bluuebunny/crossref_metadata_2025 huggingface dataset:
Correspondence of conduction band minima and electron mobility maxima in dielectric liquids
Authors: Holroyd Richard A. , Cipollini Ned E.
Published: February 2003

Conduction band energies are reported for neopentane and tetramethylsilane up to the critical point.(AIP)
Pseudopotential study of some prominent band systems of the spectra of the I2 molecule
Authors: Das G. , Wahl A. C.
Published: February 2003

Using pseudopotential multiconfiguration self-consistent field (MCSCF) techniques several states of the I2 molecule are studied to explain some important band systems of the spectra of iodine vapor. Spectroscopic parameters of the states X 1Σg+, D 1Σg+, B 3Π0 +u, Π1u3, Π2u3, Π03 +g, Π1g3, Π2g3 are evaluated and compared with known experimental data. Attempts are made to resolve questions in regard to the assignments of molecular states to the above band systems as well as those pertaining to the position and symmetries of various curves that have remained only partially answered over the years.
An intermolecular force model for (HF)2
Authors: Klein Michael L. , McDonald Ian R. , O’Shea Séamus F.
Published: February 2003

An intermolecular potential function describing the interaction between two rigid HF molecules has been obtained by fitting to the ab initio potential energy surface of Yarkony et al. [J. Chem. Phys. 60, 855 (1974)]. In addition, allowance is made for the spherically averaged intermolecular dispersion interaction. The potential function so derived has been used in a molecular dynamics simulation of liquid HF at a temperature of T=278 K and a volume of 20 cm3 mol−1. Results for the radial distribution functions and the diffusion coefficient are presented.
Time resolved study of the uv and near uv continuums of xenon
Authors: Millet P. , Birot A. , Brunet H. , Galy J. , Pons-Germain B. , Teyssier J. L.
Published: February 2003

The spectroscopic analysis of xenon at pressures between 50 and 700 torr shows the presence of several continuums over a wavelength range of 110–700 nm. The kinetics of two of them, 173 and 210 nm, are studied. In both cases, the shape of the light pulse, reconstituted by a time-amplitude conversion method, is defined by a difference of two exponential terms. These terms represent the formation and the decay of the molecular species. The variation of the time constants with pressure allows the reaction constants of the various processes in the kinetic scheme to be found. The continuum in the vuv is brought about by the 3Σ+u state formed by three-body collisions: k= (8.0±0.7)10−32 cm6 s−1 and the lifetime τ=102±2 ns; in the near uv, the molecular state has a shorter lifetime τ′1=8.2±0.5 ns but is formed like the previous one by three-body collisions: k3= (2.3±0.06)10−30 cm6 s−1. The near uv xenon emission constants ave very close to those we previously reported for argon and krypton.
Fine structure of the metastable a 3Σu+ state of the helium molecule. Further results
Authors: Lichten W. , Wik T.
Published: February 2003

The previous results of the measurement of the fine structure of molecular helium have been extended to the N=5 rotational level, v=0, a 3Σu+. The results fit the parameters obtained from lower rotational levels within the experimental errors.
Photon and positive ion production from collisions of superthermal hydrogen atoms with lithium atoms and molecules
Authors: Crooks Jon B. , Way Kermit R. , Yang Sze-Cheng , Wu Chung-Yung Robert , Stwalley William C.
Published: February 2003

Photon and positive ion production from superthermal collisions of hydrogen atoms with lithium atoms are reported. The superthermal H atoms are collided with an intense supersonic lithium beam. The results in the 1–10 eV collision regime are reported.(AIP)
Semiclassical theory of collision-induced vibration–rotational transitions. Application to methylhalides
Authors: Miklavc Adolf , Fischer Sighart
Published: February 2003

A theory of collision-induced vibrational transitions in polyatomic molecules is presented in which the effects of molecular rotation are included. Translations are treated classically and the molecule itself is considered as classical top with internal degrees of freedom, i.e., normal mode vibrations, treated quantum mechanically. The theory is successfully applied to interpret the behavior of the vibrational relaxation rates of methylhalides upon the mass of the collision partner.
Some corrected integral equations and their results for the square-well fluid
Authors: Smith William R. , Henderson Douglas
Published: February 2003

Extensions of the hypernetted chain (HNC) Percus–Yevick (PY), and mean spherical approximation (MSA) integral equations which incorporate corrections to part of the usual closure relations between h (r) and c (r) are derived. These are evaluated numerically in the case of a square-well fluid with a well width of 0.5σ, where σ is the hard-core diameter. The corrected HNC and PY equations are shown to be related to the usual HNC and PY theories in the same way that the optimized cluster theory is related to the MSA. These equations were originally derived by Lado some time ago using Fourier transform techniques. An advantage of our formulation is that we are also able to make contact with the recent PY, MSA, and HNC perturbation equations of Henderson and colleagues and of Madden and Fitts. The numerically determined equations of state and radial distribution functions are compared with the computer simulation results and with previously reported integral equation results. The corrected HNC equation is found to give results superior to any of the other approximations.
High temperature thermodynamics of the titanium–oxygen system for O?O/Ti?1
Authors: Tetot R. , Picard C. , Boureau G. , Gerdanian P.
Published: February 2003

The Tian–Calvet microcalorimetric method has been improved in order to determine ΔH (O2), the partial molar enthalpy of mixing of oxygen in interstitial solid solutions for compositions O/Ti<1. The results of this study differ substantially from the published data which are discussed. Moreover, it has been possible to determine the composition of the phase boundaries at 1323 K.
Stochastic classical trajectory approach to relaxation phenomena. I. Vibrational relaxation of impurity molecules in solid matrices
Authors: Shugard Mary , Tully John C. , Nitzan Abraham
Published: February 2003

We present a theory of impurity vibrational relaxation in condensed media based on computer simulation of the classical equations of motion of the impurity molecule and a small number of neighboring host atoms. The host atoms are in communication with the remainder of the lattice through the presence of stochastic forces and damping terms that are constructed from knowledge of the phonon spectrum of the solid. Temperature is introduced via the fluctuation–dissipation theorem. The method is applied here to a Cl2 impurity molecule imbedded in an argon matrix. The dependence of energy relaxation and dephasing times on interaction parameters is monitored, and comparison is made with recent spectroscopic measurements on this system.
Induced dissociation of NO(B 2Π, v′=9) by N2
Authors: Hikida T. , Mori Y.
Published: February 2003

A rate of decrease of NO concentration induced by the 184.9 nm mercury line was measured by noting the reduction in the fluorescence intensity at low NO pressures. The quantum yield of NO disappearance in a pure NO system is found to be constant at NO pressures between 0.04 and 1.1 torr. It was concluded that an overall efficiency of the production of NO(A 2Σ+, v′?3) from NO(B 2Π, v′=9) collisionally induced by N2 is 43%∼71%, and the residual 29%∼57% ascribed to the collision induced dissociation. The energy transfer efficiency yields an emission quantum yield of NO(B 2Π, v′=9) of 0.010∼0.016 at zero NO pressure. Previously reported quenching rate constants of NO(B 2Π, v′=9) by NO, He, H2, CO, CF4, N2, and CO2 are recalculated.
Adiabatic potential energies for NaK+, NaRb+, NaCs+, KRb+, KCs+, RbCs+, Na+2, K2+, Rb+2, and Cs+2 molecular ions
Authors: Valance A.
Published: February 2003

By using Hellmann-type model potentials for alkali atoms, the many-electron problem of the alkali molecular ions is reduced to a three-body problem. The Σ adiabatic potential curves have been calculated for ground and excited states of diatomic molecules formed from an alkali atom (Na, K, Rb, Cs) and an alkali ion (Na+, K+, Rb+, Cs+). All the ions turn out to be stable, and the energies we obtain are believed to be reliable within a few hundredths of an electron volt.
The mixing distance
Authors: Ruch Ernst , Schranner Rudolf , Seligman Thomas H.
Published: February 2003

Mixing character denotes a property concerning the composition of sets. It was first used in order to present criteria for ligand systems in molecules that assure the existence of chiral isomers. Since then the concept of mixing character has been found to have further fields of applications in physics and pure mathematics. Various theorems have been given in the meantime that are reviewed here mostly in the form of equivalent definitions. The mixing distance is another, still more general concept suggested by a study of the time dependent behaviour of nonisolated thermodynamical systems. It describes a dissimilarity of probability distributions, the decrease of which characterizes irreversible phenomena. In the present paper a variety of equivalent definitions and theorems concerning the mixing distance are presented that are of use for further applications. Moreover, a theorem is deduced which is a generalization of a fundamental theorem by Hardy, Littlewood, and Polya on inequalities. Applications of the results given in the present paper will be explored in a subsequent publication that is mostly concerned with the concept of statistical information.
Radiative transition probabilities for the B 1Π–X 1Σ+ and B 1Π–A 1Σ+ bands of 7LiH
Authors: Zemke Warren T. , Way Kermit R. , Stwalley William C.
Published: February 2003

The recently reported [J. Chem. Phys. 66, 5412 (1977)] hybrid potential curves for the X 1Σ+ and A 1Σ+ states of LiH and the herein reported hybrid potential curve for the B 1Π state of LiH are combined with the ab initio transition moments of Docken and Hinze [J. Chem. Phys. 57, 4936 (1972)] to calculate radiative transition probabilities between all B 1Π (v′?2) and all X 1Σ+ (v″?23) and A 1Σ+ (v″?26) vibrational levels of 7LiH. The strongest single emission band found is the B 1Π (v′=2) →X 1Σ+ (v″=23) band between the highest ’’long-range’’ levels in each potential. For all B 1Π levels the emission is dominated by B→X rather than B→A emission.
Radiative lifetimes for vibrational levels of the B 1Σ state of 7LiH
Authors: Zemke Warren T. , Stwalley William C.
Published: February 2003

Newly calculated radiative transition probabilities for the B 1Σ→X 1Σ+ and A 1Σ+ emission bands of 7LiH (preceding paper) are used to calculate the radiative lifetime of the various vibrational levels (0⩽v′⩽2) of B 1Π LiH. An estimate of the B→X bound–free emission probability is also included, although the lifetimes are dominated by the B→X bound–bound emission. The calculated radiative lifetimes increase rapidly with v′ from 11.3 nsec at v′=0 to 17.0 nsec at v′=1 and then 24.0 nsec at v′=2.
Raman-active modes of alpha silicon nitride
Authors: Kuzuba Takashi , Kijima Kazunori , Bando Yoshio
Published: February 2003

Raman spectra of powder and single crystals of alpha silicon nitride have been measured at room temperature. More than twenty Raman lines were observed for annealed white powder samples and dominant lines were at 259, 365, 515, 668, 868, 915, 976, and 1034 cm−1. The former three lines were observed also for the single crystals in spite of strong fluorescence. These small wavenumber phonons could tentatively be assigned to collective vibration modes based on a reduction scheme for the irreducible representation of the space group of the crystal.
Theory of collisions between an atom and a diatomic molecule in the body-fixed coordinate system.a) I. Coupled differential equation and asymptotic boundary conditions
Authors: Choi B. H. , Poe R. T. , Tang K. T.
Published: February 2003

The body-fixed (BF) formulation for atom–diatom scatterings is developed to the extent that one can use it to perform accurate close-coupling calculation, without introducing further approximation except truncating a finite basis set of the target molecular wave function, on the same ground as one use the space-fixed (SF) formulation. In this formulation, the coupled differential equations are solved an the boundary conditions matched entirely in the BF coordinate system. A unitary transformation is used to obtain both the coupled differential equation and the boundary condition in BF system system from SF system. All properties of the solution with respect to parity are derived entirely from the transformation, without using the parity eignfunctions of the BF frame. Boundary conditions that yield the scattering (S) matrix and the reactance (R) matrix are presented for each parity in both the far asymptotic region (where the interaction and the centrifugal potentials are both negligible) and the near asymptotic region (where the interaction potential is negligible but the centrifugal potential is not). While our differential equations are the same as those derived by others with different methods, our asymptotic boundary conditions disagree with some existing ones. With a given form of the BF coupled differential equations, the acceptable boundary conditions are discussed.
Theory of collisions between an atom and a diatomic molecule in the body-fixed coordinate system.a) II. Close-coupling calculation for rotational transitions
Authors: Choi B. H. , Poe R. T. , Tang K. T.
Published: February 2003

Based on the close-coupled differential equation and boundary conditions in the body-fixed coordinate system developed in the preceding paper, a numerical procedure is introduced for computing the atom–diatom scattering cross sections. An accurate close-coupling calculation is carried out in the body-fixed formulation on the same ground as in the space-fixed formulation. The numerical example explicitly demonstrates the equivalence of the two formulations. It was found that, for the rotational excitation of H+H2 collision, the magnetic quantum numbers (K) projected onto the bodyfixed axis do not conserve, even in the approximate sense, in the body-fixed S matrix for small total angular momentum, although the range of differences between the initial and the final magnetic quantum numbers tends to narrow down for large total angular momentum. Furthermore, the dominant contributions of these quantum numbers to the transition probabilities are not confined to a particular value, e.g., zero, for small total angular momentum. These results are consistent with recent analyses by others that the K quantum number is conserved only under very limited conditions.
Sound propagation along a line of plait points of the ternary system methanol–nitrobenzene–iso-octane
Authors: D’Arrigo G. , Tartaglia P.
Published: February 2003

At 1 atm and in a given temperature range the ternary liquid system methanol–nitrobenzene–iso-octane has two separate binodal curves which meet at both plait points when temperature is decreased. We have determined the plait point line extending from the binary system methanol–iso-octane to nitrobenzene–iso-octane. Ultrasonic absorption coefficient and velocity measurements, performed along this line as a function of temperature and frequency, seem not to confirm theoretical predictions. Possible discrepancies between theory and experiments are discussed.
Rotating frame NMR relaxation study of gaseous ClF
Authors: Gillen K. T. , Douglass D. C. , Griffiths J. E.
Published: February 2003

This paper describes the first application of rotating frame NMR techniques to a gas phase system. Experiments were run on the linear diatomic molecule ClF at room temperature and various gas densities ranging from 13 to 28 amagat. By combining 19F rotating frame results with 19F spin–lattice relaxation time TF1 results, values of the chlorine spin–lattice relaxation time TCl1 and the gas phase chlorine to fluorine spin–spin coupling constant JFCl were derived. Since ClF is a linear molecule, its relaxation times, TCl1 and TF1 lead directly to values of the reorientational and angular velocity correlation times, τϑ,2 and τJ, respectively. The ratio τJ/τϑ,2 is found to be equal to 1.38±0.15, independent of gas density. This result is compared to various theories which relate τJ and τϑ,2, and it is shown that none of these theories adequately describe the gas phase reorientational motions of ClF. Rotating frame and spin–lattice relaxation time measurements were also made in the liquid and plastic crystalline solid phases of ClF. The reorientational correlation times derived from this data have an Arrhenius dependence on temperature with an activation energy of 1.2 kcal/mole. In addition, the analysis indicates that the liquid phase 19F to 35Cl spin–spin coupling constant Jliq35 is equal to 770±10 Hz; this is approximately 10% smaller than the 855±10 Hz determined for Jgas35 from the gas phase experiments.
An electron diffraction study of perfluoroneopentane, C(CF3)4
Authors: Oberhammer Heinz
Published: February 2003

The molecular structure of C(CF3)4 in the gas phase has been determined by electron diffraction. By comparison of the experimental mean square amplitudes with the respective spectroscopic values, a torsional force constant fτ∼0.55 mdyn Å was estimated. The scattering intensities were interpreted with a molecular model of T symmetry without large amplitude torsional motions (’’rigid’’ model): r0α(C–C) =1.562(3) Å, r0α(C–F) =1.325(2) Å,&FCF=108.1° (0.2), and τ=18.3° (0.5). τ is the torsional angle of the CF3 groups from the staggered positions. This model agrees very well with the results of CNDO/2 calculations which also predict a potential barrier at the staggered position and an equilibrium configuration with τ∼18°.
Molecular motions in liquid. II. Deuteron relaxation study of the rotation of highly symmetrical molecules in solutions
Authors: McGaughy Tim W. , Wu Sheila Y. C. , Fung B. M.
Published: February 2003

The deuteron spin–lattice relaxation times (T1) of adamantane-d16, tris(3-deutero-2,4-pentadionato) aluminum, α,α-dideuterotetraethylammonium iodide, and α,α-dideuterotetrabutylammonium iodide in several solvents are studied as functions of temperature. The rotational correlation times (τc) for the solute molecules were obtained from the T1 data. The results were analyzed in terms of a dimensionless parameter κ, which is the ratio between experimental τc and the value of τc calculated from the Debye–BPP equation. It seems that for molecules with small κ (slip boundary condition), the value of κ increases with the increase of temperature and for molecules with κ closer to one (stick boundary condition), the value of κ decreases with the increase of temperature.
Thermodynamics of the lanthanide trifluorides. I. The heat capacity of lanthanum trifluoride, LaF3 from 5 to 350°K and enthalpies from 298 to 1477°K
Authors: Lyon William G. , Osborne Darrell W. , Flotow Howard E. , Grandjean Fernande , Hubbard Ward N. , Johnson Gerald K.
Published: February 2003

The heat capacity of a sample of LaF3 was determined in the temperature range 5–350°K by aneroid adiabatic calorimetry and the enthalpy from 298.15 to 1477°K by drop calorimetry. The heat capacity at constant pressure C°p(298.15°K), the entropy S° (298.15°K), the enthalpy [H° (298.15°K)−H° (0)] and the Planck function −[G° (298.15°K)−H° (0)]/298.15°K; were found to be (90.29±0.09) J °K−1⋅mole−1, (106.98±0.11) J °K−1⋅mole−1, (16717±17) J mole−1, and (50.91±0.05) J °K−1⋅mole−1. The thermal functions from the present research were extended up to the melting temperature (1766°K) by combination with previously published results. The anomalously high heat capacity from about 1100 to 1766°K is discussed.
Perturbation theory for molecular fluids: Third-order term in the Pople expansion
Authors: Gray C. G. , Gubbins K. E. , Twu C. H.
Published: February 2003

We derive the expression for the third-order perturbation term A3 in the Pople expansion of the Helmholtz free energy, for an arbitrary anisotropic intermolecular pair potential. The corresponding expression for the second-order perturbation term g2 in the expansion of the angular pair correlation function is also obtained. We then apply this expansion, and also a Padé approximation to the series, to the case in which the molecules interact with an anisotropic charge overlap model proposed by Pople. Comparison of the calculated internal energies with molecular dynamics results for this model show that the Padé gives good results in the range −0.2?δ?0.35, where δ is an anisotropic shape parameter (positive for prolate and negative for oblate spheroids). This range includes small polyatomic molecules (CO2, ethane, N2, etc.). We also apply the theory to binary mixtures in which one of the molecular species obeys a spherical Lennard-Jones potential while the other obeys spherical Lennard-Jones plus the Pople anisotropic overlap model. The anisotropic overlap forces have little effect on the phase diagram for such small polyatomics, in contrast to the large effect of electrostatic forces.
Semirigorous bounds for the dipole moments and transition moments of the LiH molecule
Authors: Langhoff Stephen R. , Chong Delano P.
Published: February 2003

Weinhold’s formula for the upper and lower bounds to transition moments is extended to include transitions between states of the same symmetry. Chong’s semirigorous expression for the lower bound to the overlap between the approximate and the true wavefunctions is studied and applied to the calculation of error limits for the dipole moments and transition moments of LiH at R=3.015 bohr. With high-quality wavefunctions, the results are: μ (X 1Σ+) =5.836±0.262 D; μ (A 1Σ+) =−5.078±0.344 D; w (X 1Σ+) =0.94 (+0.13, −0.18); w (X 1Σ+−B 1Π) =1.29±0.23 ea0; and w (A 1Σ+−B 1Π) =1.82±0.24 ea0.
Hydration water–external water interactions around Cr3+ ions
Authors: Caminiti R. , Licheri G. , Piccaluga G. , Pinna G.
Published: February 2003

A hydration model for the Cr3+ ion, suggested by the bond valence analysis, is tested against x-ray diffraction data obtained from aqueous solutions of chromium chloride and nitrate about 1–2M. According to this model, the [Cr(H2O)6]3+ ions interact with 12 water molecules through short and linear H bonds, the water molecules nearest neighbor to the Cr3+ ion having a trigonal orientation (i.e., they point the negative end of their dipole vector towards the metal ion). The results show that such a model agrees with experimental data somewhat better than a model in which the water molecules nearest the cations have a pyramidal orientation (i.e., they point a lone pair towards the ion).
Theoretical study of molecular dipole moment functions. II. The d 3Δ and a′ 3Σ+ states of CO
Authors: Kirby K. , Liu B.
Published: February 2003

Approximate dipole moment functions for the d 3Δ and a′ 3Σ+ states of CO have been calculated using configuration interaction wavefunctions including internal and semi-internal electronic correlation effects. The best theoretical dipole moments for individual vibrational levels are in good agreement with experimental data. The theoretical dipole moment functions are of higher accuracy than those derivable from existing experimental data.
Quantum theory of anharmonic oscillators: From independent oscillators to spherically coupled oscillators
Authors: Hioe F. T.
Published: February 2003

We study properties of the energy levels of d coupled anharmonic oscillators d=1,2,... characterized by the Hamiltonian H=1/2Σdi=1 (p2i+ω2ix2i)+λp2m (x1,...xd), and in particular when P2m (x1,...,xd) =x2m1+x2m2+... +x2md and when P2m(x1,..., xd) = (x21+x22+...+x2d)m,m=2,3,... . The general picture of energy level crossings in these two special cases is discussed. Some numerical data on the energy levels and density of states are presented and compared with those obtained from our approximate analytic expressions.
Chemiluminescent reactions of group IIIb atoms with O2: Spectral simulations and extended energy dependence
Authors: Manos D. M. , Parson J. M.
Published: February 2003

Spectral simulations have been performed of visible chemiluminescence from crossed-molecular-beam reactions of La, Y, and Sc with O2. Experiments analyzed include previous thermal energy results, as well as new hyperthermal energy measurements using an O2/He seeded beam. The simulations allow more precise determinations of product monoxide vibrational energy distributions and also provide information on product rotational energy distributions. Previous indications of statistical behavior in the product energy distributions are confirmed. Deviations from the information–theoretic prior translational energy dependence of rate coefficients occur for the endoergic formation of YO(B 2Σ) and ScO(A 2Π.
Calculations of the electronic structure and transitions of actinide metal hexafluorides
Authors: Boring Michael , Hecht Harry G.
Published: February 2003

SCF-Xα-SW calculations are reported for the actinide metal hexafluorides UF6, NpF6, and PuF6. Eigenvalues and charge densities analyzed according to angular momentum contributions within atomic spheres are given for the ground states, and several transitions have been calculated using the electronic transition state concept.
Photoelectron spectra of acetylene with HeI, HeII, Zr Mζ, and Mg Kα radiation sources
Authors: Cavell Ronald G. , Allison David A.
Published: February 2003

Valence level photoelectron spectra of gaseous acetylene excited by HeI (21.217 eV), HeII (40.8 eV), Zr Mζ (151.4 eV) with Mg Kα (1253.6 eV) radiations have been obtained. With one exception, the 3σg band under Mg Kα excitation, all of the expected valence level excitations are observed in each case. The best measured orbital ionization potentials are 1πu (11.41 eV), 3σg (16.76 eV), 2σu (18.71 eV), and 2σg (23.65 eV). All values except that for 1πu are adiabatic values. Relative photoionization probabilities (cross sections) have been determined for each of the radiations and compared to those estimated theoretically. The low calculated cross sections for 3σg excitation with Mg Kα radiation provides an explanation for the lack of an observable band due to this ionization in the photoelectron spectrum. A prominent ’’shake-up’’ peak is observed at 27.6 eV in both the Mg Kα and Zr Mζ excited valence shell photoelectron spectra although it is more pronounced in the former. Similarly the C1s core spectrum shows several ’’shake-up’’ peaks which have been assigned with the aid of CNDO calculations.
Quasiclassical trajectory calculations compared to quantum mechanical reaction probabilities, rate constants, and activation energies for two different potential surfaces for the collinear reaction H2+I→H+HI, including dependence on initial vibrational state
Authors: Gray Joni C. , Truhlar Donald G. , Clemens Laura , Duff James W. , Chapman Frank M. , Morrell Glenn O. , Hayes Edward F.
Published: February 2003

Quantum mechanical calculations are compared to quasiclassical trajectory forward (QCT) calculations for the collinear, endoergic reaction H2(n1)+I→H+HI for two different potential energy surfaces, a rotated-Morse-curve (RMC) surface and the semiempirical valence-bond surface of Raff et al. Vibrationally state-selected reaction probabilities and rate constants and Arrhenius parameters are presented. Thermally averaged rate constants and their Arrhenius parameters are also given. For one of the potential energy surfaces, quasiclassical trajectory reverse histogram (QCTRH) calculations were also performed. The results show that classical mechanics and quantum mechanics are in significant qualitative agreement for state-selected properties. Specifically, for the n1=0 state of the Raff et al. surface the quantum mechanical reaction probabilities are very small (less than 0.005) and the QCT method predicts this state to be totally non-reactive. For all other states on both surfaces quantum mechanics and QCT and QCTRH results all agree that reaction probabilities attain much higher values (up to 0.85). For both surfaces quantum mechanical and QCT results predict that excited vibrational states make significant contributions to the thermal reaction rates, although the methods disagree as to which vibrational state is quantitatively most important. Quantitative agreement with quantum mechanical results is obtained only with the QCTRH method for thermally averaged rate constants (agreement within 2%) and with both QCT and QCTRH methods for the Arrhenius parameters (agreement within a few tenths kcal mol−1 for activation energy). However, to achieve such agreement the QCT method had to be suitably modified to correct unphysical discrepancies in the threshold energy region. We present tables of these and many other results as a function of temperature. These should be useful in assessing the validity of trajectory studies of various kinds of reaction attributes under conditions where they are used to interpret experiments.
Statistical mechanics of Ising chains in random magnetic fields
Authors: Morgenstern Ingo , Binder Kurt , Baumgärtner Arthur
Published: February 2003

For a model of heteropolymer ’’melting,’’ we study an Ising model where the field on each spin can randomly take one of the two values H±h. Several numerical methods for the calculation of the free energy and its derivatives are developed, making use of a transfer matrix representation of the partition function and mathematical theorems on random matrices due to Bellman. Monte Carlo computations due to Landau and Blume on the model with H=0 are extended to the case H≠0 and compared with the above results. The efficiency of our other numerical methods is found to be better by more than one order of magnitude than the Monte Carlo technique, as far as the calculation of energy, magnetization, etc. is concerned. But the Monte Carlo technique also yields time-dependent correlation functions and information on the concentrations of clusters of subsequent up (or down) spins. These quantities are compared to the corresponding ones of the ordinary Glauber model. We find that these quantities can fairly be approximated by the Glauber ones, but using a suitably renormalized correlation length. These results support the ’’coarse-graining approximation’’ proposed for the statistical mechanics of heteropolymers.
Isotopic ternary diffusion of the carbon tetrachloride–cyclohexane system
Authors: Oishi Y. , Kamei Y. , Sumie H.
Published: February 2003

Interdiffusion experiments by a capillary-cell method were carried out for the 14CCl4–12CCl4–C6H12 and CCl4–14C6H12–12C6H12 systems, which were designed to be binary diffusion chemically but ternary diffusion with respect to isotopic composition. The diffusion amounts of radioactive tracers were determined by a liquid scintillation counter. The experimental results were in good agreement with the theoretical calculation by a ternary diffusion equation using the self-diffusion coefficients of the components. A mathematical solution of the ternary diffusion equation necessary to the calculation was derived for the boundary condition of capillary-cell diffusion.
Vibration, rotation spectra, and conformations of cyclooctanone
Authors: Rounds Thomas C. , Strauss Herbert L.
Published: February 2003

We have taken the Raman spectra, low-frequency infrared spectra, and low-resolution microwave spectra of cyclooctanone. The vibrational and rotational information is combined with molecular mechanics calculations to provide a model of parts of the conformational energy surface. The lowest energy conformation is shown to be the boat–chair–3 in agreement with previous work. The microwave spectrum is the first example of a low resolution spectrum of a c-dipole R branch for an oblate rotor. The rotational constants are 1910±5, 1680±30, and 1100±100 MHz. The structure and the potential function for cyclooctane are determined.
Comments on the closure problem in the statistical theory of fluids
Authors: Kayser R. F. , Raveché H. J. , Wood W. W.
Published: February 2003

It is shown that if the BBGKY hierarchy is truncated by the approximation for the quadruplet correlation function g1234=g123g124g134g234/ [g12g13g14g23g24g34], the resulting system of equations yields solutions for g12 and g123 which are path dependent. This result is consistent with an earlier argument by Raveché and Green that the closure leads to a nonconservative force on a particle in a fixed triplet of particles. The magnitude of the path dependence is investigated and its consequences are discussed.
Laser induced production of excited states of PH and PH2 from phosphine
Authors: Sam C. L. , Yardley James T.
Published: February 2003

Luminescence from the Ã excited states of PH and PH2 has been observed following irradiation of PH3 with an ArF excimer laser (193.3 nm). Initial vibrational distributions in PH2(Ã) have been determined. The large population in v′2=0 may be understood in terms of the Franck–Condon principle in view of the similarities in geometry of PH3(Ã) and PH2(Ã). While formation of PH2(Ã) is linear in laser intensity, corresponding to a simple one-photon dissociation process, PH(A) is produced in a two-photon process. Lifetimes and cross sections for quenching by PH3 have been measured for vibrational levels of PH2(Ã) and for spin–orbit subcomponents of PH(A). The quantum yield for photochemical production of PH2(Ã) at low laser intensities has been measured to be 0.014±0.006.
Brownian dynamics as smart Monte Carlo simulation
Authors: Rossky P. J. , Doll J. D. , Friedman H. L.
Published: February 2003

A new Monte Carlo simulation procedure is developed which is expected to produce more rapid convergence than the standard Metropolis method. The trial particle moves are chosen in accord with a Brownian dynamics algorithm rather than at random. For two model systems, a string of point masses joined by harmonic springs and a cluster of charged soft spheres, the new procedure is compared to the standard one and shown to manifest a more rapid convergence rate for some important energetic and structural properties.
Unlinked cluster effects in molecular electronic structure. II. Pair correlations in the molecules HCN and HNC
Authors: Taylor Peter R. , Bacskay G. B. , Hush N. S. , Hurley A. C.
Published: February 2003

Valence-shell correlation energies for the HCN and HNC molecules are analyzed into pair contributions at the independent-pair, CI, and coupled-pair level. The correlation effects for each system are very similar, and are easily related to the spatial extension and interpenetration of the localized SCF orbitals which form the reference configuration. In addition to the recently proposed ’’coupled-pair approximation’’ (CPA), two approximate methods, including the widely-used CEPA technique, are used, and the results are compared with those obtained using the full treatment. The CPA″ method proposed earlier is found to give energy results in agreement with the full CPA to ’’chemical accuracy’’ (1kcal/mole); the agreement obtained with CEPA is not as good, although there is still a substantial improvement over the CI values.
The renormalized Numerov method applied to calculating bound states of the coupled-channel Schroedinger equation
Authors: Johnson B. R.
Published: February 2003

The renormalized Numerov method, which was recently developed and applied to the one-dimensional bound state problem [B. R. Johnson, J. Chem. Phys. 67, 4086 (1977)], has been generalized to compute bound states of the coupled-channel Schroedinger equation. Included in this presentation is a generalization of the concept of a wavefunction node and a method for detecting these nodes. By utilizing node count information it is possible to converge to any specific eigenvalue without the need of an initial close guess and also to calculate degenerate eigenvalues and determine their degree of degeneracy. A useful interpolation formula for calculating the eigenfunctions at nongrid points is also given. Results of example calculations are presented and discussed. One of the example problems is the single center expansion calculation of the 1sσg and 2sσg states of H+2.
Lifetime of the BH A1Π state excited by a pulsed dye laser
Authors: Dufayard J. , Nedelec O.
Published: February 2003

The radiative lifetime of the BH, A1Π, v′=0 state is measured by pulsed dye-laser excitation. The result, τ(ns) =125±5, agrees with two recent calculations.
Time resolved emission from OH(C2Σ+) produced by the pulse radiolysis of water vapor
Authors: Quickenden T. I. , Irvin J. A. , Sangster D. F.
Published: February 2003

Pulse radiolysis was used to study lifetimes and rate constants for quenching by H2O of water vapor fragments emitting in the range 210–360 nm. The radiative lifetimes of OH(C2Σ+, v=0,1), measured at the bandheads of the (1–8), (1–9), and (0–9) bands of the C2Σ+→A2Σ+ transition and analyzed by a deconvolution method were 3.8±0.5, 3.6±0.3, and 3.9±0.5 ns, respectively. Quenching rate constants at 292 K were (1.7±0.3) ×10−9, (1.6±0.2) ×10−9, and (2.2±0.3) ×10−9 cm3s−1 molecule−1 for these bands, (0.53±0.02) × 10−9 cm3s−1 molecule−1 for the OH A2Σ+ →X2Π, (0–0) band and (12.8±1.1) × 10−9 cm3s−1 molecule−1 for an unidentified band at 253–254 nm. The two long lived emissions reported by Remy [Spectrosc. Lett. 4, 319 (1971)] at the head of the (0–9) band of the OH C2Σ+ →A2Σ+ transition were not present.
Infrared intensities: Polar tensors and charge flux parameters
Authors: Prasad P. L.
Published: February 2003

An attempt has been made to streamline the procedure for analysis of infrared intensities of fundamental bands through polar tensor calculations. Different methods used in the literature to calculate the rotational contributions have been compared and a correlation has been pointed out. Using the atomic charge model, a generally applicable expression relating an atomic polar tensor to the equilibrium atomic charges and their flux terms has been derived. The bond moment model has also been used to obtain an analogous expression relating the atomic polar tensor to the bond moments and their derivatives. However, the final equations of these two models indicate that, irrespective of the model chosen for the interpretation of infrared intensities, one would obtain identical information.
On magnetic transitions and the interpretation of the partial wave parameter in the CS and IOS approximations in molecular scattering theory
Authors: Khare V. , Kouri D. J. , Pack R. T
Published: February 2003

The recent discovery by Khare that choosing the CS partial wave parameter ? to be the initial orbital angular momentum, li, leads to a simple differential scattering amplitude for definite polarization transitions is examined in detail. It is found that the resulting scattering amplitude formula, which is a rotation of the usual McGuire–Kouri formula, predicts nonzero magnetic transitions in all frames except that whose Z axis always points in the final observation direction ?. A detailed comparison of li and lf labeling is made and it is shown that both lead to nondiagonal approximations to the p-helicity amplitude, TJ(jλ‖j0m0), and to differential scattering amplitudes which have the proper limiting behavior at small and large scattering angles. In addition it is shown that both li and lf labeling yield identical results for all degeneracy averaged cross sections, including the general relaxation cross sections. Further, we show rigorously that if the quantization axis is along a direction perpendicular to the plane of the incident and final momenta, then the li and lf labeled cross sections are identical. It is argued on the basis of available numerical results and on physical grounds that the li-labeled CS is preferred over the lf CS for calculating magnetic transitions quantized along the incident momentum. We further expect the lf CS to be preferred for calculating magnetic transitions quantized along the final momentum. However, other ? choices may be better yet for magnetic transitions in general.
Elementary properties of an energy functional of the first-order reduced density matrix
Authors: Donnelly Robert A. , Parr Robert G.
Published: February 2003

The Hohenberg–Kohn theorem implies the existence of an energy functional based solely on the first-order reduced density matrix of the ground state of an atomic or molecular system. Application of the variational principle for the functional EvM[γ] generates a set of coupled Euler equations for the representation coefficients and spin orbitals of a rank-M approximation to the exact ground-state density matrix. Defining the (assumed Hermitian) kernel FM[γ;x′,x]≡δEvM/δγ (x,x′), the equations in an arbitrary representation for the approximate density matrix, γ (x,x′) =ΣijMψ1(x) γijψj* (x′) are the following: ℱdξFM[γ;x′,ξ]ψi(ξ) =μψi(x′); i=1, 2,...,M; ℱdξFM[γ;x′,ξ] ΣMiψi(ξ) γ ij=ΣMiψi(x′) λij; j=1, 2, ...,M. The quantity μ is the chemical potential of the system of interest and the λij are a set of M2 Lagrange multipliers constraining the orthonormality of the spin orbital basis {ψ}. The coefficients γij must be chosen such that FM has the degenerate eigenvalue spectrum, FiiM=μ, i=1, 2,...,M, for all partially occupied orbitals. The spin orbitals, for a fixed set of coefficients, must be simultaneously determined so that λ is Hermitian. Provided all occupation numbers lie on the open interval (0,1), the stationary density matrix itself obeys the eigenvalue equation ℱdξFM[γ;x,ξ]γ (ξ,x′) =μγ (x,x′), and for any stationary density matrix the following commutation rules are valid: [FM[γ], γ]=0; [λ, γ]=0. The matrices γ and λ consequently can be brought simultaneously to diagonal form, and the canonical representation of the energy functional provides an eigenvalue equation determining the natural spin orbitals. The value of the chemical potential is μ=εi/ni, i=1, 2, ...,M; ε=diag (λ); from which follows the distribution function governing the occupation numbers of a stationary density matrix. Two limiting forms of the variational principle are examined, the exact and Hartree–Fock functionals, and related previous work by Gilbert is discussed. The physical content of the equations is illuminated by identification of the chemical potential as the negative of the electronegativity; Sanderson’s Principle of Electronegativity Equalization follows.
Theoretical determination of molecular structure and conformation. II. Hydrogen trioxide—a model compound for studying the conformational modes of geminal double rotors and five membered rings
Authors: Cremer D.
Published: February 2003

The internal rotational surface of hydrogen trioxide has been calculated with the Hartree–Fock method using basis sets with and without polarization functions and optimizing all structural parameters. These calculations have been repeated at the level of Rayleigh–Schrödinger–Mo/ller–Plesset (RS–MP) perturbation theory in order to study the role of correlation effects on barrier values and structures. The relative energies as well as the computed geometrical parameters underline the importance of polarization functions. Although the intrapair correlation contributions significantly stabilize the planar conformations of H2O3, the net effect of correlation effects on the conformational potential is moderate because of well-balanced interpair contributions of opposite sign. As in the case of H2O2, the correlation effect on the relative energies further decreases if the basis set is improved. On the other hand, reliable structural parameters can only be achieved at the RS–MP level by employing a large augmented basis. The calculated equilibrium RS–MP structural parameters of H2O3 are: R (OO) =143.9 pm, R (OH) =97.2 pm, α (OOO) =106.3°, β (OOH) =100.2°, ϑ=78.1°. Bond angles and OO bond lengths are strongly coupled to the rotational angles. A simultaneous rotation of both OH bonds is hindered by large barriers of 22.5 and 11.5 kcal/mole. These potential maxima can be surrounded in a stepwise flip-flop rotation of the OH groups. The barriers of this rotational process turn out to be the saddlepoint energies (6.5 and 5.4 kcal/mole) of the internal rotational surface. It is shown that a close relationship exists between the flip-flop rotation of the geminal double rotor and the pseudorotation of five membered rings. Using the calculated conformational potential V (ϑ1,ϑ2), the prediction is made that the envelope form of 1,2,3-trioxolane is more stable than the corresponding twist form.
Third-order nonlinear mixing in polydiacetylene solutions
Authors: Shand M. L. , Chance R. R.
Published: February 2003

Third-order mixing has been measured in solutions of the polydiacetylenes. The Raman molecular vibration contribution to the third-order susceptibility χT(3) (−ω3, ω1, ω1, −ω2) has been characterized completely. A surprisingly strong polymer two-photon absorption contribution to χT(3) was found. The cross section for two-photon absorption at 2ω1=32 000 cm−1 is 6×10−47 cm4 sec photon−1 (polymer repeat unit)−1. The polymer nonresonant susceptibility could not be determined because of the strong two-photon contribution to χT(3).
Structural phase transformations and temperature dependent Raman spectra of Cs2LiFe(CN)6
Authors: Swanson B. I. , Lucas B. C. , Ryan R. R.
Published: February 2003

Structural phase transformations have been observed for Cs2LiFe(CN)6 at ∼221 and 170 °K. Aspects of the phase II (221°⩾T⩾170 °K) structure have been probed using Raman scattering, x-ray diffraction, and optical methods. The distortion of the cubic (Fm3m) to the tetragonal (I4/m or P4/mnc) cell proceeds along the F1g symmetry rotary mode. The second phase change at 170 °K involves Cs+ translation. Striking differences have been observed in the Raman spectra of the iron and related Cs2LiM(CN)6 (M=Cr+3, CO+3, and Ir+3) salts. These differences are discussed in terms of the dynamic Jahn–Teller distortion in the iron salt which is not present in the related Cr+3, Co+3, and Ir+3 salts.
Multiphoton ionization spectroscopy: A theoretical analysis of the NO spectrum
Authors: Cremaschi P. , Johnson P. M. , Whitten J. L.
Published: February 2003

The multiphoton ionization spectrum of the NO molecule is described theoretically by calculations of absorption and ionization cross-sections. Both perturbation theoretic (short-time) and rate equation (long-time) descriptions of the stepwise excitation and ionization process are considered. Under the present experimental conditions the two approaches are shown to give qualitatively similar results. Two cases of four-photon absorption are treated: in the first, called a 2+2 process, resonance occurs on absorption of the second photon; and in the second, 3+1 process, resonance occurs at the third photon level. For the wavelength range considered, there is one state, the A 2Σ+, in the former category and six possible choices for the latter. The 2+2 process is shown to have the higher intensity. For most of the resonant states, relative calculated ionization cross sections are in accord with experiment.
Inverse Raman scattering: Continuous generation in optical fibers
Authors: Stone J.
Published: February 2003

Continuous inverse Raman scattering has been observed in several liquids. The scattering cell is in the form of a hollow silica fiber several meters in length with a 4 μm diameter core. The excitation source is a krypton laser providing about 20 mW of power in the fiber core, giving an excitation power density of about 105 W/cm2, and the continuum source is a high-pressure xenon arc lamp.