bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin–orbit coupling in the excited states of ferricytochrome c and deoxyhemoglobin studied by magnetic circular dichroism
Authors: Livshitz M. A. , Arutyunyan A. M. , Sharonov Yu. A.
Published: February 2003

Magnetic circular dichroism of ferricytochrome c and deoxyhemoglobin has been measured through their Soret bands at 300 and 80 °K. The MCD of both molecules is found to be temperature dependent (as 1/T) and to have derivative shape in respect to absorption band. The observed MCD is concluded to be the sum of closely spaced paramagnetic C-type effects of opposite signs. The most striking observation is the sign difference for MCD spectra of low spin (S=1/2) ferric heme in cytochrome c and high spin (S=2) ferrous heme in deoxyhemoglobin. The obtained results are interpreted in terms of spin orbit coupling. Two possible mechanisms of spin orbit coupling are discussed. One of them is the usual interaction of the angular momentum of an electron with its own spin, the other is the interaction of circular orbital motion of an electron with a foreign spin located at the metal atom inside the circular current. The two mechanisms give spin orbit coupling constants of opposite sign. The observed MCD seems to indicate the former mechanism to be dominant in the deoxyhemoglobin and the latter one to be dominant in ferricytochrome c.
Electron impact investigation of electronic excitations in furan, thiophene, and pyrrole
Authors: Flicker Wayne M. , Mosher Oren A. , Kuppermann Aron
Published: February 2003

The electronically excited states of furan, thiophene, and pyrrole have been studied by electron impact at scattering angles from 0° to 80°, and impact energies of 30 and 50 eV. Low-lying features at 3.99 and 5.22 eV in furan, 3.75 and 4.62 eV in thiophene, and 4.21 eV in pyrrole are identified as singlet → triplet transitions. The locations and, for furan and thiophene, the energy splittings of these excitations suggest that they are analogous to the lowest π → π* singlet → triplet transitions in benzene, and that these heterocycles have appreciable aromatic character. A weak feature observed in pyrrole at 5.22 eV is attributed to an optically forbidden singlet → singlet transition. In all three molecules, transitions to several superexcited states are observed.
Optimization of diatomic state mixing in diatomics-in-molecules theory: The CHn potential-energy surfaces
Authors: Eaker Charles W. , Parr Christopher A.
Published: February 2003

The diatomics-in-molecules (DIM) theory is extended to include larger valence bond (VB) basis sets and the optimization of mixing between the diatomic VB structures. This mixing is essential to the calculation of DIM potential-energy hypersurfaces (PEH) using basis sets large enough to generate more than one diatomic state of a given symmetry. In keeping with the philosophy of DIM, the diatomic state mixing is treated as being independent of the number of atoms in the molecule. The method is used to calculate ground and excited state potential energies for CH2, CH3, and CH4. These extended DIM results demonstrate a number of improvements over earlier DIM methods and are in good agreement with ab initio and experimental results.
Attractive well of He–He from 3He–4He differential elastic scattering measurements
Authors: Burgmans A. L. J. , Farrar J. M. , Lee Y. T.
Published: February 2003

The elastic differential cross section for 3He–4He was measured at a relative collision energy of 0.799×10−14 erg, approximately five times the well depth. The data are fitted to a multiparameter potential form with ε/k=10.57 °K and rm=2.97 Å. Comparisons with recent experimental and theoretical helium potentials are made. No evidence for a significant isotope effect in the 3He–4He and 4He–4He interactomic potentials is found in this work.
Computer simulation of anisotropic molecular fluids
Authors: Kushick J. , Berne Bruce J.
Published: February 2003

We have extended the molecular dynamics method to permit the simulation of systems containing cylindrically symmetric molecules with arbitrary eccentricity. This extension is accomplished by means of a potential energy function which models the primary interaction effects of molecular anisotropy, and which is mathematically convenient for computer use. The method is then applied to two problems, one involving the stability of the nematic liquid crystal phase, and the other illustrating the effect of cooperative reorientation on spectral line shapes.
Optical linewidths in strongly absorbing molecular crystals
Authors: Greer William L.
Published: February 2003

To explain large optical absorption linewidths in strongly absorbing molecular crystals, we introduce a line broadening theory which includes exciton destruction at a crystal surface. When this surface decay channel is included for strongly allowed transitions, the average exciton lifetime is very short since most of the excited molecules are initially near the illuminated surface. We develop the theory in general and apply the results to the lowest singlet–singlet transition in crystalline anthracene. This exciton quenching mechanism accounts for the width of the b-polarized anthracene linewidth at T=0 °K. We also report calculations for crystalline tetracene, and phenanthrene, but are unable to draw any firm conclusions because of experimental ambiguities.
Perturbative solution of equations of motion for excitation and ionization processes
Authors: Simons Jack , Jo/rgensen Poul
Published: February 2003

The equations of motion (EOM) which correspond to electronic excitation or ionization events are analyzed within the framework of perturbation theory. The choice of the Hartree–Fock Hamiltonian as the zeroth order Hamiltonian permits the perturbation equations to be solved in a convenient closed form. A comparison of the results for excitation processes with those given by the random phase approximation (RPA) is made. The role of two particle–two hole excitation operators, which are absent in the RPA, is discussed. Finally, connections are made between the Green’s function approach to calculating ionization energies and the perturbation theory treatment of the EOM corresponding to ionization processes.
rf spectrum and hyperfine structure of formic acid
Authors: Chardon Jean-Claude , Genty Claude , Guichon Daniel , Theobald Jean-Gérard
Published: February 2003

Several transitions of rf spectrum of K-type doubling of HCOOH were observed, using a molecular beam spectrometer with 1 kHz resolution. The hyperfine structure for about ten transitions is resolved. The spin–rotation coupling constants of the two protons can be deduced. We find Maa1=−7.50±0.2 kHz, Mbb1=−7.2±4 kHz, Mccu1= 7.5±4 kHz, Maau2=−6.55±0.2 kHz, Mbbu2=8.2±4 kHz, Mccu2=−8.6±4kHz. The constants labeled 1 refer to the proton bounded to the oxygen atom.
The effect of quasispherical solutes on the nematic to isotropic transition in liquid crystals
Authors: Martire D. E. , Oweimreen G. A. , Ågren G. I. , Ryan S. G. , Peterson H. T.
Published: February 2003

When nonmesomorphic solutes are added to nematic liquid crystals, the nematic–isotropic transition temperature is depressed and a two-phase region is observed. The slopes, βn and βi, of the nematic and isotropic phase boundary lines in the reduced nematic–isotropic transition temperature (T*) vs solute mole fraction (x) diagrams are reported for binary mixtures of quasispherical solutes with nematic liquid crystals. The systems studied are Me4Sn, Et4C, Et4Sn, Pr4Sn, Bu4Pb, and Bu4Sn (Me = methyl, Et = ethyl, Pr = propyl, and Bu = butyl), mixed with p-methoxybenzylidene-p′-n-butylaniline (MBBA), and CCl4 mixed with p-p′-di-n-hexyloxyazoxybenzene (DHAB). Also reported are infinite dilution solute activity coefficients for several mixtures involving Et4C and CCl4. The experimental results are compared with predicted values from statistical–mechanical theories based on (a) a lattice model of hard rectangular parallelepipeds and cubes, (b) a virial expansion treatment of hard spherocylinders and spheres, and (c) a proposed modification of a mean field treatment (Maier–Saupe type) of axially symmetric and spherical molecules. All three models correctly predict the observed trend of increasing βn and βi with increasing solute size and yield predicted slopes which are at least within a factor of 2 of the experimental slopes. The modified mean field approach is found to give the best agreement with the activity coefficient data. A simple experimental method is proposed for estimating the effect of potential impurities (x?0.01) on the nematic–isotropic transition, and possible directions for future research in this area are suggested.
Quantum mechanical scattering studies using 2D cubic spline interpolation of a potential-energy surface
Authors: Sathyamurthy N. , Kellerhals G. E. , Raff L. M.
Published: February 2003

The quantum mechanical scattering results for a collinear A+BC exchange reaction using an analytic surface are compared with those obtained by the use of the corresponding spline fitted surface. (AIP)
Scattering of high-velocity He and Ar beams by methane, silane, and germane
Authors: Amdur I. , Engler M. J. , Paulsen D. E. , Jordan J. E. , Mason E. A.
Published: February 2003

Fast He and Ar beams have been scattered by room-temperature CH4, SiH4, and GeH4 to obtain average atom–molecule potentials for He–CH4, He–SiH4, He–GeH4, Ar–CH4, and Ar–GeH4. Somewhat unexpectedly, the potential for He–GeH4 was intermediate between He–CH4 and He–SiH4; this apparent discrepancy, however, correlates with the bond polarities. The potential for Ar–CH4 can be satisfactorily predicted from that for He–CH4 by means of simple potential models and combination rules. The analogous prediction for Ar–GeH4 is unsatisfactory; reasons for the discrepancy are discussed.
van der Waals interactions of Π-state linear molecules with atoms. C6 for NO(X 2Π) interactions
Authors: Nielson Glen C. , Parker Gregory A. , Pack Russell T
Published: February 2003

Formulas are derived for the van der Waals Cn coefficients for the interaction of a diatomic molecule in a Π electronic state with an S-state atom. Two triatomic states arise from the degenerate Π state. The average of the two energies has the usual Legendre polynomial (PL) angular dependence, but the difference in energies of the two states is shown to have associated Legendre polynomial (PML with M=2) angular dependence. Procedures for including spin orbit coupling are included, and the extension to interactions of Δ- and Φ-state molecules is discussed. Values of the spherical part of the C6 coefficients for the interaction of NO with He, Ne, Ar, Kr, Xe, H, Li, Na, K, Rb, Cs, H2, N2, O2, CO, CO2, and NO are obtained from frequency-dependent polarizability data using Padé approximants. In addition, estimates of all the induction and angle-dependent parts of C6 are given for the NO–atom interactions.
Crystal Coulomb energies. V. The phase transition in Wurster’s blue perchlorate
Authors: Metzger Robert Melville
Published: February 2003

In an extension of earlier work on Wurster’s blue perchlorate, it is shown that Madelung energy calculations by Ewald’s method account fairly well for the small observed enthalpy of transition at 186 °K; the Madelung energy differences are probably due only to observed rearrangements in the perchlorate geometry. The Madelung energy does not, however, favor the large extent of alternation in cation–cation distances determined in the low-temperature crystal structure; this finding may shed some light on the mechanism of transition between the high temperature Curie–Weiss paramagnet and the low-temperature spin-paired diamagnet for this pseudo-one-dimensional organic crystal.
Configuration interaction calculations of low-lying electronic states of O2,O2+, and O22+
Authors: Beebe Nelson H. F. , Thulstrup Erik W. , Andersen Andreas
Published: February 2003

Minimal basis full valence CI calculations of potential curves are reported for more than 300 low-lying states of O2, O+2, and O2+2. A large number of new bound states of O+2 and some metastable states of O2+2 are predicted, and from a comparison with known states of O2 and O+2, predictions are made for the spectroscopic constants of the as yet experimentally unknown states.
Crossed-beam study of the reaction H3+(D2,H2)D2H+
Authors: Vestal M. L. , Blakley C. R. , Ryan P. W. , Futrell J. H.
Published: February 2003

A new crossed-beam apparatus has been applied to a study of the dynamics of simple proton and deuteron transfer reactions [M. L. Vestal, Ph. D. Dissertation, University of Utah, Salt Lake City, Utah (1975)]. The results of detailed studies of the reactions H+3(D2,H2)D2H+ and D+3(H2D2)H2D+ are presented. Results are also reported on the reactions H+3(Ar,H2)ArH+ and H+3(N2,H2)N2H+. The experimental results are presented as contour maps of relative intensity normalized for Cartesian velocity coordinates plotted superimposed on the Newton diagram as described by Cross and Wolfgang [J. Phys. Chem. 73, 743 (1969)]. The data are also presented in an intensity contour plot using the relative translational energy and center-of-mass scattering angle as rectangular coordinates. This method for plotting data from crossed-beam experiments, which was developed in this work, has the advantage that the relative differential cross sections as functions of relative translational energy of the products and center-of-mass scattering angle are directly displayed. Product angular distributions obtained by integrating the contour diagrams over the relative translational energy distributions are also given.
Semiclassical theory of inelastic molecular collisions: Rotational transitions in small-angle dipole–dipole scattering
Authors: Gislason E. A. , Herschbach D. R.
Published: February 2003

The angular distribution of small-angle scattering is calculated for collisions of polar molecules. As found in previous calculations of the total cross section, the magnitude and form of the scattering vary drastically with the amount of inelastic energy transfer between rotation and translation. Collisions with various orientations of the increments Δj1 and Δj2 in the rotational momenta of the two molecules also give markedly different contributions. A semiclassical treatment of the inelastic scattering amplitude is used, with a random phase approximation for the strong-coupling realm at small impact parameters and the Born approximation for the weak-coupling realm at very large impact parameters. A classical time-dependent perturbation calculation is also carried out using a ’’flywheel’’ approximation which averages over the unperturbed rotational motion of the molecules during the collision. These small-angle scattering calculations give good agreement with the angular distribution measurements on CsCl+SbCl3 made by Helbing and Pauly. The resolution correction for total cross section measurements is also derived from these calculations and is found to bring theoretical and experimental cross sections into reasonable correspondence for several systems. The main results are given as simple, closed formulas in terms of reduced variables and are compared with those for the spherically symmetric r−3 and r−6 potentials.
Analysis of tunable diode laser spectra of the ν4 band of 12C316O2
Authors: Weber W. H. , Maker P. D. , Peters C. W.
Published: February 2003

Current-tunable thin-film PbTe diode lasers have been used to obtain Doppler-limited resolution of the ν4 asymmetric stretch band of C3O2 in the region 1565–1600 cm−1. Roughly 70% of the interval was covered using different modes of three lasers, each mode giving a tuning range of 1–3 cm−1. Absolute spectral calibration was obtained from NH3 and H2O, together with the channel spectrum of a 4-cm Ge etalon recorded simultaneously using a double beam technique. Rotational constants were determined for the ν4 fundamental band and five different hot bands associated with the thermally excited low frequency bending mode ν7. The band origin for the ground state transition is 1587.390±0.002 cm−1 and the ν7 hot bands are shifted progressively to lower frequency. The systematic shift of the hot bands was verified independently with temperature difference spectra from a Fourier transform spectrometer.
Raman antiresonance: De-enhancement of Raman intensity by forbidden electronic transitions
Authors: Stein Paul , Miskowski Vincent , Woodruff William H. , Griffin James P. , Werner Kirk G. , Gaber Bruce P. , Spiro Thomas G.
Published: February 2003

The intensities of the Raman lines of the transition metal complexes Co(en)33+, PdCl4=, PdBr4=, and PdI4=, have been investigated as a function of excitation energy in the vicinity of vibronically allowed ligand field electronic transitions. Whereas resonance enhancement usually results in local maxima in Raman intensities at the energies of allowed electronic transitions, we observe minima at the energies of these electronically forbidden transitions. These minima are ascribable to interference between the weak scattering from the forbidden electronic states and strong preresonance scattering from higher energy allowed electronic states. The excitation profiles can be reproduced with a three-state scattering model, using reasonable parameters.
Efficient CI calculations utilizing the symmetric group
Authors: Gallup G. A. , Norbeck J. M.
Published: February 2003

Gallup has recently given a solution to the problem of determining an orthogonal representation matrix for an arbitrary permutation of the symmetric group in terms of sandwich representations. In this paper it is shown how this provides a means for the precalculation and storage of the necessary distinct coefficients needed in the construction of the various Hamiltonian matrix elements of an orthogonal orbital CI calculation. This method has the advantage over those published previously in that the spin degeneracy problem is handled more efficiently. It is shown that this procedure can be utilized with both the ’’construction and storage’’ algorithms and, also, the recently developed ’’direct vector’’ methods when dealing with large Hamiltonian matrices.
The dielectric polarizability of benzene as a function of temperature and pressure
Authors: Vij J. K. , Scaife W. G. S.
Published: February 2003

Measurements of the relative permittivity and density of benzene have been made at temperatures between 25 and 100 °C and at pressures ranging from 246 bar (25 °C) to 3433 bar (100 °C). Permittivity was measured at 1 kHz. The macroscopic dielectric polarizability has been calculated from these data. Measured values have been fitted to polynomial equations with good accuracy, and this has facilitated comparison with other published work. The isochoric values of polarizability vary with inverse temperature in a manner consistent with an equivalent root-mean-square dipole moment of 0.15 D.
Spectra and structure of organophosphorus compounds. XV. Microwave spectrum of ethylphosphine
Authors: Durig J. R. , Cox A. W.
Published: February 2003

The microwave spectra of CH3CH2PH2, CH3CH2PHD, and CH3CH2PD2 have been recorded in the range 18.0 to 40.0 GHz. A-type transitions were observed and assigned for both gauche and trans conformers of ethylphosphine, and b-type transitions observed and assigned for the gauche conformer. The dipole moment components for the gauche conformer were determined from the Stark effect to be: ‖μa‖= 0.86±0.01, ‖μb‖=0.73±0.07, ‖μc‖=0.45±0.05, and ‖μt‖=1.22±0.07 D. For the trans conformers, there was only one component of the dipole moment and it had a value of ‖μa‖= ‖μt‖=1.226±0.005 D. The relative intensity of nine pairs of lines for the gauche and trans were measured at room temperature, and from the ratio of intensities it was found that ethylphosphine exists as a 45% gauche and 55% trans mixture with an energy difference of 200±100 cm−1 and the trans the more stable conformer. With reasonable assumptions for the ethyl moiety, the following structural parameters were calculated: &CCP=110.1±0.2°, rPC=1.880±0.0002 Å and PH2 dihedral angle = 61±2° and for the gauche conformer &CCP= 115.2±0.2°, rPC=1.876±0.002 Å and PH2 dihedral angle = 180±2°.
A simple approach to the equilibrium statistical mechanics of two-dimensional fluids
Authors: Andrews Frank C.
Published: February 2003

A simple statistical mechanical theory previously developed for three-dimensional hard spheres is applied to a system of two-dimensional hard disks to obtain analytical equations for activity and pressure. The first order result, based on only the third virial coefficient, fits the molecular dynamics data for fluid disks significantly better than the seven-term virial series, but (unlike the case in three dimensions) not so well as the scaled particle theory. The second order result, involving the fourth virial coefficient, is the equal of the Padé approximant (3,4) with seven correct virial coefficients built in, and is significantly better than the scaled particle theory. The simple theory is surprisingly accurate even for the hard disk crystal. A simple theory of the two-dimensional Lennard-Jones fluid is obtained by incorporation of attractive wells with a hard core of temperature-dependent diameter. Comparison of the theory with the 17 high-density, supercritical pressures obtained by Fehder using molecular dynamics shows deviations averaging only 3 1/2%. Agreement with the high-density, low-temperature data obtained by Tsien and Valleau using Monte Carlo techniques is not so good. Calculations for the Lennard-Jones 6–12 potential are compared with calculations for the 6–12–3 potential, proposed as more suited than the 6–12 for adsorbed gases.
A simple approach to the equilibrium statistical mechanics of Lennard-Jones fluids
Authors: Andrews Frank C.
Published: February 2003

A simple statistical mechanical theory previously developed for hard spheres and for two-dimensional fluids is applied to three-dimensional particles interacting through a Lennard-Jones 6–12 potential. The results are compared with the molecular dynamics experiments of Verlet, with surprisingly good agreement. Employing the potential parameters obtained for argon from second virial coefficient data results in pressure isotherms which fit the experimental data of Michels with greater accuracy than the choice of potential warrants.
The infrared and Raman spectra of matrix isolated binary and mixed mercury halides
Authors: Givan A. , Loewenschuss A.
Published: February 2003

Raman and ir spectra in the stretching region of all HgX2 and HgXY molecules (X,Y=Cl, Br, I) trapped in solid Kr at 20 °K are reported. Bands are assigned to modes of monomers and dimers. Bond stretching and interaction force constants are calculated and compared. The possibility of a slightly bent structure for several monomers is indicated. The dimer structure is shown to be centrosymmetric in all cases and the identity of the bridged halogen is suggested for the ’’mixed’’ dimers.
High-temperature fast-flow reactor kinetic studies. The AlO/O2 reaction near 1400 K
Authors: Felder William , Fontijn Arthur
Published: February 2003

A high-temperature fast-flow reactor (HTFFR) has been adapted to the study of the kinetics of diatomic radicals via laser induced fluorescence. In this work, the homogeneous gas-phase reaction of AlO with O2 has been investigated near 1400 K. The reaction proceeds via AlO(v)+O2→AlO2 +O; k (v) = (3.1±1.7) ×10−13 ml molecule−1⋅sec−1, with no discernible difference between AlO in the v=0 and 1 vibrational levels.
Theory of rubberlike elasticity
Authors: Wall Frederick T. , Mandel Frederic
Published: February 2003

A statistical mechanical equation of state for rubberlike elasticity can be derived by considering the effect of macroscopic strains on the polymer chain length distributions. In the earliest theories, it was assumed that no intramolecular forces, including excluded volume effects, existed in the polymer, thus implying a Gaussian length distribution. Using more general distribution functions, which, among other things, take into account excluded volume effects, we have derived a more refined equation of state for rubber. The results actually show little improvement over theories based on Gaussian distribution. It is suggested that cognizance of maximum chain lengths, intermolecular interactions and energy considerations will be required before achieving significant improvements in the theories.
Many-body perturbation theory applied to eight states of BH
Authors: Stern Peter S. , Kaldor Uzi
Published: February 2003

The energy of the ground and seven excited states of BH was calculated using many-body perturbation theory (MBPT). The usual Goldstone diagrammatic expansion was applied to the ground state, and the Brandow formulation of degenerate MBPT was applied to the excited states. Corrections to third order (inclusive) were calculated. The resulting vertical excitation energies agree with experiment to better than 3% (about 0.1 eV). Transition moments are also reported.
Optical and microwave properties of metal–ammonia solutions
Authors: Cohen Morrel H. , Webman Itzhak , Jortner Joshua
Published: February 2003

In this paper we present an analysis of the optical and microwave properties of metal–ammonia solutions in the concentration range 2–9 MPM. The analysis rests on the physical picture of a continuous metal–nonmetal transition, intermediated by microscopic inhomogeneities originating from bimodal concentration fluctuations. Effective-medium theory for the complex dielectric constant gives a good account of the optical properties of Li—NH3 in the energy range 0.6–1.4 eV. On the other hand, effective-medium theory is inadequate for the microwave properties, and results of numerical simulation are presented.
Selective excitation and decay of the fluorescence emission arising from the 5D4 state of Tb3+ in POCl3:SnCl4
Authors: Tokousbalides P. , Chrysochoos J.
Published: February 2003

Light excitation of Tb3+ in POCl3:SnCl4 at 488±1 nm giving rise to direct population of the 5D4 state, is accompanied by fluorescence emission whose decay is a simple exponential. On the other hand, indirect population of the 5D4 state, via excitation with shorter wavelengths and relaxation of higher excited states of Tb3+, gives rise to fluorescence emission characterized by a very complex decay law. The nature of the complex decay and the conditions at which maximum fluorescence intensities are attained are discussed. The fluorescence lifetime of the 5D4 state, τ4, is independent of [Tb3+] but decreases slightly at higher temperatures. This is attributed to a temperature dependent quenching process of the 5D4 state of Tb3+ by the solvent.
A theoretical investigation of the solid-state synthesis of (SN)x
Authors: Baughman R. H. , Chance R. R. , Cohen Marshall J.
Published: February 2003

The solid-state polymerization of S2N2 to (SN)x is investigated as it relates to the molecular, crystallographic, and defect structures of this superconducting polymer. The least motion principle predicts that polymerization should occur by a nonunique reaction to form cis–trans polymer chains normal to the 21 axis of the precursor phase. The origin of the disordered structure observed in partially polymerized S2N2 is explained by the occurrence of two symmetry equivalent reaction modes, which produce chains related by a center of symmetry. Both monomer and polymer phases have 2/m point symmetry, but the twofold axes are orthogonal. Consequently, the statistical symmetry of (SN)x is mmm, which is manifest (as a function of thermal history) either by twinning, molecular scale disorder, the statistical nature of the relationship between S2N2 and (SN)x crystal orientations, or a combination of these possibilities. In agreement with prediction, this symmetry is produced by equal population of the twin crystals previously observed in (SN)x. Coordinates associated with disordered chains in partially polymerized S2N2 are successfully predicted by this reaction theory. Fractionally occupied sites are observed in the polymer corresponding to (SN)x chains with different orientations, but the same chain axis direction. The geometry of one of these chains is substantially different from that of the major chain component.
On the long-range configuration interaction between ionic and covalent states
Authors: Janev R. K.
Published: February 2003

The problem of long-range configuration interaction between ionic and covalent states is considered. The existing methods for calculation of this interaction are discussed. An asymptotically exact expression for the long-range configuration interaction at the crossing point of diabatic ionic and covalent potentials is derived. Using this expression the adiabatic energy splitting at the crossing point for H*+H, M+H, and M+O systems (M = alkali atom) is calculated. The results are compared with those obtained by LCAO and variational calculations.
Molecular beam kinetics: Optical model for reactive scattering of alkali atoms and alkyl iodides
Authors: Kinsey J. L. , Kwei G. H. , Herschbach D. R.
Published: February 2003

Angular distributions of reactively scattered alkali iodides have been measured for reactions of thermal beams of Rb and Cs atoms with beams of alkyl iodides RI, where R=CH3, C2H5, n- and i-C3H7, n-C4H9, and n-C5H11. When shifts expected from kinematic differences are taken into account, the qualitative features are found to confirm the results previously obtained for the analogous K atom reactions. The reaction cross sections increase with the size of the alkali atom, from ∼35 Å2 for K+CH3I to ∼45 Å2 for Rb and ∼75 Å2 for Cs. The fall off in intensity of elastically scattered alkali atoms at wide angles also increases for K→Rb→Cs. The anisotropic angular distribution of products, the magnitude of the reaction cross section, and the fall off of the wide-angle elastic scattering for the K, Rb, and Cs systems are correlated in terms of an extended optical model which simply assumes hard sphere interactions for both the entrance and exit trajectories. The reaction probability derived from the data by use of the optical model is large only for collisions which reach the repulsive wall region but even there it is well below unity for thermal energy collisions.
Infrared chemiluminescence studies of chlorine substitution reactions with brominated unsaturated hydrocarbons
Authors: Durana Jean F. , McDonald J. D.
Published: February 2003

The arrested relaxation infrared chemiluminescence technique has been used to investigate the chlorine atom substitution reactions of various olefinic compounds and bromobenzene. Analysis of the infrared emission spectra of the reaction products allows the determination of the product vibrational energy distribution. The observed vibrational energy distributions are compared to those which would be obtained if the products exhibited a statistical vibrational energy distribution. It was found that for the aromatic substrate the product vibrational energy distribution was statistical, while nonstatistical distributions were obtained for olefinic substrates in which Cl was substituted for Br. The implications of the results are discussed in the framework of the current theory of intramolecular energy transfer.
Infrared chemiluminescence studies of the reactions of oxygen (3P) atoms with carbon disulfide and carbon monosulfide
Authors: Hudgens Jeffrey W. , Gleaves John T. , McDonald J. D.
Published: February 2003

The reactions of O(3P) atoms with CS2 and CS were studied by the technique of arrested relaxation infrared chemiluminescence. Emissions from the products CS, SO, and CO were observed from the reaction O+CS2. The CO product channel of O+CS2 is shown to be active and displays a double maxima vibrational population distribution. Models are proposed to account for this population distribution. No emission from the previously reported OCS product was observed, indicating that this product channel is almost inactive with respect to energy partitioning into the stretching modes of OCS. A populuation distribution of CO from the reaction O+CS is reported and is in agreement with previously published results measured by intracavity laser techniques.
Interpretation of the absorption spectrum of silver atoms isolated in a xenon matrix
Authors: Forstmann F. , Kolb D. M. , Schulze W.
Published: February 2003

In contrast to the usual three line absorption spectra which are observed when metal atoms with one valence electron are isolated in noble gas matrices, the spectrum of Ag in Xe exhibits two unique features. It shows four absorption lines, and the relative intensities of two lines depend strongly on the matrix temperature. These experimental results are explained by a model which assumes that in addition to the crystal field splitting the Ag P3/2,jz=±3/2 level interacts with a Xe 6s level giving rise to an additional splitting.
Theory of surface tension for molecular liquids. II. Perturbation theory calculations
Authors: Haile J. M. , Gray C. G. , Gubbins K. E.
Published: February 2003

A general perturbation expansion for the surface tension of a molecular liquid is considered, and the first order term is evaluated. For the special case of a Pople reference potential, perturbation terms up to the third are evaluated for both the general interface and for the Fowler model (abrupt vapor–liquid transition). A Padé approximant to this latter series, similar to that used by Stell, Rasaiah, and Narang for the free energy, is proposed and is used to calculate the effects of dipolar and quadrupolar intermolecular forces on the surface tension. The effects of anisotropic overlap and dispersion forces are also computed, using the series terminated at the second order term. The Padé approximant is also compared with experimental data for hydrogen bromide; using the Fowler approximation, good results are obtained for the low temperature liquid.
A molecular dynamics study of vibrational relaxation in a diatomic molecular liquid
Authors: Riehl J. P. , Diestler D. J.
Published: February 2003

In an effort to gain some insight into vibrational relaxation in liquids, a molecular dynamics investigation of a one-dimensional model of a diatomic molecular liquid has been carried out. The model consists of 100 heteronuclear diatomics arranged head to tail. The potential energy binding the atoms of each diatomic is taken to be strictly harmonic. Only interactions between nearest atoms of neighboring diatomics are taken into account, and these are of the Lennard-Jones (12,6) form. The vibrational lifetime τ′ and dephasing time τ have been computed for the system at various temperatures and densities. Both τ and τ′ decrease as the temperature increases at constant density or as the density increases at constant temperature. For all cases considered, τ<τ′. It is concluded that concerted collective motions apparently play a dominant role in vibrational relaxation in this system.
Study of excitation transfer in a flowing helium afterglow pumped with a tuneable dye laser. III. Transfer and quenching reactions of the He2(3p 3Π) molecule
Authors: Collins C. B. , Johnson B. W.
Published: February 2003

The collisional transfer of excitation from the He2(3p 3Πg) state to other electronically excited states energetically lying within a few KT is examined by optically pumping a flowing helium afterglow with a tuneable dye laser. Rate coefficients for the transfer of excitation to states conserving spin, particularly 3d 3Πu and 3d 3Δu, are found to be greater than 10−10 cm3/sec, resulting in a rapid thermalization of electronic and rotational energy. Relative probabilities of spontaneous radiation for transitions in the visible wavelength range from the product states are found to be 1 and 1/3 for the 3Πu and 3Δu states, respectively, relative to that from the initial 3Πg state. The absence of significant fluorescence from singlet states tends to confirm the conservation of spin during such reactions.
Angular distribution of product internal states using laser fluorescence detection: The Ba+KCl reaction
Authors: Smith Gregory P. , Zare Richard N.
Published: February 2003

The gas-phase reaction Ba+KCl→BaCl+K has been investigated under crossed beam conditions using laser fluorescence detection of the BaCl and K products. The angular distributions of individual BaCl vibrational states have been obtained. For low v, forward and backward peaks are observed; for high v, insufficient product translational energy is present to resolve separate peaks; and for all v, approximately 58% of the BaCl product is forward scattered. The reaction is interpreted as proceeding through an osculating complex. Although this complex is estimated to live one-half of a revolution, the energy partitioning is decidedly nonrandom. The peak of the vibrational product population occurs near v=7, and considerable rotational excitation is present.
Vibrational levels of heteronuclear rare gas van der Waals molecules
Authors: Bobetic M. V. , Barker J. A.
Published: February 2003

Vibrational levels for the diatomic heteronuclear van der Waals molecules formed from ground-state helium, neon, argon, krypton, and xenon are calculated using available potential functions based on other kinds of experimental information.
Electron spin resonance studies of peroxy radicals labeled with 17O in polytetrafluoroethylene
Authors: Che M. , Tench A. J.
Published: February 2003

The ESR spectrum of the radicals formed by the reaction of oxygen with γ-irradiated polytetrafluoroethylene (PTFE) has been obtained using oxygen isotopically labeled with 17O. The presence of lines from two oxygen nuclei both labeled with 17O confirms that peroxy radicals are formed. Two types of peroxy radicals are discussed; firstly, the peroxy chain radical (–CF2–CF(O1Ȯ2)–CF2) with g⊥=2.0220, g∥=2.0060, a∥(1) =40±1 G, a∥(2) =89±1 G at 300 K, and gzz=2.0380, gyy=2.0065, gxx=2.0026, axx(1) =46±1 G, axx(2) =107±1 G at 77 K and secondly, the peroxy propagating radical (–CF2–CF2(O1Ȯ2)) with giso=2.004, aiso(1) =13±1 G, aiso(2) =26.5±1 G at 300 K and identical parameters to the peroxy chain radical at 77 K. The temperature dependence of the ESR spectra is analyzed in terms of the rotational freedom in the polymer. The peroxy chain radical undergoes rotation along the polymer chain axis and the peroxy propagating radical also has this rotation about the chain axis and in addition rotates about the C–O bond which is nearly perpendicular to the main chain axis.
Generalized Langevin equation approach for atom/solid-surface scattering: General formulation for classical scattering off harmonic solids
Authors: Adelman S. A. , Doll J. D.
Published: February 2003

A general theoretical framework for introducing many-body or lattice effects into gas/solid scattering is presented. The theory is presently restricted to classical scattering off harmonic lattices but is otherwise completely general. It is nonperturbative and valid for arbitrary lattice temperature. The theory is based on a formulation of lattice dynamics suggested by and related to the Kubo–Mori theory of generalized Brownian motion. This formulation leads to a generalized Langevin equation (GLE) in which only the coordinates of the gas atom and the n∼1–6 surface atoms directly struck by the gas atom appear explicitly. The remainder of the lattice, which functions as a harmonic heat bath, affects the collision through a friction kernel and a Gaussian random force appearing in the GLE. The GLE can be solved in terms of a tractable number of (n+1) -particle gas–surface trajectories using approximate stochastic techniques. Stochastic solution yields thermally averaged temporal gas particle probability distribution functions (pdf). From the long time limit of these pdf’s all temperature dependent gas–surface cross sections can be found. In the limit of zero friction, the theory gives a convenient method for calculating atom–oscillator thermally averaged cross sections which circumvents laborious Monte Carlo classical trajectory sampling and which can be generalized to treat other gas phase collision problems.
Theory of dynamic light scattering from polydisperse systems
Authors: Aragón S. R. , Pecora R.
Published: February 2003

Analytical expressions for the light scattering autocorrelation function of Schulz distributed Rayleigh–Debye particles are presented. The theory is shown to be valid for spheres, thin rods, disks, and Gaussian coils executing translational diffusion. The polydisperse form factors for these shapes are also given. Analysis of polydisperse data with the expressions given yields the diffusion coefficient of the number average species and the Schulz polydispersity parameter. The effects of polydispersity on the angular dependence of the decay time and the conditions under which the form factor can be neglected are discussed.
Collision-induced spectra of rare gas mixtures: Experimental results and empirical relations
Authors: Bar-Ziv Ezra , Weiss Shmuel
Published: February 2003

Translational absorption spectra were obtained for He–Kr and He–Xe mixtures at 300 °K and for He–Ar, He–Kr, He–Xe, Ne–Ar, Ne–Kr, and Ne–Xe mixtures at 480 °K. These spectra, as well as other rare gas translational spectra available from the literature, were found to obey a rule of corresponding states when expressed in terms of reduced frequencies and intensities. The peak frequencies and intensities, the half-widths and spectral moments, were found empirically to vary as simple functions of the temperature and could be correlated quantitatively with molecular properties. On the basis of these correlations the characteristics of as yet unmeasured spectra could be predicted.
Photoionization and Rydberg states of N2
Authors: Duzy Carolyn , Berry R. Stephen
Published: February 2003

The frequencies and intensities of transitions to Rydberg levels, the direct photoionization cross section, and the angular distribution of photoelectrons of N2 have been calculated for processes associated with N+2(X 2Σ+g) and N+2(A 2Πu). The theoretical model is based on a Hartree–Fock wavefunction for the ground state of N2, and excited state wavefunctions derived from an irreducible-tensorial one-center representation of the effective potential of the N+2 core. The calculations were carried out for several internuclear distances, especially to try to interpret the dependence of the angular distribution on the final vibrational state.
Autoionization of N2
Authors: Duzy Carolyn , Berry R. Stephen
Published: February 2003

Autoionization of N2 has been investigated theoretically, for the energy region between the threshold for production of N+2 in its ground state, and the threshold for production of the first excited state of N+2. Both vibrationally induced and electronically induced autoionization were studied. Rates for the former process, originating with Rydberg states in the npσu 1Σ+u(v′≳0) and npπu 1Πu (v′≳0) series, are of order 1010 sec−1 or slower, and correspond to linewidths of 0.2 cm−1 or less. Electronically induced autoionization is faster, with typical rates 1011–1012 sec−1, corresponding to linewidths of 0.5–5 cm−1, consistent with observations.
X-ray diffraction study of the average solute species in CaCl2 aqueous solutions
Authors: Licheri G. , Piccaluga G. , Pinna G.
Published: February 2003

The structure of several CaCl2 aqueous solutions was studied by means of x-ray diffraction. It is demonstrated that the solutions can be treated as being composed of independent hydrated ions, and for this reason the structural problem is limited to the study of close hydration. This description allows the calculation of structure functions in very good agreement with experimental data when using coordination number six and octahedral geometry for both the ionic species present.
Superstructure and modulation wave analysis for the unidimensional conductor hepta- (tetrathiafulvalene) pentaiodide
Authors: Johnson Carroll K. , Watson Charles R.
Published: February 2003

When acetonitrile solutions of tetrathiafulvalene [i.e., (C3S2H2)2; herein called TTF] and iodine, I2, are allowed to mix by diffusion, monoclinic crystals are formed with the approximate composition (TTF)7I5. These crystals have an electrical conductivity along the needle axis c of 300 ohm−1⋅cm−1 at room temperature. A complete crystal structure analysis based on an approximate supercell with a=48.016(16) Å, b= 16.041(6) Å, c=24.877(7) Å, β=91.31(2) °, Z=12 (RRF)7I5 was carried out using space group P21/a with 225 nonhydrogen atoms in the asymmetric unit. The TTF molecules stack along c and form a TTF subcell a1=a/3, b1=b, c1=c/7, Z1=4 TTF and subcell symmetry C2/m. The iodine atoms are in chains along c and form an A-centered sublattice complex (space group A2/m) with a2=8.213 Å, b2= b, c2=5.023 Å, β2=103.0°, and Z2=2 I. The supercell space group P21/a is the mathematical intersection of the two subcell space groups. The supercell is only approximate because 5c2=25.113(14) Å which is about 1% longer than 7 c1; consequently, the particular crystal studied has the formula (TTF) I0.7076. The crystallographic R (F2) index is 10% for the 3715 x-ray data with intensity greater than 1 sigma and 12% for the complete set of 5733 independent reflections. The stacked TTF molecules are displaced from their ideal sublattice complex positions by displacement waves with rigid-body translational and rotational components. One- and three-dimensional Fourier analyses of the displacements show that TTF molecules are displaced predominantly by translational displacements along b and torsional rotations about c and that the periodicities are related to the iodine sublattice complex. A similar analysis for the iodine substructure show modulations related to the TTF sublattice complex; thus the modulation waves of the system are related to the dual sublattice complex geometries. Special techniques were developed for solving and refining dual-sublattice-complex crystal structures using a principle that interacting sublattice complexes Fourier transform as convoluting reciprocal lattices. Application of these principles to another dual-sublattice-complex problem, the chimney ladder structure Mn15Si26, is discussed.
On the evaporation of small ions from charged droplets
Authors: Iribarne J. V. , Thomson B. A.
Published: February 2003

Experiments are briefly reported which show that small ions separate or ’’evaporate’’ from evaporating droplets carrying electrical charges. A theoretical argument is developed to find in which conditions this ion evaporation can occur; to that end solvation free enthalpies of cluster ions are derived from existing experimental data and the absolute reaction rate theory is applied. The conditions for ion evaporation are compared with those for Rayleigh instability and it is shown that the first process should occur only when the drop reaches sizes of the order of 10−6 cm. The ion evaporation process must be operative in the evaporation of highly electrified cloud droplets when their solute concentration is low.
Study of the structure of molecular complexes. XIII. Monte Carlo simulation of liquid water with a configuration interaction pair potential
Authors: Lie George C. , Clementi E. , Yoshimine M.
Published: February 2003

A water–water interaction potential obtained from configuration interaction calculations has been used to simulate liquid water, at 25 °C, by a Monte Carlo technique. The resulting radial distribution functions and x-ray and neutron scattering intensities are compared with experiment and found to be in satisfactory agreement. Some thermodynamic properties are also computed and discussed. The overall agreement seems to indicate that many-body effects contribute little in determining the structure of liquid water, although they seem to be important for an accurate simulation of internal energy and related quantities.