bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum mechanical reactive scattering for three-dimensional atom plus diatom systems. I. Theory
Authors: Schatz George C. , Kuppermann Aron
Published: February 2003

A method is presented for accurately solving the Schrödinger equation for the reactive collision of an atom with a diatomic molecule in three dimensions on a single Born–Oppenheimer potential energy surface. The Schrödinger equation is first expressed in body-fixed coordinates. The wavefunction is then expanded in a set of vibration–rotation functions, and the resulting coupled equations are integrated in each of the three arrangement channel regions to generate primitive solutions. Next, these are smoothly matched to each other on three matching surfaces which appropriately separate the arrangement channel regions. The resulting matched solutions are linearly combined to generate wavefunctions which satisfy the reactance and scattering matrix boundary conditions, from which the corresponding R and S matrices are obtained. The scattering amplitudes in the helicity representation are easily calculated from the body fixed S matrices, and from these scattering amplitudes several types of differential and integral cross sections are obtained. Simplifications arising from the use of parity symmetry to decouple the coupled-channel equations, the matching procedures and the asymptotic analysis are discussed in detail. Relations between certain important angular momentum operators in body-fixed coordinate systems are derived and the asymptotic solutions to the body-fixed Schrödinger equation are analyzed extensively. Application of this formalism to the three-dimensional H+H2 reaction is considered including the use of arrangement channel permutation symmetry, even–odd rotational decoupling and postantisymmetrization. The range of applicability and limitations of the method are discussed.
Interpretation of the vibrational spectrum of crystalline phenanthrene
Authors: Godec J. , Colombo L.
Published: February 2003

Couplings between inter- and intramolecular vibrations have been investigated. In normal-mode calculations a program has been used which allows all possible couplings between molecular and crystal vibrational modes. Several low-frequency molecular modes coupled to lattice vibrations have been isolated. A complete assignment of the phenanthrene crystal spectrum is presented and the intermode mixing occurring in the region from 1550 to 1250 cm−1 is discussed.
Effects of electron correlation on physical quantities expressed as second-order perturbation energies
Authors: Hiroike Eiko
Published: February 2003

A physical quantity of a molecule which can be expressed as second-order perturbation energy is investigated, by using the modified Hartree–Fock operator proposed by Huzinaga and Arnau. The calculation shows that the electron correlation in the ground electronic state is much more important than that in the intermediate excited states. The electron correlation in the ground state increases the absolute value of the calculated quantity, if the intermediate excited states are the triplets. The reverse effect can be expected, if the intermediate excited states are the singlets.
Absolute total elastic cross sections for collisions of oxygen atoms with the rare gases at thermal energies
Authors: Aquilanti V. , Liuti G. , Pirani F. , Vecchiocattivi F. , Volpi G. G.
Published: February 2003

Absolute total elastic cross sections for collisions of ground state O atoms with He, Ne, Ar, Kr, and Xe have been measured as a function of velocity in the range 0.6–2.0 km sec−1. The data are deconvoluted in the center-of-mass system and treated in terms of model potentials for the involved interactions. For the heavier rare gases a glory structure has been observed and the possible role played by multiple potentials on such structure is discussed.
19F and 31P magnetic shielding anisotropies and the F–P–F bond angle of PSF3 in a smectic liquid crystal solvent
Authors: Montana Anthony J. , Zumbulyadis Nikolaos , Dailey Benjamin P.
Published: February 2003

The 19F and 31P magnetic shielding anisotropies of thiophosphoryl fluoride have been determined at a single temperature and in the smectic liquid crystal phase solely, using 4-n-octyloxybenzylidene-4′ amino acetophenone (OBAA) as an orienting solvent. Measurements of the F–P–F bond angle are also reported. The absolute sign of the indirect P–F spin–spin coupling constant is found to be negative, and the anisotropy in this quantity is assumed to be negligible. In addition, the 31P spectra of phosphorus trifluoride, dissolved in a smectic liquid crystal solvent, is also investigated in this study, and the value of Δσ obtained in the smectic phase for PF3 is found to be in disagreement with the previous value measured in the nematic liquid crystal phase.
Temperature dependence of O(1D) rate constants for reactions with O2, N2, CO2, O3, and H2O
Authors: Streit G. E. , Howard Carleton J. , Schmeltekopf A. L. , Davidson J. A. , Schiff H. I.
Published: February 2003

Absolute rate constants and their temperature dependencies for the deactivation of O(1D) by five important atmospheric gases are reported. O(1D) atoms are produced by photolysis of ozone at 266 nm and the atoms are directly observed in time resolved decay of the O(1D) →O(3P) radiation at 630 nm. Gases which only quench O(1D) (O2, N2, and CO2) are observed to have a small negative temperature dependence while O3 and H2O, which also have a reactive channel, display no temperature dependence. Arrhenius expressions for the reactions measured are (A in units of 10−10 cm3/molecule⋅ s, E in cal/mole) O2(T=104–354 K) 0.29 exp(134/RT), N2(T=104–354 K) 0.20 exp(214/RT), CO2(T=139–200 K) 1.2 and (T=200–354 K) 0.68 exp(233/RT). The rate constants for O3 and H2O are 2.4×10−10 and 2.3×10−10 cm3/molecule⋅ s over ranges of 103–393 K and 253–353 K, respectively. The results are compared with other energy dependent measurements and with the theories reported in the literature.
Simple theory of diffuse vibrational structure in continuous uv spectra of polyatomic molecules. I. Collinear photodissociation of symmetric triatomics
Authors: Pack Russell T.
Published: February 2003

A theory for the direct photodissociation of polyatomic molecules is presented, and it is shown that uv absorption spectra into simply dissociative upper electronic states can have considerable vibrational structure. This provides a simple interpretation of many of the ’’diffuse vibrational bands superimposed on continua’’ often seen in polyatomic spectra.
Rate constants for the gas–phase reactions of OH radicals with ethylene and halogenated ethylene compounds
Authors: Howard Carleton J.
Published: February 2003

Rate constants are reported for the reactions of OH radicals with six different ethylene compounds: C2H4, C2H3Cl, CH2CF2, C2HCl3, C2F3Cl, and C2Cl4. Measurements are made with a discharge-flow system using laser magnetic resonance detection of OH. Rate constants are given for the reactions in a helium buffer gas over the range 0.7–7 torr at 296 K. The mechanism for the reactions appears to involve an attack by the OH radical on one of the carbon atoms, thus breaking the pi bond. The resulting activated complex may be stabilized by collision with a buffer molecule or in some cases may form a new product by ejecting a Cl atom. All of the reactions show some mixed bimolecular and termolecular behavior with some becoming totally bimolecular within the range studied. The reactions are all very fast with rate coefficients in the range (2–6) ×10−12 cm3/molecule ⋅s, except for C2Cl4 which is about 1.7×10−13 cm3/molecule ⋅s. The application of these rates and mechanisms to atmospheric chemistry is discussed.
Translational energy dependence of the branching fraction and cross sections for the decay of collision complexes: K+CsF, RbF
Authors: Stolte S. , Proctor A. E. , Bernstein R. B.
Published: February 2003

The reactions CsF+K→KF+Cs−1.8 kcal mol−1 (I) and RbF+K→KF+Rb+1.5 kcal mol−1 (II) have been studied by the crossed molecular beam technique over a range of relative translational energy ?tr from 3 to 8 kcal mol−1. Both reactions, (I) and (II), are found to proceed via the formation of long-lived MFK complexes (M≡Cs, Rb). However, a strongly different reactivity behavior is observed, attributable mainly to the difference in sign of the exoergicities of the reactions. Angular distributions of reactive (R) and nonreactive (N) scattering show characteristic bimodal structure due to the (nearly) symmetric forward–backward peaking in the center-of-mass (c.m.) system. The reactive branching fraction FR=σR/(σR+σN) for each reaction has been determined at five values of ?tr by analysis of the angular distributions of the reactive and nonreactive scattering (and appropriate integration in the c.m. system). For the endoergic reaction (I) FR is small, increasing with ?tr, while for the exoergic reaction (II) FR?1/2, decreasing slightly with Ētr. These results are qualitatively in accord with simple phase-space branching theory. The cross section for complex formation σC=σR+σN is found to decline with energy, as expected on the basis of the orbiting-capture (centrifugal barrier) model. Based on an analysis of the low angle, ’’pseudoelastic’’ scattering, dominated by the long-range attractive potential, it has been possible to scale the measured scattered intensities and thus estimate the absolute magnitude of the cross sections. Values of σC were found to be of the order of 100 Å2. Approximate c.m. differential cross sections have been obtained by an iterative fitting procedure that satisfactorily reproduced the laboratory scattering data. A simple, uncoupled, angle-recoil velocity distribution function of the conventional 1/sinϑ form (with a slightly energy-dependent osculation) and a modified Maxwellian recoil distribution has been found to be adequate. The average relative translational energy of the scattered products, ?′tr, is found to increase essentially linearly with increasing ?tr. The theoretical implications of the present experimental results are discussed.
Fitting an a
b i
n
i
t
i
o HF–HF potential surface
Authors: Alexander Millard H. , DePristo Andrew E.
Published: February 2003

The angular dependence of the ab initio rigid-rotor HF–HF surface of Yarkony et al [J. Chem. Phys. 60, 855 (1974)] is fitted with a form appropriate for future quantum and semiclassical scattering calculations, namely a triple series in Legendre polynomials in the molecule–molecule body–fixed angles. The grid of ab initio points is not dense enough to permit a precise fit to the surface, particularly at small center-of-mass separations. Nevertheless, a reasonably accurate fit, which also gives a good description of the HF dimer, can be attained with ∼30 angular terms. The final body-fixed expansion coefficients were transformed to give 20 angular terms in a space-fixed (SF) frame. For the six largest SF terms, exponentials of various arguments as well as inverse powers were used to fit the dependence on the center-of-mass scattering coordinate. A total of 18 parameters were involved. Asymptotically, the interaction potential goes to the expected dipole–dipole plus dipole–quadrupole form. A simple, empirical modification allows the surface to be used for ro-vibrationally inelastic collisions.
Formation of N2 C 3Πu and B 3Πg in collisions of metastable Ar with N2
Authors: Krenos J. , Bruno J. Bel
Published: February 2003

Molecular beam measurements of the optical emission from Ar* and N2 system are reported.(AIP)
The measurement of a positive charge mobility larger than that of the excess electron in irradiated liquid t
r
a
n
s-decalin
Authors: de Haas Matthijs P. , Hummel Andries , Infelta Pierre P. , Warman John M.
Published: February 2003

The ion mobility for irradiated trans decalin below 10°C is reported.(AIP)
Effect of an external electric field on the yield of trapped electrons in a γ-irradiated hydrocarbon glass
Authors: Kato Noriyuki , Kimura Toyoaki , Fueki Kenji
Published: February 2003

The effect of an external electric field on the yield of trapped electrons in a γ-irradiated hydrocarbon glass at 77°K are reported.(AIP)
A new method for accurately approximating individual T-matrix elements in atom–diatom collisions
Authors: Kouri Donald J. , Shimoni Yair
Published: February 2003

A method for accurately approximating T-matrix elements in atom−diatom collisions is presented. Calculations are given for hydrogen helium collisions.(AIP)
The bimolecular thermal rate coefficient calculated from Monte Carlo integration over relative velocity and orbital angular momentum
Authors: Porter R. N. , Thompson D. L.
Published: February 2003

The thermal collision rate coefficients of two hard spheres has been calculated by using Monte Carlo method. (AIP)
Anomalous T7 Raman spin-lattice relaxation rate of low spin cytochrome P-450 from P
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o
m
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s p
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a
Authors: Herrick R. C. , Stapleton H. J.
Published: February 2003

Electron spin-lattice relaxation measurements were made on camphor-free low spin ferric cytochrome P-450 from Pseudomonas putida. Data were taken between 1.75–13 K at X and Ku band microwave frequencies using the technique of pulse saturation recovery. The experiment revealed an anomalous Raman relaxation rate varying in the low temperature limit as T7 rather than T9, the latter being expected for a Kramers ion. We discuss this anomaly and show how it suggests that the ferric spin system relaxes to thermal equilibrium through interactions with a two dimensional phonon spectrum. The planar structure of the heme complex adds credibility to this interpretation.
Determination of the zero-field splitting of Fe3+ in cytochrome P-450cam from electron spin-lattice relaxation rates
Authors: Herrick R. C. , Stapleton H. J.
Published: February 2003

Energies of the two excited crystal field doublets are determined for the S=5/2 manifold of Fe3+ in camphor-bound cytochrome P−450 from Pseudomonas putida using the temperature dependence of the associated Orbach relaxation rates. The measured energies of this zero-field splitting are Δ1/k=9.5±2.8 K and Δ2/k=29.8±1.9 K above the ground doublet. Relaxation data are reported on frozen solutions of P−450cam at microwave frequencies of 9.480 and 16.495 GHz and at temperatures between 1.5 and 2.5 K. If the two energy levels are related to a single ligand field parameter, D, using the constraint on E/D imposed by the measured g values of the ground doublet, then a fit of the relaxation data yields values for D/k of 5.0±0.2 K and E/k of 0.435±0.02 K. These ligand field parameters, in turn, place the excited states at Δ1/k=10.7±0.5 K and Δ2/k=30.5±1.2 K, consistent with the constraint-free determination.
Extended diffusion of a symmetric top molecule with internal rotation
Authors: Bull T. E.
Published: February 2003

Gordon’s extended J-diffusion theory is used to calculate the reorientational correlation times and NMR spin–rotational relaxation rates of nuclei attached to a symmetric top molecule with internal motion. The molecular motions and lattice averages are calculated using classical mechanics. The exact classical solutions are used for the case where the internal rotation and molecular symmetry axes are coincident. However, for the other cases approximate solutions are derived which are valid when the moment of inertia of the internal rotor is much less than the moments of inertia of the whole molecule. The calculations include quantitative predictions for the variation of the correlation times and relaxation rates with the height of the barrier to internal rotation.
Vibronic spectra and lattice dynamics of Cs2MnF6 and A12MIVF6:MnF2−6
Authors: Chodos S. L. , Black A. M. , Flint C. D.
Published: February 2003

The 2Eg→4A2g luminescence spectra of Cs2MnF6 and A12MIVF6:MnF2−6(A1=K, Rb,MIV=Si; A1=Cs,MIV=Si,Ge) are reported, In each case the spectrum can be analyzed into (a) the magnetic dipole allowed pure electronic orgin, (b) a set of one phonon sidebands characteristic of the lattice, (c) several bands involving two lattice phonons, (d) three strong vibronic origins corresponding to the odd vibrational modes of the anion, (e) progressions in up to three quanta of the three even anion modes based on the strong vibronic origins, and (f) bands involving combinations of one internal mode and one or two lattice phonons. Apart from small differences in the vibrational frequencies, the only difference between the spectra of the pure and the diluted compounds is the observation of the transverse–longitudinal (TO–LO) splitting of the ν3 and ν4 internal modes and an additional small splitting of the ν4 TO mode in the pure compound. The spectra are compared with the predictions of a simple lattice dynamical model for Cs2MnF6. The spectrum of Cs2GeF6:MnF2−6 is complicated by interaction between the localized ν3 mode of MnF2−6 and the ν3 band of the host lattice. The intensity mechanisms for the features (a) – (f) are discussed.
Absolute rate constants for O+NO+M(=He, Ne, Ar, Kr) →NO2+M from 217–500 K
Authors: Michael J. V. , Payne W. A. , Whytock D. A.
Published: February 2003

Flash photolysis of NO coupled with time resolved detection of O via resonance fluorescence has been used to obtain rate constants for the reaction O+NO+M→k1NO2+M at temperatures from 217–500 K in four different inert gases. The measured rate constants in Arrhenius form are k1,He= (10.8±1.2) ×10−33 exp(1040±60/1.987T), k1,Ne= (9.33±1.10) ×10−33 exp(1030±60/1.987T), k1,Ar= (9.01±1.16) ×10−33 exp(1180±70/1.987T), and k1,Kr= (9.52±1.10) ×10−33 exp(1140±70/1.987T) in units of cm6 molecule−2 sec−1. These results are discussed and compared with earlier work.
Particle motions in superionic conductors
Authors: Rahman A.
Published: February 2003

The motion of ions in Ca2+F2− has been studied by molecular dynamics. The results show that, at 2.525 g cm−3 and 1590 K, the F−’s have a constant of self-diffusion of 2.6×10−5 cm2 sec−1 and the Ca2+’s form a stable lattice. It is found that half of the F−’s occupy the octahedral sites of the fcc Ca2+ lattice. The details of the self-diffusion process is analyzed showing the presence of a wave-vector dependent long relaxation time in the decay of 〈exp(ik⋅u(t) 〉, which is the Fourier transform of the displacement u(t) of the F− ions.
Impact parameter calculations for low energy H++H and H++D collisions
Authors: Schinke Reinhard
Published: February 2003

Elastic differential cross sections for the scattering of low energy protons (15<Ec.m.<142 eV) on hydrogen and deuterium have been calculated using the adiabatic impact parameter method. The agreement with recently measured cross sections and with other theoretical predictions is reasonably good even for very low energies and larger scattering angles. Furthermore, we studied the influence of more realistic trajectories instead of straight-line ones, and also the inelasticity induced by the rotational coupling 〈2pσμ‖iLy‖2pπμ〉 at small internuclear distances.
Direct determination of the second refractivity virial coefficient of CH4
Authors: St-Arnaud J. M. , Bose T. K.
Published: February 2003

The experimental method for the direct determination of the second refractivity viral coefficient has been described. There is reasonable agreement between the experimental result and the classically calculated theoretical value for the second refractivity virial coefficient of methane.
Collision dynamics of three interacting atoms: Electron transfer in the reactions of K+Br2, BrI, and I2
Authors: Yuan Jian-Min , Micha David A.
Published: February 2003

Stripping reactions of K with Br2, BrI, and I2 at hyperthermal energies have been theoretically studied with particular emphasis on the electron transfer and direct rearrangement stages of the reactions. Electron transfer was investigated with a stochastic model based on Landau–Zener transition probabilities for atom–diatomic collisions. Results show that vibrational distributions of the negative diatomic halogen ions immediately after electron transfer are determined by a vertical transition mechanism. A comparison was then made between experimental and theoretical velocity distributions of products K+I2 and Br2, with a model based on diatomic momentum distributions. This provides evidence that a fraction of the vibrationally excited Br−2 and I−2 ions relax as they react with K+. The theoretical results are consistent with available experimental results. This is also the case for K+BrI, in connection with calculated velocity and angular distributions of products, and branching ratios.
Fluorescence and dissociative energy transfer in high pressure Ar–HCN mixtures excited by relativistic electrons
Authors: Zamir E. , Szöke A. , Osgood R.
Published: February 2003

Studies of the radiation from Ar–HCN and Ar–H2O mixtures, excited by relativistic electrons from a Febetron 706 electron gun, are presented. The energy deposited by the electrons channels rapidly into the Ar* and Ar2* states; then by dissociative collisions with HCN it is transferred partly into the CN(B) state and partly into a reservoir state [most probably the CN(A) state] with near unit efficiency. Fluorescence emission from the electronic states A (2Πi) and B (2Σ+) of the CN radical, as well as the emission from the Ar2* excimer state, were measured for an Ar pressure range of 750–9000 torr [15–180 psi  (absolute)], and an HCN pressure range of 0.2–13 torr. The quenching rates of Ar* metastable and the Ar2* excimer states, by collision with HCN molecules, were measured to be 6×10−10 and 1×10−9 cm3 sec−1, respectively. Our results suggest that population inversion can be achieved by collisional dissociation of simple molecules with excited rare gas atoms and excimers. Indeed the peak CN(B) population density was found to be 1.5×1015 cm−3, which corresponds to an optical gain for the B–X transition of 0.4 cm−1 if the ground state is empty. A computer kinetic model is presented that explains the time dependence and intensity of the CN(B) emission. In Ar–H2O mixtures the reaction rate for quenching of Ar2* excimer by H2O molecules is extremely high; however, the yield into the OH(A 2Σ+) is only 3%.
Rotational tunneling splitting of the NH4 ion in NH4ClO4 studied by inelastic neutron scattering
Authors: Prager M. , Alefeld B.
Published: February 2003

The tunneling splitting of the NH4-librational ground state in NH4ClO4 has been measured by high resolution inelastic neutron scattering at a temperature of 4.5 K. The spectrum shows four tunnel lines at energy transfers of 1.63±0.20, 4.06±0.20, 5.52±0.10, and 7.10±0.10 μeV. A discussion of the hindrance potential is given.
A comparison of exact classical and quantum mechanical calculations of vibrational energy transfer
Authors: Gordon Robert J.
Published: February 2003

Exact classical and quantal calculations of vibrational energy transfer were compared to determine the conditions under which classical mechanics is reliable. A detailed study of collinear collisions between an atom and a harmonic oscillator with a repulsive exponential interaction showed that the average classical and quantal energy transfer agree within a few percent, if the translational energy exceeds the vibrational spacing, and if the average energy transfer does not change sign as the collision energy is varied slightly. Additional collinear calculations with (i) a Morse oscillator and an exponential interaction and (ii) a harmonic oscillator with a Lennard-Jones interaction confirmed this result, except for the case of a deep potential well. In this case sticky collisions can occur, and the agreement is poorer. For collinear collisions of two harmonic oscillators with a repulsive exponential interaction, the agreement for T→V energy transfer was poorer than in the atom–diatom case. Good agreement was obtained for V→V transfer, with both classical and quantum calculations favoring resonant collisions. In order to calculate individual transition probabilities, a number of classical quantization methods were tested. The two moment method of Truhlar and Duff was found to work well, and was used to calculate integral cross sections for the vibrational relaxation of He+O2(v=1). For this system a potential energy surface consisting of a harmonic breathing sphere and a repulsive exponential interaction was used to calculate the integral cross sections σvv′ for the inelastic transitions v→v′. The classical values of σ10, σ12, σ13, and σ14 calculated by the two moment method were in satisfactory agreement with the quantum results for reduced translational energy ?t≡Et/h/ω?1, 2, 4, and 9, respectively. The resulting rate constants kvv′ were a factor of 2 too small for T≳300 K, and a factor of 1.25 too small for T≳500 K. The usual bin or histrogram method for quantizing the classical energy transfer produced an anomalous threshold of ?t≳3 for σ10 and σ12, and still higher values for the more endoergic transitions. The resulting k10 was a factor of 106 too small at 300 K and a factor of 2 too small at 1400 K. In addition we found that equating the P10 transition probability with the average reduced energy transfer gave accurate values of k10 for 300 <T<1000 K. However, equating P12(P10) with the fraction of trajectories resulting in energy gained (lost) by the oscillator produced excessively high values of k12 and k10. Finally, we found that the Landau–Teller model is in good agreement with the quantum mechanical calculations of k10, k12, and k13, up to a single arbitrary normalization constant.
Classical S-matrix limit of wave packet dynamics
Authors: Heller Eric J.
Published: February 2003

The asymptotic (h/→0) equivalence of the Miller–Marcus classical S-matrix theory and Gaussian wave packet dynamics is shown. This result is not suprising, but the analysis yields considerable insight into both methods. Both approaches are seen to rely upon a linear response of dynamical variables against small changes in initial conditions. However, the two theories ’’back off’’ the h/→0 limit in a very different manner. Wave packets emerge as a kind of a priori uniformization procedure as opposed to the a posteriori uniformizations of classical S-matrix theory. In certain contexts the wave packets are shown to provide a parabolic cylinder function uniformization of the primitive semiclassical result. Wave packets in generalized coordinates are discussed. Analogy with classical S-matrix theory suggests new procedures for through-barrier tunneling of individual wave packets.
Ion–neutral reactions of Al+ with N2, O2, and N2O
Authors: Rutherford J. A. , Vroom D. A.
Published: February 2003

Ion–neutral collisions between Al+ and N2, O2, and N2O have been studied in the energy range from 1 to 5000 eV. All processes considered are endothermic. For those processes where reaction occurs, cross sections have been determined. Upper limits on cross sections are given where no measurable signals could be detected.
On the origin of broad band optical emission from Mo, Nb, and W bombarded by heavy ions
Authors: Rausch E. O. , Bazhin A. I. , Thomas E. W.
Published: February 2003

Continuum emission has been observed when Mo, W, and Nb targets were bombarded with 10–30 keV, Ne+ and Ar+. The emission occurs only when the environment of the target chamber contains an oxygen partial pressure of 2×10−9 torr or above; for lower pressures the emission is absent. Identical continua are also observed when the metal oxides are bombarded with Ne+ and Ar+; similar spectral features, though with changed relative intensities, are seen when the targets are bombarded with O+ and O2+ ions in the absence of O2 gas in the vacuum environment. A significant feature of these continua is that the emitting species extend for some mm beyond the bombarded surface. We suggest that the source of the emission is sputtered oxides of the target. The variation of emission intensity with oxygen partial pressure and bombarding ion beam current is consistent with a mechanism where the oxide is formed by the simultaneous sputtering of an adsorbed oxygen atom and a metal atom from the bulk material.
Use of pseudopotentials within the floating spherical Gaussian orbital method: Calculations on methane
Authors: Topiol Sid , Frost Arthur A. , Ratner Mark A. , Moskowitz Jules W.
Published: February 2003

The utility of nonempirical pseudopotentials in floating spherical Gaussian orbital (FSGO) calculations is examined. Calculations on the methane molecule with various popular pseudopotentials reveal that the best pseudopotentials may not be the most compatible with FSGO’s, but that in all cases, proper treatment of the angular momentum dependence is important.
A study on molecular reorientational motion of benzene molecule and intermolecular interaction in the mixture of chloroform and benzene by Raman spectroscopy
Authors: Nomura Hiroyasu , Koda Shinobu , Miyahara Yutaka
Published: February 2003

The reorientational correlation time of benzene molecule in chloroform–benzene mixture was measured by the method of the Raman line shape analysis. The reorientational correlation times thus obtained changed with the mole fraction of chloroform in the mixture owing to the interaction between chloroform and benzene. In addition, the behavior of the isotope structure of the ν3 band of chloroform and the Raman shifts of the ν1 band of chloroform in the chloroform–benzene mixture are also reported here.
Structure of solid ethylene-d4
Authors: Press W. , Eckert J.
Published: February 2003

The two solid phases of deuterated ethylene (C2D4) have been investigated using neutron diffraction. The recently detected high pressure phase II is found to form a bcc structure of the space group Im3m with the molecules orientationally disordered. For the normal solid phase I the measurements confirm the orientationally ordered arrangement belonging to the space group P21/n.
Trajectory calculations on the fluorine methane chemical laser reaction
Authors: Gauss Arthur
Published: February 2003

Fluorine atoms react with methane at low collison energies (∼1 kcal/mole) according to the chemical-laser reaction F+CH4→HF+CH3. At somewhat higher energies (1–1.5 eV) the reaction F+CH4→FCH3+H is possible. The fluorine–methane system was treated as a three-particle system consisting of a fluorine atom, a hydrogen atom, and a methyl radical. A three-parameter, LEPS (London, Eyring, Polanyi, Sato) potential-energy surface was adopted for the interaction potential. By adjusting these parameters so as to force certain properties of the surface to agree with experiment, an optimized LEPS surface was obtained from which cross sections were generated for the reaction channel F+CH4→HF+CH3. These cross sections were used to calculate a thermal rate constant that agrees approximately with experiment.
NMR investigation of ammonium ion motions in two ammonium bisulfates
Authors: Watton A. , Reynhardt E. C. , Petch H. E.
Published: February 2003

Nuclear magnetic second moment and spin–lattice relaxation time studies have been performed over the temperature range 77–388 K for two ammonium bisulfates; the ferroelectric NH4HSO4 and the antiferroelectric (NH4)3H(SO4)2. The results suggest a rapid general reorientation of the NH4 + ions over the whole temperature range in both materials, brought about by the superposition of a threefold reorientation on two less hindered twofold reorientations. The NH4HSO4 shows an additional mechanism, absent from the (NH4)3H(SO4)2 results, which is attributed to a loss of distortion of the NH4 + tetrahedron at high reorientational frequencies.
Characterization of the ground and excited states of lanthanum oxide through bimolecular oxidation of La metal with O2, NO2, N2O, and O3
Authors: Gole James L. , Chalek Carl L.
Published: February 2003

Using a beam–gas arrangement, we have studied the chemiluminescent emission which results when a thermal beam of La atoms (1750–2400 K) intersects a tenuous atmosphere (10−6 to 10−4 torr) of one of the thermal oxidants O2, NO2, N2O, or O3 (300 K). The La–O2 reaction is characterized by visible chemiluminescence from the B 2Σ+ and C 2Π states of LaO. The La–NO2, La–N2O, and La–O3 reactions are characterized by emission from the B 2Σ+, C 2Π, and D 2Σ+ states of LaO. In addition all four systems are characterized by extensive emission from the A 2Π state of LaO. From the chemiluminescent spectrum for the La–O2 system, a minimum value of 8.19±0.04 eV is deduced for the dissociation energy of lanthanum monoxide. This lower bound is in good agreement with previous mass spectrometric determinations (8.28±0.11 and 8.38±0.2 eV). We discuss the temperature dependence of the four chemiluminescent reactions deducing an upper bound for the heat of vaporization of lanthanum metal. We combine the results of our temperature dependent studies with reactant–product correlations and demonstrate the manner in which this blend can be used to elucidate the significance and dynamics of reaction of low lying atomic states in the oxidation reactions of high temperature metallic beams.
Negative ion formation in cerium triiodide
Authors: Chantry P. J.
Published: February 2003

An apparatus is described which permits heating of solid samples to temperatures up to ∼1000 °K, and confinement of the resulting vapor in a collision chamber held at a suitably higher temperature. The collision chamber is traversed by an electron beam and the resulting ions are identified by mass analysis. Measurements are reported of the negative ions produced by electron impact on CeI3 molecules in the vapor phase. Fragment ions I−, I−2, CeI−, and CeI−2 are observed, and their appearance potentials are interpreted in the light of available knowledge of bond strengths (D) and affinities (A). Resulting derived quantities include D (CeI2–I) ?3.0 eV; A (CeI2) ?0.3 eV; D (CeI–I2) ?5.7 eV; D (Ce–I) ?3.8 eV, and D (Ce–2I) ?8.0 eV. CeI−3 is also observed, formed by direct attachment of very low energy electrons, and additionally by the charge transfer reaction CeI−2+CeI3→CeI−3+CeI2, suggesting that the affinity of CeI3 exceeds that of CeI2. In addition to the ions formed by electron impact, measurements of the background ion signals of I− and CeI−4 are reported and interpreted to give the heat of formation of gaseous CeI−4, ΔHf, 298 [CeI−4(g)]=−193 kcal/mole.
I=5/2 NMR in the quadrupole regime: Chemical shift in 121Sb2O3
Authors: von Meerwall E. , Creel R. B. , Griffin C. F.
Published: February 2003

We report the NMR observation of the transition between the lowest levels of an I=5/2 nucleus (121Sb in Sb2O3 powder) subject to a strong quadrupole interaction of zero asymmetry and a weaker Zeeman interaction. We simulate the powder pattern in first order Zeeman perturbation, with emphasis on the dipole broadening of the edge discontinuity near ν=3ν0. Using numerical evaluation of the exact theory, we determine the transverse chemical shift component σ⊥ and the strength νQ of the quadrupole interaction from the field dependence of the resonance frequency.
Diffusion coefficients of histone (lysine rich) by quasielastic laser scattering
Authors: Chen F. C. , Yeh A. , Chu B.
Published: February 2003

Time-dependent correlation functions of histone lysine-rich (HL) in tris buffer (0.01M tris, 0.14M NaCl at pH=8) were measured by means of a 96-channel single-clipped digital photon correlation spectrometer over a range of scattering angles at 25°C and three different concentrations (3.4, 4.5, and 7.1 mg/ml). Several models as well as the method of cumulants were used to analyze our experimental data which were found to contain at least two decay times. By approximating the heterogeneous lysine-rich histone and its aggregates as spheres of two distinct sizes, we obtained a molecular weight of 1.1×104 for our unaggregated (HL) histone and a corresponding diffusion coefficient D° of 8.5×10−7 cm2/sec at 25°C and infinite dilution. Our diffusion-coefficient results differ from a previous linewidth study of arginine-rich histone by a factor of 10. It implies that in quasielastic laser scattering large aggregates, even though small in number, can play an extremely important role in data analysis and must be taken into account properly.
The disordered Ising chain: Equivalent formulations for the thermodynamics
Authors: Chalupa J. , Grinstein G. , Wortis Michael
Published: February 2003

The free energy of a one-dimensional spin-1/2 Ising model in which the exchange constant between each neighboring pair of spins and the magnetic field at each spin site are random variables may be expressed in terms of the solution to a homogeneous integral equation derived by Vedenov and Dykhne and by Fan and McCoy. Earlier, using this model to calculate the melting curve of DNA, Lehman and McTague had given two equivalent inhomogeneous equations which determine the free energy. These formalisms are shown to be equivalent by tranforming the homogeneous equation into the inhomogeneous ones. Also, a formal representation of the free energy as an infinite continued fraction is given.
Theoretical study of intermolecular correlation effects on simple liquid properties obtained by x-ray diffraction
Authors: Piliavin Michael A. , Pings Cornelius J.
Published: February 2003

This work reports a theoretical study of x-ray scattering from simple liquids when environmental effects are included. An instantaneous configuration-dependent scattering factor is defined for a molecule in a liquid. Using statistical mechanics and physical principles, an expression is derived that corrects the usual scattering equations for both coherent and incoherent radiation. Using the new results, scattering data from several states of liquid helium and liquid argon are analyzed. Comparison of correlated scattering factors and isolated molecule scattering factors indicate that corrections are significant only in the vicinity of the hard core radius and for values of the wave vector s≳0.5 Å−1. Incorporating correlation effects into scattering data for these liquids, the resultant radial distribution function peak is depressed an average of 1% and computed potential well depths lowered by an average of 5%. Although treatment of data in this manner leads to better coincidence with theoretical predictions, the accuracy with which data for simple liquids may be obtained at the present time may not warrant a complete treatment as presented here. However, indications are that in polar and oriented liquids it is unjustified to leave out environmental effects when an accurate treatment is desired.
Energy partitioning and isotope effects in the fragmentation of triatomic negative ions: Monte Carlo scheme for a classical trajectory study
Authors: Goursaud S. , Sizun M. , Fiquet-Fayard F.
Published: February 2003

A simple molecular model is associated with an analytical semiempirical potential energy surface and a Wigner representation of the initial conditions of dissociation. This model is used to interpret some experimental data dealing with the dissociation of triatomic negative ions, i.e., the isotope effects and the partitioning of available energy between translational and internal energies of the recoiling fragments.
Off-diagonal spin–orbit and apparent spin–spin parameters in carbon monosulfide
Authors: Cossart D. , Bergeman T.
Published: February 2003

From a detailed study of the uv spectrum of carbon monosulfide (including new line measurements to be reported elsewhere) we report here values for the vibronic spin–orbit perturbation interactions, the reduced electronic interactions, and the apparent molecular orbital spin–orbit integral, a, for perturbations between A 1Π or a 3Π states and the d 3Δi, e 3Σ−, or a′ 3Σ+ states. Although for four of six of these pairs of coupled states, the empirical values for a are within the range 289–297 cm−1, the set of six values ranges from 243 to 314 cm−1, each being about 20% larger than the results of configuration interaction calculations by Robbe and Schamps. Hence the hypothesis that a is effectively constant is not entirely substantiated for CS. We find that the effective Coriolis interaction elements within the triplet manifold are surprisingly small; from six 3Π–3Σ± perturbations we obtain 〈L+〉 =0.04±0.04. We also present values for effective spin–spin parameters for a number of 3Σ+ and 3Σ− vibrational levels and consider the off-diagonal spin–orbit contributions from coupling with A 1Π and a 3Π. After these terms are subtracted out, the residual spin–spin terms are −2.89 and 3.02 cm−1 for a′3Σ+ and e3Σ−, respectively, which represent primarily the effect of the 3Σ+1–3Σ−1 spin–orbit interaction.
Determination of the Einstein A coefficient for the ?→? transition of ammonia-d3
Authors: Gregory T. A. , Lipsky Sanford
Published: February 2003

The fluorescence of ND3 has been observed for excitation into the ?←? system at 213.86 nm. The quantum yield for this transition is 8.3×10−5. With this quantum yield and the known rotational linewidth of the upper electronic state, an Einstein A coefficient is obtained that compares favorably with a value calculated from the emission intensity and absorption strength of the (ν1′,ν2′=0,0) ↔ (ν1″,ν2″ =0,2) vibronic bands. The average of these two values is A=3.6±0.3×107 sec−1. The underlying continuum of the ?←? absorption system, attributed to the predissociation of ND3, is invoked to explain most of the discrepancy between the above value for A and that predicted by the equation of Strickler and Berg. A weaker, more diffuse emission has also been observed from ND3 for excitation into the ?←? system at 206.24 nm with fluorescence quantum yield of 1.1×10−5.
Cross sections for excitation of the potassium resonance doublet in collisions between potassium atoms and alkali ions
Authors: Aquilanti V. , Casavecchia P. , Grossi G.
Published: February 2003

Excitation of the K(4p 2P3/2,1/2) resonance doublet in collisions between K atoms and the alkali ions has been investigated in a crossed ion-atom beam apparatus by the measurement of the emitted radiation. Absolute total inelastic cross sections and the ratio of production of the fine structure components have been measured at ion energies lower than 3.0 keV, and are discussed with reference to the properties of potential energy curves for the asymmetric alkali dimer ions.
Close coupling studies of rotational excitations of Ar+N2 and of H++H2 collisions
Authors: Choi B. H. , Tang K. T.
Published: February 2003

The rotational excitations in Ar+N2 and H++H2 are studied by the close coupling formulation of the differential equations of scattering. (AIP)
On the use of the sudden approximation for vibrational excitation in high-energy collisions, and the sensitivity of the results to the choice of potential energy surface
Authors: Skodje Rex T. , Gentry W. Ronald , Giese Clayton F.
Published: February 2003

We evaluate the sudden approximation for vibrational excitation in H++H2 collisions in the context of the semiclassical DECENT model for the collision dynamics. The sudden approximation fails to reproduce quantitatively the results of a full dynamical treatment at relative kinetic energies less than 500 eV. We find substantial differences between our sudden-approximation cross sections calculated using an accurate adiabatic potential energy surface and those of Collins and Cross obtained using a diatomic-in-molecules potential energy surface. (AIP)
Tests of INDO/1s and INDOXI/1s methods for the calculation of the static potential for electron scattering by CO
Authors: Truhlar Donald G. , Van-Catledge Frederic A.
Published: February 2003

The semiempirical molecular orbital methods are used to calculate the equilibrium, geometry ground-state potential for N2 and CO. It is demonstrated that the potential thus calculated is useful for electron scattering calculations.(AIP)
Scattering of high-velocity He atoms by hydrocarbons
Authors: Jordan J. E. , Mason E. A.
Published: February 2003

An experimental test is proposed to verify whether the scattering properties of C(CH3)4 by the atoms are caused by four C-C bands or by four CH3 groups.(AIP)
Vibrational spectra of molecular ions isolated in glassy and crystalline alkali metal oxyanion salt matrices
Authors: Ritzhaupt G. , Devlin J. P.
Published: February 2003

Molecular anions (NO−3 and ClO−3) have been isolated in glassy alkali metal oxyanion matrices (MClO3 and MClO4) at 80°K so that the splittings of the impurity molecular ion degenerate modes become a more direct measure of the anion site asymmetry in amorphous salt media. In general it is found that the individual components of the impurity ion ν3 asymmetric stretching band are much sharper and the splitting of the ν3 components significantly reduced over values for pure glasses or molten salts. Because of the band narrowing, distinct maxima are observed for both ν3 components for KNO3 and NaClO3, for which a doublet structure has been inferred but not previously observed. Of principal interest is the observation that the isolated NO−3 ν3 splitting, for a LiClO4 or KClO4 glass matrix, is unchanged by crystallization of the salt. In other words, the vibrational data show that the distortion experienced by the NO−3 anion in an amorphous salt is not appreciably different than for an asymmetric site in a perchlorate crystal. Consequently, the vibrational data are no more indicative of ion-pair configurations in the glass or molten salt phase than for the crystal phase.
Photodissociation and photodetachment of molecular negative ions. III. Ions formed in CO2/O2/H2O mixtures
Authors: Cosby P. C. , Ling J. H. , Peterson J. R. , Moseley J. T.
Published: February 2003

Total photodestruction cross sections for O2−, O3−, O4−, O2−⋅H2O, CO4−, CO3−, and CO3−⋅H2O have been measured over the range from 6950 to 4579 Å (1.78–2.71 eV). In most cases the photodestruction of these ions can be attributed to specific photodissociation or photodetachment processes. The ions HCO3− and HCO3−⋅H2O have also been investigated, and upper limits determined for their total photodestruction. The experiments were performed using a drift tube mass spectrometer coupled with an argon ion laser and a tunable dye laser. The cross section values vary from 2×10−20 to 1×10−17 cm2, and in most cases photodissociation is the predominant process. In CO3− and O3− evidence is found for bound, predissociating excited states.
On the composition of nuclei in binary systems
Authors: Reiss H. , Shugard M.
Published: February 2003

It is shown that some past thermodynamic treatments of the so-call ’’classical’’ nucleus for nucleation in a liquid–liquid miscibility gap have neglected certain important terms. These occur in the chemical potential and are associated with the dependence of interfacial tension on composition. A careful thermodynamic development is presented which yields the more complete result. In 1959 Cahn and Hilliard (CH) presented a thermodynamic theory for the nucleus based on the use of ’’gradient’’ terms in the interfacial transition zone in place of the conventional interfacial tension. The properties of their nucleus differed appreciably from those of what they termed the ’’classical’’ nucleus in connection with which more conventional interfacial concepts are used. For example, at the spinodal, the CH nucleus has no free energy of formation and is of infinite size with a composition infinitesimally different from that of the parent solution while the ’’classical’’ nucleus requires finite free energy, has finite size, and a composition close to that of one branch of the coexistence curve. There are many other differences. However, when the ’’classical’’ nucleus is subjected to the complete thermodynamic treatment it assumes all of the features of the CH nucleus, and proves to be essentially equivalent. Since the CH method and the classical have certain complementary features, one or another is the most useful depending on the problem involved. Both Heady and Cahn (HC) and Sundquist and Oriani (SO) have performed experiments which indicate that the conventional theory of nucleation fails for supercoolings within a miscibility gap. Although the analysis in this paper indicates that their estimates of the thermodynamic properties of the nucleus, from experimental data, via the so-called ’’tangent rule’’ may be incomplete, the more precise free energy barrier is found to be even smaller than their estimate, thus adding strong support to their claim that the conventional theory fails.