bluuebunny/crossref_metadata_2025 huggingface dataset:
Deuterium shifts in the high resolution photoelectron spectra of acetaldehyde
Authors: Cvita? T. , Güsten H. , Klasinc L.
Published: February 2003

By comparing the high-resolution photoelectron spectra of acetaldehyde and three of its deuterated derivatives (CH3CDO, CD3CHO, and CD3CDO) in the first system (?), the assignment of six vibrational modes in the ground state of the acetaldehyde ion was possible. The vibronic structure of this system is very sensitive to deuteration of the CH3 or CHO group, showing that the active vibrations include complex motions of all the hydrogen atoms in acetaldehyde. The most prominent vibrations are the CH bending and CH3 deformation modes which reveal that the oxygen lone pair electrons play an important role in determining the bond angles in the acetaldehyde ion.
A generalized diffusion equation for nonuniform fluid systems, with application to spinodal decomposition
Authors: Abraham Farid F.
Published: February 2003

Using a recent microscopic theory to describe the thermodynamics of nonuniform fluids, we develop a generalized diffusion equation which may be used to study phase separation. The linear approximation of this diffusion equation is identical in form to Cahn’s diffusion equation in his study of spinodal decomposition, but the amplification factor is quantitatively different and may be evaluated from the microscopic properties of the uniform fluid state. Predictions of the amplification factor are presented for a single component Lennard-Jones fluid at different points in the spinodal region.
Detonation failure diameter studies of four liquid nitroalkanes
Authors: Tarver C. M. , Shaw R. , Cowperthwaite M.
Published: February 2003

Studies of detonation failure were made on four liquid nitroalkanes (nitromethane, 1,1-dinitroethane, 1,1-dinitropropane, and 2,2-dinitropropane) under the extreme conditions of lead block confinement and Dremin’s weak shell confinement. Shock-induced reaction times and failure wave velocities in decaying detonation waves were also measured and used in the Dremin–Trofimov model to calculate the failure diameters of the these unconfined liquids. The Dremin–Trofimov model gave good values of the unconfined failure diameters when the Chapman–Jouget (CJ) pressures were accurately known and the experimental shock-induced reaction times and failure wave velocities were used in the calculations.
On exponential time decay in relaxation
Authors: Cukier R. I. , Hynes James T.
Published: February 2003

A new mechanism for approximate exponential relaxation is discussed which is significantly less restrictive than the two commonly accepted origins of exponential decay. In this mechanism, the decay rate of a time correlation function or nonequilibrium average is approximated by its exact initial value. A rationale for this approximation is discussed and related to suppression of nonlinear effects in the mode coupling formulation of relaxation. The accuracy of the approximation is demonstrated by comparison with known results for several examples of relaxation. This accuracy is maintained both where standard arguments would imply marked nonexponential behavior and where standard approximations are very poor.
Associative ionization in collisions between metastable helium and atomic nitrogen and oxygen
Authors: Neynaber R. H. , Magnuson G. D.
Published: February 2003

Absolute and relative cross sections were obtained for the associative ionization (AI) reactions He*+N→HeN++e and He*+O→HeO++e by a merging-beams technique from nominally 0.01 to 1.5 eV for the first reaction and 0.01 to 0.2 eV for the second. The He* represents a composite of He(2 1S) and He(2 3S), and the N and O represent composites of ground and metastable states. Although the observation of AI between two excited reactants is rare, evidence is presented for such an observation between excited He and excited N.
Chemical pumping of the water vapor laser. II
Authors: Downey Gale D. , Robinson Dean W.
Published: February 2003

Laser emission at 273.03, 262.33, and 590.24 cm−1 has been observed from flash photolysis of H2 and O3 mixtures, in addition to that at 285.55 cm−1, which was previously reported. All four lines are assigned to laser transitions arising from the (100)131,12– (010)1311,2 resonance in H2O. This lasing has been shown to be pumped by the reaction sequence O3→hν O(1D)+O2(1Δg), (1); O(1D)+H2→OH†+H, (2); H+O3→OH†+O2, (3); OH†+H2→H2O†+H, (4b), where H2O† subsequently emits. The vibrational excitation of OH† is effective in overcoming the activation energy barrier of Reaction (4b).
On the existence of semiclassical eigenvalues for irregular spectra
Authors: Miller William H.
Published: February 2003

It is shown that the semiclassical limit of eigenvalues for a multidimensional system can exist even when a complete set of ’’good’’ action variables (i.e., quantum numbers) do not.
Molecular dynamics study of the effects of ions on water microclusters
Authors: Briant C. L. , Burton J. J.
Published: February 2003

We report a molecular dynamics study of water ion microclusters. This study concerns clusters containing Na+, Rb+, Br−, and I− and up to eight water molecules, and larger clusters containing Cs+ and F− and up to 29 water molecules. For each cluster we calculated the total cluster energy, radial density functions, dipole orientations of water molecules around the ion, and effective ionic radii. The ion lowers the cluster energy by a considerable amount, depending to a great extent on the ionic radius. The ion strongly orients all of the water molecules in the cluster. The coordination numbers of the ions depend primarily on ion size and to a lesser extent on charge sign. Our calculated effective ionic radii are in reasonable agreement with the Pauling radii.
NMR investigations of solid (CH3)3CCOOH (trimethylacetic acid) and (CH3)3CCOOD
Authors: Albert S. , Gutowsky H. S. , Ripmeester J. A.
Published: February 2003

(CH3)3CCOOH (trimethylacetic or pivalic acid) and (CH3)3CCOOD have been investigated in the plastic and brittle modifications by pulsed and continuous wave proton magnetic resonance methods between 77 °K and the melting point (310 °K). For the low-temperature phase of (CH3)3CCOOD, the second moment and spin–lattice relaxation time (T1) of the protons are in agreement with a combination of methyl group (C3) and t-butyl group (C3′) reorientations having activation energies (Ea) of 2.35±0.15 and 4.00±0.25 kcal/mole, respectively. In the high-temperature plastic phase above the transition at 280 °K, overall molecular tumbling with an Ea of 6.0±0.6 kcal/mole governs T1, and self-diffusion with an Ea of 12±2 kcal/mole is evident from the spin–lattice relaxation time in the rotating frame (T1ρ). Also, it is found that T1ρ falls significantly below T1 in the 30° just below the transition. The deviation increases to as much as an order of magnitude as the transition temperature is approached, being about threefold larger for the protonated form of the acid than for the deuterated. This behavior is consistent with the slow onset of molecular tumbling. We suggest that the faster rate in the protonated compound may be attributed to the importance of quantum mechanical tunneling in the breaking and reforming of hydrogen bonds during the tumbling process.
Quasielastic laser light scattering of phosphatidylcholine vesicles
Authors: Chen F. C. , Chrzeszczyk A. , Chu B.
Published: February 2003

Experiments are reported on the angular and the spectral distribution of scattered light for phosphatidylcholine vesicles formed by ultrasonic irradiation under nitrogen in 1 mM CsCl(D2O) solution and subsequent filtration using a VCWP 01300 millipore filter of 1000 Å nominal pore size. Analysis of the time-dependent single-clipped photocount autocorrelation function reveals that a trace amount of about one part per thousand of relatively polydispersed large fragments with an estimated average size of about 1.1×103 Å is contaminating the smaller vesicles. The trace contaminants are very difficult to detect by other more standard methods, such as ultracentrifugation and gel permeation chromatography. Furthermore, the cumulant method is not likely to yield a quantitative determination of the diffusion coefficient and the size of the main vesicle component because very small amounts of large particles actually contribute significantly to light scattering. We have resolved the time-correlation function into two exponentials. By assuming that the phosphatidylcholine vesicles behave like Stokes spheres, we have obtained a reasonable value of 3.1×102 Å as the average diameter of those vesicle spheres.
Repulsive potentials for Cl−–R and Br−–R (R=He, Ne, and Ar) derived from beam experiments
Authors: Kita S. , Noda K. , Inouye H.
Published: February 2003

Repulsive potentials for Cl−–R and Br−–R (R=He, Ne, and Ar) have been derived from the experimental values of integral scattering cross sections of the ions in the energy range 0.5–4 keV. The potentials are well represented by an exponential form, V (R) =A exp(−αR). The numerical values of the parameters, A (eV) and α (Å−1), are as follows: Cl−–He, 255, 2.88; Cl−–Ne, 820, 3.05; Cl−–Ar, 1470, 3.01; Br−–He, 365, 2.92; Br−–Ne, 985, 3.05; and Br−–Ar, 1420, 2.83. The potential parameters are found to be closely related to the electronic charge distributions in the colliding pairs on the assumption of overlapping of the electron clouds.
Rotational excitation of symmetric top molecules by collisions with atoms: Close coupling, coupled states, and effective potential calculations for NH3–He
Authors: Green Sheldon
Published: February 2003

The formalism for describing rotational excitation in collisions between symmetric top rigid rotors and spherical atoms is presented both within the accurate quantum close coupling framework and also the coupled states approximation of McGuire and Kouri and the effective potential approximation of Rabitz. Calculations are reported for thermal energy NH3–He collisions, treating NH3 as a rigid rotor and employing a uniform electron gas (Gordon–Kim) approximation for the intermolecular potential. Coupled states is found to be in nearly quantitative agreement with close coupling results while the effective potential method is found to be at least qualitatively correct. Modifications necessary to treat the inversion motion in NH3 are discussed briefly.
Negative ENDOR study of an irradiated single crystal of triglycine sulfate and its ferroelectric phase transition
Authors: Kotake Yashige , Miyagawa Ichiro
Published: February 2003

With the use of the negative ENDOR technique an x-ray irradiated crystal of triglycine sulfate was studied over the temperature range from 170 to 420 K (Tc=322 K). Within the 11–17 MHz frequency range, signals from more than four different types of protons were detected. Each of these proton signals including the one from H7 is a singlet when T≳Tc, while the signal splits into a double when T<Tc. Although the splitting depends on temperature, no evidence for line broadening was detected. This temperature behavior was explained in terms of a simple quantum-tunneling process, the exchange integral (Γ) of which was estimated to be 102 cm−1 in order of magnitude.
Optical intensities of holmium in tellurite, calibo, and phosphate glasses
Authors: Reisfeld R. , Hormadaly J.
Published: February 2003

The intensities of the electric dipole transitions of Ho3+ in three oxide glasses have been obtained from the absorption spectra in the visible and ir for tellurite glasses, and in the uv, visible, and ir parts of the spectrum for calibo and phosphate glasses. From the experimental values of the oscillator strengths and calculated matrix elements, the Judd–Ofelt intensity parameters were obtained by least-squares analysis. Radiative transition probabilities from the emitting (5S2, 5F4) and 5F5 levels to all lower states were calculated using these parameters. Emission and excitation spectra and the decay times of the (5S2, 5F4) fluorescence were measured. It was found that the fluorescence in tellurite glass has intensities two orders of magnitude higher than in the other two oxide glasses. A concentration dependence study of the fluorescence in tellurite glass was performed. A mechanism for the quenching is proposed.
Zwanzig’s perturbation method applied to the thermodynamic properties of dense noble gases
Authors: Clippe Paulette , Evrard Roger
Published: February 2003

Zwanzig’s perturbation method leads to power series in 1/T for the thermodynamic properties and the compressibility of simple gases or liquids. To check the convergence of these series, the precision of limited 1/T expansions is obtained by comparison with the experimental results for argon and xenon. The expansion coefficients are determined by minimizing the relative mean square deviations. The expansions for the thermodynamic functions have a remarkable precision, even when restricted to three terms (two for the internal energy). The relative deviation is typically of the order of 10−4 to 10−3 for the whole range explored experimentally (from normal conditions to rather far in the liquid state). The coefficients obtained by this procedure are functions of the density. The dependence is very smooth. It is shown that this dependence can be approximated by an expansion in powers of the density, restricted to two or three terms. Analytical expressions are obtained for these terms by means of a cluster type analysis. Three of these coefficients, the expression of which is rather simple, are calculated using the Lennard-Jones potential as an a priori potential, and compared to the results of the fitting. For each coefficient the comparison gives a value of the hard-sphere diameter which is an arbitrary parameter in Zwanzig’s method. The three values obtained in this way are in reasonable agreement.
Rigid cage photodissociation dynamics: A double minimum problem for ICl in Ne and Ar lattices
Authors: Bondybey V. E. , Brus L. E.
Published: February 2003

Excitation into the continuous visible absorption of ICl in Ne and Ar lattices produces both vibrationally relaxed BO+ and A 3π1 fluorescences. Photoselection studies show these emissions result from excitation of the BO+, and not the stronger 1π1, repulsive continuum. Negligible angular reorientation accompanies the photodissociation–recombination process, even for excitation 0.8 eV above the BO+ dissociation barrier. Normalized excitation spectra show that the deactivation process producing v=0 A 3π1 occurs only for excitation above the gas phase dissociation barrier. It is concluded that in the solid the avoided crossing between BO+ and CO+ is preserved, and that the observed dynamics reflect inclusion of an effective matrix potential to give a double minimum in the BO+ state.
O(1S) production from oxygen atom recombination
Authors: Slanger Tom G. , Black Graham
Published: February 2003

An overall rate coefficient of 1.4×10−30 exp(−1300/RT) cm6 molecule−2⋅sec−1 was determined for oxygen atom recombination leading to production of O(1S). This rate coefficient refers either to the recombination of three oxygen atoms (the Chapman mechanism) or to the more conventional recombination of two oxygen atoms with a third body, followed by energy transfer from an activated O2 molecule to a third O(3P) atom (the Barth mechanism). Measurements were made between 200 °K and 300 °K, representative of the thermospheric region in which the green airglow [the 5577 Å O(1S) →O(1D) transition] is observed.
The quantum mechanical behavior of a particle between ellipses
Authors: Switkes Eugene , Russell Eric L.
Published: February 2003

The quantum mechanical behavior of a particle constrained between two confocal ellipses is investigated as a model for cyclic pi systems with nondegenerate energy levels. The solutions of the Schrödinger wave equation for this system are analytic: the Mathieu functions. Effects of boundary curvature and annulus constriction on the wave functions and eigenvalues are determined and discussed. Low lying states may exhibit tunneling in regions of negative angular kinetic energy. As examples of an application to chemical systems, the model is calibrated to reproduce low lying π–π* transitions in several substituted benzenes. The limiting one dimensional problem of a particle-on-an-ellipse is discussed.
Infrared absorption studies on Ni(CN)42− doped NaCl crystals
Authors: Jain S. C. , Warrier A. V. R. , Abha Mrs.
Published: February 2003

Infrared absorption spectrum of NaCl crystals doped with Ni(CN)42− shows the presence of this complex in the crystal in C4v and C2v site symmetry corresponding to the cation vacancy in the 〈100〉 direction above the plane of the ion and along 〈110〉 direction in the plane of the ion, respectively. X irradiation of these crystals produces Ni(CN)4n−, where n=3,4, and 5, giving rise to Ni ion in 1+, 0+, and 1− charge states, as shown by the new set of infrared bands. The infrared absorption from heat treated crystals give evidence for the migration of cation vacancies.
Differential elastic cross sections for high angle electron scattering by He in the intermediate energy region
Authors: Srivastava Santosh K. , Trajmar Sandor
Published: February 2003

Measurements for the angular distributions of elastically scattered electrons from He atoms are reported for impact energies ranging from 5 eV to 75 eV. Differential cross sections for scattering angles between 90° and 135° are also reported. (AIP)
Scattering of high-velocity He atoms by C(CH3)4 and Si(CH3)4
Authors: Amdur I. , Marcus A. B. , Jordan J. E. , Mason E. A.
Published: February 2003

Fast He beams have been scattered by room-temperature C(CH3)4 and Si(CH3)4 to obtain average atom–molecule potentials. The results do not correlate in any simple way with previous work on He–CH4 and He–SiH4; in particular, the present systems cannot be represented satisfactorily as clusters of four CH4 molecules. Moreover, the effective He⋅⋅⋅H potentials deduced from the present results are much larger than the effective He⋅⋅⋅H potential deduced from He–CH4 results. Possible interpretations of these results are discussed.
Photophysics of low lying electronic states of Cl2 in rare gas solids
Authors: Bondybey V. E. , Fletcher Christine
Published: February 2003

Chlorine emission in solid rare gases was studied. The molecules excited into either the BO+u or into the 1Π1 state continuum undergo a fast radiationless transition and vibrational relaxation and emit from the v=0 level of a new low lying electronic state. This new state with vibrational spacing ωe?280 cm−1 is located 650 cm−1 below the B3Π (O+u) and shows a long lifetime of 76 ms in argon. We present arguments for assigning the emission to the 3Π (2u) spin–orbit component. The cage effect on photodissociation and the B state excitation spectrum were also investigated. It is shown that the transition between the bound and continuous absorption region is gradual for guest molecules in solids, unlike the gas phase. While the low vibrational levels show only sharp zero phonon lines, the higher levels broaden and develop intense phonon wings due to increased coupling with the lattice and finally merge smoothly into the continuum.
The probability of spin patterns in the Lenz–Ising model
Authors: Verhagen A. W. M.
Published: February 2003

It is shown that the probability distribution of spin patterns in the Lenz–Ising model may be represented mathematically by a two parameter Markov process without involving the partition function, first determined by Ising . The coupling constant J between the spins and the magnetic field H are expressed in the parameters a and b of the Markov process. The Markov representation thus obtained is then used to find and verify the magnetization per spin derived by Ising and is shown to provide a new method for determining the partition function. The Markov representation found, is also used to develop closed formulas for the two spin probability and for the mean product of spins as a function of the integer distance of their locations.
Temperature dependence of the vibration–vibration de-excitation rates of HF(v=n)+HF(v=0) →HF(v=n−1)+HF(v=1) for n=2−5
Authors: Shin H. K. , Kim Y. H.
Published: February 2003

Temperature dependence of the de-excitation rates of HF(v=n)+ HF(v=0) →HF(v=n−1)+HF(v=1)+ΔE for n=2−5 has been studied for the range of 200 to 2000 °K based on both the energy transfer mechanism through the formation of nonrigid dimers at lower temperatures and through the rotational motion of the colliding molecules at higher temperatures. In the nonrigid dimer model, the energy mismatch is transferred to the restricted translational motion of individual molecules of the dimer, and in the rotational model, it is transferred to the rapid rotational motion of the colliding molecules. Below 300 °K, the de-excitation rate coefficient decreases with increasing n, while it increases with n above 300 °K. This variation has been explained in terms of the magnitudes of ΔE and the vibrational matrix element. A strong negative temperature dependence of the rate coefficient is found for n=2 at low temperatures but no such variation is seen for n=5. For intermediate values of n, a negative but weak temperature dependence is found.
Microwave spectrum of methylfluorogermane, CH3GeH2F
Authors: Krisher Lawrence C. , Morrison John A.
Published: February 2003

Microwave spectra of three isotopic species of CH3GeH2F have been investigated in the region 10 000–30 000 MHz. The height of the potential barrier hindering the internal rotation of the methyl group was determined to be 940±30 cal/mole, from A–E frequency differences, using the PAM method through fourth-order perturbations. Dipole moment components μa= 2.32±0.10 D, μb=1.00±0.10 D, giving a resultant molecular μ= 2.53±0.15 D, were obtained from Stark effect measurements. Bond moments are derived for germanium compounds as μGe→H=1.0 D and μGe→F=3.3 D.
Photodissociation of NO2 in the region 458–630 nm
Authors: Creel C. L. , Ross John
Published: February 2003

Measurements on the photodissociation of NO2 into NO+O2 at wavelengths from 457.9 to 630 nm are shown to be consistent with the reaction NO2* +NO2→2NO+O2. The extent of dissociation is determined by measuring the O2 pressure produced during photolysis with high intensity laser irradiation. The quenching of the photodissociation is determined for the inert gases CO2 and Xe. The energy dependence of the rate coefficient of the above reaction is fitted to an RRK model, which indicates the contribution of a very small number of degrees of freedom (?3) so that it is possibly the energy distribution within a single NO2*, rather than an activated complex, which is important in determining the dissociation. A composite of our data with that of others demonstrates the existence of another dissociative mechanism in the region 430–400 nm. The variation of the rate coefficient with energy of this dissociation of NO2* into NO+O is fitted with a model of activation in many degrees of freedom.
Outer-sphere electron-transfer reactions in polar solvents
Authors: Efrima Shlomo , Bixon Mordechai
Published: February 2003

A model for outer-sphere electron-transfer reactions in polar solutions is suggested. It is based on the idea of dividing the system into two subsystems, a classical solvent and quantum mechanical interacting molecules. The solvent is looked upon as the source of an external field and is coupled parametrically to the reacting species. The model is analytically solved, under some approximations, for the transfer probability. Using a specific macroscopic model of the solvent a usable expression for the rate constant is given. Operational and physical criteria are developed regarding the problems of adiabaticity, nonadiabaticity, and independence on the solvent dynamics.
Debye–Hückel theory for rigid-dipole fluids
Authors: Ramshaw John D.
Published: February 2003

The dipolar analog of classical linearized Debye–Hückel theory is formulated for a finite fluid system of arbitrary shape composed of rigid polar molecules. In contrast to the ionic case, the dipolar Debye–Hückel (DDH) theory is nonunique due to an inherent arbitrariness in the choice of a local field E*. This nonuniqueness is expressed in terms of a parameter ϑ related to the ellipticity of the spheroidal cavity used to define E*. The theory then leads to an expression for the direct correlation function c (ϑ) as a function of ϑ. Only the short-range part of c (ϑ) depends upon ϑ; the long-range part equals −φd/kT for all ϑ, where φd is the bare dipole–dipole potential. This result for c (ϑ) implies the existence of the dielectric constant ε for all ϑ and leads to a formula for ε (ϑ). The DDH results for c (ϑ) and ε (ϑ) are formally identical to the ’’mean-field’’ results of Ho/ye and Stell (obtained for an infinite system by a γ→0 limiting procedure) in which ϑ represents a ’’core parameter.’’
Pressure effects on conformational equilibria. Difference in volume between conformers of 1,1,2-trichloroethane
Authors: Christian S. D. , Grundnes J. , Klaboe P.
Published: February 2003

The effect of pressure on the equilibrium between conformers of 1,1,2-trichlorocyclohexane has been studied using infrared spectra obtained with the diamond anvil cell. Changes in relative intensities of infrared bands show that the population of the more polar conformer (Cs symmetry) increases relative to that of the less polar conformer (C1 symmetry) with increasing pressure. Volume differences for converting the less polar to the more polar conformer are −3.8 cm3/mol in pure liquid and −1.8 cm3/mol in CS2 solution. These results are in agreement with values calculated by K. R. Crook and E. Wyn-Jones [J. Chem. Phys. 50, 3445 (1969)].
Comparison of the Rabitz effective potential and the general potential in the treatment of collisional transfer of rotational energy
Authors: Mehrotra Suresh C. , Boggs James E.
Published: February 2003

A recent paper [Rabitz, J. Chem. Phys. 57, 1718 (1972)] has suggested the use of an effective potential for the computation of collision-induced rotational energy transition probabilities. This comment discusses the nature of agreement to be expected when the method is applied to the calculation of collision-induced lifetimes of a rotational absorption line. (AIP)
Crystal structure refinements with generalized scattering factors. III. Refinement of 1, 1′-azobiscarbamide and melamine, 2,4,6-triamino-s- triazine, at the octopole level
Authors: Cromer Don T. , Larson Allen C. , Stewart Robert F.
Published: February 2003

Single crystal x-ray diffraction data for 1,1′-azobiscarbamide, C2H4N4O2, and melamine (2,4,6-triamino-s-triazine), C3N6H6, have been refined using one-center generalized x-ray scattering factors through the octopole level. This work is an extension of previous work in which the crystal structures of these compounds were refined using one-center dipole and quadrupole population parameters and two-center monopole paramaters to account for the bonding electron density. The one-center octopole model accounts for bonding electron density more efficiently than the two-center model. Radial parameters in the Slater-type functions used to compute scattering factors were also refined. In both compounds, radial parameters about 7% smaller than molecular optimized values were found. Interatomic distances are not very sensitive to the model. In melamine, all C–N distances increase by about 0.004 Å for models with octopoles. Also, if octopoles are used on the nitrogen atoms, all N–H distances become approximately equal and have values consistent with the centroid of the hydrogen atom electron density being displaced about 0.07–0.08 Å into the bond. By using the molecular symmetry and applying appropriate linear constraints to the least-squares matrix, dramatic improvements can be made over a spherical atom model with very few additional parameters. Electric field gradients at the nuclei (i.e., atomic positions determined by the refinement of the x-ray data) have been calculated for all atoms. These calculations included penetration integrals from the multipole functions of all atoms within a 7 Å radius.
The microwave spectrum of chloroacetaldehyde
Authors: Ford Robert G.
Published: February 2003

Chloroacetaldehyde has been shown by microwave spectroscopy to exist in two conformations, one with the chlorine and oxygen atoms cis and the other with these two atoms trans. The rotational constants in the ground vibrational states are, for the cis form: A=15 189.90, B=3858.50, C=3135.55 MHz, and for the trans form: A=33 609.44, B=2693.64, and C=2549.46 MHz. The quadrupole coupling constants are, cis: χAA=−18.03, χBB=−18.20, and χCC=36.24 MHz and trans: χAA=−50.09, χBB=12.56, and χCC=37.53 MHz. For the trans form, six excited vibrational states for the torsion were assigned, and the unusual change in rotational constants with vibrational quantum number was attributed to a small bump in the potential function at the trans position.
Quantum state dependent velocity distribution in Na2 molecular beams
Authors: Bergmann K. , Hefter U. , Hering P.
Published: February 2003

A strong correlation of the velocity distribution in a Na2 beam with the internal energy of the molecules is found, by using the technique of laser induced fluorescence. (AIP)
Magnetic and thermodynamic properties of potassium ferricyanide from 0.4 to 4.0 °K in magnetic fields up to 22 000 G directed along the crystallographic a axis
Authors: Fritz J. J. , Cesarano J. , Goto T.
Published: February 2003

The heat capacity of K3Fe(CN)6 has been measured in fields of 0, 1400, 2800, 7000, 12 000, 16 300, and 21 500 G, from 0.4 to 4 °K, along with observations of intensity of magnetization and of the course of both temperature and magnetization along isentropes. These data are presented along with values of the entropy of the salt, as a function of field and temperature, derived from them. All properties show the effects of strong antiferromagnetic interactions.
On predicting quantal cross sections by interpolation: Surprisal analysis of j
zCCS and statistical j
z results
Authors: Goldflam Rudolf , Kouri Donald J.
Published: February 2003

New methods for predicting the full matrix of integral cross sections are developed by combining the surprisal analysis of Bernstein and Levine with the jz-conserving coupled states method (jzCCS) of McGuire, Kouri, and Pack and with the statistical jz approximation (Sjz) of Kouri, Shimoni, and Heil. A variety of approaches is possible and only three are studied in the present work. These are (a) a surprisal fit of the j=0→j′ column of the jzCCS cross section matrix (thereby requiring only a solution of the λ=0 set of jzCCS equations), (b) a surprisal fit of the ?=0 Sjz cross section matrix (again requiring solution of the λ=0 set of jzCCS equations only), and (c) a surprisal fit of a ?≠0 Sjz submatrix (involving input cross sections for j,j′?? transitions only). The last approach requires the solution of the λ=? set of jzCCS equations only, which requires less computation effort than the effective potential method. We explore three different choices for the prior and two-parameter (i.e., linear) and three-parameter (i.e., parabolic) fits as applied to Ar–N2 collisions. The results are in general very encouraging and for one choice of prior give results which are within 20% of the exact jzCCS results.
Cluster statistics of the lattice gas model in three and two dimensions
Authors: Müller-Krumbhaar H. , Stoll E.P.
Published: February 2003

Cluster statistics in the lattice gas system were evaluated in three dimensions (d=3) below the critical point, and in two dimensions (d=2) above Tc using a Monte Carlo method. Defining clusters as sets of l particles connected by nearest-neighbor bonds, we found remarkable deviation from semiphenomenologic cluster probability formulas below Tc. This deviation is attributed to the formation of spongelike noncompact macroclusters near the percolation temperature Tp<Tc. Above Tc the cluster probabilities in two dimensions may be scaled in the variable ?= (1−Tc/T) lσ with σ=0.53 below Tc. In contrast to the two-dimensional case of T<Tc here the cluster formulas cannot explain the distribution up to clusters with l?2000 particles. For T→∞ (d=2) the cluster probability pl decays as pl∼exp(−constlζ) with ζ?1 for sufficiently large l. This supports recent arguments that the Griffiths singularity for dilute systems is an essential one.
Photofragmentation of linear triatomics
Authors: Atabek O. , Beswick J. A. , Lefebvre R. , Mukamel S. , Jortner J.
Published: February 2003

This paper is concerned with a complete quantum mechanical treatment for the photofragmentation of linear triatomic molecules, going beyond the Golden rule calculation and quasidiatomic approximation. Harmonic valence type potentials are assumed for the bound motions, while an exponential potential describes the unbound motion. An analytical expression for the final vibrational distribution is obtained. This explicitly incorporates the final states interactions which are responsible for the V–T energy transfer during the half-collision following the bond breaking. The two-dimensional Franck–Condon factors are evaluated using the Airy approximation, and a simplified statistical procedure to incorporate rotational distributions is presented. This treatment is applied to the photodissociation of ICN and HCN, and the effects of deuteration on linewidths are analyzed. A fit to the available experimental probability distribution leads to physically acceptable parameters for the repulsive potential.
Regular chemisorption of hydrogen on graphite in the CO–NDO approximation. II
Authors: Dovesi Roberto , Pisani Cesare , Ricca Franco , Roetti Carla
Published: February 2003

The crystalline orbital–NDO method is applied to study regular chemisorption of atomic hydrogen on a graphite monolayer, in the 1:1 hydrogen–carbon atomic ratio. Relaxation of the adsorbent is taken into account. The energy band structure shows that the phase produced by chemisorption is an insulator. Population analysis and mapping of the electron density in real space reveals a direct bond established between each hydrogen atom and the underlying carbon atom. This picture is confirmed when examining the total and projected densities of states.
Vibronic coupling of pyridine in the nπ* excited state
Authors: Mochizuki Yoko , Kaya Koji , Ito Mitsuo
Published: February 2003

The electronic absorption spectra and Raman spectra of pyridine and pyridine-d5 were measured. The vibrational analysis of the nπ* absorption spectrum and the preresonance Raman effect showed that the CH out-of-plane bending vibration ν10a(a2) (of the ground and excited-state frequencies 886 and 331 cm−1 for pyridine) is responsible for the vibronic coupling between the lowest nπ* state and the second lowest ππ* state.
Resonance Raman scattering from metastable O2 molecules in γ-irradiated NaClO3: Excitation profile, polarization measurements, and decay kinetics
Authors: Bates J. B. , Stidham H. D.
Published: February 2003

Resonance Raman effects have been observed with the 1544 cm−1 O–O stretching mode of a metastable O2 species (O2*) in γ-irradiated NaClO3. An excitation profile of the 1544 cm−1 band was determined from the scattering intensity measured with exciting lines from 457.9 to 625.6 nm, and the overtones, 2ν to 4ν, were observed with 457.9 nm excitation. Linear depolarization ratios (ρl) were measured as a function of exciting line wavelength from 457.9 to 514.5 nm. An average value of ρl∼0.42 was found from z (xz) y and z (yx) y scattering, but a pronounced dispersion was observed in ρl for z (yz) y scattering. The change in intensity of the 1544 cm−1 band observed over a period of days showed that the O2* species decays by a first order process at 300 K with a half-life of 1.4 days. A model of O2* consisting of a weakly bound complex [X,O2], where X is a radiation produced radical or ion, is discussed.
High temperature thermodynamics of palladium–hydrogen. II. Temperature dependence of partial molar properties of dilute solutions of hydrogen in the range 500–700 K
Authors: Boureau G. , Kleppa O. J.
Published: February 2003

The thermodynamic properties of hydrogen in dilute solutions in palladium have been studied in the temperature range 500–700 K both by the equilibrium method and by calorimetry. In this range the partial enthalpies and excess entropies of hydrogen increase very significantly with temperature. This suggests the existence of a ’’soft’’ transition for the dissolved hydrogen atoms. The experimental values of the partial excess entropies of hydrogen in palladium may be explained by assuming occupancy by hydrogen of both tetrahedral and octahedral interstitial sites at room temperature or by the modification of the vibrational spectrum of palladium. The further increase of the excess entropy above room temperature may be due to the gradual accumulation of a communal entropy of R between room temperature and 700 K.
Heat capacity and entropy of MnF2 from 10 to 300 °K. Evaluation of the contributions associated with magnetic ordering
Authors: Boo W. O. J. , Stout J. W.
Published: February 2003

The heat capacity of a sample of MnF2 consisting of crystals larger than 2 mm has been measured between 10 and 300 °K. The peak in heat capacity associated with the antiferromagnetic ordering is at 67.30 °K. Measurements with small temperature rise show the shape of the heat capacity curve near the anomaly. The corresponding states approximation for evaluating the lattice heat capacity is tested in regions where the magnetic contributions are calculable. Magnetic contributions to the heat capacity and entropy are tabulated between 10 and 100 °K. Smooth values of the total heat capacity, entropy, enthalpy, and Gibbs energy are tabulated between 10 and 300 °K. Values at 298.15 °K are C°P=15.96 cal °K−1 mole−1, S°=22.04 cal °K−1 mole−1, H°−H°0=3106 cal mole−11.
On the multidimensional surface intersection problem and classical trajectory ’’surface hopping’’
Authors: Stine J. R. , Muckerman J. T.
Published: February 2003

It is found that within the two (electronic) -state approximation, the multidimensional surface intersection problem may be reduced to an equivalent local one-dimensional curve crossing problem. The unique direction along which the adiabatic surfaces avoid a crossing is found to be normal to the ’’surface of avoided intersection.’’ One may apply this result to the surface hopping trajectory method of Tully and Preston without having to define the surfaces of avoided intersection beforehand. Furthermore, the Landau–Zener transition probability at such an avoided intersection may be calculated from information obtained along the trajectory. These results are applied to trajectory calculations of H+2+H2 collisions.
Rotational magnetic moment spectra of a series of tetrahedral molecules
Authors: Ozier I. , Lee S. S. , Ramsey N. F.
Published: February 2003

The molecular beam magnetic resonance method has been used to study the rotational magnetic moment spectrum of each of a series of tetrahedral XY4 molecules in which nucleus X has no spin and nucleus Y has a spin of one-half. The transitions observed involve the reorientation of the rotational angular momentum relative to an external magnetic field in the high-field limit. It is shown that to excellent approximation the transition frequencies depend on only two molecular constants: the rotational g factor gJ and the average spin rotation constant ca of nucleus Y. For each molecule, both constants were determined. The results are for CH4 gJ=+0.31338(4) nm, ca=+10.5(5) kHz; for SiH4 gJ=−0.27036(50) nm, ca=+3.6(6) kHz; for GeH4 gJ=−0.10815(14) nm, ca=+4.0(3) kHz; for CF4 gJ=−0.03124(5) nm, ca=−6.78(6) kHz; for SiF4 gJ=−0.03193(4) nm, ca=−2.45(8) kHz; for GeF4 gJ=−0.02658(5) nm, ca=−1.85(5) kHz. For each tetrafluoride, the sign of ca was taken from earlier theoretical work; all other signs were determined experimentally here. In all cases where comparison values are available, the agreement is good. The application of these measurements to investigations of molecular electronic properties and of nuclear spin relaxation processes is discussed.
Electron–electron double resonance study of magnetic energy transfer between trapped electrons and radicals in organic glasses: Relation between dipolar cross relaxation times and dipolar interaction distances
Authors: Lin D. P. , Feng D. F. , Ngo F. Q. H. , Kevan Larry
Published: February 2003

Electron–electron double resonance (ELDOR) has been used to measure cross-relaxation times between trapped electrons and trapped radicals produced by γ irradiation of 2-methyltetrahydrofuran and 3-methylhexane organic glasses. The cross-relaxation times are measured as a function of temperature, radiation dose, and the frequency difference Δf of the microwave frequencies used. The cross-relaxation times are nearly temperature independent and depend on Δf2 at doses where the spin concentrations approach uniformity; these features indicate the dominance of single step over multistep cross-relaxation processes. Equations have been derived to relate the dipolar cross-relaxation distance to the measured cross-relaxation times, and it is suggested that the cross-relaxation line shape is Lorentzian in magnetically dilute systems. Typical electron–radical correlation distances in these organic glasses are 10 Å.
Hybrid theory calculation of electron–N2 scattering at 5 and 10 eV
Authors: Chandra N. , Temkin A.
Published: February 2003

Hybrid theory results pertaining to e–N2 scattering have been evaluated for differential elastic and first vibrational excitation cross sections at 5 and 10 eV. Comparison with the recent experiment of Chutjian, Srivastava, and Trajmar is good, although there is an indication that the calculated nonresonant (adiabatic-nuclei) contribution is somewhat too small. A short discussion engendered by this point is given.
Natural iteration method and boundary free energy
Authors: Kikuchi Ryoichi
Published: February 2003

The natural iteration technique, which was proposed by the author as a method of solving equations of the cluster variation method, is extended to the case in which variables are subject to subsidiary conditions due to symmetry requirements; the subsidiary conditions are treated by minor iterations at each step of the major iteration. The technique of evaluating the second order transition point for such problems is presented; the technique applies, in general, to problems for which the number of variables is large. As examples, cluster variation methods using a five-point W-shaped cluster and a six-point double-square cluster are presented for the two dimensional Ising model. An improved proof of the scalar product (SP) expression for the boundary free energy is given. The results of the examples are used in the SP expression to evaluate the boundary free energy of the Ising model in order to test the accuracy of the approximations involved.
Luminescence and infrared absorption from laser excitation of trapped electrons in aqueous glasses
Authors: Gillis Hugh A. , Walker David C.
Published: February 2003

When samples of trapped electrons in 9.5M LiCl and 3.1M MgCl2 aqueous glasses at 77 K were bleached by single pulses of 694 nm light from a Q-switched ruby laser, infrared absorption was produced, and luminescence observed in the near ultraviolet and visible. The luminescence had a spectrum centered at 400–420 nm and its intensity was measured over eight decades of time (100 ns to 10 s) following the laser pulse. Over much of this period the luminescence intensity was inversely proportional to the time. No such effects were found for trapped electrons in NaOH or K2CO3 glasses nor in γ-irradiated LiCl or MgCl2 glasses when an electron scavenger was present. This suggests that optical excitation on the low energy side of the visible absorption band causes trapped electrons to be released from their traps, after which they may be temporarily caught in shallow traps from which they tunnel to radiation produced reaction partners, as has been observed during pulse radiolysis.
Analytical evaluation of multicenter integrals for Slater-type orbitals. III. Two-center exchange integrals
Authors: Guseinov I. I.
Published: February 2003

The general two-center exchange integrals with an arbitrary combination of quantum numbers of Slater-type atomic orbitals are evaluated analytically. The final results are expressed through the new auxiliary functions for which have been obtained recurrence relations and analytical formulas.
Magnetothermodynamics of Nd(C2H5SO4)3⋅9H2O. II. Determination of absolute temperature scales and other properties below 0.5 °K with constant fields along the c axis
Authors: Fisher R. A. , Hornung E. W. , Brodale G. E. , Giauque W. F.
Published: February 2003

The magnetic moment of a 3.920 cm diam spherical single crystal of Nd(C2H5SO4)3⋅9H2O has been measured below 0.5 °K after cooling by demagnetization from fields of 25, 15, 10, and 5 kG along the c axis. Small amounts of irreversibility, measured by ’’entropy gain,’’ enabled correction to true magnetic moments on isentropes. Equilibrium between the lattice and electron systems was lost at fields above about 40 kG and temperatures below 0.5 °K. Entropy gain values were recorded for 0, 1000, 2500, and 5000 G on isoerstedics. An ’’adiabatic demagnetization–sample isolation calorimeter’’ was used to measure enthalpy as a function of entropy by means of electrical heating, thus enabling the determination of the thermodynamic temperature scales along the above constant and zero fields as a function of entropy. The temperature dependent component of the initial susceptibility (χ0−χT−ind) obtained from the magnetic moment data leads to the relation (χ0−0.00341) =1.2114 [1+0.0135/ T −2.69×10−4/T2+1.02×10−6/T3] cm3/mole NES, which is valid down to 0.014 °K. Below this temperature the susceptibility is independent of temperature although both the entropy and temperature continue to decrease. It was shown that the magnetic component of the heat capacity tail, after correction for the known nuclear effects of 143Nd and 145Nd, agreed with theoretical calculations based on ideal dipole–dipole interactions, thus confirming that mechanism. CH=0=2.266×10−3/T2−8.45×10−5/ T 3+1.44×10−3 T3 gibbs/mole NES. The limiting low temperature susceptibility was found to be 85.6 cm3/mole Nd3+ which extrapolates to the temperature dependent saturation moment, 10 036 G⋅cm3/mole Nd3+, at a critical field of 117 G. A heat capacity maximum occurred at 0.014 °K. The temperature, relative enthalpy, relative internal energy, heat capacity, and magnetic moment were tabulated as a function of entropy, over the range 0.01–0.5 °K for zero field. Tabulations are also included for 1000, 2500, and 5000 G.
Multiple scattering from fixed scattering centers
Authors: Stocker Verena , Secrest Don
Published: February 2003

General formulas are derived for the T matrix for multiple scattering from an assembly of scattering centers, in terms of the T matrices for the individual centers. These formulas are restricted to scattering from centers which are fixed in the sense that they may move only around equilibrium positions fixed in space. The use of the formulas involves only finite matrix operations. The formulas are valid for any number of centers and scattering at any nonrelativistic energy.
Quantum corrections to the momentum distribution of moderately dense Boltzmann gases. II. Hard sphere potentials
Authors: Rainwater J. C. , Snider R. F.
Published: February 2003

Methods developed in the preceding paper are used to calculate the leading quantum corrections to the momentum distribution of a hard-sphere Boltzmann gas. The correction term is linear in Planck’s constant and is ’’nonexponential’’ for large momenta, for which it is asymptotically proportional to p−6. Such behavior is pathological and suggests that the hard sphere is not a useful model for the calculation of quantum corrections to gas phase transport properties.