bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Diffusion Factors for the 4He–3He System
Authors: Taylor W. L. , Weissman Stanley
Published: February 2004

The thermal diffusion factor for the 4He–3He system has been measured from 200 to 900°K and as a function of composition at 215, 273, 373, and 473°K. These measurements were made in a 20-tube trennschaukel which allowed the use of a rather small temperature difference relative to the absolute temperature. The other experimental parameters were adjusted to minimize the corrections for trennschaukel operation. The data demonstrate a marked decrease in αT with increasing temperature and a composition dependence of approximately 10%. The experimental values were compared to theoretical calculations using six different intermolecular potentials. The Lennard-Jones (12–6) and modified Buckingham (exp-6) potentials were inadequate but two recently proposed multiparameter functions represent the data quite well.
Perturbation Theory and the Radial Distribution Function of the Square-Well Fluid
Authors: Smith W. R. , Henderson D. , Barker J. A.
Published: February 2004

Perturbation theory is used to derive the first-order term of the inverse temperature expansion of the radial distribution function (RDF) for a fluid whose molecules have a hard core. Exact and approximate expressions, based on the local compressibility approximation, the superposition approximation (SA), and the Percus-Yevick theory (PY) are derived. Numerical results are examined in the case of the square-well potential with wellwidth 0.50. The RDF resulting from the exact and SA expression yield good results for the equation of state down to reduced temperatures below β ε=1.
Statistical Thermodynamic Theory for Adsorption Isotherms
Authors: Heer C. V.
Published: February 2004

It is shown that the natural expansion parameter in the grand canonical ensemble for monolayer surface coverage is the expansion of the logarithm of the number of adsorbed molecules, ln N¯a, as a polynomial expansion in ln z/z0=ln P/P0=(μ−μ0 )/ kT. For the heterogeneous localized site model this expansion truncates after the squared term in the expansion, and the linear dependence of the monolayer surface coverage adsorption isotherms, as a function of (μ−μ0)2= (kT ln P/P0)2, has a natural explanation.
Molecular Vibrations in a Crystal Lattice: The Normal Coordinate Treatment of Cs2LiCo(CN)6
Authors: Swanson Basil I. , Jones Llewellyn H.
Published: February 2004

A normal coordinate analysis including lattice modes has been carried out for Cs2LiCo(CN)6. The majority of the changes in frequency found for the normal modes of Cs2LiCo(CN)6 with respect to the isolated ion Co(CN)6−3 can be reproduced without changing the intramolecular potential constants. However, the internal valence CN force constant for Cs2LiCo(CN)6 is shown to be higher than that of Co(CN)6−3. The low frequency modes are characterized by extreme mixing of intra- and intermolecular vibrations.
Absorption Coefficients of Helium between 599 and 610 Å; Transition Moment for He2 A1Σu+←X1Σg+
Authors: Chow K. W. , Smith Allan Laslett , Waggoner M. G.
Published: February 2004

Absorption coefficients of helium have been measured in the region of the continuum-bound transition A1Σu+←X1Σg+ of He2 (599–610 Å) for temperatures of 77, 200, and 298°K. The absorption coefficient k is proportional to the square of the helium density n2. The quantity k/n2, ranging between 10−39 and 10−42 cm5, is in excellent agreement with the continuum-bound absorption coefficients of He2 A←X calculated by Sando and Dalgarno, supporting a value of 0.20 a.u. for the electronic transition moment of He2 A←X between 2 and 3 Å.
Calculated Spectroscopic Parameters and the Intermediate Spin-Orbit Coupling Diagram in the Interpretation of 5f4 AmO2+ Spectra
Authors: Varga L. P. , Mann J. B. , Asprey L. B. , Reisfeld M. J.
Published: February 2004

Ab initio relativistic SCF Dirac-Fock and Dirac-Slater calculations of the free-ion Coulomb interaction parameter, F2, and the spin-orbit coupling parameter, ζ, have been made for all known oxidation states of actinides, thorium through nobelium. These calculated parameters, when normalized to the experimental spectroscopic parameters, were used to initiate least-squares fits to nine experimental electronic energy levels of anhydrous KAmO2CO3, and to 15 levels of aqueous AmO2+ in 1M DClO4–D2O. Correlation with 35 lower levels of the f4 intermediate spin-orbit coupling diagram allowed term assignments to be made to the experimental free-ion levels. Some differences in term assignments were noted between the solution and solid state spectra, but substantial agreement was found between the AmO2+ spectra taken in 1M DClO4–D2O measured here and some earlier AmO2+ spectra taken in 1M HClO4. The ``best'' values for the spectroscopic parameters of 5f4 Am (V) were: F2=254, F4=30.0, F6=4.95, and ζ=2976 cm−1. The predicted trends for these parameters for the heavy actinides is discussed.
3d Wavefunctions in 57Fe Mössbauer Spectroscopy
Authors: Cosgrove J. G. , Collins R. L.
Published: February 2004

In a remarkable article, Ganiel has shown that 57Fe quadrupole splitting due to a single 3d electron is constant, for any real wavefunction with real coefficients spanning either the T2g or Eg subspaces. We examine here the effects on Vzz and η and show that these vary in complex fashion. Hence, the sensitive effects of structure and bonding on the efg tensor can be buried in a constant quadrupole splitting for this case, and the values of Vzz and η must be extracted by magnetic perturbation or other methods if the nature of the 3d wavefunctions is to be determined.
Fragmentation Mechanisms for Metal Hexacarbonyls by Deconvolution—Convolution of Ionization Efficiency Data
Authors: Flesch G. D. , Svec H. J.
Published: February 2004

Deconvolution—convolution techniques show that fragmentation of W (CO)6+ and its daughter ions occurs in the mass spectrometer through one reaction in which loss of three carbonyl groups occurs, five reactions involving loss of two carbonyl groups, and five reactions in which a single carbonyl group is lost. The number of such reactions for Mo(CO)6 are 0, 5, and 6, respectively, while for Cr(CO)6 they are 2, 4, and 4, respectively. It could not be determined whether the loss of multiple groups occurs simultaneously, or stepwise in a time short compared to the residence time of the ions in the ionization chamber. The techniques used were successful only when corrections were applied to account for competition taking place among the various reactions. Relative electron multiplier gains for the various ions studied are reported and vary from 0.89 to 1.26 compared to 1.00 for M(CO)6+.
Angular Velocity Correlation Functions and High-Frequency Dielectric Relaxation
Authors: Anderson J. E. , Ullman Robert
Published: February 2004

The angular velocity correlation function can be studied through measurements of dielectric relaxation and far-infrared absorption. Relations between these quantities are described in this article, and the data of Davies, Pardoe, Chamberlain, and Gebbie are analyzed. Velocity correlation times are obtained for molecules in four simple liquids. Hubbard has obtained a theoretical expression linking the velocity correlation time, the orientation correlation time, and the molecular moment of inertia. This expression is experimentally verified for molecules in nonviscous liquids. Certain paradoxical predictions are found when this expression is applied to viscous liquids and solids. This article considers stochastic models for relaxation, in which the probability of molecular reorientation is modulated by fluctuations in the intermolecular environment. These stochastic models lead to orientation and velocity correlation functions that are consistent with experimental observations.
On the Dependence of Vibrational Raman Intensity on the Wavelength of Incident Light
Authors: Albrecht A. C. , Hutley M. C.
Published: February 2004

Experiments on the wavelength dependence across the visible region of the intensity of the 1334-cm−1 Raman line of p-nitroaniline (PNA) are analyzed from a general theoretical viewpoint. When theory is simplified to correspond to the PNA example, two obvious sources of Raman intensity are apparent. One is based on a possible shift of equilibrium nuclear position along the 1334-cm−1 mode upon exciting PNA into its first excited singlet state (in the near ultraviolet). The other source deals with vibronic coupling of the first excited electronic state with a whole family of states in the deep ultraviolet having similar polarizations. It is seen how this second mechanism appears to be the dominant one in this case. The absolute scattering cross section for the 1334 cm−1 is given and is found to agree with the order of magnitude estimates calculated theoretically.
Ab Initio Calculation of the Electronic Structure and Spectrum of Co(NH3)63+; Comparisons with Isoelectronic CoF63−
Authors: Kalman B. L. , Richardson James W.
Published: February 2004

Hartree—Fock—Roothaan LCAO MO SCF calculations, with the fixed core approximation plus limited configuration interaction, are reported for the ground and some excited states of Co(NH3)63+. Results are discussed with respect to the effects of ligand—ligand interaction, varying the radial part of the Co 3d AO basis functions, maintaining orthogonality of ligand t1u and a1g symmetry orbitals to Co 3s and 3p orbitals, and including configuration interaction. The calculated d—d excitation energies agree very well with experiment, and a reasonable binding energy is estimated. These results are contrasted with previous calculations on CoF63− to analyze how the metal—ligand interaction differs between the so-called ``covant'' and ``ionic'' cases. An analysis of why 1A1g is the ground state for the NH3 complex and 5T2g is the ground state for the F− complex is given along with a discussion of the parameter 10Dq.
Calculation of the Width of Narrow Shape Resonances
Authors: Bain R. A. , Bardsley J. N.
Published: February 2004

A quantum technique is described for the calculation of the energy and width of shape resonances. It appears to be the only such method applicable to resonances with very long lifetimes. Results for a Lennard-Jones potential are presented and compared with previous quantum and semiclassical calculations.
Studies of the Vaporization Mechanism of Gallium Arsenide Single Crystals
Authors: Lou C. Y. , Somorjai G. A.
Published: February 2004

The kinetics of vaporization of gallium arsenide single crystals into vacuum have been investigated using microbalance and mass spectrometric techniques in the temperature range 700–900° C. Although gallium arsenide vaporized incongruently to yield liquid gallium and arsenic vapor molecules, initial steady state evaporation rates can be obtained in the temperature range of study. The total evaporation rates and the activation energies of vaporization were found to be the same for both (111) and (1¯1¯1¯) faces. The initial vacuum vaporization rates of gallium arsenide single crystals are lower than the maximum rates calculated from equilibrium vapor pressures by about a factor of six and the activation energy of vaporization is Δ H*=90±3 kcal/mole. When excess gallium liquid was placed on top of the vaporizing surface, the rate increased by a factor of 2 while the activation energy remained virtually unchanged. Both Te-doped and Zn-doped GaAs samples have lower evaporation rates than the pure gallium arsenide crystals. The activation energy for Te-doped samples is 90 kcal/mole, the same as that found for pure samples. However the activation energy of vaporization is lower for the Zn-doped samples (76 kcal/mole). When excess gallium liquid was placed on top of the surface of these doped samples, the vaporization rate was found again to have increased with the activation energies remaining the same as those without excess liquid gallium. The vapor compositions for the (111) and (1¯1¯1¯) faces were found to be different by mass-spectrometric studies. Vaporization of the (111) face yielded only tetramers (As4). However, during the vaporization of the (1¯1¯1¯) crystal face both the tetramers (As4) and the dimers (As2) were detected. Excess gallium liquid on top of the crystal surfaces does not seem to affect the vapor compositions significantly. Based on these experimental results at least two reaction steps in the sequence of reactions leading to vaporization of gallium arsenide single crystals can be distinguished. (1) The availability of arsenic vacancies VAs or divancies VAsVGa at the vaporizing surface appears to control the rate of sublimation. (2) Once these defects are created the vaporizing arsenic molecules break away from the lattice in a subsequent rapid reaction step which does not control the rate but establishes the vapor compositions over the two different crystal surfaces.
Effect of Oxygen on the Soft X-Ray Appearance Potential Spectrum of Chromium
Authors: Houston J. E. , Park Robert L.
Published: February 2004

Soft x-ray appearance potential spectra have been obtained for clean and oxygen-exposed chromium surfaces. The measurements were made with a simplified spectrometer which uses the walls of the vacuum chamber as the photoelectric soft x-ray detector. The oxygen exposure gives rise to a multipeaked structure corresponding to the excitation of the oxygen K shell, with a threshold at 529.1±0.5 eV. In addition, the detailed spectra for the L excitation of chromium are markedly altered. The L3 threshold is increased from 573.5 to 574.1 eV, and the L3 peak width, which is related to the width of the unfilled d band, increases by 0.8 eV. Although the absolute thresholds are accurate to only about ± 0.5 eV, changes of less than 0.1 eV are easily observed. The detailed form of the fine structure between the L2 and L1 excitations, which is due to characteristic loss replicas of the major peaks, is also found to change as a result of the oxygen exposure.
Experimental Investigation of the Energetics of Ion—Molecule Reactions of Ground State C+ Ions with N2 and O2
Authors: Leventhal J. J.
Published: February 2004

The energetics of ion—molecule reactions of ground state C+ ions with O2 and N2 molecules has been investigated. The results indicate that products of both of these reactions are formed in highly excited internal energy states and, in addition, product ions are observed only in the forward direction in the center-of-mass system.
Vibrational, torsional, and librational excitons in molecular crystals: Raman spectra of neat and isotopic mixed durene
Authors: Prasad Paras N. , Kopelman Raoul
Published: February 2004

A theoretical comparison of the conventional phonon and exciton approaches is made and the validity of the concept of a librational exciton is discussed. An experimental investigation of the Raman active librations, torsions, and other vibrations, in the neat and isotopic mixed crystals of durene at 100 and 25°K, is presented. The results obtained are explained in a uniform and consistent way by using the exciton concept (librational exciton, torsional exciton, and vibrational exciton). The librational excitons obey the amalgamation limit while the torsional and vibrational excitons fit the separated band limit of the mixed crystal. Davydov splitting has been observed on one torsional, one vibrational but not on any librational excitons (phonons). Intermolecular contributions to the methyl torsions are discussed.
General theory of elastic light scattering
Authors: Blum L. , Frisch H. L.
Published: February 2004

A general theory of elastic light scattering is presented. The incoming and scattered light are described by the coherency matrix, which is written in spherical tensor form. The coherency matrix has three tensorial components in our representation: a scalar (the intensity), an axial vector (the ellipticity), and a second rank tensor (directly related to the inclination of the optical axes). It is shown that using Racah algebra, the components of the coherency matrix for the incident and scattered light can be related by rather compact formulas, involving Wigner's 9-J symbols. The simplicity of the treatment allows us to include any higher multipole effects in the scattering, like the magnetic dipole and electric quadrupole contributions. For the pure electric dipole scattering, our theory gives a unique interpretation of the scattering in terms of moments of the molecular correlation function. Only two moments can be observed when the correlations are short compared to the wavelength of the light, while, for long ranged correlations, it would be possible in principle to discriminate between the various contributions by analyzing the angular dependence of the scattered light. A short survey of the real systems in which this might be the case is given.
Relaxation processes in excited CO states. I. Spin multiplet relaxation and radiative lifetimes of CO(d3Δ)ν=5
Authors: Slanger T. G. , Black G.
Published: February 2004

Observations made of the d3Δ→a3 Π 5,0 band of CO demonstrate that the d3Δν=5 level has a radiative lifetime strongly dependent on rotational level. This is a consequence of the interaction between d3Δν=5 and the nearby A 1Πν=1 level, which mixes the two states and causes strong d3Δν=5→ X1Σ+ radiation to compete with d→a radiation as a depopulating mechanism from d3Δν=5. Because of the selection rules governing optical transitions and perturbations, it is only the Ω 1 level of d3Δν=5 that is strongly perturbed, and relaxation of Δ13 to Δ23 and Δ33 as a function of rare gas collisions has been observed. Relaxation by Ar takes place at close to hard sphere collision frequency, with He being 5.5 times less efficient.
Mean square endpoint separation of off-lattice self-avoiding walks
Authors: Grishman Ralph
Published: February 2004

Ten thousand off-lattice self-avoiding walks of 500 steps were generated using a new algorithm combining the features of the enrichment procedure of Wall and Erpenbeck and the dimerization procedure of Alexandrowicz. The mean square endpoint separation was tabulated as a function of the number of steps in the walk and fitted to the equation 〈 R N2〉=A Nγ, where N is the number of steps in the walk. A value for γ of 1.204± 0.014 was obtained, in excellent agreement with values for on-lattice walks. Earlier investigators using off-lattice self-avoiding walks probably obtained higher values of γ because they were limited to 100-step walks.
Light scattering from a racemic solution of optically active molecules
Authors: Pomeau Y.
Published: February 2004

The spontaneous thermal fluctuations arising in a racemic solution of two stereoisomers may create a fluctuating optical activity that scatters an incident beam of light. The polarization and angular distribution of this light allow a separation of this scattering effect from those effects due to the other kinds of fluctuation of the dielectric tensor. The spectral intensity of this light has a Lorentzian shape of width proportional to Daq2, where Da is a diffusion coefficient.
Polarization of two-photon excited fluorescence
Authors: McClain W. M.
Published: February 2004

The problem of the polarization dependence of molecular fluorescence excited by simultaneous absorption of two different photons is solved exactly for the case of randomly oriented molecules which do not rotate between the absorption and emission acts. It is found that seven molecular parameters are available from such a study, including the relative values of the critical parameters δF, δG, and δH which characterize the symmetry of the two-photon excited state. The results are compared with another author's study of this problem, which concluded that only five parameters were measureable.
On a modified INDO SCF MO CI method
Authors: Yoshida Zen-ichi , Kobayashi Tsunetoshi
Published: February 2004

A new semitheoretical formula for the core resonance integral which contains no arbitrary adjusting molecular parameter is introduced in the semiempirical INDO SCF MO CI method. This SCF method is applied to ethylene, formaldehyde, trans-acrolein, trans-glyoxal, formamide, ketene, diazomethane, acetone, and methanol as well as acetone-methanol 1:1 hydrogen bonding models. The agreement between the calculated transition energies and the observed ones was quite satisfactory.
Test of RRKM theory. Rates of decomposition in the series of chemically activated 2-n-alkyl radicals from C4 to C16
Authors: Hardwidge Edward A. , Rabinovitch B. S. , Ireton Robert C.
Published: February 2004

The rates of decmposition of chemically activated 2-n-alkyl radicals in the series C4–C16 were measured by an internal comparison method at 300°K in the pressure region centered at 0.01–0.1 torr. Activation was by H-atom addition to the appropriate α-olefin. The substrate species have a minimum energy of Ω 40 kcal mole−1. The consequences of radical isomerization are discussed. A limitation of the present activation technique is illustrated. Theoretical Marcus-Rice rate constants agree well with the experimental values. Earlier experimental evidence that all degrees of freedom of smaller radicals must be treated as active is now extended to the C16 member of the series, and the continued applicability of the conventional theoretical treatment is demonstrated for the very large species. Within the accuracy of the work, internal energy is shown to be effectively randomized in the time interval between stabilizing collisions, even for the largest member of the series. The observed rate constant decline from Ω 107 to 102  sec−1, from smallest to largest member of the series, is mitigated somewhat by a concomitant increase in the average energy of the activated species due to intrinsic thermal energy. At a fixed energy value chosen, for example, as 47 kcal/mole−1, which is a representative value of the spectrum of energies of decomposing radicals over the whole series, it is estimated that the rate constants k47 decrease from Ω 2× 108  to  Ω 1  sec−1 in the series. Data for the decomposition of chemically activated 2, 3-dimethylbutyl-2 radicals are presented for a wide range of pressure. The deactivation efficiency of H2 relative to a strong collider is again found to be ∼ 0.2, thus reconfirming the constancy of this value as independent of radical size for a homologous series of large radicals having near-constant energetics.
Dynamics of collinear A + BC systems
Authors: Hijazi Nasrat H. , Laidler Keith J.
Published: February 2004

A pair of coordinates, one along the minimum reaction path and one normal to it, is employed to treat the collinear dynamics of processes of the type A+B−C→A−B+C. Two potential-energy surfaces are considered: Surface I in which the activated state lies in the approach portion of the reaction coordinate, and Surface II in which it lies in the retreat coordinate. It is shown analytically, in agreement with previous computer calculations, that for Surface I relative translational energy is effective in surmounting the barrier, and that vibration energy is ineffective. For Surface II vibrational energy is effective and relative translational energy ineffective. Consideration is also given to the effects of the relative masses of A, B, and C in determining the energy distribution of the products. Two cases are considered: (1) A light and B and C heavy (L+HH), and (2) A and B heavy and C light (H+HL). It is shown that Case (1) tends to lead to products of high translational and low vibrational energy, whereas Case (2) favors high vibrational energy and low translational energy.
Distribution of reaction products (theory). VIII. Cl+HI, Cl+DI
Authors: Parr C. A. , Polanyi J. C. , Wong W. H.
Published: February 2004

The dynamics of the thermal (300°K) reactions Cl+HI → ClH+I and Cl+DI → ClD+I have been examined by the classical trajectory method, in 3D. The Cl+HI reaction has also been studied at an enhanced (6 kcal mole−1) collision energy. The potential-energy hypersurface was the same as that used earlier [J. Chem. Phys. 49, 5189 (1968)]. Though it is a highly repulsive energy surface it is able to account for the efficient vibrational excitation of the molecular product for the mass combination characteristic of this reaction. The effect of changing the mass combination from H+LH (heavy+light-heavy; masses mCl+mHI) to L+HH (light+heavy-heavy; masses mH+mCl2) on the Cl+HI surface has been explored using a full 3D set of trajectories at 300°K. The effect is to markedly reduce the ``mixed energy release'' responsible for the efficient vibrational excitation on the repulsive surface. Vibrational and rotational excitation in the reaction products is correspondingly diminished, and translational excitation is enhanced. The efficient vibrational and rotational excitation for H+LH (Cl+HI), and contrasting behavior for L+HH (H+Cl2) have been observed in infrared chemiluminescence experiments. The present findings are therefore in accord with earlier proposals that both these reactions involve predominantly ``repulsive'' energy release. The computed product angular distribution for the Cl+HI reaction at 300°K was almost isotropic, in contrast to the exclusively backward-hemisphere scattering for the L+HH mass combination on the same energy surface. At 6 kcal mole−1 collision energy the computed angular distribution of HCl from the Cl+HI reaction showed exclusively sharply-forward scattering, in accord with the results of recent molecular beam experiments [J. D. MacDonald and D. R. Herschbach (unpublished)]. Enhanced collision energy gave rise to a small decrease in the computed mean product vibrational excitation, a small increase in mean product rotational excitation and a large increase in product translational excitation. These changes in product energy distribution are in qualitative accord with the findings from infrared chemiluminescence and molecular beam studies at enhanced collision energy. The overall conclusion is that the repulsive LEPS (London, Eyring, Polanyi, Sato) potential-energy hypersurface used here and in our earlier work, provides an acceptable (though not unique) first approximation to the actual interaction potential.
Magnetic field dependence of thermal correlations in molecular gases
Authors: Mehaffey J. R. , Garisto Frank , Kapral Raymond , Desai Rashmi C.
Published: February 2004

The effect of a magnetic field on the time-dependent correlation functions appropriate to the thermal conductivity and self-diffusion in a dilute molecular gas is investigated. For the thermal conductivity and the energy current correlations, calculations are made for the rough sphere interaction as well as for nitrogen gas. For the calculation of the velocity correlation function, the rough sphere model is used to study the effects due to correlations arising from terms odd in angular momentum. The qualitative similarity that is found in various diagonal correlation functions and in the oscillating structure that is found in many transverse correlation functions is discussed.
Studies in molecular Compton scattering. II. The Compton profile of C4H8O2-dioxane, isobutyric, and n-butyric acids
Authors: Epstein Irving R. , Williams Brian G. , Cooper Malcolm J.
Published: February 2004

The Compton profiles of MoKa x rays inelastically scattered from three liquids of molecular formula C4H8O2 (dioxane, n-butyric and isobutyric acids) are compared with one another and with theoretical profiles computed from localized molecular orbital wavefunctions. The three experimental profiles are found to be not significantly different from one another, in agreement with the theoretical model, but they differ slightly from the theoretical profiles.
Interpretation of the far infrared spectra of the dimers of HCl and of DCl trapped in monoatomic solids
Authors: Girardet C. , Robert D.
Published: February 2004

A computation of the far infrared spectral properties due to the orientational motions of hydracid and deuterid dimers trapped in a noble gas solid matrix is proposed. The molecules of the dimers are located at fixed distances, which have been calculated by using a cell model for the representation of the solid containing the impurities. An asymptotic method is proposed that is particularly suitable when the orientational dependent part of the interaction potential between impurities is large compared with the rotational energy of the free molecules. The numerical study of the orientational quantum states of the HCl–HCl, DCl–DCl, HCl–DCl, and DCl–HCl dimers enables the building of the theoretical spectra. The comparison with the corresponding experimental data shows that the present calculations of orientational motions of dimeric impurities in solids give a fairly consistent description of the spectra. The nearly orthogonal equilibrium configuration of the molecular axes in these dimers obtained here, due essentially to the quadrupole-quadrupole interaction, is consistent with the well-known ``zig-zag'' chain in the hydracid pure solids. Moreover, the dependence of the observed spectra on the nature of the monoatomic matrix is taken into account through the variation of the intermolecular distance in the dimer with the matrix under consideration.
On a semiclassical study of molecular collisions. I. General method
Authors: Neilsen Walter B. , Gordon Roy G.
Published: February 2004

A method has been developed for calculating rotationally inelastic cross sections of atom-diatom collisions in a semiclassical approximation (classical path, quantum internal states). An analysis of the relations among the intermolecular potential, the cross sections, and the experimental quantities indicates that many experiments related to inelastic scattering give significant information about the intermolecular potential. A computer program embodying this method of calculation has been developed and tested. Quantities related to experimental measurements have been calculated to within experimental accuracy in a reasonable computing time, which suggests that the information about the intermolecular potential contained in various experimental results can be extracted by a semiclassical calculation.
Lifetimes and quenching cross sections of I2(B 3ΠOu+)
Authors: Capelle Gene A. , Broida H. P.
Published: February 2004

Fluorescence lifetimes, self-quenching cross sections, and foreign gas quenching cross sections have been measured for I2B3ΠOu+) by direct observation of fluorescence decay for excitation in the region 640–499.5 nm, corresponding to excited electronic state levels between v′ ≈ 5 and v′ ≈ 70, close to the dissociation limit. The foreign gas experiments represent the first measurement of foreign gas quenching rates using lifetime methods. A pulsed tunable nitrogen-laser-pumped-dye laser with a linewidth of 0.3 to 0.7 nm and a pulse time of less than 10−8 sec was used as the excitation source. Lifetimes were found to be strongly dependent on v′, varying from less than 0.4 μsec to greater than 7 μsec. Self-quenching cross sections showed less v′ dependence, varying between 47 and 90 × 10−16 cm2. Foreign gas quenching cross sections were measured for Ar, Br2, CO2, H2, He, Kr, N2, NO, Ne, O2, SF6, and Xe, and showed a dependence on both v′ and the gas used. Values for light gases, such as H2 and He, were typically 1× 10−16 cm2 or less, while values for Xe were as high as 23 × 10−16 cm2.
Raman spectra of crystalline cyclopropane, cyclopropane-d6, and C3H6–C3D6 solid solutions
Authors: Bates John B.
Published: February 2004

Raman spectra of crystalline C3H6 and C3D6 were measured over the frequency range of their external and internal modes at 80°K. Spectra also were recorded for C3H6–C3D6 solid solutions containing 5% by volume of the solute species. External phonons were identified at 132, 118, 109, 100, and 92 cm−1 in solid C3H6 and at 110, 99, 91, and 76 cm−1 in solid C3D6. These bands were tentatively assigned to the librational modes based on observed relative intensities and isotopic frequency shifts. Raman spectra of a liquid C3H6 and C3D6 measured at 203°K also are reported.
Theory of electrode processes
Authors: Schmidt P. P. , Mark H. B.
Published: February 2004

The transfer of an electron from a metal electrode to an electroactive species in the interface is central to electrochemical equilibrium and kinetic analyses. The purpose of this paper is to present a discussion of the theory of electron transfer based on a linear response analysis. We base our theoretical considerations on the Yamamoto reaction rate theory; Yamamoto's theory is an outgrowth of the Kubo linear response theory. The rate constant and ultimately the exchange current expressions we obtain are derived from a model representation of the electrode interface. This model is a generalization of one considered by Dogonadze and Chizmadzhev. In particular, we examine an outer sphere type transfer mechanism, but we allow for the following effects: (1) the effect of reactant center of mass motions and transport to a most favorable electron exchange configuration, (2) the effect of internal vibronic interactions within the electroactive species, and (3) the effect of strong electron exchange interactions. This last effect precludes the direct use of quantum mechanical perturbation theory to obtain the rate constant expressions. For our model system we obtain general rate expressions valid for adiabatic to nonadiabatic transfers. This follows from the generality of the Yamamoto theory. We find particularly that the effects of reactant transport and internal vibronic contributions can be cast into a virial form for the rate constant. Moreover, the activation energy, in the Arrhenius sense, contains new terms relating specifically to the new effects we consider, namely, transport and vibronic effects.
Zero-field level crossing and optical radio-frequency double resonance studies of the A 2Σ+ states of OH and OD
Authors: German K. R. , Bergeman T. H. , Weinstock E. M. , Zare R. N.
Published: February 2004

We have performed Hanle effect and double resonance measurements on the ν′= 0, N′= 2, J′= 3/2 level of the OH A 2Σ+ state and on the ν′= 0, N′= 1, J′= 3/2 level of the OD A 2Σ+ state using atomic line excitation. The double resonance signal is followed as a function of static magnetic field. For OH the Zeeman splitting is found to be linear up to the highest fields investigated whereas in OD the deviations from linearity yield a value for the combination of hyperfine constants b+c/5= 121± 14 MHz. In the case of OH, both the F′ = 1 and F′ = 2 hyperfine components contribute to the Hanle signal; in the case of OD, the Hanle signal arises almost entirely from the F′ = 5/2 component. In the former case, measurement of the relative intensities of the F′ = 1 and F′ = 2 double resonance signals gives the relative populations of these components. From the linewidths of the zero-field level crossings, along with the analysis of the optical double resonance data, the radiative lifetimes for the above (ν′,N′,J′) levels of the A 2Σ+ states of OH and OD are determined to be 0.58±0.05 and 0.65±0.05 μsec, respectively.
Electronic and vibrational relaxation in biacetyl vapor
Authors: McClelland Gary M. , Yardley James T.
Published: February 2004

The fluorescence decay of biacetyl vapor has been directly measured as a function of excitation wavelength with medium resolution (10–30 Å) using a tunable dye laser. At low pressures the decay appears to be reasonably exponential with no evidence for quantum beats or other reversible behavior which might have been anticipated due to the low density of triplet vibronic levels to which energy conserving transitions apparently take place. The low pressure lifetime varies smoothly from ∞ 14 nsec for excitation near 4450 Å to ∞ 6 nsec for excitation at 3720 Å. Molecular collisions with ground state biacetyl and with added Ar vibrationally relax the excited molecules but do not quench the electronic excitation. Biacetyl removes ∞ 700 cm−1 of vibrational energy per collision while Ar removes ∞ 90 cm−1.
EPR studies of [CuCl4· 2NH3]2− complex
Authors: Narayana P. A. , Sastry K. V. L. N.
Published: February 2004

Expressions have been derived for the spin Hamiltonian parameters g∥, g⊥, A, and B for Cu24 with a sixfold coordination and having a tetragonal distortion with the unpaired electron in a predominantly d3z2−r2 orbital, using LCAO-MO scheme. Overlap integrals have been considered in treating σ bonds. The theory has been applied to [CuCl4 · 2NH3]2− complex in ND4 Cl single crystal. It is found that this complex exhibits strong out of plane π bonding.
General theory of electron transfer reactions
Authors: Schmidt P. P.
Published: February 2004

This paper reports the examination of the correspondence between the general theory of electron transfer reactions based on the use of Yamamoto's rate theory and the general transition state theory developed by Marcus. In all limits, adiabatic to nonadiabatic, this theory yields rate constant expressions identical to those obtained by Marcus. The theory presented in this paper develops from the nonequilibrium statistical mechanical view of chemical reactions with the use of Marcus's general averaging techniques. These techniques apply to the reaction hyperspace, and their use yields rate constant expressions which depend on the nuclear exchange matrix elements. These matrix elements are generally assumed responsible for inducing the electron transfer from a donor to an acceptor species.
Direct current conduction in ammonium and potassium dihydrogen phosphate
Authors: Harris L. B. , Vella G. J.
Published: February 2004

Experiment, plus critical discussion of previous work, suggests the following. Conductivity is primarily due to the migration of L defects (proton vacancies), the enthalpy for L-defect mobility being 0.53 eV in KDP and 0.46 eV in ADP. Such L defects are produced by impurities, but there is an additional tendency towards incipient decomposition in both crystals. This leads to a high-temperature conductivity which, in KDP, is associated with the formation of water molecules and the thermal generation of L defects and, in ADP, with the formation of ammonia molecules and the thermal generation of proton vacancies in the ammonium lattice (A defects). The enthalpy of L-defect formation in KDP is 0.46 eV; that for A-defect formation in ADP is 0.19 eV. Previously reported overheating effects are spurious. The conductivity is independent of field.
Spin-lattice relaxation and the anisotropic part of the H2–He and H2–Ne intermolecular potential
Authors: Riehl J. W. , Fisher C. J. , Baloga J. D. , Kinsey J. L.
Published: February 2004

The spin-lattice relaxation time of H2 infinitely dilute in He and Ne gases has been measured from 20–140 °K. Scattering cross sections for molecular reorientation and rotational excitation of H2 in collision with He and Ne have been computed. By comparison between experiment and calculation, using theoretical relationships between cross sections and measured relaxation rates, parameters are obtained for the anisotropic part of the H2–He and H2–Ne potential surfaces.
Dielectric properties of polyelectrolytes. IV. Calculation of dielectric dispersion by a stochastic model
Authors: Warashina Akira , Minakata Akira
Published: February 2004

The theory of the dielectric dispersion of a rodlike polyelectrolyte derived by Oosawa on the basis of thermal fluctuation of the counterion concentration is rewritten by a discrete charged site model and stochastic behavior of the counterions. The values of dielectric increment, conductivity increment and relaxation time are derived as functions of the charge density, number of sites, length of the polyion and transition rates of counterions between two adjacent sites. The expressions are given for two cases; the number of bound ions to a single site is 0 or 1, and in the other case the number is not limited, the latter case containing Oosawa's result. The effect of counterion-counterion interaction on each Fourier mode of the fluctuation is evaluated in some cases. It is large for the fluctuation of longer wavelength, which broadens the dispersion pattern.
Measurements of vibrationally excited molecules by Raman scattering. I The yield of vibrationally excited nitrogen in the reaction N+NO → N2+O
Authors: Black Graham , Sharpless Robert L. , Slanger Tom G.
Published: February 2004

The reaction of nitrogen atoms with nitric oxide leads to vibrationally excited nitrogen. In the presence of molecular nitrogen, V-V exchange processes rapidly establish a modified distribution for which a measurement of N2(ν=1) is adequate to determine the total vibrational energy yield of the reaction. The measurements of N2 (ν=1) have been made by Raman spectroscopy using the intensity of the Q branch of the anti-Stokes line at 4382 Å (using 4880 Å Ar+ laser radiation). The system sensitivity is determined using heated nitrogen. The measurements have established that 25 ± 3% of the available energy (3.27 eV) appears as vibrational energy and that the vibrationally excited nitrogen is an initial product and does not result from collisions of translationally hot oxygen atoms with nitrogen.
Quenching rate constants for CO(a3Π; ν′=0,1,2)
Authors: Taylor G. W. , Setser D. W.
Published: February 2004

The quenching rate constants for CO (a 3Π; ν′=0,1,2) with H2, D2, N2, O2, NO, CO, CO2, COS, CS2, SO2, NH3, C2N2, CH4, C2H2, C2H4, C2H6, C2F6, and SF6 have been measured in a discharge-flow apparatus. The sources of CO(a 3Π) were the interaction of Ar(3P0, 2) or He(23S) atoms with carbon dioxide. The bimolecular-quenching coefficients are [inverted lazy s] 10−10 cm3 sec−1, except for N2, CO2, C2F6, and SF6, which range from 10−11 to 10−12 cm3 sec−1. Only the rate constants for N2, CO, and CS2 showed a dependence upon the vibrational excitation of CO(a). For these reagents, the mechanism for quenching is discussed; the reaction with N2(X) yields significant amounts of N2(A). The CO(a) + NO(X) reaction is of particular interest because the β- and γ-band emission can be used to identify the NO(A and B) products and to provide a diagnostic test for the presence of CO(a 3Π). The reaction between N2(A 3 Σu+; ν′=0,1) and CO(X) is discussed in an appendix.
Intramolecular vibrational energy transfer: A study of representations
Authors: Kay Kenneth G. , Rice Stuart A.
Published: February 2004

In this paper we report a study of possible representations for the description of intramolecular energy transfer. Our ultimate goal is the definition of a scheme suitable to the description of a molecule undergoing dissociation which is valid everywhere along the reaction path. For this reason we study three sets of basis functions for dynamical calculations of intramolecular vibrational energy transfer in one-dimensional, bound or metastable, triatomic molecules having one harmonic and one Morse bond. The different sets result from different definitions of bond coordinates and different methods for separating the bond motions. For Basis Set 1, the two bond coordinates are internuclear distances between adjacent atoms and the interbond coupling is caused by kinetic energy cross-terms. For Basis Sets 2 and 3 the coordinates are the distance between adjacent atoms in the harmonic bond and the distance between the dissociable atom and the remaining diatomic. The separation of coordinates for Basis Set 2 is analogous to the ``static'' resolution of bond motions in collision theory while the separation of coordinates for Basis Set 3 is an adiabatic separation. The nature and mechanism of bond coupling in the adiabatic approximation is analyzed in detail and dominant contributions are identified. We find that the relative merits of the basis functions depend strongly on the masses of the atoms and the harmonic frequencies of the bond. When the vibrational frequency of the harmonic bond exceeds the frequency for small oscillations of the Morse bond, Basis 3 is usually superior to both Bases 1 and 2. When the opposite condition holds and the mass of the central atom is (modestly) large relative to the masses of the other atoms, Basis 1 is usually superior. The conditions which favor the adiabatic separation are similar to those which favor the ``perturbed stationary states'' approximation in collision theory. The weak energy-dependence of the basis sets is explained in terms of a strong dependence of the optimal bond coordinates upon the interatomic distances.
NMR in the quadrupolar regime: Chemical shifts, asymmetry parameter, and angular orientation
Authors: Creel R. B. , von Meerwall E. , Griffin C. F. , Barnes R. G.
Published: February 2004

Degenerate perturbation theory, exact analytic solutions, and numerical calculations were used to determine the frequency of transition between the lowest two energy levels of a spin I = 3/2 nucleus experiencing a large quadrupole interaction in an applied field in a single crystal. It is shown how the field dependence of the appropriate resonance experiment may be used to extract the characteristic quadrupole frequency νQ and the components of the chemical shift tensor σ, and how the resonance position as a function of the angle φ′ of orientation of the crystal about the axis of the NMR receiver coil depends on the orientational Euler angles as well as on the quadrupolar asymmetry parameter η and the shift components. This theory is applied in our experiments to α-para-dichlorobenzene. In a combined self-consistent least-squares fit of the exact expressions to the field dependences and the φ′ dependence of the resonance position, using the value νQ = 34.262 MHz from the literature, the chemical shift components were found to be σx=0.000± 0.001. σy=0.003± 0.001, and σz=−0.001± 0.001, assuming that the principal axes of the chemical shift tensor are coincident with those of the quadrupole tensor. The asymmetry parameter was found to be η = 0.0712± 0.0005: this and our own value for νQ are in excellent agreement with values determined by other methods. Additionally, the Euler angles of orientation of the single crystal in the mounting were determined (within an eightfold ambiguity) to within ± 0.8°.
Semiclassical approximations for scattering by nonlocal potentials. II Simple applications to atomic collisions
Authors: Gerber R. B.
Published: February 2004

The effective-mass method for treating scattering by nonlocal potentials described in a previous publication. is applied to some problems in atomic collision theory. The applications are based on an effective equation for scattering in the elastic channel when coupling with other channels is included, giving rise to a nonlocal effective potential. We use the effective-mass theory to analyze the influence of coupling with closed channels on the elastic scattering in atom-atom collisions and point out that this may lead to a new type of rainbow effect. We show that strong interchannel coupling results in the appearance of poles and zeros in the effective mass and that the latter may lead to compound-state resonances and orbiting effects. It is observed that the occurences of Fesbach resonances in molecular encounters is always reflected in the presence of zeroes in the corresponding effective mass. We also employ the effective-mass method to deal briefly with the familiar problem of curve crossing and nonadiabatic transitions in atomic collisions.
Line shape of the Doppler-limited infrared magnetic rotation spectrum of nitric oxide
Authors: Blum F. A. , Nill K. W. , Strauss A. J.
Published: February 2004

A fully resolved, Doppler-limited magnetic rotation spectrum of the R (13/2)1/2 absorption line in the fundamental (ν = 0 → ν = 1) vibration-rotation band of NO has been obtained using a cw, tunable PbSSe semiconductor diode laser.