bluuebunny/crossref_metadata_2025 huggingface dataset:
A classical statistical theory for chemical reactions
Authors: Wagner Albert F. , Parks Eric K.
Published: February 2003

A trajectory approach is used to derive cross section expressions for the reactive and dissociative products of an A + BC collision in the statistical approximation. The formalism is sufficiently general to accommodate any definition of the strong coupling region. The theory is shown to satisfy time reversal symmetry. The role of canonical variables in statistical theories and the nature of the statistical approximation on a trajectory level are clarified. Problems of implementation are discussed for a variety of strong coupling regions and quantum statistical theories are reviewed in relation to the present classical formalism.
A theoretical study of the strongly coupled T×t Jahn–Teller system
Authors: Shultz M. J. , Silbey R.
Published: February 2003

We investigate the Jahn–Teller effect for strong coupling between a triply degenerate electronic state and a triply degenerate vibrational mode (T×t). We derive approximate analytical expressions for the lowest energy levels for finite but large coupling constant k, and have calculated the splitting between these levels. Our splitting between the lowest T and A states agrees well with the numerical data. We also have derived approximate analytical expressions for the absorption spectrum for all k. Our spectra are in reasonable agreement with the numerically calculated spectra.
Cooperative radiation accompanying photon-exchange interaction between neighboring atoms
Authors: Brown Samuel H. , Chiu Ying-Nan , Raman V. Sethu
Published: February 2003

The radiative processes involving two interacting neutral atomic systems are studied by the third-order scattering matrix formalism of modern quantum electrodynamics. Two bound electrons on different nuclei are allowed to interact through the exchange of scalar, longitudinal, and transverse photons and one system either emits or absorbs radiation in a one-photon process. The third-order S-matrix is reduced to the U-matrix which is rigorously evaluated in the nonrelativistic limit. This evaluation produces new radiative interaction transition operators which are different from those obtained by earlier investigators. These new radiative transition operators presented here should be useful for studying molecular interactions producing cooperative optical phenomena.
Comparison of quantum and experimental rotational transition probabilities for H+–H2 collisions at 3.7 eV
Authors: McGuire Paul , Rudolph Klaus , Toennies J. Peter
Published: February 2003

Rotational energy transfer in collisions of protons with hydrogen molecules is discussed. (AIP)
Infrared studies of HCl/DCl mixed crystals in the first overtone region
Authors: Shala F. , Cahill J. E.
Published: February 2003

Spectra of HCl/DCl mixed crystals in the first overtone region have been measured and are consistent with previous spectra of the pure crystals and their assignments. The most prominent additional feature in the mixed crystals is the ν01HCl plus ν01DCl simultaneous transition. The gas-to-solid shifts in ωe and ωeχe were used to test the Lippincott–Schroeder potential and an analogous potential based on the Morse function. Calculations indicate a large effect of the hydrogen bond interaction on the translational lattice vibrations. The gas-to-solid increases in both the HCl bond length and ωeχe make substantial contributions to the frequency shifts.
On the optical rotation of one linearly polarized beam of light by a second linearly polarized beam of light
Authors: Harris Robert A.
Published: February 2003

It is shown that one beam of linearly polarized radiation may be rotated by a second beam of linearly polarized radiation. The condition for this effect to occur is that the medium in which the two beams mutually interact is optically active.
Molecular effects on inner-shell photoabsorption. K-shell spectrum of N2
Authors: Dehmer J. L. , Dill Dan
Published: February 2003

K-shell photoabsorption spectra of the first-row diatomic molecules N2, CO, and NO are known to depart drastically from the behavior characteristic of K-shell excitation in atoms. Below the K-shell thresholds these spectra are dominated by a single, very intense peak rather than normal Rydberg structure, and the first 10–20 eV of the continuum exhibit a broad band of enhanced absorption, rather than a monotonic decrease. We use the multiple-scattering model to compute the discrete part and the first 100 Ry of the photoionization continuum for K-shell photoionization of N2. This calculation accounts for both novel features described above and shows that they arise from centrifugal barrier effects manifested as shape resonances in high-l components of the final state wavefunctions. These effects are molecular in origin, resulting from the interaction between the photoelectron and the anisotropic molecular field. We also discuss the energy dependence of the photoelectron angular distributions, Kronig structure in the high-energy continuum, bearing of the present results on valence-shell spectra, and the likelihood of widespread observation of shape resonances in ionization processes in other molecules.
Calculations of perturbation parameters between valence states of CS
Authors: Robbe J. M. , Schamps J.
Published: February 2003

Wavefunctions, SCF–CI energies, and properties (dipole moment) of low-lying electronic states of CS have been computed. Using these wavefunctions, ab-initio calculations of parameters characteristic of the perturbations occurring between the valence states of CS have been performed. The results confirm the experimental deperturbation analysis of Cossart and Bergeman. Comparison with the corresponding perturbations in CO is examined and predictions about the magnitude of corresponding perturbations in heavier molecules (CSe, CTe) are reported.
Pressure-broadened linewidths of nitric oxide
Authors: Tejwani G. D. T. , Golden Bruce M. , Yeung Edward S.
Published: February 2003

N2-broadened linewidths of NO in the 5.4 μ band have been measured. This provides a means of determining the quadrupole moment of NO, which has been poorly measured so far. Using the Anderson–Tsao–Curnutte theory of line broadening, and this new value, 2.4×10−26 esu⋅cm2, for the quadrupole moment of NO, self-broadened and foreign-gas (N2 and O2) -broadened linewidths of NO at 300°K for all important infrared transitions are calculated. In the self-broadening calculations, dipole–dipole, dipole–quadrupole, quadrupole–dipole, quadrupole–quadrupole, induced, and dispersion interactions were taken into account. For the case of foreign-gas broadening, dipole–quadrupole, quadrupole–quadrupole, dipole–hexadecapole, quadrupole–hexadecapole, induced, and dispersion interactions were considered. Air-broadened linewidths of NO have also been computed at 200, 250, and 300°K.
Optimized diatomics-in-molecules potential energies for H3 and H4
Authors: Eaker Charles W. , Parr Christopher A.
Published: February 2003

Several variants of diatomics-in-molecules (DIM) theory are used to calculate the potential-energy hypersurfaces (PEH) for H3 and H4. The minimum basis set calculations yield qualitatively incorrect PEHs for these systems. Extension of the basis set to include the excited 2S* state or ionic states of hydrogen can result in a good ’’optimized’’ DIM PEH for H3, but the H4 energies remain poor. Extension of the theory to include triatomic contributions explicitly does not correct the H4 energies in the minimum basis set application.
On the molecular motion in liquid neopentane
Authors: Olsson L. G. , Dahlborg U. , Larsson K. E.
Published: February 2003

The molecular dynamics in liquid neopentane at 265°K has been investigated by cold neutron scattering experiments. The neopentane molecule is spherically symmetric, and the ratio of the moment of inertia and the molecular mass is fairly large. The assumption that the rotational and translational modes of motion are uncoupled should therefore be reasonable. Furthermore, the contribution from the torsional motion of the CH3 group is rather well separated from the scattered spectrum owing to the motion of the rigid molecule. For the rigid molecule motion the following result is then obtained: (1) The translational motion is reproduced only by models, which take the encaging effects into account. The more advanced models based on the memory function approach or on the linear response theory can only partly reproduce the observed spectra. A scaling procedure involving the use of liquid argon data fails to describe the liquid neopentane data. It seems that a model somewhere in between the simpler relaxing cage model and the more advanced memory function models should best describe the data. (2) The rotational motion is not quite reproduced by models assuming infinitely short collisions causing small angular reorientations during a period of free or slightly damped rotations between the collision events. It seems clear that in denser media the collision has to be included in the description of the rotational diffusion. The angular velocity autocorrelation function roughly resembles the linear velocity autocorrelation function, except for differing time scales. It therefore seems probable that an acceptable description of the rotational diffusion should involve not only a memory function characterized by the δ function in time but rather a function similar to those produced to describe translational motion in liquids.
An inverse approach to the theory of fluids
Authors: Fesciyan S. , Frisch H. L.
Published: February 2003

We construct a random process to simulate a model mixture (in any number of dimensions) at equilibrium. The system is exactly soluble but has an underlying potential dependent on macroscopic parameters. We argue that regarded as an approximation to a physical system its behavior can be interpreted as a phase separation. We argue that a general approximate theory of fluids might be built along the lines suggested in this paper.
Pairwise trapping of radicals in single crystals of n-decane irradiated at 1.5 and 4.2°K
Authors: Iwasaki Machio , Toriyama Kazumi , Muto Hachizo , Nunome Keichi
Published: February 2003

The electron spin resonance spectra of single crystals of n-decane-d22, n-decane-h22, and their mixtures irradiated and measured at 1.5 and 4.2°K have been studied to shed light on the mechanisms of alkyl radical formation in saturated hydrocarbons. From the analyses of low temperature spectra and of the spectral changes caused by thermal annealing, it is suggested that almost all alkyl radicals are inherently formed in pairs and that the initial radical pair formation is fairly random especially for distant radical pairs, although there is some preference in the short range reactions for forming very close radical pairs with separation shorter than 6 Å. The predominant radical pairs in deuterated crystals irradiated at 1.5 and 4.2°K have separations ranging 6–25 Å. The spatial distribution of the generation of paired radicals depends upon irradiation temperature. Radical site migration takes place even at 35°K. There is a remarkable mass effect on the spatial distribution of the paired radicals. The deuterated crystals give much smaller spatial distribution. Random scission of the C–H bonds at any carbon atom seems to take place at 4.2°K.
A derivation of the cell cluster theory for harmonic solids
Authors: Huckaby Dale A.
Published: February 2003

The cell cluster algorithm for the calculation of the free energy of harmonic solids is obtained as a resummation of the central moment expansion of the free energy. The nth term in the central moment expansion corresponds to n-step closed walks on the lattice, whereas the nth correction term in the cell cluster expansion corresponds to closed walks of any number of steps which visit n lattice sites.
Nuclear magnetic relaxation of 119Sn, 35Cl, and 127I in two symmetric top molecules, SnCl3I and SnI3Cl, in liquid mixtures
Authors: Sharp Robert R. , Tolan John W.
Published: February 2003

119Sn nuclear magnetic relaxation times were measured for the two symmetric top chloroiodides of tin in the liquid state using pulsed nuclear magnetic resonance. The temperature and magnetic field dependence of T1 and T2 of 119Sn in SnCl3I and SnI3Cl were studied to identify and separate relaxation mechanisms. The longitudinal relaxation rates were found to arise from competing scalar and spin–rotation interactions, while the transverse rates are completely scalar dominated. T1’s of both SnICl3 and SnCl3I show evidence of a maximum in (T1)−1scalar when T2(127I) equals the difference of the 119Sn and 127I Larmor frequencies. This behavior is predicted by Abragam’s ’’scalar relaxation of the second kind.’’ The maximum occurs near the melting points in a 5 kG field and was used indirectly to determine 127I relaxation times. A least-squares analysis of these results permitted direct determination of three tin–halogen scalar coupling constants: J (119Sn–127I) =1638 Hz for SnCl3I, J (119Sn–127I) =1097 Hz for SnI3Cl, and J (119Sn–35Cl) =421 Hz for SnI3Cl. Rotational correlation times and halogen relaxation times were also measured as a function of temperature. The analysis failed to reveal a T1 component due to chemical shift anisotropy for any of the compounds at or below 13.3 kG. A comparison of molecular rotational correlation times with those of the unmixed tetrahalides, SnCl4 and SnI4, indicates that electric dipole forces and shape effects associated with deviations from tetrahedral symmetry are less important determinants of the rotational diffusion tensor than is intermolecular rotational friction resulting from London dispersion forces. The effect on rotational diffusion constants of varying the composition of the medium was examined and found to be small.
Mössbauer spectroscopic studies of frozen aqueous solutions of Fe3+ salts
Authors: Mo/rup S. , Knudsen J. E. , Nielsen M. K. , Trumpy G.
Published: February 2003

Frozen aqueous solutions (FAS) of Fe3+ salts have been investigated by use of Mössbauer spectroscopy in order to study the conditions for formation of glasses. A general discussion of spin–spin relaxation in glasses is given, and we discuss how changes in the spin–spin relaxation time can be attributed to changes in the average separation between the iron ions. In the FeCl3–H2O system, it was found that homogeneous glasses are easily formed when the salt concentration is larger than 3.5 moles FeCl3 per 100 moles H2O. In more dilute samples, ice crystallizes during cooling, while the salt concentration of the solution increases. At low temperatures the crystallization terminates and the remaining liquid solidifies into a glass. During exposure at 200 K, the dilute samples change irreversibly. This is discussed in terms of a metastable phase diagram. The properties of frozen solutions with other glass forming agents such as NO3−, ClO4−, and glycerol are also discussed. In some systems it was found that the states obtained after cooling depend critically on the cooling rate.
Elastic and rotationally inelastic diffraction of hydrogen molecular beams from the (001) face of LiF at 80°K
Authors: Boato G. , Cantini P. , Mattera L.
Published: February 2003

The in-plane scattering of H2 molecules at thermal energies from the (001) face of LiF was studied at low temperatures, by means of nozzle beam techniques. Both elastic and rotationally inelastic diffraction peaks were resolved over a wide range of incident and final angles. Taking into account the properties of the supersonic beam, diffraction probabilities were derived for the observed peaks. A discussion of the results in light of the present theories is given. The large probability of occurrence of rotational transitions in the presence of the surface is pointed out.
Thermal expansion and Grüneisen parameters of a polyoxymethylene crystal
Authors: White G. K. , Smith T. F. , Birch J. A.
Published: February 2003

The linear thermal expansion coefficient α of polyoxymethylene has been measured parallel (∥) and normal (⊥) to the symmetry axis, from 2 to 32 K, 55 to 90 K, and at 283 K. Below 100 K, α∥ is small and negative, while α⊥ is relatively large and positive. The heat capacity has been measured from 2 to 18 K and values have been calculated for the principal Grüneisen parameters γ, γ⊥, and γ∥. The first two are nearly constant at ∼+1.3 from 3 to 80 K, while γ∥ has a value of ∼−1.1 at helium temperatures but becomes positive at higher temperatures.
The elimination of degeneracies in spin systems of magnetically equivalent nuclei by nematic solvents and spin tickling
Authors: Courtieu Jacques , Fagerness Paul E. , Grant David M.
Published: February 2003

Unique new observables for spin systems composed of magnetically equivalent nuclei can be obtained by dissolving symmetric molecules in nematic solvents and then utilizing nuclear magnetic double resonance techniques. Proper manipulation of both the decoupling radiofrequency and the observing FT pulses allows one to prepare the spin system so that a degenerate transition can be separated into its component parts. These techniques are exhibited for the AX2 spin system and can be expected to be very useful in the study of relaxation in more complex coupled systems, such as A3, AX3, A2X2, etc. Also, different relaxation rates for the singlet and triplet transitions can be observed for these two components of the central line. The nonexponential behavior of this particular combination line in the absence of tickling is thereby readily explained.
Ionization enhanced diffusion
Authors: Peak D. , Corbett J. W. , Bourgoin J. C.
Published: February 2003

The general three-dimensional diffusion equations, along with the corresponding tensor diffusivities, are established for the normal ionization-enhanced diffusion mechanism (which is equivalent to a general two-channel diffusion mechanism) and for the Bourgoin mechanism, the latter being explicitly developed for the diamond lattice.
The hyperfine structure of 7LiI by molecular beam techniques
Authors: Jacobson Abram R. , Ramsey Norman F.
Published: February 2003

The v=0, J=1,2 radio-frequency spectra of 7LiI have been observed in a molecular beam electric resonance spectrometer. The measured hyperfine structure parameters are (all units kilohertz): idoine electric quadrupole coupling, eqQI −198478.627(10), −1985503.955(50); lithium electric quadrupole coupling, eqQLi 171.000(30), 171.08(18); idoine spin–rotation, C1 6.8039 (8); lithium spin–rotation, C2 0.754(3); tensor spin–spin, C3 0.627(2); scalar spin–spin, C4 0.062(1); iodine magnetic octupole coupling, ‖eωΩ‖<0.002; iodine electric hexadecapole coupling, ‖ehH‖<0.075 (The first column of values is for J=1; the second, for J=2).
Molecular alignment and photofragment spectroscopy
Authors: Ling Joyce H. , Wilson Kent R.
Published: February 2003

By illumination with polarized light, molecules with a dissociative absorption can be aligned by the selective photodissociation of different M states at different rates, as was first shown by Dehmelt and co-workers for H+2. We have extended this technique to neutral molecules, demonstrating it for a diatomic, IBr pumped by the second harmonic of a neodymium laser at 18 780 cm−1, by observing the recoiling Br fragments with photofragment spectroscopy. Classical and quantum calculations of the selective photodissociation effect give equivalent predictions except in the limit in which only a few M states remain populated. Several methods are discussed for experimentally monitoring the degree of alignment as a function of light flux: (i) the change in fragment flux, (ii) the change in relative strength of two transitions of different symmetry as reflected in their joint angular distributions, and (iii) the change in the shape of the angular distribution of the recoiling atomic fragments for a single transition. The first two methods are demonstrated for IBr molecules. In addition, experiments using two sequential light pulses are suggested, the second pulse monitoring the alignment produced by the first either through the photofragment angular distribution or through absorption. Our results show that at achievable light fluxes, molecules with dissociative transitions of moderate strength can be strongly aligned. Molecular populations can be prepared which contain only a few M states for each J, or even only M=±J. This technique can potentially provide a wide variety of aligned molecules for molecular beam or bulb studies of relaxation as well as elastic, energy transfer, and reactive scattering, and can provide further directionality for photon and fragment angular recoil studies.
Electronic–vibrational energy transfer from Br(4 2P1/2) to HCN, and deactivation of HCN (001)
Authors: Hariri A. , Petersen A. B. , Wittig C.
Published: February 2003

A pulsed dye laser has been used to photolytically produce electronically excited bromine atoms in the 4 2P1/2 state in gas mixtures containing HCN. By monitoring the time resolved fluorescence from the (001) state of HCN, it was possible to determine the rate coefficient for electronic–vibrational (E–V) energy transfer from Br(4 2P1/2) to HCN. Rate coefficients for the deactivation of HCN(001) were also measured for the collision partners HCN, Br2, and Ar.
A shock tube study of the reaction of H atoms with DF
Authors: Bott Jerry F.
Published: February 2003

The reaction rate of H with DF has been measured at temperatures between 2100 and 3900 °K in a shock tube study. The measurements indicate that the sum of the two reaction rates for H+DF→HD+F (rate k3) and H+DF→D+HF (rate k4) has an activation energy of 33 700 cal/mol⋅sec. These data establish upper limits for each of the rate coefficients and should serve as a guide for theoretical calculations.
The effect of the surface structure of Pt on its electronic properties and the adsorption of CO, O2, and H2: A comparison of Pt(100) – (5×20) and Pt(100) – (1×1)
Authors: Helms C. R. , Bonzel H. P. , Kelemen S.
Published: February 2003

We describe studies of the Pt(100) – (1×1) and Pt(100) – (5×20) surfaces with LEED, UPS, AES, and flash desorption spectroscopy. The clean Pt(100) – (1×1) surface is prepared by adsorbing CO, then reacting it off with oxygen ions in the form of CO2. The clean (1×1) surface formed is metastable, converting back to the (5×20) surface at 125 °C. This and other evidence leads us to the conclusion that the (5×20) surface is the clean equilibrium structure. The electronic structure of the (1×1) surface is characterized by a surface state or resonance 0.25 eV below the Fermi level, which is not observed on the (5×20) surface. Although O2 and H2 do not chemisorb at room temperature for exposures less than 102 equivalent monolayers on the (5×20) surface, the (1×1) surface readily chemisorbs O2 and H2. It is suggested that the structure sensitivity of the O2 and H2 chemisorption observed may be due to the corresponding change in surface electronic structure. CO adsorbs on both the (5×20) and (1×1) surfaces. At 0.5 saturation CO coverage on the (1×1) surface a previously unreported C(2×2) LEED pattern is observed. This same LEED pattern can be obtained from the (5×20) surface if a saturation coverage of CO is adsorbed and then partially desorbed at 140 °C.
Correlations in the liquid–vapor interface
Authors: Wertheim M. S.
Published: February 2003

A liquid–vapor system in a gravitational field is examined using the grand canonical distribution functions ρs(r1...rs) and direct correlation functions cs(r1...rs) for a nonuniform system. The limit of zero field is taken under the assumption that ρ1(z) approaches a limit representing a two-phase system. The limiting behavior is discussed in terms of an infinite continuous matrix calculated from c2(r1,r2) and ρ1(z). The vanishing of eigenvalues in zero field implies the appearance of long-ranged correlations. The correlations are shown to be in the horizontal directions, confined to the interface, and macroscopic in range. The situation in an interface is briefly contrasted with the effect of a rigid wall in order to illustrate the fact that spontaneous symmetry breaking rather than the inhomogeneity of ρ1(z) is responsbile for the long-ranged correlations. The invariance properties of a system in a gravitational field are used to give a new derivation of the conventional choice of the dividing surface. A microscopic expression for the surface tension is used to calculate the range of the interfacial correlations.
Effects of secondary ligands on the electronic structure of uranyls
Authors: Walch P. F. , Ellis D. E.
Published: February 2003

The effects of secondary ligands on the electronic structure of uranyl, UO2 ++, are investigated in a perturbing point ion model, making use of the relativistic Dirac–Slater molecular orbital (MO) approach. Variation of ’’crystal-field splittings’’ with primary U–O bond length is explored; relaxation of the uranyl MO’s is taken into account by self-consistent iterations. The theoretical splittings are found to agree rather well with the x-ray photoemission spectroscopy (XPS) data of Veal et al. Comparison is made with optical data and reasons are given for the poor agreement.
A temperature dependence kinetics study of the reactions of Cl (2P3/2) with O3, CH4, and H2O2
Authors: Watson R. , Machado G. , Fischer S. , Davis D. D.
Published: February 2003

The technique of flash photolysis–resonance fluorescence has been utilized to study the temperature dependences of two chlorine atom reactions of considerable fundamental importance to stratospheric chemistry. These reactions have been studied using a wide range of experimental conditions to ensure the absence of complicating secondary processes. The reactions of interest with their corresponding rate constants are expressed in units of cm3 molecule−1  s−1: Cl+O3→ClO O2 (k1), ΔU°298=−164 kJ mol−1, k1 = (3.08±0.30) ×10−11 exp[−(576±60/RT)], (220–350) K; Cl+CH4→CH3+HCl (k2), ΔU°298=−164 kJ mol−1, k2 = (7.44±0.75) ×10−12 exp[−(2437±110/RT)], (218–401) K. In addition, the followong reaction was studied at 300 K: Cl+H2O2→HCl+HO2 (K3), ΔU°298=−56.8 kJ mol−1, k3?5.8×10−13 (±factor 2.0), 300 K. A direct implication of the new rate data is the need to revise downward by a factor of 2.4 to 3 the magnitude of the ozone perturbation predicted by earlier model calculations due to the presence of ClOx species in the stratosphere.
Electronic and vibronic states of uranium hexafluoride in the gas and in the solid phase at very low temperatures
Authors: Lewis W. B. , Asprey L. B. , Jones L. H. , McDowell R. S. , Rabideau S. W. , Zeltmann A. H. , Paine R. T.
Published: February 2003

Complex vibronic structure has been observed in the electric-dipole-forbidden charge transfer absorption bands of solid and matrix-isolated UF6 in the temperature range 8–14 K. These bands have their maximum intensity near 260 and 375 nm. Associated with the 260 nm band are four electronic transitions with origins at 30 331, 31 032, 32 120, and 32 821 cm−1, the first two being observed directly. Two more no-phonon transitions are associated with the weak band at 375 nm, one at 24 564 cm−1 and another at 25 265 cm−1. These levels are assigned via a weak j-j coupling scheme as excitations from the ligand t1uσ orbital to empty uranium 5f orbitals. Uranium spin–orbit coupling in UF6 charge transfer states strongly resembles that of UF6 −. Several progressions in the symmetric stretch frequency ν1=580–595 cm−1 are present which have as their origins various combinations of the above electronic levels with the bending modes ν4, ν5, and ν6 or their overtones 2ν4, 2ν5, and 2ν6. Temperature effects, which account for the principal differences between the gas and solid spectra, are also discussed. A much more intense band at 214 nm is lacking in vibronic structure and is attributed to an allowed charge transfer transition.
Self-diffusion of oxygen in single crystal thorium oxide
Authors: Ando Ken , Oishi Y. , Hidaka Y.
Published: February 2003

Self-diffusion coefficients of the oxygen ion in a ThO2 single crystal were determined in the temperature range 845–1646°C by the gas–solid isotopic exchange technique using 18O as a tracer. The self-diffusion coefficients determined in the higher temperature range were represented as D=5.73×10−2 exp(−49.9×103/RT) cm2/sec and interpreted to be for intrinsic diffusion due to Frenkel-type defects. Those determined in the lower temperature range were represented as D=1.00×10−6 exp(−17.6×103/RT) cm2/sec and interpreted for extrinsic diffusion. By using these data, it was elucidated that the charge carrier for ionic conduction in ThO2 was the oxygen ion. Activation energies for oxygen permeation in ThO2 and for oxidation of thorium metal were compared with that for oxygen self-diffusion in ThO2.
A modified CNDO method for saturated hydrocarbons, amines, alcohols, and ethers
Authors: Kao James W. H. , Chung-Phillips Alice
Published: February 2003

A modified CNDO method for the calculations of binding energies and conformational properties of saturated organic molecules is proposed. Modifications concern the evaluation of the core integrals only. Results of calculations on selected compounds containing hydrogen, carbon, nitrogen, and oxygen using standard geometrical models are reported. For binding energies, the mean deviations between calculated and experimental values are ±1.6 kcal mole−1 for 16 hydrocarbons including adamantane, ±2.0 kcal mole−1 for 12 amines, and ±2.2 kcal mole−1 for 14 alcohols and ethers. The calculated relative energies of conformational isomers are generally acceptable, but those for the skeletal isomers are unsatisfactory. Further comparisons with experimental values are made for the first ionization potentials, the dipole moments, and the equilibrium geometries of a few small molecules.
Density induced transitions in the mobility of electrons in a fluid hydrocarbon
Authors: Dodelet Jean-Pol , Freeman Gordon R.
Published: February 2003

A maximum in the electron mobility versus density is reported for the polyatomic molecular liquid, 2,2-dimethylbutane. Also, enhanced electron scattering is observed in the gas phase at densities just below the critical density. (AIP) 147
The anharmonicity of the OH stretching vibration of hydrogen bonded methanol in binary systems
Authors: Péron J.-J. , Sandorfy C.
Published: February 2003

It has been reported in the literature, that in certain cases the formation of weak hydrogen bonds has a decreasing effect on the mechanical anharmonicity of the OH stretching vibration. We re-examined this problem in the case of methanol with a number of proton acceptors. The result is that for weak hydrogen bonds the anharmonicity constant is practically the same as for the free species, and then it increases with increasing hydrogen bond energy. In no case could a decrease in the value of the anharmonicity constant be confirmed.
Conservation of spin angular momentum in proton transfer to C−(4S)
Authors: Tanaka K. , Betowksi L. D. , Mackay G. I. , Bohme D. K.
Published: February 2003

The rate constants for the proton-transfer reactions of C−(4S) with HCl, HCN, H2S, SiH4, and CH3COCH3 have been measured at 296±2°K with the flowing afterglow technique. The reactions with CH3COCH3 and SiH4 which must involve a spin-forbidden proton transfer, were observed to proceed at low probabilities which can be accounted for by the violation of the Wigner–Witmer spin conservation rule. The probability of proton transfer is observed to be enhanced considerably (×10) for the more exothermic reactions with H2S, HCN, and HCl in which the spin-allowed production of the low-lying excited CH(4Σ) state is energetically accessible.
Spectroscopic studies of hydrated cyano and cyano–halide complexes of platinum (starting materials for the preparation of one-dimensional conductors)
Authors: Ferraro John R. , Basile Louis J. , Williams Jack M.
Published: February 2003

Infrared studies from 4000–80 cm−1 were conducted on various hydrates of cyano and cyano–halide complexes of Pt(II) and Pt(IV). Tentative assignments for the vibrations involving the Pt atom, and for the water modes, were made. The latter assignments were based on a comparison with deuterated salts. Comparisons of the results obtained for these starting materials used in the preparation of one-dimensional electrical conductors, with those of the conductors themselves are given.
Application of ’’multiple basis set technique’’ to the RPA and PVA equations
Authors: Deguchi Kisaburo
Published: February 2003

We propose the ’’modified’’ RPA (MRPA) and ’’modified’’ PAV (MPVA) equations using the ’’modified’’ Hartree–Fock one-particle Green’s function. It is shown that when we choose the ’’modified’’ particle states in the vertex which represents a simultaneous creation (or annihilation) of two particle–hole pairs, there are two cases [(i) and (ii)]. Case (i) is what has been discussed by Ishihara and Poe, and case (ii) is an artificial exchange type of case (i). The MRPA including the contribution of particle–hole EPV ladder diagrams is derived by using case (ii). On the other hand, MPVA including the contribution of particle–hole EPV ring or ladder diagrams is derived by using case (i) or case (ii). Also, the application of case (ii) to the correlation-energy diagram, the self-energy diagram, and the augmented RPA is discussed.
Close-coupling calculations of differential cross sections for elastic scattering and rotational excitation of hydrogen molecules by electrons at 10 and 40 eV
Authors: Truhlar Donald G. , Brandt Maynard A.
Published: February 2003

We have performed close-coupling calculations including two rotational states for electron scattering by hydrogen molecules at 10 and 40 eV impact energies. The effective interaction potential was taken as a sum of the static, exchange, and polarization interactions. With no empirical parameters, good agreement with experiment was obtained for the angle dependences and magnitudes of the differentual cross sections for both pure elastic scattering and rotational excitation except that there are discrepancies in the elastic scattering at small scattering angles where the experiments are least reliable. Variations of the forms of the exchange and polarization potentials were examined and the effect on the cross sections was small.
Electron scattering by N2 at 5 and 10 eV: Rotational–vibrational close-coupling calculations and crossed beam studies of vibrational excitation
Authors: Truhlar Donald G. , Brandt Maynard A. , Chutjian A. , Srivastava Santosh K. , Trajmar S.
Published: February 2003

The ratios of differential cross sections for excitation of the first excited vibrational state to differential cross sections for elastic scattering of N2 have been measured at scattering angles ranging from 20° to 135° at 5 and 10 eV impact energies. Using previously measured and normalized elastic differential cross sections for N2, the ratios have been converted to inelastic cross sections. Laboratory-frame close-coupling calculations using a four-state vibrational–rotational basis set and an effective interaction potential developed previously are reported at both energies. It is shown that the four-state treatment of this potential scattering model can account for the approximate magnitude and the qualitative behavior of the cross sections, but there are some significant quantitative differences between theory and experiment.
Probability of escaping neutralization when the mobility is field dependent
Authors: Mozumder A.
Published: February 2003

The probability of an ion escaping neutralization is calculated for the case where the electron mobility is field dependent and the results are compared with experimental data for neopentane.(AIP)
An analysis of the use of completely minimizing gauge functions in the calculation of the magnetic properties of molecular systems
Authors: Walnut Thomas H.
Published: February 2003

An analysis is made of the general problem of finding a gauge function that completely minimizes the magnitude of the diamagnetic contribution to the magnetic susceptibility of molecular systems having many paired electrons. The following things are found: (1) Many-electron gauge functions are needed for the complete minimization. (2) Except in cases of very high symmetry, the minimizing gauge function necessarily has finite discontinuities. (3) When this gauge is used in the Hamiltonian, the first−order wavefunction is found to be a solution to the unperturbed Schrödinger equation everywhere but at the points where the gauge is discontinuous. (4) Also, when this gauge is used, the off-diagonal elements of the matrix of the first-order Hamiltonian with the unperturbed wavefunctions as a basis can be expressed in terms of integration over only the nodal hypersurface of one of the unperturbed wavefunctions. (5) The minimizing gauge and the probability density define a 3N-dimensional current that has the property of not flowing across any of the nodes of the unperturbed wavefunction.
The effects of hindered rotation of the ammonium ion on nuclear magnetic spin–lattice relaxation
Authors: Watton A.
Published: February 2003

The reorientational mechanism of an ammonium ion, NH4 +, in a solid is modeled as two independent stochastic Poisson processes corresponding to the twofold and threefold reorientations. Autocorrelation functions and the associated power spectra are calculated on this basis and applied to the development of expressions for the proton spin–lattice relaxation times in the laboratory and rotating frames. Certain special cases are considered and some conclusions drawn for the analysis of reorientational mechanisms from nuclear magnetic spin–lattice relaxation results.
Perturbation theory for anisotropic fluid transport coefficients
Authors: Mo Kingtse C. , Starling Kenneth E.
Published: February 2003

A first order perturbation theory for the transport coefficients of anisotropic fluids is derived in the spirit of the Pople expansion for thermodynamic properties. For a specified transport coefficient, the corresponding unaveraged time correlation function is expanded in the anisotropic perturbation potential about the isotropic reference system correlation function. Expansion of all terms in the correlation function, including the propagator and, therefore, the Liouville operator, the flux for the specified transport coefficient, and the distribution function leads to the appropriate perturbation expression for each transport coefficient. The pertinent relations are presented for the coefficients of self-diffusion, viscosity, and thermal conductivity. The applicability of the perturbation theory is demonstrated for viscosity.
Theory of molecular photofragmentation
Authors: Mukamel Shaul , Jortner Joshua
Published: February 2003

In this paper we advance a unified theoretical scheme for the description of direct photodissociation and predissociation of polyatomic molecules. In the case of direct photodissociation we consider energy-resolved variables. i.e., the cross sections for photon absorption, for elastic and inelastic photon scattering, and for the populations of different dissociative channels. For predissociation we consider both time-resolved and energy-resolved experimental observables. The various cross sections relevant for the description of a direct photodissociation process were formally expressed by introducing a distorted wave basis to specify the eigenvalues of the nuclear states on the dissociative potential and advancing a general wave operator which is completely defined within the dissociative potential surface. Explicit expressions for the cross sections were derived with a proper account for radiative coupling effects. Utilizing projection operator techniques we have demonstrated that to a low (second) order in radiative interactions, which costitute an excellent$approximation to the problem at hand, the photodissociation process is isomorphous with a coherent superposition of full collision processes on the electronically excited nuclear potential surface. Similar theoretical techniques are utilized for the study of energy-resolved and time-resolved observables in predissociation. Subsequently, we have invoked a set of systematic approximations to reduce the formal expression to a tractable form. The Heitler K matrix formalism is utilized, and the introduction of the first-order approximation for the K matrix results in explicit expressionss for the time- and energy-resolved observables in photofragmentation, where the cross sections are expressed in terms of products of an initial coupling matrix, the wave operator matrix, and a radiative interference matrix. This formalism is then adopted for the special case of linear photofragmentation of triatomics. Analytical, quantum mechanical expressions for the experimental observables and, in particular, for the vibrational energy distribution of the photofragments were derived for a linear triatomic, where the interfragment replusion is exponential and the diatomic fragment is characterized by a harmonic potential. The effects of intercontinuum coupling on the vibrational energy distribution in the predissociation of XCN (X=H, Cl, Br, and I) molecules in the energy range ∼6.5–10.5 eV were investigated.
Intensities of infrared transitions in N2O and H2CO by electron impact spectroscopy
Authors: Kuyatt C. E. , Mielczarek S. R. , Weiss Morris J.
Published: February 2003

Measurements of relative intensities of infrared transitions in N2O and H2CO have been made using forward inelastic scattering of 100 eV electrons. Agreement with previous infrared and electron impact measurements is satisfactory, showing that infrared intensities can be obtained from electron scattering measurements without the need for pressure broadening or corrections for the spectrometer slitwidth.
Thermoluminescence and electron spin resonance studies of x-irradiated L-alanine:Cr3+ single crystals
Authors: Cooke D. W. , Alexander C.
Published: February 2003

Single crystals of x-irradiated L-alanine:Cr3+ have been studied between 90 and 300 K by electron spin resonance (ESR) and thermoluminescence (TL) techniques. Ultraviolet (uv) photobleaching of the Cr3+ electron traps and L-alanine radical centers was also investigated. The results demonstrate that the x-ray generated radical centers can be destroyed by uv-induced electron transport activity, and this destruction follows first order kinetics. Also, the transformation of the primary neutral radical species to a secondary radical in L-alanine was found not to be induced by intermolecular electron transport. The TL glow was determined to proceed by first-order kinetics at a temperature of 160 K with an activation energy of 0.3 eV and a frequency factor of 1.0×108 s−1. It is suggested that the TL glow may arise from both the decay of the primary cation radical species in L-alanine and the bleaching of the Cr3+ electron traps, and that the Cr3+ impurity acts to enhance the free radical thermoluminescence.
Raman spectrum of (NH4)2TiF6 and trigonal Cs2TiF6
Authors: Ohe W. von der
Published: February 2003

The polarized Raman spectra of (NH4)2TiF6 and trigonal Cs2TiF6 are studied at 85 and at 300 K. All seven Raman active fundamental vibrations of Cs2TiF6 and 13 of the 14 Raman active fundamental vibrations of (NH4)2TiF6 are identified. The missing band of the (NH4)2TiF6 spectrum is assigned to the NH4 + ion rotary normal vibration. The bandwidths of the NH4 + internal and the lattice vibrations of (NH4)2TiF6 increase strongly between 85 and 300 K. It is surmised that the unobserved NH4 + ion rotary band has a large bandwidth at these temperatures, caused by reorientational motions of the ammonium ions. The crystal structure of (NH4)2TiF6 suggests that orientational disorder of the NH4 + ions may exist; however, an order–disorder phase transition involving this disorder cannot take place. The undamped mode frequency of the A1g species lattice antitranslational vibration of (NH4)2TiF6 decreases by 11 cm−1 between the temperatures studied. In the Raman spectra of both crystals the intensity of the Eg (octahedral) species TiF6 2− internal band is 2 to 3 orders of magnitude weaker than the intensity of the other two TiF6 2− ion internal Raman bands. The Jahn–Teller effect, suggested to explain the low intensity of the Eg vibration of several other XY6 complex ions, cannot occur in Cs2TiF6 and (NH4)2TiF6. Two previously published criteria for detecting hydrogen bonding effects in the infrared absorption spectra of complex ammonium halide crystals are manifest in the Raman spectrum of (NH4)2TiF6 also.
Theory of collision-induced forbidden Raman transitions in gases. Application to SF6
Authors: Samson R. , Ben-Reuven A.
Published: February 2003

A recent measurement by Holzer and Ouillon of the symmetry-forbidden Raman bands ν3(F1u) and ν6(F2u) of gaseous SF6 reveals a pressure dependence of the scattering cross section, i.e., the scattering process involves pairs of colliding molecules. The conventional Raman selection rule which holds for the ordinary dipolar polarizability, is violated by higher-multipolar (so called hyper-)polarizabilities. A theory is developed which enumerates all significant single-molecule and pair contributions to the scattering cross section involving various hyperpolarizability tensors. Numerical values of the latter quantities are determined by comparison with experiment. Analysis of forbidden Raman bands can thus be used as a source of information on higher-multipolar optical response functions.
The accuracy of first-order density matrices obtained by electronic structure methods involving the valence electrons only
Authors: Euwema Robert N. , Kahn Luis R.
Published: February 2003

First-order density matrices are obtained from all-electron unrestricted-Hartree–Fock (UHF) calculations and from effective-core-potential valence-electron UHF calculations for the silicon and argon atoms, and for the Si2 molecule. The density matrices are compared by means of their derived X-ray scattering factors, directional Compton profiles, and the charge density, at selected points in k and r space.
Vibrational populations in the F+H2 chemical laser: V→V and V→R,T energy transfer corrections
Authors: Krogh Ole D. , Stone Donald K. , Pimentel George C.
Published: February 2003

The population of vibrational states in the HF laser system is considered. The corections in the vibrational energy transfer are postulated. (AIP).
Radiationless relaxation in solids as measured by a heat-pulse technique
Authors: Robin M. B. , Kuebler N. A.
Published: February 2003

The heat resulting from the radiationless relaxation of electronic excitations in solids can be followed thermometrically on a submicrosecond time scale using a superconducting bolometer as detector. Details of the technique are described, and illustrated with the relaxation profiles of Cr(III) ion excited in Al2O3, LiTaO3, and MgO host lattices.