bluuebunny/crossref_metadata_2025 huggingface dataset:
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o and model potential calculations for the ground state of SO2
Authors: Huzinaga S. , Yoshimine M.
Published: February 2003

A b initio and model potential SCF MO calculations have been carried out for the ground state of SO2, using Gaussian-type functions. The equilibrium geometry is computationally determined to a good accuracy with d-type function added on both S and O. Agreement between the results of the full ab initio and model potential calculations is very satisfactory.
Energy transfer from linear stacks of tetracyanoplatinates(II) to rare earth ions
Authors: Yersin Hartmut
Published: February 2003

M2[Pt(CN)4]3⋅nH2O compounds (with M3+=Sm3+, Eu3+, Tb3+,...) represent a new solid state class for investigations of nonradiative excitation energy transfer. The donors are linear stacks (columns) of square planar [Pt(CN)4]2− complexes and the acceptors are rare earth ions which are located between the stacks. Radiationless energy transfer and sharp line rare earth ion emission have been observed for Sm2[Pt(CN)4]3⋅18H2O (SmCP) and Eu2[Pt(CN)]3⋅18H2O (EuCP) but not for Tb2[Pt(CN)4]3⋅21H2O (TbCP), although Tb3+ generally is a bright emitter. The results are discussed in the scope of the Förster–Dexter theory of resonance energy transfer. It is seen that the spectral overlap integral vanishes for TbCP but not for SmCP nor EuCP. The energy transfer only (or predominantly) occurs from the lower excited state of tetracyanoplatinate stacks. Using emission lifetime data, a transfer rate of 108–109 sec−1 is obtained as a lower limit. Such a high rate can only be explained, as an estimate shows, by an exchange transfer mechanism. The spectroscopic properties of the tetracyanoplatinates(II) with and without acceptor ions in the neighborhood are compared.
Lattice dynamics, thermodynamic functions, and phase transitions of p-dichloro- and 1,2,4,5-tetrachlorobenzene
Authors: Bonadeo H. , D’Alessio E. , Halac E. , Burgos E.
Published: February 2003

The thermodynamic properties and phase transitions of p-C6H4Cl2 and 1,2,4,5-C6H2Cl4 have been studied, using an intermolecular potential function of the atom–atom type. The Debye–Einstein approximation to the density of states is checked against the complete calculation for the case of p-C6H4Cl2. This approximation is sufficiently accurate for the calculation of thermodynamic properties. The behavior of the free energy in the vicinity of the phase transition is studied for both crystals. The calculations are consistent with experimental data.
Molecular Rydberg transitions. IX. Term value/ionization energy correlations
Authors: McGlynn S. P. , Chattopadhyay S. , Hochmann P. , Wang H.-t.
Published: February 2003

The linear correlations of Rydberg energy versus ionization potential [S. Chattopadhyay, P. Hochmann, and S. P. McGlynn, J. Chem. Phys. 65, 3341 (1976)] for p6, s2, and d10s2 atoms are extended to open-shell s1, p5, p4, and p3 systems. The intercepts lead to the concept of an ’’average (or zero-order) member of a group’’. The slopes exhibit a 1/(n̄*)2 dependency, where n̄* is the average effective quantum number. This fact establishes a connection with the quantum defect approach. The molecular Rydberg correlations [P. Hochmann, P. H. Templet, H.-t. Wang, and S. P. McGlynn, J. Chem. Phys. 62, 2588(1975)] are extended to different molecular groups. The standard deviations are seldom larger than 1000 cm−1 and often less than 100 cm−1. It is concluded that these correlations constitute a potent assignment device.
Theoretical studies of hydrogen rare gas complexes. II. NenH and NenH+ clusters
Authors: Matcha Robert L. , Milleur Mac B. , Meier Paul F.
Published: February 2003

The structures and energies of NenH and NenH+ clusters are found by ab initio LCAO–MO–SCF calculations. The relative stability of the various complexes is explored. The cluster Ne2H+ is found to be bound by 11.42 kcal/mole with respect to Ne and NeH+ and by 61.06 kcal/mole with respect to separated atoms. Based on the Ne2H calculations and earlier related calculations on He2H, it may be inferred that the ground X 2Σ1g+ potential energy curve of Ne2H crosses the excited A 2Σ1g+ potential energy curve near the minimum of the latter. This suggests metastable states at small distances.
Mobilities and longitudinal diffusion coefficients for Cs+ ions in He and Ne gas
Authors: Pope W. M. , Ellis H. W. , Eisele F. L. , Thackston M. G. , McDaniel E. W. , Langley R. A.
Published: February 2003

Ion mobilities and longitudinal diffusion coefficients of Cs+ are measured in He and Ne gas using the drift tube mass spectrometer.(AIP)
Studies in statistical mechanics of Coulombic systems. III. Numerical solutions of the HNC and RHNC equations for the restricted primitive model
Authors: Larsen B.
Published: February 2003

An efficient and accurate numerical procedure is used to solve the HNC and RHNC integral equations for charged hard spheres, the so-called restricted primitive model (RPM) for electrolyte solutions and molten salts. The computed thermodynamic quantities and correlation functions are found to be in good but not excellent agreement with Monte Carlo (MC) results for densities and temperatures corresponding to the molten-salt regime. Comparisons with the mean spherical approximation (MSA) and the truncated Γ2 approximation (TΓ2A) are also made.
Some weight factor considerations on group relaxation in a polystyrene matrix
Authors: Lakshmi A. , Walker S. , Weir N. A. , Calderwood J. H.
Published: February 2003

Dielectric absorption studies have been made on p-halobenzaldehydes, 3,5-dichlorobenzaldehyde, 4-pyridine aldehyde, p-nitro-, p-cyano-, p-dimethylamino-, p-methoxybenzaldehyde, and p-tolualdehyde in a polystyrene matrix. All four p-halobenzaldehydes appear to have an almost constant enthalpy of activation of ∼29 kJ mol−1, which has been deduced from a log Tτ vs 1/T plot. This value is typical of Caromatic–CHO relaxation when no enhanced conjugation is present. However, the value may not be precise since the group and molecular process overlap, although the group process contribution predominates. In the analysis of such systems as p-XC6H4–CHO it is necessary to take into account the relative magnitude of the weight factors C1 and C2 for the molecules and group processes, respectively. The present study examines mainly variation in the C1/C2 ratio by introducing various substituents in the para positions and notes the influence on the Eyring parameters, the relaxation time, and the apparent dipole moment.
Raman studies of the bending and librational bands from water and ice VI to ∼12 kbar at 32°C
Authors: Walrafen G. E. , Abebe M.
Published: February 2003

Raman data have been obtained from water and ice VI in the region from about 300–4000 cm−1 to pressures near 12 kbar at 32°C. Little, if any, hydrogen-bond breakage is indicated, in agreement with thermodynamic results. Some implications of Fermi resonance are discussed.
Spectroscopic studies of diatomic noble gas halides. III. Analysis of XeF 3500 Å band system
Authors: Tellinghuisen Joel , Tellinghuisen Patricia C. , Tisone G. C. , Hoffman J. M. , Hays A. K.
Published: February 2003

B→X spontaneous and stimulated emission spectra of XeF have been photographed at medium resolution (2.0 Å/mm) and vibrationally analyzed. The assignments are made with the aid of trial-and-error Franck–Condon calculations and band profile simulations, which are described in detail. The strong laser emission near 3511 Å is primarily due to densely overlapped rotational lines in the 1–4 vibronic band, and that near 3532 Å probably includes numerous rotational transitions in the 0–2, 0–3, and 1–6 bands.
Temperature dependence of the solvated electron optical absorption band in liquid propane: Comparison of theory and experiment
Authors: Kevan Larry , Gillis Hugh A. , Fueki Kenji , Kimura Toyoaki
Published: February 2003

The optical spectrum of solvated electrons in liquid C3D8 was measured by pulse radiolysis from 91–131 K and a spectral shift of 0.10 eV was observed. The structured semicontinuum model for electron binding in alkanes was used to calculate the optical transition energy vs temperature and quantitative agreement was obtained which supports this model. It is concluded that the optical spectrum is dominated by a bound–bound transition.
Concentration fluctuation process in ethanol–water mixture
Authors: Kono Ryusuke , Yamaoka Toshihiko
Published: February 2003

Shear and longitudinal relaxation data are reported for aqueous solution of 23 mole % ethanol. Measurement of shear impedance in the temperature range +20 to −40 °C and frequency range 8.6–740 MHz indicates a composite spectra of double or triple relaxation. Longitudinal data are measured by Brillouin scattering and pulse techniques in a frequency range from 20 MHz to 6 GHz. Complicated processes involved are interpreted in terms of additive contributions to longitudinal moduli, comprising (1) structural viscoelastic relaxation of the spectra employed in shear data; (2) a relaxation of concentration fluctuation with a modified form of Romanov and Solovyev.
The ESR study of the ĊF3⋅⋅⋅F radical in irradiated trifluoroacetamide single crystals
Authors: Kalyanaraman B. , Kispert L. D.
Published: February 2003

ESR and deuteration studies of x-irradiated trifluroacetamide crystals at 77 °K show that the ĊF3(A) radical initially formed interacts with a fluorine nucleus on a neighboring molecule, resulting in an additional fluorine doublet of Az=10 G, Ay?Ax?1 G. This previously unobserved spectrum decays with time at 77 °K and is irreversibly replaced by the ESR spectrum of ĊF3(B) that is stable to 200 °K. Based on an INDO calculation, the formation of ĊF3(A) occurs when the crystallographic intermolecular F⋅⋅⋅CF3 distance in the parent compound decreases from 3.77 to 2.4 Å upon radical formation at 77 °K. Following the formation of ĊF3(A), the F⋅⋅⋅ĊF3 distance increases with time or temperature to approximately 3.0 Å.
The spin magnetism of α, α′-diphenyl-β-picrylhydrazyl (DPPH)
Authors: Grobet P. , Van Gerven L. , Van den Bosch A.
Published: February 2003

Magnetic susceptibility measurements are performed on DPPH–benzene complex and solvent-free DPPH in the temperature range 300–2.2 K and in a field range 6–20 kOe. The experimental values of the DPPH–benzene complex fit the Brillouin function for noninteracting paramagnetic centers (S=1/2); at temperatures below 4 K; however, a systematic deviation is observed. The values in solvent-free DPPH obey the same law at temperatures above 150 K. Below this temperature a strong deviation occurs, and below 10 K the susceptibility even decreases with decreasing temperature. This deviation is attributed to electron spin pairing. In solvent-free DPPH less than 1 % of paramagnetic centra is left at 2.2 K.
The use of optical enantiomers in studying the mechanism of chlorine-38 for chlorine substitution in condensed phase
Authors: Wu Jiann-long , Boothe Thomas E. , Ache Hans J.
Published: February 2003

The effect of solvents on the course of the 38Cl for Cl exchange in S- (+) - and R- (−) -2-chloro-1-propanol is investigated.(AIP)
Inelastic scattering at moderate collision energies
Authors: Olsen David P. , Wartell Michael A.
Published: February 2003

A modification of the sudden approximation called the relaxed sudden approximation is reported which provides a quantitative description of inelastic collisions.
An atom–dipole interaction theory of the hyperpolarizability contribution to the optical activity of molecules
Authors: Sundberg Kenneth R.
Published: February 2003

The atom–dipole interaction model formulation of the polarizability theory of optical activity is generalized to include hyperpolarizability effects. This is done by considering the response of the optical rotation of a high frequency light signal to the intensity and orientation of the electric vector of another low frequency but intense light signal. The molecular polarizabilities are written in terms of the two-, three-, and four-atom relay tensors and the electric vector of the low frequency field. Expressions are derived for the electric displacement and magnetic induction vectors, and values for the refractive indices of two different elliptically polarized light waves are extracted from Maxwell’s equations. Lastly, expressions for the optical rotation rate and the ellipticity rate are derived, and a sample calculation is performed on the halomethane CHFClBr.
Excited intermediates in the Hg-photosensitized reaction of O2 detected by energy transfer
Authors: Hippler H. , Wendt H. R. , Hunziker H. E.
Published: February 2003

The reaction Hg(6 3P)+O2 was investigated by modulation kinetic spectroscopy, in excess inert gas and in the presence of small partial pressures of glyoxal, biacetyl, and napthalene. These energy acceptors were excited efficiently to their lowest triplet states by electronic energy transfer from a long-lived (τ?5 μsec) excited intermediate formed in the Hg*+O2 reaction. Phase shift measurements showed the rate of energy transfer to be quite fast, as indicated by the rate constants (at 1 atm and 313 °K, in 1011 liters/mole sec) 0.96±0.19, 0.63±0.13, and 2.1±0.5 for glyoxal, biacetyl, and naphthalene, respectively. Overall efficiencies for transfer from Hg* via the intermediate to the acceptors were 0.4, 0.2, and 0.2 in the same order. Rate constants for quenching of the acceptor triplet states by O2 were also determined. The intermediate appears to react with O2 by a process whose rate varies with the square of the O2 pressure. It is not identical with vibrationally excited ground state O2 whose absorption spectrum is also detected during the reaction. This is shown by the effect of CO2 which quenches the vibrational excitation while leaving the energy transfer unaffected. It is concluded that the intermediate is an O2 molecule in one of the A, C, or c states or, less likely, an excited HgO2 complex.
Primary reactions in crystalline Rochelle salt studied by pulse radiolysis and EPR spectroscopy. The decarboxylation of the acyloxy radical ion
Authors: Samskog P.-O. , Nilsson G. , Lund A.
Published: February 2003

The acyloxy radical ion −O2CCHODCHODCȮ2 (I) was identified in irradiated Rochelle salt by combining the techniques of pulse radiolysis and EPR spectroscopy. This primary radical gives hyperfine couplings due to 13C, 1H, and 23Na and has a broad optical absorption band with the peak at 405 nm. It decomposes by decarboxylation in a first order decay. The half life at 22 °C is 55 ns and the activation energy for decarboxylation is 7.5 kcal mol−1. The G value for the CO2 formation is 2.7 and the extinction coefficient of I is 900M−1 cm−1. No effects of the ferroelectricity of the salt on εmaxG were found.
Study of the Ar–N2 interaction. I. Electron gas model (Gordon–Kim model) potential calculation
Authors: Kim Yung Sik
Published: February 2003

The interaction potential between Ar and N2 is calculated for various angular orientations using the Gordon–Kim electron gas model. The spherically averaged potential is compared with the available experimental potentials. The agreement is very good, as good as the agreement found in the cases of atom–atom interactions. This is quite unlike the other atom–molecule interactions treated by the electron gas model, where the molecules involved were polar. The calculated anisotropy coefficient is larger than the widely used value of Pattengill et al., but it is in the direction of the more recent empirical value of Kistemaker and de Vries.
Light scattering near the plait point of a ternary liquid mixture: Ethanol–water–chloroform
Authors: Ohbayashi K. , Chu B.
Published: February 2003

Critical exponents γx and νx obtained from the angular distribution of scattered intensity measured at relatively large temperature distances [t= (T−Tc)/Tc≳5×10−4] from the plait point gave values of 1.40±0.02 and 0.73±0.04 which are in good agreement with the values γx=γ/(1−α) =1.23/(7/8) =1.41 and νx=ν/(1−α) =0.63/(7/8) =0.72 obtained by renormalization of critical exponents for binary fluid mixtures.
The low Reynolds number translational friction of ellipsoids, cylinders, dumbbells, and hollow spherical caps. Numerical testing of the validity of the modified Oseen tensor in computing the friction of objects modeled as beads on a shell
Authors: Swanson Eric , Teller David C. , de Haën Christoph
Published: February 2003

A method is presented by which low Reynolds number translational friction coefficients of objects of arbitrary shape can be computed. Each object was modeled by a shell of small beads describing the surface of the object, and translational friction coefficients were computed using the modified Oseen tensor of Rotne and Prager [J. Chem. Phys. 50, 4831 (1969)]. The bead size, and therefore their number, was varied, and translational friction coefficients were extrapolated to zero bead size. The accuracy of the method in predicting translational friction coefficients was established by comparison to cases for which exact solutions are known. This leads to the conjecture that the method is exact in the limit of infinitesimal bead size. Finally, shell model calculations on cylinders were shown to agree closely with experimentally determined settling rates.
Chemi-ionization in collisions of metastable helium with metastable helium
Authors: Neynaber R. H. , Magnuson G. D. , Tang S. Y.
Published: February 2003

Absolute and relative cross sections were obtained for the Penning-ionization (PI) reaction He*+He*→He+He++e and the associative-ionization (AI) reaction He*+He*→He+2+e. The studies were made using a merging-beams technique for a relative kinetic energy W of the rectants from nominally 0.01 to 10 eV. The He* represents a composite of about 13% He(2 1S) and 87% He(2 3S). The He*–He* system is found to be attractive with a well depth of approximately 0.5 eV. The PI reaction is directed with most of the Penning ions scattered in the direction of the parent He*. The fraction of AI to total ionization (AI plus PI is only a few percent. Cross sections for total ionization vary as W−0.38 for W<0.1 eV. At W=0.033 eV our absolute total ionization cross section of 112×10−16 cm2 agrees, within mutual errors, with the values obtained from most other experiments and from theory.
A kinetic theory ansatz for correlated collisions
Authors: Snider R. F.
Published: February 2003

A distinction is made between the distribution function for molecules just about to collide from the distribution function for molecules just finishing a collision, and from the distribution function for an average molecule in the midst of free flight. With the introduction of a free flight duration probability distribution, a connection is made between these three distribution functions. Combined with the first BBGKY equation in the linearized instantaneous collision approximation, the recent result of Lindenberg and Cukier [J. Chem. Phys. 67, 568 (1977)], on correlated collisions is rederived.
Temperature dependence of HF vibrational relaxation
Authors: Poulsen Lise Lotte , Billing Gert D. , Steinfeld J. I.
Published: February 2003

Semiclassical calculations of rate constants for energy transfer in an HF gas from 300 to 3500 K are reported. The potential hypersurface used was an analytic fit to recent SCF calculations plus the experimental dispersion potential. Good agreement with experiments was obtained without further adjustment of the potential parameters.
Theory of V–V and V–T/R energy transfer for HF (n=1 to 7)+HF (0)
Authors: Billing Gert D. , Poulsen Lise Lotte
Published: February 2003

Rate constants for vibrational relaxation of HF in vibrational states n=1 to 7 are calculated semiclassically for HF(n)+HF. The variation with n agrees well with experiment. The absolute values are about 55% of the experimental results. Orbiting collisions are important. The relaxation mechanism found disagrees with three well-known more approximate theories. V–T/R transfer is found to be important especially for the higher levels. A renormalization procedure is suggested as a remedy for the well-known numerical inaccuracy of trajectories with very long-lived collision complexes. This renormalization was not important for the present work.
Librational modes in partially disordered NH4Br below its 235°K disorder–order phase transition temperature
Authors: Buhay H. , Sokoloff J. B. , Perry C. H.
Published: February 2003

Polarized Raman scattering from single domain NH4Br has been measured in the frequency region of the librational mode at temperatures near but below the order–disorder phase transition temperature Tλ=235°K. The libronic excitation frequency decreases as Tλ is approached from below and the linewidth exhibits an Arrehenius-type temperature dependence with an activation energy of 1.07 kcal/mole. We analyze the libronic frequency shift by including a contribution to the ammonium ion torsion constant due to the disorder dependent NH+4–NH+4 interaction. Also, the polarized measurements indicate a strong temperature dependent, broad (∼70 cm−1) band at 279 cm−1 and at low temperatures, possibly due to disorder induced, first order Raman scattering at the sites of the disordered ammonium ions and suggest a larger bandwidth for the librational mode dispersion curve than has been measured for the low temperature ordered phase of ND4Cl.
Quantum mechanical equations of change. I
Authors: Hirschfelder Joseph O.
Published: February 2003

Simple, but completely general, equations of change are derived for a property, χ†𝒪Ψ of a quantum mechanical system, where χ (r,s,t) and Ψ (r,s,t) are any two wavefunctions satisfying a time-dependent Schrödinger equation with the same Hamiltonian H, and 𝒪 is an arbitrary operator. For a Hamiltonian H0= (2m)−1 p2+V (r) the equations of change of angular momentum density and kinetic energy density are derived. The equations of change are developed for systems having Breit–Pauli type Hamiltonians which involve spin as well as external static electromagnetic fields and relativistic corrections. The velocity operator ṙ is shown to contain a spin-dependent term. The relativistic correction to the kinetic energy (p2)2 term is not consistent with the equation of continuity. An expression is derived for the rate of ’’spin flipping’’ of a hydrogen atom in an external electromagnetic field. Methods are derived for projecting the equations of change onto real three-dimensional space. Natural spin orbitals are useful for describing the equation of continuity in three dimensions; however, they cannot describe the equation of motion or the other equations of change.
N (1A
g), T (3B1u), and V (1B1u) states of vertical ethylene
Authors: Brooks Bernard R. , Schaefer Henry F.
Published: February 2003

We present the most exhaustive theoretical studies to date of the nature of the lowest (ππ*) singlet state of vertical C2H4. Basis sets as large as double zeta plus polarization plus diffuse functions were used in conjunction with large scale configuration interaction, including as many as 7064 1B1u configurations, constructed from 31 898 Slater determinants. The lowest total energy obtained was −78.0284 hartree, significantly lower than any previous variational result. A key to determining the spatial extent of the vertical V state was provided in the important paper by McMurchie and Davidson, who showed how critical it is that the CI wavefunction be invariant to transformations within the π* (b3u) orbital space. However the actual value of 〈ψ‖Σi x2i‖ψ〉 obtained here, ∼27 a.u., is somewhat larger than that of McMurchie and Davidson. We conclude that the V state is intermediate in its spatial extent between valence and Rydberg character. However, it is also seen that variational energies are very insensitive to the value of 〈x2〉 predicted. That is, by raising the vertical excitation energy of the V state by only 0.1 eV, the intermediate spatial extent suggested by the variational principal becomes markedly more valencelike. The latter observation serves to explain the experimental spectra of Miron, Raz, and Jortner.
Total cross sections for symmetric charge transfer reactions of O+2 in selected translational and internal energy states
Authors: Baer Tomas , Murray P. Terrence , Squires Larry
Published: February 2003

Total cross sections for the symmetric charge transfer reactions of O+2(X 2Πg) in selected translational and vibrational energy states have been measured in a single chamber experiment using a combination of photoion–photoelectron coincidence and ion time-of-flight analysis. The ion vibrational states and laboratory translational energies investigated were v=0–7 and 1–40 eV, respectively. The experimental results are compared to recently calculated symmetric charge transfer cross sections using the multistate impact parameter theory. We find that the theory overestimates the cross section by approximately a factor of 2. In addition, the theory predicts a slow drop in the cross section as a function of vibrational energy for v≳3, whereas the experiments indicate that the cross sections remain high and even increase with v for v≳5.
Calculated long-range interactions and low energy scattering in He+H, Ne+H, Ar+H, Kr+H, and Xe+H
Authors: Das G. , Wagner Albert F. , Wahl A. C.
Published: February 2003

The van der Waals (VDW) forces in rare-gas hydride systems are evaluated through the use of the multiconfiguration self-consistent field (MCSCF) method. For Kr–H and Xe–H, a pseudopotential variant of the MCSCF method is used. For each system, a potential energy curve is fit to the calculated potential energies, the VDW well depth and equilibrium position are determined, and the low energy total elastic cross sections are computed as a function of relative velocity. The calculated cross sections are in good to excellent agreement, for He–H, Ar–H and Xe–H, and in fair agreement, for Ne–H and Kr–H, with the most recent experimental measurements.
Far infrared single crystal study of p-diiodobenzene
Authors: Clayman B. P. , Farnworth B. , Ward R. W.
Published: February 2003

The far-infrared transmission spectrum of p-diiodobenzene was measured as a function of temperature and polarization. Eleven absorption lines were observed at 4 K. Six were assigned, on the basis of their polarization dependences, to vibrational modes of the molecular lattice. The remaining lines were found to be due to either intramolecular modes or Raman-active librational lattice modes which exhibit some infrared activity. Upon heating through the phase transition at 326 K, the two B3u modes disappear and are replaced by another strong band. This is interpreted as due to a structural distortion along the crystalline c axis. No evidence of soft mode behavior near the transition is observed.
Computer studies of dynamics in one dimension: Hard rods
Authors: Haus J. W. , Raveché H. J.
Published: February 2003

Results of molecular dynamics simulations are reported with emphasis on the relaxation of an initially ordered array of hard rods in one dimension. It is found that at high densities the pressure accurately approaches the exact value for the infinite system, which corresponds to a uniform fluid, before the singlet and pair configuration space distribution functions have completely relaxed to the equilibrium state. The velocity autocorrelation function is computed over a wide range of times, which includes the region where it is negative, and compared to the exact solution for the infinite system.
Optical–optical double resonance with two dye lasers: Rotational analysis of the E 2Σ–B2Σ system of Ca35Cl
Authors: Domaille Peter J. , Steimle Timothy C. , Harris David O.
Published: February 2003

A complete rotational analysis of the E 2Σ–B 2Σ system of CaCl has been accomplished using two tunable dye lasers. The first cw laser is tuned to a known B 2Σ–X 2Σ transition to produce a finite concentration of molecules in a particular quantum state. Subsequently, a second pulsed dye laser is used to record the E 2Σ–B 2Σ excitation spectrum from this state prepared level. The method vastly simplifies an otherwise congested molecular spectrum. The data are combined with previous microwave measurements on the X 2Σ state and optical data on the B 2Σ–X 2Σ system to give the following molecular constants (cm−1). Uncertainties are 95% confidence limits in the last digit.
Infrared spectra of chemisorbed CO on Rh/γ–Al2O3: Site distributions and molecular mobility
Authors: Yao H. C. , Rothschild Walter G.
Published: February 2003

Chemisorption of CO on a 0.92 wt. % Rh/γ-Al2O3 catalyst gave three species of adsorbed CO molecules: Species RhCO, at about 2000 cm−1; species Rh(CO)2, showing a doublet with peak frequencies at 2100 and 2030 cm−1; and a bridged species Rh2CO, leading to a very broad band peaked between 1850 and 1900 cm−1. The thermostability of these adsorbed species is in the sequence Rh2CO≳RhCO≳Rh(CO)2. Only the doublet band of Rh(CO)2 and the very broad band of the bridged species Rh2CO were found on well dispersed Rh metal in its δ phase. The band contours of the RhCO and Rh(CO)2 species were Fourier transformed into the time domain. The result showed that the configuration RhCO was spread over an approximately four times wider distribution of adsorption sites (surface–adsorbed CO interactions) than that of the Rh(CO)2 species. Furthermore, it was shown that the CO molecules adsorbed as RhCO species are ’’floppy,’’ undergoing some type of fast (probably librational) motion with a characteristic time of 0.1×10−12 sec. On the contrary, the CO molecules adsorbed as RH(CO)2 obey a slow modulation regime, with a characteristic time of about 3×10−12 sec. It is pointed out that this greatly different behavior may be of significance with regard to the selectivity and activity of the different catalytic sites as well as to the directional properties of the metal–carbon bond orbitals.
Generalized valence-bond investigation of the reaction H+Br2 →HBr+Br
Authors: Baybutt Paul , Bobrowicz Frank W. , Kahn Luis R. , Truhlar Donald G.
Published: February 2003

A b initio quantum mechanical calculations have been carried out to predict the H+Br2→HBr+Br potential energy surface. We used ab initio effective core potentials and an extended valence basis set including polarization functions on each center and carried out open-shell self-consistent-field calculations in the generalized valence bond–perfect-pairing (GVB–PP) approximation. The orbitals of this calculation were used as a starting point for eight-configuration–configuration-interaction (GVB–CI) calculations. The CI calculations not only bring in electron correlation effects but also make up to a large extent the inability of the GVB–PP calculation to adequately treat the recoupling of orbitals which occurs near the transition state. The classical barrier height is predicted to be about 12 kcal mole−1 by the GVB–PP calculations and about 3.0 kcal mole−1 by the GVB–CI calculations. The latter value is in reasonable agreement with the experimental Arrhenius activation energy. The saddle point is predicted from the GVB–CI calculations to occur for a linear geometry with an H–Br separation 46% greater than in HBr but a Br–Br separation only 6% greater than in Br2. The CI calculations lead to only 30% attractive energy release along a rectilinear path and predict that the energy increases only about 2.4 kcal mole−1 for a 25° bend near the saddle point. We present results for a wide range of geometries which illustrate the phenomenon of dual surfaces for a GVB–PP self-consistent-field calculation on a reactive system.
Elastic interaction of tunneling impurities in solids
Authors: Mokross B. J. , Pirc R.
Published: February 2003

The tunneling model for dipolar impurities in solids is applied to a study the static collective behavior of systems with large impurity concentrations. A rigorous formal result for the elastic constants is derived predicting anomalous softening near the phase transition corresponding to orientational ferroelastic ordering of the impurities. The nature of the phase transition is studied within the mean field approximation and examples of second and first order transitions are given for typical cases of impurity equilibrium orientations. Application to mixed KCl1−xCNx crystals and to pure KCN is discussed in the light of recent experimental and theoretical work.
Measurements of 4.2 μm CO2 pressure broadening by using an HBr chemical laser
Authors: Oodate Hitoshi , Fujioka Tomoo
Published: February 2003

The pressure broadening of CO2(0000→00°1) transitions has been studied by using an HBr chemical laser. By measuring the absorption of the HBr laser beams by CO2 gas, the coefficients of broadening have been obtained as a function of the rotational quantum number J. The coefficient is expressed as Δν= (5.2±0.5)−(0.05±0.01) J (MHz/Torr). This equation is in good agreement with data from other reports. From the measurement the Einstein A coefficient has been calculated as A= (1.3±0.2) ×102 (sec−1). The effects of He and N2 collision partners have been measured.
A simple theoretical model for the van der Waals potential at intermediate distances. II. Anisotropic potentials of He–H2 and Ne–H2
Authors: Tang K. T. , Toennies J. Peter
Published: February 2003

A simple model proposed in an earlier paper [J. Chem. Phys. 66, 1496 (1977)] is applied to the prediction of the radial V0(R) and anisotropic parts v2(R) of the van der Waals potentials, V (R,γ) =v0(R)+v2(R) P2 (cosγ), where R is the distance between centers of mass and γ is the angle between R and the molecular axis, for He–H2 and Ne–H2. All the parameters used in the model are derived either from ab initio SCF data on the repulsive potential calculated by Hariharan and Kutzelnigg or from perturbation calculations of Meyer of the long range dispersion terms and their angular dependence. The predicted v0 and v2 radial dependences for He–H2 are compared with several of the latest ab initio CI-type calculations. For Ne–H2, for which ab initio potentials are not available in the potential well region the results are compared with the most reliable experiments. In addition the predicted potentials are used to calculate the orientation dependence of total integral cross sections for direct comparison with measurements by Reuss and co-workers for both systems. In all cases excellent agreement within a few percent is obtained. These results demonstrate for the first time that the model also describes the repulsive potential up to energies of about 10 meV. The possible physical implications of the model potential are briefly discussed.
Fictitious spin 1/2 operator formalism for multiple quantum NMR
Authors: Vega Shimon
Published: February 2003

A formalism is presented that describes the time behavior of the spin density matrix of a nuclear spin system with arbitrary spin in terms of fictitious spin −(1/2) operators. This formalism is an extension of that used earlier for nuclei with spin I=1. For a spin system with n eigenstates we define for every pair of eigenstates ‖i〉 and ‖j〉 three operators Ii−jp, with p=x, y, and z, according to the three 2×2 Pauli matrices σx, σy, and σz. These operators together constitute a complete set of n2−1 independent Hermitian operators, and we can write the n×n density matrix and the spin Hamiltonian of the system in terms of the Ii−jp operators. The commutation relations among the operators make it possible in many cases to solve the equation of motion of the density matrix analytically. Three examples of the use of the Ii−jp operators are presented. Firstly a system of noninteracting spins with I=1 is considered. The Ii−jp operators for this case are compared with the Iq,k operator defined earlier. The cw signal intensities of the single and double quantum transitions for the I=1 spin system are derived. Secondly a spin system with I=3/2 is described as a simple extension of the use of the Ii−jp operators. The excitation and the detection of the triple quantum coherence are discussed for noninteracting nuclei in solids. Finally the double quantum effects in a system of two interacting spins with I=1/2 are discussed.
A molecular dynamics simulation of dephasing in liquid nitrogen
Authors: Oxtoby David W. , Levesque D. , Weis J. -J.
Published: February 2003

We relate the dephasing of molecular vibrations in liquids to certain correlation functions involving only the translational and rotational degrees of freedom; these correlation functions are then determined through a classical molecular dynamics simulation of rigid, nonvibrating molecules. Using a Lennard-Jones atom–atom potential for N2 (liq) near its boiling point, we calculate a dephasing time of 62 psec, in good agreement with picosecond pulse and isotropic Raman linewidth measurements. The importance and characterisic time scales of different dephasing mechanisms are studied, and the significant effect of vibrational anharmonicity is demonstrated.
Matrix radiolysis and photoionization of CF2Cl2 and CF3Cl. Infrared spectra of CF2Cl+ and the parent cations
Authors: Prochaska Frank T. , Andrews Lester
Published: February 2003

The ’’Freon’’ molecules CF2Cl2 and CF3Cl have been subjected to matrix radiolysis and photoionization during condensation with excess argon at 15 K. Infrared spectra showed stable and free radical products and new absorptions due to charged species. The molecular ion bands exhibited different behavior on filtered mercury arc photolysis. New 1415 and 1515 cm−1 absorptions decreased by 220–1000 nm photolysis are assigned to CF2Cl+2 and CF3Cl+. Other absorptions eliminated by mercury arc light, some of which were produced on photolysis of sodium–chlorofluoromethane samples, are attributed to molecular anions. The vibrational assignments were verified by carbon-13 isotopic studies.
Viscosity measurements and structural properties in aqueous NiCl2 solutions
Authors: Maisano G. , Migliardo P. , Wanderlingh F. , Fontana M. P.
Published: February 2003

We measured viscosity as a function of concentration in an aqueous solution of NiCl2. We also measured compressibility and density in the same system. The data are discussed in the frame of existing phenomenological theories. In all cases it appears that some structural changes take place at a given concentration. We also propose a new phenomenological equation that describes the viscosity in terms of a function of the concentration, that turns out to have a rather universal character being able to describe also the behavior of other properties such as compressibility and density. The building up of some sort of structure can easily be revealed by such a treatment, also in comparison with other experimental results.
1
3C and 19F nuclear relaxtion in CFBr3
Authors: Huang Shaw-Guang , Rogers Max T.
Published: February 2003

13C and 19F nuclear magnetic relaxation rates in liquid CFBr3 have been measured at 14.1 kG. By assuming that the motion of the molecules at low temperatures follows the classical diffusion model, the contributions of various relaxation mechanisms have been resolved and the spin–lattice relaxation times of bromine isotopes estimated. In addition, the scalar coupling constants between 19F and 79Br and between 13C and 79Br have been estimated to be 30.5±1.5 Hz and 124.2±7.0 Hz, respectively.
Molecular dynamics of t
e
r
t-butanol studied by neutron inelastic scattering
Authors: Amaral L. Q. , Vinhas L. A.
Published: February 2003

Molecular dynamics of tert-butanol in two crystalline phases and in the liquid state was investigated by cold neutron scattering in the temperature interval 8–35 °C. Inelastic spectra remained essentially the same, indicating short range order in the liquid state. A frequency spectrum obtained from the sum of seven Gaussian functions fitted the measured time-of-flight distribution and allowed assignment of peak positions. A barrier V1= (4.0±0.2) kcal/mol for CH3 internal rotation was obtained; results are compatible with a second order term V2?−0.1V1. Quasielastic line broadening and Debye–Waller factors were analysed in terms of models for molecular diffusion and the results compared with NMR data. It is concluded that cooperative rotational diffusion occurs both in solid and liquid states.
Ring puckering in the 1B2(n, 3s) Rydberg electronic state of cyclobutanone
Authors: Drury-Lessard C. R. , Moule D. C.
Published: February 2003

The first vacuum ultraviolet absorption spectrum of cyclobutanone has been photographed under conditions of moderately high resolution. This system, which is given the assignment ?1B2(n, 3s) ←?1A1, has been observed to have unusually discrete rotational and vibrational fine structure. To higher frequencies from a weak (0–0) band are a pair of weak vibronic bands at (+105) and (+196) cm−1 which are assigned to the ring puckering sequence transitions (1–1) and (2–2). From a fit of the energy levels derived for the upper state to a quartic–quadratic potential function it was determined that the C1C2C3C4 carbon atoms are coplanar in this state. The increase in puckering frequency from 35 to 140 cm−1 is interpreted in terms of a large increase in ring strain on excitation.
The kinetics of solvent reorientation in hydroxylated solvents from the exciting-wavelength dependence of chromophore emission spectra
Authors: Milton John G. , Purkey Robert M. , Galley William C.
Published: February 2003

The disappearance of the exciting-wavelength dependence of the phosphorescence spectra of polar, aromatic chromophores in supercooled glycol–water mixtures is utilized to monitor the kinetics of solvent reorientation. Reorientation times in the nanosecond to second range are obtained for (3:2 v/v) glycerol–water and (1:1 v/v) ethylene glycol–water at 140–240 °K. The results suggest that the process is one involving a cluster of solvent molecules and in which the chromophore plays a relatively passive role. Steady-state data and direct measurements of phosphorescence shifts as a function of time indicate that the solvent reorientation process is nonexponential in nature. The decay function derived from the temperature dependence of the steady state data is consistent with the decays observed directly as a function of time. Interpretation of this nonexponential decay in terms of a summation of rate processes leads to a distribution dominated by two reorientation rate constants. The relative contributions of the slow and faster reorientation rate constants in addition to their activation parameters differ for the glycerol–water and ethylene glycol–water mixtures.
Energy transfer in A 2Σ+ OH. II. Vibrational
Authors: Lengel Russell K. , Crosley David R.
Published: February 2003

Vibrational energy transfer within the A 2Σ+ state of OH and OD has been studied. A frequency doubled tunable dye laser excites individual N′, J′ levels in v′=1 or 2, and the intensities of rotationally resolved fluorescence emitted in the presence of collision partners (He, Ar, H2, D2, and N2) furnished state-to-state transfer rates. It is found that the transfer rates are strongly dependent on initial rotational level (decreasing as Ni increases), that the final rotational state distributions are near thermal but hot, that isoenergetic transfer is small, and that the magnitudes for transfer 1→0, 2→1, and 2→0 are all similar. The rates themselves are large; for example, with N2, k1→0 (Ni=3) =1.7×10−10 cm3 sec−1. The results, taken together, are supportive of a long-lived collision in which anisotropic attractive forces are of importance in the dynamics of the entrance channel.
Temperature dependence of electron spin-lattice relaxation of methyl radicals in glassy organic matrices:Relation to environmental dynamics and radical decay
Authors: Michalik Jacek , Kevan Larry
Published: February 2003

The electron spin-lattice relaxation of trapped methyl radicals in methanol , 2−methyltetrahydrofuran, and 3−methylhexane glasses has been directly studied as a function of temperature from 5-100 K by the saturation recovery method. The relaxation rate remains fast at low temperatures and shows a large component linear in temperature. This is interpreted in terms of the recently developed model of tunneling relaxation involving modulation of the electron nuclear dipolar interaction by tunneling of nuclei in the radical’s environment [J.Phys.Chem.81,456 (1977)]. Deuteration experiments show that CH3 and [J.Phys.Chem.81,456 (1977)]. Deuteration experiments show that CH3 and CD3 have the same relaxation rate while it is decreased by about four−fold by deuterating the matrix. There also appears to be a correlation between the spin-lattice relaxation rate and the decay of methyl radicals in these matrices.
Vibrational normal modes of SiO2. III. α-Berlinite (AlPO4) and its relations to Γ–A phonon dispersion curves in α-quartz
Authors: Etchepare J. , Merian M.
Published: February 2003

The valence force field, previously obtained to describe the vibrational normal modes of quartz, cristobalite, and tridymite forms of SiO2 (parts I and II), has been used to calculate the phonon dispersion curves and elastic constants of α-quartz. The reasonably good fit to the experimental data suggested that the same valence force field may be valid in α-berlinite, an isomorph of α-quartz. The following results confirm the analogy between SiO2 and AlPO4.
An EPR–ENDOR study of phosphorus in phenacite
Authors: DuVarney R. C. , Garrison A. K.
Published: February 2003

An EPR and ENDOR study on a phosphorus impurity in natural single crystals of phenacite (Be2SiO4) is reported. The EPR studies on this strongly coupled electron–nuclear spin system include the forbidden or ΔMF=0 transitions. The nuclear g factor of the impurity ion which was calculated from an analysis of the forbidden transitions shows the impurity to be 31P. The principal values and directions of the electronic g tensor and the hyperfine coupling tensor were determined through a least-squares fit to the data employing direct diagonalization of the Hamiltonian matrix. ENDOR studies show a superhyperfine (shf) coupling of this center to several near neighbor 9Be nuclei. The shf coupling parameters for three 9Be nuclei were determined and are presented along with a detailed model of the center and a discussion of the crystallographic positions of the Be nuclei. Our analyses indicate a P5+ ion substitutes for a Si ion at a normal site and is converted to P4+ by x rays.
The temperature dependence of the rate constant for Cl+NO+N2 → NOCl+N2
Authors: Lee J. H. , Michael J. V. , Payne W. A. , Stief L. J.
Published: February 2003

The rate constant for the reaction Cl+NO+N2→k1 ClNO+N2, of interest in stratospheric chemistry, has been measured by the flash photolysis–resonance fluorescence technique over the temperature range 200–400 K. The measured rate constants obey the Arrhenius equation k1,N2= (1.18±0.10) ×10−32 exp[(532±20)/T] cm6 molecule−2 sec−1. At room temperature with the two additional third bodies, He and Ar, the measured termolecular rate constants are k1,He= (4.11±0.20) ×10−32 and k1,Ar= (4.40±0.30) ×10−32 cm6 molecule−2 sec−1. These results are theoretically discussed and are compared with previous work.
Rate constants for the reactions of O−, O2−, NO2−, CO3−, and CO4− with HCl and ClO− with NO, NO2, SO2, and CO2 at 300 K
Authors: Dotan I. , Albritton D. L. , Fehsenfeld F. C. , Streit G. E. , Ferguson E. E.
Published: February 2003

The rate constants for several ion–molecule reactions involving chlorine-containing ions or molecules have been measured at 300 K with a flowing afterglow apparatus. These include the reaction of O− with CCl4, several negative ions with HCl, ClO− with several neutrals, and Cl− with O3. These reactions are used to place limits on the electron affinity of ClO: E.A.(ClO) =1.95±0.25 eV. The implications of these results to the negative ion chemistry of the atmosphere are discussed.