bluuebunny/crossref_metadata_2025 huggingface dataset:
Associative ionization in U + O and U + O2 collisions
Authors: Fite W. L. , Lo H. H. , Irving P.
Published: February 2004

Collisions between thermal energy uranium atoms and oxygen atoms and molecules have been studied in four experiments. A triple crossed beam experiment has determined that the ratio of effective cross sections for the associative ionization processes U + O → UO+ + e and U + O2 → UO2 + e is 97±20. An experiment measuring the number of ions formed per unit length by uranium atoms passing through O2 has determined that the absolute cross section for U + O2 → UO2+ + e is 1.68±0.27 × 10−17 cm2. A total attenuation experiment indicates that the total reaction cross section between U and O2 is 1.78±0.45×10−15 cm2, implying that over 99% of the reactions lead to the neutral products UO+O while less then 1% give associative ionization. A modulated beam mass spectrometry experiment, employing phase spectrometry, indicates that the activation energy for U + O2 → UO2+ + e is extremely small if existent at all. Two Appendices treat the relations between effective cross sections as measured in various experiments to true cross sections as derived from theory and the generation of phase shifts in modulated beam experiments where a beam is detected by reactions with a Maxwellian gas.
Infrared reflection from the internal mode of crystalline lithium hydroxide
Authors: Carlson R. E. , Decius J. C.
Published: February 2004

In the lithium hydroxide crystal, the transition moment of the A2u internal mode lies normal to the naturally occurring crystal face, so that the transverse frequency for the mode may not be directly observed in an infrared transmission spectrum. It has been demonstrated previously that under this condition, infrared reflection spectra using transverse magnetic polarization at finite incidence angles show a reflection maximum above the longitudinal frequency. A comparison of theoretically generated reflectivity curves with the experimental spectra reported here yield values for the longitudinal and transverse frequencies. The dipole derivative for the hydroxide stretching mode calculated from these frequencies is in good agreement with previously reported values.
Study of the electronic structure of molecules. XXI. Correlation energy corrections as a functional of the Hartree-Fock density and its application to the hydrides of the second row atoms
Authors: Lie George C. , Clementi Enrico
Published: February 2004

A semiempirical functional of the Hartree-Fock density is presented for estimates of the correlation energy correction. The functional is similar to the one proposed by Gombas and is (a) parametrized with reference to few atomic systems, and (b) is modified as to reproduce the atomic correlation correction not only for closed but also for open shell systems. The functional is then applied to the ground state function of the hydrides LiH(1Σ+), BeH(2Σ+), BH(1Σ+), CH(2Π), NH(3Σ−), OH(2Π), and HF(1Σ+). Several internuclear distances have been considered for each hydride, scanning the potential energy curve from the repulsive region to the dissociation products (∼ 10 a.u.). For these points a simple multiconfigurational function (consisting of no more than three configurations) was computed to obtain Hartree-Fock functions with proper dissociation behavior (H-F-P-D functions). The semiempirical functional was applied both to the traditional H-F functions and the H-F-P-D functions in order to study how to select a proper reference wavefunction. The computed binding and a number of spectroscopic constants from vibrational and rotational analysis are discussed. The new semiempirical functional of the electronic density appears to be a rather promising one for reliable estimates of the correlation energy correction.
Dielectric and pressure virial coefficients of imperfect gases: Hexadecapolar system
Authors: Hosticka Charlene , Bose T. K.
Published: February 2004

Dielectric and pressure virial coefficients of SF6 have been determined at 323.3, 348.3, and 373.9 K. Attributing the temperature dependent contribution of the second dielectric virial coefficient to dipole moments induced in one molecule by the hexadecapole moment of a second gives (5.40±0.7)×10−41 esu · cm4 for the molecular hexadecapole moment of SF6. The hexadecapole moment of SF6 derived from pressure second virial coefficients is (5.75±0.3)×10−41 esu · cm4.
Mössbauer resonance studies in magnetically diluted Eu–Ca hexammines
Authors: Parker F. T. , Kaplan Morton
Published: February 2004

The Mössbauer effect in 151Eu is used to examine the mixed hexammines Eux Ca1−x(NH3)6, with x = 0.012 and 0.092, and comparison is made to the apparent lack of conduction electron effects on the europium ionic and nuclear properties in Eu(NH3)6. In zero external magnetic field, very broad lines are seen, indicative of weakened dipolar spin relaxation. For the 1.2% Eu sample, the single Lorentzian linewidth at 4.2 K is the broadest yet seen, 19 mm/sec, with little structure evident. The linewidth decreases with small applied fields, becoming some 30% narrower. Analysis of small field data in terms of slow-relaxation-limit parameters yields an effective axial electronic-splitting parameter D≈ + 30 mK at 4.2 K. Spectra obtained in large external fields yield hyperfine fields Heff = − 326 (3) and − 330 (3) kOe for the 1.2% and 9.2% samples, respectively. These values are in good agreement with Heff = − 324 (3) kOe obtained with Eu(NH3)6, quite similar to ESR results obtained in dilute Eu–NH3 solutions, and indicate the lack of conduction-electron-polarization effects on the hyperfine fields. Intermediate field spectra are analyzed in terms of relaxation. The Eu(NH3)6 rates and the rates obtained in the dilute samples at small external fields are consistent with an f1/2 relaxation rate, where f is the Eu fractional concentration. For larger fields, the rate in the dilute samples slows as a function of applied field divided by the temperature. This is qualitatively explained by ionic line narrowing, with concomitant loss of ionic transitions due to energy conservation requirements. The data for the 1.2% Eu sample in high fields are also used to estimate an upper limit of Korringa relaxation to the conduction band, yielding a result considerably smaller than expected for Eu2+ in conductors.
Theory of reaction product velocity distributions
Authors: Whipple E. C.
Published: February 2004

A general method has been developed for calculating reaction product velocity distributions for bimolecular inelastic reactions. The method is based on the treatment of the reaction as a collision process and is an extension to inelastic collisions of the usual collision integral in the Boltzmann equation. The result is applicable to arbitrary velocity distributions of the initial reactants and to arbitrary differential cross sections for the reaction. The method is illustrated by calculating the product velocity distributions for hard sphere reactions and for isotropic constant mean-free-time reactions, with Maxwellian velocity distributions for the initial reactants. These results are compared with the unimolecular decomposition approximation. The application of the method to the interaction of crossed beams and to the interaction of a beam with a Maxwellian gas is also discussed.
Avoided crossings in diatomic molecule bound states: Model calculations for coupled harmonic oscillators
Authors: Redding Rogers W.
Published: February 2004

Calculations are described in which interacting pairs of harmonic oscillator potential functions are used to simulate the avoided crossing problem in bound states of diatomic molecules. Results for three such models using a new method proposed by Gordon are compared with those obtained by standard methods.
Electric field broadening of the 1A1(2) transition in azulene
Authors: Mathies Rich , Albrecht A. C.
Published: February 2004

The change in the dipole moment of azulene upon excitation from the ground to the second excited state is deduced from electric field broadening experiments. A detailed study of the 0–0 band of this transition in a rigid solution of 3-methylpentane (3-MP) using polarized light shows that the change in the dipole moment (Δμ) is 1.23±0.14 D and that the transition moment is parallel to this vector. This value is compared with the results of the Stark effect in mixed crystals and with molecular orbital calculations. A less detailed study has been performed on the vibrationally excited bands of this transition. In addition, calculations of the polarizabilities of the first two excited states of azulene are reported and compared with recent experimental results in mixed crystals.
Stability analysis of a model reaction network using graph theory
Authors: Clarke Bruce L.
Published: February 2004

The stability of a model chemical reaction network which is unstable with respect to both homogeneous and inhomogeneous perturbations far from equilibrium is analyzed using a graph theoretic approach. Equations for the boundary of stability and the frequency and wavelength of the unstable perturbation at the boundary are obtained by interpreting the dominant graphs in the stability inequality geometrically. It is found that perturbations within a broad of wave vectors become unstable together at the point of marginal stability and that usually across this band ω(k) ∝ k−1. Of the hundreds of graphs in the stability inequality only a very few play a role in the instability. Most of these are abnormal cycle graphs through the autocatalytic vertex and the reminder are maximum overlap graphs from the diagonal term of the Hurwitz determinant. The three destabilizing graphs give insight into the normal modes associated with the three unstable regions. Comparison of this analysis with an earlier computer analysis of the same model network clearly demonstrates the power of the graph theoretical approach.
Self-diffusion coefficients and rotational correlation times in polar liquids. VI. Water
Authors: O'Reilly D. E.
Published: February 2004

A new model for liquid water is presented. As a first approximation (A) the liquid is considered as a quasi-hard-sphere fluid and the scaled particle theory is employed to calculate the work (w) required to create a vacancy of molecular dimension using the observed density of water. In the second approximation (B) a quasilattice model is invoked which is based on the Ice VII structure and the density and isothermal compressibility of water are computed using the values of w calculated in approximation A. A final approximation (C) is based on the Ice Ic structure. In this approximation the temperature and pressure dependence of self-diffusion, viscosity, and nuclear relaxation times are evaluated. The agreement of the model with experiment is good and only a few parameters enter into the calculation, and these have magnitudes that are physically reasonable. Results of molecular dynamics calculations on water obtained by Rahman are presented which are interpreted to show that molecular rotation in water occurs in rather large excursions of relatively short time duration. For times between the large angular reorientations, librational motions occur which do not result in a large amount of net molecular reorientation. It is proposed that the large amplitude reorientations result from hard molecular collisions. These results confirm the conclusions of earlier work on other liquids. The anisotropy of the rotational correlation time of rank 2 (τ2) in an asymmetric top molecule is derived based on the finite step rotation hypothesis. Available experimental values of τ2 for liquid water are summarized and compared with the results of the model.
Investigations of ESR superhyperfine structure for the cubic Gd3+ center in CaF2, SrF2, and BaF2
Authors: Lee Sook , Bevolo Albert J. , Yang Chi-Chung
Published: February 2004

A partially resolved superhyperfine structure has been observed in the ESR spectra of the cubic Gd3+ center in CaF2, SrF2, and BaF2. This superhyperfine structure has been satisfactorily analyzed in terms of the interaction of the Gd3+ ion with its eight nearest-neighbor 19F nuclear spins associated with the cubic Gd3+ center. The values of the fluorine superhyperfine interaction constants T∥ and T⊥ obtained by this analysis are (in units of MHz): T∥=7.5±0.2, T⊥=−6.7± 0.2 for SrF2; T∥=8.0±0.3, T⊥=−5.9± 0.3 for BaF2; and T∥=8.1±0.2, T⊥=−7.1± 0.2 for CaF2 (which agree with those determined previously by ENDOR).
Molecular beam and trajectory studies of reactions of H+ with H2
Authors: Krenos J. R. , Preston R. K. , Wolfgang R. , Tully J. C.
Published: February 2004

We have employed two complementary techniques, molecular beam experiments and ``trajectory surface hopping'' theory, to investigate proton-hydrogen molecule scattering at relative energies between 1 and 7 eV. Absolute cross sections, product translational energy distributions, and product velocity contour diagrams have been obtained from both theory and experiment for the H+ + D2 and D+ + HD isotope arrangements. Agreement is excellent, particularly for a theory which involves no empirical information and no adjustable parameters. By combining results from experiment and theory we have been able to develop a fairly complete, reliable, and simple picture of the dynamics of this elementary collision process. For relative energies below about 3 eV the reaction involves a short-lived collision intermediate, whereas above 4 eV it proceeds by a predominantly direct, impulsive mechanism. Above 5.5 eV momentum transfer is well represented by a hard-sphere collision model involving only short-range repulsive forces. The avoided intersection of the two lowest singlet potential energy surfaces of H3+ is of primary importance in determining the partitioning of energy among products, the likelihood of electronic transitions, the angular and velocity distributions of products, and the competition among various rearrangement, charge transfer, and fragmentation channels.
Effect of temperature on the rates of reaction of excess electrons in liquid hydrocarbons
Authors: Beck G. , Thomas J. K.
Published: February 2004

The effect of temperature on rates of reaction of electrons with biphenyl in n-hexane, cyclopentane, and iso-octane has been studied. The experimental data fit an Arrhenius plot of log k vs 1/T giving activation energies of 6.4, 4.2, and 0.51 kcal/mole, and A factors of 4.4 × 1016, 4.9 × 1015, and 3.2 × 1013 in n-hexane, cyclopentane, and iso-octane, respectively. The A factors for the reactions are discussed in terms of the quasi-free nature of the electron.
Time dependent effects in microwave spectroscopy: Theory and double resonance experiments on OCS
Authors: Brown Steven R.
Published: February 2004

The time dependence of the weak field microwave absorption spectrum of the J = 1 → 2 transition of OCS under amplitude modulated pumping of the J = 0 → 1 transition has been observed with submicrosecond resolution by using a 100 MHz bandwidth video spectrometer and a multichannel signal averager. In order to relate the observed time dependent power absorption to the dynamic process of rotational energy transfer a theory relating the power absorption and the energy level populations has been developed. It is found that the time variation of the power absorption is not simply proportional to time variation of the population difference between the two levels connected by the weak field. Equations are derived which describe the time evolution of these quantities immediately following inception and termination of the pump signal. It is found that, for practical reasons, the period immediately following termination of the pump signal is the best time to study collisional energy transfer. Observation of the pressure dependence of the absorption relaxation during this period led to a value of Pτ = 28.1 μ · μsec for the product of the pressure and the mean time between rotationally inelastic collisions.
Influence of the nuclear spin on the thermomagnetic torque
Authors: Burgmans A. L. J. , Wang F. C. , Adair T. W.
Published: February 2004

The thermomagnetic torque in rarefied polyatomic gases is a result of the precession of the molecules around the direction of the external field. In the case of a strong magnetic field (Paschen-Back regime) this precession is determined by the rotational angular momentum of the molecules. In weak magnetic fields the angular momentum of diamagnetic molecules is coupled to the nuclear spin which influences the molecular precession and thus the thermomagnetic torque. In this paper experiments on the thermomagnetic torque in HD, n-D2, and n-H2 are reported in both strong and weak magnetic fields. Large deviations from an H / p behavior are found as a consequence of the spin coupling.
Laser photodetachment determination of the electron affinities of OH, NH2, NH, SO2, and S2
Authors: Celotta R. J. , Bennett R. A. , Hall J. L.
Published: February 2004

Using a fixed frequency argon ion laser we have studied the energy spectra of electrons photodetached from OH−, NH2−, NH−, SO2−, and S2−. We determined the following electron affinities: EA(OH)= 1.829−0.014+0.010 eV, EA(NH2)=0.779±0.037 eV, EA(NH)=0.38±0.03 eV, EA(SO2)=1.097±0.036 eV, and EA(S2)=1.663±0.040 eV. Additionally, the angular distribution anisotropy parameter β was measured for OH− and NH2− at 4880 Å, as −0.993 ± 0.040, and 0.027±0.012, respectively, and information about negative ion vibrational constants is presented.
Raman spectra of gases. XI. Methyl torsional overtones in the ethyl halides
Authors: Durig J. R. , Bucy W. E. , Carreira L. A. , Wurrey C. J.
Published: February 2004

A series of peaks in the Raman spectra of gaseous CH3CH3, CH3CH2Cl, CH3CH2Br, CH3CD2Br, CD3CH2Br, CD3CD2Br, CH3CH2I, CH3CD2I, and CD3CH2I have been observed and assigned to the torsional overtones, (Δν = 2) of the methyl group. From these spectroscopic data, barriers to internal rotation have been calculated for the ethyl halides. For the compounds where the barriers are accurately known from previous work, the values obtained in this study agree quite well. The value for the internal rotational barrier in ethyl iodide is 3.67 ± 0.01 kcal/mole, which is considerably higher than the value previously reported from microwave studies. It is shown that Raman spectroscopy can be a convenient technique for obtaining torsional barrier heights when one uses the Δν = 2 quantum jumps of the torsional motion.
Molecular Zeeman effect, electric dipole moment, and boron nuclear hyperfine coupling constants in HBS
Authors: Pearson E. F. , Norris C. L. , Flygare W. H.
Published: February 2004

The zero-field microwave spectra of the J =0 → J = 1 transitions in H11B32S, D11B32S, and D10B32S have been observed under high resolution to give the boron nuclear quadrupole coupling constants of eqQ = −3.72±0.03 MHz for 11B and eqQ = −7.91±0.03 MHz for 10B and the nuclear magnetic spin rotation constants along the axis perpendicular to the internuclear axis of M⊥=−7.2 ± 3.0 kHz for 11B and 1M⊥=−2.6 ± 1.0 kHz for 10B. The magnitude of the electric dipole moment was measured by high electric fields (Stark effect) to give |μ| = 1.298 ± 0.005 D. High magnetic fields (Zeeman effect) were used to measure the molecular g values and magnetic susceptibility anisotropies. The results are g⊥=−0.0414 ± 0.0002 and χ⊥−χ∥=7.2 ± 0.5 × 10−6 erg/G2· mole for H11B32S and g⊥=−0.0356 ± 0.0002 and χ⊥−χ∥=9.8 ± 2.1 × 10−6 erg/G2· mole for D11B32S. The resultant molecular electric quadrupole moment is Q∥ =2.7±0.6 × 10−26 esu · cm2 and the g values from the H11B32S–D11B32S isotopic pair were used to determine the sign of the electric dipole moment, + HBS −.
Selection of self-consistent-field orbitals
Authors: Gilbert T. L.
Published: February 2004

A procedure introduced by Davidson for selecting orbital bases on the occupied and virtual Hartree-Fock manifolds is shown to be equivalent to a procedure introduced by Adams.
Dielectric relaxation in water in the neighborhood of 4°C
Authors: Grant E. H. , Sheppard R. J.
Published: February 2004

The complex permittivity of water has been measured at seven temperatures between 3 and 5°C over a frequency range of 0.4–4 GHz. The data are analyzed first in terms of a small but significant distribution of relaxation times of magnitude larger than that observed previously and then as two separate Debye process having relaxation times separated by a factor of ∼2. It is shown that one possible interpretation of these observations is that a bond breaking process takes place in which the rate of formation of one bonded molecules from two bonded molecules depends upon whether the latter are bonded symmetrically or unsymmetrically. The value of the high frequency permittivity (ε∞) calculated from this model is shown to agree well with experiment. There is no evidence of any abrupt changes (``kinks'') greater than random experimental error in the temperature variation of the dielectric parameters of water between 3–5°C.
High resolution photodetachment study of OH− and OD− in the threshold region 7000–6450 Å
Authors: Hotop H. , Patterson T. A. , Lineberger W. C.
Published: February 2004

The photodetachment of OH− and OD− ions has been studied in the range 7000–6450 Å, utilizing a tunable, narrow-bandwidth (0.5–1 Å) dye laser as the light source. A detailed comparison of the observed cross section with model calculations is made, yielding the following results: E.A.(OH)=(14 723±15) cm−1, E.A.(OD)=(14 703±15) cm−1. The observed isotope effect for the electron affinity can be ascribed almost entirely to differences in the position of the ground rotational state in OH(2Π3/2) and OD(2Π3/2); the implications of this result for the vibrational frequency of the negative ions are discussed. The energy dependence of the observed cross section indicates the influence of the electron-permanent dipole moment interaction in the final channel on the threshold behavior, which is found to be sharper than that expected in the absence of such an interaction.
Light scattering due to spontaneous fluctuations in a binary reacting fluid mixture
Authors: Huang Ming-Nan , Schwarz W. H.
Published: February 2004

Light scattered from a binary, viscous, heat conducting, diffusive, and reacting mixture by spontaneous fluctuations was theoretically examined using the hydrodynamical approach with a generalized form for Fick's law that was obtained by a thermodynamical theory based on the entropy inequality. An additional inertial-diffusive term occurs in the diffusion equation and results in another Lorentzian contribution to the Rayleigh line and also adds to the non-Lorentzian contribution to the Brillouin doublet. Explicit results for the autocorrelation functions and spectra are presented for (1) a binary, viscous, diffusive, thermally conducting mixture without reaction and (2) a binary, viscous, thermally conducting reacting mixture without diffusion. Comparison of the theoretical spectrum for a gaseous xenon-helium mixture to experimental data demonstrates the importance of the inertial-diffusive term and provides an explanation of the failure of the classical hydrodynamical theory. In addition, the case of acetic acid was treated as a reacting binary mixture of monomers and dimers, and the theoretically calculated Landau-Plaszek ratio was compared to experimental data.
On the implication of the theory of Ichimaru: Physical properties of degenerate electron liquid
Authors: Jain Madhu , Jain S. C.
Published: February 2004

Calculations are performed for various physical quantities such as the pair correlation function, compressibility, etc., for an interacting electron liquid by solving the set of self-consistent equations of the theory of Ichimaru. Comparison is made with other recent theories. It is found that even though being physically more sound, it does not give quite satisfactory results of g(r) and the compressibility sum rule in comparison to both the original theory of Singwi et al. and its modified version by Vashishta and Singwi. A modification in the theory of Ichimaru is discussed which may lead to remarkable improvement in the results.
On the structure of the 14N nuclear quadrupole resonance line of hexamethylenetetramine
Authors: Colligiani A. , Ambrosetti R. , Salvetti F.
Published: February 2004

The structure of the hexamethylenetetramine 14N nuclear quadrupole resonance line has been studied in detail on a powdered sample at 77°K. An improved, frequency-stabilized spectrometer, interfaced to a digital computer, was used in resolving fine details of the experimental lineshape. The line shape could be fitted by the sum of two Gaussian lines of suitably chosen width, frequency, and amplitude.
Vibrational normal modes of SiO2. I. α and β quartz
Authors: Etchepare J. , Merian M. , Smetankine L.
Published: February 2004

A theoretical study of the vibrational modes of α and β quartz has been carried out, using some recent experimental results on the β form. It is shown that a single valence force field can account for the optical frequencies of both crystalline forms. The infrared and Raman intensities were also calculated from atomic displacements, using the method of Kleinman and Spitzer; the results seem satisfactory on the whole.
On the estimate of the three-body contribution to time-correlation functions for transport coefficients. II
Authors: Eu Byung Chan
Published: February 2004

By making use of some of the results obtained by Faddeev for a three-particle system, we estimate the three-body contribution of the quantum mechanical self-diffusion coefficient for a two-dimensional fluid with a view to resolving the question of its divergence. We find that the three-body contribution 𝓧123 is O(ε−2) instead of O(ε−2logε). Some comments are made on the mathematical difficulties with the analysis appearing in the literature associated with the logε dependence of the classical three-body contribution. According to the cluster expansion method we developed, based on Zwanzig's theory on time-correlation function for transport coefficients, the ε−2 dependence of the three-body contribution 𝓧123 leads to an ordinary power series in density for transport coefficients rather than to a series that includes a logarithmic density dependence. We discuss this in the paper.
Ionization energies of doubly and triply ionized lanthanides by a linearization technique
Authors: Sluis K. L. Vander , Nugent L. J.
Published: February 2004

Linear intraseries correlations of the ionization energies I3 and I4 are developed for the gaseous lanthanides. Good agreement is found between our results and previous results, where these ionization energies are more precisely known. Where these ionization energies were less precisely known, we interpolate more precise values, and we offer one explanation of why some of the previous values are slightly higher than our values.
Calculation of vibronic magnetic rotational strengths in formaldehyde
Authors: Linder Robert E. , Bunnenberg Edward , Seamans Lloyd , Moscowitz Albert
Published: February 2004

The magnetic rotational strengths (MRS) associated with the non-totally-symmetric vibrations in formaldehyde are calculated with CNDO/2 wave functions. The effects of configuration interaction are examined. We have also identified a single term that dominates the MRS. This raises the possibility of an economy of thought in attempts at correlating MRS data with molecular structure in the case of magnetic dipole allowed transitions.
Thermodynamic investigation of the gaseous molecules TiRh, Rh2, and Ti2Rh by mass spectrometry
Authors: Cocke D. L. , Gingerich K. A.
Published: February 2004

The high-temperature Knudsen effusion mass spectrometric technique has been used to determine the thermodynamic properties of the new molecules TiRh, Rh2, and Ti2Rh. The atomization energies D°0 [TiRh(g)], D°0[Rh2(g)], and ΔH°atm,0[Ti2Rh(g)] were obtained as 92.5±3.5, 67.3±5.0, and ≤238±10 kcal mol−1 or 387.0±14.6, 281.6±20.9, and ≤995.8±41.8 kJ mol−1. The corresponding standard heats of formation ΔH°f,298 for the molecules TiRh(g) and Rh2(g) were derived as 151.0±3.6 kcal (631.8±15.1 kJ) and 196.5±5.0 kcal (822.2±20.9 kJ) mol−1, respectively. These properties were derived from the enthalpies of the following reactions: ΔH°0kcalorkJRhC(g)+Ti(g)=TiRh(g)+C(g)46.9±3.0196.2±12.6TiC2(g)+Rh(g)=TiRh(g)+C2(g)41.5±4.0173.6±16.7TiRh(g)+C(graph)=RhC(g)+Ti(g)124.7±3.0521.7±12.6TiRh(g)=Rh(g)+Ti(g)91.9±3.0384.5±12.6Rh2(g)+C(g)=RhC(g)+Rh(g)−71.7±5.0−300.0±20.9Rh2(g)+2C(graph)=2RhC(g)133.3±6.0557.7±25.1Rh2(g)=2Rh(g)66.9±5.0279.9±20.9Ti2Rh(g)+Rh(g)=TiRh(g)53±8221.8±33.5The determination of the dissociation energy of the rhodium dimer allows the bond energies of TiRh and Ti2Rh to be discussed in terms of the Pauling model of a polar bond. The high bond energies of the molecules support the extention of the Brewer-Engel theory to the gas phase.
On the classical microwave and infrared pressure broadening theory for ammonia
Authors: McMahon D. R. A. , McLaughlin Ian L.
Published: February 2004

A stochastic Liouville equation has been developed to represent collision effects on the ammonia internal degrees of freedom of inversion, spatial orientation, and the ν1 fundamental mode of vibration. A modified form of Ben-Reuven's spectral shape function for the microwave spectrum in the ``single-line'' approximation is derived and shown to give a good fit to the experimental results for ND3, comparable to the earlier ``many-line'' fit, with a distribution of relaxation rates, of Maryott and Kryder. Further, it is shown that the collision induced memory loss in the absorbing dipole moment autocorrelation function determines the pressure-dependent behavior of the spectral shape function. Examples are given with special consideration of the effects of collision induced dipole reorientations and vibrational phase changes and transitions for the infrared spectrum.
Surface structure and surface tension: Perturbation theory and Monte Carlo calculation
Authors: Lee Jong K. , Barker J. A. , Pound G. M.
Published: February 2004

A Monte Carlo computation of the surface structure and surface tension of a liquid with molecules interacting according to the Lennard-Jones 12–6 potential is described. The computation demonstrates the presence of a well-developed layer structure at the surface extending to a depth of about eight molecular layers. The calculated surface tension agrees well with that predicted by Toxvaerd's extension of the Barker-Henderson perturbation theory to nonuniform fluids. The latter theory also predicts well the averaged behavior of the surface density profile (though not the development of the layered structure). This theory is used with accurate pair and triplet potentials to calculate values of the surface tension of liquid argon that agree quantitatively with experiment over a wide range of temperatures.
Condon moments for the configurational-coordinate model
Authors: Fonger W. H. , Struck C. W.
Published: February 2004

The first three moments for transitions between offset harmonic oscillators in a single configurational coordinate are derived for the Condon approximation. The derivation uses simple recursion techniques based on the Manneback recursion formulas for the vibrational overlap integrals. The first two moments are compared with moments obtained previously by quantum-mechanical transform methods and semiclassical methods.
Zero phonon transitions and interacting Jahn-Teller phonon energies from the fluorescence spectrum of α-Al2O3:Ti3+
Authors: Gächter B. F. , Koningstein J. A.
Published: February 2004

α-Al2O3:Ti3+ (300 ppm) at 10 K shows a broad fluorescence spectrum peaked at 14 380 cm−1 with a progression of small shoulders on the high energy side. At 16 216.1 and 16 178.3 cm−1 are two sharp zero phonon transitions from the Jahn-Teller distorted 2Eg to B3/2 and E1/2, respectively, of the ground term 2T2g. Two Eg phonons interacting with the ground term 2T2g have been found with the energies of 220 and 257 cm−1 for interaction with the ground state B3/2 and of 219 and 256 cm−1 for that with the first excited state E1/2. The Eg phonon interacting with the excited 2Eg electronic state has an energy of 160 ± 10 cm−1. The Jahn-Teller stabilization energy of the 2Eg state is estimated to be 3000 cm−1.
Excess kinetic energies of ionization products of electron impact processes
Authors: Levin G. , Platzner I.
Published: February 2004

The excess kinetic energies of negative and positive fragment ions produced by electron impact were determined by best fitting of calculated ion decay curves to the measured ones. The most probable kinetic energies of the ions only were calculated assuming Gaussian-like, or Maxwell-Boltzmann energy distributions. The results for O+(O2), O−(N2O), N2+(N2O), and S−(COS) are in good agreement with other reported data.
Vibrational dependence of the dipole moment in the A 3Π1 state of ICI
Authors: Cummings F. E. , Klemperèr William
Published: February 2004

The Stark effect is measured for the A3Π1←1Σ+ band system. The dipole moment of the A state as a function of vibrational level is measured to be, in Debye, ν′μ′ν′μ′ν′μ′ν′μ′72.00(± 0.15)111.85(0.10)141.75(0.05)211.15(0.15)91.95(0.05)121.80(0.10)171.50(0.15)250.6 (0.15)101.90(0.10)131.60(0.15)181.25(0.10)270.6 (0.15)The sign of the A state moments appears to be opposite to that of the X state.
Classical trajectory studies of angular distributions of reactions of deuterium atoms with iodine molecules
Authors: McDonald J. D.
Published: February 2004

A three-dimensional classical trajectory study is used to determine the effect of variation of the angular properties of LEPS-type potential energy hypersurfaces on the angular distribution of products of the reaction D + I2 → DI + I for a variety of initial translational and rotational energies. The fraction of the total available energy left in product translation is between 0.18 and 0.30 for various initial conditions. Three potential energy hypersurfaces that vary only in the position of an angle-dependent activation energy give product angular distributions that range from strongly backward to strongly sideways peaked. A very strong correlation is found between the angular properties of the surface and the product angular distribution. Requirements for surfaces needed to match the experimental angular distribution of products of reactions of D plus other halogens are also discussed.
Magnetic properties of trivalent actinides in the octahedral compounds Cs2NaMCl6
Authors: Hendricks M. E. , Jones E. R. , Stone J. A. , Karraker D. G.
Published: February 2004

The magnetic susceptibilities of U3+, Np3+, Pu3+, Am3+, Cm3+, and Bk3+ ions in an octahedral environment were measured from 3 to about 50°K with a vibrating-sample magnetometer. Each actinide ion was in a stoichiometric compound of the cubic Cs2NaMCl6 type, except for Cm3+ and Bk3+, which were doped into diamagnetic Cs2NaLuCl6. Curie-Weiss behavior was found for the uranium, neptunium, and plutonium compounds, with evidence for small distortions from octahedral symmetry in the uranium and plutonium compounds. The americium and berkelium samples displayed temperature-independent paramagnetism. For the curium sample, the free-ion moment was observed, but with deviations below 7.5°K that are attributed to crystal-field splitting of Cm3+. The following ground levels were determined: U3+, Γ8; Np3+, Γ5; Pu3+, Γ8; Am3+, Γ1; and Bk3+, Γ1. In Bk3+, a Γ1–Γ4 separation of 85 cm−1 is derived. Limits on the octahedral crystal-field parameters were established from the magnetic data and from crystal-field calculations for U3+ and Np3+, including intermediate coupling and J mixing from the first excited states. From these parameters, the complete crystal-field splitting of each actinide ion in Cs2NaMCl6 was calculated.
Energy dependence of optically induced exciton fission
Authors: Swenberg C. E. , Ratner M. A. , Geacintov N. E.
Published: February 2004

A general discussion of the kinematics of optically induced fission in organic crystals is presented. Explanations are given for the nonoccurrence of this phenomenon in certain systems, and a theoretical interpretation is offered for the photon energy dependence of the magnetic field effect on the prompt fluorescence of solid tetracene at 77°K. The structure observed by Moller and Pope below 30 000 cm−1 is interpreted as a progression in the totally symmetric C–H stretching mode, where the Franck-Condon vibrational coupling constant g for the correlated pair singlet-triplet transition is found to be of the order of unity. Several experiments to test the predictions of the theory are suggested.
Enthalpy of formation of germanium trifluoride
Authors: Wang J. Ling-Fai , Margrave J. L. , Franklin J. L.
Published: February 2004

The formation of negative ions resulting from the electron bombardment of germanium tetrafluoride has been studied as a function of the electron energy. Appearance potentials of these ions were determined and measurements of their excess kinetic energies were made for the dissociative electron attachment in order to estimate values for the enthalpy of formation of germanium trifluoride and its electron affinity.
Temperature dependence of V → R, T energy transfer probabilities in CO2(00°1) + HF/DF
Authors: Shin Hyung Kyu
Published: February 2004

Temperature dependence of vibration to rotation-translation energy transfer probabilities in CO2(00°1)+HF/DF→CO2(n m l0) + HF/DF has been investigated in the range 300–1000°K. It is shown that the negative temperature dependence of transition probabilities at lower temperatures and the appearance of the probability minimum at intermediate temperatures are due to the influence of hydrogen bond interaction.
Application of 129I Mössbauer spectroscopy to a metal iodide: [Ru(cp)2I] I3
Authors: Potasek M. J. , Debrunner P. G. , Morrison William H. , Hendrickson David N.
Published: February 2004

The 27.8 keV transition of 129I was used to study the bonding in [Ru(cp)2I]I3. The nuclear quadrupole coupling constants, isomer shifts relative to the source, asymmetry parameters, full widths at half-maximum, intensities, and asymmetries in the recoilless fraction were obtained for each of the three inequivalent iodide sites. The Mössbauer parameters for the triiodide anion agree with both NQR and Mössbauer studies on other compounds containing the triiodide anion.
Influence of pressure on the melting of rare gas solids
Authors: Reynolds C. L. , Barker R. E.
Published: February 2004

A simple equation which predicts the influence of pressure on melting points and includes anharmonicity has been applied to the rare gas solids. This equation is shown to be useful in estimating the Grüneisen parameter γG(Tm) near the melting point.
Rate constant of OH + H2 = H2O + H from 1350 to 1600 K
Authors: Gardiner W. C. , Mallard W. G. , Owen J. H.
Published: February 2004

Transient OH maxima were observed in the shock-initiated combustion of rich (H2:O2:Ar = 10:1:89) hydrogen-oxygen-argon mixtures. Computer simulations of the reaction profiles were used to compare an assumed mechanism and set of rate constants with the experimental results. The expression k3 = 5.2×1013 exp(−27 kJ/RT) cm3 mol−1 · s−1 was derived for the reaction OH + H2 = H2O + H over the temperature range 1350–1600 K. The expression k3 = 107.50T1.77 exp(−12.7 kJ/RT) cm3 mol−1 · s−1 was derived combining our results with those of previous investigations spanning the temperature range 300–1800 K.
Multiple transition points in a semiclassical treatment of electronic transitions in atom(ion)-diatom collisions
Authors: George Thomas F. , Lin Ying-Wei
Published: February 2004

A semiclassical treatment of multiple transition points for electronic transitions in atom(ion)-diatom collisions is presented. The treatment, based on a theory by W. H. Miller and T. F. George [J. Chem. Phys. 56, 5637 (1972)], involves the semiclassical evaluation of a path integral connecting the initial and final states of a given collision. The evaluation considers first the classical limit of an electronic propagator, which is a function of the time development of the nuclear degrees of freedom, and then the classical limit of a nuclear path integral containing the electronic propagator. The treatment of multiple transition points in the electronic propagator is presented in analogy with the problem of motion over multiple barriers. For transition points close in time a uniform approximation must be introduced in the evaluation of the electronic propagator. This is distinguished from another uniform approximation which might be necessary in the evaluation of the nuclear path integral. The resulting forms of classical S matrix elements derived from these approximations are given, and their application to H+ + D2 collisions is discussed.
Extreme ultraviolet photodissociative excitation of molecular oxygen
Authors: Carlson R. W.
Published: February 2004

Photodissociation processes in molecular oxygen occurring in the wavelength range 500–900 Å (14–25 eV) have been investigated through observation of the resulting atomic fluorescence radiation. The dispersed radiation from a continuous light source was used to excite the gas, and the resulting fluorescence radiation was observed in the ultraviolet and infrared. For incident wavelengths between 750 and 850 Å (14.6–16.5 eV) the OI(2p3 3s 3S0) state, from which the 1302–1306 Å resonance lines are produced, is populated by predissociation. At higher energies, between 650 and 770 Å(16.1–19.1 eV), a photodissociation process occurs which produces the OI 1302–6 Å lines. Photodissociation to produce OI(2p3 3p 5P) was found to occur in the wavelength interval 740–780 Å (15.9–16.75 eV) by observation of the resulting OIλ7773 Å radiation. Comparison of the results with the dissociation cross sections of Matsunaga and Watanabe suggests that photodissociation in the 800 Å region results in the formation of OI(2p3 3s 5S0).
Adiabatic vibrational matrix elements of R for HD+
Authors: Bishop David M.
Published: February 2004

Using an adiabatic potential energy curve for the electronic ground state (2Σ+) of HD+, we determine vibrational wavefunctions, written as 30-term combinations of Morse eigenfunctions, for various vibrational (v) and rotational (J) quantum numbers. These vibrational wavefunctions are then used to evaluate vibrational matrix elements of the internuclear separation (R) for various v and J values. An alternative calculation, first introduced by Tipping, is also investigated: namely, evaluating the matrix elements in terms of parameters of the initial potential energy curve. It is pointed out that these matrix elements of R make a dominating contribution to the dipole transition moments of HD+.
Phonon sidebands of localized excitons in molecular crystals with methyl torsions: Hexamethylbenzene
Authors: Woodruff Steven D. , Prasad Paras N. , Kopelman Raoul
Published: February 2004

Fluorescence and phosphorescence phonon sidebands of isotopic mixed hexamethylbenzene crystals at 2°K are presented. The external phonons can be observed separately from the semi-internal (methyl torsion) ones. The nature of the electronic or vibronic state has observable but not drastic effects on the exciton-phonon coupling function. Likewise, the exciton delocalization is of minor importance to the exciton-phonon function in hexamethylbenzene. The coupling between external and internal vibrations is also weak in this system. The exciton-phonon coupling appears comparable for the optical and acoustic phonons in hexamethylbenzene. The phonon sidebands give some of the phonon singularities of the low-temperature crystal.
Extended model for photochemical dissociation reactions
Authors: Kay Kenneth G.
Published: February 2004

The model for photodissociation reactions introduced by Rice, McLaughlin, and Jortner is generalized by allowing the excited molecule to decompose into several decay channels. In accordance with models for unimolecular reactions, intermediate resonance states having similar energies are assumed to couple to different channels and only resonances separated by a sufficiently large energy spacing, ε2, are taken to couple to the same channels. The molecule is shown to decay exponentially from the initially excited state at the nonradiative rate Γ1/(1+r)ℏ, where Γ1/ℏ is the nonradiative rate in the absence of resonance-channel coupling and r=πΓ2/2ε2 measures the ratio of the nonradiative resonance widths Γ2 to the energy spacing ε2. Plots of the resonance populations Pman and the channel populations Pdiss versus time consist of exponential segments linked at times t=p h/ε2, p=1,2,3,…, to yield continuous but only piecewise smooth curves. For t < h/ε2, decay from the initially prepared state populates the resonances and the channels in parallel and maintains a 1:r ratio between Pman and Pdiss. For t > h/ε2, Pman eventually approaches zero while Pdiss continues to rise towards a value of unity. The detailed shape of the population versus time curves is sensitive to the values of r, Γ1/(1+r) and ε2. This general behavior is termed ``quasisequential'' because although the populations do not satisfy conventional kinetic rate equations for consecutive decay, the evolution still resembles decay from the initial state to the resonances ``followed'' by decay from the resonances to the channels. True sequential decay occurs only when ε2 is so large that ε2≫Γ2, while the nonsequential decay previously obtained for the Rice-McLaughlin-Jortner model occurs only if ε2 is so small that h/ε2 exceeds the physically relevant time scale. We do not expect the former limiting case to be generally realized since it is inconsistent with models for unimolecular reactions which postulate that ε2≈Γ2. Although the latter limiting case may be realized for certain large molecules, we expect that many molecules will decay, instead, according to the more general quasisequential expressions which we present. The general formulas we derive are valid for all times following photoexcitation and are therefore applicable to relatively small as well as large molecules.
Nuclear magnetic relaxation of 23Na in polyelectrolyte solutions
Authors: van der Klink J. J. , Zuiderweg L. H. , Leyte J. C.
Published: February 2004

Using the cylindrical solution of the Poisson-Boltzmann equation, an expression is obtained for the nuclear spin-lattice relaxation of counterion nuclei in polyelectrolyte solutions, if these nuclei possess a quadrupole moment. The expression shows that, from a certain degree of neutralization α, the relaxation rate should be a quadratic function of α; while, in the concentration range of 0.05–1N, the concentration dependence is only slight. Experimental results for the nuclear magnetic relaxation rate of 23Na as a function of α in poly(acrylic acid) solutions of ≈0.3N concentration are shown to be in reasonable agreement with the theory. The effect of added NaCl upon the observed relaxation rate is discussed and shown to be describable by an ``additivity rule.''
Effect of fast neutron, gamma-ray, and combined radiations on the thermal decomposition of ammonium perchlorate single crystals
Authors: Herley P. J. , Wang C. S. , Varsi G. , Levy P. W.
Published: February 2004

The thermal decomposition kinetics have been determined for ammonium perchlorate crystals subjected to a fast neutron irradiation or to a fast neutron irradiation followed by a gamma-ray irradiation. Qualitatively, the radiation induced changes are similar to those obtained in this and in previous studies, with samples exposed only to gamma rays. The induction period is shortened and the rate constants, obtained from an Avrami-Erofeyev kinetic analysis, are modified. The acceleratory period constant increases and the decay period constant decreases. When compared on an equal deposited energy basis, the fast neutron induced changes are appreciably larger than the gamma-ray induced changes. Some, or all, of the fast neutron induced effects might be attributable to the introduction of localized regions of concentrated radiation damage (``spikes'') by lattice atom recoils which become thermal decomposition sites when the crystals are heated.