bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of collision-induced transition rates between rotational levels of NH3
Authors: Prakash Vinod , Boggs James E.
Published: February 2004

The method for calculating collision-induced transition rates presented in an earlier paper has been applied to four-level systems in the ammonia molecule. The transition rates in pure NH3 and in NH3 perturbed by H2, D2, HD, para-H2, N2, and O2 are calculated. The intensity changes (ΔI/I) are derived from these rates and compared with the experimental values.
Close-coupling approach to gas-solid energy transfer
Authors: Wolken George
Published: February 2004

The inelastic scattering of a gas molecule from a solid surface is treated quantum mechanically and in three dimensions using the close-coupling formalism. Energy transfer processes involving internal states of the molecule and one-phonon states of the solid are included as well as arbitrary diffractions. The phonon quantum number is replaced by a continuous variable. The dependence of the unknown wavefunction on this continuous variable is expressed as an expansion in a complete set of known functions having this continuous quantum number as argument. This substitution results in the continuously infinite set of coupled differential equations being replaced by an infinite set of discrete coupled equations. Truncating this set after a finite number of terms leads to finite sets of coupled equations which are solved by standard techniques. In applying this procedure to a simple example (which, nevertheless, provides a stringent test of the method) reasonably accurate results are obtained with a basis set of only 25 functions describing the continuous quantum number. On the basis of this test, it is suggested that this method appears to be practical for computing accurate gas-solid one-phonon energy transfer probabilities and should be most useful when many one-phonon states are involved in the collisions (thereby complimenting ``near-specular'' energy transfer theories).
Configurational properties of self-avoiding walks generated in the presence of an interacting solid barrier
Authors: Lax Melvin
Published: February 2004

Self-avoiding walks confined to the diamond lattice were generated in the presence of an interacting solid barrier by the method of exact enumeration. The behavior of some configurational properties such as the mean-square end-to-end distance, average maximum normal to the surface distance of the chains, average number of adsorbed segments, etc., was investigated as a function of the interaction energy ε. All properties studied were found to obey a simple asymptotic expression of the form ≃Nγ, where P is a generalized configurational property and γ is a critical index. Some estimates of γ as a function of ε are reported.
Valence electron studies with Gaussian-based model potentials and Gaussian basis functions. III Applications to two-valence-electron systems composed of combinations of Li, Na, H, or their unipositive ions
Authors: Switalski Jurgen D. , Huang J. T. J. , Schwartz Maurice E.
Published: February 2004

A previously developed simple valence-only electronic structure theory based on atomic core model potentials and using flexible Gaussian valence basis functions is applied to the two-valence electron systems Li2, Na2, NaLi, LiH, NaH, Li3+, Na3+, Li2Na+, LiNa2+, LiH2+, Li2H+, NaH2+, Na2H+, and H2, within the SCF MO model. Results for calculated equilibrium geometries and energy changes for certain chemical reactions are compared to the corresponding quantities from analogous all-electron ab initio calculations. The model potential results are quite similar to those from the ab initio ones and are generally satisfactory for such a simple theory. There is a tendency toward slightly long internuclear distances (average deviation of all unique independent distances is +0.06 bohr) and slightly high energy of complex relative to separate constituents (average deviation of dissociation reaction energies is −2.1 kcal/mole) in these calculations relative to the all-electron ones, the explanation of which will require future detailed analysis of both the model potential valence-electron and the ab initio all-electron calculations.
Configuration coordinate model for the hydrated electron. III. Diffusive motion
Authors: Tachiya Masanori
Published: February 2004

The diffusive motion of the solvated electron is treated by use of the configuration coordinate model. The configuration coordinate diagram appropriate to the diffusive motion of the hydrated electron is constructed by calculating the total energy of the hydrated electron under a series of orientational polarization functions which are appropriately chosen. The diffusive motion of the hydrated electron is discussed in terms of this diagram. The calculated activation energy of diffusion is 0.16 eV, which is in excellent agreement with experiment.
Nuclear magnetic resonance study of the transition metal monoborides. II. Nuclear electric quadrupole and magnetic shift parameters of the metal nuclei in VB, CoB, and NbB
Authors: Creel R. B. , Segel S. L. , Schoenberger R. J. , Barnes R. G. , Torgeson D. R.
Published: February 2004

Measurements are reported of the nuclear electric quadrupole interaction parameters (coupling constant and asymmetry) and the several anisotropic Knight shift parameters of the 51V, 59Co, and 93Nb nuclear magnetic resonance spectra in VB, CoB, and NbB monoborides, respectively. A detailed account is given of the method of extracting these parameters from the experimental spectra. The quadrupole coupling constants and asymmetry parameters are 51VB, 1.75 MHz, 0.95; 59CoB, 25.2 MHz, 0.74; and 93NbB, 20.4 MHz, 0.065. The isotropic components of the Knight shifts are all positive: 51VB, 0.32%; 59CoB, 0.69%; and 93NbB, 0.24%. Despite the close similarity in the structures of these compounds, neither the quadrupole nor Knight shift parameters scale in a simple manner with the nuclear properties. Thus, even in the cases of VB and NbB, it appears that a rigid-band type approximation furnishes a poor description of the actual changes in the electronic structure.
Assignment of the lowest 3Π and 1Π states of CaO, SrO, and BaO
Authors: Field Robert W.
Published: February 2004

New techniques for the assignment of perturbations in electronic spectra are described and applied to perturbations in the A1Σ-X1Σ bands of CaO, SrO, and BaO. These techniques utilize observed perturbation matrix elements to establish electronic and vibrational assignments of perturbing states. Using only data reported by Lagerqvist and co-workers between 1949 and 1951 it has been possible to assign perturbations of the A1Σ+ state to a 1Π state (A′1Π) and to three components of an inverted 3Π state (a3Πi). Absolute vibrational assignments have been made and the following spectroscopic constants obtained (in cm−1 with one standard deviation uncertainty in the last digit in parentheses): CaOSrOBaOA′1Πa3ΠiA′1Πa3ΠiA′1Πa3Πiν008564(16)8225(25)9794(10)9055(5)17 568(10)17 372(10)A (3Π)⋯−58(3)⋯−70(2)⋯−105(10)ωe557.5(86)556.2(100)460.3(8)463.5(8)448.3(7)448.3(7)ωexe3.31(20)3.30(22)1.61(5)1.61(5)2.39(13)2.39(13)Be0.3353(68)0.3353(68)0.2610(5)0.2584(5)0.2244(5)0.2244(5)αe0.0015(7)0.0015(7)0.0023(4)0.0020(2)0.0014(2)0.0014(2)The A′1Π-a3Π energy separations are small, and the a3Π state, the lowest state which dissociates to ground state atoms, lies at surprisingly high energy. The X1Σ+ state is now proven to be the ground state of BeO, MgO, CaO, SrO, and BaO.
Intermolecular potential function model for crystalline hexachlorobenzene
Authors: Bates J. B. , Busing W. R.
Published: February 2004

An intermolecular potential function model based on atom-atom interactions was developed for crystalline hexachlorobenzene. The potential was constructed from terms including Coulomb interaction, van der Waals attraction, and exponential repulsion. Potential energy parameters were varied to obtain the best agreement between observed and calculated lattice energy, lattice parameters, molecular orientation, and optically active external mode frequencies. The results are compared with two other recently proposed potential function models for hexachlorobenzene.
Generalized oscillator strengths through the water vapor spectrum to 75 eV excitation energy; electron kinetic energy 500 eV
Authors: Lassettre Edwin N. , White E. Roderick
Published: February 2004

Generalized oscillator strengths (GOS) as functions of momentum change are reported for four peaks in the electron impact spectrum of water vapor. Differential generalized oscillator strengths are also reported at seven points in the continuum. Extrapolated (to ΔP=0) oscillator strengths are given at even finer intervals. Most of the experiments were done at about 500 eV kinetic energy, but two transitions were studied at 400 eV kinetic energy to test the Born approximation.
Structural aspects of nonlinear optics: Optical properties of KIO2F2 and its related iodates
Authors: Bergman J. G. , Crane G. R.
Published: February 2004

We report our measurements on KIO2F2 and compare these results with the parent MIO3 compounds where M denotes H, Li, etc. Our results show that the nine observed nonlinear coefficients (d's) in these four different crystal systems, composed of IO3− and IO2F2− ions, are geometrically related to only one microscopic bond polarizability (β), the ∥ and ⊥ components of which are (3.6±0.4)×10−30 esu and (1.0±0.1)×10−30 esu, respectively. We further report that the nonlinear polarizability of the iodine lone pair is equivalent to that of an iodine-oxygen bond ∼1.85 Å. Microscopic theories relate the observed bulk nonlinear coefficients (d's) to the individual bond polarizabilities (β's) via [d = Σ(G∥β∥+G⊥β⊥)], where (β∥,β⊥) represent the ∥ and ⊥ components of the bond polarizabilities, respectively, and (G∥,G⊥) are the appropriate geometrical factors, viz., unit cell volumes and direction cosines of the bonds. Current theories maintain that β⊥ can be neglected since β∥≫β⊥. We find that while β⊥ is indeed smaller than β∥, it is not negligible, i.e., β∥∼ 3.6β⊥ for iodine-oxygen bonds. We further find that in certain cases G⊥∼ 10G∥. These two observations, which show that G∥β∥ ∼ G⊥β⊥, being previous calculations of β's and d's based on setting β⊥=0 into serious question.
Experimental and theoretical studies on the excited state polarizabilities of benzene, naphthalene, and anthracene
Authors: Mathies Rich , Albrecht A. C.
Published: February 2004

Through electric field perturbation techniques, the change in the trace of the polarizability tensor upon electronic excitation, as well as one component of that tensor, have been determined for the 1La and 1Lb transitions in naphthalene and for the 1La transition in anthracene. Also, a revised estimate of the change in the in-plane polarizability for the 1A1g→1B2u (1Lb) transition in benzene is given. These experiments have been carried out on the 0–0 band for the 1La transitions and on the first vibronically allowed band for the 1Lb transitions. In all cases, these experiments were performed with the aromatic hydrocarbon dissolved in a rigid amorphous solution of 3-methylpentane (3-MP) at 77°K. These results are compared with values derived from π-electron (PPP-SCF) and all valence electron (CNDO/S) calculations. Finally, computed ground state polarizabilities are compared with existing experimental results, and calculations of electric field induced oscillator strengths for the 1La and 1Lb transitions in benzene are reported.
Effect of spatial dispersion on the S-polarized optical properties of a slab dielectric
Authors: Philpott Michael R.
Published: February 2004

A microscopic theory of the reflection, transmission, and absorption of S-polarized light by a slab dielectric consisting of N planes of molecules is developed. The interactions between molecules are assumed to be of the point dipole type. The change in the internal and exciting electric fields in the surface planes is included since a rigorous solution of Maxwell's equations is obtained. The results of the macroscopic theory of Kliewer and Fuchs are recovered in the limit that dipole interactions between crystal planes are negligible compared to interactions within a plane. Calculations exploring the effects of spatial dispersion and slab thickness on the power spectra are described.
Vibrational spectra of matrix isolated alkali metal chlorate ion pairs
Authors: Smyrl Norman , Devlin J. Paul
Published: February 2004

The alkali metal chlorates have been found to volatilize without dissociation so that matrix isolation of the molten salt vapors permits spectroscopic study of the vibrational modes of the chlorate anion in the monomeric M+ClO3− ion pairs. The spectra clearly show evidence of the cation polarization of the anion since well-separated doublets have been observed for ν3 and ν4, both of which are doubly degenerate for the undistorted anion. However, the ν3 splitting is small compared to the splitting of the analogous mode for the nitrate monomers, M+NO3−, and also by contrast, the chlorate splitting is insensitive to a change in metal cation. The vibrational data have been used to deduce a modified valence force field for the ion pairs which shows a strong anion polarization, increasing through the series from potassium to lithium. Nevertheless, the force fields confirm that the anion distortion is relatively small compared to that reported for the nitrate anion in the M+NO3− monomers. Some infrared and Raman bands have also been detected for the dimeric (MClO3)2 species, but with the possible exception of KClO3, the dimer concentration in the matrices was quite low suggesting that the dimer is only a minor component of the molten chlorate vapors.
Effective pair potentials for liquid Na and liquid K
Authors: Ailawadi Narinder K. , Banerjee P. K. , Choudry A.
Published: February 2004

Recent x-ray structure data has been used to generate effective pair potentials for liquid sodium and liquid potassium. This is done on the basis of three current theories (Percus-Yevick, hypernetted chain, and Born-Green) which relate the effective pair potential to the radial distribution function. Qualitatively, all the three pair potentials have similar features. Contrary to the recent suggestion of Howells and Enderby, the Born-Green theory seems to be equally applicable to liquid metals.
Numerical results on the radius of gyration of surface interacting self-avoiding walks
Authors: Lax Melvin
Published: February 2004

Information on , the radius of gyration of surface interacting self-avoiding walks, has been obtained by the method of exact enumeration. In particular, it was found that in the limit  ≃ A Nγ where γ ≃1.23. The configurational ratio /, where  is the mean square end-to-end distance, was found to reach a limiting value of 0.1355 in the presence of a barrier as opposed to the known value of 0.157 obtained in the absence of a barrier.
Disappearances of COOH infrared bands of benzoic acid
Authors: Hayashi S. , Umemura J.
Published: February 2004

Infrared spectra of benzoic acid and benzoic acid-d were obtained in the range of temperatures from liquid nitrogen to liquid helium. The C=O stretching band at 1688 cm−1, the strongest absorption band of this compound in the over-all infrared region at room temperature, decreases in intensity with decreasing temperature and disappears near liquid-helium temperatures. Near this temperature, also lost was the band at 959 cm−1 which has been assigned to the OH out-of-plane vibration. For the deuterated species both bands at 1689 and 1679 cm−1, which have been interpreted as splitting due to Fermi resonance of the C=O stretching vibration, were lost. Close to the positions of these lost bands, alternative bands, which are assignable to the same modes and increase in intensity with decreasing temperature, are found. The results support the postulate proposed in our earlier work that two distinct equilibrium configurations of benzoic acid dimer coexist in the crystal.
Angular momentum adapted wavefunctions and their reduced transition density matrices
Authors: Hunter L. W.
Published: February 2004

The construction of angular momentum adapted kets is discussed first. The reduced transition density matrices of two arbitrary angular momentum adapted states are then expressed in terms of rotationally invariant components and in terms of ``standard state'' matrix elements. The latter results reduce to formulas obtained by McWeeny and Mizuno for spin angular momentum density matrices.
Equations of motion method: Excitation energies and intensities in formaldehyde
Authors: Yeager Danny L. , McKoy Vincent
Published: February 2004

We have used the equations of motion method to study the excitation energies and intensities of electronic transitions in formaldehyde. The calculated excitation energies and oscillator strengths agree well with experiment and suggest explanations for some unusual features recently observed in the optical absorption and electron scattering spectrum of formaldehyde in the vacuum ultraviolet.
Theoretical basis for the Rouse-Zimm model in polymer solution dynamics
Authors: Zwanzig Robert
Published: February 2004

This article presents a generalization of some recent work by Bixon on the theoretical foundations of the Rouse-Zimm model in polymer solution dynamics. In particular, a procedure is described for constructing the ``best possible'' Rouse-Zimm model for an arbitrary polymer, starting from the equilibrium distribution of polymer conformations and using either Kirkwood's generalized diffusion dynamics or stochastic dynamics. The method is based on an application of linear response theory to the calculation of certain time correlation functions for polymer dynamics.
Electron spin resonance study of γ-irradiated cadmium formate dihydrate and manganese(II) ions in cadmium formate dihydrate
Authors: Booth R. J. , Herring F. G.
Published: February 2004

ESR spectra of radiation induced Cd+ ions have been observed in monoclinic Cd(HCO2)2 · 2H2O at 77 K. A single-crystal study showed that there is a preferred capture by Cd2+ ions occupying the more asymmetric of the two cation sites. A comparative study of Mn2+ ions, substitutionally introduced into Cd(HCO2)2 · 2H2O, carried out at room temperature confirmed this result. The Mn2+ ions showed no preference for either of the sites. The results indicate that there is little distortion of the crystal structure on cooling or when the electron excess center is produced.
Phenomenological manifestations of quantum-mechanical tunneling. I. Curvature in Arrhenius plots
Authors: Stern Marvin J. , Weston Ralph E.
Published: February 2004

The extent of nonlinearity that quantum-mechanical tunneling, through one-dimensional Eckart barriers, can produce in Arrhenius plots is calculated as a function of barrier height (V*), barrier ``frequency'' (ν*), and temperature range. It is shown that Arrhenius-plot curvature is not a simple function of the extent of tunneling but is favored by high barriers and values of u*=h ν*/k T around 8. The experimental significance of the predicted extent of nonlinearity is discussed in general and with regard to actual cases for which curved Arrhenius plots have been interpreted as manifestations of tunneling.
Study of molecular rotations in some aromatic compounds by cold-neutron scattering
Authors: Trepǎdus V. , Râpeanu S. , Pǎdureanu I. , Parfenov V. A. , Novikov A. G.
Published: February 2004

The rotational motion of benzene, toluene, and phenol molecules in the liquid state has been studied by incoherent inelastic neutron scattering. The experiments have been carried out at DIN-1 spectrometer in Dubna. The observed area and broadening of the quasielastic peaks as a function of momentum transfer have been compared with those predicted by Larsson models. The area of the quasielastic peak as a function of κ2 shows a slightly oscillatory behavior. For the linewidth curves this behavior is smeared out by the term containing the classical diffusion constant that is larger than the term containing the Bessel functions. The transient nature of the liquids is discussed. The main parameters describing the molecular rotations obtained from the best fits are reported. By using the extrapolation technique, the generalized frequency distributions are obtained. These spectra show distinct peaks especially in the region 15–250 cm−1. All the corresponding transitions are in good agreement with the optical spectroscopic measurements.
Ab initio configuration interaction studies of the π-electron states of benzene
Authors: Hay P. Jeffrey , Shavitt Isaiah
Published: February 2004

Ab initio configuration interaction studies of the π-electron states of benzene were carried out with a double-ζ basis set of contracted Gaussian functions augmented by two diffuse π functions on each carbon atom. The core potential of the σ electrons was obtained from an all-electron SCF calculation on the ground state. Vertical excitation energies of 5.00, 7.64, and 8.34 eV were obtained for the 1B2u, 1B1u, and 1E1u states, respectively, corresponding to the e1g→e2u excitation; the first two of these levels have a valencelike electron distribution, but the 1E1u state was found to have a diffuse 1e2u natural orbital, with  = 38 bohr2. The analogous set of triplet states, all of which are valencelike, have calculated vertical excitation energies of 3.83 (3B1u), 4.98 (3E1u), and 7.00 eV (3B2u). The low-lying valence states 1E2g (8.33 eV) and 3E2g (7.28 eV) were found to have substantial double-excitation character, but no additional valence E2g states were obtained. Many other states, including quintets, Rydberg levels, and positive ion states, were computed and correlated with experimental data, where available. Discrepancies between computed and experimental energy levels are probably due in large measure to the frozen σ core approximation employed in this work, though basis set limitation may also play a part in some cases. An examination of the characteristics of the computed wavefunctions does not support some of the concepts used as a basis for semiempirical π-electron theories.
Transient absorption and emission and the measurement of T1 and T2 in the J O→1 rotational transition in OCS
Authors: McGurk J. C. , Hofmann R. T. , Flygare W. H.
Published: February 2004

Stark switching microwave experiments on transient absorption and transient emission that allow the measurement of T1 and T2 in the J = 0→1 transition in OCS are described. The results from the transient absorption experiments are T1 = (26±4) × 10−6 sec · mtorr and T2 = (33±7) × 10−6 sec · mtorr. The results of the transient emission experiments give T2 = (31±3) × 10−6 sec · mtorr. Thus, T1 = T2 within the experimental uncertainties. We also demonstrate the effects of π/2 and π pulses by using Stark switching.
Diffusion and field-gradient effects in NMR Fourier spectroscopy
Authors: Kaiser R. , Bartholdi E. , Ernst R. R.
Published: February 2004

In NMR Fourier transform spectroscopy, rf pulses are periodically applied to a spin system to generate a sequence of free induction decays which form the basis of spectroscopic measurements. In inhomogeneous magnetic fields, distortions of the free induction decay arise from superimposed spin-echo effects. They are strongly dependent on molecular diffusion which is also responsible for the nonexponential envelope of the echo train observed in a stopped pulse experiment. These effects are investigated by means of two independent methods, the Fourier expansion method and the partition method. The results are discussed and used to explain measurements made on a one-spin system. The influence of echoes on the sensitivity of Fourier transform spectroscopy is considered, and it is concluded that the achievable gain does not normally outweigh the complications arising from retention or enhancement of echoes. Experimental parameters are derived for efficient suppression of echoes by means of a periodically pulsed magnetic field gradient.
Temperature dependent 13C NMR and ir studies in Fe(CO)5−x(PF3)x, X = 0, 1, 2, 3, and 4
Authors: Mahnke H. , Clark R. J. , Rosanske R. , Sheline R. K.
Published: February 2004

The 13C NMR spectra for members of the series Fe(CO)5−x(PF3)x, where x = 0, 1, 2, 3, and 4 were studied for temperatures between + 25° and − 100 °C and carbon-phosphorus and carbon-fluorine spin coupling constants evaluated. The infrared spectra were also studied within the same temperature limits in the CO-stretching region and mole fractions for the different isomers within each composition x were evaluated at each temperature. The magnitude of the observed JCP spin-coupling constants can be accounted for by using the experimentally determined mole fractions and the trans, cis, and vicinal coupling constant increments. The magnitude of these three coupling constant increments were determined by using a set of observed coupling constants and the mole fractions. By using the mole fractions together with the time-averaged 13C chemical shifts, the chemical shift difference δσ0 between the axial and equatorial sites is found to be 17.7±1.5 ppm. Using this value and relaxation rates determined in earlier work, the frequency of exchange between axial and equatorial sites is calculated to be 1.1×1010 sec−1 in the five-coordinate nonrigid Fe(CO)5 molecule. This is the first time such a surprisingly fast flip frequency has been measured for such a large molecule.
Study of the electronic structure of molecules XXII. Additional ab initio computations for the barrier to internal rotation in polynucleotide chains
Authors: Lie George C. , Clementi Enrico
Published: February 2004

In a previous paper of this series (paper XIX) we reported an ab initio computation for the barrier to the internal rotation in the sugar-phosphate-sugar complex, C10H19O8P; the barrier corresponds to the configuration with ω″ = 45°, ω′ = Ψ′ = Ψ″ = φ′ = 0°, and φ″ varies from 0° to 360°. Here we repeat the same study with the C10H18O8P− complex (where one proton of the phosphate group has been removed). The new potential curve shows essentially a parallel displacement in total energy relative to the previously computed one. In addition we report two new computations of the barriers obtained by varying φ′ from 0° to 360°, while keeping ω″ = 45° and ω′ = Ψ′ = Ψ″ = φ″ = 0° (using Olson and Flory's notation). Again the Hartree-Fock model predicts similar features for the rotational barriers of the two complexes C10H19O8P and C10H18O8P−. The calculated barrier heights are 4.0, 3.2, and 7.0 kcal/mole for the φ″ variation in the C10H19O8P complex, and 5.7, 3.2, and 8.2 kcal/mole in the C10H18O8P− complex. The barrier heights for the φ′ variation are 18.8 and 30.3 kcal/ mole for C10H19O8P, and 34.8 and 35.2 kcal/mole for C10H18O8P−. Finally, the total energy for the internal rotation of φ″ is decomposed into a sum of contributions, representing either the electronic rearrangement following the rotation for a number of fragments composing the C10H18O8P− complex, or the pairwise interaction of such fragments during the rotation. The location of the potential minima and maxima is predicted by the pairwise interaction of the fragments. The energy for the rearrangement within each fragment is large.
Model of pre-existing traps for electrons in polar glasses
Authors: Tachiya M. , Mozumder A.
Published: February 2004

A model of pre-existing traps for electrons in polar glasses is presented. It is assumed that the condensed medium consists of a large number of cells and that each cell is composed of a certain number of molecular dipoles. Two specific cases are investigated. In one case each cell consists of four tetrahedrally located dipoles. In the other it consists of six hexahedrally located dipoles. However, it is assumed that the orientation of the dipoles is totally random. In both cases it is found that the electron is bound inside the cell if the sum of the radial components of the dipole moments in the cell is greater than 3.78 D. The energy of the bound state is calculated as a function of the sum of the radial components of the dipole moments. The relative number of cells with the sum of the radial components of the dipole moments lying between q and q + d q is calculated as a function of q. From these two quantities the relative number of pre-existing traps with the binding energy of the electron lying between E and E + d E is calculated as a function of E.
Modification of the exact finite method for boundary tension calculations on a hard sphere lattice gas
Authors: Woodbury George W.
Published: February 2004

The exact finite method, developed largely by Runnels, is modified so that calculations can be made of the properties of a single phase in equilibrium with other phases. The modification also allows the calculation of some boundary properties. Application of the method is made to the hard sphere lattice gas on a triangular lattice with first and second nearest neighbor exclusions. The results in this paper are in general agreement with earlier work on the same model: ρ/ρ0=0.78±0.01 and 0.69±0.01; lnzt = 1.715±0.02; Pt/kT =0.475±0.004. Two boundaries are investigated, the surface between two crystalline phases of different order, and a free surface. Boundary tensions and excess surface densities indicate this model has more complicated surface structures than those found earlier in another hard sphere lattice gas (square lattice-nearest neighbor exclusions).
Raman spectra of gases. XII. Twisting mode and barriers to planarity and interconversion in 2,3-dihydropyran, 1,4-dioxene, and cyclohexene
Authors: Durig J. R. , Carter R. O. , Carreira L. A.
Published: February 2004

The Raman spectra of gaseous 2,3-dihydropyran, 1,4-dioxene, and cyclohexene have been recorded in the low frequency region. Both the low frequency ring-twisting and ring-bending modes have been observed. The bending modes had ``type B'' band contours and provided little information on the potential surface. The ring-twisting overtones were of Alg species and had very sharp Q branches. The numerous hot bands associated with these ring-twisting overtones confirm the earlier assignment of the twisting mode from the far infrared analysis of the bend and difference tone of the twist and bend for 2,3-dihydropyran. Our assignment of the twisting mode in 1,4-dioxene required a reassignment of the bending mode for this molecule. By using these data, potential barriers to planarity and interconversion have been estimated by using perturbation theory. Analysis of the ring twisting mode in cyclohexene was carried out in a similar manner. The barrier of 2630±200 cm−1 to interconversion for cyclohexene was found to be nearly the same as that found for the oxygen containing molecules, but the barrier of 8800±1700 cm−1 to planarity was significantly larger than the corresponding quantity for the other molecules.
Large angle inelastic scattering of Na+ by D2
Authors: Dimpfl William L. , Mahan Bruce H.
Published: February 2004

We report measurements of the inelasticity of the large angle scattering of Na+ by D2, HD, and H2 in the initial relative energy range 0.74–16.9 eV. The interpretation of the vibrational inelasticity leads to the conclusion that perpendicular (C2ν) rather than collinear conformations of the Na+–D2 system produce the most intense inelastic scattering. The results of exact classical trajectory calculations which elucidate the effects of oscillator orientation and internal potential function on the inelasticity of collisions are presented. By fitting the calculated inelasticities to the experimental data, we have deduced both the energy and length parameters of a two term exponential repulsive potential for this system.
Hydrogen bonding in the bihalide ions
Authors: Jiang George J. , Anderson George R.
Published: February 2004

A study of hydrogen (H) bonding in the bihalide ions HCl2−, HBr2−, HI2−, and BrHCl− is reported. Using a semiempirical method reported earlier for HF2− and H5O2+ ions, this study extends the calculations to a series of H bonded species for which comparatively limited amounts of data are available. This procedure has enabled us to quantitatively discuss the shape of the potential energy surface governing the vibrational motion of the complex, to predict properties not yet observed in the laboratory, and to suggest a means by which the vibrational states of the complex (X–H⋯Y) may be correlated with those of its component parts (X–H and H–Y).
Collision-induced dissociation of 0.4–2.6 keV H2+ and D2+
Authors: Anderson S. J.
Published: February 2004

The energy distributions for protons (deuterons) from the collision-induced dissociation of H2+ (D2+) ions incident upon inert gas atom targets at energies in the range 0.4–2.6 keV have been measured. By modeling the ion source plasma an estimate of the vibrational distribution function of the primary beam has been obtained and used in a generalized spectrometer efficiency function to transform the spectra into the center-of-momentum frame of the ions. The resulting distributions are interpreted in terms of two main dissociation mechanisms: electronic excitation and polarization-induced vibrational-rotational excitation. Fine structure appearing in some spectra is attributed to rotational predissociation of a projectile-target complex.
Rotational spectral line broadening of OCS by noble gases
Authors: Cady W. A.
Published: February 2004

The theory of the pressure broadening of rotational spectra is described using (for the first time) the Magnus approximation to calculate the relevant S matrices. The latter's unitary character is thereby maintained. The relative contributions of the attractive and repulsive anisotropy terms in the interaction potential is investigated for the system of a linear molecule broadened by a noble gas atom. A ``centrifugal'' approximation is also introduced to write the linewidth expression in a closed analytic form and to simplify the computation. It is shown to be a good approximation for the systems investigated. An additional approximation described in an appendix can also be introduced, but it is valid only for systems in which the repulsive anisotropy does not make a significant contribution to the linewidth.
13C splittings from some hydroxycyclohexadienyl radicals derived from aromatic polycarboxylates
Authors: Filby W. G. , Günther K.
Published: February 2004

The ESR spectra of hydroxycyclohexadienyl radicals derived from the anions of pyromellitic and benzene-pentacarboxylic acids have been observed in a rapid flow systen (Ti/H2O2). Owing to their highly charged nature, the radical lifetimes were sufficiently enhanced so that 13C satellite lines could be observed in natural abundance. The numerical values and assignments of the hyperfine coupling constants suggest a planar system and can adequately be described by a Karplus-Fraenkel treatment.
Search for superradiant emission from ``complex'' organic molecules in the vapor phase
Authors: Pappalardo R. , Shapiro S. L. , Ahmed S. , Alfano R.
Published: February 2004

Vapors of perylene, coronene, 9–10 diphenyl-anthracene, dimethylpopop, rubrene, and rhodamine B have been optically pumped with picosecond pulses from a mode-locked, frequency-doubled ruby laser, in an attempt to produce single-pass superradiant emission in the respective broad-band emission. The results were negative or inconclusive. The feasibility of achieving population inversion in vapors of ``complex'' organic molecules is qualitatively discussed.
On the Herzfeld theory of metallization. Application to doped semiconductors, electron-hole liquids in semiconductors, and expanded states of simple metals
Authors: Berggren K.-F.
Published: February 2004

On classical grounds, Herzfeld in 1927 proposed a model which predicted that an element would become metallic when its molar volume became equal to or less than its refractivity. Recently, Ross has investigated this criterion by comparing its predictions with calculations on the rare gases and hydrogen, and with high pressure experiments on iodine and the alkali halides. Ross's investigation is here supplemented by applying the criterion to several systems of low density, and again Herzfeld's model is found to be surprisingly accurate. A connection with Mott's theory for the metal-nonmetal transition is briefly mentioned.
Isotope effects on the vapor phase second virial coefficients of the deuterated methanes
Authors: Fang Albert Y. , Van Hook W. Alexander
Published: February 2004

Isotope effects on the second virial coefficients of CH4, CH3D, CH2D2, CHD3, and CD4 have been measured between 110 and 300°K, by a differential expansion technique. The isotope effects obeyed the law of the mean to within the experimental precision (about ±0.2 cc/mole). That for CD4/CH4 is given by B(CD4) − B(CH4) = (2.08±0.14) +(399.8±24.2)/T. ΔB/B amounts to approximately 2% at 110°K increasing to 9% at 300°K. Our analysis indicates that the most important contribution to the virial coefficient isotope effect is due to the isotope effect on the molecular polarizability. The value for this effect extracted from the data is consistent with that derived by other methods. The effects correspond to isotopic differences on the Lennard-Jones constants of (σCH4 − σCD4)/ξCH4 = −0.013 ± 0.005 and (εCH4 − εCD4)/εCH4 = 0.005 ± 0.005. These are shown to be consistent with isotope effects on intramolecular C–H and CD bond lengths via a simple model calculation. Consistency with condensed phase molar volume isotope effects is also demonstrated.
Measurements of vibrationally excited molecules by Raman scattering. II. Surface deactivation of vibrationally excited N2
Authors: Black Graham , Wise Henry , Schechter Samuel , Sharpless Robert L.
Published: February 2004

Wall de-excitation of N2(v=1) was studied on a variety of different solid surfaces. Using 4880 Å laser radiation, we used the intensity of the Q branch of the anti-Stokes Raman scattering at 4382 Å to monitor the N2(v=1) concentration. The vibrationally excited nitrogen was produced by a thermal source and by a microwave discharge. The results were interpreted in terms of the two-dimensional diffusion equation with Poiseuille flow. The two sources of N2(v=1) gave somewhat different values for the wall deactivation coefficient γ. Furthermore, the results with the microwave source depended on the length of exposure of the surface to the afterglow. The observed differences are probably related to the fact that the microwave source also produces atoms and the thermal source does not. The lowest values of γ were recorded for quartz and Pyrex after 24 h of exposure to the afterglow. The results are interpreted in terms of a mechanism of heterogeneous vibrational de-excitation.
Vibrational energy transfer in CO from 100 to 300 °K
Authors: Stephenson John C. , Mosburg Earl R.
Published: February 2004

The laser fluorescence method, whereby CO molecules are optically pumped from the vibrational level v=0 to the v=1 state by frequency-doubled pulses from a CO2 laser, has been used to determine vibrational energy transfer rate coefficients for CO. Rates for the V-V exchange processes CO(0)+N2(1)→CO(1)+N2(0) and CO(1)+CO(1) →CO(0)+CO(2), and for the deactivation of CO(1) by H2 have been measured in the range 100°K ≤ T ≤ 300°K. The probability of energy transfer from N2 to CO decreases slightly as T decreases in this range, while the probability of the CO–CO V-V process is approximately proportional to T−1. Rate coefficients were also measured at T =297°K for the deactivation of CO(1) by the polyatomic molecules CH4, C2H4, C2H6, HCOOH, CH3COOH, CH3CHO, CH3OH, C2H5OH, H2O, D2O, H2S, and C4H10.
Bond-function analysis of rotational barriers: Methanol
Authors: Kern C. W. , Pitzer R. M. , Sovers O. J.
Published: February 2004

Our previous bond-function analysis of internal rotation in ethane is extended to methanol with the essential result that the dominant contribution to the barrier in these two molecules has the same origin, namely the overlap (exclusion-principle) interaction between closed-shell, localized bonds. The role of the CH3OH lone-pair orbitals is investigated. It is concluded that their main effect on the barrier is in partially shielding the oxygen nuclear charge from the bonding electrons. The amount of screening they provide is nearly independent of conformation. The potential energy functions of the staggered and eclipsed forms of methanol are studied with a double-zeta Slater basis. The calculated angles of methyl tilt are 3.4° and − 1.8°, respectively; the inclusion of tilt raises the barrier height by about 25%. The dipole moment is determined as a function of the rotational angle.
Dissociation energies of 7LiD
Authors: Stwalley William C. , Way Kermit R. , Velasco R.
Published: February 2004

The B1Π−X1Σ+ absorption spectrum of 7LiD has been reexamined. Evidence for an additional vibrational level (ν′=3) in the upper state has been found. Because this vibrational level is extremely close to the dissociation limit, only J′ = 1 and J′ = 2 levels occur. This additional information provides an improved dissociation limit of 34671.5±0.4 cm−1, 1.5 cm−1 lower and 20 times more precise than previous results. From this result, dissociation energies of 19767.7±0.4 cm−1 for the X state, 8588.4±0.9 cm−1 for the A state, and 201.8±0.4 cm−1 for the B state of 7LiD are derived.
Electronic structures of polymers using the tight-binding approximation. III. Density matrix approach to poly-L-alanine and polyglycine-water complex by the CNDO/2 method
Authors: Imamura Akira , Fujita Hiroko
Published: February 2004

In the present paper, formulas for calculating the electronic structure of polymers are derived in terms of the density matrix by the tight-binding approximation using the CNDO/2 method. This formalism was successfully applied to poly-L-alanine, which was difficult to treat by the usual SCF procedure because of the divergent behavior of the iterative calculation. The obtained result indicates that the right-handed α-helical conformation is more stable than the left-handed one and the planar one in agreement with experiments. The analysis of the total energy leads to the finding that the interaction between the methyl group and the carbonyl group is responsible for determining the relative stability of two α helices. Finally, the effect of water hydrogen-bonded to polyglycine was studied from the view point of the polymer effect.
Effects of molecular motion in the ESR spectrum of BrO32− ions in KBrO3 single crystals
Authors: Byberg J. R. , Jensen S. J. Knak , Kirkegaard B. S.
Published: February 2004

The ESR spectra at X band of BrO32− defects in KBrO3 crystals are investigated in the temperature interval 26–250°K. Spectra recorded below 115°K correspond to three distinct orientations of BrO32− in the lattice. Above 115°K the three spectra merge into a single spectrum. The observed spectral changes are described in terms of the jump model, assuming that BrO32− ``jumps'' between the three equivalent orientations. The model describes satisfactorily the temperature dependence of positions and shapes of all hyperfine lines between 80 and 160°K except for the static field B0 directed along the trigonal axis of the crystal. Assumption of a moderate temperature dependence of the static spin Hamiltonian extends the range of agreement with experiment to 200°K for most orientations of B0.
Stieltjes imaging of photoabsorption and dispersion profiles
Authors: Langhoff P. W. , Corcoran C. T.
Published: February 2004

Variational and moment-theory techniques for the construction of accurate approximations to photoabsorption and dispersion profiles in atoms and molecules are described and applied to simple atomic systems. It is shown that appropriately defined principal pseudostates, when employed in ab initio variational calculations, furnish the discrete transition frequencies and oscillator strengths that provide so-called principal representations of spectral moments. The Tchebycheff-Stieltjes-Markoff moment theory ensures that the principal frequencies and strengths furnish the information necessary for constructing convergent images of both the discrete and continuum portions of photoabsorption profiles. Evaluation of the appropriate principal value integrals results in convergent Stieltjes images of the associated photodispersion profiles. Detailed applications in the cases of the negative hydrogen ion and atomic hydrogen show that the Stieltjes imaging procedure is rapidly convergent for both the discrete and continuum portions of absorption and dispersion profiles in simple systems. Additional illustrative applications in the cases of atomic helium and lithium show that photoabsorption profiles with simple structures can be accurately imaged even when the pseudostates employed are not necessarily principal ones. The present development extends previously described variational and moment-theory techniques for approximating frequency-dependent dipole polarizabilities in their analytic regions to the real frequency axis within photoabsorption intervals. Moreover, the Stieltjes theory shows that conventional configuration interaction methods with square-integrable basis functions can be employed in the calculation of principal pseudostates and associated photoabsorption and dispersion profiles, thereby avoiding the explicit construction of accurate approximations to the complete set of discrete and continuum eigenstates required in more customary approaches.
Intermolecular potential between an atom and a diatomic molecule: The structure of ArCIF
Authors: Harris Stephen J. , Novick Stewart E. , Klemperer William , Falconer Warren E.
Published: February 2004

The radio-frequency and microwave spectrum of Ar35ClF has been measured by molecular beam electric resonance spectroscopy. The molecular constants are: Ar35ClF¯Ar37ClF¯B1327.113(5)MHz1319.650(5)MHzDJ4.66(20)kHz4.72(20)kHzμa1.053(3)DeqQa−140.869(15)MHz−111.053(15)MHzThe atomic arrangement is Ar–Cl–F and the vibrationally averaged argon-chlorine distances are 3.3301(1) and 3.3290(1) Å in Ar35ClF and Ar37ClF, respectively. The Ar–ClF bond stretching frequency is 47 cm−1. From the value of eqQa the equilibrium structure is linear with an angle bending frequency of 41 cm−1. The linear structure is striking evidence against the validity of an additive pair potential for an atom and a diatomic molecule. The observed structure is well predicted by Walsh's rule for triatomic molecules.
Calculation of ionization probability from experimental data
Authors: Santos A. F. dos , Figanier J.
Published: February 2004

In this paper the description is made of a mathematical method of estimating the probability of ionization of molecules from experimental data, assuming that the emission energy of the ionizing electrons is known. The method does not require any assumption about the shape of the experimental curves outside the range of the equipment and makes it possible to obtain a certain noise removal by using physical knowledge about the ionization probability. The method is tested through an artificial example, the results being in closer agreement with the ``true'' curve than those obtained by other methods.
Quantum ergodicity and vibrational relaxation in isolated molecules
Authors: Nordholm K. Sture J. , Rice Stuart A.
Published: February 2004

Recent advances in classical ergodic theory have produced qualitative information about the dynamics of anharmonic systems that is relevant to internal molecular dynamics and to unimolecular reaction rate theories. We describe here the results of an attempt to translate this progress into quantum molecular dynamics. Existing theories of quantum ergodicity are found to be ill suited to our task, so an extended concept of quantum ergodicity closely adhering to the well established classical concept is suggested. The new concept has the desired relevance to relaxation processes in isolated molecules, and it allows straightforward numerical investigation of molecular models. We report results for several triatomic models and one model of a linear molecule with four atoms. A prevalence of nonergodic behavior is observed for energies below the minimum required for dissociation.