- Email: [email protected]
Thermal conductivities of some polyatomic gases at moderately high temperatures
Classified
abstracts
472-486
ing in coadsorbed mixtures of hydrogen and deuterium. The desorption spectrum of hydrogen from these metals dosed at 100°K contains two peaks, a and B. The distribution of the isotopes in the desorbed phase formed from coadsorbing H, and D, indicates that the a peak is due to an atomic species in the case of iridium and rhodium and a molecular species in the case of tungsten. The vacuum techniques, temperature measurement and control and flash-desorption spectrometry are described in some detail. V J Miieault and R S Hansen, J Chem Phys, 45 (6), IS Sept 1966, 2240-2250. 40 472. Experimental and theoretical considerations for ionization of
simple hydro-carbons, H,, D,, H,O and the rare gases by 2.2 MeV c( particles and by electrons in a mass spectrometer. (USA) Emphasis is placed on experimental details which lead to results which are more accurate than those reported in a previous study. The mass spectra produced by 2.2 MeV a-particles show the same fragments as those produced by electrons with the same velocity, but the abundance of some fragment ions differ by a factor of four. Mass spectra produced by 75eV electrons also show significantly more dissociative ionization than those produced by 2.2 MeV a particles. P S Rudolph and C E Melton, J Chem Phys, 45 (6), 15 Sept 1966, 2227-2232. 473. Molecular-beam scattering from the (111) plane of silver.
40 (USA)
The spatial distributions of molecular beams of CH,, NH,, Ar and Xe scattered from the (111) plane of an epitaxially grown Ag single crystal were examined both during growth of the Ag crystal and immediately afterward. No distinction between these modes was observable. NHS, the most strongly interacting gas, gave rise to nearly diffuse scattering, while Ne was nearly specularly directed. The heavier gases (Ar and Xe) exhibited scattering maxima lying between the specular direction and the tangent to the surface (supraspecular scattering), with the location of the maxima depending in a complex manner on the angle of incidence of the beam and on the beam energy. Reference is made to previous publications which describe the basic apparatus. H Saltsburg and J N Smith, J Chem Phys, 45 (6), 15 Sept 1966, 2175-2183. 474. Inelastic excitation transfer in helium.
(USA)
The positive column of a helium glow discharge was irradiated with intense 5J16A (2lS-3rP) light and it was found that the population of the 3lP state was markedly increased without affecting the discharge parameters. An upper limit of 4 x IO-” cm2 was placed on the cross section for transfer of excitation by neutral collision in the reaction He (31P)+He+(3SP)+He. M P Teter and W W Robertson, J Chem Phys, 45 (6), 15 Sept 1966, 2167-2169. 40 475. Selective enhancement in hydrogen-like molecules with the rare gases 1. H, with Ar and Kr. (USA) The selective enhancement of the Hz spectrum in the vacuum-uv
region when excited with Ar has been studied and the results extended to include some additional evidence with Kr as well as with Ar. Details of the experimental technique are given, including bake-out procedure, pressure ranges used and the method of detection. It is concluded that resonance fluorescence offers a generally satisfactory explanation of selective enhancement but collisions of the second kind also offer a possible explanation. There is little evidence for such collisions involving metastable atoms. S Takezawa er ul, J Chem Phys, 45 (6)) 15 Sept 1966,2000-2010. 40 476. Chemisorptlon of hydrogen on tungsten (100). (USA) P J Estrup and J Anderson, J Chem Phys, 45 (6)) I5 Sept 1966, 22542260. 40 477. Thermal accommodation coefficients of helium on tungsten and
hydrogen on hydrogen-covered tungsten at 325”, 403” aud 423°K. (USA) H Y Wachman, J Chem Phys, 45 (5), 1 Sept 1966, 1562-1568. 40 478. Atom-atom ionization cross sections of the noble gases-argon, krypton, and xenon. (USA) Shock tube measurements have been made of the initial shockproduced ionization in argon, krypton and xenon. Details of the 124
shock tube system, including the vacuum system, are given. The experimentally determined values of ionization cross-sections are compared with theory. A J Kelly, J Chem Phys, 45 (5), I Sept 1966,1723-1732. 40 479. Mass-spectrometric investigation of the nickel-fluorine surface reaction. (USA) Measurements have been made of the reaction of polycrystalline nickel (900°K to 1600°K) with fluorine at pressures between lo-’ and lo-’ torr. Gaseous NiF, NiF, and F are the major products and are formed rapidly on the surface at rates linear with fluorine pressure. Various details of the vacuum apparatus and the techniques used are given. J D McKinley, J Chem Phys, 45 (51, I Sept 1966.1690-1693. 40 480. Thermal conductivities of some polyatomic gases at moderately
high temperatures. (USA) Thermal conductivities of nitrous and nitric oxides, carbon tetrafluoride, silicon tetrafluoride, sulfur hexafluoride, and boron trifluoride have been determined at moderately high temperatures (about 60°C to 400°C in different cases). The experimental results are compared with the results of several approximate theories of heat conduction in polyatomic gases. The thermal-conductivity cell is described in some detail. P Choy and C J G Raw, J Chem Phys, 45 (51, I Sept 1966,1413-1417. 40 481. Photoionization of high-temperature vapours. I. The iodides of sodium, magnesium and thallium. (USA)
Photoionization efficiency curves of high-temperature species have been obtained with a vacuum-ultra-violet monochromator, a mass spectrometer and a molecular-beam source of high-temperature vapours. Experimental ionization potentials are discussed. Some details of the apparatus are given, including the vacuum system and the oven. J Berkowitz and W A Chupka, J Chem Phys, 45 (4), 15 Aug 1966. 1287-1298. 40 482. Low-pressure study of heterogeneous hydrogen-deuterium exchange at steady state. (USA)
The hydrogen-deuterium exchange reaction on a clean molybdenum filament has been investigated at pressures of 1Om8to 1O-6 torr and temperatures of 25” to 800°C using a steady-state approach. The exchange rates were measured with a mass spectrometer. The total sticking probabilities (about 0.4) are pressure independent at temperatures above 200°C declining to 0.2 at 25°C and are identical for the different hydrogen species. B Bergsnov-Hansen and R A Pastemak, J Chem Phys, 45 (41, 15 Aug 1966,1199-1204. 40 483. Low-energy large-angle electron scattering spectrum of helium.
(USA) A low-resolution electron scattering spectrometer, containing helium at a typical pressure of lo?, is described. Various transitions are discussed in terms of scattering angle. J P Doerlng, J Chem Phys, 45 (3), 1 Aug 1966,1065-1066. 40 484. Energy transfer in ion-molecule reactions in the methane system.
(USA) Cross Sections for the reactions of CH+, with CH, have been measured by determining the pressure-dependent loss of CH+, in the mass spectrum of methane produced by electron impact in the mass spectrometer ion source. A Giardlni-Guidoni and L Friedman, J Chem Phys, 45 (3) 1 Aug 1966,937-943. 40 485. Electron-impact ionization cross sections II. Classical calculations. (USA)
Absolute cross sections for single ionization of the atomic elements have been calculated using the classical method of Gryzinski. They are in good agreement with experimental cross sections. They differ significantly, however, from certain of the values of Otvos & Stevenson. F E Stafford, J Chem Phys, 45 (3), 1 Aug 1966,859~862. 486. Helium recombination in a radio-frequency discharge.
The radiative-collisional
recombination
40 (USA)
rate involving the abundant
abstracts
472-486
ing in coadsorbed mixtures of hydrogen and deuterium. The desorption spectrum of hydrogen from these metals dosed at 100°K contains two peaks, a and B. The distribution of the isotopes in the desorbed phase formed from coadsorbing H, and D, indicates that the a peak is due to an atomic species in the case of iridium and rhodium and a molecular species in the case of tungsten. The vacuum techniques, temperature measurement and control and flash-desorption spectrometry are described in some detail. V J Miieault and R S Hansen, J Chem Phys, 45 (6), IS Sept 1966, 2240-2250. 40 472. Experimental and theoretical considerations for ionization of
simple hydro-carbons, H,, D,, H,O and the rare gases by 2.2 MeV c( particles and by electrons in a mass spectrometer. (USA) Emphasis is placed on experimental details which lead to results which are more accurate than those reported in a previous study. The mass spectra produced by 2.2 MeV a-particles show the same fragments as those produced by electrons with the same velocity, but the abundance of some fragment ions differ by a factor of four. Mass spectra produced by 75eV electrons also show significantly more dissociative ionization than those produced by 2.2 MeV a particles. P S Rudolph and C E Melton, J Chem Phys, 45 (6), 15 Sept 1966, 2227-2232. 473. Molecular-beam scattering from the (111) plane of silver.
40 (USA)
The spatial distributions of molecular beams of CH,, NH,, Ar and Xe scattered from the (111) plane of an epitaxially grown Ag single crystal were examined both during growth of the Ag crystal and immediately afterward. No distinction between these modes was observable. NHS, the most strongly interacting gas, gave rise to nearly diffuse scattering, while Ne was nearly specularly directed. The heavier gases (Ar and Xe) exhibited scattering maxima lying between the specular direction and the tangent to the surface (supraspecular scattering), with the location of the maxima depending in a complex manner on the angle of incidence of the beam and on the beam energy. Reference is made to previous publications which describe the basic apparatus. H Saltsburg and J N Smith, J Chem Phys, 45 (6), 15 Sept 1966, 2175-2183. 474. Inelastic excitation transfer in helium.
(USA)
The positive column of a helium glow discharge was irradiated with intense 5J16A (2lS-3rP) light and it was found that the population of the 3lP state was markedly increased without affecting the discharge parameters. An upper limit of 4 x IO-” cm2 was placed on the cross section for transfer of excitation by neutral collision in the reaction He (31P)+He+(3SP)+He. M P Teter and W W Robertson, J Chem Phys, 45 (6), 15 Sept 1966, 2167-2169. 40 475. Selective enhancement in hydrogen-like molecules with the rare gases 1. H, with Ar and Kr. (USA) The selective enhancement of the Hz spectrum in the vacuum-uv
region when excited with Ar has been studied and the results extended to include some additional evidence with Kr as well as with Ar. Details of the experimental technique are given, including bake-out procedure, pressure ranges used and the method of detection. It is concluded that resonance fluorescence offers a generally satisfactory explanation of selective enhancement but collisions of the second kind also offer a possible explanation. There is little evidence for such collisions involving metastable atoms. S Takezawa er ul, J Chem Phys, 45 (6)) 15 Sept 1966,2000-2010. 40 476. Chemisorptlon of hydrogen on tungsten (100). (USA) P J Estrup and J Anderson, J Chem Phys, 45 (6)) I5 Sept 1966, 22542260. 40 477. Thermal accommodation coefficients of helium on tungsten and
hydrogen on hydrogen-covered tungsten at 325”, 403” aud 423°K. (USA) H Y Wachman, J Chem Phys, 45 (5), 1 Sept 1966, 1562-1568. 40 478. Atom-atom ionization cross sections of the noble gases-argon, krypton, and xenon. (USA) Shock tube measurements have been made of the initial shockproduced ionization in argon, krypton and xenon. Details of the 124
shock tube system, including the vacuum system, are given. The experimentally determined values of ionization cross-sections are compared with theory. A J Kelly, J Chem Phys, 45 (5), I Sept 1966,1723-1732. 40 479. Mass-spectrometric investigation of the nickel-fluorine surface reaction. (USA) Measurements have been made of the reaction of polycrystalline nickel (900°K to 1600°K) with fluorine at pressures between lo-’ and lo-’ torr. Gaseous NiF, NiF, and F are the major products and are formed rapidly on the surface at rates linear with fluorine pressure. Various details of the vacuum apparatus and the techniques used are given. J D McKinley, J Chem Phys, 45 (51, I Sept 1966.1690-1693. 40 480. Thermal conductivities of some polyatomic gases at moderately
high temperatures. (USA) Thermal conductivities of nitrous and nitric oxides, carbon tetrafluoride, silicon tetrafluoride, sulfur hexafluoride, and boron trifluoride have been determined at moderately high temperatures (about 60°C to 400°C in different cases). The experimental results are compared with the results of several approximate theories of heat conduction in polyatomic gases. The thermal-conductivity cell is described in some detail. P Choy and C J G Raw, J Chem Phys, 45 (51, I Sept 1966,1413-1417. 40 481. Photoionization of high-temperature vapours. I. The iodides of sodium, magnesium and thallium. (USA)
Photoionization efficiency curves of high-temperature species have been obtained with a vacuum-ultra-violet monochromator, a mass spectrometer and a molecular-beam source of high-temperature vapours. Experimental ionization potentials are discussed. Some details of the apparatus are given, including the vacuum system and the oven. J Berkowitz and W A Chupka, J Chem Phys, 45 (4), 15 Aug 1966. 1287-1298. 40 482. Low-pressure study of heterogeneous hydrogen-deuterium exchange at steady state. (USA)
The hydrogen-deuterium exchange reaction on a clean molybdenum filament has been investigated at pressures of 1Om8to 1O-6 torr and temperatures of 25” to 800°C using a steady-state approach. The exchange rates were measured with a mass spectrometer. The total sticking probabilities (about 0.4) are pressure independent at temperatures above 200°C declining to 0.2 at 25°C and are identical for the different hydrogen species. B Bergsnov-Hansen and R A Pastemak, J Chem Phys, 45 (41, 15 Aug 1966,1199-1204. 40 483. Low-energy large-angle electron scattering spectrum of helium.
(USA) A low-resolution electron scattering spectrometer, containing helium at a typical pressure of lo?, is described. Various transitions are discussed in terms of scattering angle. J P Doerlng, J Chem Phys, 45 (3), 1 Aug 1966,1065-1066. 40 484. Energy transfer in ion-molecule reactions in the methane system.
(USA) Cross Sections for the reactions of CH+, with CH, have been measured by determining the pressure-dependent loss of CH+, in the mass spectrum of methane produced by electron impact in the mass spectrometer ion source. A Giardlni-Guidoni and L Friedman, J Chem Phys, 45 (3) 1 Aug 1966,937-943. 40 485. Electron-impact ionization cross sections II. Classical calculations. (USA)
Absolute cross sections for single ionization of the atomic elements have been calculated using the classical method of Gryzinski. They are in good agreement with experimental cross sections. They differ significantly, however, from certain of the values of Otvos & Stevenson. F E Stafford, J Chem Phys, 45 (3), 1 Aug 1966,859~862. 486. Helium recombination in a radio-frequency discharge.
The radiative-collisional
recombination
40 (USA)
rate involving the abundant