate (RNH) hosts have been studied at different temperatures. The values of the parameters are computed using a rigorous least-squares fitting procedure in which all the resonant line positions obtained for various orientions of the external magnetic field are fitted simultaneously. While the room-temperature results (in the hosts characterized by La, Ce, Pr, Nd, Sm, Dy, Er, Yb, and Y) are used to study the systematics exhibited by the zero-field splitting parameters b20 and b22, the liquid nitrogen and liquid helium temperature results (in the hosts characterized by La, Pr, and Sm) have been used to deduce the absolute signs of the parameters, as well as the temperature variation of the parameters b20 and b22. It is found that, within experimental error, the values of b20 and of b22 are the same for those hosts R(NO3)3⋅6H2O for which R=Pr, Nd, Sm,Dy,Y, and Er; these values of b20 and b22 are close to those for the Yb(NO3)3⋅6H2O host, but are significantly different for those for the La(NO3)3⋅6H2O and Ce(NO3)3⋅6H2O hosts. The sign of b20 is found to be negative for all the hosts investigated at liquid helium temperature. A comparison is presented of the systematics of the spin Hamiltonian parameters for the RNH hosts with those for other hydrated rare-earth hosts. It is found, contrary to the behavior in other hosts, that the parameter b20 does not exhibit a linear dependence upon the host rare-earth ion radius.
Distored-wave Born calculations of V–V energy transfer
Authors: Eberhardt W. D. , Stettler J. D. , Witriol N. M. , Sung C. C.
Published: February 2003

The temperature dependence of the cross section for intermolecular vibration–vibration (V–V) energy transfer processes is calculated in the distorted-wave Born approximation with a thermal average over relative velocities. The molecular elastic scattering is assumed to be dominated by a hard core from which the distorted wave functions are calculated. Different forms of the potential (Vin) responsible for the V–V energy transfer have been used in the calculation. For near resonance a positive temperature dependence of the V–V cross section is found regardless of whether Vin is an exponential function (’’short range’’) or an inverse power function 1/r5 (’’long range’’). It is demonstrated numerically that the temperature dependence is very sensitive to the magnitude of energy defect ΔE. In general, the positive temperature dependence becomes negative when ΔE becomes sufficiently large. The accuracy of various numerical approximations used in the literature is also investigated.
High temperature Raman band contours and vibrational analysis of arsenic oxide vapors
Authors: Rytter E. , Goates S. K. , Papatheodorou G. N.
Published: February 2003

Raman spectra of vapors over arsenic oxide have been obtained at temperature up to 1200 K. Three Raman bands not reported previously have been observed and vibrational–rotational contours for E and F species fundamentals of As4O6 have been resolved. A band of medium intensity at 410 cm−1 was found to be polarized and its relatively high intensity was attributed to Fermi resonance between the 2ν6 and the ν2 modes. A valence force field calculation has been carried out, and the mean amplitudes of vibration and Cartesian displacements of As4O6 have been evaluated. The vibrations have been compared with AsO3 fundamentals by a group theoretical correlation method.
Temperature dependence of electronic to vibrational energy transfer from Br(42P1/2) to 12CO2 and 13CO2
Authors: Reisler Hanna , Wittig Curt
Published: February 2003

Temperature dependent quenching cross sections for the collisional deactivation of Br(42P1/2) by 12CO2 and 13CO2 were determined by monitoring the time resolved molecular fluorescence from the ν3 vibrational mode of CO2. These cross sections decrease with increasing temperature in the range 296–600 °K, indicating that near resonant channels dominate the quenching processes in both molecules. The room temperature rate coefficients for the quenching of Br* by 12CO2 and 13CO2 are (5.0±0.2)105 and (2.3±0.1)105 sec−1 torr−1, respectively, with about half of the quenching collisions resulting in excitation of the ν3 mode in the case of each molecule. By monitoring the amplitudes of the ν3 fluorescence signals from 13CO2 at different temperatures, the temperature dependence of the electronic to vibrational (E→V) energy transfer cross sections into states containing ν3 excitation was obtained. The experimental results are compared with calculations of E→V energy transfer cross sections which are based on long-range multipolar interactions.
Classical inelastic scattering in Li+H2: A comparison of different potential energy surfaces
Authors: Wagner Albert F. , Wahl Arnold C. , Karo Arnold M. , Krejci Robert
Published: February 2003

Four different ab initio calculations were used to determine four sets of potential energies at a common set of geometries for the Li+H2 collision system. The four calculations involved choices between a moderate and a large basis set and between the Hartree–Fock and the multiconfiguration-self-consistent field formalisms. Only the nonreactive ground electronic state surface was examined. An analytic functional form was least squares fit to each set of potential energies to produce four analytic potential energy surfaces. Classical trajectories at energies below the reaction threshold were run on each surface. The trajectories were analyzed to obtain the inelastic cross sections, differential cross sections, and average energy loss as a function of angle. The comparison of these collision observables from surface to surface was used to characterize the chemical accuracy of each surface. All four surfaces, from the least to the most accurate, produced significant amounts of rotational excitation.
Optimization of orbitals for multiconfigurational reference states
Authors: Dalgaard Esper , Jo/rgensen Poul
Published: February 2003

The problem of finding orbitals, which make the total energy stationary, when the ground state or reference state is of the multiconfigurational form, is analyzed in this paper. Particular attention is given to the quadratically convergent methods. Orbital variations are generated by unitary transformations and an expansion of the total energy through second order in the parameters used to define these transformations provides a characterization of the stationary point, which is reached at convergence, as well as estimates of second order properties. Effective one-particle potentials are analyzed and it is emphasized that only certain blocks of the Fock matrix are determined by the generalized Brillouin theorem. In an analysis of the convergence properties of the various methods it is shown that the Hartree–Fock procedure can be brought to converge for stable states of a given symmetry if the blocks of the Fock matrix, which are not determined by the Brillouin theorem, are chosen in an appropriate fashion. The procedures, which we discuss, are finally compared to currently employed techniques including direct energy optimization procedures, energy weighted steepest descent methods and generalizations of Roothaans equations.
Theory of exchange narrowing in low-dimensional correlated spin systems
Authors: Cheung T. T. P. , Soos Z. G.
Published: February 2003

Linear response theory is extended to magnetic resonance absorption (EPR) in low-dimensional networks with strong isotropic exchange J0 between adjacent spins. Previous high temperature results are generalized to the regime kT≳J0≫h/ω0, where ω0 is the Larmor frequency, in which spin correlations leading to temperature dependent EPR linewidths can be included by taking thermal averages over the dominant isotropic exchange interaction. Mori’s generalized Langevin equation gives the absorption profile I (ω−ω0) by a memory function which explicitly treats the slow decay of spin correlations in low-dimensional systems, thus identifying diffuse contributions to four-spin correlation functions without decoupling. The theory is illustrated for two-dimensional antiferromagnetic MnCl−24 layers with dipolar broadening, where it yields the general angular dependence of the EPR linewidth. Approximate computations of long-time cutoffs, their experimental determination, and the relation of the general theory to previous RPA treatments are discussed.
Application of generalized cumulant expansions to the theory of electron spin echo phase memory decay in liquids
Authors: Stillman Arthur E. , Schwartz Robert N.
Published: February 2003

A generalized cumulant expansion theory for electron spin relaxation in liquids is presented which describes the phase memory decay found in pulse experiments. It is found that for pulse times τ≫τc, the two-pulse electron spin echo envelope decays exponentially, and for motionally narrowed systems, the phase memory decay rate is given by the elements of the Redfield relaxation matrix. For radicals undergoing slow rotational reorientation, the phase memory time is shown to be sensitive to both the rotational correlation time and the assumed dynamical model for rotational diffusion even for correlation times so long that the cw EPR spectra appear to be rigid. If τ≳τc, the echo envelope is found to decay in a complex, oscillatory manner.
Long-range interactions of the thallium 7 2S1/2 state and broadening and shift of the thallium violet and green lines by rare gases
Authors: Wu C. Y. Robert , Stwalley William C. , Proctor TImothy R.
Published: February 2003

The long-range interaction coefficients (C6, C8, C10) of the Tl(7 S1/2) atom with rare gases are calculated. The pressure-induced broadening and shift of the thallium resonance lines in the presence of rare gases are then calculated using these long-range coefficients and impact theory. We find that higher order van der Waals forces are not negligible compared to the leading −C6/R6 dispersion force in terms of their contributions to the broadening and shift.
Temperature dependence of the rate constants for reactions of O(1D) atoms with a number of halocarbons
Authors: Davidson J. A. , Schiff H. I. , Brown Terry J. , Howard Carleton J.
Published: February 2003

Absolute rate constants for the deactivation of O(1D) by six halocarbons have been measured over the temperature range 173–343 K using the time resolved decay of the O(1D→3P) emission at 630 nm. The rate constants showed no dependence on temperature within the precision of the measurements. The rate constants (in units 10−10 cm3 molecule−1 s−1) are as follows: CCl4,3.1±0.9; CFCl3,2.2±0.7; CF2Cl2,1.45±0.5; CHFCl2,1.9±0.6; CHF2Cl,0.95±0.3; and CF2ClCFCl2,2.0±0.6. These results have been combined with the rate constants for O(1D) reactions with a number of similar compounds and analyzed according to a simple scheme that assigns a rate constant to each atom attached to carbon. Thus, rate constants for ethane and methane molecules containing hydrogen, fluorine, and chlorine are given by the simple expression k (CnHaFbClc) =0.32a+0.030b+0.74c (in units of 10−10 cm3 molecule−1 s−1). This equation can be used to accurately predict halocarbon rate constants that have not been measured.
On the efficiency of rate processes. Power and efficiency of heat engines
Authors: Gutkowicz-Krusin Dina , Procaccia Itamar , Ross John
Published: February 2003

We analyze the power and efficiency of heat engines which operate subject to irreversible heat flow. First, we consider a specific model, with a cycle for an ideal gas similar to that of a reversible Carnot engine (’’isothermal cycle’’), and find the maximum power, and efficiency at the point of maximum power (ηm), for given heat bath temperatures and compression ratio. We prove that the cycle chosen produces more power than any other conceivable cycle in the limit of large compression ratio; the derivation is made for an ideal or van der Waals gas as a working fluid, but this is not restrictive in this limit. We use these results to obtain a general formulation, of upper bounds on power and ηm, valid for isothermal cycles to study the dependence of these quatities on the form of the law of irreversible heat conduction. We find that ηm depends only on the heat bath temperatures and the form of the irreversible rate process, but is independent of the material properties of the system. The dependence of ηm on the form of the rate process suggests the concept of ’’efficiency of rate processes.’’
Cation dynamic studies in n-propylammonium chloride, CH3(CH2)2NH3Cl, by NMR
Authors: Albert Shmuel
Published: February 2003

Pulsed and continuous wave proton magnetic resonance techniques have been used to study the low and room temperature modifications of CH3(CH2)2NH3Cl (n-propylammonium chloride or PACl) and CH3(CH2)2ND3Cl (d3-PACl) over the temperature region 77 °K to ∼ 346 °K. The proton static spin–lattice relaxation time (T1) and second moment data in the ordered low temperature phase are consistent with a model where only CH3 and CH3+NH3+ group rotation about their three-fold axes take place in d3-PACl and PACl, respectively. At each temperature the methyl group rotation is faster than that of NH3+ and the respective activation energies are 2.4 (±0.15) and 3.7 (±0.2) kcal/mole for CH3 and NH3+ rotation. For the room temperature phase of both salts relatively fast chain rotation about their long chain axis with independent CH3 +NH3+ group rotation was found from second moment analysis. The activation energy obtained for this motion from the T1 data is 2.5 (±0.2) kcal/mole. The reported phase transition exhibits an appropriate discontinuity in the T1 curve at 186±2 °K and seems to be associated with the dynamic disorder. The reorientations and phase transitions in the corresponding modifications of the n-alkylammonium chloride series is discussed in the light of our results and other published data.
Applications of field theoretical methods to the calculations of solvent-induced chirality and infrared band shapes in strongly interacting solvents. II
Authors: Paul R.
Published: February 2003

The use of the field theoretical Green’s function method for the calculation of solvent-induced chirality and the appearance of dipole forbidden transitions is presented. The relationship between the Green’s function method and the usual correlation function methods is indicated and certain unifying features between several different physical phenomena are pointed out.
Quantum corrections to the equilibrium properties of a dense fluid with square-well plus hard-core potential
Authors: Singh N. , Sinha S. K.
Published: February 2003

Using the modified WK expansion of Slater sum, a simple theory for evaluating thermodynamic properties of a dense semiclassical fluid is developed. The theory has been applied to calculate the quantum corrections to the equation of the state and excess Helmholtz free energy of a dense fluid with square-well plus hard-core potential. The results for the first two quantum corrections are reported in analytic form.
Accurate photoionization thresholds by multiphoton ionization: Pyrrole
Authors: Williamson Ashley D. , Compton R. N. , Eland J. H. D.
Published: February 2003

Multiphoton ionization spectroscopy has been used to measure ionization threshold for pyrrole.(AIP)
X-ray diffraction study of liquid neopentane in the temperature range −17 to 150°C
Authors: Narten A. H.
Published: February 2003

The x-ray diffraction pattern of liquid neopentane has been measured at eight different temperatures between the melting point (−17°C) and the critical point (161°C). In the data analysis, the methyl groups were treated as single scattering centers, and the molecular structure derived from the large-angle part of the x-ray data was found to be the same as that found for the low density vapor. Subtraction of the molecular structure yields a set of distinct structure functions descriptive of intermolecular atom pair correlations. It is shown that a realistic model for the orientational correlations between molecules in the liquid must reproduce the experimental structure functions beyond the first maximum. The radial distribution functions derived from the data indicate well defined Me⋅⋅⋅Me contacts between neighboring molecules at low temperature (high density).
The Padé approximants for two-body multipole–multipole dispersion interaction
Authors: Yousif F. N. , Shukla G. C.
Published: February 2003

The two-body dispersion interactions between multipoles of the hydrogen atoms have been worked out using [2,1] and [3,2] Padé approximants and generalized Casimir–Polder integral formulas. Energy coefficients which appear in the expression for the interaction energy of E2 (H–H), obtained up to the term R−16, are in agreement with those of Dalgarno and Meath.
Statistical thermodynamics of dissociating gases and plasmas
Authors: Pitzer Kenneth S.
Published: February 2003

When a dissociation equilibrium is present, the complete phase space should be allocated consistently to either the associated or dissociated species without duplication or omission of any important region. While this problem is trivial in many systems at low pressure, it becomes important and complex for an ionizing system at high pressure. A feasible division is proposed and equations are presented for both the dissociated (ionized) and associated species. It is suggested that any extensive tabulation of properties of ionizable species be made in a manner consistent with the principles outlined.
ESR and ENDOR study of 5′dCMP at 6 K
Authors: Close David M. , Bernhard William A.
Published: February 2003

The ESR spectra of single crystals of deoxycytidine 5′-phosphate⋅H2O (5′dCMP), x irradiated at 11 K and observed at 6 K, exhibit signals from three distinct free radicals. Analysis of the ENDOR spectra from two of these radicals indicates that these result from oxidation and reduction of the cytosine base. The reduced species exhibits hyperfine coupling to the C6–Hα proton (Aiso(H6) =−1.392 mT). The oxidized species exhibits hyperfine couplings to the C5–Hα proton (Aiso(H5) =−1.495 mT), N1 and N3, (Aiso(N1) ∼0.5 mT), (Aiso(N3) ∼0.25 mT) and to the C1′–Hβ proton (Aiso(Hβ) =1.483 mT). The third free radical has ESR spectra characteristic of an oxygen centered defect and is thought to be a hole located primarily on the C3′–O3′ oxygen, but shared with a neighboring HO–PO−3−CH2- group.
Electron spin resonance of CrO43− in Li3PO4, Li3VO4, and Li3AsO4
Authors: Greenblatt M. , Pifer J. H.
Published: February 2003

The single crystal electron spin resonance of CrO43− in Li3PO4, Li3VO4, and Li3AsO4 has been studied at 4.2 K. The ESR data show highly unusual g values which have a much greater deviation from 2 than previously observed for Cr5+ in tetrahedral coordination. In all three compounds the 3d1 electron has a dz2 ground state with a small admixture of higher states due to a distortion of the chromate tetrahedra which leaves only a mirror plane symmetry. The g values and hyperfine data for 53Cr are fitted to crystal field equations including higher order terms in the energy separation of the ground state doublet, and the crystal field parameters obtained reveal an extremely small distortion of the CrO3−4 in the high temperature phase in Li3PO4. The distortions in the low temperature phase of Li3VO4 and Li3AsO4 are of a different nature and larger than in the phosphate but are still much smaller than in previously studied compounds containing CrO43−. There is no evidence for a Jahn–Teller distortion in any of the samples. The observed variation of linewidth with orientation in these systems which closely follows the angular variation of g values is attributed to small variations in the size of the distortion of the tetrahedra.
Local mode oscillator strengths in benzene
Authors: Burberry Mitchell S. , Albrecht A. C.
Published: February 2003

Experimentally, benzene C–H and C–D stretching modes are seen to behave as one dimensional oscillators with respect to both eigenenergies and oscillator strengths. Simple local mode models based on either Morse or quartic power series potential wavefunctions predict the correct behavior for the oscillator strength from the infrared to the visible red special region. However, it appears unlikely that the coefficients of the expanded dipole moment operator may be easily determined by a fit to the observed oscillators strengths of a Local Mode progression.
The vibrational dependence of the electric dipole moment in d3Δi CO
Authors: Lisy James M. , Klemperer William
Published: February 2003

The Stark effect in several vibrational levels of the d 3Δi state of CO has been measured by laser induced molecular beam electric resonance spectroscopy. The electric dipole moments are The value of the dipole moment at the equilibrium internuclear separation is estimated to be μe=0.72 D with the sign −CO+. Comparison of the experimental results with recent electron structure calculations is discussed.
A spin anomaly and second order substituent effect for localized spin orbitals
Authors: Purcell Keith F. , Zapata J. P.
Published: February 2003

The spin polarization pattern of geminal CH bond pairs was determined using the UHF-INDO finite perturbation technique. (AIP)
Photodissociation of vibrationally excited Ar2+ formed by associative ionization
Authors: Rose T. L. , Katayama D. H. , Welsh J. A. , Paulson J. F.
Published: February 2003

The photodissociation cross sections of a beam of Ar2+ formed by associative ionization in a conventional electron impact ion source have been measured over the wavelength range from 265 to 715 nm. The measured cross sections are for transitions from the 2Σu+ ground state to the repulsive 2Σg+ excited state and are dependent on the ion source conditions. At low pressures (0.01 Torr) in the ion source, the cross section is 1×10−17 cm2 and varies little over the entire wavelength range. When pressures are increased to 0.1 Torr, a peak in the cross section at about 300 nm is obtained with a value of 1.7×10−17 cm2. A simplified two state mechanism involving high and low lying vibrational levels of Ar2+ in its ground state is proposed to explain the qualitative effects of pressure on the cross sections. Measurement of the Ar2+ and Ar+ beam currents as a function of repeller voltage showed that collisional dissociation is occurring in the ion source under conditions of relatively high pressure and positive repeller voltage at rates comparable to the Langevin rate. With zero repeller voltage an average collisional stabilization rate coefficient of 8×10−11 cm3 sec−1 molecule−1 is obtained for vibrational relaxation of Ar2+ from ’’high’’ to ’’low’’ lying levels. Using the calculated cross sections of Michels and Wright [J. Chem. Phys. 69, 5151 (1978)] for each vibrational level, a vibrational population is derived from the observed cross section versus wavelength plot. A comparison of the vibrational population derived from the low and high pressure results confirms that collisional relaxation is occurring, but that at 0.1 Torr the distribution in the ion source is still ’’hotter’’ than a 300° K Boltzmann distribution.
The use of static and dynamic physical property measurements to infer structural properties of associated liquids: Acetic acid–water
Authors: Sims Robert W. , Willicott III M. Robert , Inners R. R.
Published: February 2003

The anomalies which occur in most static and dynamic physical property measurements on solutions of water in acetic acid can be used with critical analysis to infer associative molecular structures. The anomalies indicate significant structural changes. Proton magnetic resonance chemical shifts for acetic acid–water solutions show a significant structural change occurring in the region of equal molar concentration. Literature values of carbon-13 spin–lattice relaxation times, density, molar enthalpy of mixing, index of refraction, and relative viscosity for acetic acid–water solutions also show anomalies in the region of equal molar concentration. Careful measurement of carbon–13 spin–lattice relaxation time for 20 wt. % water in acetic acid was compared with literature values. A critical analysis of these anomalous physical properties infer a preponderance of the dihydrated dimeric acetic acid structure. Microwave absorption at 10.525 GHz for acetic acid–water solutions was found to have a significant structural change occurring in the region of 70 wt. % water. The deviation appeared in the exponential response of microwave adsorption for polar liquids. It was found that literature values of carbon-13 spin–lattice relaxation times, molar enthalpy of mixing, and carbon-13 chemical shifts for acetic acid–water solutions also show anomalies in the region of 70 wt. % water. Critical analysis of these measurements and their anomalies imply a dihydrated monomeric acetic acid structure predominates from approximately 70 wt. % water in acetic acid to infinite acetic acid dilution.
Atomic migration in solid sodium
Authors: O’Reilly D. E.
Published: February 2003

Vacancy single jump and double jump diffusion and associated coefficients of self-diffusion are calculated for solid sodium using values of the migration and formation energies from both static and dynamic calculations reported in the literature. The calculated pre-exponential factors for both types of diffusion are in good agreement with the experimental results of Mundy on solid sodium.
Doubly resonant three-photon spectroscopy
Authors: Andrews D. L.
Published: February 2003

Multiphoton spectroscopy is increasingly being used for the study of molecular excited states. The increase in the transition rate under resonance conditions can be exploited as a means of locating new states, and the dependence of the rate on the photon polarizations gives information about state symmetries. In this paper, expressions for the rate of doubly resonant three-photon absorption are derived, and it is shown how these results can be applied to various other stimulated processes. It is also demonstrated how the relative orientations of molecular transition moments can be found by performing a specified set of experiments with different polarizations. In addition to providing symmetry information, this method may prove a valuable means of testing molecular wave function calculations for biological molecules.
Characteristics of trapped electrons and electron traps in single crystals
Authors: Budzinski Edwin E. , Potter William R. , Potienko George , Box Harold C.
Published: February 2003

Two additional carbohydrates are reported whose crystal structures trap electrons intermolecularly in single crystals x irradiated at low temperature, namely sucrose and rhamnose. Five carbohydrate and polyhydroxy compounds are now known which exhibit this phenomenon. The following characteristics of the phenomenon were investigated: (1) the hyperfine couplings of the electron with protons of the polarized hydroxy groups forming the trap; (2) the distances between these protons and the trapped electron; (3) the spin density of the electron at the protons and (4) the relative stabilities of the electron trapped in various crystal structures.
Collisional ionization in the presence of intense laser radiation: Quantum-mechanical calculations for He* (3S)+Ar±h/ω→He+Ar+(2P)+e−
Authors: Bellum John C. , George Thomas F.
Published: February 2003

We present a quantum-mechanical coupled-channels approach for studying laser-assisted collisional processes leading to transitions between discrete and continuum electronic states. This coupled-channels approach is an approximate application of our more general quantum-mechanical formalism for treating bound-continuum collisional transitions assisted by intense laser radiation, and uses discretization procedures to deal with the continuum states, and so-called electronic-field representations to account for the presence of intense laser fields. We discuss in detail all approximations leading to our coupled-channels approach. We then use our approach to calculate laser-assisted Penning ionization of Ar by He* (1s2s,3S) for the specific cases of radiation from the 10.6 μm line of a CO2 laser of intensity near 1.6×108 W/cm2, and the 1.315 μm line of an iodine laser of intensity near 109 W/cm2. We obtain ionization cross sections (per unit emitted-electron energy ε) dσ/dε as a function of ε. dσ/dε reflects a spectrum of emitted-electron energies that exhibits pronounced laser-modified collisional effects. The usual field-free spectral region around ε0(?0.149 hartree) is augmented by new spectral regions governed by radiative coupling and located near ε+(−)?ε0+(−) h/ω, where h/ω is the laser’s photon energy. Compared to their field-free counterparts, these laser-modified spectral contributions are more sharply peaked and favor Penning ionization over associative ionization more strongly. In carrying out these calculations we treat the radiative coupling in the dipole approximation. By analyzing this radiative coupling for He* (1s2s,3S)+Ar Penning ionization, we show that it rigorously vanishes asymptotically. We use this fact to propose a physically reasonable functional form for such radiative coupling between bound and continuum electronic states.
Photoionization thresholds of divalent rare earth ions in alkaline earth fluorides
Authors: Pedrini Christian , McClure Donald S. , Anderson Charles H.
Published: February 2003

The minimum energy for the onset of photoconductivity has been measured for the ions Ho2+, Dy2+, and Tm2+ in CaF2, SrF2, and BaF2. This energy is identified with the difference between the impurity level and the bottom of the conduction band. The value of this energy difference is given to within 0.5 eV by a simple electrostatic model including corrections for polarization and for the change of the positions of the ions surrounding the impurity in the crystal.
Line shapes of charge-transfer spectra
Authors: McHale Jeanne , Simons Jack
Published: February 2003

The theoretical description of condensed-media line shapes of electronic transitions, as developed in earlier papers, is applied to the charge-transfer (CT) spectra of the complexes mesitylene:tetracyanoethylene (Mes:TCNE) and anthracene:chloranil (AN:CA). Results are compared with those previously published for benzene:iodine (Bz:I2), and the factors which contribute to line broadening (inhomogeneous broadening, the Franck–Condon profile, and donor–acceptor vibrational motion) are discussed. The results of an attempt to determine the contributions to the line shape made by intermolecular orbital couplings are presented. In addition, the Bz:I2 CT spectrum is reinvestigated, and the question of which ionization potential of benzene is involved is addressed.
Effects of fluctuation on dissipative structures. II. Appearance of optically active states as dissipative structures
Authors: Iwamoto Kazutoshi , Senō Manabu
Published: February 2003

Two chemical systems which fall into chiral states after starting from an optically inactive state are proposed. These optically active states are realized as dissipative structures and consequently disappear when the chemical system comes close to the equilibrium state. These chemical systems involve stereospecific and autocatalytic processes. The stereospecificity is characteristic of enzymatic processes in living systems and the asymmetric syntheses which take place universally in all living systems. The idea proposed here would open a way to an explanation for asymmetric syntheses in living systems.
The ionization of PCl6− in the solid state under pressure. I. Phase diagram of phosphorus pentachloride
Authors: Cahay R. , Whalley E.
Published: February 2003

It is suggested that the PCl6− ion should ionize to PCl4+ and 2Cl− in the solid under pressure, and evidence has been sought by measuring the phase diagram of phosphorus pentachloride, which has the constitution PCl4+PCl6−. Two new phases were discovered, one of which is wholly metastable relative to the ordinary phase.
Ruthenium (III) -doped silver bromide and silver chloride: An EPR study
Authors: Corrigan D. A. , Eachus R. S. , Graves R. E. , Olm M. T.
Published: February 2003

Ru3+ and Ru2+ ions are substitutionally incorporated into melt-grown crystals of AgBr and AgCl. The d5 trivalent ion predominates in samples prepared in oxidizing environments, such as Br2 and Cl2, and it has been the subject of a detailed magnetic resonance study. It is distributed between four structurally inequivalent lattice sites in both salts. These sites are distinguished by the arrangement of charge-compensating silver-ion vacancies in the two closest cation subshells. Reasonable dopant-vacancy configurations have been deduced from the EPR data.
Coupled-channel study of halogen (2P) + rare gas (1S) scattering
Authors: Becker C. H. , Casavecchia P. , Lee Y. T. , Olson R. E. , Lester W. A.
Published: February 2003

Quantum mechanical coupled-channel (CC) scattering calculations are reported using realistic adiabatic potentials for the 2P+1S interaction of F–Ar, F–Xe, and Cl–Xe. Differential cross sections dσ/dω derived from a simple elastic approximation appropriate for large spin orbit interactions accurately reproduce all the gross features computed by the coupled-channel method. This finding supports the extraction of interaction potentials from laboratory differential cross sections I (ϑ) via an elastic analysis. Integral inter and intramultiplet changing cross sections are expressed conveniently in terms of Grawert’s B(j, j’;g) coefficient. Information on the collision dynamics is extracted by following the partial wave dependence of selected B(j, j’;g). Classical turning point analysis, based on the values of the large l-waves for which these partial wave contributions Bl(j, j’;g) begin to rise above zero, leads to the conclusion that both intermultiplet and first order forbidden intramultiplet transitions are caused by a single localized nonadiabatic coupling region at the position of complex crossing of the Ω=1/2 adiabatic potentials. Small amplitude oscillations or perturbations in the CC calculated dσ/dω and in the experimental I (ϑ) are thought to be examples of Stükelberg oscillations, though quantitative agreement between these quantities is not obtained. The energy dependence and interference structure of the computed B(j, j;g) are briefly discussed, as is the approximation of the constant spin orbit interaction over the experimentally accessible range of internuclear distances.
Theoretical study of the X1Σ+, A1Π, C1Σ− and E1Σ+ states fo the SiO molecule
Authors: Langhoff Stephen R. , Arnold J. O.
Published: February 2003

The self-consistent-field plus configuration-interaction method has been used to compute potential energy curves and certain one-electron properties for the X1Σ+, C1Σ−, A1Π, and E1Σ+ states of SiO. This study employed a basis consisting of 51 Slater-type orbitals which is an expanded version of the one reported by McLean and Yoshimine. The computed ground-state dissociation energy (De) of 8.1 eV is in excellent agreement with the experimental value of 8.26±0.13 eV. The theoretical ground-state electric dipole moment function is in good agreement with the experimental curve constructed from the microwave data for the v=0–3 vibrational levels. Einstein A coefficients for vibration–rotation transitions computed from existing theoretical and experimental data are in good agreement. The E1Σ+ state is shown to dissociate adiabatically to ground-state atoms over a potential barrier with a maximum near 5 bohr. Calculated transition probabilities and radiative lifetimes for the A1Π–X1Σ+ and E1Σ+–X1Σ+ band systems agree well with recent laboratory experiments. Absorption cross sections as a function of wavelength have been computed and used to determine the opacity of SiO boundary layers that will form on the surface of probe vehicles entering the Jovian atmosphere at high speeds. These calculations demonstrate that the brilliant shock layer emission will be significantly absorbed by the SiO A1Π–X1Σ+ and SiO E1Σ+–X1Σ+ band systems in the boundary layer in the spectral region between 170 and 230 nm.
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o SCF MO calculations of the potential surfaces of thiocarbonyls. II. H2CS, HFCS, CIFCS, and Cl2CS
Authors: Kapur A. , Steer R. P. , Mezey P. G.
Published: February 2003

Potential energy surfaces and equilibrium geometries for the ground and first excited triplet states of H2CS, HFCS, ClFCS, and Cl2CS have been calculated using ab initio SCF MO methods. The triplet state out-of-plane bending mode frequencies have been calculated using a perturbation theoretical treatment and a suitable analytic approximation to the potential along the out-of-plane bending coordinate. Where experimental results are available, good agreement exists between calculated and experimental data. The equilibrium out-of-plane angle in the lowest triplet state is correlated with the decrease in the p electron density on the carbon atom accompanying the change from the planar to the equilibrium out-of-plane conformation.
Vibrational analysis and normal coordinate calculations of the acenaphthene molecule and crystal
Authors: Furić K. , Colombo L. , Baranović G. , Ljucaj A.
Published: February 2003

The internal and external spectra of the acenaphthene crystal have been studied using Raman spectroscopy. The assignment of the observed spectra is supported by normal coordinate calculations in the crystal frame. Consequences of the low accuracy in determining the hydrogen-atom positions are discussed.
Electronic spectroscopy of UF6 and WF6 by electron impact
Authors: Rianda Ronald , Frueholz Robert P. , Kuppermann Aron
Published: February 2003

The electron-impact excitation spectra of uranium hexafluoride (UF6) and tungsten hexafluoride (WF6) have been studied experimentally at impact energies of 30, 50, and 75 eV and at scattering angles from 5° to 80°. Eleven features in UF6 are observed with maxima at 3.26, 4.2, ∼4.7, 5.8, 7.0, 7.86, 9.26, 11.01, 11.75, 12.5, and 13.2 eV. Four features in WF6 are observed with maximum intensity at 7.25, 7.9, 8.5, and 9.85, in good agreement with optical work. In addition, three previously unobserved features in WF6 at 11.75, 12.6, and 13.5 eV are reported. Similarity between the spectra of UF6 and WF6 suggests that the primary contribution to the absorption intensity in UF6 above 5.8 eV and in WF6 results from charge transfer transitions from fluorine p orbitals to metal d orbitals. Tentative assignments based in part on recent theoretical studies are made.
The first ionization potentials of the transition metals
Authors: Rauh E. G. , Ackermann R. J.
Published: February 2003

The appearance potentials of the transition metals yttrium through molybdenum, ruthenium through palladium, and lanthanum through platinum have been determined by electron impact. A method of simultaneous and intercomparative measurements with known standards was used. Corrections to the appearance potentials for thermally excited levels in the atoms and for possible ionization paths to other than the ground states of the ions are discussed and used to deduce the ionization potentials.
The singular points of frequency-dependent polarizabilities from time-dependent Hartree–Fock theory
Authors: Santry D. P.
Published: February 2003

It is shown that, with a simple basis set, the singular frequencies calculated from time-dependent Hartree–Fock (TDHF) theory can be equal to those calculated from the virtual orbital approximation to electronic excitation energies. The well known inadequacies of this approximation suggest that TDHF theory may be of limited value for the study of atomic and molecular excited states, unless special care is exercised in the selection of the atomic orbital basis set.
Electrical resistance and defect structure of stable and metastable phases of the system Nb12O29–Nb2O5 between 800 and 1100 °C
Authors: Marucco J. F.
Published: February 2003

The defect structure of oxides of the system Nb12O29–Nb2O5 have been studied by thermogravimetry and electrical resistance measurements. It has been clearly established that the stable oxides Nb2O5−x, Nb25O62−x, and Nb12O29−x are related to oxygen vacancies. On the other hand, the metastable phase of reduction of Nb2O5−x may be related to interstitial trivalent cations and it is suggested that such a defect of structure may be a step before the formation of crystallographic shear planes. In that case, the electric conductivity has been found to resemble a hopping process.
Parity and differentiability restrictions on the electric field dependence of the mobility of charged particles in gases and liquids
Authors: Baird James K.
Published: February 2003

The electric field dependences of mobility of excess electrons in liquid neopentane, given by Mozumder and Carmichael2 is examined from the point of view of parity invarance and differentiability.(AIP)
Response to ’’Parity and differentiability restrictions on the electric field dependence of the mobility of charged particles in gases and liquids’’
Authors: Carmichael Ian
Published: February 2003

The field dependence of electron mobility in liquid and gases is discussed in particular Baird’s1 use of the formula for field dependence of electron mobility in liquid neopentane is commented upon.(AIP)
Rotational motions of NH+4 groups in NH4ZnF3 studied by quasielastic neutron scattering
Authors: Steenbergen Chr. , de Graaf L. A. , Bevaart L. , Bartolomé J. , de Jongh L. J.
Published: February 2003

The rotational behavior of the ammonium groups in the high-temperature cubic phase of the perovskite NH4ZnF3 has been investigated, using incoherent quasielastic neutron scattering. The measurements were carried out for various wave vector transfers between 0.68 and 5.52 Å−1 and for temperatures between the transition temperature of 115.1 and 300 K. The data are compared with some reorientational jump models. It is assumed that in the cubic phase the NH4 group is a slightly distorted tetrahedron, apparently due to strong hydrogen–fluorine interactions. The degree of distortion could, however, not be determined. On the time scale of the experiment (?3 ps) the reorientational behavior of the NH4 group can be described by 90° jumps about its axis of smallest moment of inertia. Residence times between 0.4 and 7 ps were found. Their temperature dependence follows an Arrhenius behavior, yielding Ea/kB=580±15 K, which agrees with calculations for the quantum mechanical energy level scheme.
Laser-induced chemiluminescence study of the HgCl (B→X) transition: Formation, radiation, and quenching processes
Authors: Tang K. Y. , Hunter R. O. , Oldenettel J. , Huestis D. L.
Published: February 2003

The formation, radiation, and quenching of HgCl(B 2Σ+) have been investigated using a laser-induced chemiluminescence technique. Hg/Cl2/Ar mixtures were irradiated at 253.7 nm by a frequency-doubled nitrogen-pumped dye laser. The Hg(6 3P1) reacted with Cl2 to yield HgCl(B 2Σ+). The time behavior of the HgCl(B 2Σ+) →HgCl(X 2Σ+) fluorescence was analyzed to obtain the following rate coefficients:
Solute orientation behavior in nematic solutions: Trichlorobenzene in MBBA
Authors: Lee Y. P. , Gilson D. F. R.
Published: February 2003

1,3,5-trichlorobenzene is used as a probe to study the order parameters in MBBA. The NMR spectrum of 1,3,5-trichlorobenzene in MBBA is reported. (AIP)
Electronic spectroscopy of 1,3-cyclopentadiene, 1,3-cyclohexadiene and 1,3-cycloheptadiene by electron impact
Authors: Frueholz Robert P. , Flicker Wayne M. , Mosher Oren A. , Kuppermann Aron
Published: February 2003

The electronic spectra of three conjugated cis-dienyl systems, 1,3-cyclopentadiene, 1,3-cyclohexadiene, and 1,3-cycloheptadiene have been investigated using electron-impact spectroscopy. Spectra were obtained at impact energies ranging from 20 to 75 eV and scattering angles from 5° to 80°. A single singlet → triplet transition was observed for each molecule at 3.10, 2.94, and 2.99 eV, respectively. Information on the Franck–Condon envelopes was obtained for these transitions. The N→V1, N→V2, and V3, and several Rydberg transitions were also observed in each substance. Some previous unreported superexcited states lying above the first ionization potential were detected.
Nucleation of electrically charged droplets
Authors: De Bibhas R.
Published: February 2003

The presence of a finite electric potential in many nucleation environments is discussed. It is contended that this potential introduces a nontrivial modification in the conventional nucleation theory. (AIP)
Vibrational relaxation HF (v=3,4) by H2, D2, and CO2
Authors: Douglas D. J. , Moore C. Bradley
Published: February 2003

The vibrational relaxation of HF (v=3, 4) in H2, D2, and CO2 has been studied by pumping HF directly from v=0 to v=4. The relaxation rates at 293±2 K of HF (v=3) and HF (v=4) were found to be k3T(H2) = (3.1±0.6) ×10−13 and k4T(H2) = (4.7±1.2) ×10−13 in H2, k3T(D2) = (1.34±0.26) ×10−12 and k4T(D2) = (3.34±0.60) ×10−12 in D2, and k3T(CO2) = (1.01±0.16) ×10−11 and k4T(CO2) = (2.25±0.43) ×−10 in CO2 respectively, all in cm3 molecule−1 s−1. The observed relaxation rate for HF(v=4) in CO2 did not depend on the rotational state which was initially excited for J=0–5.
Thermochemical properties of gaseous Li3O and Li2O2
Authors: Wu C. H. , Kudoa) H. , Ihle H. R.
Published: February 2003

Besides LiO and Li2O, the gaseous species Li2O2 and Li3O were observed by mass spectrometric measurements over solid lithium oxide. From the measurements of the gaseous equilibria Li2O(g)+Li2(g) ?Li3O(g)+Li(g), 2 Li2O(g) ?Li3O(g)+ LiO(g), Li2O2(g)+Li2(g) ? 2 Li2O(g) and Li2O2(g)+ Li2(g) ?Li3O(g)+LiO(g), the atomization energies d°0(Li3O) =229.0±10 kcal/mol and D°0(Li2O2) 293.0±12 kcal/mol were obtained. The ionization potentials were determined as I.P.(Li3O) =4.54±0.2 eV and I.P.(Li2O2) =7.88±0.2 eV, from which the binding energies D°0(Li3O+) =438.0±15 kcal/mol and D°0(Li2O2+) =425.0±16 kcal/mol result. The heats of formation were determined as: ΔH°0(Li3O) =−(54.5±10) kcal/mol and ΔH°0(Li2O2) =−(98.0±12) kcal/mol.