bluuebunny/crossref_metadata_2025 huggingface dataset:
Cutoff-free theory of impact broadening and shifting in microwave and infrared gas spectra
Authors: Leavitt Richard P. , Korff David
Published: February 2003

A cutoff-free impact theory of pressure broadening and shifting of rotation and rotation–vibration spectra in gases is derived. The theory is based on the ATC (Anderson–Tsao–Curnutte) theoretical framework and uses a linked-cluster theorem for degenerate states to obtain a form for the interruption function S(b) in which the dependence on the interaction potential is exponential. S(b) is bounded for 0⩽b⩽∞, allowing integrals over the impact parameter b to be performed without resort to a cutoff. Earlier impact theory results are shown to be limiting cases of our result. Results for broadening cross sections are obtained for certain ideal cases and compared to corresponding ATC results.
Predissociation spectroscopy of O+2: a 4Πu (v′′=6–11)→b 4Σ−g (v′=5–9)
Authors: Hansen J. C. , Graff M. M. , Moseley J. T. , Cosby P. C.
Published: February 2003

Moderate-resolution spectra (Δλ=0.25 Å) have been obtained for the (5,6), (5,7), (6,7), (6,8), (7,8) (7,9), (8,9), (8,10), and (9,11) bands of the transition O+2 (a 4Πu→b 4Σ−g), where the upper b state levels are all predissociated. The study was made by observing the resulting O+ photofragments using a coaxial beams photofragment spectrometer. The results are used to obtain values of the vibrational band origins and term values. The remaining molecular constants are, within the resolution of this work, consistent with calculations based on previously determined Dunham coefficients.
A consistent spherical potential function for para-hydrogen
Authors: McConville G. T.
Published: February 2003

Several potential functions have recently been proposed to fit physical properties of hydrogen. We have calculated phase shifts for five of these functions and obtained second virials, bound state energy differences, and total and differential scattering cross sections to compare to the experimental data. We find that none of the previously proposed potentials can represent more than two of the above properties of para-hydrogen. Using the Hartree–Fock dispersion form proposed by Ahlrich et al., but changing the damping constant D from 1.28 to 1.31, a consistent representation is found for all the data except the differential scattering data. To fit the differential scattering data, the collision energy used in the calculation must be 3% larger than the stated value. This difference is within the experimental uncertainty of the differential scattering experiment.
Gas phase multiphoton photodissociation of Mn2(CO)10: The effect of collisions on photofragmentation
Authors: Rothberg L. J. , Gerrity D. P. , Vaida V.
Published: February 2003

Multiphoton dissociation of Mn2(CO)10 followed by multiphoton ionization of the generated fragments is accomplished with a single tunable pulsed dye laser. Efficient dissociation to bare Mn atoms occurs over a broad range of wavelengths via a sequential photodissociation mechanism. Spectral changes upon addition of buffer gases are shown to reflect collisional effects on intermediates in the dissociation process.
Raman scattering of adsorbed molecules
Authors: Ueba H. , Ichimura S.
Published: February 2003

The excitation energy dependence of the surface enhanced Raman scattering of adsorbed molecules is calculated based on the effective resonance model for a molecule–metal system. As a consequence of the effective resonant Raman process of the adsorbed molecule, a remarkable departure from an ω4 law is obtained near the excitation energies which satisfy the resonant condition. The significance of the substrate metal on the degree of the enhancement is discussed with the use of a result that the position of the effective resonant level is closely connected with that of the Fermi level. A comparison with the recent experimental results on the excitation profiles is also made.
Mode specific vibrational energy transfer in CH3F–N2O mixtures
Authors: Huddleston R. K. , Weitz Eric
Published: February 2003

Fluorescence signals have been observed from the symmetric stretching and bending fundamentals of N2O in CH3F–N2O mixtures following excitation of CH3F by a Q-switched CO2 laser. The rise rates of the N2O fluorescence signals show that energy is transferred selectively from CH3F to the symmetric stretch of N2O despite the fact that overtones of the N2O bending mode are more nearly in resonance with CH3F states expected to be involved in the energy transfer process. Vibrational energy transfer studies of the same two modes in pure N2O, in which the symmetric stretch is depleted by N2O laser radiation, provide independent measurements of rate constants necessary for a kinetic analysis of the CH3F–N2O results. In pure N2O a rate of 28±1.5 msec−1 Torr−1 is assigned to equilibration of the symmetric stretching fundamental with a component of the overtone of the bending mode. A mechanism for energy transfer in CH3F–N2O mixtures is proposed which explains the important features of the experimental observations in this system and is consistent with the results in pure N2O. This model allows an upper limit to be placed on the rate constant for direct energy transfer from CH3F to the bending mode manifold of N2O, and therefore a lower limit for the actual specificity of intermolecular energy transfer is determined.
Monte Carlo simulations of liquid and solid nitrogen based on an a
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o MO–LCAO–SCF–CI potential
Authors: Jönsson B. , Karlström G. , Romano S.
Published: February 2003

Monte Carlo simulations of liquid and solid nitrogen have been performed using intermolecular potentials obtained from quantum mechanical calculations. Essentially, two intermolecular potentials have been used: one calculated with a minimal basis set and the other with an extended basis set including polarization functions. Good agreement with experimental results is obtained provided three conditions are fulfilled: (i) the dispersion interaction must be calculated with a large basis set, (ii) the so called basis set superposition error must be corrected for via counterpoise calculations, and (iii) the quadrupole moment for the monomer must be properly described. Various analytical forms of the intermolecular potential have been tested, and the second virial coefficient has been calculated and shown to be a valuable tool in assessing the accuracy of different intermolecular potentials.
MQDT analysis of predissociation. I. A two channel problem with semiclassical scattering parameters
Authors: Colle Renato
Published: February 2003

Diatomic predissocitaion (case I) is treated in the framework of the multichannel quantum defect theory (MQDT) by adapting the Child and Bandrauk formulation. Analytical expressions are given for the scattering parameters of a two channel problem in terms of WKB phase integrals and of crossing parameters. Resonances in scattering and photoabsorption spectra are identified as the points of steepest rise of an effective phase shift, and analytical expessions are derived for both linewidths and energy shifts. A sample calculation shows the effects of coupling with the B 3Σ−u state upon the partial elastic cross section of two oxygen atoms colliding in the 5Πu channel.
A nonempirical SCF–MO study of the validity of the Solomon–Bloembergen equation for the hexa-aquonickel (II) ion
Authors: Kowalewski Jozef , Laaksonen Aatto , Nordenskiöld Lars , Blomberg Margareta
Published: February 2003

Nonempirical SCF–MO calculations of the effective distance between the ligand nuclei and the unpaired electron spins in the triplet ground state (3Ag) of the hexa-aquonickel (II) ion are presented and the validity of the point dipole approximation in the Solomon–Bloembergen equation is discussed. The calculations show that the effective distance between the oxygen atom and the unpaired electron is significantly shorter than the internuclear oxygen–nickel distance. For the case of the hydrogen atom, the point dipole approximation functions very well. Calculations of the isotropic hyperfine coupling constants are also reported.
Kinetic energy density functional of Hückel theory for planar hydrocarbons
Authors: Pucci R. , March N. H.
Published: February 2003

In this paper, Hückel theory is viewed as an approximate density functional theory. It is shown to follow from the assumption that the single-particle kinetic energy density t[ ρ] has the property that its functional derivative satisfies the two conditions . . . . . plus the assumption that the exchange potential tends to zero at infinity, which is true, for example, with the Dirac–Slater ρ1/3 potential. On the other hand, from statistical theory appropriate for large numbers of electrons, it is known that . . . . . where d is the dimensionality. Hückel theory is therefore seen to correspond to the choice d=2.
Hyperfine interactions of Fe and Cu substitutional impurities in argon matrix
Authors: Braga M. , Taft C. A.
Published: February 2003

Spin-polarized multiple-scattering–Xα calculations have been performed on a MAr12 (M=Fe,Cu) cluster in order to describe the transition metal atoms trapped in a crystalline argon matrix. The calculated charge and spin densities are used to interpret the EPR and Mössbauer hyperfine parameters. The different bonding mechanisms contributing to the metal atom–rare gas matrix interaction are also investigated.
Nonlinear transport processes in gases
Authors: Eu Byung Chan
Published: February 2003

By applying the modified moment method to nonlinear transport phenomena in dilute gases and from the stationary solutions of the evolution equations derived from the Boltzmann equation, we have obtained in this paper nonlinear transport coefficients which are given, for example, by the formula ζ(Ω)=ζ0 sinh−1γΩ/γΩ, ζ=2η or λ, where Ω=∥[∇u](2)∥ or ∥∇ logT∥, γ=[ζ0(μrkBT/2)1/2]1/2/pd, and ζ0=2η0 or λ0 with u, T, μr, p, d, η0, and λ0, respectively, being the fluid velocity, temperature, reduced mass of particles, pressure of the gas, the size parameter (diameter) of the particle, the Chapman–Enskog shear viscosity, and heat conductivity. The formula reduces, if Ω is small, to the Chapman–Enskog theory transport coefficient and, if the density is vanishingly small, to the rarefied gas dynamics result for the transport coefficient. The γ as given provides for the first time a completely molecular expression for the ’’relaxation time’’ in Eyring’s theory of non-Newtonian flow.
An extended mean spherical approximation for Coulombic systems
Authors: Medina-Noyola Magdaleno , McQuarrie Donald A.
Published: February 2003

A systematic series of extensions of the mean spherical approximation is presented and is used to calculate the structural and thermodynamic properties of the restricted primitive model at reduced temperatures and densities comparable to the molten salt region.
Mobilities and interaction potentials for K+–Ar, K+–Kr, and K+–Xe
Authors: Lamm D. R. , Thackston M. G. , Eisele F. L. , Ellis H. W. , Twist J. R. , Pope W. M. , Gatland I. R. , McDaniel E. W.
Published: February 2003

Mobilities for K+ ions in Ar, Kr, and Xe gases have been measured at 300 °K in a drift tube spectrometer over a wide range of E/N (the ratio of the electric field intensity to the neutral gas number density). New data for K+–Kr and K+–Xe are presented here. The Viehland–Mason kinetic theory of ionic mobility, being valid for arbitrary E/N, is employed to calculate theoretical mobilities by utilizing electron gas–Drude model potentials of Gordon and Waldman for K+–Ar, K+–Kr, and K+–Xe. The results of these calculations are compared with the experimental data. Using the Gordon and Waldman potentials as a starting point, an iterative scheme, employing the experimental data directly, is used to develop ’’experimental’’ potentials. The new potentials are tabulated and compared to the Gordon and Waldman potentials.
The wave vector dependence of diffusion coefficients in photon correlation spectroscopy of protein solutions
Authors: Oh Young S. , Johnson Charles S.
Published: February 2003

The mutual diffusion coefficient Dm was measured by means of photon correlation spectroscopy (PCS) for bovine serum albumin (BSA) at pH 4.7 and ionic strength I≃0.12 M. The BSA concentrations ranged from 1.00 to 10.7 g/dℓ and the magnitude of the scattering wave vector K varied from 3.21×104 to 3.51×105 cm−1. It was found that Dm=D0[1−(0.0166±0.0009)C], where D0=(5.92±0.04)×10−7 cm2/s corrected to water at 20 °C and the C measured in units of g/dℓ. The quantity Cn/K3, where Cn is the concentration in number of solute particles per cm3, ranged from 2 to 27 000, but this had no influence on the measured values of Dm. This work does not support the idea that the small size of K−1 or the small number of molecules contained in the volume K−3 affects the magnitudes of diffusion coefficients determined by PCS for proteins at moderate ionic strengths.
Reorientations of octahedral SiF26− ions in solid Na2SiF6 by NMR
Authors: Watton A. , Koster E. , Petch H. E.
Published: February 2003

Temperature dependences of the 19F NMR absorption line second moment and spin–lattice relaxation times (T1 and T1ρ, respectively) in Na2SiF6 indicate the presence of a general reorientation of two independent types of SiF26− ions with activation energies of 33±1.3 and 49.0±2.4 kJ/mole. The motions are discussed in terms of the crystal structure, and related to observations of the chemically similar (NH4)2SiF6.
Depolarized Rayleigh light scattering studies of concentrated aqueous nitrate solutions
Authors: Carpio Ronald A. , Mehicic Mehmed , Yeager Ernest
Published: February 2003

Interferometric measurements of the reorientational relaxation time τ of the nitrate anion in concentrated aqueous calcium nitrate and zinc nitrate solutions have been made as a function of temperature and composition. Arrhenius plots of τ for Ca(NO3)2⋅XH2O, where X=4,5, and 5.6 and Zn(NO3)2⋅5H2O are linear and yield activation energies in the range of 5.6 and 8.3 kcal/mole. The data for Ca(NO3)2⋅3.91H2O, which cover the most extensive range of viscosity and temperature, were non-Arrhenius and were best fitted by the Vogel–Tamman–Fulcher equation from which an ideal glass transition temperature was derived. The viscosity dependence of τ for both the Ca(NO3)2 and Zn(NO3)2 solutions was found to be between that predicted by the classical Stokes-Einstein equation and that predicted using slip hydrodynamic boundary conditions. Nitrate rotation was found to be slower in Ca(NO3)2 solutions than in the corresponding Zn(NO3)2 solutions.
Raman light scattering studies of the depolarized Rayleigh wing of liquids and solutions
Authors: Perrot Michel , Brooker Murray H. , Lascombe Jean
Published: February 2003

Raman spectra of the depolarized Rayleigh wing region (10–300 cm−1) of a number of liquids and solutions have been recorded in digital form employing signal averaging techniques. The symmetrized I(?) spectra have been recast in an I(?)?2 format which transforms the Rayleigh spectra into forms directly comparable to far-infrared absorption. The major advantage of this procedure is that it suppresses the exciting line and emphasizes the weak low frequency peaks. As a result, the basic characteristics of the ’’peaks’’ previously reported are confirmed with improved precision. Peaks have also been observed for the first time for cyclohexane, acetone, and n-tetradecane. These peaks appear to reflect the short-time behavior of the external coordinates of individual anisotropic molecules and should not be confused with fundamental vibrational or negative combination modes. For liquid benzene, studies of the effects of concentration change (in carbon tetrachloride), temperature change, and isotopic substitution clearly showed that the peak originates in hindered librational oscillations of individual benzene molecules. Temperature variation studies revealed that the peak maximum decreased with increased temperature, which was exactly the opposite of that reported from infrared studies.
Vibrational relaxation of DF(v=1 and 3) in H2, D2, N2, and HF at 200 K
Authors: Bott J. F.
Published: February 2003

The laser-induced fluorescence technique was used to measure the rate coefficients for the deactivation of DF(v=1) and DF(v=3) in H2, D2, N2, and HF at 200±5 K. The rate coefficients for deactivation by H2, N2, and HF were found to scale with v as v1.9±0.1, essentially the same as the scaling at 295 K. The relaxation rates for DF(v=1) were compared with data obtained at higher temperatures. At 200 K, the exchange probability of HF(1)+H2(0) was the same as that of DF(1)+D2(0) (within 10%) when the endothermicities were considered.
Rate parameters for the reaction of atomic hydrogen with dimethyl ether and dimethyl sulfide
Authors: Lee J. H. , Machen R. C. , Nava D. F. , Stief L. J.
Published: February 2003

Absolute rate constants for the reaction of atomic hydrogen with dimethyl ether (DME) and dimethyl sulfide (DMS) were obtained using the flash photolysis–resonance fluorescence technique. Under conditions where secondary reactions are avoided, rate constants for the H+DME reaction over the temperature range 273–426 K are well represented by the Arrhenius expression k1=(4.38±0.59)×10−12 exp(−1956±43/T) cm3 molecule−1 s−1. The corresponding Arrhenius expression for the H+DMS reaction over the temperature range 212–500 K is k2=(1.30±0.43)×10−11exp(−1118±81/T) cm3 molecule−1 s−1. The Arrhenius plot for k2 shows signs of curvature, however, and separate Arrhenius expressions are derived for the data above and below room temperature. These results are discussed and comparisons are made with previous determinations which employed flow discharge and product analysis techniques.
Charge transfer to a solvent state. VI. Inter-relation between electrochemical and photoionization data of a solute in condensed phase
Authors: Truong T. B.
Published: February 2003

The electrochemical data obtained from aqueous solutions of tryptophan, of indole, and from tryptophan in ethanol agree well with those derived from the photoionization mechanism which is based on a charge transfer solute–solvent complex model (Ref. 1), particularly the conduction band depth V0, the effective cavity radius r, hence the solvation energy of the solute cation. A relationship is now established between the electrochemical data and the photoionization data. This relationship permits one to deduce V0 and the oxidation energy eEox1/2 of a solute in a solvent when its photoionization data are known or vice versa.
Analysis of the Grüneisen parameters of some fcc metals by an improved elastic force model
Authors: Gupta O. P. , Kharoo H. L.
Published: February 2003

An analysis of the temperature dependence of Grüneisen parameters of copper, silver, gold, and aluminium is performed in terms of the elastic constants and their pressure derivatives by a new lattice dynamical model. The model satisfies the symmetry requirements of the lattice and the lattice is in equilibrium without recourse to external forces. The microscopic Grüneisen parameters gq,j are calculated as a function of wave vector q, along the principal symmetry directions, (100), (110), (111), (210), (211), and (221), and the values are averaged over the wave vector space in the first Brillouin zone. For the evaluation of integrals, the modified Houston’s method is used. The Grüneisen parameters computed in our present study show reasonably satisfactory agreement with experimental measurements.
Mass spectrometric study of the stabilities of gaseous carbides of vanadium, niobium, and molybdenum
Authors: Gupta Satish K. , Gingerich Karl A.
Published: February 2003

The gaseous molecules VC, NbC, NbC2, MoC, and MoC2 have been identified in a mass spectrometric study of the Knudsen effusate from the niobium–graphite and vanadium–niobium–molybdenum–graphite systems at high temperatures. Third-law enthalpies of the various reactions involving these species were determined from the experimental equilibrium measurements and estimated thermodynamic functions. The reaction enthalpies in conjunction with published thermodynamic data yielded the thermochemical values (kJ mol−1, kcal mol−1): D°0(VC) = 419±24, 101.1±5.7; DH°at,0(VC2) = 1178±17, 281.1±4.1; D°0(NbC) = 564±13, 134.8±3.1; DH°at,0(NbC2) = 1257±13, 300.4±3.1; D°0(MoC) = 478±16, 114.2±3.8; and DH°at,0(MoC2) = 1101±20, 263.1±4.8. In addition, the bond energies D°0(V–C2) = 572±19 kJ mol−1, or 136.6±4.6 kcal mol−1; D°0(Nb–C2) = 650±16 kJ mol−1, or 155.4±3.8 kcal mol−1; and D°0(Mo–C2) = 494±22 kJ mol−1, or 118.1±5.4 kcal mol−1 were also calculated. The results are discussed in relation to the stabilities of previously known gaseous mono- and dicarbides of transition metal.
Stability and criticality of the stationary solutions of the nonlinear Fourier equation in Frank–Kamenetzki’s theory
Authors: Meinköhn Dirk
Published: February 2003

Frank-Kamenetzki’s theory of thermal explosions rests on the investigation of the boundary value problem of a certain nonlinear Fourier equation. For this, a method of analytic continuation of known solutions is proposed which uses the maximum of the temperature distribution as the continuation parameter. The proposed method is worked out for those cases where the location of the temperature maximum is determined by the symmetry of the problem. It is then shown to result in a simple classification of the stability properties of the thermal system and a characterization of the dependence of the solutions on the temperature maximum for several different classes of rate functions (linear, concave, or convex, etc., in their dependence on the temperature over a certain temperature range).
The overtone stretching Raman spectrum of HDO in liquid D2O
Authors: Belsley K. , Sceats Mark G.
Published: February 2003

The overtone Raman spectrum of HDO in liquid D2O is presented. The dominant feature of the OH stretching overtone occurs at higher frequencies than expected and this is attributed to a strong hydrogen bonding dependence of the second derivative of the anisotropic polarizability tensor along the OH stretching normal coordinate.
Finite time optimizations of a Newton’s law Carnot cycle
Authors: Salamon Peter , Nitzan Abrahan
Published: February 2003

We treat the problem of optimal finite time operations of a heat engine using an arbitrary working fluid and working between two constant temperature heat reservoirs. We work in a simplified framework (’’Newton’s law thermodynamics’’) which considers only losses associated with the heat exchange processes. We find the operations which maximize power, efficiency, effectiveness, and profit and those which minimize the loss of available work and the production of entropy. We find that all these optimal operations take place with the working fluid exchanging heat at a constant rate with each reservoir (implying a constant rate of entropy production) and undergoing adiabatic processes instantaneously. We define ’’Carnot space’’ to be the set of all operations of the engine which consist of constant rate heat exchanges and instantaneous adiabats. All optimal operations are points in this space which is shown (within the model) to be three dimensional. The different optimal operations with different connotations of ’’optimal’’ as described above are compared within this framework. To further study the economic implication of this model we also view the operation of the engine as an economic production process with work as its output. We obtain a simple analytical form of the production function and see repeatedly that maximum profit operation is a compromise between operation which maximizes the power and operation which minimizes the loss of available work. The path of maximum profit is obtained as a function of the costs of power and of availability.
Modification of the overlap potential to mimic a linear site–site potential
Authors: Gay J. G. , Berne B. J.
Published: February 2003

A modification of the overlap potential of Berne and Pechukas is proposed. The overlap strength and range parameters are used in a new functional form resulting in a single-site potential which closely resembles a linear site–site potential.
Rotational energy transfer in Na*2 (A Σ) colliding with Xe, Kr, Ar, Ne, He, H2, CH4, and N2: Experiment and fitting laws
Authors: Brunner Timothy A. , Smith Neil , Karp Allan W. , Pritchard David E.
Published: February 2003

Using the method of laser-induced fluorescence, we have measured level to level rate constants for rotational energy transfer (RET) in Na*2 colliding with Xe, Kr, Ar, Ne, He, H2, N2, and CH4. For each target gas we varied the initial rotational quantum number ji over a wide range, typically 4–100, and measured approximately 60 rate constants with an average error of between 6% and 9%. The resulting base of 479 rate constants is used to test several recently proposed fitting laws. The energy corrected sudden scaling law of DePristo et al., when combined with the assumption of a power gap law for the basis rate constants kl→0, fit with only 3 parameters all of the data for a given target gas with 7%–12% average percentage deviation. Our statistical power gap law worked well and was generally the best law for those data sets with only one value of ji. The worst fits in all cases considered here were those using the exponential gap law of surprisal theory.
Molecular beam photoionization study of CO, N2, and NO dimers and clusters
Authors: Linn S. H. , Ono Y. , Ng C. Y.
Published: February 2003

Photoionization efficiency (PIE) data for (CO)+2, (N2)+2, and (NO)+2 have been obtained near the thresholds using the molecular beam method. The ionization energies (IE) for (CO)2, (N2)2, and (NO)2 were measured to be 13.05±0.04 eV (950±3 Å), 14.69±0.05 eV (844±3 Å), and 8.736±0.002 eV (1419.2±0.3 Å), respectively. Using these values, the known IE’s for CO, N2, and NO, and the estimated binding energies for (CO)2, (N2)2, and (NO)2, the bond dissocations energies for CO+⋅CO, N+2⋅N2, and NO+⋅NO were deduced to be 0.97±0.04, 0.90±0.05, and 0.598±0.006 eV, respectively. From the analysis of the PIE curve for (NO)+2, the IE’s of (NO)2 to NO+(?1S+, v = 1)⋅NO and NO+(?1S+,v = 2)⋅NO were determined to be 8.997±0.007 eV (1 378±1 A°) and 9.253±0.013 eV (1 340±2 A°), respectively. This measurement supports the conclusion that the bonding of NO+ in NO+⋅NO is stronger than that of NO, but weaker than that of NO+. The IE’s for (CO)3, (N2)3, and (NO)n = 3–6 were also measured.
On a model chemical system showing competitive phenomena
Authors: Iwamoto Kazutoshi , Senō Manabu
Published: February 2003

The behavior of a model chemical system composed of two subsystems having common characteristics is studied. In this chemical system, a small difference in the rate constants of the common step of the two subsystems causes a large change in the concentrations of the reaction intermediates in the steady state as a result of competition between the two subsystems. The change of steady state is very drastic and extremely sensitive to changes in external constraints.
Picosecond pulse induced transient molecular birefringence and dichroism
Authors: Waldeck David , Cross Albert J. , McDonald Daniel B. , Fleming Graham R.
Published: February 2003

Excitation of dye molecules in fluid solution can lead to transient birefringence (caused by change in the polarizability anisotropy) and transient dichroism (caused by change in the absorption cross section). In the anisotropic absorption method of Shank and Ippen, both effects are observed, and in some cases the measured signal is dominated by the birefringence contribution. Very small amounts of external birefringence can lead to erroneous values for the rotational reorientation time. We present an analysis of these effects in a Jones matrix formalism, and use the results to show how to obtain correct reorientation times. The changes in polarizability anisotropy for the dyes oxazine-725 and DODCI are evaluated as +75 and +4 Å3, respectively, at 585 nm and we believe these to be the first direct measurements of this change between ground and first singlet states. The rotational reorientation times of four molecules in ethanol are presented and compared with hydrodynamic predictions.
Large multiconfiguration self-consistent-field wave functions for the ozone molecule
Authors: Laidig William D. , Schaefer Henry F.
Published: February 2003

The electronic structure of the ozone molecule is of particular interest in light of Goddard’s characterization of the ground state as a biradical. Rigorously optimized multiconfiguration self-consistent-field (MCSCF) wave functions of varying size have been determined here for ozone via newly developed techniques utilizing the unitary group approach. The largest of these ab initio MCSCF wave functions includes 13 413 configurations, i.e., all singly- and doubly excited configurations relative to the two reference configurations required for the biradical description of ozone. The convergence of the MCSCF procedures is discussed, as well as the structure of the MCSCF wave functions, and the effectiveness of different orbital transformations. There is a significant energy difference (0.034 hartrees) between the MCSCF wave functions involving one and two reference configurations. This gives emphasis to the fact that orbital optimization alone cannot compensate for the exclusion from the wave function of important classes of configurations. A simple test for the determination of the fraction biradical character of systems such as ozone suggests 23% biradical character for 03 at its equilibrium geometry.
Theory of cooperative high-spin⇄low-spin transitions in iron (III) compounds induced by the molecular distortions
Authors: Sasaki Naoyuki , Kambara Takeshi
Published: February 2003

The high-spin?low-spin transitions in iron (III) compounds are studied on the basis of the ligand field theory using the model in which the coupling between the iron ion and the intramolecular distortion is the driving force for the spin state transitions. The intermolecular coupling between the molecular distortions is taken into account and the distortions are treated dynamically. Two kinds of the molecular distortions, the uniform dilation and the uniaxial distortion, are considered. The discontinuous high-spin?low-spin transitions may be induced by the coupling with the uniaxial distortion, while the continuous spin state transitions arise from the coupling with the uniform dilation. Temperature dependences of equilibrium cooperative displacement of the ligands, high-spin and low-spin fractions of iron (III) ions, effective magnetic moment, quadrupole splitting in Mössbauer spectra, and internal magnetic field in NMR spectra are calculated based on the model as functions of the coupling strength between iron and the molecular distortion. It is shown that the essential features of the observed temperature dependences may be reproduced consistently in the various quantities by the present model.
Density of states and the velocity autocorrelation function derived from quench studies
Authors: Grest G. S. , Nagel S. R. , Rahman A. , Witten T. A.
Published: February 2003

We show how, for a harmonic solid, the density of normal mode states and the velocity autocorrelation function can be found by analyzing the temperature of the solid after its kinetic energy has been abruptly quenched. In a molecular dynamics simulation of an interacting Lennard-Jones system we show what happens to these results as the solid is made anharmonic and how, in the liquid state, these techniques can be used to study the role of anharmonicity in the velocity autocorrelation function.
High resolution infrared studies of dynamics in low temperature matrics: Vibrational dephasing for SeF6 in noble gas solids
Authors: Jones Llewellyn H. , Swanson Basil I.
Published: February 2003

High resolution infrared absorption spectra for the y3 mode of SeF6 in low temperature noble gas matrices have been observed. A remarkable amount of structure is observed leading to the conclusion that multiple trapping sites as well as site symmetry splittings, similar to those observed previously for SF6, are common. Temperature dependent studies give a rich display of dynamics arising from host–guest interactions. These give evidence for dynamic exchange among equivalent low symmetry sites within a given trapping cage. This exchange is evidence for a dephasing of the components of y3 by a local site phonon mode in resonance with part of the phonon bath. Unexpected matrix shifts and intensity changes with temperature have been observed. Accurate isotope shifts, especially in a neon matrix, are shown to be useful for calculation of potential constants. A discussion of host–guest interactions, dephasing, and dynamic site exchange in these matrices is given.
Diffusion of interacting particles: Light scattering study of microemulsions
Authors: Cazabat A. M. , Langevin D.
Published: February 2003

We have studied both the intensity and the autocorrelation function of the light scattered by water in oil microemulsions. A dilution procedure was used, which allowed us to extract from the experimental data information about droplet sizes and virial coefficients. It was found that in most cases, the droplets do not behave like hard spheres and that supplementary interactions must be taken into account. As pointed out recently by A. Vrij, these interactions can be treated as a perturbation to interpret the intensity data. Recent theoretical analyses of macromolecular diffusion allow one to interpret also the diffusion coefficient data. The agreement between theory and experiments is qualitatively good.
Absorption spectrum of the 2600 Å transition of benzene in cryogenic liquids
Authors: Bernstein E. R. , Lee J.
Published: February 2003

Absorption spectra of the 2600 Å system (1B2u←1A1g) of benzene dissolved in cryogenic liquids N2, CO, CF4, CH4, NF3, C2H6, and C3H8 are obtained and reported. As in the gas phase spectrum, the dominant series is the vibronically induced 610 10n (n = 1,⋅⋅⋅,5). No rotational or hot band structure has been observed in any of the solvents. The following features have been identified in the spectra: 6101n0, 620, 610810ln0, 6109101n0, 6108109101n0, and 6107101n0. In addition, N2, Co, CF4, NF3, and CH4 induce the (0,0) and 110 transitions while C2H6 and C3H8 induce 6101n0 and 620. Linewidths range from 50 cm−1 (N2) to 250 cm−1 (C3H8) and are temperature independent for a given solvent. Gas to liquid shifts are found to vary from −250 to −300 cm−1 throughout the series of solvents used and to be temperature independent. Solvent perturbations are in general unique and characteristic of particular solvents.
Glauber exchange effect in e−–Li elastic collision
Authors: Gien T. T.
Published: February 2003

The Glauber exchange effect, so far neglected in all previous Glauber calculations of e–Li scattering, is evaluated and included into the analysis of e–Li elastic collision at intermediate energies. It is found that the inclusion of the exchange effect modifies drastically the differential cross sections at lower scattering energies (20 eV). The Glauber results with exchange still fail, however, to provide a good agreement with experimental data of e–Li differential cross sections which have been made available recently in the literature at 20 and 60 eV.
Bimolecular and ‘‘three-body’’ quenching of paschen-1s argon atoms by N2, H2, and O2 and effects of N2 on the yield of the first triplet argon excimer
Authors: Loeb D. W. , Chen Mon-Chao , Firestone R. F.
Published: February 2003

Rate constants for bimolecular quenching of Ar (1s) resonance-state and metastable atoms by N2, H2, and O2 have been measured by fast absoprtion spectrophotometry at argon pressures in the 102–103 Torr region at 298 K. ’’Three-body’’ quenching attributed to collisional relaxation of vibrationally excited dissociative excimer molecules by molecular quenching agents has been observed to occur efficiently for all Ar (1s) atoms in the presence of H2 and O2, but only for the resonance-state Ar (1s) species in the presence of N2. A discussion and analysis of the temporal behavior and the yield of Ar2 (3S+u) molecules in the context of the mechanism for Ar (1s) atom decay and excimer formation indicates that the predominant precursors of the first triplet argon excimer in Ar/N2 mixtures are probably Ar (3P2) atoms and Ar2 van der Waals molecules, the latter through the agency of N2 (C 3Ru) at higher N2 concentrations.
Complex angular momentum analysis of diffraction scattering in atomic collisions
Authors: Connor J. N. L. , Farrelly D. , Mackay D. C.
Published: February 2003

The application of complex angular momentum techniques to diffraction scattering in elastic atom–atom collisions is investigated. Two different semiclassical methods have been used. In the first method, complex saddle points associated with the semiclassical integral representation for the scattering amplitude are employed. The second method is the Regge pole approach to elastic scattering. The first calculations are reported in which the semiclassical uniform Airy approximation using complex angular momenta has been applied to the dark side of a rainbow. Good agreement with partial wave results is obtained for the uniform Airy and Regge pole theories, with the Regge pole approach the easier to apply. The accuracy of the transitional Airy and primitive semiclassical approximations has also been studied. The effect of neglecting the scattering from the repulsive core of the potential is investigated. This case arises in the elastic scattering of chemically reactive systems when strong absorption is present. In addition, the effect on diffraction scattering of damping out the attractive part of a Lennard-Jones potential has ben studied until just the repulsive core remains.
Boron atom reactions. II. Rate constants with O2, SO2, CO2, and N2O
Authors: DiGiuseppe T. G. , Davidovits P.
Published: February 2003

The gas phase reactions of atomic boron with O2, SO2, CO2, and N2O have been studied using a new flow tube apparatus. Boron atoms were produced in a microwave discharge of a 0.02% mixture of diborane in argon. The bimolecular rate constants at 300 °K were obtained by measuring the density of boron down the flow tube as a function of reactant density. The rate constants for the O2, SO2, CO2, and N2O reactions are, in units of cm3 molecule−1 sec−1, 4.6±1.8×10−11, 1.1±0.4×10−10, 7.0±2.8×10−14, and 2.1±0.8×10−14, respectively. These results are compared with the rates measured for the reactions of the group IIA and IVA atoms. The patterns observed in the data are noted and a possible mechanism is discussed.
Photodissociation of the alkali iodides at 347.1 nm: Experimental angular distributions and dynamic model for their interpretation
Authors: Anderson William R. , Wilson Bradley M. , Ormerod Raleigh C. , Rose Timothy L.
Published: February 2003

The angular distributions of the alkali photofragment resulting from photodissociation of a molecular beam of NaI, KI, CsI, or RbI by a pulsed, linearly polarized laser beam at 347.1 nm have been measured. At the wavelength used, only production of ground state atoms is energetically feasible. The angular distributions indicate a trend in the perpendicular:parallel transition ratio from about 4:1 for NaI to about 2:1 for RbI and CsI. This interpretation assumes Hund’s case (c) coupling and excited states of pure perpendicular or parallel symmetry. A new model was developed to calculate the laboratory distribution from any center of mass distribution, including those resulting from multiphoton or saturated transitions. The individual counting model (ICM) simultaneously takes into account contributions from excited state lifetime, rotational distribution, and translational motion of the molecule. It is concluded that further study of the systems at several wavelengths in the lowest energy absorption band is necessary to unambiguously characterize the symmetry and electronic coupling of the low-lying excited states of the alkali iodides.
13C NMR study of the ‘‘bilayer’’ phase transitions in (C10H21NH3)2CuCl4
Authors: Koželj M. , Rutar V. , Zupančič I. , Blinc R. , Arend H. , Kind R. , Chapuis G.
Published: February 2003

The two structural phase transitions in the perovskite type layer structure compound (C10H21NH3)2CuCl4 have been studied by single crystal 13C NMR. The paramagnetic shifts due to the Cu++ ions have been evaluated and subtracted from the experimental data to yield the 13C chemical shift tensors as a function of temperature. The results show in agreement with the DTA data that the transition from the low temperature to the intermediate temperature phase is connected with a partial melting of the alkylammonium chains and the vanishing of the average chain tilt, whereas the transition to the high temperature phase is accompanied by the onset of flipping of the polar heads and an associated rotation of the chains around the long axis. The two transitions are thus analogous to the ones found in lipid bilayer membranes and (C10H21NH3)2CdCl4 but the sequence of the two successive transitions is exchanged.
Lateral interaction effects on the reaction of CO2 and oxygen adsorbed on Ag(110)
Authors: Barteau M. A. , Madix R. J.
Published: February 2003

The effect of oxygen adatom coverage and order upon the formation of CO3 intermediates via CO2+O(a)→CO3(a) was examined on the Ag(110) surface. The reaction probability for CO2 was found to be strongly dependent upon the oxygen adlayer. Adsorption of CO2 upon an ordered oxygen adlayer at 300 K occurred with a net reaction probability of the order of 10−2 or less, and resulted in the formation of (1×2) domains of CO3 which caused compression of the adsorbed (n×1) oxygen atom chains as determined by LEED experiments. Adsorption of CO2 upon a disordered oxygen adlayer at 170 K occurred with an initial sticking probability of unity; however, the saturation coverage of CO3 intermediates formed was less than the initial oxygen atom coverage. Adsorption of CO2 upon an ordered oxygen adlayer at 170 K occurred with lower reaction probability than at 300 K, indicating that the order of the oxygen adlayer strongly affected the CO2 reaction kinetics. In all cases the reaction of CO2 was hindered by increasing the initial oxygen atom coverage.
Site distribution studies of Rh supported on Al2O3—An infrared study of chemisorbed CO
Authors: Cavanagh R. R. , Yates J. T.
Published: February 2003

Using infrared spectroscopy, chemisorbed CO has been employed as a surface probe to observe differences in Rh site distributions on Al2O3-supported Rh. It has been found that higher loadings of Rh lead to Rh site distributions resembling those found on Rh(111) single crystals, whereas low Rh loadings produce isolated Rh sites preferentially. The isolated Rh sites yield infrared spectra characteristic of a species Rh(CO)2. Chemisorption of oxygen onto the CO-covered surface effectively eliminates crystalline Rh sites, leaving only the isolated Rh sites which maintain their bonding to CO as seen by infrared spectroscopy. Estimates of the infrared extinction coefficient for Rh(CO)2 have been made. The results are consistent with data from other laboratories which indicate that the Rh is in a Rhd+ oxidation state.
Surface interactions in the Pt/γ-Al2O3 system. II. Dynamics of CO chemisorption by infrared fluctuation spectroscopy
Authors: Rothschild Walter G. , Yao H. C.
Published: February 2003

A consistent picture relating the nature of the surface phases of Pt on g-Al2O3 with the asymmetric shapes of the infrared profiles of chemisorbed CO is given. Observed quantities are (i) the absorption coefficient of the profile of the CO stretching fundamental as a function of temperature-controlled desorption steps, (ii) spectral second and third band moments, (iii) frequency shifts of the peak absorption, and (iv) particle size distribution of Pt on the alumina. Derived quantities are correlation times for the mobilities of the CO molecules on their adsorption sites, based on a simple model of vibrational dephasing determined by essentially 1:1 nearest-neighbor interactions (breakdown of the central limit theorem). It is concluded that the motional freedom (’’wagging’’ or ’’nearest-site hopping’’) of the chemisorbed CO molecules increases with increasing predominance of the particulate phase over the dispersed phase of Pt on g-Al2O3, reflecting the stronger platinum–alumina interactions in the dispersed phase.
Time-resolved spectroscopy of macromolecules: Effect of helical structure on the torsional dynamics of DNA and RNA
Authors: Millar D. P. , Robbins R. J. , Zewail A. H.
Published: February 2003

The torsional rigidity of DNA and RNA is measured via the fluorescence depolarization technique.(AIP)
Electron energy loss spectroscopic study of CO on Pt(111)
Authors: Avery Neil R.
Published: February 2003

High resolution electron energy loss spectroscopic data for the high coverage (q≳0.5) phase of CO on a Pt(111) surface show that adsoprtion occurs without any detectable changes to the characteristic vibrational modes of the admolecule. This is seen as evidence that a uniaxial compression of the admolecules does not occur, but that instead the coverage increase is accomodated by introducing coherently spaced packing faults into tje half-monolayer c(4×2) structure.
Characteristics of the Gaussian-type orbitals
Authors: Tatewaki Hiroshi
Published: February 2003

It is shown that, contrary to the common belief, Gaussian-type atomic functions are quite acceptable basis functions for molecular calculations. The GTO’s become more satisfactory for atoms with electrons with higher angular momentum. (AIP)
Electric dipole moment of KrSO3
Authors: Leopold K. R. , Bowen K. H. , Klemperer W.
Published: February 2003

The radiofrequency spectrum of KrSO3 is reported. A beam of KrSO3 was produced by expanding a mixture of Ar, Kr and SO3 at 900 Torr through a nozzle at 25°C. The Stark spectrum and dipole moment are reported.
Comment on the dissociation energy of NaH+(X 2Σ+)
Authors: Liu B. , Olson R. E. , Saxon R. P.
Published: February 2003

It is argued that the discrepancy in the dissociation energy calculations of NaH+ of Ref. 1 and Ref. 2 is due entirely to different methods of calculations of De from the ab initio electronic energies.
Comment on the dissociation energies of AH+ ground states
Authors: Rosmus P. , Meyer W.
Published: February 2003

The calculated method for dissociation energy of AH+ molecules is discussed, for a running from Li to Cl. The calculations of dissociation energy are compared with measured values. (AIP)
MCSCF pseudopotential calculations for the alkali hydrides and their anions
Authors: Stevens Walter J. , Karo Arnold M. , Hiskes John R.
Published: February 2003

Multiconfiguration self-consistent-field calculations have been carried out on the X 1S+ and a 3S+ states of LiH, NaH, KH, RbH, and CsH, and on the X 2S+ states of their respective anions. Pseudopotentials, including core polarization terms, have been used to replace the core electrons, resulting in simple two- and three-electron calculations. Comparisons of the neutral potential curves with experiment and other ab initio calculations (where available) show very good agreement. The agreement with ab initio calculations on LiH− and NaH− is also very good. Adiabatic electron affinities have been calculated for LiH (0.293 ev), NaH (0.316 eV), KH (0.437 eV), RbH (0.422 eV), and CsH (0.438 eV).
On the structure of the biaxial and uniaxial smectic-B-type phases of 1̄4̄S5, and the apparently second-order phase transition between them
Authors: Ekachai Arun , de Vries Adriaan , Neubert Mary E. , Spielberg N.
Published: February 2003

The biaxial smectic-B-type phase of 4-n-pentylbenzenethio-4′-n-tetradecyloxybenzoate (1̄4̄S5) has been studied along with its uniaxial smectic-l B phase. The results are interpreted in terms of identical layer structures in both phases (with the molecules tilted with respect to the layer normal) but with different kinds of disorder (within the layers and between the layers). The transition between the two phases appears to be second order.