bluuebunny/crossref_metadata_2025 huggingface dataset:
Principles of electronic structure in transition metal complexes. Additive ligand electronic effects and core–valence ionization correlations for Mo(CO)6−n(PMe3)n where n=0, 1, 2, 3
Authors: Lichtenberger Dennis L. , Kellogg Glen Eugene , Landis George H.
Published: July 2002

Gas phase core photoelectron spectroscopic (XPS) results are reported for a series of trimethylphosphine substituted molybdenum carbonyls: Mo(CO)6, Mo(CO)5(PMe3), cis-Mo(CO)4(PMe3)2, trans-Mo(CO)4(PMe3)2, and fac-Mo(CO)3(PMe3)3. Core ligand additivity, defined as a constant shift in core ionizations with each successive step of ligand substitution, is indicated by these data. The shift per phosphine substitution is −0.65±0.10 eV for the molybdenum 3d5/2 ionization, −0.75±0.11 eV for the carbon (carbonyl) 1s ionization, and −0.78±0.09 eV for the oxygen 1s ionization. Comparison of core and valence data sets for these complexes illustrates a second principle, core–valence ionization correlation. The ratio of the Coulombic valence metal d level shifts to the core metal shifts is 0.74±0.06. This trend, in a system with extensively delocalized metal orbitals, shows that core and valence photoelectron spectroscopies are intimately related and that key additional understanding of electron distributions and bonding can be obtained from correlating the information of these techniques. Simple models for both the ligand additivity and core–valence ionization correlation principles are presented to demonstrate the fundamental features and possible limitations of these principles.
An exact asymptotic relation for the atomic and molecular wave function
Authors: Dawson K. A.
Published: July 2002

The conventional Schrödinger equation for an arbitrary molecular system is written in terms of generalized hyperspherical polar coordinates. This results in some simplification for the purposes of asymptotic analyses. Some comments on the relationship of this construction to collective behavior in atoms are made.
On the measurement of molecular anisotropies using laser techniques. II. Differential absorption of circularly and linearly polarized light
Authors: Bain A. J. , McCaffery A. J.
Published: July 2002

In this paper we describe a method which yields an unambiguous measure of the state multipolar moments of an anisotropic array of the angular momentum components of an assembly of ground state molecules. The method involves the measurement of circularly and linearly dichroic, single photon absorption and through such measurements, state moments having K≤2 may be directly obtained. The advantages of this technique over polarized laser fluorescence are discussed.
The ideally polarizable interface: The metallic boundary limit
Authors: Alastuey A. , Jancovici B. , Blum L. , Forrester P. J. , Rosinberg M. L.
Published: July 2002

The model of a classical one-component plasma in the vicinity of a metallic hard wall is shown to be a limiting case of an ideally polarizable interface.
Stationary transport with partially reflecting boundary conditions. II
Authors: Cole R. G. , Protopopescu V. , Keyes T.
Published: July 2002

We consider the stationary monoenergetic transport equation (the Lorentz model) in a semiinfinite geometry with most general nonmultiplying boundary conditions at the wall x=0, accounting for absorption, specular, diffuse, and ‘‘selective’’ reflection, or combinations thereof. Performing the numerical study of a (partially) ‘‘thermalizing’’ wall, we investigate the density profile n(x), the Milne extrapolation length xM, and the space dependent diffusion coefficient D(x) as functions of the accomodation and ‘‘selection’’ coefficients. The inversed density profile (equivalent to a negative diffusion coefficient) is numerically computed. As a simple analytically solvable example, a discrete velocity model is discussed in the Appendix.
Theory of laser-stimulated surface processes. II. A generalized-master-equation approach to energy transfer between an IR laser, an adspecies, and phonons
Authors: Beri A. C. , George Thomas F.
Published: July 2002

The time evolution of the vibrational states of an adspecies–surface bond (adbond) excited by IR laser radiation and coupled to phonon modes of the solid is obtained by numerical solution of a generalized master equation. For three levels of a system composed of an atom adsorbed at the end of a linear chain, the average adbond energy is seen to have a monotonic and an oscillatory component. Under certain resonance conditions, energy is continuously absorbed by the adbond from both the laser and the phonons. The Markovian approximation is shown to be inappropriate for this case, and a measure of non-Markovian behavior is proposed. Feedback and synergistic effects are discussed.
Effect of pressure on rotational isomerism of chloroacetone in carbon disulfide
Authors: Taniguchi Yoshihiro , Sawamura Seiji , Murakoshi Isao
Published: July 2002

The effect of pressure on the conformational equilibrium of chloroacetone in carbon disulfide was measured using a high pressure infrared spectroscopy with a diamond anvil cell at the region of C=O and C–Cl stretching vibrational bands up to 12 kbar. The observed frequencies of the C=O stretching vibration decreased with increasing pressure by −0.56 cm−1 kbar−1 for the higher frequency bands and −0.47 cm−1 kbar−1 for the lower frequency bands. The frequencies of C–Cl bands at 6 kbar increased by 0.33 cm−1 kbar−1 for the higher frequency and 0.57 cm−1 kbar−1 for the lower frequency. The pressure effects on the frequency shift were discussed with respect to Bauer and Magat’s theory of solvent shift and intermolecular forces. The volume changes for the transformation from the conformer assigned to the lower frequency to the conformer assigned to the higher frequency were determined to be −1.6±0.1 cm3 mol−1 for C–Cl band and −1.5±0.2 cm3 mol−1 for C=O band. These observed volume changes were considered to be the result of three possible factors: the intrinsic volume difference between isomers which is 0.66 cm3 mol−1; the packing effect of the solute and solvent, 0 to −1.8 cm3 mol−1; and the solvent effect, −3.0 cm3 mol−1. From the pressure dependence of the frequency shifts of the C=O and C–Cl stretching vibrations and the volume changes for the conformational isomerism, it is clear that the lower frequency bands are assigned to the less polar form and the higher frequency bands to the more polar form.
Br* fluorescence from VUV photodissociation of HBr
Authors: Nee J. B. , Suto M. , Lee L. C.
Published: July 2002

The vacuum ultraviolet fluorescence of Br atoms resulting from photodissociation of HBr was observed using both synchrotron radiation and argon discharge lamp as light sources. The fluorescence spectrum in the 150–165 nm region was dispersed and identified. Both the absorption and fluorescence cross sections were measured in the excitation wavelength region of 105.6–109 nm. The upper limit of HBr dissociation energy is determined to be 3.65±0.03 eV.
Momentum eigenfunctions in the complex momentum plane. VI. A local potential function
Authors: Lassettre Edwin N.
Published: July 2002

The square root of the charge density for an atom, or molecule with fixed nuclei, in its lowest electronic state (assumed to be nondegenerate and a singlet) satisfies a Schrödinger type equation with a local potential function. In momentum space the Schrödinger equation becomes: (i) 1/2 (P2+P20)χ +∫v(Q−P)χ(Q)(dQ)=0 with (ii) v(q)=[1/(2π)2]∫eiq⋅r V(dr) and q=Q−P,P0=(−2E)1/2 and χ is the momentum eigenfunction. The potential function V depends on the many-electron eigenfunction and thus provides no means for numerical calculation. However, less direct methods are available for characterizing a function by investigating its singular points. This is not readily applicable to the potential function V but is well suited to the study of the amplitude function v(q). The location and nature of singular points in the complex q plane have been obtained. The positions of the singular points are related by simple formulas to the ionization potentials of the neutral molecule and the positive ion and, except by accident, are branch points. Convergent series expansions in suitable variables are developed and the potential function is recovered by inverting the Fourier integral (ii). V for an atom is expressed as the sum of a Coulomb term, a series of Yukawa potentials e−αir/r,

and a series of functions L/r with L=∑∞m=0(m+1)(−αir/2)m /Γ2(m/2+1). The singular points of v(q) occur in pairs, ±iαi, on the imaginary axis. The constants αi are related to ionization potentials which can be determined by experiment. Singular points have also been located for the one-electron model proposed by Slater. A similar expansion for an atom gives a Coulomb term, a sum of Yukawa potentials, and a series of functions L(αir)/r. The numerical study of Garvey and Green used one Coulomb and three Yukawa potentials and obtained good agreement in energy calculations. The present research suggests that their potential function be supplemented by the function L(αir)/r.
Spectra and structure of organophosphorus compounds. XXIV. Microwave, infrared, and Raman spectra, conformational stability, and vibrational assignment for chloromethylphosphonic difluoride
Authors: van der Veken B. J. , Coppens P. , Johnson R. D. , Durig J. R.
Published: July 2002

The microwave spectrum of chloromethylphosphonic difluoride, ClCH2P(O)F2, has been investigated in the region from 26.5 to 39 GHz. The a-type R branch transitions have been assigned for both the 35Cl and 37Cl isotopic species for the trans conformer on the basis of the rigid rotor model. For the ground vibrational state the rotational constants for the 35Cl isotope were found to be A = 4392.4±2.3, B=1543.36±0.01, and C=1512.30±0.01 MHz and for the 37Cl isotope: A=4395.3±2.7, B=1502.04±0.01, and C=1472.54±0.01 MHz. With reasonably assumed structural parameters for the C–H and P=0 distances as well as the HCH angle, a diagnostic least-squares adjustment was utilized to obtain the other six structural parameters. The dipole moment components were determined from the Stark effect to be ‖μa‖ =2.28±0.05, ‖μb‖ =0.75±0.02, and ‖μt‖ =2.40±0.02 D. The infrared (3500–40 cm−1) and Raman (3500–20 cm−1) spectra of the gas and solid have been recorded. Additionally, the Raman spectrum of the liquid has been recorded and qualitative polarization values have been obtained. Both

the trans and gauche conformers have been identified in the vibrational spectrum of the fluid phases. From a temperature study of the Raman spectrum of the liquid phase the enthalpy differencebetween the trans and gauche conformers was determined to be 370±50 cm−1 (1.06 kcal/mol) with the trans conformer being thermodynamically preferred. Band contour simulation of the infrared gas phase bands also shows that the trans conformer is more stable in this phase. Upon crystallization only the trans conformer remains in the solid state. The asymmetric torsion for the trans conformer was observed as a series of closely spaced Q branches beginning at 82.5 cm−1 and falling to lower frequency and the corresponding transitions for the gauche conformer begin at 72.9 cm−1. These transitions have been used to obtain the potential constants for the asymmetric rotation. All of the normal modes have been assigned based on band contours, depolarization values, and group frequencies. A normal coordinate calculation has been carried out by utilizing a modified valence force field to calculate the frequencies and the potential energy distribution. All of these results are compared to similar quantities in some corresponding molecules.
Transmission function vs energy splitting in tunneling calculations. II. Computer simulation results
Authors: Lau K. F. , Weiner J. H.
Published: July 2002

An idealized model for the quantum tunneling of a particle in interaction with a heat bath is studied by computer simulation. The model may be motivated by consideration of a bound hydrogen–oxygen pair in a metal lattice; the H atom is treated quantum mechanically, the O atom is treated classically, and a double-well potential couples the two. In order to represent the O atom interactions with the rest of the lattice as heat bath, its motion is described by a classical Langevin equation. Computer simulation of the model shows that, with all other parameters held fixed, tunneling through low energy barriers is governed by energy splitting, while for high energy barriers the transmission approach agrees well with simulation results.
Analysis of dielectric loss data using the Williams–Watts function
Authors: Weiss George H. , Bendler John T. , Dishon Menachem
Published: July 2002

There are many polymeric materials whose dielectric properties can be derived from the Williams–Watts relaxation function φα(t)=exp [−(t/τ)α] . In this paper we propose a method for estimating the parameters α, τ, and ε(0)−ε(∞), from dielectric loss data. In contrast to earlier techniques the parameters can be estimated one at a time. Simple approximations to the required functions are given accurate to better than 1%.
Oxidation of BrO−3 in solid matrices studied by ESR. Environment-dependent electronic ground state of bromine trioxide
Authors: Byberg J. R.
Published: July 2002

Bromine trioxide was prepared in KClO4 crystals doped with BrO−3 by reaction with radiation-induced holes at ∼30 K. The observed ESR spectrum bears no resemblance to that ascribed earlier to BrO3, produced analogously in KNO3. While BrO3 is structurally analogous to ClO3, having a large spin density on the bromine atom, the electron spin in BrO*3, the novel form of bromine trioxide, occupies a nonbonding orbital on the oxygen atoms. This finding is attributed to an unusually small spacing of the upper electronic levels which allows perturbations from the actual crystalline environment to govern the electronic ground state of bromine trioxide. An ESR signal associated with self-trapped holes in x-irradiated KBrO3 is consistent with the species BrO*3, which may be the ‘‘normal’’ form of bromine trioxide.
On the phase transition of purple NH4–TCNQ (I)
Authors: Terauchi Hikaru , Kozaki Takashi , Nishihata Yasuo , Sakashita Hirofumi , Yoshikawa Masanobu , Nakashima Shinichi
Published: July 2002

The x-ray diffraction measurement of purple NH4–TCNQ (I) crystal has been carefully carried out near the phase transition temperature (Tc =303 K). The anomalous part of the temperature dependence of the lattice parameter is proportional to the superlattice intensity below Tc. The diffuse scattering can be detected just above Tc.
Statistical mechanics of supercoiling-induced B-to-Z transitions in a closed circular DNA: One-dimensional model system with a double quadratic displacement potential and long range interactions
Authors: Miyazawa Sanzo
Published: July 2002

A configurational partition function for transitions between the right-handed B helix and the left-handed Z helix in a closed circular double stranded DNA is formulated in an idealized model. The twisting potential of base pairs is assumed to be a double quadratic potential with two minima at the B and Z forms and nearest neighbor coupling between base pair twists to be harmonic. In addition, long range interactions attributable to the conservation of linking number between two closed DNA strands are approximated by a harmonic potential of the writhing number that is equal to the linking number minus the total twist. Interactions between phonons and B-Z junctions are neglected as well as interactions between junctions. The configuration partition function is formulated for two cases, one that all base pairs can take the Z form as well as the B form, and another that only part of DNA can take the Z form. Then it is applied to analyzing B-to-Z transitions induced by changing the linking number of a closed circular DNA. The characteristics of B-to-Z transitions are examined in detail as well as experimental data analyses.
Theory of the effect of strong vibronic coupling on circular dichroism spectra
Authors: Dewey T. G.
Published: July 2002

Circular dichroism line shape functions are derived for a system consisting of two excited electronic states coupled to a single harmonic vibrational mode. A microscopic quantum field representation is used to develop the time-dependent one-exciton Green’s functions for two different models of optical activity: the one-electron model and the coupled oscillator model. An analytic form of the Green’s functions for these models is derived using an approximate diagonalization in the strong coupling limit of a general two-level exciton–phonon Hamiltonian [Friesner and Silbey, J. Chem. Phys. 75, 5630 (1981); Friesner, ibid. 76, 2129 (1982)]. Simulated spectra are presented which demonstrate differences between the coupled oscillator and one-electron mechanisms. Possible applications and extensions of this theory are discussed.
Electron spin resonance line shapes of randomly oriented molecules in septet and nonet states by a perturbation approach
Authors: Teki Yoshio , Takui Takeji , Yagi Hirofumi , Itoh Koichi , Iwamura Hiizu
Published: July 2002

The electron spin resonance line shapes of randomly oriented molecules in septet and nonet states are analyzed in terms of the formulas derived from a perturbation treatment to third-order in the fine-structure energy. The method is applied to a ground-state septet hydrocarbon, 3, 3′-diphenylmethylenebis (phenylmethylene), and a ground-state nonet hydrocarbon, m-phenylenebis[(diphenylmethylen-3-yl)methylene], randomly oriented in mixed polycrystalline powders of benzophenone. It is shown that the g factor and the fine-structure parameters are determined from the line shapes of a K-band spectrum with nearly the same accuracy as in a single-crystal experiment. Extra lines have been observed in addition to the canonical lines corresponding to the external magnetic field along the principal axes of the fine-structure tensor. The appearance of extra lines in the spectra of septet and nonet molecules is discussed relative to the third-order perturbation theory.
Temperature dependence of the isotope effect in dissociative attachment
Authors: Christophorou L. G.
Published: July 2002

The isotopic dependence of the cross section for dissociative attachment is shown to be a function of temperature.
Accurate leading term of the relativistic dispersion force between two ground-state hydrogen atoms
Authors: Koga Toshikatsu
Published: July 2002

Using a special form of the nonrelativistic first order perturbation wave function reported very recently for the van der Waals interaction between two ground-state hydrogen atoms, we show that an accurate leading term (proportional to α2R−4) of the relativistic dispersion force of this system can be obtained in an extremely simple manner.
Q-band ESR studies on the origin of magnetic anisotropy in tetrahalogenated semiquinones
Authors: Prabhananda B. S. , Felix Christopher C. , Hyde James S. , Walvekar Anand
Published: July 2002

The g-tensor components associated with tetrachloro-, tetrabromo-, and tetraiodo-benzosemiquinones in frozen solutions of dimethylsulfoxide and ethanol-D at 135 K have been measured by ESR spectroscopy at Q band (35 GHz). Spin-orbit interactions on the halogens make a significant contribution to the g tensor; components in the plane of the aromatic ring, (gx and gy) are enhanced, whereas the component perpendicular to the ring (gz) is decreased. Related solvent effects have been observed in the spectrum of tetraiodobenzosemiquinone; in going from dimethylsulfoxide to ethanol gx and gy were found to increase, whereas gz decreased. It is argued that the positive contribution to gx and gy arises from the participation of halogen pz orbitals in the molecular π orbitals and that the negative contribution to gz in part reflects spin density on the halogens due to σ–π interaction induced configurational admixture in the wave function. Possible participation of halogen d orbitals is discussed. The dominant part of the solvent dependence of the g tensor components is suggested to result from changes in the energy separation between the orbital of the unpaired electron and lone-pair orbitals on the halogens.
Study of electron wave functions in uranium tetrachloride by neutron scattering
Authors: Lander G. H. , Brown P. J. , Spirlet M. R. , Rebizant J. , Kanellakopulos B. , Klenze R.
Published: July 2002

Neutron experiments have been performed to measure the induced spin density distribution in single crystals of uranium tetrachloride at low temperature. A structural refinement has also established the atomic positions and thermal parameters at low temperature and these are in agreement with earlier studies. The spin-density distribution, determined with polarized neutrons, shows small but significant deviations from that expected from the single-ion crystal-field model. Fourier difference maps show a small depletion of the (5f) density near the U site and a small positive increase ∼1 Å from the U site and principally along the shorter U–Cl bonds. We ascribe this to population of a 6d (x2−y2) orbital. No significant spin density is associated with the Cl site. Model calculations are presented which qualitatively account for the observed effect and involve electron transfer from the 5f to the 6d antibonding orbital formed as a result of a covalent interaction between the U 6d and Cl p states. This is the first direct observation of covalency in systems involving 5f 6d electrons.
Screening in chemisorption theory
Authors: van Santen Rutger A.
Published: July 2002

A theory is presented that makes it possible to discuss the effect of plasmon screening on the chemisorption energy as a function of the bond strength/plasmon energy ratio. The correlation effects are shown to disappear for strong bonding and to cancel out in the limiting case of weak bonding. Significant effects are found in the intermediate bonding range, when the tunneling frequency of the adsorbate electrons is of the same order of magnitude as the plasmon frequency. For values representative of chemisorption of hydrogen to a transition-metal surface the contribution to the bond energy may be of the order of 20%. The quantum theoretical analysis leads to effective potentials, which can be readily incorporated into the Newns–Anderson type chemisorption Hamiltonian. Explicit expressions for the screened exchange and the Coulomb hole contributions are derived.
Thermodynamic lengths and intrinsic time scales in molecular relaxation
Authors: Feldmann Tova , Andresen Bjarne , Qi Anmin , Salamon Peter
Published: July 2002

A connection is made between a thermodynamic length defined on the full space of statistical mechanical states and dissipation (entropy produced) in any irreversible process undergone by a system interacting with an environment which is in equilibrium. Vibrational and rotational relaxation are studied for the two cases when the environment has a fixed temperature and when its temperature varies with time. The metric lower bound on entropy produced is found to be excellent. The variation of the instantaneous relaxation time of these microscopic systems is contrasted with the behavior of a macroscopic conjugate-linear (Onsager-type) system.
Infrared laser spectrum of the fundamental band of CO+ (X 2Σ+)
Authors: Davies P. B. , Rothwell W. J.
Published: July 2002

Nine P and R components of the fundamental band of 12C16O+ have been measured using velocity modulation detection. Observed spin-rotation splittings are in agreement with calculated values derived from microwave spectroscopy of the ion. The band center lies at 2183.9193(10) cm−1.
Local spin density functional analysis of exchange and correlation effects on some first row diatomic molecules
Authors: Kemister Gary , Nordholm Sture
Published: July 2002

We have constructed an extended Hartree–Fock computational method and program which is very similar to standard quantum chemical program packages for molecular electronic structure calculations but allows exchange and/or correlation to be treated by a local approximation as an option. The local spin density functionals accounting for exchange and/or correlation can be included in the self-consistent field (SCF) iterations to examine their effect or added in the final estimation of the total energy to gain efficiency at an often marginal loss in accuracy. We report calculations for H2, HF, N2, F2, and OH− in modest basis sets to examine the effect of local approximations for exchange and/or correlation on the bond strength, bond length, and vibrational frequencies of small covalently bonded molecules. The results show a systematic pattern which can be understood in terms of the dependence of the Hartree–Fock exchange effect on the spatial extent of the canonical orbitals.
A diagrammatic construction of a Rayleigh–Schrödinger multiple perturbation theory
Authors: Cullen John M. , Lipscomb William N. , Zerner Michael C.
Published: July 2002

A Rayleigh–Schrödinger multiple perturbation theory is presented in a general formulation useful for energy evaluations beyond the Hartree–Fock level. This theory allows one to computationally take advantage of the structure of the basis set. For example, three- and four-center-like integrals appearing in the second quantized form of the Hamiltonian may be treated as higher order perturbations. Explicit formulas for the wave function to second order and energy to fourth order are also diagrammatically derived. As examples the theory is applied to aromatic cyclic polyenes within the PPP approximation. A perturbation sequence is defined by the magnitude of the integrals. Within this model errors of less than 1 kcal/mol can be obtained even while neglecting 50% of the integrals up to fourth order. Preliminary studies with ab initio calculations show that even a greater percentage of two electron integrals can be neglected with little loss of accuracy when using this scheme.
Angular dependence of Doppler profiles of atomic emission produced in electron–molecule collisions: Estimation of anisotropy parameters
Authors: Nakashima Keiji , Ogawa Teiichiro
Published: July 2002

The angular dependence of Doppler profiles of atomic fluorescence produced in electron impact dissociation of molecules was simulated in consideration of the effect of the anisotropy of dissociation and the ‘‘polarization’’ in magnetic sublevel. The asymmetry parameter b and the polarization of the electric vector of emission Jp are key parameters of Doppler profiles for the excited atom of known translational energy distribution. The difference of two Doppler profiles taken at 90° and 45°, which is denoted as angular difference Doppler profile, is shown to be useful to estimate these two key parameters.
The microwave spectrum of the PCl radical in the X 3Σ− state
Authors: Minowa Tatsuya , Saito Shuji , Hirota Eizi
Published: July 2002

The microwave spectrum of the P35Cl radical in the ground state has been observed by using a source modulation microwave spectrometer. The PCl radical was produced in a 3.5 m long free space cell by a dc glow discharge in the PCl3 gas. The seven rotational transitions of N=5←4 up to 11←10 were observed in the frequency region of 75 to 169 GHz. The observed spectral lines, 105 in total, were analyzed to give the molecular constants: B0=7558.3464(13), D0=0.006 372 1(45), γ0=−91.525(30), λ0=127 542.92(81), and λD=0.136 76(66), all in MHz with three standard errors in parentheses. The magnetic hyperfine coupling constants have also been determined for both the phosphorus and chlorine nuclei. By comparing these constants with the atomic values the spin density and the s character of the unpaired electron orbital have been calculated to be 87.2% and 0.86% for P and 14.1% and 0.11% for Cl. The Cl nuclear electric quadrupole coupling constant has been determined to be −44.6(15) MHz with the three standard deviation in parentheses.
Infrared diode laser spectroscopy of the PCl radical
Authors: Kanamori Hideto , Yamada Chikashi , Butler James E. , Kawaguchi Kentarou , Hirota Eizi
Published: July 2002

The vibration-rotation spectrum of the PCl radical has been observed by infrared diode laser spectroscopy. The radical was generated by an ac discharge in a PCl3 and H2 mixture. The observed lines have been assigned to the v=1–0 and v=2–1 bands of P35Cl and to the v=1–0 band of P37Cl. All the observed lines were included in a least-squares analysis, where ground-state parameters were fixed to microwave values and isotopic relations were assumed to hold for molecular constants of the two isotopic species. The equilibrium values for vibrational changes of the rotational, the spin–spin interaction, and the spin-rotation interaction constants have thus been determined very accurately. It was found that the sign of the αλ constant of PCl is the same as that of NCl, but is opposite to those of O2, SO, S2, and SeO.
The driven Floquet oscillator
Authors: Thiele Everett , Stone James
Published: July 2002

We present an analytical solution for the driven Floquet oscillator equation (i.e., Hill’s equation with a driving term). This equation arises, without the driving term, in the analysis of the stability of periodic solutions in nonlinear system. With the driving term, one includes the interaction with an external field. For quasiperiodic motion we find sharp resonances at the Fourier component frequencies of the Floquet oscillator and corresponding ‘‘line strengths.’’ For chaotic motion there are only broadened spectral features.
Precision ozone vapor pressure measurements
Authors: Hanson David , Mauersberger Konrad
Published: July 2002

The vapor pressure above liquid ozone has been measured with a high accuracy over a temperature range of 85 to 95 K. At the boiling point of liquid argon (87.3 K) an ozone vapor pressure of 4.03×10−2 Torr was obtained with an accuracy of ±0.7%. A least square fit of the data provided the Clausius–Clapeyron equation for liquid ozone; a latent heat of 82.7 cal/g was calculated. High precision vapor pressure data will aid research in atmospheric ozone measurements and in many laboratory ozone studies such as measurements of cross sections and reaction rates.
Role of dielectric screening in atom–surface interactions
Authors: Schwartz Carey
Published: July 2002

The effect of dielectric screening of a substrate by an overlayer is calculated. Both the overlayer and substrate are modeled as dielectric continua which are then treated by linearized hydrodynamics. The effect of dielectric screening is a shift of the plane to which the total van der Waals interaction is referenced. It is found that models of the atom–surface interaction based upon the pairwise summation of atom–atom potentials underestimate the total van der Waals interaction as a result of ignoring dielectric screening. Detailed calculations are then carried out for helium interacting with a rare-gas-coated silver surface.
Collisional energy transfer and macroscopic disequilibrium. Application to azulene
Authors: Forst Wendell , Barker John R.
Published: July 2002

The theory of macroscopic observables, which allows a model-independent analysis of collisional relaxation, is applied to selected high-quality experimental data on infrared fluorescence (IRF) from collisional deactivation of azulene excited to ∼30 000 cm−1 by single-photon absorption from a 337 nm laser. Particular attention is paid to obtaining a secure relation between the experimental IRF intensity signal and the azulene bulk-average vibrational energy 〈〈y〉〉. The azulene system turns out to be special in two respects: the initial population distribution immediately following the laser shot can be reasonably approximated by a delta function distribution, and the time decay of 〈〈y〉〉 is a simple exponential over almost half the energy range. Under these conditions, it can be shown that the initial value of the macroscopic bulk-average energy transfer observable 〈〈ΔE〉〉 is identical to the microscopic per collision average 〈ΔE〉, which, in the azulene case, obeys the linear sum rule, i.e., is linearly dependent on excitation energy. These conclusions, which are free of assumptions concerning the nature of the transition probability, as well as the actual numerical values obtained, are in substantial agreement with the results of an earlier analysis of the data, which used a different approach based on the same microcanonical relationship connecting fluorescence intensity and vibrational energy.
Vibrational energy transfer in HBr–C2D2 mixtures
Authors: Breshears W. D. , Smith I. W. M.
Published: July 2002

Infrared fluorescence from HBr and C2D2(ν3) has been measured following irradiation of HBr–C2D2 mixtures with a pulsed HBr laser. The fluorescence decay from both species yields the total rate constant for deactivation of HBr(v=1) by collisions with C2D2, k=(1.6±0.1)×104 s−1 Torr−1. The exponential rise of C2D2(ν3) fluorescence is characterized by the rate constants k=(3.4±0.2)×104 s−1 Torr −1 for collisions with both C2D2 and HBr, and k=(5.5±2.3)×103 s−1 Torr−1 for collisions with added Ar. A model developed to fit the observations implies that ν3 is populated indirectly by transfer from another, unidentified, level of C2D2, and that the exponential rise constants refer to transfer from ν3 to this level.
Optical dephasing in organic amorphous systems. A photon echo and hole-burning study of pentacene in polymethylmethacrylate
Authors: Molenkamp Laurens W. , Wiersma Douwe A.
Published: July 2002

Picosecond photon echo experiments on pentacene in polymethylmethacrylate (PMMA) show that the homogeneous width exhibits a T1.3 temperature dependence. This behavior is ascribed to coupling of the pentacene transition to randomly distributed low-frequency excitations in the amorphous host. A calculation of the resulting homogeneous width is presented which uses optical Redfield theory as a starting point. From the results of this calculation we conclude that the coupling between the pentacene molecule and the host low frequency excitations is of static dipolar nature and that the density of states of these excitations varies as ω0.3. Results of nonphotochemical hole-burning experiments on the same system are also reported. Comparison of these results with the ones obtained by the photon echo method indicates, that in the hole-burning experiments, the hole width and its temperature-induced broadening are dominated by spectral diffusion.
Structure of solid t-butyl cyanide: Interpretation of experimental data by means of molecular dynamics simulation
Authors: Ferrario Mauro , McDonald Ian R. , Klein Michael L.
Published: July 2002

Molecular dynamics calculations have been carried out on the disordered phase I of solid t-butyl cyanide. The nature of the orientational disorder has been investigated using a variety of intermolecular potentials based on site–site interactions between rigid molecules. The potentials were parametrized, in part, to the properties of the low-temperature, monoclinic phase II. In phase I, rotation around the C–C≡N axis is found to occur on a picosecond time scale, in good agreement with deductions based on neutron scattering data. No evidence has been obtained for preferred orientations for the molecular symmetry axis. The intensities of Bragg and diffuse scattering have been calculated and compare favorably with neutron scattering results. The lattice vibrations have been investigated and it is found that the transverse acoustic phonons are heavily damped, at least for those wave vectors accessible in the simulations.
Concentrated polymer solutions: Nonuniform concentration profiles in tube flow
Authors: Brunn P. O. , Kaloni P. N.
Published: July 2002

The encapsulated FENE dumbbell model has been found highly successful to predict the rheological behavior of concentrated polymer solutions and melts. Here we extend the model to apply to nonuniform flows, with particular emphasis on viscometric flows. For the special case of tube flow nonuniform concentration profiles are predicted, which depend crucially upon the model parameters. Though migration to and away from the tube axis is clearly asserted, the final nonuniformity is rather small in either case.
The liquid–vapor interface of a binary liquid mixture near the consolute point
Authors: Schmidt James W. , Moldover Michael R.
Published: July 2002

The liquid–vapor interface above mixtures of isopropanol (i-C3H7OH) and perfluoromethylcyclohexane (C7F14) has been studied in the vicinity of the consolute point (Tc=363 K). As three-phase coexistence is approached, the excess fluorocarbon adsorbed at this interface increases; the adsorption is expected to diverge at Tc for a mixture of the critical composition. A simple model of the interface which incorporates the adsorption anomaly is compared with our ellipticity measurements. Both the model and our data yield ellipticities which have a finite maximum at 0.1 K above Tc. (In general, the ellipticity is not a monotonic function of the adsorption.) The calculation of the ellipticity uses an exact numerical integration of Maxwell’s equations for a model dielectric constant vs height profile. The model dielectric constant profile for the critical composition is consistent with a short-ranged density vs height profile between the vapor and the liquid mixture as well as a much longer ranged composition vs height profile expected at a boundary of a mixture near its consolute point. The liquid–vapor correlation length (0.6 nm) was estimated from the ellipticity data far from Tc. The correlation length for the composition profile was found by combining our interfacial tension data taken below Tc with a compilation based on two-scale-factor universality. Ellipticity data for noncritical compositions are presented; however, their analysis will be presented elsewhere.
Squeezed spin states
Authors: Macomber James D. , Lynch Robert
Published: July 2002

The squeezed states of a spin-1/2 particle are described, and the response of such a particle to sudden illumination by a resonant, circularly polarized, coherent electromagnetic wave in the absence of relaxation is given. It is shown that the resultant undamped Torrey nutations (Rabi flops) lead to periodic squeezing of the spin states. The error ellipsoids associated with the minimum-uncertainty states for this system are presented. The implications of these results for the squeezing of the field vectors of the electromagnetic radiation emitted by spins and quasi-two-level atomic systems (in states which have been prepared by coherent transient driving fields) are pointed out.
Collisional energy transfer of vibrationally highly excited molecules. V. UV absorption study of azulene
Authors: Hippler H. , Lindemann L. , Troe J.
Published: July 2002

Vibrationally highly excited azulene molecules in the electronic ground state (excitation energy 〈E〉=30 600 cm−1) were produced by excitation with a N2 laser. The stepwise deactivation of the excited molecules in collisions with a variety of 23 inert bath gases was monitored by time-resolved hot UV absorption spectroscopy at 290 nm. Using previously determined calibration curves of the absorption coefficient at 290 nm as a function of the excitation energy 〈E〉, energy-loss curves 〈E(t)〉 were recorded and analyzed with respect to the average energies 〈ΔE〉 transferred per collision. The dependencies of 〈ΔE〉 on the excitation energy 〈E〉 were derived. In most cases, 〈ΔE〉 was found to be only weakly dependent on 〈E〉 above 10 000 cm−1, whereas a stronger rise with energy became apparent only at lower energies. A comparison with earlier IR emission experiments on the azulene system is given.
Conducting polymer solutions: An EPR and INDO/CI study of a radical cation observed in conducting poly( p-phenylene sulfide) solutions
Authors: Murray Daniel P. , Kispert Lowell D. , Frommer Jane E.
Published: July 2002

We report here the observation of resolved EPR hyperfine couplings for the conducting polymer AsF5-doped poly( p-phenylene sulfide), dissolved in liquid AsF3. Correlation of the EPR and INDO results indicates that the observed signal is due to a nonplanar sulfur-centered radical cation with the hyperfine pattern arising from the coupling of the electron to the four meta 1H’s on the adjacent phenyl rings.
EPR and electronic absorption studies of vanadyl ions in the Cd(NH4)2(SO4)2⋅6H2O single crystals
Authors: Satyanarayana N. , Radhakrishna S.
Published: July 2002

EPR studies of vanadyl (VO2+) impurity ions in the Cd(NH4)2(SO4)2⋅6H2O) (CdASH) crystals are reported at 9.4 GHz. The VO2+ ions are found to substitute the divalent cadmium site and have fixed orientations along Cd–Ow bond directions. The angular variation of the EPR spectra in the a*b, bc, and ca* planes are used to determine the principal g and A values and their direction cosines for the V=O orientations with different populations. A correlation between the two V=O orientations and the metal–water bond directions is observed. The observed superhyperfine structure with the intensity ratio 1:4:6:4:1 is attributed to the interaction of a single unpaired electron with the two pairs of equivalent protons through the oxygen ligands and it indicated the amount of delocalization of unpaired spin density from the vanadium nucleus. The electronic absorption spectrum of VO2+ ions in the CdASH lattice was studied at 80 and 300 K. The characteristic spectrum of the VO2+ ion had four absorption bands at 12 158, 13 888, 18 640, and 28 409 cm−1. From the analysis of the spectrum, the first three bands were attributed to d–d transitions and the last band to characteristic charge transfer for the VO2+ ion. The results indicate a tetragonal site symmetry for VO2+ ions in this lattice. The band positions were calculated using the energy expressions and compared with the observed band positions to confirm the above transitions. The best fit values of the crystal field (Dq) and tetragonal (Ds and Dt) parameters were evaluated from the observed band positions.
Momentum space properties and local density approximations in small molecules: A critical appraisal
Authors: Allan Neil L. , Cooper David L.
Published: July 2002

Electron densities obtained from high-quality wave functions are used to assess critically functionals for a variety of molecular properties. We concentrate mainly on those linking the electron density to the moments of momentum, since these relate directly to experimental observables. We also examine exchange and Coulomb functionals, gradient corrections, and information entropies. We determine whether any of the functionals can be considered useful for chemical applications. We examine a range of light molecules near equilibrium geometry, a series of light diatomic hydrides over a range of internuclear distance, and atoms in a range of chemical environments. Closed- and open-shell systems are considered. Large basis sets are used throughout and, for the studies dependent on internuclear separation, we employ correlated wave functions with proper dissociation.
A dipole-supported state in cyanomethyl anion, the conjugate base of acetonitrile. Rotational band assignments in the electron photodetachment spectrum of −CH2CN
Authors: Marks Jeffrey , Wetzel Donna M. , Comita Paul B. , Brauman John I.
Published: July 2002

We report the 1 cm−1 resolution electron photodetachment spectra of cyanomethyl anion and its deuterated analog, trapped and detected in an ion cyclotron resonance spectrometer. Many sharp resonances were observed in the threshold region corresponding to rovibrational transitions from the ground electronic state to a dipole-supported state of the anion which subsequently undergo electron autodetachment. An assignment of the rotational transitions has been carried out, yielding rotational constants. Using spectral band intensities, we have estimated the electron binding energy of the dipole-supported state as 0.020 (±0.006) eV. The adiabatic electron affinities of the neutral radicals ⋅CH2CN and ⋅CD2CN are found to be 1.560±0.006 and 1.549±0.006 eV, respectively. Features of the dipole-supported state in this system have been compared to those in acetaldehyde enolate.
Ni2+–Fe2+ exchange in FeSiF6 ⋅ 6H2O
Authors: Rubins R. S.
Published: July 2002

An anomalously large D parameter determined previously for the Ni2+ EPR spectrum in FeSiF6 ⋅ 6H2O perpendicular to the crystal c axis at 4.2 K is reinterpreted as a reduction of the effective value of g⊥ through Ni2+–Fe2+ exchange. Assuming a superexchange interaction of the form J S ⋅ S′ between a Ni2+ ion and each of its nearest neighbor Fe2+ ions, the resulting value J=+ (0.048±0.005) cm−1 is consistent with the values obtained for similar systems. Direct effects of the exchange interaction on the D and E parameters are shown to be negligible.
Canonical formalism in equilibrium thermodynamics
Authors: Rey de Luna A. , Zamora M.
Published: July 2002

Gibbs’ principle is extended to systems subject to generalized constraints. It is shown that equilibrium thermodynamics can be presented under a canonical structure. Also, it is shown that the canonical phase space provides a natural representation for equilibrium states.
Reply to Comment on electron mobility in the liquid isomeric pentanes
Authors: Freeman Gordon R.
Published: July 2002

Electron mobility in liquid hydrocarbons correlates with molecular sphericity, not symmetry. Accurate measurement of structure factors S(k,ω) of liquid isomeric hydrocarbons is a useful new source of information.
Scaling theory: Energy sudden and dynamically modified relations
Authors: Eno Larry
Published: July 2002

An approach is described for dynamically modifying energy sudden (ES) collisional scaling relations. It is based upon a generalized form of perturbation theory (PT), which contains ES dynamics as the zeroth order approximate. The corresponding first order PT scattering matrix is further modified by exponential unitarization (EPT). Our scaling relations take on the following structure: an input column of S-matrix elements (back) projects through first order EPT (and hence in an approximate fashion), onto the corresponding column of ES elements; a set of ES scaling coefficients (forward) projects these elements onto a new column; the new column (forward) projects through again first order EPT, onto the corresponding scaled column. The effectiveness of this approach is illustrated by application to a simple classical path three-state problem. Two slightly different versions of the approach are compared. We also examine how ‘‘column based’’ scaling predictions compare with ‘‘single element based’’ predictions. Finally, a number of avenues for further development and application are discussed.
Centrifugal distortions in molecules: An a
b i
n
i
t
i
o approach
Authors: Lohr Lawrence L. , Popa Jean-Michel J.
Published: July 2002

An ab initio approach to the theoretical description of centrifugal distortions in molecules is presented. The method is based on the calculation of the electronic energy changes and gradients accompanying rotationally induced distortions. A centrifugal distortion pathway in nuclear coordinate space is defined. Results are presented at the HF/6-31G** level for NH3, CH4, BF3, and SF6, and at the Guillemin–Zener level for H+2. Quartic centrifugal distortion parameters are computed for each molecule, with distortion anisotropies presented in the form of tensor coefficients. Centrifugally induced electric dipole moment coefficients are presented for CH4 and BF3 together with dipole moment changes for NH3. Agreement with experiment and with conventional theoretical descriptions is generally quite satisfactory, particularly for the tensor coefficients representing the cubic anisotropy in the distortions of the spherical tops CH4 and SF6.
Collisional deactivation of I(5 2P1/2) by F2
Authors: Berman Michael R. , Whitefield Philip D.
Published: July 2002

The collisional deactivation of I*(5 2P1/2) by F2 was studied in a flow system by monitoring the time-resolved infrared emission from I*. The excited iodine atoms were produced by 266 nm laser photolysis of CF3I. A dark reaction between CF3I and F2 hindered experimental measurements and complicated their interpretation at high F2 concentrations.The data obtained at F2 concentrations at which the extent of the dark reaction was minimal gave the total deactivation rate constant (quenching and reaction) of I* by F2, kF2=(5±3)×10−14 cm3 molecule−1 s−1.