bluuebunny/crossref_metadata_2025 huggingface dataset:
On the role of Fermi resonance in the spectrum of water in its condensed phases
Authors: Sceats Mark G. , Stavola M. , Rice Stuart A.
Published: February 2003

In this paper we present a theoretical analysis of the intramolecular stretching spectrum of D2O in H2O and H2O in D2O for both ice I and amorphous solid water H2O(as). The model includes the dependence of the harmonic stretching (krr) and stretch–stretch interaction (krr′) force constants on hydrogen bonding as well as Fermi resonance between the stretching fundamentals and the bending overtone. Provided that the width of the bending mode is broadened by intermolecular coupling, then the model reproduces the anomalously large widths and splittings in the stretching spectrum recently reported by Devlin et al. for D2O in H2O ice I and H2O(as). The value of the Fermi resonance interaction force constant k122 required to fit these spectra is accounted for by diagonal harmonic terms in the valence force field representation of the intramolecular potential.
Low frequency Raman scattering and glass transitions in alkali metaphosphate glasses
Authors: Miller Philip J.
Published: February 2003

An investigation of the low frequency Raman scattering spectra of the alkali metaphosphate glasses (MPO3)n (M=Li,Na,K,Cs) has revealed in the calculated Raman spectral density of states a low frequency band of oscillators between 30 and 70 cm−1. The frequency of the band maxima were found to vary directly as the metal–oxygen force constant and as the inverse of the square of the metal–oxygen separation. The analogous bands in the devitrified glass, or crystal, spectra were not observed and they are assigned as the librational motion of the metaphosphate groups about the metal cation sites in the glass induced by the disorder. A linear relationship between the glass transition temperatures and the frequencies of the band maxima is demonstrated. An analysis of the results has suggested that the glass transformation occurs when sufficient thermal excitation of these oscillators results in exceeding an energy barrier necessary for the rearrangements of the metaphosphate groups about the cation in the glass. The results also illustrate that differences between the glass transition temperatures of amorphous P2O5 and each of the glasses in the series arises directly from the differences in the zero point energy contributions of the low frequency mode to the internal energy of these materials.
Fragmentation of SO+2 prepared in state selected vibrational levels
Authors: Weiss Morris J. , Hsieh Ta-Cheng , Meisels G. G.
Published: February 2003

The threshold photoelectron (TPE) and TPE-coincident photoion (CPI) mass spectra of SO2 have been determined over the energy range 15.844 to 16.674 eV with a resolution of about 0.018 eV FWHM. This is sufficient to prepare most individual vibronic states in populations exceeding 85%. In the 2B2 state, excitation of the stretching mode up to ν1=5 is observed, while in the same state the ν2 bending mode may be excited concurrently with not more than one quantum. In this energy range SO+ formation sets on at 15.930±0.005 eV, suggesting that the onset at 0° K should be 15.965 eV±0.005 eV. S+ is produced over a very narrow energy range only; the onset is at 16.334 eV, coincident with the (310 2B2 state of SO2+; S+ disappears at 16.674 eV. This is interpreted in terms of competition between the assymetric stretch mode and the bending mode for intermodal energy transfer from the symmetric stretch mode, with excitation of the bending mode required to give S+.
Characterization of the ?′ state of ammonia observed by three-photon, gas-phase spectroscopy
Authors: Nieman George C. , Colson Steven D.
Published: February 2003

A new state of ammonia has been characterized by means of three-photon absorption (four-photon ionization) spectroscopy. A comparison of the three-photon (MPI) and one-photon (VUV) techniques indicates that the ? excited state gives identical spectra in both cases, but that the ? state appears in the VUV while the nearly isoenergetic ?′ state appears strongly in the MPI spectra. For linearly polarized light the one- and three-photon relational selection rules and intensity factors are found to be nearly identical. Rotational analyses of several bands of both NH3 and ND3 are presented, and these rotational constants are used to simulate the experimental spectra. By analogy with the united atom approximation, it is proposed that the ?′ and not the ? state results from a 2pa″ 2 to 3pa″ 2 excitation and that excitations to 3d orbitals should be considered in any theoretical discussion of the electronic structure of ammonia.
Differential scattering of polarized molecules: Computations for He+CO
Authors: Monchick Louis
Published: February 2003

Calculations have been carried out on the differential scattering cross sections of polarized CO molecules colliding with He atoms. The results are qualitatively different from similar calculations carried out for He–HCl collisions. A rough coupled states theory enables a qualitative interpretation of the elastic scattering and, by inference, suggests that experiments, such as are involved in these calculations, are a true measure of the molecular anisotropy.
Exact local density method for linear harmonic oscillator
Authors: Lawes G. P. , March N. H.
Published: February 2003

Using an exact form for the particle density for N particles moving independently in a linear harmonic oscillator potential, a differential equation is derived for the particle density. This is then shown to be exactly that which is obtained from a local density assumption for the kinetic energy density t, in the form −1/2Σψi(δ2/δx2) ψi. The form of the kinetic energy density functional is then discussed in this example. The implications for wider classes of potential are briefly referred to.
Multiple chemical waves induced by applied electric field
Authors: Schmidt S. , Ortoleva P.
Published: February 2003

In the most common chemical wave medium, the Belousov–Zaikin–Zhabotinsky reaction, most relevant species are ionic. We show that when an electric field is imposed across nonlinear chemical waves in ionic media the system may support multiple types of waves not present when the applied fields is turned off. It is demonstrated that waves may be stopped (i.e., have zero velocity) or that as the applied field is changed beyond a critical level, waves may change discontinuously in character and even reverse their direction of propagation. The potentiality of the induction of a variety of phenomena due to the presence of applied fields seems great.
The internal optic modes of NaClO3/NaBrO3 mixed crystals
Authors: Nichols Henry F. , Frech Roger
Published: February 2003

The internal optic modes of BrO3− and ClO3− ions are studied in a series of NaClO3/NaBrO3 mixed crystals over the entire relative concentration range. Raman spectra and near-normal incidence infrared reflectivity spectra of single mixed crystals and Raman spectra of microcrystalline mixed crystal powders are presented and discussed. Mode mixing of the ν1 and ν3 modes of BrO3− was studied as a function of concentration, and a near accidental degeneracy of ν1 and ν3 was noted in the high dilution limit of matrix isolated BrO3− in a host NaClO3 crystal.
Slater transition-state calculations of shake-up energies in Ne, Ar, and Kr
Authors: Sen K. D.
Published: February 2003

The shake-up transition energies in Ne, Ar and Kr have been calculated using the Hartree-Fock-Slates transition-state theory. The results are compared with those of Hartree-Fock and experimental studies, in order to evaluate the utility of the transition state theory.(AIP)
Determination of ultra-low vapor pressures by submicron droplet evaporation
Authors: Ray Asit K. , Davis E. James , Ravindran Periasamy
Published: February 2003

Vapor pressures as low as of order 10−8 mm Hg (10−10 atm) have been determined by measuring the diffusion-controlled evaporation rates of single submicron droplets suspended in an electric field in the path of a laser beam. Using Mie theory to ascertain the droplet radius as a function of time from light-scattering data, the vapor pressures of dioctyl phthalate (DOP), dibutyl sebacate (DBS), and dibutyl phthalate (DBP) have been determined at temperatures near room temperature. In addition to vapor pressures, heats of vaporization and Lennard-Jones molecular interaction parameters are determined from the experiments.
Measurements of vibrational excitation of N2, CO, and NO by low energy proton impact
Authors: Krutein J. , Linder F.
Published: February 2003

Differential scattering experiments are reported for proton impact on N2, CO, and NO in the energy range Elab=30–80 eV. The measurements include the range of very small scattering angles around 0° as well as the rainbow region. The vibrationally resolved energy-loss spectra show a relatively low vibrational inelasticity for all three systems. Differential cross sections, transition probabilities, and the mean vibrational energy transfer are presented. Rotational excitation is indicated by the broadening of the energy-loss peaks which is most significant for H+–NO. The small-angle scattering data for vibrational excitation in CO show good agreement with the impact parameter theory using the known long-range interactions for this system.
Dependence of nuclear spin polarization intensities on the plane of polarization of the exciting light. A caveat
Authors: Roth Heinz D. , Schilling Marcia L. Manion , Hutton Richard S.
Published: February 2003

The dependence of nuclear spin polarization effects on the plane of polarization of the exciting light has been evaluated for a wide range of radical (ion) pair reactions. The observed variations are of the same order of magnitude and in the same direction as an artifact expected on the basis of optical principles.
Permanent and induced dipole requirements in a
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o calculations of electron affinities of polar molecules
Authors: Garrett W. R.
Published: February 2003

Through the use of a molecular pseudopotential method, we determine the a approximate magnitudes of errors that result when electron affinity determinations of polar negative ions are made through ab initio calculations in which the use of a given basis set yields inappropriate values for permanent and induced dipole moments of the neutral molecule. These results should prove useful in assessing the adequacy of basis sets in ab initio calculations of molecular electron affinities for simple linear polar molecules.
Fluorescence lifetime studies of NO2. III. Mechanism of fluorescence quenching
Authors: Donnelly V. M. , Keil D. G. , Kaufman F.
Published: February 2003

NO2 fluorescence, excited by fixed visible frequencies of a Nd-YAG laser, was measured as a function of time, pressure, and fluorescence wavelength. The low resolution fluorescence spectrum at all excitation wavelengths consists of strong banded features, assignable to ground state vibrational progressions, superimposed on an apparent continuum. The ratio of banded-to-continuum intensity decreases with increasing pressure, indicating that the continuum is partially of collisional origin at high pressures. There is also a red shift of fluorescence at high pressures, indicative of vibrational relaxation within the emitting state. A residual continuum is found under collision-free conditions (0.1–0.01 mtorr) and ascribed to violation of the ΔK=0 selection rules in the initially excited levels of the highly perturbed 2B2 state. The time dependent decay of fluorescence excited at the banded features contains a fast component kB and a weaker, long-lived component kC, identified with the underlying continuum. Rate constants of kB=5.9×10−10 and kC=1.1×10−10 cm3 sec−1 were measured for quenching by NO2. The slow process has been identified with stepwise vibrational quenching while the fast process is best interpreted as a collision induced change in the rotational quantum state of the initially excited state. Computer modelling was used to fit the pressure dependence of the banded-to-continuum intensity ratio and of the fluorescence red shift, using the measured low-pressure spectrum, the two measured quenching rate constants, and a single adjustable parameter Δεvib=1000±500 cm−1, the amount of vibrational energy transferred per vibrational–quenching collision. Quenching rate constants kB and kC were also measured for He, Ar, O2, N2, D2, H2, SF6, CO2, ND3, NH3, H2O and D2O. They range from 0.38 to 2.0 times gas kinetic for kB and from 0.041 to 0.52 times gas kinetic for kC.
A Mössbauer temperature study of a cold nematic liquid crystal: Nematic glass–supercooled nematic
Authors: LaPrice Walter J. , Uhrich David L.
Published: February 2003

A 0.2% (by weight) solution of 1,1′-diacetylferrocene (DAF) in n- (p-methoxybenzylidene) -p-butylaniline (MBBA) was prepared and studied with the Fe-57 Mössbauer effect. The Mössbauer parameters were observed for the temperature range 110–300 K. The recoil-free fraction (f) data showed that the MBBA crystal phase exhibited Debye behavior for the entire temperature range with a Mössbauer–Debye temperature (ϑL) of 70 K. The lower temperature data for the cold nematic also gave a linear lnf vs T plot with ϑL=47 K for the MBBA glass. The ϑL for the nematic glass was indepentent of molecular orientation. The nematic glass–supercooled nematic transition was determined to be Tg=181 K from the deviation of the lnf vs T curve from linear behavior. The nematic glass provided a nonvanishing temperature independent contribution to the Fe-57 vibrational ellipsoil (εL). Above 180 K εL became temperature dependent. Line broadening and a reduction of the quadrupole splitting were observed for the supercooled nematic with increasing temperature in the range 220–240 K. We interpret these results in terms of a model for rotational diffusion of the DAF molecule in the MBBA supercooled nematic. The rotational diffusion appears to occur without simultaneous translational diffusion.
Some inequalities among expectation values of one-electron operators in atomic systems
Authors: Gadre Shridhar R.
Published: February 2003

In equalities among various one-eletrcon expectation values in atome are derived with the sole assumption of monotonically decreasing P(r) and P(P). (AIP)
The Hellmann–Feynman theorem for open-shell and multiconfiguration SCF wave functions
Authors: Yurtsever Ersin , Hinze Juergen
Published: February 2003

It is shown that the Helmann-Feynman theorem holds for equivalence restricted open-shell and general multi-configuration SCF type wave functions constructed from a set of orthonormal orbitals. (AIP)
A photoionization study of ion pair formation from CFCl3
Authors: Ajello J. M. , Rayermann P.
Published: February 2003

The first observations of ion pair formation from CFCL3 by UV photoionization are reported.
Comment on TO–LO splitting in disordered phases of ice
Authors: Whalley E. , Klug D. D.
Published: February 2003

It is argues that transverse longitudinal optical splitting occurs in the O-H stretching region of the vibrational spectrum of ice because of the strong infrared absorption in this region. (AIP)
On the contribution of direct intermacromolecular interactions to the viscosity of a suspension of hard spheres
Authors: Phillies George D. J.
Published: February 2003

The contribution of the contact interaction to the shear and bulk viscosities η and ηv of a suspension of hard spheres : is evaluated by use of the Green–Kubo integral forms. To lowest (second) order in the volume fraction φ, η=η0(1+13.44φ2) and ηv=ηv0(1+4.32η0φ2). Since [J. Chem. Phys. 67, 4690 (1977)] direct interactions contribute to the drag coefficient f in first order in the density, a sphere suspension whose dissipative properties include a substantial contribution from direct intermacromolecular interactions is predicted not to show Debye-type behavior, i.e., for such a system f/η will not be independent of concentration.
Partially diffusion-controlled recombination
Authors: Sano Hisatake , Tachiya M.
Published: February 2003

We extend Tachiya’s method for treating totally diffusion-controlled recombination of a pair of particles to partially diffusion-controlled recombination. The differential equation satisfied by the survival probability of the pair is derived, and solved for several cases of practical interest. Recent experiments on the solvated electron yield in liquid ammonia are analyzed by use of the present theory. It is confirmed that the rather high yield of solvated electrons in irratiated liquid ammonia is due to the slowness of the recombination reaction e−s+NH+4.
The dispersed fluorescence spectrum of NaAr: Ground and excited state potential curves
Authors: Tellinghuisen Joel , Ragone Anthony , Kim Myung Soo , Auerbach Daniel J. , Smalley Richard E. , Wharton Lennard , Levy Donald H.
Published: February 2003

The van der Waals molecule NaAr has been prepared by supersonic free jet expansion of a mixture of sodium, argon, and helium. The A 2Π←X 2Σ+ electronic transition has been excited by a tunable dye laser and the resulting A→X fluorescence has been studied. The dispersed fluorescence spectra display both discrete and diffuse features, corresponding to transitions from excited vibrational levels of the A state to bound and unbound levels of the X state. The characteristic reflection structure in the bound-free spectra permits an unambiguous assignment of the vibrational numbering in the A state. This assignment and the previously measured spectroscopic constants are used to calculate the potential curve of the A state. The discrete structure in the fluorescence spectra is analyzed and, together with the previous measurements, is used to determine the potential curve of the X state in the well region. The repulsive part of the X curve is then deduced through trial-and-error simulation of the biund-free spectra. The potential curves derived in this work are compared critically with results of several previous experimental and theoretical studies of NaAr.
Molecular bonding in Group IIA dimers Be2–Ba2
Authors: Jones R. O.
Published: February 2003

Binding energy curves for low-lying states of Group IIa dimers Be2–Ba2 have been calculated using the local spin-density functional formalism. Where band spectroscopic data are available (Mg2, Ca2), the agreement with experiment is generally good. Bonding trends across the series show some remarkable irregularities, which correlate well with trends in the corresponding bulk materials but which do not follow the trend in the atomic polarizabilities. In the density functional picture, the binding in the Σg+1 states is due to sp- and sd -hybridization resulting from the overlap of charge densities on neighboring atoms. Further experimental work, particularly on Be2 and Sr2, is necessary to clarify the nature of bonding in these systems.
Effects of hydrogen bonding upon the anisotropic reorientation of 2,6-dichlorophenol
Authors: Kratochwill Alwin , Vold Robert L. , Vold Regitze R.
Published: February 2003

The effects of hydrogen bonding upon molecular reorientation in the system dichlorophenol/pyridine/carbon tetrachloride have been studied using nuclear magnetic spin–lattice relaxation techniques. A complete analysis of the relaxation behavior of individual lines in the strongly coupled AB2 spin system of 2,6-dichlorophenol-0-d combined with 13C relaxation rates allowed determination of all three principal components of the rotational diffusion tensor for dichlorophenol. The formation of a pyridine–dichlorophenol hydrogen bond has the effect of slowing down molecular reorientation of both molecules about axes perpendicular to the hydrogen bond while leaving motion about the hydrogen bond axis almost unaffected.
Scaled electron gas approximation for intermolecular forces
Authors: Waldman Marvin , Gordon Roy G.
Published: February 2003

An electron gas theory for intermolecular forces due to Gordon and Kim is modified by multiplicative scaling factors for the kinetic, exchange, and correlation terms in the energy functional. The scale factors are determined uniquely by the condition that the energy functional yield correct results for the corresponding terms in an atom isoelectronic to the molecular systems of interest. The calculated intermolecular forces are in better agreement with experimental data for light neutral atoms such as helium. For systems involving ions and/or heavier neutral atoms, agreement with experiment is not significantly better or worse than with the original theory.
Generalized electron gas–Drude model theory for ion–molecule forces
Authors: Waldman Marvin , Gordon Roy G.
Published: February 2003

A polarized electron-gas theory of intermolecular forces is developed for the case of a spherical ion interacting with a linear molecule. The theory includes, in a unified way, overlap repulsion effects, Coulomb forces, induction effects, and the (small) dispersion forces. Numerical application is made to the cases, Li+–H2 and Li+–N2, and excellent agreement is found with elaborate quantum mechanical calculations for these systems. Comparison with scattering experiments suggests that these measurements correspond to the repulsive potential wall for the orientation of lowest energy, rather than to a uniform average over all orientations.
Resonance-enhanced multiphoton ionization and fragmentation of molecular beams: NO, I2, benzene, and butadiene
Authors: Zandee L. , Bernstein R. B.
Published: February 2003

Using the technique of laser ionization mass spectrometry, studies have been carried out of multiphoton ionization (MPI) and fragmentation of molecules under collision-free conditions. MPI spectra and mass fragmentation patterns are obtained via irradiation of isolated molecules by a pulsed, tunable dye laser focused down on a molecular beam traversing the ion-source region of a quadrupole mass filter. At each resonance, corresponding to m-photon ionization of an n-photon-excited intermediate state, the fragmentation pattern of the ions is measured. Resonance-enhanced MPI/mass spectra provide detailed information on the identity and relative abundances of the ionic fragments formed in the overall n+m photoionization process. From a knowledge of the appearance potentials of the various fragment ions, the minimum number of photons absorbed per molecule can be deduced. Increasing the laser pulse peak energy (or fluence) increases the average number of photons absorbed and thus the extent of fragmentation. However, even at the highest laser peak power densities used, the ionization (and fragmentation) remains extremely wavelength selective; the nonresonant contribution to the ionization is only a small fraction of the resonance-enhanced ion yields. Detailed experimental results on the 2+m photon ionization of benzene (the Johnson band, near 391 nm) are reported. Under strong focusing conditions, the most abundant ion is found to be C+, which implies the absorption of as many as 9 photons per molecule during the 6 ns pulse length of the laser. For I2, two different (n=2) bands were studied: for the Dalby system (near 372 nm), m=1 and 2, while for the Goodman band (near 585 nm), m=4. For trans-1,3-butadiene (near 387 nm), products requiring m=4 are observed. It is estimated that under the conditions of the present experiments ?10−4 of the beam molecules within the focal region are ionized by the laser pulse.
The equilibrium structure and rotational constant of HCC+
Authors: Montgomery John A. , Dykstra Clifford E.
Published: February 2003

Using ab initio electronic structure techniques, the equilibrium structure of HCC+ has been predicted and the resulting equilibrium rotational constant (Be) is 44.3 GHz. Through comparison of the experimentally determined J=1→0 transition frequency with a similarly calculated Be for HNN+, the J=1→0 transition in HCC+ is predicted to occur at 88.2 GHz. Isotopic substitution gives a rotational constant (Be) for DCC+ of 36.3 GHz. An estimate of the hyperfine interaction leads to the prediction that the rotational spectrum of DCC+ will consist of three lines around 72.6 GHz with separations of 0.09 and 0.06 MHz. While error limits from theoretical determinations are not clear cut, the use of a large basis set and careful treatment of electron correlation suggest that an experimentally determined transition frequency for HCC+ is most likely to be within ±0.3 GHz of 88.2 GHz.
Velocity correlations in a family of simple soft core liquids
Authors: Wijeyesekera Sunil D. , Kushick Joseph N.
Published: February 2003

We have used molecular dynamics to study velocity correlation functions in a family of model liquids with continuous repulsive interaction potentials. As the softness of the potential was changed, systematic variations were found in the negative region of the correlation function. The use of a pure repulsive potential somewhat softer than r−12 resulted in dynamic features very similar to an ordinary Lennard-Jones (12–6) liquid, and a still softer core induced oscillations in the correlation function. The observed behavior is interpreted in terms of the temporal coherence of backscattering events.
Internal heavy atom effect on the triplet spin sublevels of the lowest triplet state of naphthalene. I. Radiative and nonradiative decays of the spin sublevels of 1-halonaphthalenes
Authors: Saigusa Hiroyuki , Azumi Tohru
Published: February 2003

The mechanism of the internal heavy atom effect is discussed from the viewpoints of the dynamic and spectral properties of the triplet spin sublevels of 1-halonaphthalenes. The heavy atom effect on the radiative rate constant for phosphorescence emission in the O–O band is most prominent in the Tx emission, somewhat less in the Ty emission, and is small in the Tz emission. (The x and y axes correspond to the long and short axes of the naphthalene molecule, and the z axis is perpendicular to the molecular plane.) The heavy atom effect on the nonradiative decay rate constant is most prominent in the decay of the Tx and Ty sublevels and is small in the decay of the Tz sublevel. These experimental results are interpreted in terms of a mechanism in which spin-orbit coupling involving the halogen atomic orbital plays an essential role. The heavy atom enhancement in the radiative and nonradiative decay of the Tx sublevel is mainly governed by the spin–orbit coupling between the (ππ*) triplet state and (σπ*) or (πσ*) singlet states. The heavy atom enhancement in the radiative and nonradiative decay of the Ty sublevel is, on the other hand, mainly due to the spin–orbit coupling with (nπ*) singlet states, where n stands for the halogen nonbonding orbital lying along the x axis. The radiative and nonradiative decay of the Tz sublevel, however, is not influenced by the heavy atom because the spin–orbit coupling involving the halogen atomic orbital does not possess one center terms.
The effect of a magnetic field on the thermal conductivity of NO–N2 and NO–H2 mixtures
Authors: Bhanja Sisir , De Udayan , Barua A. K.
Published: February 2003

The fractional change of the longitudinal coefficient of heat conductivity, (Δλ⊥/λ), due to a magnetic field applied normal to the temperature gradient in a hot-wire thermal conductivity cell, has been studied for the NO–N2 and NO–H2 mixtures at different concentrations. The contribution, to (Δλ⊥/λ), of the Senftleben–Beenakker effect in the diamagnetic gas (N2 or H2) has been observed at the higher values of applied H/p, where H is the strength of the magnetic field, and P, pressure. Neglecting this feature, we have interpreted the results by applying an extension of Köhler and Raum’s theory. The relevant effective cross sections have also been evaluated from the experimental data.
The adiabatic semiclassical perturbation theory for vibrationally inelastic scattering. II. Three-dimensional treatment
Authors: Cross R. J.
Published: February 2003

The adiabatic theory of vibrationally inelastic scattering of the previous paper is formulated in three dimensions. Additional terms are present due to the angle dependence of the adiabatic reference potential Vo(r,R,γ). The theory is formulated so that the user can select various options to treat the various degrees of freedom. The orbital angular momentum is approximated by either the sudden or classical limits. The rotational angular momentum is either quantized or treated by the sudden approximation. The resulting coupled equations of motion may be solved numerically or by an exponential semiclassical perturbation theory.
The role of unpaired forces in the lattice dynamics of covalent crystals
Authors: Kushwaha M. S. , Kushwaha S. S.
Published: February 2003

To study the lattice dynamics of covalent crystals, a model which, in addition to central (two-body) forces, involves unpaired forces of the type of D.C. Gazis, F. Herman, and R.F. Wallis [Phys. Rev. 119, 533 (1960)] has been developed. The model is used to calculate the phonon dispersion relations of diamond, silicon, and germanium at all the irreducible points of the first Brillouin zone and to calculate phonon density of states, lattice specific heats, and Debye characteristic temperatures. The R. Brout [Phys. Rev. 113, 43 (1954)] sum rule for ionic crystals as extended by H.B. Rosenstock [Phys. Rev. 129, 1959 (1963)]; H.B. Rosenstock and G. Blanken [Phys. Rev. 145, 546 (1966)] for diamond and zincblende crystals has also been verified by calculating the compressibilities of the above crystals. The model satisfies all the symmetry requirements of the perfect crystals. Results show reasonably good agreement with available experimental data.
The adiabatic distorted wave infinite order sudden (ADWIOS) approximation for the calculation of inelastic molecular collision cross sections
Authors: Eno L. , Balint-Kurti G. G.
Published: February 2003

A new approximate method is presented for the rapid calculation of vibrationally–rotationally inelastic molecular collision cross sections. The method treats the coupling between the rotational states, belonging to the same vibrational level, using the sudden approximation. The vibrational states are treated using an adiabatic basis. With this basis it is found that a first order distorted wave approximation gives good agreement with fully converged close coupling calculations. Some previously developed techniques are extended to permit reliable analytic expressions to be formulated for the angle fixed S matrix elements which appear in the theory. The great computational efficiency of the method is based on these analytic formulas which eliminate the need for the numerical solution of differential equations and for the numerical evaluation of difficult integrals. The angle fixed S matrices which result are then treated within the framework of the recently developed sudden approximation to yield inelastic cross sections. The method is applied to the calculation of vibrationally–rotationally inelastic cross sections for the He+H2 system and comparisons are made with close coupling calculations which are fully converged in both rotational and vibrational basis. Analysis of the results shows that for the He+H2 system the sudden approximation fails significantly within the n=1 vibrational manifold at total energies below 1.1425 eV but the validity of the approximation clearly improves with increasing energy. The He+He2 system was used in the present work as it was the only suitable one for which exact calculations were available in the literature for comparison purposes. For heavier systems the sudden approximation will be valid at much lower energies.
A new method for the exact calculation of vibrational–rotational energy levels of triatomic molecules
Authors: Shapiro M. , Balint-Kurti G. G.
Published: February 2003

A new method is presented for the calculation of the vibrational–rotational energy levels of a triatomic molecule. The method provides a means of solving Schödinger’s equation for the bound energy levels of a triatomic system as exactly as desired. The relative motion of the atoms is governed by a potential energy surface, which can be of arbitrary form, but must, naturally, be specified. The method utilizes the well developed techniques of molecular scattering theory and is formulated in a body-fixed reference frame. The bound state energies appear in the theory as first order poles of a specially constructed T matrix element. Because the analytic behavior of these poles, as a function of the energy, is well defined, the exact bound state energies are easily found. The theory has been applied to the water molecule and results are presented for the lowest five vibrational–rotational energy levels corresponding to zero total angular momentum. These results agree well with previously published values.
High overtones of C–H stretch in liquid benzene measured by laser optoacoustic spectroscopy
Authors: Patel C. K. N. , Tam A. C. , Kerl R. J.
Published: February 2003

We present a first measurement of the absorption profile of the eighth harmonic of the C–H stretch in liquid benzene using a recently developed optoacoustic absorption measurement technique involving a pulsed dye laser and submersed piezoelectric transducer. The absorption maximum occurs at 21 040±7cm−1, with a peak absorption coefficient of (9.2±1.5) ×10−5 cm−1. The full linewidth of the absorption profile is 354±9cm−1. We have previously reported similar measurements for the sixth and seventh harmonics. We have also obtained spectra of lower harmonics by conventional spectrophotometry. We make a comparative survey of the studies of this series of overtone absorptions. With our accurate determination of the nth harmonic absorption for large n, we propose an improved anharmonic formula to fit the experimental peak positions. We also note that the absorption linewidth increases linearly with n in liquid benzene.
Laser-induced photodissociation of chloroethane molecular ions in the gas phase
Authors: Morgenthaler Lee N. , Eyler John R.
Published: February 2003

Photodissociation of the chloroethane molecular ion (C2H5Cl+) has been carried out in a pulsed ion cyclotron resonance (icr) mass spectrometer using a flashlamp-pumped dye laser. The relative photodissociation cross section and the ratio of the cross sections for the production of the two photoproduct ions (C2H4+, C2H5+) are reported as a function of excitation wavelength betwen 691 and 455 nm. Structure observed in both the photodissociation spectrum and the branching ratio spectrum indicates that dissociation occurs predominantly from excited electronic states of the molecular ion. Some indication of the qualitative features of the excited state potential surfaces is also given.
Theory of the deviation from the Ruedenberg energy relation for molecules
Authors: Mucci J. F. , March N. H.
Published: February 2003

Ruedenberg has proposed that for self-consistent field (SCF) methods, E=3/2Es, where E is the total energy and Es the eigenvalue sum. Here the deviation Δ=E−3/2Es is studied. Deviations of both signs are, in principle, possible. The most transparent form for Δ is that derived from a low order gradient expansion in the electron density. Writing the result of this expansion in terms of the chemical potential μ, it can be seen that when μ is large and negative, Δ is also large and negative. If the relation between μ and electronegativity proposed by Parr et al is used, the strongly electronegative elements will result in Δ large and negative. This prediction is confirmed from available numerical SCF calculations.
Potential energy curves for diatomic zinc and cadmium
Authors: Bender Charles F. , Rescigno T. N. , Schaefer Henry F. , Orel A. E.
Published: February 2003

Molecular electronic structure theory has been applied to the low-lying electronic states of Zn2 and Cd2. Gaussian basis sets of size Zn  (13s 9p 5d) and Cd  (15s 11p 7d) have been optimized in atomic calculations on the ground 1S and excited 3P electronic states. The general contraction scheme of Raffenetti has been used to reduce these primitive Gaussian bases to size Zn  (5s 4p 1d) and Cd  (6s 4p 2d) without any degradation in the atomic SCF energies. Following X 1Σ+g ground state SCF calculations, full configuration interaction was performed for the four valence electrons. The resulting potential energy curves for Zn2 and Cd2 are, with some notable exceptions, qualitatively similar. In the case of Cd2, we have obtained potential curves which include spin–orbit coupling and have carried out a detailed analysis of the fluorescence intensity from the first 1u (3Σ+u) excited state.
Energy dependence of the differential cross sections for simple models of ion-induced dipole capture collisions
Authors: Bearman Gregory H. , Gentry W. Ronald
Published: February 2003

At low relative kinetic energies, the product angular distributions characteristic of the short range part of a reactive scattering event may become distorted by a long range attractive force. We examine this behavior for several different simple models of direct, short range encounters, each of which is coupled at long range to an attractive potential term proportional to r−4. The long range attraction does not generally lead to symmetric angular distributions for low-energy capture collisions. The anisotropy of the differential cross section which is observed at high energies may be preserved at extremely low kinetic energies, or it may be substantially altered toward either more symmetric or less symmetric distributions. It is even possible for a distribution which is forward-peaked at high energy to become backward-peaked at low energy, and vice versa. These results suggest that caution is warranted when one wishes to interpret a change in the product angular distribution, in going from high kinetic energies to low kinetic energies, as due to a change in the short range reaction mechanism.
A generalized phase shift approach to the semiclassical S matrix
Authors: Curtiss C. F.
Published: February 2003

The relation between the generalized phase shift and semiclassical S matrix formulations of molecular scattering theory is discussed. It is shown that the classical limit of the generalized phase shift is the modified action. The set of coupled first order or ’’trajectory’’ equations provides an exact quantum formulation of scattering theory which leads smoothly to the semiclassical formulation.
Low frequency vibrational spectra and internal rotation of 2-chlorobuta-1,3-diene, propenoyl fluoride, and propenoyl chloride
Authors: Durig J. R. , Church J. S. , Compton D. A. C.
Published: February 2003

The infrared and Raman spectra of gaseous 2-chlorobuta-1,3-diene, propenoyl fluoride, and propenoyl chloride have been recorded below 300 cm−1. It was observed that the low frequency spectra of these three molecules were quite similar. The infrared spectrum of 2-chlorobuta-1,3-diene exhibited a series of sharp torsional transitions whereas in the Raman spectrum a B-type band was observed. These torsional frequencies have been assigned to the s-trans conformer and no evidence for a higher energy conformer was observed. In the infrared and Raman spectra of the propenoyl halides, bands assigned to the torsional series of both conformers have been observed. The analyses of these spectra were simplified by comparison with that of the 2-chlorobuta-1,3-diene. Asymmetric potential functions and values for ΔH for propenoyl fluoride and propenoyl chloride were calculated. The enthalpy differences of 36 and 215 cm−1 between the lowest energy levels of the s-trans and s-cis wells for the propenoyl fluoride and chloride, respectively, were obtained.
Microwave, infrared, and Raman spectra and structure of germyl isothiocyanate
Authors: Durig J. R. , Li Y. S. , Sullivan J. F.
Published: February 2003

The microwave spectra of H3 70Ge 14NCS, H3 72Ge 14NCS, H3 74Ge 14NCS, the corresponding -d3 compounds, H3 70Ge 15NCS, H3 72Ge 15NCS, H3 74Ge 15NCS, and H3 74Ge 14N 13CS have been recorded and analyzed from 12.4 to 40.0 GHz. The spectra are consistent with those for a symmetric top with a very low-frequency bending mode. Relative intensity measurements of the excited states indicate that the GeNC bending mode is about 50 cm−1. The rs distance for the Ge–N and N=C bonds were determined to be 1.817±0.015 Å and 1.144±0.015 Å, respectively. Other structural parameters were estimated which were consistent with the rotational constants of the 10 isotopic species. Infrared spectra of gaseous and solid GeH3NCS and GeD3NCS and Raman spectra of the corresponding liquids and solids were recorded from 30 to 3000 cm−1. The vibrational spectra of the gases are only consistent with a molecule with C3v symmetry. A complete vibrational analysis is presented and a normal coordinate calculation has been carried out.
Electroneutrality effects on aluminum order in sodium feldspar: A two-dimensional model
Authors: Andersen Gregory R. , Mazo Robert M.
Published: February 2003

A two-dimensional analog model for the mineral albite is investigated in order to evaluate the effect of local charge neutrality on the aluminum–silicon order–disorder in the crystal. The configurational entropy and order parameter, as functions of the temperature, are calculated within the quasichemical approximation. Model calculations using our definition of local charge balance show a significant change in the temperature dependence of the entropy and order parameter over what would be expected if local charge balance were not rigorously obeyed.
Relations between SCF and Slater’s orbital energies in closed-shell configurations of isoelectronic atoms and ions
Authors: François A. , Pujol L.
Published: February 2003

Simple relations between SCF and Slater’s orbital energies are established in closed-shell atomic electronic configurations. Using elementary screening constants taken from the literature, ionization potentials of various isoelectronic ions are evaluated and compared with experimental values.
An ENDOR study of the geometry of the lowest triplet state of benzil
Authors: Chan I. Y. , Heath Barbara A.
Published: February 2003

We present the results of our optically detected ENDOR investigation of the lowest triplet state of benzil. The interaction between the total electron spin and nuclear spins placed at strategic positions throughout the molecule was used to probe the molecular geometry. 13C substitution at the carbonyl carbons led to the dihedral angle, while proton A tensors were used to deduce the ring twist. The geometric information resulted from a point–dipole calculation which reproduced the 13C and proton A tensors by optimizing geometry and spin density distribution. A dihedral angle of 157° was found, substantially larger than the ground state value of 111°, though significantly different from a trans-planar configuration. The ring twist angle was found to be 24°.
Line shapes for attachment of threshold electrons to SF6 and CFCl3: Threshold photoelectron (TPSA) studies of Xe, CO, and C2H2
Authors: Ajello J. M. , Chutjian A.
Published: February 2003

Using the technique of threshold photoelectron spectroscopy by electron attachment (TPSA), the shapes of the threshold electron attachment cross sections for SF6 and CFCl3 are determined by direct photoionization measurements of the 2P1/2 level of Xe+. The observed TPSA line shape is deconvoluted using a Lorentizian attachment profile with full-width at half-maximum of 30 meV for SF6 and 25 meV for CFCl3. In addition, TPSA spectra of the ground electronic states of CO+ and C2H2+ are reported. In CO+ the intensity of the threshold spectral features are dominated by autoionization, while for the vibrational features of C2H2+ direct photoionization is more important. The two processes (autoionization and direct ionization) are characterized by different TPSA spectral line profiles.
Photovoltaic properties of metal-free phthalocyanines. I. Al/H2Pc Schottky barrier solar cells
Authors: Loutfy Rafik O. , Sharp James H.
Published: February 2003

The photovoltaic properties of Schottky barier solar cells, made by dispersing particles of the x form of mental-free phthalocyanine in a binder polymer and sandwiching between NESA (SnO2/Sb) and aluminum electrodes, have been studied. A power conversion efficiency of over 6% for transmitted light at low power densities (0.06 W/m2) has been obtained for monochromatic irradiation at 670 nm. At peak solar power density (1400 W/m2) the extrapolated power conversion efficiency (η) for transmitted 670 nm irradiation decreases to 0.01%. The decrease in η with intensity was attributed to a space charge limitation due to nonlinear resistance. The devices exhibit Voc’s as high as 1.1 V, but are still limited by a field dependent quantum efficiency. Analysis of the action spectra of these devices revealed the formation of a thin photoactive depletion region (∼400 Å) at the semiconductor/metal interface. These devices are capable of capturing 30% of the solar spectrum within the photoactive region. The effect of pigment loading, cell thickness, light intensity, binder materials, doping and dye sensitization has been studied. Based upon sunlight absorption, theoretical efficiencies for these devices appear high.
Reactive quenching studies of Xe  (6s, 3P2) metastable atoms by chlorine containing molecules
Authors: Kolts J. H. , Velazco J. E. , Setser D. W.
Published: February 2003

The XeCl* emission spectrum has been used to study the reactions of Xe  (6s, 3P2) metastable atoms with 20 chlorine containing reagents. Although the total quenching rate constants are large, only Cl2, the mixed halogens and Group VI chlorides have high product branching fractions for XeCl* excimer formation. From analysis of the low pressure XeCl* emission spectra, the ratios for XeCl  (III,1/2 or B,1/2) and XeCl  (II,3/2 or C,3/2) formation were determined. Using results presented in the following paper, the vibrational energy distributions of the XeCl* molecules also can be estimated. A wide difference, depending upon reagent, is observed for the vibrational energy disposal. The short wavelength limit of the XeCl  (B–X) emission can be used to assign upper limits to D°0  (R–Cl) and this work gives D°0  (SCl–Dl) ?44.7; D°0  (ClS2–Cl) ?46.2, D°0  (SOCl–Cl) ?53.9; D°0  (SO2–Cl) ?58.5, and D°0  (PCl2–Cl) ?77.7 kcal mole−1. For purposes of comparison, the XeCl* emission spectra also were obtained from the reaction of Xe  (6s, 3P1) resonance atoms with Cl2, PCl2, CCl4, and COCl2. The branching ratios and energy disposal for Xe  ( 3P2) and Xe  ( 3P1) reactions appear to be qualitatively similar. Based upon all of these data, the dynamics of the reactions between Xe  ( 3P2) and the chlorine containing reagents are discussed and compared to the models in the literature used previously for the reactions of alkali metal atoms with halogen containing molecules. Characteristic XeI* and XeBr* spectra from Xe  ( 3P2) atom reactions are included in an Appendix.
Thermochemical properties of the gaseous tantalum fluorides
Authors: Lau K. H. , Hildenbrand D. L.
Published: February 2003

The gaseous tantalum fluoride species TaFn, with n=1 to 5, were generated under equilibrium conditions by admitting SF6(g) to a tantalum effusion cell at temperatures in the range 1000–2500 K. Mass spectrometry was utilized to establish the species identities and then to study several reaction equilibria. Reaction enthalpies were derived primarily by second law analysis, from which the standard enthalpies of formation at 298 K of TaF5 (−424.6 kcal/mol), TaF4 (−305.2 kcal/mol), TaF3 (−194.0 kcal/mol), TaF2 (−68.7 kcal/mol) and TaF (69.2 kcal/mol) were derived, all ±3 kcal/mol. Estimated thermodynamic functions of the Ta–F species, based on data for the neighboring tungsten fluorides, were found to be quite compatible with the equilibrium data. Equilibrium gas phase compositions in the Ta–F system, calculated over a range of temperatures for several pressures using the data reported here, correlate closely with kinetic data on the reaction of Ta with F atoms. The sharp decline in reaction rate above 2000 K can be accounted for on purely thermodynamic grounds.