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15 Jun 1973

Volume 58, Issue 12, pp. 5193-5845

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Inelastic neutron scattering study of the ``rotator'' phase transition in n ‐nonadecane

John D. Barnes

J. Chem. Phys. 58, 5193 (1973); http://dx.doi.org/10.1063/1.1679130 (9 pages) | Cited 77 times

Online Publication Date: 22 August 2003

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A simple kinematic model for rotational jump diffusion of a normal alkane about its long axis (circular random walk model) is developed. Inelastic neutron scattering data obtained on the Fermi chopper time‐of‐flight instrument at the National Bureau of Standards reactor using an incident neutron wavelength of 2.47 Å (Δλ/λ ≃ 3.8%) are compared with the predictions of the model. Data taken below the temperature of the ``rotator'' phase transition in n ‐nonadecane (295 °K) show no quasielastic scattering due to diffusive motions. Data taken in n ‐nonadecane in its disordered solid phase show quasielastic scattering consistent with the circular random walk model. Estimates for values of the model parameters of 3.5 psec. for τ1 and N ≥ 8 are obtained.

Dissociation of carbon dioxide behind reflected shock waves

Anthony M. Dean

J. Chem. Phys. 58, 5202 (1973); http://dx.doi.org/10.1063/1.1679131 (7 pages) | Cited 15 times

Online Publication Date: 22 August 2003

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The apparent dissociation rate of CO2 has been measured by monitoring infrared emission from dilute CO2∕Ar mixtures behind reflected shock waves. These experiments covered the temperature range of 3700–5500 °K and a pressure range of 500–800 torr. The Arrhenius parameters (inunitsofcubiccentimetersmolecule−1⋅second−1) of k1 are: log A = −9.98±0.09 and Ea = 84.72±1.84 kcal/mole. The effect of impurities was minimized by keeping background pressures in the shock tube below 5×10−5 torr. Additional runs with 150 and 465 ppm CH4 added to 1% CO2∕Ar mixtures were also made. Assuming CH4 was the only impurity in those runs, numerical integration calculations of the likely mechanism were performed. Quantitative agreement with the experimental results was obtained using literature values for all rate constants and the value of k1 reported above. These results strongly suggest that the impurity levels in the ``clean'' CO2∕Ar system were indeed low (∼ 10 ppm) and thus could not account for the anomalously low value of Ea. This amount of impurity can raise the activation energy for the dissociation by less than 3 kcal∕mole. It is suggested that Ea for the dissociation under these experimental conditions is thus less than 90 kcal∕mole.

Hyperfine interactions and electron spin distribution in triplet state phenanthrene

R. Peter Frosch, Antonio M. Ponte Goncalves, and Clyde A. Hutchison

J. Chem. Phys. 58, 5209 (1973); http://dx.doi.org/10.1063/1.1679132 (7 pages) | Cited 7 times

Online Publication Date: 22 August 2003

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The anisotropic proton hyperfine interactions with the electrons of the triplet state phenanthrene molecule in diphenyl single crystals at ∼ 77°K were measured by electron paramagnetic resonance spectroscopy. The distribution of spin in the triplet state phenanthrene molecule was deduced from these measurements and compared with theoretical estimates of the spin densities for triplet state phenanthrene, phenanthrene negative ion, and phenanthrene positive ion.

On an evaluation of the accuracy of the uniform semiclassical approximation for differential elastic scattering cross sections

J. M. Mullen and B. S. Thomas

J. Chem. Phys. 58, 5216 (1973); http://dx.doi.org/10.1063/1.1679133 (6 pages) | Cited 18 times

Online Publication Date: 22 August 2003

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The uniform approximation to the differential elastic scattering cross section is extended to allow direct comparison of approximated cross sections with cross sections computed by exact evaluation of the partial wave sum using WKB phase shifts. Results of calculations are presented and an assessment is made of the accuracy and utility of the uniform approximation.

Matrix infrared spectrum and bonding in the monoiodomethyl radical

David W. Smith and Lester Andrews

J. Chem. Phys. 58, 5222 (1973); http://dx.doi.org/10.1063/1.1679134 (8 pages) | Cited 11 times

Online Publication Date: 22 August 2003

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The codeposition of CH2I2 diluted in argon with 6Li, 7Li, Na, or K atoms produces new infrared absorptions attributable to the alkali iodide and the CH2I free radical. The identity of the radical is confirmed by reacting the CHDI2, CD2I2, and CH2IBr precursors with alkali atoms. Absorptions assigned to the symmetric H�C�H bend, the symmetric C�I stretch, and the out‐of‐plane hydrogen bend are supported by vibrational analysis. The high C�I force constant (2.81±0.04 mdyn∕Å) indicates pi bonding in CH2I.

Vibrational relaxation of CO by O atoms

R. E. Center

J. Chem. Phys. 58, 5230 (1973); http://dx.doi.org/10.1063/1.1679135 (7 pages) | Cited 20 times

Online Publication Date: 22 August 2003

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The vibrational relaxation of carbon monoxide by atomic oxygen has been measured behind incident shock waves in the temperature range of 1800–4000 °K. The atomic oxygen was produced by the rapid thermal decomposition of ozone. The experimentally derived relaxation times can be expressed in the form p τCO�O = exp(54 T−1/3−7.3)μsec⋅atm, which corresponds to a collisional probability of the order of 10−2 for the vibration‐translation energy transfer. This is from two to three orders of magnitude larger than the probability for self‐relaxation by CO over the same temperature range.

Time resolution and characteristics of a broadband picosecond continuum and light gate

C. A. G. O. Varma and P. M. Rentzepis

J. Chem. Phys. 58, 5237 (1973); http://dx.doi.org/10.1063/1.1679136 (10 pages) | Cited 25 times

Online Publication Date: 22 August 2003

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A broadband continuum which last a few picoseconds can be generated in isotropic materials such as liquid H2O or D2O by single picosecond pulse excitation. It is demonstrated that the blue part of the spectrum is delayed relative to the red portion. A spectral analysis reveals a stimulated inverse Raman band around 260 cm−1 to the blue of the first anti‐stokes emission. We offer two alternative explanations for this observation. The open time of the light gate is shown to depend on various parameters and in the case of a CS2 shutter, it may be extended over much longer time intervals than the pulse duration. At the same time we have observed depolarization and isotropic scattering of the interrogating light.

Velocity distribution measurements of 0.06–1.4 eV argon and neon atoms scattered from the (111) plane of a silver crystal

R. B. Subbarao and D. R. Miller

J. Chem. Phys. 58, 5247 (1973); http://dx.doi.org/10.1063/1.1679137 (11 pages) | Cited 23 times

Online Publication Date: 22 August 2003

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Velocity distribution and out‐of‐plane density distribution measurements are reported in detail for 0.6–1.4 eV argon and neon atoms scattered from the (111) plane of single silver crystals. Incident energies were selected to probe the regime of epithermal scattering where significant changes in scattering direction were previously found to occur. Velocity and density distributions are combined and integrated to yield total transfer coefficients. The change in scattering direction is found not to be related to a transition to structure scattering but rather to a decrease in normal momentum transfer as the total scattering becomes more elastic. Structure scattering effects are more apparent in differential momentum transfer data which show a transfer of momentum from normal to tangential components, in agreement with calculations by McClure. The width of the scattering would therefore be a better parameter to indicate structural effects. An anomaly in the direction of energy transfer also appears which suggests that energy may be transferred from the crystal to the gas even though the mean incident energy may be greater than the mean lattice energy. In general the qualitative results of McClure for differential momentum transfer and of Oman for integrated transfer characteristics of the specific argon‐silver interaction appear to be substantially correct.

Cation self‐diffusion in single‐crystal MgO

B. J. Wuensch, W. C. Steele, and T. Vasilos

J. Chem. Phys. 58, 5258 (1973); http://dx.doi.org/10.1063/1.1679138 (9 pages) | Cited 54 times

Online Publication Date: 22 August 2003

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Cation self‐diffusion coefficients have been obtained for MgO in an argon atomosphere over a temperature range 1000–2400°C from concentration gradients determined with the aid of mass spectrometry. The problems associated with use of the short‐lived radioisotope 28Mg were avoided by employing the stable isotope 26Mg as a tracer. Samples were prepared utilizing vapor‐exchange, thick‐film, and semi‐infinite source boundary conditions at high, intermediate, and low temperatures, respectively, and were protected from contamination and volatilization by encapsulation in cylinders of pressed MgO powder. No significant difference in transport behavior was noted between crystals of moderate quality and those of the highest purity presently available. The temperature dependence of the diffusion coefficients may be represented by an activation energy of 2.76±0.08 eV and D0 of 4.19×10−4 cm2/sec. These parameters are comparable to those previously reported for impurity ion diffusion. The activation energy obtained is interpreted as that for cation migration. Previous measurements of cation self‐diffusion coefficients obtained with the short‐lived radisotope 28Mg are an order of magnitude larger and had been interpreted as intrinsic diffusion. The discrepency is attributed to doping introduced by the 28Si decay product of 28Mg.

Negative ion reactions with neutral ozone

J. A. Rutherford, B. R. Turner, and D. A. Vroom

J. Chem. Phys. 58, 5267 (1973); http://dx.doi.org/10.1063/1.1679139 (5 pages) | Cited 3 times

Online Publication Date: 22 August 2003

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Charge transfer reactions between O−,O2−,OH−, and NO2− and O3 have been studied to obtain cross sections for information of O3− The charge transfer reaction O3− on NO2 has also been remeasured. The range of ion energies considered extends from 1 to 500 eV. Upper limits have been obtained for the charge transfer cross section of F−, Cl−, and CO3−, with O3. The results show that the electron affinity of O3 must be close to accepted value of approximately 2 eV. The method used to produce a neutral beam of pure O3 is discussed.

Kinetic study of electronically excited phosphorus atoms, P(32DJ, 32PJ), by atomic absorption spectroscopy. II

A. U. Acuna, D. Husain, and J. R. Wiesenfeld

J. Chem. Phys. 58, 5272 (1973); http://dx.doi.org/10.1063/1.1679140 (8 pages) | Cited 2 times

Online Publication Date: 22 August 2003

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Electronically excited phosphorus atoms in the P(32DJ) and P(32PJ) states have been generated in the gas phase by pulsed photolytic irradiation and monitored by means of absorption spectroscopy using attenuation of atomic resonance radiation. The kinetic decay of these two low-lying, optically metastable states has been studied in the presence of the following collision partners: Ar, Kr, Xe, N2, CO, NO, Co2, N2O, PCl3, CH4, and C2H4, and second-order constants are reported for the removal processes at 300°K.

Ultraviolet absorption spectra of CdCH3, ZnCH3, and TeCH3

P. J. Young, R. K. Gosavi, J. Connor, O. P. Strausz, and H. E. Gunning

J. Chem. Phys. 58, 5280 (1973); http://dx.doi.org/10.1063/1.1679141 (4 pages) | Cited 38 times

Online Publication Date: 22 August 2003

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Ultraviolet absorption spectra were recorded for the transient radicals CdCH3, ZnCH3, and TeCH3 produced in the flash photolysis of the appropriate dimethyl metals. For CdCH3 and ZnCH3 two systems were observed and assigned to the two transitions  2E←math2A1 and math 2E←math2A1. For the TeCH3 radical only one system was observed which was assigned to the math←math transition. The progressions in the spectra are assigned to the upper state carbon‐metal stretching vibration (ν′3) and CH3 symmetric deformation vibrations (ν′2).

Polyhedral clathrate hydrates. XVII. Structure of the low melting hydrate of n-propylamine: A novel clathration framework

C. S. Brickenkamp and D. Panke

J. Chem. Phys. 58, 5284 (1973); http://dx.doi.org/10.1063/1.1679142 (12 pages) | Cited 3 times

Online Publication Date: 22 August 2003

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The crystal structure of the monoclinic modification of n-propylamine clathrate hydrate has been determined at −100°C. The space group is P21/n with cell dimensions, a = 12.43,b = 20.73,c = 17.28 Å. and β=89.3°. The water framework is described as a packing of small unoccupied 11 hedra and large concave polyhedra. The disordered amine molecules occupy convex regions of the concave polyhedra with the amine nitrogens hydrogen bonding to the framework.

Water molecule interactions. Stability of cyclic polymers

Barry R. Lentz and Harold A. Scheraga

J. Chem. Phys. 58, 5296 (1973); http://dx.doi.org/10.1063/1.1679143 (13 pages) | Cited 53 times

Online Publication Date: 22 August 2003

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Ab initio LCAO‐SCF molecular orbital calculations have been carried out with an extensive basis set to determine the stabilization energies of a cyclic trimer, a cyclic tetramer, and various noncyclic oligomers of water. The cyclic trimer is shown to be less stable than the noncyclic one. It is concluded that appreciable nonadditive effects are not present in cyclic polymers of water and that these structures show no special stability (compared to noncyclic ones) other than that to be expected from their extra hydrogen bond. Finally, the results of these and similar calculations are used to calculate the lattice energy of ice I, which agrees well with the experimental value.

Endpoint distribution of self‐avoiding walks

Ralph Grishman

J. Chem. Phys. 58, 5309 (1973); http://dx.doi.org/10.1063/1.1679144 (6 pages) | Cited 15 times

Online Publication Date: 22 August 2003

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The dimerization algorithm for the generation of self‐avoiding walks was modified to generate a large number of walks with a relatively large endpoint separation. Walks of up to 512 steps were generated on the square and cubic lattices using this modified algorithm. From these walks the distribution of endpoint x coordinates of self‐avoiding walks was accurately determined over a much wider range than would be possible using earlier techniques. The distributions obtained were found to be in general agreement with those proposed earlier for shorter walks by Domb, Gillis, and Wilmers.

Dielectric relaxation of 1‐alkenes

John Crossley

J. Chem. Phys. 58, 5315 (1973); http://dx.doi.org/10.1063/1.1679145 (4 pages) | Cited 6 times

Online Publication Date: 22 August 2003

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Dielectric constants and losses have been measured for 1‐hexene, 1‐octene, 1‐decene, 1‐dodecene, 1‐tetradecene, 1‐pentadecene, 1‐hexadecene, 1‐heptadecene, and 1‐octadecene as pure liquids at up to 10 frequencies between 1 and 140 GHz at 25°C. The mean relaxation times, τ0, and viscosities, η, increase significantly with increasing chain length; however, the parameter τ0/η reaches a maximum for 1‐dodecene and then decreases with increasing chain length. The results are compared with those obtained for other n‐alkyl compounds containing a polar end group.

Significance of both polarizability and polarizing power of cations in nitrate vibrational spectra

Murray H. Brooker and Max. A. Bredig

J. Chem. Phys. 58, 5319 (1973); http://dx.doi.org/10.1063/1.1679146 (3 pages) | Cited 17 times

Online Publication Date: 22 August 2003

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Vibrational frequencies of the NO3− ion in matrix‐isolated monomers of several nitrates MNO3 are shown to correlate with the polarizing power of the cation M+,P ≡ (z/r)/Seff, properly defined as the quotient, rather than the product, of the ionic potential, z∕r, and a factor Seff = (5z1.27)/(r(1/2)I) (Ahrens, 1954) representing the efficiency with which the electron shell of the cation screens its nuclear charge. For molten nitrates MNO3, this correlation breaks down: in the condensed state, the polarizability of the cation, a, becomes important as the result of the mutual enhancement of the polarization of a given cation by several anions. A correlation of ν1 with the product of cation polarizing power and polarizability, P a, is presented.

ESR spectrum and structure of the MgOH radical

J. M. Brom and W. Weltner

J. Chem. Phys. 58, 5322 (1973); http://dx.doi.org/10.1063/1.1679147 (9 pages) | Cited 25 times

Online Publication Date: 22 August 2003

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The MgOH molecule has been trapped in solid argon and neon at 4 °K, and its ESR spectrum measured. It has been isolated in these matrices by (1) code positing Mg atoms with a matrix gas containing 1% H2O2, (2) codepositing Mg atoms with a matrix gas and the products of a microwave discharge of H2O vapor, or (3) passing the metal atoms, along with H2O vapor, through a tantalum cell at 1700 °C before quenching in the matrix gas. g tensors and nuclear hyperfine components for interaction with 25Mg and H were determined. In both argon and neon these magnetic tensors appear to have axial symmetry, indicating that the molecule is probably linear (2Σ ground state). In neon g‖ = 2.0017(1),g⊥ = 2.0007(1),∣A‖(25Mg)∣ = 312.7(3) MHz,∣A⊥(25Mg)∣ = 300.7(3) MHz,∣A‖(H)∣ = 14.8(3) MHz,∣A⊥(H)∣ = 10.1(3) MHz. Spin density distribution derived from hyperfine splittings places a majority of the spin on Mg and implies that the molecule is highly ionic. A CNDO calculation slightly favors a linear structure and supports the observed spin distribution. Trapped Mg+ and probably MgO2H were also observed in the ESR spectra. The large excess of Mg atoms in the matrices dominated the optical absorption spectrum in the ultraviolet.

Glory scattering in molecular collisions. III. Collisions between indistinguishable molecules

Louis Biolsi

J. Chem. Phys. 58, 5331 (1973); http://dx.doi.org/10.1063/1.1679148 (8 pages) | Cited 5 times

Online Publication Date: 22 August 2003

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An extended distorted‐wave treatment is used to obtain formal expressions for the total cross section when two indistinguishable rigid diatomic molecules, with orbital and nuclear spin angular momenta, collide. Explicit expressions for the cross section are obtained through second order, including the lowest order inelastic effects. An expression for the total inelastic cross section is also given. The results are compared with the corresponding results when distinguishable molecules collide.

Raman spectra and structure of B2F4 in the gaseous and solid states

J. R. Durig, J. W. Thompson, J. D. Witt, and J. D. Odom

J. Chem. Phys. 58, 5339 (1973); http://dx.doi.org/10.1063/1.1679149 (5 pages) | Cited 3 times

Online Publication Date: 22 August 2003

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The Raman spectra of B2F4 have been recorded from 25 to 1500 cm−1 with the sample in both the gaseous and crystalline states. An assignment of the normal vibrations of the molecule in the planar form is presented. No evidence could be found for the conversion from the D2h form in the solid to a nonplanar D2d form in the gas as had been previously reported. It appears that the rule of mutual exclusion is retained in the spectra for the vapor and liquid states and that the molecule has D2h symmetry in all physical states. The optically active translations and librations have been observed in the low frequency infrared and Raman spectra of the solid, respectively. Intermolecular force constants have been calculated.

Relaxation of the proton spin dipolar energy in hexagonal ice

G. F. Bruno and M. M. Pintar

J. Chem. Phys. 58, 5344 (1973); http://dx.doi.org/10.1063/1.1679150 (10 pages) | Cited 1 time

Online Publication Date: 22 August 2003

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The relaxation time of the proton spin dipolar energy, T1D in hexagonal ice was measured to be 35 μsec at −24°C. Within the accuracy of the experiment (±9%), no anisotrpy was observed when the crystal was rotated around the b axis. Measurements of the spin‐lattice relaxation time in the rotating frame T1ρ are reported for different rf fields, H1 at −2.4 and −24°C. At the lower temperature, at H1 of 7 G, T1ρ was anisotropic ([invertedlazys]24%) if the crystal was rotated around the b axis. This anisotropy is primarily a result of the anisotropy of the proton dipolar specific heat. The Slichter‐Ailion parameter p was calculated for rotational jumps accompanying the ultra slow diffusion of the water molecule. If two protons only are considered (one water molecule), the parameter p is isotropic and equals −0.2. The calculation was made also for the two water protons and two first neighbors. The isotropic average of this p is −0.05 if rotational jumps around two axes are excluded. If the ice lattice is simulated by using groups of four protons, p remains very small. It varies between −0.07 and 0.00 if the crystal is rotated around its b axis. At −24°C, using the calculated p and the experimental T1D, we estimate the correlation time for the diffusion to be 37 ± 6 μsec.

Relaxation of vibrationally excited HF in levels v=1 and v=2. II. By CH4, C2H6, C3H8, C2H2, and C2H4

K. G. Anlauf, P. H. Dawson, and J. A. Herman

J. Chem. Phys. 58, 5354 (1973); http://dx.doi.org/10.1063/1.1679151 (4 pages) | Cited 16 times

Online Publication Date: 22 August 2003

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The rate constants for the vibrational deactivation of HF(v = 1,2) by CH4, C2H6, C3H8, and C2H2 were measured by monitoring the decay of HF† rotation‐vibration emission in a fast flow system. For these hydrocarbons the energy transfer processes are very efficient. In the case of C2H4 the rate constant could only be estimated.

Simplest halogen atom plus alkali dimer potential surface: F+Li2→LiF+Li

Peter K. Pearson, William J. Hunt, Charles F. Bender, and Henry F. Schaefer

J. Chem. Phys. 58, 5358 (1973); http://dx.doi.org/10.1063/1.1679152 (6 pages) | Cited 20 times

Online Publication Date: 22 August 2003

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Ab initio electronic structure calculations have been carried out to investigate some features of the potential energy surface for the chemical reaction F+Li2→LiF+Li. The basis set of contracted Gaussian functions was of ``double zeta plus polarization'' quality, with an additional set of p functions on F added to describe F−. Single‐configuration and two‐configuration self‐consistent‐field calculations are reported here. A minimum energy path was obtained for the collinear reaction, but the most important feature determined was the nature of the potential minimum due to the FLi2 complex. For linear F�Li�Li, this complex is bound by 4 kcal∕mole relative to separated LiF + Li. The attraction is much stronger, 34 kcal, for C2v geometry, and this species is predicted to have a bond angle of 99° and Li�F bond distance of 1.79 Å. Several excited electronic states of FLi2 are discussed briefly.

Thermochemical and kinetic information from metastable decompositions of ions

Cornelius E. Klots

J. Chem. Phys. 58, 5364 (1973); http://dx.doi.org/10.1063/1.1679153 (4 pages) | Cited 89 times

Online Publication Date: 22 August 2003

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Formulations are examined for connecting average kinetic energies of the products of a unimolecular decomposition with the total available energy. A straightforward method for the calculation of kinetic shifts is then described. Existing data suggest, nevertheless, that the effective number of internal degrees‐of‐freedom for energy disposal may be greater than the physical number, a result inaccessible to existing theory. A formal reconciliation is indicated here.

Adiabatic reference functions and chemical reactions

Edward J. Shipsey

J. Chem. Phys. 58, 5368 (1973); http://dx.doi.org/10.1063/1.1679154 (5 pages) | Cited 8 times

Online Publication Date: 22 August 2003

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An adiabatic differential equation describing chemical reaction is developed which allows convenient application of the reference function technique. The resulting equations are a generalization of Eu's equations for inelastic scattering. Some properties of these equations are discussed and a stationary principle derived for them.
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