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15 Jun 1970

Volume 52, Issue 12, pp. 5977-6453

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New Partitioning Perturbation Theory. I. General Formalism

Phillip R. Certain and Joseph O. Hirschfelder

J. Chem. Phys. 52, 5977 (1970); http://dx.doi.org/10.1063/1.1672896 (11 pages) | Cited 64 times

Online Publication Date: 8 September 2003

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By the use of partitioning techniques, a general formalism is developed for considering degenerate, almost‐degenerate, and electron‐exchange perturbation problems. In effect, we generalize the Van Vleck–Kirtman approach to arbitrary orders and arbitrary normalization and obtain three types of approximations: In the modified Kirtman treatment the functions through the Nth order are fully normalized and the energies are obtained as the roots of the secular equation. The DE–FOP–VIM approximation is the same except that the normalization of the functions is energy optimized. The Kirtman approximation uses the same functions as the modified Kirtman but the energies are obtained as the roots of a much simpler secular equation which results from a factorization of the original secular equation (except for terms of order 2N + 2). The Kirtman energies are not upper bounds. Löwdin's formalism is equivalent to the Modified Kirtman with the exception that Löwdin uses intermediate normalization. Electron exchange problems are considered more explicitly in a companion paper with the use of symmetry considerations.

New Partitioning Perturbation Theory. II. Example of Almost Degeneracy

Phillip R. Certain, David R. Dion, and Joseph O. Hirschfelder

J. Chem. Phys. 52, 5987 (1970); http://dx.doi.org/10.1063/1.1672897 (6 pages) | Cited 10 times

Online Publication Date: 8 September 2003

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A system of two coupled simple harmonic oscillators where many of the energy levels are almost degenerate doublets serves as an excellent “guinea pig” for testing many perturbation techniques including the modified Kirtman, Kirtman, and DE–FOP–VIM treatments discussed by Certain and Hirschfelder in a companion paper. These methods are compared with the “usual” approach to almost‐degenerate problems which makes the zeroth‐order energies of the doublet pair degenerate by a suitable choice of the zeroth‐order Hamiltonian. In addition, four types of Rayleigh–Schrödinger expansions are considered. The best values of the energy are given by the Kirtman treatment. However, the DE–FOP–VIM and the modified Kirtman procedures give values almost as good, and have the added advantage that they give upper bounds to the energy of the states which are considered.

New Partitioning Perturbation Theory. III. Applications to Electron Exchange

Phillip R. Certain and Joseph O. Hirschfelder

J. Chem. Phys. 52, 5992 (1970); http://dx.doi.org/10.1063/1.1672898 (8 pages) | Cited 21 times

Online Publication Date: 8 September 2003

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A new partitioning perturbation technique provides a rigorous derivation and generalization of the Hirschfelder–Silbey formalism for treating electron exchange problems. A new method of solving the first‐order perturbation equation is introduced. The first‐order wavefunction is the sum of the polarization function which describes van der Waals correlations and an exchange function which introduces ionic terms. The exchange function is determined variationally for both the ground‐state H+H+ and H+H interactions. In the many‐electron case, the first‐order equation reduces to a set of one‐ and two‐electron equations.

Crystal Structures of the Three Modifications of Nitrogen 14 and Nitrogen 15 at High Pressure

A. F. Schuch and R. L. Mills

J. Chem. Phys. 52, 6000 (1970); http://dx.doi.org/10.1063/1.1672899 (9 pages) | Cited 99 times

Online Publication Date: 8 September 2003

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We have determined from x‐ray diffraction photographs that high‐pressure γ N2 is tetragonal with two molecules per unit cell in special position f of space group P42 / mnm. At an average pressure and temperature of 4015 atm and 20.5°K, respectively, the unit cell dimensions are a  =  3.957Å and c  =  5.109Å, giving a molar volume in good agreement with that from p–V–T measurements. The β N2 solid modification, which is contiguous with the melting curve, remains hexagonal up to at least 4125 atm and 49°K where the unit cell constants are a  =  3.861Å and c  =  6.265Å. Over the pressure range investigated, the c / a ratio is very close to the ideal value for closest packing of hard spheres. The atomic positions in hexagonal (β) N2, which are known to be highly disordered at low pressure, show no evidence of ordering at the highest pressures studied. The third allotrope, α N2, is cubic at 3785 atm and 19.6°K with four molecules in a unit cell 5.433 Å on a side. Both the Pa3 and P213 space groups, which have been reported at zero pressure, appear to be spatially possible at limiting high pressures for α N2. However, from our diffraction measurements on the cubic solid at all pressures, we were unable to prove the existence of the P213 structure. The measurements on pure 30N2 show that this isotope also exists in the same three solid modifications as 28N2 with cell dimensions that are similar for both isotopes. However, the transition to γ N2 at 20°K for the mass‐15 isotope occurs 400 atm lower than that for the mass‐14 isotope.

Ionic Collision Processes in Water Vapor

K. R. Ryan

J. Chem. Phys. 52, 6009 (1970); http://dx.doi.org/10.1063/1.1672900 (8 pages) | Cited 12 times

Online Publication Date: 8 September 2003

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Some ionic collision processes in water vapor have been studied by the techniques of high‐pressure single‐source mass spectrometry. Rate coefficients for reactions resulting from collisions of H2O+ with H2O, and of OH+ with H2O have been studied as a function of primary‐ion translational energy over the energy range of 0–8 eV. For purposes of calibration and comparison, the reaction leading to CH5+ production in methane gas has also been studied over the same primary‐ion energy range. The rate coefficient for H3O+ production from H2O+ / H2O collisions was found to drop from a value of 26 × 10−10 cm3 molecule−1⋅sec−1 for thermal ion reactions to a value of less than half of this for ions with a maximum energy of 4 eV. H3O+ production from OH+ / H2O collisions was found to proceed with a rate coefficient of 20 × 10−10 cm3 molecule−1⋅sec−1 for ions of thermal energy, but this coefficient had dropped to zero as the maximum ion energy was increased to 0.8 eV. Evidence is presented to support the contention that although H3O+ production decreases as the OH+ energy increases, the rate of removal of OH+ continues with high cross section The results indicate that in the ion energy region above 0.8 eV, OH+ is removed exclusively by charge transfer to H2O.

Effect of Pressure on Naphthalene‐d8 Phosphorescence in Durene Crystals

R. A. Beardslee and H. W. Offen

J. Chem. Phys. 52, 6016 (1970); http://dx.doi.org/10.1063/1.1672901 (5 pages) | Cited 8 times

Online Publication Date: 8 September 2003

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The phosphorescence lifetime of C10D8 in durene mixed crystals has been studied in the temperature range 77–320°K and under pressures of 0–30 kbar. Matrix compression to 30 kbar shortens the triplet lifetime at 77°K about 20%. At higher temperatures where thermally activated quenching is evident, the triplet decay is very sensitive to pressure and becomes nonexponential with increasing pressure. Compression decreases the activation energy and high concentrations of defects increase the pre‐exponential factor. The phosphorescence quenching is ascribed to charge‐transfer interaction with the host molecules at structural defects in the crystal lattice.

Shock Wave Compression of Benzene, Carbon Disulfide, Carbon Tetrachloride, and Liquid Nitrogen

Richard D. Dick

J. Chem. Phys. 52, 6021 (1970); http://dx.doi.org/10.1063/1.1672902 (12 pages) | Cited 84 times

Online Publication Date: 8 September 2003

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Hugoniot data to several hundred kilobar have been obtained for benzene, carbon disulfide, carbon tetrachloride, and liquid nitrogen. Standard high explosive techniques were used for generating the shock waves. Experimentally measured quantities were transformed to pressure and volume data by the impedance match method. The shock‐particle velocity data for the liquids are described by a linear relationship, however, a quadratic in particle velocity also provides an adequate representation of the data for carbon tetrachloride and liquid nitrogen. Benzene undergoes a transition at 133 kbar and carbon disulfide at 62 kbar. These transitions are accompanied by a volume decrease of approximately 16%. A double shock‐wave structure, observed in many solids which undergo a transition, was not observed in benzene and carbon disulfide. There is some evidence that carbon tetrachloride and liquid nitrogen undergo a transition at 165 and 135 kbar, respectively. Hugoniot curves calculated from a Lennard‐Jones and Devonshire (6‐9) and a modified Buckingham exp‐6 intermolecular potential fit the liquid nitrogen experimental Hugoniot curve between 20 and 170 kbar.

Hyperfine Structure Constants of HF and DF

J. S. Muenter and William Klemperer

J. Chem. Phys. 52, 6033 (1970); http://dx.doi.org/10.1063/1.1672903 (5 pages) | Cited 217 times

Online Publication Date: 8 September 2003

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The radio frequency spectrum of HF and DF is measured by the molecular‐beam electric resonance method. The measurements are in the lowest vibrational state (υ  =  0) and first rotational state (J  =  1). The constants obtained are:
math
The electron coupled spin–spin interaction, JHF  =  + 530Hz.

Nuclear Quadrupole Coupling Tensors of 27Al in Andalusite (Al2SiO5)

S. S. Hafner, M. Raymond, and Subrata Ghose

J. Chem. Phys. 52, 6037 (1970); http://dx.doi.org/10.1063/1.1672904 (5 pages) | Cited 10 times

Online Publication Date: 8 September 2003

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The nuclear quadrupole coupling tensors of 27Al at the two crystallographically nonequivalent Al3+ sites in andalusite, Al2SiO5, have been determined from nuclear magnetic resonance measurements. For this, the Hamiltonian matrix for the mixed magnetic and electrostatic interaction was diagonalized and a minimization technique based on the least‐squares principle was used. The quadrupole coupling constants and asymmetry parameters are:
math
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The site assignment which cannot be made from NMR data alone is based on point charge calculations (point multipole model). Previous assignments concluded from EPR data of Fe3+ and Cr3+ impurities at the Al3+ sites are confirmed. The principal axes of the magnetic Fe3+ and Cr3+ tensors deviate from the 27Al tensor axes by 1°–10°.

Electron Injection into Quinone Crystals

Mitsuyuki Soma

J. Chem. Phys. 52, 6042 (1970); http://dx.doi.org/10.1063/1.1672905 (3 pages) | Cited 3 times

Online Publication Date: 8 September 2003

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Photostimulated electron injection from an ethanol or water electrode into single crystals of tetrahalo‐substituted p‐benzoquinones was observed. The electron transfer processes involve the excited quinone molecules. By the addition of appropriate electron donor molecules such as p‐phenylenediamine to the electrode, electron injection in the dark could be observed. Excited chlorophyll molecules also caused electron injection to be enhanced.

Gol'danskii–Karyagin Effect in Dimethyl Tin Difluoride

R. H. Herber and Subhas Chandra

J. Chem. Phys. 52, 6045 (1970); http://dx.doi.org/10.1063/1.1672906 (4 pages) | Cited 19 times

Online Publication Date: 8 September 2003

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The temperature dependent asymmetry in the intensity of the two components of the Mössbauer resonance doublet in dimethyl tin difluoride can be related to the mean‐square amplitudes of vibration parallel and perpendicular to the cylindrical molecular symmetry axis, and hence to the anisotropy of the Mössbauer–Lamb faction (the Gol'danskii–Karyagin effect). With an assignment of the Δm  =  1 and Δm  =  0 transition in the Mössbauer spectrum based on a simple bond character description, an asymmetry ratio A  =  Mπ / Mσ of 0.78 ± 0.06 is derived from the Mössbauer data. This is in good agreement with the value A  =  0.72 derived from precision x‐ray diffraction data on (CH3)2SnF2 and constitutes an independent check on the presence of the Gol'danskii–Karyagin effect in such solids.

Test of the Monte Carlo Method: Fast Simulation of a Small Ising Lattice

R. Friedberg and J. E. Cameron

J. Chem. Phys. 52, 6049 (1970); http://dx.doi.org/10.1063/1.1672907 (10 pages) | Cited 81 times

Online Publication Date: 8 September 2003

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A very fast stochastic procedure is used to generate samples of configurations of a 4 × 4 periodic Ising lattice in zero field. Running on the IBM 7094, we require only 15 μsec to process each site (cf. Yang who required 300 μsec on the 7090) and hence we generate 4000 completely new configurations each second. Our main results are based on samples of 106 configurations at each of 10 temperatures; we also took samples of 107 configurations at three temperatures. The 4 × 4 lattice can be solved exactly without much difficulty. Hence our data give information about the Monte Carlo method itself, especially its rate of convergence. We define the statistical inefficiency (SI) in a variable as the limiting ratio of the observed variance of its long‐term averages to their expected (Gaussian) variance. (Thus, if the SI is 3, then averages of the variable taken over Monte Carlo runs of three million configurations will be as accurate as averages over one million configurations drawn randomly from the true ensemble. The SI accounts for correlations between configurations closely following one another in the Monte Carlo run.) We find that for this lattice the SI in energy never exceeds ½, and that its maximum occurs slightly above the temperature which is critical for the infinite lattice. We confirm earlier statements that the influence of the initial configuration is lost very quickly, except when two phases coexist.

Magnetic Susceptibility of IrO2 and RuO2

W. D. Ryden and A. W. Lawson

J. Chem. Phys. 52, 6058 (1970); http://dx.doi.org/10.1063/1.1672908 (4 pages) | Cited 12 times

Online Publication Date: 8 September 2003

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We have measured the magnetic susceptibility of IrO2 and RuO2 in the temperature range 4.2–300°K using the Faraday technique. We find for RuO2 at 300°K χa  =  1.09 × 10−6cm3/g and χa / χc  =  0.80, and for IrO2 at 300°K χa  =  0.92 × 10−6cm3/g and χa / χc  =  1.19. Our results are discussed and compared with the behavior of the susceptibility of some of the transition metals. The temperature dependence of χm in RuO2 is quite similar to that for some transition metals. The temperature dependence of χm in IrO2 below 30°K is quite different possibly owing to trace impurities.

Some Ion–Molecule Reactions of H3+ and the Proton Affinity of H2

J. A. Burt, J. L. Dunn, M. J. McEwan, M. M. Sutton, A. E. Roche, and H. I. Schiff

J. Chem. Phys. 52, 6062 (1970); http://dx.doi.org/10.1063/1.1672909 (14 pages) | Cited 71 times

Online Publication Date: 8 September 2003

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The flowing afterglow technique has been used to study the reactions of H3+ with a number of neutral reactants at thermal energies. Proton transfer was the only primary reaction observed with N2, CO, CO2, N2O, NO, CH4, C2H2, H2O, and NH3. Both proton transfer and dissociative charge transfer were observed with C2H4 and C2H6, while dissociative charge transfer is the exclusive primary process with NO2. Secondary reactions were observed with NO, C2H6, C2H4, and C2H2. Cluster ions were formed between NO+ and NO2 and H2O, between H3O+ and H2O, CO2, and CO, and between NH4+ and NH3 and H2O. Proton transfer was also observed between HN2+ and CO2, N2O, CH4, and H2O, and between HO2+ and H2 and N2. Rate constants were obtained for these reactions and are discussed. Limits could be placed on the proton affinity (P.A.) of H2 from the failure to observe rapid proton transfer to O2 and the observation of proton transfer to N2. These indicate 4.2 < P.A. (H2)< 4.7 eV with a recommended value of 4.4 eV. The technique can be used to measure relative proton affinities of gases.

Correlation Effects on ππ* Transition Energies in the Series of Linear Polyenes. III Dynamical Correlation Effects

Armelle Denis and J. P. Malrieu

J. Chem. Phys. 52, 6076 (1970); http://dx.doi.org/10.1063/1.1672910 (14 pages) | Cited 8 times

Online Publication Date: 8 September 2003

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An optimization of the 2pz atomic orbitals is rederived for the ground‐state energy of conjugated systems. Within some reasonable assumptions, this optimization (analogous to that proposed by Silverstone and Joy) allows the orthogonalized 3pz atomic orbitals to be considered as v rtual orbitals in the CI calculation when one starts from a SCF calculation performed in the minimal basis set of optimized n  =  2 atomic orbitals. The reorganization of the π* MO in the ππ* excited state leads to a spatial expansion in the singlet state and a spatial contraction in the triplet state. But this effect is less and less important when the dimension n of the π system increases, and the corresponding energetic correction decreases as n−2. A less pronounced effect is obtained on the π singly occupied orbital; the doubly occupied MO's are not significantly modified in the singlet state. The role of the 3pz atomic orbitals in the correlation effects on the transition energies is much more important. It is not mainly due to the π→3pz monoexcited configurations (which only give a correction proportional to n−1) but to the doubly and triply excited states: Their correction tends towards a constant value which has been estimated.

Vibrational Spectra and Structure of Oxalyl Chloride in the Crystalline and Fluid States

J. R. Durig and S. E. Hannum

J. Chem. Phys. 52, 6089 (1970); http://dx.doi.org/10.1063/1.1672911 (7 pages) | Cited 18 times

Online Publication Date: 8 September 2003

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The vibrational spectrum of oxalyl chloride, [COCl]2, has been recorded between 33 and 4000 cm−1. The infrared spectra of the oxalyl chloride molecule have been examined in the solid, liquid, and gaseous states. The Raman spectra of the solid and liquid have also been observed, and qualitative depolarization ratios have been measured. The vibrational spectrum of the crystalline material has been interpreted on the basis of C2h molecular symmetry and D2h15 space group symmetry. All 12 of the normal vibrations have been assigned, and the barrier to internal rotation around the C☒C bond has been obtained. Nine bands appear in the infrared and Raman spectra of the liquid/gaseous states which do not appear in the spectra of the solid. In light of depolarization data and the frequencies for the vibrations of the trans isomer, these bands are interpreted as arising from a cis rotamer. A temperature study was made in order to determine the relative stability of the rotamers. The trans isomer was found to be 2.2 kcal/mole more stable than the cis form. A rough estimate of the equilibrium mixture at room temperature based on intensities and an assumed equilibrium constant gives a value of 15%–20% for the cis isomer.

Vibrational Spectra and Structure of Small Ring Molecules. XVI. Vibrational Analysis and Ring‐Puckering Vibration of 1‐Pyrazoline

J. R. Durig, J. M. Karriker, and W. C. Harris

J. Chem. Phys. 52, 6096 (1970); http://dx.doi.org/10.1063/1.1672912 (12 pages) | Cited 5 times

Online Publication Date: 8 September 2003

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The infrared spectrum of gaseous 1‐pyrazoline has been measured from 33 to 4000 cm−1. The infrared and Raman spectra of the corresponding liquid sample have also been recorded. A vibrational assignment of the fundamentals is proposed which is consistent with the Cs equilibrium configuration. The assignment is based on the gas‐phase band contours, the depolarization values, and group frequency correlations. A series of 13 pronounced Q branches was observed in the far‐infrared spectral region, and they have been attributed to the strongly anharmonic ring‐puckering vibration. Although the far‐infrared frequencies could be reproduced by two different potential functions, a double minimum potential of the form V  =  23.40(z4 − 4.40z2) where z is the reduced ring‐puckering coordinate provides the most satisfactory interpretation of all the spectral data. The height of the inversion barrier is calculated to be 113 cm−1, and the equilibrium angle between the two dihedral planes of the puckered ring is 19.7° ± 1.0°. The results are compared with those obtained on cyclopentene.

Spectra and Structure of Small Ring Compounds. XIX. Vibrational Analysis and the Barrier to Pseudorotation of Germylcyclopentane

J. R. Durig and J. N. Willis

J. Chem. Phys. 52, 6108 (1970); http://dx.doi.org/10.1063/1.1672913 (12 pages) | Cited 21 times

Online Publication Date: 8 September 2003

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The infrared spectrum of germylcyclopentane in the gaseous state has been recorded from 4000 to 33 cm−1 and that of 1, 1‐dideutero‐1‐germylcyclopentane has been recorded from 4000 to 250 cm−1. The Raman spectra of the two liquids have been recorded and depolarization values determined. The data rule out the planar configuration for the germylcyclopentane molecule and are shown to be consistent with the twisted C2 molecular structure. The 39 normal modes have been assigned on the basis of their depolarization values, infrared band contours, isotopic shift factors, band intensities, and “group frequencies.” The ring‐bending mode was found at 113 cm−1 in the vapor phase of the “light” compound. The ring‐twisting mode for the d0 and d2 compounds was found at 273 and 269 cm−1, respectively, in the Raman spectrum. The 113‐cm−1 band in the light compound was found to be the first of a series of Q branches running to lower frequency. This series has been interpreted in terms of a relatively high barrier to pseudorotation. From midinfrared sum bands a similar series of transitions were obtained for the pseudorotation of the d2 compound. A potential function of the form V  =  − (2043 / 2)(1 − cos2θ) − (21 / 2)(1 − cos6θ) was found to fit nine observed far‐infrared transitions of the ring‐puckering mode. The calculated barrier to pseudorotation was 5.9 ± 0.1 kcal/mole for the “light” compound, and the spectroscopically derived parameter mq02 was found to be 18.7 × 10−40 g⋅cm2. The barrier in the corresponding d2 compound is estimated to be 6.0 ± 0.3 kcal/mole. The barriers are considerably higher than one might expect from existing theories and data on torsional barriers.

Ozone Ultraviolet Photolysis. I. The Effect of Molecular Oxygen

D. Biedenkapp and Edward J. Bair

J. Chem. Phys. 52, 6119 (1970); http://dx.doi.org/10.1063/1.1672914 (7 pages) | Cited 27 times

Online Publication Date: 8 September 2003

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To clarify the role of molecular oxygen in the photolytic decomposition of ozone, measurements of mixtures of ozone with helium, nitrogen, or oxygen were analyzed by the intermediate quantum yield method which separates effects due to fast and slow reactions by measuring the fast components shortly after flash photolysis. Analysis of the results gives the following rate constants (in liters/mole⋅second): O2 + O(1D) → O2(1Σg+) + O(3P),k4b  =  1.5 ± 0.8 × 1011;O2(1Σg+) + O3 → 2O2 + O(3P),k3b  =  4.0 ± 0.5 × 109. The efficiency of (4d) for forming O2(1Σg+) is found to lie in the range 1.0  ≥  α > 0.6. As a consequence of the high value of (k4b), which was previously neglected, rate constants reported previously should be revised as follows: O(1D) + O3 → 2O2,k2a  =  4 ± 2 × 1010;O(1D) + N2 → O(3P) + N2,k4a  =  2 ± 1 × 1010;O(1D) + Xe → O(3P) + Xe,k4c  =  5 ± 2 × 1010. The quoted error limits are those which represent the fit of the data to the assumed mechanism with appropriate allowances for uncertainties due to minority processes.

5142‐Å Transition in Thiophosgene (π* ← n); Rotational Analysis and Excited‐State Structure

John R. Lombardi

J. Chem. Phys. 52, 6126 (1970); http://dx.doi.org/10.1063/1.1672915 (4 pages) | Cited 7 times

Online Publication Date: 8 September 2003

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Rotational structure is observed in the 210310410 vibronic band of the lowest singlet π* ← n transition of thiophosgene (5142 Å). Computer analysis gives three excited‐state moments of inertia, from which, assuming a value for the C☒S bond length, an excited‐state structure may be determined.

Double Excitation in the Infrared Spectra of Self‐Associated Alcohols

M. Asselin and C. Sandorfy

J. Chem. Phys. 52, 6130 (1970); http://dx.doi.org/10.1063/1.1672916 (5 pages) | Cited 13 times

Online Publication Date: 8 September 2003

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At liquid‐nitrogen temperature, in glassy matrices, self‐associated alcohols exhibit two bands in the region of the first overtone of the OH stretching vibration. The one of lower frequency is shown to be the overtone, and the one of higher frequency a band due to simultaneous excitation by one quantum in two OH groups linked by hydrogen bonding.

Theoretical Investigations of Gas–Solid Interaction Phenomena. IV Spatial and Velocity Distributions

J. Lorenzen and L. M. Raff

J. Chem. Phys. 52, 6134 (1970); http://dx.doi.org/10.1063/1.1672917 (7 pages) | Cited 14 times

Online Publication Date: 8 September 2003

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A study of the spatial and final velocity distributions for gaseous particles reflected from a solid surface is reported. The three‐dimensional classical model previously used by the authors is employed to study the scattering distributions as functions of the incident particle velocity, the velocity distribution in the incident beam, and surface temperature. The broadness of the spatial scattering distributions is predicted to decrease with increasing incident velocity. The spatial distribution peak position is specular for large incident velocity, shifts toward the surface for intermediate velocity, and approaches the surface normal for small incident velocity. The model indicates that the spatial distribution dependence upon initial velocity causes velocity‐selected and thermal beams to give similar spatial scattering. For hot surfaces the spatial scattering is indicated to be a rather insensitive function of surface temperature. The velocity distributions of reflected particles are predicted to be non‐Maxwellian, bimodal for large incident velocities, and clearly different for velocity‐selected and thermal incident beams. The results indicate that final velocity distribution measurements may be the most informative characteristic of gas–solid interaction phenomena.

Self‐Diffusion and Radical Recombination in Imidazole Single Crystal

A. R. McGhie, H. Blum, and M. M. Labes

J. Chem. Phys. 52, 6141 (1970); http://dx.doi.org/10.1063/1.1672918 (4 pages) | Cited 7 times

Online Publication Date: 8 September 2003

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Self‐diffusion measurements in imidazole single crystal in the a crystallographic direction were performed with either Cl4 or tritium bound to nitrogen as tracers. Radical recombination studies were also performed as an independent method of assessing diffusive motion in the crystal. From both of these studies, it is concluded that, in the temperature range 80–90°C, self‐diffusion and radical recombination occur by a vacancy‐controlled bulk diffusion process. There is no indication that cooperative transport of protons through the crystal, which dominates the conduction process in the c direction, and appears as a component of the conduction process in the a direction, is at all operative in the diffusion process.

Total Elastic Cross‐Section Measurements for Argon on Argon

Bernard Baratz and R. P. Andres

J. Chem. Phys. 52, 6145 (1970); http://dx.doi.org/10.1063/1.1672919 (6 pages) | Cited 6 times

Online Publication Date: 8 September 2003

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Total elastic scattering cross sections for argon on argon are presented as a function of the relative velocity of collision. The “glory” extrema predicted to be present as well as the correct velocity dependence for a potential with long‐range 1 / r6 behavior are observed. The data, while not of sufficient quality to be inverted directly, yield constraints on the shape and position of the argon potential well.

Collisional Excitation of Small Molecular Ions

M. H. Cheng, M. H. Chiang, E. A. Gislason, B. H. Mahan, C. W. Tsao, and A. S. Werner

J. Chem. Phys. 52, 6150 (1970); http://dx.doi.org/10.1063/1.1672920 (7 pages) | Cited 52 times

Online Publication Date: 8 September 2003

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We have determined velocity vector distributions for NO+ and O2+ scattered from helium. As expected, the small angle scattering is elastic, but at angles greater than 60°, inelasticity which increases with the scattering angle is apparent. For angles greater than 100°, this inelasticity represents vibrational excitation of the molecule–ion. For initial relative kinetic energies between 4.3 and 25 eV and 180° scattering, the variation of the inelasticity is consistent with a new, corrected version of the classical theory of vibrational excitation. Three methods of calculating the angular variation of the inelasticity are presented and found to be consistent with the experimental data.
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