bluuebunny/crossref_metadata_2025 huggingface dataset:
Absolute infrared intensities of cyclopropane-d and cyclopropane-d6: Dipole moment derivatives and polar tensors
Authors: Levin Ira W. , Pearce Robert A. R.
Published: February 2003

Integrated infrared absorption intensities for the fundamental vibrations of gas-phase cyclopropane-d0 and cyclopropane-d6 were experimentally determined using nitrogen pressure-broadening techniques. Although the experimental data are insufficient to resolve the relative sign combinations for the (∂P/∂Qi) and (∂P/∂Sj) charge distribution parameters in the A2′′ symmetry species, a definitive relative sign choice is indicated for the E′ dipole moment gradients. The normal coordinate transformations required for the dipole derivative analysis are based on the highly reliable force field derived by Duncan and Burns [J. Mol. Spectrosc. 30, 253 (1969)]. For ease both in computing the atomic polar tensor elements of cyclopropane and in comparing cyclopropane force constants and dipole derivatives to related systems, the Duncan and Burns potential function is recast in terms of a set of more convenient internal valence force constants. (∂P/∂Qii) dipole gradients determined by semiempirical CNDO/2 molecular orbital calculations are used to indicate a preferred sign for the dipole derivatives. Atomic polar tensors for the carbon and hydrogen atoms of cyclopropane are calculated and compared to those for methane and ethylene. The effective charge parameter for the hydrogen atom in cyclopropane is also discussed.
Homogeneous nucleation of bubbles in solutions at pressures above the vapor pressure of the pure liquid
Authors: Forest T. W. , Ward C. A.
Published: February 2003

The homogeneous nucleation of bubbles in liquid-gas solutions is considered theoretically and experimentally. The stability of a homogenous liquid phase is shown to be specified by the critical radius, Rc. If Rc is negative or infinite, then the liquid is stable; however, if Rc is positive then the liquid is metastable. The prediction of the pressure at which nucleation occurs follows from nucleation theory. At a given temperature, the presence of a dissolved gas is shown to significantly raise the pressure at which nucleation occurs. These predictions were experimentally tested for ethyl ether droplets containing dissolved nitrogen using an isothermal decompression technique. Results are presented for a range of gas concentrations including values for which it is predicted that nucleation should occur at pressures greater than the vapor pressure of the pure liquid. Good agreement between theoretical and measured nucleation pressures was obtained.
Molecular reorientation in solid perchloryl fluoride
Authors: Ripmeester J. A. , Garg S. K. , Davidson D. W.
Published: February 2003

Results of pulsed 19F NMR studies of spin-lattice relaxation times of solid C1O3F give a single reorientational correlation time with an activation energy of 6.9 kcal/mol, an energy so high as to suggest that the residual entropy is due to the ’’freezing-in’’ of orientational disorder. The low-temperature 19F line shape yields a chemical shift anisotropy of 570±20 ppm.
A classical/semiclassical theory for the interaction of infrared radiation with molecular systems
Authors: Miller William H.
Published: February 2003

A classical model for the interaction of molecular systems with infrared radiation is presented. It differs from the usual ’’semiclassical theory of radiation and matter’’ in that the molecular system is treated by classical rather than quantum mechanics, and the radiation field is described, as in Jaynes’ neoclassical theory, as classical (mechanical) harmonic oscillators rather than as a classical field (i.e., via Maxwell’s equations). The classical Hamiltonian for the composite system—molecules, radiation, and their interaction—is thus that of a completely mechanical system, and its classical dynamics is determined by computing the classical trajectories of the system. Quantum mechanical interference and tunneling effects can be built into the description within the framework of the classical S-matrix theory. Even within the strictly classical limit of the model, it is shown that all dynamical effects in the interaction of radiation and matter are obtained; in the perturbative limit, for example, it is shown that absorption and induced emission, and even spontaneous emission, which is often difficult to obtain in other classical or semiclassical models, appear in a completely straightforward manner.
Radiative lifetime and collisional quenching kinetics for the XeF (B1/2) state
Authors: Fisher Charles H. , Center Robert E.
Published: February 2003

A state-selective laser-induced-fluorescence technique has been used to determine the radiative lifetime and collisional quenching kinetics for the XeF (B 1/2) excited state. Ground state XeF molecules, formed by flash dissociating a mixture of UF6 and Xe diluted in He, are excited to the B state by 351 nm XeF laser pulse. The subsequent fluorescence decay of the v′=0 level is monitored at 353 nm using a spectrometer-fast photomultiplier combination. Collisional quenching rate coefficients for the collision partners He, Ne, Xe, F2, and NF3 are reported. Broadband fluorescence emission at 460 nm has also been observed and is interpreted to result from collisional transfer from the B to the C state of XeF.
The structure and vibrational frequencies of ionic clusters
Authors: Martin T. P.
Published: February 2003

The table configurations of ionic clusters having the compositions (MX)n and (MX2)n are determined by numerically minimizing the total energy. Both rigid ion and polarizable ion models are used to describe the two particle interactions. Clusters of a given size and composition are found to have many stable configurations. In order to find as many stable configurations as possible, classifications based on the arrangement of small stable subunits are often helpful. In general, (MX)n clusters have high symmetry and often resemble small portions of NaCl or wurtzite lattices. (MX2)n clusters, on the other hand, often occur in forms having no symmetry, indicating their tendency to form disordered solids even with purely ionic interactions between atoms. Certain cluster sizes, for example n=5,7,11, and 13 for NaCl, have low binding energies which present barriers to crystal growth. The second derivatives of the total energy with respect to atomic displacements were evaluated numerically and the dynamical matrix diagonalized to give the vibrational frequencies of each cluster. Comparison is made with previously reported experimental infrared absorption spectra of (LiF)n and with new spectra of (PdCl2)n.
Resonance Raman spectra of inorganic salt vapors I. Palladium (II) and Copper(II) chloroaluminates
Authors: Papatheodorou G. N. , Capote M. A.
Published: February 2003

Resonance Raman spectra of vapor molecules formed by reacting gaseous aluminum chloride with solid PdCl2 and CuCl2 have been measured in the temperature range from 500 to 900 K and at total pressures up to 30 atm. The main features of the Raman spectra of the Pd–Al–Cl gaseous molecule are three polarized bands at 298, 176, and 84.5 cm−1. The excitation profiles of these bands exhibit minima in the vicinity of the maximum Pd(II) ligand field absorption, thus suggesting the presence of a center of symmetry in the molecule. A D2h molecular symmetry is proposed for the PdAl2Cl8 vapor complex having Pd(II) as a central atom in square planar coordination. The Raman spectra of the Cu–Al–Cl vapors are interpreted to account for two different molecular species. Three polarized bands at 281, 174.5, and 84.5 cm−1 are assigned to preresonance enhanced A1 fundamentals of the CuAl2Cl8 molecule. Two strong bands at 448 and 291.5 cm−1 and their combinations and ovetones are assigned to resonance enhanced A1 fundamentals of the CuAlCl5 molecule having the Cu(II) in a trigonal coordination. Raman band intensity measurements using different laser line intensities suggest an increasing spectroscopic temperature and decomposition of the complex: CuAl2Cl8(g) →CuAlCl5(g)+AlCl3(g).
Directionality dependence of lattice models for solutions with closed loop coexistence curves
Authors: Andersen G. R. , Wheeler J. C.
Published: February 2003

Two lattice solution models of systems which exhibit lower critical solution temperatures and closed-loop coexistence curves are generalized to allow for arbitrary directionality in their interactions. It is found that in both models a substantial widening of the curves results from increasing the degree of directionality of the interaction between unlike molecules. One of these, an exactly soluble decorated latice model, produces reasonable quantitative agreement with the coexistence curves for the systems glycerol + guaiacol, glycerol + m-toluidine, and glycerol + benzylethylamine. Hydrogen bond energies obtained from the generalized decorated lattice model are in reasonable agreement with those found in real systems.
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o calculations of the collision-induced dipole in He–H2. I. A valence bond approach
Authors: Berns R. M. , Wormer P. E. S. , Mulder F. , Avoird A. van der
Published: February 2003

The collision-induced dipole in the system He–H2 is calculated in the multistructure Valence Bond method, using the nonorthogonal monomer orbitals. In the region around the collision diameter, which contributes most to the collision-induced ir absorption, the long range results (the leading terms are the quadrupole-induced dipole on He with R−4 dependence and the dispersion dipole with R−7 dependence) are modified by overlap effects. The short range behavior is determined, moreover, by the appearance of other important terms, the exchange dipole and the overlap-induction dipole on H2, which vanish in the long range. Since all the short range contributions have approximately the same (exponential) dependence on the intemolecular distance, they can be collected and added as a single exponential dipole function to the R−4 and R−7 long range terms. Of the latter terms the R−7 dispersion dipole is of little importance.
Field-induced surface reactions for the 1-hexene–water system
Authors: Okuyama F. , Beckey H. D.
Published: February 2003

Interactions of 1-hexene, a standard olefine compound, with water under high-field conditions were investigated by means of field ionization mass spectrometry. The FI mass spectrum of a 1-hexene–H2O mixture was characterized by extremely abundant H3O+ ions, part of which possibly resulted from the water protonation induced by chemisorbed 1-hexene ions. Other principal reaction products were CnH2nOH+(n=1–3) and CnH+2n+1 (n=4,5) ions due to surface reactions in which water directly took part. In addition to these ions, C7H+14 and C7H+15 ions were observed in relative intensities slightly lower than 1%, and they are believed to have originated in a recombination reaction between radical fragments of 1-hexene physically bound to water adlayers.
Vibrational anharmonicity constants for SF6. I. A 16 μ diode laser study of transitions in the ν4 region
Authors: Person W. B. , Kim K. C.
Published: February 2003

A total of eight empirical anharmonicity constants have been determined from diode laser studies of the ν4 vibrational transitions in SF6. The transitions from the low excited states on the 16 μ region were recorded using semiconductor lasers with a long optical path absorption cell. The relative intensities of the corresponding Q branches were related to the population distribution in the temperature range from 160 to 300 K in order to make the spectroscopic assignments of the ν4 hot band transitions. These measured states represent some 86% of the total population distribution of the SF6 molecules at 300 K. Theoretical models based on Morse potential functions are discussed and the results from the model calculations are compared with the experimental vibrational anharmonicity constants.
Associative ionization of uranium and thorium in collisions with ozone
Authors: Patterson T. A. , Siegel M. W. , Fite W. L.
Published: February 2003

Associative ionization channels in the U and Th with O3 systems are observed in a crossed beams apparatus with positive and negative ion mass spectrometric detection, and cross sections for open channels are measured. Electron impact ionization is used to measure beam intensities. The ozone beam is modulated, and phase spectrometry is used to demonstrate ozone beam purity. Measured cross sections (labeled by charge products) are 2×10−16(UO+2,e),2×10−16(UO+,e), 2×10−19(ThO+3,e),1×10−17(ThO+2,e), 4×10−16(ThO+,e),1×10−18(ThO+,O−2), and 2×10−18(ThO+2,O−) cm2 multiplied by the ratio of the cross sections for the production of O+2 by electron impact ionization of O3 and O2, and in the case of thorium, also multiplied by the ratio of thorium and uranium electron impact ionization cross sections.
Vibrational tuning of the proximity effect in radiationless transitions
Authors: Wassam W. A. , Lim E. C.
Published: February 2003

The QSM approach to molecular relaxation phenomena is employed in a theoretical investigation of the relationship between selected vibrational excitation and the proximity effect. It is shown that selected vibrational excitation may be employed to tune vibronic interactions in radiationless transitions. Excitation of vibronically active, non-totally symmetric modes amplifies the proximity effect, while vibrational excitation of totally symmetric modes diminishes this effect.
S2 fluorescence and excitation spectra in solid Ar
Authors: Bondybey V. E. , English J. H.
Published: February 2003

Study of the S2 emission and excitation spectra in solid Ar suggests reassignment of the fluorescence. The absorbing B 3Σ−u state undergoes efficient nonradiative transition into a lower lying electronic state correlating with two 3P sulphur atoms, probably the B″ 3Πu state. This reassignment is consistent with recent observations of the S2 emission in matrix thermoluminescence experiments. Both the B 3Σ−u and the B″ 3Πu state are even in the solid strongly perturbed.
High spin molecules: ESR and optical spectroscopy of MnH (7Σ) and MnH2 (6A1) at 4 °K
Authors: Van Zee R. J. , DeVore T. C. , Wilkerson J. L. , Weltner W.
Published: February 2003

MnH and MnH2 molecules, and their deuterated counterparts, have been trapped in argon and neon matrices at 4 °K and observed via infrared, visible, and electron-spin-resonance spectrscopy. The data for MnH support the gas-phase 7Σ ground-state assignment and yield the magnetic parameters ‖A (H) ‖?20, ‖A∥(Mn) ‖=322(6), ‖A⊥(Mn) ‖=299(2) MHz, g⊥=2.001(1) (assuming g∥ =ge), D=−0.002(1) cm−1. The derived MO description is in essential agreement with the ab initio calculations of Bagus and Schaefer. Infrared data indicate that MnH2 is bent at a bond angle of 117±30°, and stretching force constants are derived. ESR spectra variations with the matrix used and with isotopic substitution indicate motional effects in some matrices. It is concluded that the ground state is 6A1 with ‖D‖=0.20(2) cm−1 and with the probable hyperfine parameters ‖A (H) ‖=36, ‖Axy(Mn) ‖ =73 MHz, where xy is an average axis perpendicular to the H–H direction. The bent molecule is justified by Walsh-type theory applied to transition-metal dihydrides. There are indications that the MnH3 molecule may have also been observed.
ELDOR detection of ENDOR transitions in irradiated organic crystals
Authors: Kispert L. D. , Chen T. C. S. , Hill J. R. , Clough S.
Published: February 2003

The electron–electron double resonance (ELDOR) spectra of free radicals in γ-irradiated 4-methyl-2,6-ditertiarybutylphenol single crystals and a deuterated derivative having all the hydrogen atoms except those of the 4-methyl group replaced by deuterium contain an unusually narrow ELDOR line (p–p=90 kHz) when highly saturating observing conditions, large pump power, and 100 kHz field modulation are used. The narrow ELDOR line corresponds to a flip of a proton spin relative to the sum of the hyperfine and external field. The transition is driven by the two microwave fields acting together and occurs when the difference of two frequencies is equal to the nuclear resonance frequency. It has previously been observed by ENDOR, but the ELDOR measurements have better sensitivity at higher temperatures. This suggests that ELDOR detection of ENDOR transitions may have wide utility in the accurate measurement of hyperfine interaction parameters.
Exactly solvable models for vibronic coupling in molecular spectroscopy. III. The pseudo Jahn–Teller effect
Authors: Henneker W. H. , Penner A. P. , Siebrand W. , Zgierski M. Z.
Published: February 2003

A model system consisting of two electronic manifolds coupled through a nontotally symmetric mode of vibration is solved exactly and self-consistently by the method described in Paper I [J. Chem. Phys. 65, 2071 (1976)]. As in I, the model is defined in terms of harmonic diabatic potentials, but the restriction to harmonic adiabatic potentials, applied in I, is lifted here. As a result, the adiabatic coupling operator which has the same analytical form as in I, can assume a much wider range of values. It leads to adiabatic potentials which in general are anharmonic and may exhibit a double minimum. The coupling is taken to be an odd function of the vibrational coordinate so that it describes the (pseudo-) Jahn–Teller effect. Absorption and emission spectra are calculated for selected combinations of four spectroscopic parameters: (1) the electronic energy gap; (2) the diabatic harmonic frequency difference; (3) a linear adiabatic coupling parameter; and (4) a nonlinear (quasiquadratic) adiabatic coupling parameter. In the appropriate limits, the results are shown to reduce to analytical weak- and strong-coupling results, but the model is shown to differ from the molecular dimer model which also permits exact numerical solution for arbitrary coupling. The calculated spectra are interpreted in terms of a number of basic characteristics. Recognition of these characteristic spectral patterns may be helpful in the analysis of vibronically contaminated spectra. For certain combinations of parameter values, the model predicts strong and possibly anomalous solvent and isotope effects. As an example, the vibrational structure of the lowest singlet absorption band of pyrazine is analyzed and shown to indicate evidence for nonlinear vibronic coupling.
Host lattice effects in the EPR spectra of Gd3+ ion in some hydrated lanthanide sulfates
Authors: Malhotra V. M. , Bist H. D. , Upreti G. C.
Published: February 2003

Electron paramagentic resonance (EPR) studies of Gd3+ in single crystals of Ln2(SO4)3⋅8H2O (where Ln=Pr, Nd, Sm, Dy, and Er as well as Y) have been carried out at 9.4 GHz and 297 K. The spin-Hamiltonian parameters have been evaluated for each host. An empirical, linear relationship is found to exist between the magnitude of the Gd3+ spin-Hamiltonian parameter b02 and the ionic radius of the lanthanide host. A similar relationship is found between the ionic radius of the lanthanide host and the total zero field splittings. A nonlinear relationship is observed between the magnitude of the spin-Hamiltonian parameter b22 and the ionic radius of the host lanthanide. In the sulfates the b02, the b22, and the total zero field splitting show a variation opposite to that predicted on the basis of a point charge model. The EPR results on the sulfates have been compared with our results in LnCl3⋅6H2O.
Open shell self-consistent-field theory
Authors: Adams William H.
Published: February 2003

A prescription is given for constructing a single Fock operator for an open shell system when the one-electron, spinless density matrix is diagonal in the occupied orbitals. This Fock operator may be used when there are two or more open shells of the same symmetry, but an upper bound to the total energy is obtained only for the lowest energy state of any symmetry. We apply the prescription to the class of systems considered by Roothaan and Bagus, and show that it is an extension of Roothaan’s coupling operator theory. In calculations on 14 open shell atomic states the Roothaan–Bagus equations required more CPU time to converge than ours in every case, and more iterations in six cases. Level shifting of the proposed Fock operator did not consistently improve the convergence rate.
Radiationless transitions in gaseous nitrogen heterocyclics: Energy dependence of internal conversion in quinoline and isoquinoline
Authors: Okajima S. , Lim E. C.
Published: February 2003

Energy dependence of luminescence from quinoline and isoquinoline vapors indicates that S1→S0 internal conversion, already important at zero excess vibrational energy, becomes the dominant photophysical process with vibrational excitation of the molecule in S1. This is predicted to be a general phenomenon for molecules with closely spaced, lowest energy, nπ* and ππ* singlet states.
Temperature dependence of resonance Raman scattering from O−3 ions in NaClO3 and model for metastable oxygen
Authors: Bates J. B.
Published: February 2003

Irradiation of NaClO3 with γ rays produces O−3 ions on at least two nonequivalent sites. The Raman intensities of the nν1 (n?2) overtones of one set (A) of ions display a marked dependence on the sample temperature between 30 and 60 °K. Model calculations suggest that this effect may be due to a shift with temperature of the distance between the potential energy minima of the 2B1 ground and the 2A2 excited state along the normal coordinate of ν1. The decay with time of the nν1 intensities of the B set of O−3 ions at constant temperature is accompanied by an increase in the overtone intensities of the A set. The kinetics of these changes support a model of the metastable oxygen species consisting of a weakly bound complex of O−3 with O2, [O−3, O2].
Band structure and spontaneous polarization of ferroelectric LiNbO3
Authors: Kam Kam-shing , Henkel John H. , Hwang Hsing-chow
Published: February 2003

The electronic band structure of ferroelectric LiNbO3 has been calculated using a plane-wave–Gaussian basis set and an Xα exchange. The spontaneous polarization of ferroelectric LiNbO3 is then calculated by the assumption that the boundaries of a neutral molecule are represented by minimum surface contours of the electronic charge density. The calculated room-temperature value is 97 μc/cm2, which agrees reasonably well with the experimental value of 71±2 μc/cm2 measured by Wemple et al. with a field reversal method.
Isotope effect on the zero point energy shift upon condensation. I. Formulation and application to ethylene, methane, and fluoromethanes
Authors: Kornblum Zvi C. , Ishida Takanobu
Published: February 2003

A method of evaluating the isotope effect (IE) on the zero point energy (ZPE) shift upon condensation due to the London dispersion forces in the liquid has been formulated. It is expressed to the first order, as a product of an isotope-independent liquid factor and a factor of isotopic differences in gas-phase properties. The theory has been tested by calculating the effective atomic charges for carbon and hydrogen in ethylene, according to the CNDO/2 molecular orbital algorithm, and it correctly predicts the magnitude of the IE on the ZPE shift and the first-order sum rules involving the isotopic ethylenes. However, it fails to explain the difference in vapor pressures of isotopic isomers. The theory has also been applied to the D/H and to the 13C/12C isotope effects in methane and fluoromethanes. The results obtained from the CNDO/2 calculations have been compared with the experimental values of the total infrared absorption intensities and of the IE on the ZPE shift of isotopic methanes. Based on these calculations, the molecular properties that enhance the stronger dispersion forces in the liquid phase between the lighter molecules than between the isotopically heavier molecules, and hence favor a large IE on the ZPE shift, have been deduced.
Laser photodetachment electron spectrometry of methoxide, deuteromethoxide, and thiomethoxide: Electron affinities and vibrational structure of CH30, CD30, and CH3S
Authors: Engelking P. C. , Ellison G. B. , Lineberger W. C.
Published: February 2003

Photodetachment of the three anions CH3O−, CD3O−, and CH3S− by a fixed-frequency argon ion laser at 488 nm and subsequent energy analysis of the photoelectrons yields the photoelectron spectra of these species. From the spectra, electron affinities were determined: E.A.(CH3O) = (1.570±0.022) eV, E.A.(CD3O) = (1.552±0.022) eV, E.A.(CH3S) = (1.882±0.024) eV. From the vibrational structure appearing in the spectra, and the shifts observed upon deuteration, the predominant motion excited in the neutral upon photodetachment of CH3O− and CD3O− is found to be the symmetric hydrogen umbrella bend at 1325±30 and 1010±30 cm−1, respectively. In CH3S both the symmetric hydrogen bend and the carbon–sulfur bond stretch (680±40 cm−1) are excited. From the observed hot bands, some vibrational frequencies of the negative ions are also derived.
Lifetimes of the MgH (MgD) and HgH (HgD) A 2Π states excited by a pulsed dye laser
Authors: Nedelec O. , Dufayard J.
Published: February 2003

Radiative lifetimes are measured by dye laser excitation. The results are, in ns, The MgH result agrees with the theoretical value of 41 ns. The electronic transition moments of the A 2Π–X 2Σ+ transitions agree with those of the s–p transitions for the respective metals.
Electrical conduction through adsorbed monolayers
Authors: Polymeropoulos E. E. , Sagiv J.
Published: February 2003

Electrical conduction was studied in Al/adsorbed monolayer/Al junctions. The adsorbed monolayers were long chain saturated fatty acids (23 to 14 carbon atom chain), short chain perfluorinated fatty acids (10 to 7 carbon atom chain), and n-octadecyl-trichlorosilane. The current observed decreased rapidly with decreasing temperature from 295 K to approximately 77 K at which point the decrease in current with decreasing temperature became very small. At room temperature (295 K) there was no definite relation between the dc conductivity and the length of the fatty acids. At 77 K and lower temperatures, however, the dc conductivity was exponentially dependent on the fatty acid chain length. These results suggest that at 77 K and lower temperatures the conduction mechanism is tunneling through the monolayer. The tunneling barrier height was found to be of the order of 2.8 and 5.2 eV for fatty acids and perfluorinated fatty acids, respectively. By artificially producing molecular holes in monolayers it was shown that in the presence of such holes the current increases by at least one order of magnitude while the effective barrier height is lowered by 10%. Differences between the present results and those previously obtained with monolayers deposited from an air–water interface (Langmuir–Blodgett monolayers) are discussed.
Unlinked cluster effects in molecular electronic structure. I. The HCN and HNC molecules
Authors: Taylor P. R. , Bacskay G. B. , Hush N. S. , Hurley A. C.
Published: February 2003

Extensive calculations on the molecules HCN and HNC have been performed using our recently proposed ’’coupled-pair approximation’’ (CPA) in a basis of nonorthogonal independent-pair natural orbitals. A number of linear geometries are used for both systems, allowing prediction of equilibrium geometry, rotational constants and force constants for the stretching vibrational modes. The CPA values are in substantially better agreement with experimental results (where available) than those obtained from variational CI calculations including all double excitations, and can be generated with little extra computational effort. In addition, several approximate coupled-pair techniques, which require no more effort than a CI calculation, are investigated in order to estimate their accuracy relative to the full coupled-pair method. Using the bond-stretching potentials, we have calculated vibrational energy levels and transition energies. Again, the values obtained by the CPA method are in better agreement with experiment than the CI results—vibrational transitions are predicted to about 90 cm−1 (3%). Inclusion of the unlinked cluster terms is shown to be essential for this agreement, and the use of the CPA in the nonorthogonal IPNO basis results in a compact and powerful formalism within which all important dynamical correlation effects may be calculated.
The relation between orbital SCF energies and total SCF energies in positive atomic ions
Authors: Wu Shinn-Tyan
Published: February 2003

It is contended that the relation proposed by Ryedenberg and Fraga2 regarding the total Hartree-Fock SCF energy of atomic ions is invalid. (AIP)
Vibrational relaxation in the para-H2–4He system: Comparison of coupled-channel, coupled-states, and effective potential methods
Authors: Raczkowski Andrew W. , Lester William A. , Miller William H.
Published: February 2003

Coupled-channel scattering calculations are performed in the energy range of 0.9 to 2.0 eV using both the Gordon–Secrest and the extended Tsapline–Kutzelnigg potentials. Vibrational relaxation rates for p-H2–4He are computed over the temperature range 50 to 2000 °K. Cross sections and relaxation rates are compared to results of coupled-states and effective potential calculations. We find quantitative agreement with coupled-states results and order-of-magnitude agreement with effective potential results. At high temperatures (around 1000 °K), relaxation rates computed using coupled-channel cross sections with both the extended TK and GS potentials agree well with experiment. At low temperatures (50 to 500 °K), the present CC–GS results lie a factor of 4 above the experimental data, while the CC–TK results are at least a factor of 10 below experiment.
Magnetic and thermal properties of terbium ethylsulfate
Authors: Neogy D. , Chatterji A. , Neogy A.
Published: February 2003

A theoretical study of the magnetic and thermal properties of terbium ethylsulfate(TbES) has been made with a crystal field(CF) obtained by slightly modifying the one proposed by Hufner to get the best fit to the observed absorption spectra. The theoretical results have been compared with all the available experimental data on TbES. A good overall explanation to the observed nature of variation of χ∥ and χ⊥ is obtained. The agreement between the theoretical and experimental g values is excellent. A Schottky anomaly obtained at around 0.25 K agrees well with that observed by Hirvonen et al.; another Schottky peak is predicted at about 60 K. One interesting aspect of the present analysis is that almost all the principal features of the magnetic, thermal, and optical properties of TbES at high temperatures as well as at liquid helium temperatures could be explained moderately well with a single CF alone. An analysis of all the experimental data suggests that the separation between the ground singlets, Δ, which profoundly influences the magnetic and thermal properties only at very low tempeatures, is very close to 0.56 K. An experimental investigation of χ⊥ below 100 K and that of the Schottky heat capacity around 60 K is recommended for further confirmation of the CF used in the present work for which the parameters are, C20=110.6, C40=−75.0, C60 =−34.0, and C66=406.0, all in cm−1. The calculations have been carried out in the intermediate coupling scheme.
Quantum corrections to the equation of state of a fluid with square-well plus hard-core potential
Authors: Singh N. , Sinha S. K.
Published: February 2003

A method developed in the previous paper for evaluation of quantum corrections to the equations of state of a fluid is extended to cover the case of the square-well plus hard-core potential. Explicit expressions are given for the first two quantum corrections to the third virial coefficient at high temperature. We find that the quantum corrections to the higher virial coefficients depend on the depth and breadth of the well.
Polarized Raman scattering studies of chain orientation in hydrostatically extruded polypropylene
Authors: Satija Sushil K. , Wang C. H.
Published: February 2003

Polarized Raman scattering measurements have been used to study chain orientation statistics in uniaxial hydrostatically extruded isotactic polypropylene. By investigating the CH2 twisting mode at 1256 cm−1, quantitative results for <P2(cosϑ) ≳ and <P4(cosϑ) ≳ have been obtained. Functions <P2(cosϑ) ≳ and <P4(cosϑ) ≳ are the second and fourth moments of the orientational distribution function, where ϑ is the angle between the chain axis and the direction of extrusion. Alignment of polymer chains has been found to increase with the increase of extrusion ratio. The measured <P2≳ values are found to be in good agreement with the birefringence data. Values of orientational order parameter <P4≳ for an extruded polymer are reported for the first time.
Effects of impurity scattering and transport topology on exciton migration and trapping: An experimental study of quasi-one-dimensional molecular crystals
Authors: Dlott D. D. , Fayer M. D. , Wieting R. D.
Published: February 2003

A series of experiments in which the time resolved triplet x-trap emission from single crystals of 1,2,4,5-tetrachlorobenzene (TCB) at 1.35 °K is presented for various concentrations of the doped-in scattering impurity, d2-TCB. It is demonstrated that exciton-impurity scattering is the dominant process affecting macroscopic exciton transport and trapping. The time-dependent trapping rate is found to be proportional to the inverse square root of the scattering impurity concentration in agreement with theoretical prediction. This implies that transport is close to strictly one-dimensional. Excellent agreement between the data and a model involving microscopically incoherent transport is found, but the data also shows generally good agreement with a model employing microscopically coherent transport. From the concentration dependence and time-dependent trapping curves, an upper bound of ∼5×103 sec−1 can be placed on the frequency of multidimensional steps between one-dimensional chains. Transport is macroscopically diffusive. The basic parameters characterizing long range exciton migration and trapping are obtained.
Thermodynamic stability and phase transitions in systems with a chemical reaction
Authors: Gitterman M. , Steinberg V.
Published: February 2003

Instability in a system with a chemical reaction occurs at those values of the thermodynamic variables which correspond to an appearance of multiple solutions of the law of mass action. As a result of the first order phase transition, the system separates into several phases with different reactant concentrations. Several descriptions of the isomerization reaction are presented, namely, the model of a regular solution, the van der Waals approximation, and the lattice gas model.
Photodissociation spectroscopy of 03−
Authors: Cosby P. C. , Moseley J. T. , Peterson J. R. , Ling J. H.
Published: February 2003

The photodissociation cross section of gas-phase O3− has been measured using a tunable dye laser over a wavelength range of 6400–5080 Å. The cross section exhibits considerable structure which is consistent with dissociation from vibrational levels of a quasibound excited electronic state. Analysis of the structure indicates progressions in two vibrational modes of the excited state. Photodissociation spectra of ions prepared in both excited and ground vibrational levels also yields two vibrational frequencies for the ground X 2B1 state and an apparent rate coefficient for vibrational relaxation in O2. The molecular constants determined here for the two O3− electronic states are compared with those obtained from absorption spectra of the ion in other media. Identification of the dissociating state is discussed.
Laser fluorescence study of vibrational energy equilibration in CH3F:O2 mixtures: ’’Impurity’’ molecules as probes of mode to mode energy flow pathways
Authors: Preses J. M. , Flynn G. W. , Weitz Eric
Published: February 2003

The equilibration of CH3F vibrational modes with O2 has been studied in a CH3F/O2 mixture using infrared laser fluorescence techniques. Under ’’low level excitation’’ experimental conditions, all CH3F modes are shown to come into equilibrium with oxygen at the same rate, indicating that the CH3F modes are tightly coupled by collisions on the time scale of CH3F/O2 equilibration. The concept of vibrational quanta conservation is introduced and shown to be a powerful diagnostic method for mapping vibration–vibration energy transfer pathways in small molecules. A comparison is made of the observed results in CH3F/O2 mixtures with a previous study of CH4/O2.
Crossed molecular beams kinetics: SnI and SnCl recoil velocity spectra from Sn+CH3I,n-C3H7I, and CCl4 and a lower limit for D(SnI)
Authors: Parr Timothy P. , Behrens Richard , Freedman Andrew , Herm Ronald R.
Published: February 2003

Laboratory (LAB) angular and time-of-flight (TOF) recoil velocity spectra of SnI and SnCl products formed by crossing an effusive Sn beam with CH3I, n-C3H7I, and CCl4 nozzle beams have been measured in a molecular beam apparatus equipped with an electron bombardment ionizer–quadrupole mass filter detector unit. Product center of mass (c.m.) recoil angle and energy distributions have been fit to the data by convoluting the c.m.→LAB transformation equations over measured speed distributions for both beams and the instrumental TOF response function. The Sn+CH3I and n-C3H7I reactions proceed via a direct interaction mechanism which favors scattering of SnI into the backward c.m. hemisphere (backward scattering denotes a reversal in Sn-atom direction during the reactive encounter). The SnCl from Sn+CCl4 is scattered predominantly sideways, probably also via a direct reaction mechanism. The Sn+CH3I reaction produces a more sharply backward peaked SnI c.m. product angular distribution with higher product recoil energies than does the Sn+n-C3H7I reaction. All of these reaction characteristics are strikingly similar to the best experimental information which is available for the analogous alkali atom reactions. Qualitative observations are also reported on the relative reactivities of Sn with CH3I,n-C3H7I, CCl4,i-C3H7I, CH3Br, CF3Br, C2Cl4, and SF6. A rigorous lower limit for the Sn–I bond energy is also established, D00(SnI) ?230 kJ/mole.
Mechanism and rates of rotational relaxation of CO2(001) in He and Ar
Authors: Preston Richard K. , Pack Russell T
Published: February 2003

Cross sections and rate constants for rotational relaxation of C02(001) in He and Ar are calculated using realistic (electron gas plus van der Waals) potential energy surfaces and 22 000 classical trajectories. Some propensity for small Δj transitions over large Δj transitions is noted, but there is certainly no Δj=±2 selection rule, and transitions with Δj as large as 30 are important in the relaxation kinetics. Calculated rates are compared with experiment and found to be within a factor of 2 for the total rate of relaxation into a depleted level. Relaxation of levels other than the depleted level is also modeled, and it is found that the present method, in contrast to earlier models, gives excellent agreement with experiment. It is suggested that the transitions used in multiline energy extraction from CO2 laser amplifiers be spread out rather than adjacent.
Differential elastic scattering of He* (21S) by Ar, Kr and Xe: Repulsive rainbows and optical potentials
Authors: Martin D. W. , Gregor R. W. , Jordan R. M. , Siska P. E.
Published: February 2003

Elastic scattering angular distributions of He* (21S) with Ar, Kr, and Xe measured in crossed atomic beams at collision energies from 0.4–2.8 kcal/mole are analyzed using a physically motivated optical potential model. The resulting potentials show some features expected on the basis of the analogous Li–rare gas potentials: monotonically increasing van der Waals well depths ε in the sequence Ar, Kr, Xe, and nearly constant well position rm. However, structure occurs in the repulsive parts of the potentials in the form of a local slope maximum (force minimum) at low positive potential energy, as suggested by other studies. The potential energy at the slope maximum decreases monotonically in the Ar, Kr, Xe sequence, while its position increases monotonically. The slope maximum is manifested in the angular distributions through the appearance of rainbow scattering peaks for Ar and Kr at angles well removed from those at which attractive rainbows are expected, with both repulsive and attractive rainbows evident in the same distribution. The resonance widths are constrained to be simple exponentials. Table I contains all potential parameters derived. Reasonably good agreement is obtained between measured total ionization cross sections and quenching rate constants and those calculated from the optical potentials.
Molecular diffusivities of H2 16O, HD16O, and H2 18O in gases
Authors: Merlivat Liliane
Published: February 2003

Isotopic effects on the molecular diffusion coefficients of H2 16O, HD16O, and H2 18O have been determined by two independent methods. In the first one, the evaporation of liquid water under controlled laminar flow conditions was investigated. In the second one, the transport of water vapor through a diffusion tube was measured. The molecular diffusion coefficient of natural water vapor in nitrogen was redetermined. At 21 °C and P=760 Hg mm, D=0.244±0.004 cm2/sec. For the isotopic molecules we have DHD16O/DH216O=0.9757±0.0009 and DH218O/DH216O=0.9727±0.0007. Agreement between the data obtained in the pure gas phase experiment and the two-phase experiment shows that the condensation coefficients of the isotopically substituted molecules are identical. Interpretation of the isotopic effects on molecule diffusivities indicates that the relative mass differences between H2 16O, HD16O, and H2 18O alone cannot account for the experimental results. This is more important for the D–H substitution in which the asymetric molecule HD16O is formed. Qualitatively, the displacement of the center of gravity of the molecules H2 16O and HD16O in this substitution can explain the observed effect. Interpretation of these isotopic effects in terms of simple kinetic theory of gases indicates that for rigid spherical molecule models with diameters Γ we have the relation ΓH218O<ΓH216O<ΓHD16O. We calculate from the experimental data ratio of the coefficients of diffusion of the three isotopic molecules in air DHD16O/DH216O=0.9757±0.0009 and DH218O/DH216O=0.9727±0.0007.
The gas phase reactions of CN and NO
Authors: Lam L. , Dugan C. H. , Sadowski C. M.
Published: February 2003

Absolute rate constants have been measured for the reactions between CN (v) and NO. Flash photolysis of cyanogen was used to generate CN (v), while laser induced fluorescence was used to monitor this radical. The depletion of CN (v) was considered in terms of the following scheme:

The following values were obtained for the rate constants: CN(v=0), k1=1.2±0.6×10−13 cm3 molecule−1⋅s−1; k3=7.7±1.4×10−31 cm6 molecule−2⋅s−1; CN(v=1), (k1+k2) =2.6±0.5×10−13 cm3 molecule−1⋅s−1; k3=3.0±1.1×10−31 cm6 molecule−2⋅S−1.
Magnetothermodynamics of antiferromagnetic, polarized ferroelectric, ferroelastic β-Gd2(MoO4)3. V. Thermodynamic temperature and other properties with heat introduction below 0.5 °K. Fields to 5 kG along the b crystal axis
Authors: Fisher R. A. , Hornung E. W. , Brodale G. E. , Giauque W. F.
Published: February 2003

Using our previously published data [J. Chem. Phys. 56, 6118–6125 (1972)] on electrically polarized β-Gd2(MoO4)3, with high fields along the b axis above 0.5 °K, as a basis, a series of isentropes from 25 000 to 0, 1000, 2500, and 5000 G was measured, to establish series of entropies at the above constant fields below 0.5 °K. Relative enthalpies at these entropies were established by calorimetric heat introduction using an ’’adiabatic demagnetization-sample isolation calorimeter.’’ The thermodynamic temperature was obtained from T= (∂H/∂S)H. The magnetic moments were determined potentiometrically at close-lying entropies and fields from 0 to 25 000 G. The magnetic susceptibility at zero field was derived. The magnetothermodynamic properties have been tabulated from 0.08 to 0.60 °K at constant fields of 0, 1000, 2500, and 5000 G, for CH, S, (H−Href), (E−Href) and M.
Exciton surface polaritons on organic crystals
Authors: Philpott Michael R. , Swalen J. D.
Published: February 2003

Exciton surface polaritons (ESP’s) are electromagnetic waves which are localized at solid surfaces and have exponentially decaying electric fields on either side of the interface. They are nonradiative, that is, they cannot be excited by photons incident on a plane surface, but they can be excited by an evanescent wave from a prism coupler not in contact with the surface for angles of incidence beyond the critical. We have identified some organic solids that could support these modes at optical and near ultraviolet wavelengths at room temperature. Calculations are presented of the attenuated total reflectivity as a function of angle of incidence at wavelengths within the polariton stop band of the solids. In addition calculations of the intensity of the electromagnetic field in the prism, gap, and sample are given to illustrate the resonance enhancement of the field intensity at the crystal surface when the ESP is excited.
A modified Oregonator model exhibiting complicated limit cycle behavior in a flow system
Authors: Showalter Kenneth , Noyes Richard M. , Bar-Eli Kedma
Published: February 2003

A reversible Oregonator model has been used to simulate recent experimental measurements by Schmitz, Graziani, and Hudson of complicated oscillations by a Belousov–Zhabotinsky system in a stirred tank reactor. The experimental observations indicate chaotic behavior of the small amplitude oscillations occurring between major excursions, but our computer simulation with a small error parameter apparently generates a true limit cycle with six relative maxima before the pattern repeats. The differences between experiment and simulation suggest the chaotic behavior observed experimentally may result from fluctuations too small to measure in any other way. The computations also indicate that reversibility of the reaction of bromate with bromide is important in a continuously stirred tank reactor under conditions such that the (unstable) steady state has a very low concentration of bromide ion.
Photoionization processes at threshold. II. Threshold photoelectron, photoionization, and coincidence ion-threshold photoelectron spectra of BF3
Authors: Batten C. F. , Taylor J. Ashley , Tsai Bilin P. , Meisels G. G.
Published: February 2003

Threshold photoelectron spectra and photoionization efficiency curves have been measured for BF3 from the onset of ionization to 19.7 eV. This range includes four electronic states of BF+3. Vertical ionization energies of 15.96, 17.12, and 19.181 eV are observed for the first, third, and fourth states, respectively. The relative ionization cross sections for production of these states agree with those previously observed in the HeI photoelectron spectrum, but the cross section for ionization in the vicinity of the second state is considerably larger in the threshold photoelectron spectrum. The vibrational structure of the neutral BF3 molecule is not observed in either the first or third electronic states of BF3+, but the symmetric stretching mode progression appears in the band for the fourth state. It appears likely that production of each of the three lowest states of the ion involves a change in molecular geometry with respect to the ground state of the neutral. A breakdown curve was obtained between ionization onset and 16.62 eV using threshold photoelectron–photoion coincidence techniques. The BF+3 ion is stable near the ionization threshold but fragmentation to BF+2 becomes predominant within the envelope of the first electronic state of BF+3. There are no additional stable states of BF+3 within the range of the coincidence measurements.