bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopic investigations of the homogeneous nucleation of nickel induced by shock pyrolysis of Ni(CO)4
Authors: Steinwandel J. , Hoeschele J.
Published: July 2002

The gas phase nucleation of nickel in argon inert gas was investigated at elevated temperatures (1200 K≤T≤2700 K) behind shock waves by using atomic absorption and cluster extinction spectroscopy. The initial degree of supersaturation was varied between 7.1≤lg (n/n∞) ≤0.0 corresponding to nickel atom concentrations 0.2×1016 cm−3≤n≤2×1016 cm−3 prior to nucleation. Within a temperature range of about 50 K up to phase equilibrium conditions, a significant change in nucleation kinetics was observed. No nucleation was observed at undersaturated conditions. The experiments are in contrast to existing nucleation theories because no critical supersaturation seems to be required in early nucleation stages.
Model of preexisting traps for electrons in polar liquids
Authors: Hilczer M. , Bartczak W. M. , Sopek M.
Published: July 2002

The statistical distributions of structure parameters and the electron energy level of the preexisting traps in polar liquids have been investigated. The TIPS model of intermolecular interactions has been applied. The numerical computations were performed for methanol and are compared with the earlier Tachiya and Mozumder calculations.
Relaxation of 6 2P3/2 metastable and 6 2P1/2 ground state atomic thallium produced in the photodissociation of thallium halide vapors at high densities
Authors: Scott D. A. , Piper J. A.
Published: July 2002

Decay rates of the 6 2P3/2 metastable and 6 2P1/2 ground state atomic thallium densities produced in UV photodissociation (at λ193, 222, 249, 308, and 353 nm) of TlI, TlBr, and TlCl molecular vapors have been measured for vapor densities from 1013 to 1017 cm−3. Dominant relaxation processes have been identified as (i) for the metastable state, collisional deexcitation by thallium halide molecules at high halide densities (≥1015 cm−3) and by free halogens and trace impurities at lower halide densities and (ii) for the ground state, diffusion in the ambient (argon/thallium halide) gas at high halide densities and volume reassociation under certain conditions at low halide densities. Cross sections and diffusion coefficients are evaluated.
‘‘Ordered’’ structure in dilute suspensions of polymer latices as studied by microscopy. Influences of charge density and size
Authors: Ito Kensaku , Nakamura Hiroshi , Ise Norio
Published: July 2002

Dilute aqueous suspensions of polystyrene-based latex particles of various charge numbers and diameters were studied by microscopy. The interparticle spacing (2Dexp) in the ordered regions was determined with the aid of an image data analyzer. The 2Dexp values were again smaller than the average spacing from concentration (2D0). Furthermore 2Dexp was smaller for more highly charged particles at a constant diameter. These observations confirmed our previous claim that there exists an electrostatic attraction between colloidal particles through the intermediary of counterions and the attraction becomes stronger with increasing number of charges of the particles. The interparticle spacing was calculated according to the theory of Sogami [J. Chem. Phys. 81, 6320 (1984)]. A close agreement was obtained for relatively low charge number particles when the fraction of the free counterions (f) was assumed to be about the same as that found by the transference experiments [J. Chem. Phys. 82, 5732 (1985)], but the agreement was not satisfactory for high charge number particles.
Absence of resonances in the elastic scattering of electrons in molecular solids
Authors: Fano U. , Stephens J. A. , Inokuti Mitio
Published: July 2002

We explain why experiments by Sanche and co-workers show no resonance effects in the elastic scattering of electrons by solid N2, while the same effects are conspicuous in inelastic channels. Briefly stated, our idea is that, once an electron is captured by a molecule in condensed matter, its charge induces an electric polarization of many neighboring molecules. The nuclear displacements arising from this polarization are unlikely to relax promptly upon electron autodetachment, thus dissipating part of the electron’s initial energy. We point out some consequences of our interpretation in contexts of interest to radiation physics and chemistry.
Vibrational circular dichroism of A2B2 molecules
Authors: Polavarapu P. L.
Published: July 2002

A2B2 molecules of C2 symmetry are considered to investigate the relation of vibrational absorption and circular dichroism (VCD) to the molecular chirality. Symmetry arguments and Sayvetz conditions are used to derive the Cartesian displacements for symmetric and antisymmetric stretching vibrations. Simple expressions are derived for the absorption and VCD intensities of these two stretching modes.
Application of spectral quantization to metastable states of C 1A′DCN
Authors: Chuljian David T. , Ozment Judy , Simons Jack
Published: July 2002

The spectral quantization method which was successfully used previously to study bound state energies and wave functions of C 1A′DCN is extended to the low-lying metastable states of this same system. The potential energy surface employed involves the same ab initio calculational data as was used in our earlier classical trajectory and purely quantal studies. Energies and wave functions for the metastable states of DCN obtained by spectral quantization are compared to those achieved in the presumably accurate quantal study. The agreement between the quantal and spectal quantized wave function is not nearly as pleasing for these metastable states as it was for the bound states.
Reflection optical activity of uniaxial media
Authors: Lalov I. J. , Miteva A. I.
Published: July 2002

The possibility to investigate optical activity of uniaxial media by measuring the difference between the intensities of reflected electromagnetic waves (emw) of different circular polarization (reflection optical activity—ROA) is discussed. The components of the gyration tensor and the polarization of the normal emw in uniaxial media are found. The reflection of emw is studied in two cases: (a) optical axis normal to the boundary; (b) optical axis normal to the plane of incidence. Three modifications of differential spectroscopy are proposed: (1) left and right circularly polarized waves—usual reflection; (2) total reflection–circular polarization (TROA); (3) total reflection of linearly polarized waves with different azimuths of vibration. The specific features of the proposed methods (ROA and TROA) are discussed as well as the possibility of studying the optical activity induced by nondegenerate and degenerate excitations (vibrations).
New series of ferroelectric liquid crystals with large spontaneous polarization and dielectric constant
Authors: Sakurai Takao , Mikami Naoko , Ozaki Masanori , Yoshino Katsumi
Published: July 2002

Two new series of ferroelectric liquid crystals derived from haloalcohols as chiral sources are synthesized and are found to exhibit an extremely large spontaneous polarization of the order of 10−8–10−7 C/cm2 and also a large dielectric constant of 102–103 in a wide temperature range.
Percolation in oil-continuous microemulsions. A dielectric study of aerosol OT/water/isooctane
Authors: van Dijk M. A. , Casteleijn G. , Joosten J. G. H. , Levine Y. K.
Published: July 2002

The percolation transition in AOT/water/isooctane microemulsions has been studied by means of dielectric spectroscopy. At the percolation threshold the conductivity of the system increases sharply and the static dielectric permittivity attains a large maximum. It is shown that the frequency dependence of the permittivity can be well described by simple scaling relations of percolation theory. The critical exponent u of the frequency dependence has been found to be equal to u=0.62±0.02 and independent of temperature and microemulsion composition. The temperature dependence of the critical volume fraction for percolation has been related to the temperature dependence of the permittivity of the system far away from the percolation threshold.
Critical dynamics of binary polymer mixtures
Authors: Fredrickson Glenn H. , Bates Frank S.
Published: July 2002

Mode coupling corrections to the thermal decay rate of binary polymer mixtures near a critical point are investigated. It is found that the classical (Van Hove) theory due to Binder breaks down in several limiting cases. In the regime qR≪1 and qξ≫1, where q is the scattering wave vector, R is the radius of gyration of a chain, and ξ is the correlation length, we find that the classical theory fails when qR≪Ne/N3/2. Here N is the number of segments on a chain and Ne is the number of segments between entanglements. In the regime qR≪1 and qξ≪1, we find a breakdown in the classical theory when ξ≫RN3/2/Ne. The thermal decay rate is predicted to vary like q3 and q2/ξ in these two new regimes, respectively. Particularly in the case of polymer mixtures below their entanglement molecular weight we expect to see the mode coupling corrections in light scattering experiments.
Time resolved study of the luminescence produced by the pulse radiolysis of D2O vapor
Authors: Quickenden T. I. , Vernon C. F. , Litjens R. A. J. , Freeman C. G. , Sangster D. F.
Published: July 2002

D2O vapor was irradiated using a 0.53 MeV pulsed electron beam and the 200–900 nm wavelength range was examined for luminescence emission from excited fragments. Spectral lines of the OD (C 2∑+→A 2∑+) and the OD (A 2∑+→X 2Π) transitions were observed, as were the Balmer transitions of deuterium between n=6→n=2 and n=3→n=2, and the oxygen transitions O+(3p 4D0→3s 4P),O(3p 5P→3s 5S0), and O(3p 3P→3s 3S0). Values were obtained for the natural lifetimes, quenching rate constants, and quenching cross sections at 298 K for the majority of the above excited species. The natural lifetimes and quenching data obtained for the transitions of excited OD and oxygen species were, as expected, similar to the values obtained for the corresponding species in H2O vapor. However, Balmer D transitions exhibited shorter natural lifetimes and smaller quenching cross sections than the corresponding Balmer H transitions. The differences in quenching rate were much larger than the effect of isotopic substitution on collision frequency. Both lifetime and quenching differences were attributed to greater population of the p sublevels in excited D as compared with H.
Raman study of mesogenic transitions in 4,4′-di-n-pentyloxyazoxybenzene (C5)
Authors: Venugopalan S. , Rossabi J.
Published: July 2002

A Raman scattering study of the solid-smectic transition in 4,4′-di-n-pentyloxyazoxybenzene (C5) has been carried out. C5 is known to exhibit a previously unrecognized, highly ordered smectic phase. We have investigated the Raman spectra of C5 in its solid, smectic, nematic, and isotropic phases, with special attention to the external mode region below 100 cm−1. At 300 K the solid phase exhibits several distinct low frequency features. These are progressively attenuated on approaching the solid–smectic transition which occurs at 342 K. The accordion mode of the pentyl chains is observable at 318 cm−1 for the solid phase, but it practically disappears in the smectic phase. This is in accord with the inference of Prasad et al. that the solid–smectic transition is accompanied by a configurational melting of the pentyl end chains. In the smectic phase, an inelastic wing due to a highly damped mode is seen below 60 cm−1; this unique signature of the smectic phase disappears in the nematic and isotropic phases. The plausible origin of this mode and its damping are considered in terms of the molecular correlation within the smectic layers.
On the nonequilibrium chemical potential of open pores in a membrane
Authors: Jou D. , Ferrer-Suquet F. , Perez C. J.
Published: July 2002

Starting from the generalized entropy of extended irreversible thermodynamics, we study the influence of the electric current on the probability of finding a system in a state of given energy and electrical conductivity. As an application, we study the probability of open and closed pores in a membrane.
The dimethyl ether–sulfur dioxide complex: A photoelectron spectroscopic study
Authors: Carnovale Frank , Peel J. Barrie , Rothwell Richard G.
Published: July 2002

The He i photoelectron spectrum of the gas-phase complex formed by dimethyl ether and sulfur dioxide has been measured using a pulsed free jet expansion of a mixture of the two gases. A spectrum stripping procedure was used to remove the respective monomer bands from the measured spectrum giving a spectrum assigned to the 1:1 complex (CH3)2O⋅SO2. Interpretation of the spectrum with the aid of ab initio molecular orbital calculations shows that ionization bands associated with (CH3)2O are increased in energy by up to 0.4 eV, whereas those associated with SO2 are decreased in energy by up to 0.9 eV. Ab initio calculations on the dimethyl ether–sulfur dioxide complex, performed at the 3-21G* level, predict an intermolecular O--S separation of 2.355 Å with this direction being displaced 30° from the symmetry axis of the (CH3)2O but approximately perpendicular to the SO2 molecular plane. The monomer dipoles are oriented approximately antiparallel in the complex.
The photophysics of gas phase europium chelates. I. Temperature dependence of luminescence
Authors: Dao Phan , Twarowski Allen J.
Published: July 2002

Luminescence lifetimes for two gas europium chelate complexes have been measured as a function of gas temperature. Following ligand excitation the rate constant for Eu(+3) 5D0→7F2 in both molecules shows an Arrhenius temperature dependence. An activation energy of 5100 cm−1 is obtained for europium (3+) tris-1, 1, 1, 2, 2, 3, 3-heptafluoro-7, 7-dimethyl-4, 6,-octanedione, Eu(fod)3, and 4100 cm−1 is obtained for the activation energy of europium (3+) tris-2, 2, 6, 6,-tetramethyl-3, 5-heptanedione, Eu(thd)3. The quantum yield for production of molecules in the luminescing Eu(+3) 5D0 state is found to be independent of temperature when either Eu(thd)3 or Eu(fod)3 is excited in the ultraviolet absorption bands of the ligands.
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o study of the J(BB) and J(BH) coupling constants in polyboranes via the coupled-Hartree–Fock and equations-of-motion methods
Authors: Galasso V. , Fronzoni G.
Published: July 2002

Coupled-Hartree–Fock and equations-of-motion calculations at ab initio level for the boron–boron and boron–proton indirect nuclear spin–spin coupling constants in a representative series of polyboranes (B2H6, B2H4, B2H−7, B3H−8, B4H10, and B5H9) are presented. The boron–hydrogen–boron coupling constant is very sensitive to molecular structure and shows neither a unique sign nor a constancy of absolute value. It is found to be negative in B2H6. On the other hand, the coupling constant for a two-center two-electron boron–boron bond is predicted to be invariably positive in sign. Results show that the positive sign must also be attributed to 1J(BH), irrespective of the bridged or normal nature of the boron–hydrogen bond.
Comment on the welding of polymer networks
Authors: Gaylord Richard J.
Published: July 2002

A simple mixture theory of the healing of polymer networks by two independent mechanisms involving the reptation of unattached chains and the retracing of dangling chains is found to be capable of showing the entire observed fracture energy vs contact time behavior.
Triplet (T1) state resonance Raman spectroscopy of some azanaphthalenes
Authors: Kessler R. J. , Tripathi G. N. R.
Published: July 2002

The time-resolved Tn←T1 resonance Raman spectra of quinoline (1-azanaphthalene), isoquinoline (2-azanaphthalene), quinoxaline (1,4-diazanaphthalene), and quinazoline (1,3-diazanaphthalene) molecules in cyclohexane solution are reported, and vibrational assignments and structural implications are discussed. In each of the four compounds, the most resonance enhanced Raman band lies in the 1340–1270 cm−1 region and corresponds to nuclear displacements involving in-plane stretching motions of the CC and CN bonds. In diazanaphthalenes, drop in the frequency of this vibration on S0 to T1 excitation (97 cm−1 in quinoxaline, 76 cm−1 in quinazoline) is observed to be higher than in azanaphthalenes (31 cm−1 in quinoline, 58 cm−1 in isoquinoline) implying pronounced elongation of the CN bonds, in comparison to the CC bonds, in the T1 states. The T1 Raman spectra of azanaphthalenes, in contrast to naphthalene, are observed to exhibit significant solvent dependency.
Ethylene adsorption on ZnO: CARS spectroscopy with optical waveguides
Authors: Wijekoon W. M. K. P. , Ho Z. Z. , Hetherington W. M.
Published: July 2002

Surface CARS spectroscopy using the planar optical waveguide geometry has been employed to study the adsorption of ethylene on a nonsingle crystal 0001 ZnO waveguide surface. The required CARS sensitivity was achieved by establishing an interference condition within a ZnO waveguide to reduce the contribution from the nonresonant susceptibility of the ZnO and to enhance the ratio of the adsorbate signal to the background signal. Under high vacuum conditions, spectra in the region of the C=C stretch provided evidence that the hydroxylated surface supported four sites for the absorption of ethylene. Physisorbed ethylene had a vibrational frequency of 1615 cm−1 and was readily desorbed. Chemisorbed species exhibited frequencies of 1602, 1590, and 1580 cm−1, and the sites are likely to be Zn2+ ions.
Temperature dependence of the EPR zero-field splitting of Mn2+ in ZnSiF6⋅6H2O
Authors: Wan K. L. , Hutton Stuart L. , Drumheller John E. , Rubins R. S.
Published: July 2002

The temperature dependence of the EPR spectrum of Mn2+ in ZnSiF6⋅6H2O was measured at 9.2 GHz between 15 and 297 K. Both the g and A tensors were found to be isotropic with values close to 2.000 and −90×10−4 cm−1, respectively. A slight decrease in the magnitude of A with increasing temperature was observed. The zero-field splitting parameters D and a–F were found to vary from −130.5×10−4 and 9.9×10−4 cm−1, respectively, at 15 K to −170.2×10−4 and 7.8×10−4 cm−1, respectively, at 297 K. The data for D below 100 K were fitted to the orbit–lattice interaction in the long-wavelength approximation with a Debye temperature of 138 K. An estimate of the low-temperature ratio of D for Ni2+ and Mn2+ in ZnSiF6⋅6H2O based on the long-wavelength fits was in good agreement with the measured ratio of 10 at 4 K.
Photodissociation dynamics of weakly bound ion–neutral clusters: SO2 ⋅ O+2
Authors: Kim Hyun-Sook , Kuo Chau-Hong , Bowers Michael T.
Published: July 2002

A photodissociation study of SO2 ⋅ O+2 is presented. The experiments were carried out on mass selected ion beams that were crossed with a polarized laser beam and then photoproducts were mass and energy analyzed. The SO2 ⋅ O+2 ions were formed by three body association reactions in a pressure and temperature dependent ion source. Studies were carried out at wavelengths of 582, 514, 488, 458, and 357±7 nm using an argon ion laser/dye laser system. Both O+2/SO2 and SO+2/O2 photoproducts were observed and the branching ratio measured as a function of λ. In addition, product kinetic energy distributions and angular distributions (asymmetry parameters) were measured and statistical phase space theory calculations were carried out. The results indicate the O+2/SO2 products are formed from photon absorption to a bound excited state at all wavelengths followed by internal conversion to the ground state and statistical vibrational predissociation. The SO+2/O2 products are formed by two mechanisms. At long wavelengths (582 nm) the products are formed exclusively by photon absorption to a bound state followed by internal conversion and statistical predissociation from the ground state. At short wavelengths (357 nm) direct dissociation from a repulsive upper state dominates. Both mechanisms are involved at intermediate wavelengths. Arguments are made that both the bound and repulsive upper states correlate to SO+2(X̃ 1A1)/O2(b 1∑+g) products and that the bound upper state corresponds to the low energy band in the photodissociation cross section measurements of Hodges and Vanderhoff and the repulsive state to the high energy band.
A revised Rydberg formula for two-electron systems. II. [Core]n
p2
Authors: Wang Hung-tai
Published: July 2002

The revised Rydberg formula (RRF) described in paper I for [core]nil2 two-electron systems with l=0 is extended here to l=1 cases. The two empirical parameters, the screening constant σl and a correction to the effective quantum number μl, in the RRF have simple dependences on l, the core charge Z, and core configurations. The accuracy of the RRF in calculating the two-electron binding energies of a variety of [core]np2 species is demonstrated and the physical interpretations of σp and μp and their relationships to σs and μs are discussed.
Defects in C(2×2) oxygen overlayers on Ni(100): The effect on vibrational spectra
Authors: Banse Barbara A. , Lloyd Kathryn G. , Hemminger John C.
Published: July 2002

We have modeled vacancy defects in C(2×2) oxygen overlayers on Ni(100) to examine the effect which such vacancies have on the vibrational spectra as measured by inelastic scattering of low energy electrons (HREELS). Particular attention has been given to the change in frequency of the collective modes of the oxygen overlayer as a function of the wave vector of the mode. We find that this frequency dispersion is modified by the vacancies and that there are distinctive changes in the expected peak shapes as a function of the scattering geometry.
Cooperative mean-frequency absorption: A two-beam two-photon process
Authors: Andrews David L. , Hopkins Kevin P.
Published: July 2002

It is shown that by a cooperative process involving virtual photon coupling between molecules, pairwise two-photon absorption can lead to molecular transitions associated with the mean of the laser frequencies in a two-beam experiment. The process is represented by A+A+ℏω1+ℏω2→A*+A*, and the selection rules are those normally applicable to two-photon absorption. The interaction may involve the excitation of chromophore pairs in polyatomic molecules, van der Waals molecules, or more usually discrete molecules in a gas or liquid. In the former case, however, dissymmetric juxtaposition of the chromophores produces a chirality which is manifest in a circular dichroism associated with the absorption process. The appropriate absorption rates are calculated using the methods of quantum electrodynamics, and the dependence on the separation of the interacting pair is examined in detail. Methods for observing the mean-frequency interaction are also outlined, and attention is drawn to a resonance condition which should appreciably enhance the absorption rate.
Toward a general theory of conical intersections in systems of identical nuclei
Authors: Keating Sean P. , Mead C. Alden
Published: July 2002

It has been shown previously that the Herzberg–Longuet–Higgins sign change produced in Born–Oppenheimer electronic wave functions when the nuclei traverse a closed path around a conical intersection has implications for the symmetry of wave functions under permutations of identical nuclei. For systems of three or four identical nuclei, there are special features present which have facilitated the detailed analysis. The present paper reports progress toward a general theory for systems of n nuclei. For n=3 or 4, the two key functions which locate conical intersections and define compensating phase factors can conveniently be defined so as to transform under permutations according to a two-dimensional irreducible representation of the permutation group. Since such representations do not exist for n>4, we have chosen to develop a formalism in terms of lab-fixed electronic basis functions, and we show how to define the two key functions in principle. The functions so defined both turn out to be totally symmetric under permutations. We show how they can be used to define compensating phase factors so that all modified electronic wave functions are either totally symmetric or totally antisymmetric under permutations. A detailed analysis is made to cyclic permutations in the neighborhood of Dnh symmetry, which can be extended by continuity arguments to more general configurations, and criteria are obtained for sign changes. There is a qualitative discussion of the treatment of more general permutations.
Collisional quenching of metastable ions by diatomic molecules
Authors: Saxena S. , Mathur K. C.
Published: July 2002

The deexcitation (quenching) of He+ ions in the 2s metastable state by collision with H2, N2, O2, CO, and NO molecules is studied using the time dependent perturbation theory. Velocity dependence of quenching cross section is presented. The results are compared with the available experimental data of Prior and Wang.
Spin-lattice relaxation of the quinoxaline triplet state in n-alkane matrices measured in zero magnetic field
Authors: Ghosh Sanjib , Petrin Michael , Maki August H.
Published: July 2002

The individual spin-lattice relaxation (SLR) rate constants (Wij) between the sublevels of the lowest triplet state of quinoxaline in n-pentane and in n-hexane Sphol’skii hosts over the temperature range of 1.2 to 4.2 K have been measured in zero applied magnetic field. The anisotropy pattern for the Wij for quinoxaline in these n-alkane hosts differs from that observed in a durene host. In durene, the SLR rate constant between the two in-plane sublevels was found to be dominant, and was suggested to occur via an Orbach relaxation process involving a localized phonon state with rotated spin axes. It is proposed here that the dominant relaxation route between the short in-plane axis sublevel (Ty) and the out-of-plane axis sublevel (Tx) observed for quinoxaline in n-alkane hosts is the result of a spin-orbit-phonon coupling. In the temperature range of 2.5 to 4.2 K, the SLR rate constant Wyx exhibits Raman relaxation with a T7 temperature dependence in an n-pentane host. In n-hexane, where the relaxation is much faster than that in n-pentane, the mechanism observed appears to be a combination of a normal direct process and a Raman process in the temperature range of 1.2 to 3.2 K. Individual decay constants for the triplet sublevels in the temperature range investigated are also presented.
Thomas–Fermi–Dirac-jellium model of the metal surface: Change of surface potential with charge
Authors: Goodisman Jerry
Published: July 2002

The Thomas–Fermi–Dirac equation is formulated for the electrons of a charged metal surface, the ionic background being represented by jellium. After transformation into dimensionless form, the equation is integrated to give the electron density and the surface potential as a function of surface charge. Calculated surface potentials for many (neutral) metals agree with the results of experiment and more sophisticated calculations. Coupling the model for the metal to a parametrized model for adsorbed water, we show that the metal can make a significant contribution to the capacitance of the interface, especially for negative surface charges.
Matrix and temperature effects on the relaxation of large molecules: A simultaneous time and spectral study
Authors: Huppert D. , Rentzepis P. M.
Published: July 2002

We present data of picosecond time-resolved unrelaxed and relaxed emission spectra of naphthazarin (H2NP) in low-temperature matrices. Risetime and decay rates of the fluorescence originating from individual excited state vibronic levels suggest that the relaxation does not follow the predicted statistical behavior, but rather proceeds via a specific pathway. The kinetic data also suggests that the proton translocation between the two oxygens may be described by a quantum mechanical mechanism. Variations with temperature and size of the host matrix molecules have been studied and their influence on the relaxation mechanism is discussed.
Brillouin scattering of carbon disulfide at pressures up to 70 kbar
Authors: Shimizu H. , Sasaki S. , Ishidate T.
Published: July 2002

Brillouin scattering was measured at room temperature in liquid and solid CS2 in a diamond anvil cell up to 70 kbar. In the liquid phase, the acoustic velocity and the refractive index were determined as a function of pressure: The former allowed us to determine the equation of state, ρ=0.206 P0.40+1.144 (1 kbar≤P≤13 kbar) with density ρ in g/cm3 and pressure P in kbar, and the latter was well fitted by the Lorentz–Lorenz relation yielding the pressure-insensitive polarizability of 8.20×10−24 cm3. In the solid phase, the pressure dependence of longitudinal- and transverse-acoustic phonon velocities was determined up to the appearance of black CS2 which was formed at pressures above 70 kbar, and the high optical and elastic anisotropy of crystalline CS2 is discussed.
Limit of the image theory for the classical decay rates of molecules at surfaces
Authors: Leung P. T. , George Thomas F. , Lee Y. C.
Published: July 2002

The limit of the classical image theory as applied to the problem of decay rates for molecules at metallic surfaces is critically examined. The validity of the inverse cube law is clarified with reference to recent experimental results.
Spectral intensities inferred from diffuse reflectance spectra of lanthanide complexes in the form of solid–solid solutions
Authors: Tandon S. P. , Gokhroo A. , Bhutra M. P. , Surana S. S. L. , Tandon K.
Published: July 2002

The Judd–Ofelt theory has so far been extensively applied to absorption and fluorescence spectra of lanthanide ions in crystal and solution state only. For the first time it has been successfully applied in the modified form to interpret the spectral intensities of solid state spectra of lanthanide ions using the diffuse reflectance technique. As an illustration the diffuse reflectance spectra of Pr3+ and Nd3+ complexes of glycine as primary ligand and ethylenediamine as secondary ligand have been reported and interpreted.
Optically nonlinear Langmuir–Blodgett films: Influence of the substrate on film structure and linear optical properties
Authors: Cross G. H. , Cade N. A. , Girling I. R. , Peterson I. R. , Andrews D. C.
Published: July 2002

Normal incidence transmission measurements and surface plasmon spectroscopy at optical frequencies are used to probe the optical and structural properties of an optically nonlinear dye, deposited onto glass and silver substrates by the Langmuir–Blodgett technique. The particular orientation and proximity to the silver surface afforded by the deposition method reveals strong molecule/metal interactions hitherto unreported for LB film assemblies on silver.
Theory of local mode excitation in polyatomics by frequency-modulated lasers
Authors: Bo-Min Xie , Jian-Qiang Ding
Published: July 2002

We investigate in this paper the possibility of local model (LM) excitation in polyatomic molecules by frequency-modulated (FM) lasers. The interaction between the LM and all other background-forming vibrational modes is treated as a perturbation, whose characteristics can be drawn from the experimental LM overtone line shapes. An integral expression describing the LM energy absorption process is obtained by which one can devise the effective experimental way to excite the LM of polyatomics by FM lasers.
The spectroscopy of the group Vlb transition metal hexacarbonyls using the electron impact method
Authors: Koerting C. F. , Walzl K. N. , Kuppermann A.
Published: July 2002

The electron energy-loss spectra of Cr(CO)6, Mo(CO)6, and W(CO)6 were measured at impact energies of 25, 50, and 100 eV and at scattering angles from 0° to 90°. The differential cross sections (DCS’s) were obtained for several features in the 3–7 eV energy-loss region. The symmetry-forbidden nature of the 1A1g→1A1g,2t2g (π)→3t2g(π*) transition in these compounds was confirmed. Several low energy excitations were assigned to ligand field transitions on the basis of the energy and angular behavior of their associated DCS’s. No transitions which could clearly be assigned to singlet→triplet excitations involving metal orbitals were located in these molecules. In addition, a number of states lying above the first ionization potential were observed for the first time. Several of these excitations seem to correspond quite well to some of the transitions observed in free CO.
State-to-state V–T transfer in HgBr(B 2Σ): A comparison with information theoretic predictions
Authors: Cheung Nai-Ho , Cool Terrill A. , Erlandson Alvin C.
Published: July 2002

The collisional relaxation of the vibrational distribution of HgBr(B 2Σ) molecules following initial laser excitation of the v=52 vibrational level has been monitored with observations of the HgBr(B 2Σ–X 2Σ) fluorescence. Spectral simulation methods, developed in previous studies of the nascent vibrational distributions of HgBr(B 2Σ) photofragment molecules, were used for the determination of vibrational state populations. State populations were measured for various degrees of relaxation as the pressure of chaperone molecules, He, Ne, Ar, Xe, and N2, was progressively increased. An exponential temporal decay characterizes the V–T relaxation of vibrational energy for each buffer gas. A single parameter, the exponential decay time for global V–T relaxation, is all that is required for an information theoretic synthesis of the entire detailed matrix of state-to-state V–T energy transfer probabilities. The computed V–T relaxation of the vibrational distribution, based on the a priori information theoretic predictions is in good agreement with experimental observations.
A general treatment of environmental effects on molecular vibrations
Authors: Severson M. W. , Schmidt P. P. , McKinley John M.
Published: July 2002

Vibrational spectroscopy is increasingly used as a selective and sensitive probe of the interaction between a given molecule and its environment. For electrochemistry, in particular, vibrational spectroscopy has been useful in the process of sorting reactive intermediates and mechanisms out of the many possibilities which present themselves. In this paper we discuss a general approach to the analysis of environmental effects on molecular vibrations. The objective is to use vibrational spectroscopy to determine values of specific parameters in a set of intra- and intermolecular pair potentials. In the body of this paper, we discuss in detail how one can manipulate a variety of model potential energy functions in order to account for environmental effects. We then apply the method to the adsorption of tetrahedral molecules on a metal surface. We report infrared spectra for sulfate ion adsorbed on a platinum electrode, and we make use of our analysis of the spectra to suggest that the sulfate anion associates with the metal through only one oxygen atom.
A light scattering study of reorientational motions in neat liquids. Pressure dependence
Authors: Lilge Dieter , Eimer Wolfgang , Dorfmüller Thomas
Published: July 2002

The reorientational correlation times of liquid diphenyl methane and of diphenyl ether have been measured by depolarized light scattering as a function of temperature and pressure. The data yield activation energies and activation volumes. The viscosity dependence of the correlation times is well described by an extended Stokes–Einstein–Debye equation. The data indicate that the reorientational motion observed can to a good approximation be described in terms of a single-molecule motion. The two sets of data obtained from the two liquids are in many respects very similar. However, the more polar diphenyl ether displays larger values of the activation parameters.
Laser separation of lithium isotopes by double resonance enhanced multiphoton ionization of Li2
Authors: Balz J. G. , Bernheim R. A. , Gold L. P.
Published: July 2002

Multiphoton ionization spectra of 7Li2, 6Li2, and 7Li6Li vapors have been measured in the 570–650 nm region using a single, low resolution, multimode cw dye laser. A number of wavelengths provide selective multiphoton ionization of one isotopic species demonstrating the possibility of efficient laser-driven isotopic separation in lithium in this wavelength region.
Collisional scaling within a multichannel square representation
Authors: Eno Larry
Published: July 2002

A new approach is examined for the state-to-state scaling of collision problems. It derives from multichannel scattering at a square interaction and is referred to as mutlichannel square (MS) scaling. Since it retains the full internal energy spectrum while approximating the radial coupling elements, it may be viewed as complementing the conventional energy sudden (ES) scaling. Some general comments are made with regard to the structure of the MS relations and we show how several attractive features of ES scaling can be matched by the new scaling. Application is made to the analysis of rotationally inelastic integral cross sections for the scattering of He from p-H2. We compare MS scaled results with both ES and modified ES results. It is found that for the range of total energies examined, the MS scaling yields results which are in good agreement with exact ones and are dramatically improved over the basic ES ones. The modified ES procedure depends upon incorporating off-energy shell effects into the ES scaling and like the MS scheme is here set up to contain a single free parameter. We find that the MS results are roughly twice as accurate as the modified ES ones. A number of avenues for further development and application of the MS scaling are discussed.
Time-independent adiabatic switching in quantum mechanics
Authors: Jaffé Charles
Published: July 2002

A time-independent quantum mechanical adiabatic switching algorithm is presented. This algorithm, which is based upon Born’s quantum mechanical adiabatic theorem, is used to calculate the energy levels and eigenstates of the Henon–Heiles Hamiltonian system. The relationship between this algorithm and similar classical algorithms are discussed with particular attention focused upon the correspondence between avoided crossings and classical nonlinear resonances.
A statistical mechanical theory of transport processes in charged particle solutions and electrophoretic fluctuation dynamics
Authors: Altenberger Andrzej R. , Dahler John S. , Tirrell Matthew
Published: July 2002

Formally exact, linearized constitutive relations are derived for the charged particle currents of an electrolyte solution acted upon by an electric field. A new analysis of electrophoretic dynamic light scattering experiments is presented and deficiencies of the traditional, phenomenological irreversible thermodynamics of ionic solutions are pointed out.
An electron diffraction and a
b i
n
i
t
i
o investigation of cyclopropylisothiocyanate
Authors: Durig J. R. , Sullivan J. F. , Berry R. J. , Cradock Stephen
Published: July 2002

The molecular structure of cyclopropylisothiocyanate, c-C3H5NCS, has been investigated at 35 °C by gas phase electron diffraction. Two distinct conformers, trans and cis, were identified with the isomeric proportion being 72±5% trans at this temperature. The structural parameters were determined by combining the electron diffraction data with the previously published rotational constants. A quadratic force field was used to calculate vibrational corrections. The important distances (r*av,Å) and angles (∠*av, deg) with their uncertainties in parentheses were determined to be for the trans conformer: r(C1–C2)=1.520(3), r(C2–C3) =1.515(3), r(N=C)=1.193(3), r(C=S)=1.574(3), r(C1–N)=1.387(5), r(C–H) =1.072(5), ∠C1NC=149.1(15), ∠C2C1N=118.9(6), ∠HCH=115.0(fixed), ∠C2C1H=117.35(fixed), and ∠NCS=177.7(20), whereas those that differed for the cis conformer were found to be: r(C1–N)=1.413(5), ∠C1NC=150.8(17), and ∠C2C1N=116.2(15). The rms amplitudes of vibration with their associated uncertainties have been determined for some of the distances. In addition, the geometry has been calculated by ab initio Hartree–Fock gradient calculations with geometry optimization at the STO-3G level and it is found that the computed structure is in reasonable agreement to the one derived from the electron diffraction experiment. Features of the structure are compared with those of similar molecules and discussed.
Self-consistent mode-coupling theory of excitation transport with long-range transfer rates in solution
Authors: Franchi Daniel S. , Loring Roger F. , Mukamel Shaul
Published: July 2002

A self-consistent mode-coupling theory for incoherent excitation transport is applied to the calculation of excitation dynamics in solution. The long time transport properties for multipolar, w(r)∼(σ/r)m, exchange, w(r)∼exp[−(r−σ)/R)], and Gaussian, w(r)∼exp[−(r2−σ2)/γ2], transfer rates are compared using the same self-consistent procedure. r is the intermolecular separation, and σ is the molecular hard-sphere diameter. Diffusive behavior is found to hold at long times in all cases. However as the transfer rates become more short range (increasing m and decreasing R and γ), the diffusion coefficient shows an abrupt variation with density, which resembles a percolation transition.
Specific heat of a high-T
c perovskite superconductor YBa2Cu3O8−δ
Authors: Shaviv R. , Westrum E. F. , Sayer M. , Yu X. , Brown R. J. C. , Heyding R. D. , Weir R. D.
Published: July 2002

Specific heat measuremnts on high transition temperature perovskite superconductor were conducted from 5.3 K to 345 K. The sample was prepared by mixing stoichiometric amounts of Yttrium oxide, BaO, and CuO so as to yield a 1:2:3 ratio of metals. T he decrease in specific heat at the transition temperature - 91 K is discussed.(AIP)
Theory of the transient electric birefringence of rod-like polyions: Coupling of rotational and counterion dynamics
Authors: Wesenberg Gary E. , Vaughan Worth E.
Published: July 2002

Expressions constructed by applying statistical mechanics to a molecular model of polyion–counterion rod assemblies are used to find values for two phenomenological parameters in the stochastic theory of Szabo, Haleem, and Eden for the transient electric birefringence of rod-like polyions. These parameters are the polyion electric polarizability and the decay rate of fluctuations in macroion dipole moment. The range of system parameters over which the model of Szabo et al. applies is delineated.
Integral equations for dense fluids: A p
r
i
o
r
i controllable approximations
Authors: Garrido P. L. , Marro J.
Published: July 2002

The functional methods developed by Yvon, Bogoliubov, Lebowitz, and Percus in the theory of fluids are applied to the derivation of new integral equations for dense fluids with an a priori knowledge of their range of validity in some sense. In particular, we find conditions in order that the resulting radial distribution function contains, at least, all the diagrams in the density (n) expansion up to order n2, n3,..., and present a method to obtain systematic corrections to familiar approximations such as the Percus–Yevick and the hypernetted-chains equations.
A time resolved EPR study on the nonphosphorescent excited triplet state of cinnoline
Authors: Terazima Masahide
Published: July 2002

The nature of the lowest triplet (T1) state of cinnoline was investigated by means of the time resolved EPR (TREPR) technique. The T1 state of cinnoline in polar solvents is assigned as 3ππ* state. The zero field splitting (zfs) in nonpolar solvents were obtained from the TREPR spectrum and a simulation spectrum with taking into consideration the population decay from the y sublevel. The zfs suggests that the T1 state is 3nπ* and a N=N part of cinnoline plays an important role for determining the triplet characters. The sublevel decay rate constants and relative populating rates were anisotropic and the decay rate constant from the y sublevel is very large (ky=3.0×106 s−1). The origin of the nonphosphorescent characters of cinnoline are discussed.
Nuclear quadrupole structure of potassium hydroxide in the 32 GHz microwave region
Authors: Raw T. T. , Yamamura T. , Gillies C. W.
Published: July 2002

A high temperature Stark and radiofrequency-microwave double resonance spectrometer was used to observe the nuclear quadrupole structure of the J=2←1 transition of 39KOH in a number of vibrational states. First order analysis of the hyperfine components gave nuclear quadrupole coupling constants of eQq=−7.23 (29) MHz for the (0000) state, eQq=−7.16 (33) MHz for the (1000) state, and eQq=−7.29 (37) MHz for the (0110) state.
One-dimensional vibrational excitons in 1,2,4,5-tetrachlorobenzene
Authors: Abramson E. H. , Jongenelis A. P. J. M. , Schmidt J.
Published: July 2002

We have studied the line shapes of vibronic transitions in the phosphorescence spectrum of the one-dimensional triplet exciton of TCB between 4.2 and 0.4 K. It is shown that also the vibrational excitons are highly one dimensional. This finding is confirmed by time-resolved emission spectra. Observed vibron bandwidths vary up to 15 cm−1 with k=0 either at the top or at the bottom of the band. In contrast to the fundamental vibrations, no overtones or combination bands give evidence of a well-defined one-dimensional quasimomentum.
Optical absorption and ESR spectroscopy of the monomerization and redimerization reaction of 9-cyanoanthracene-dimer crystals
Authors: Sixl Hans , Schmidt Gerhard , Blankenhorn Michael
Published: July 2002

The thermally and photochemically induced dissociation of 9-cyanoanthracene-dimer molecules (9-CNAD) into two monomer molecules is examined using optical spectroscopy and ESR. Optical spectroscopy gives an activation energy of 1.67(5) eV for the thermally induced formation of monomer pairs within the dimer crystal. The photoinduced reactions are examined by ESR spectroscopy of the monomer pairs. The presence of only one Δms=±1 ESR triplet line pair indicates the existence of only one photochemically active species. This results from the nondegeneracy of the ground state energies of the four dimer molecules within the unit cell. The fine structure constants D and E and the orientation of the anthracene monomer molecules have been calculated from the angular dependence of the ESR spectra. The orientation of the crystallographic unit cell axes in the crystal has been determined by Laue diffraction.
Thermodynamic properties of the mixed crystals of galvinoxyl radical and its precursory closed shell compound: The large entropy cooperating with the spin system
Authors: Awaga Kunio , Sugano Tadashi , Kinoshita Minoru , Matsuo Takasuke , Suga Hiroshi
Published: July 2002

The heat capacities of the 9:1 and 6:1 mixed crystals of the galvinoxyl radical (4-[[3,5-bis(1,1-dimethylethyl)-4-oxo-2,5-cyclohexadien-1-ylidene]methyl]-2, 6-bis(1,1-dimethylethyl)- phenoxyl) and its precursory closed shell compound, hydrogalvinoxyl, are measured between 13 and 300 K. A heat capacity anomaly due to the phase transition from the diamagnetic low-temperature (LT) phase to the paramagnetic high-temperature (HT) phase is found at 71 K in the 9:1 mixed crystal. The entropy of transition is determined to be ΔS=10.11 J K−1 mol−1, which should include the surplus change of entropy in addition to the magnetic contribution. Furthermore, it is found that the phase transition is easily quenched in the 9:1 mixed crystal by rapid cooling and the supercooled HT phase is left stable below about 50 K. The entropy of the supercooled HT phase is estimated as a function of temperature from the temperature dependence of the heat capacities of the annealed and quenched samples. The difference in entropy between the LT and the supercooled HT phases decreases monotonically with decreasing temperature from 71 K and becomes about 4 J K−1 mol−1 at 14 K, which is comparable to the magnetic contribution from the spin system still effective in the supercooled HT phase. This suggests that the surplus entropy appearing in the phase transition is lost gradually with decreasing temperature in the supercooled HT phase. In the 6:1 mixed crystal, the phase transition is no more present and only the HT phase appears.