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Electron transfer in collisions of doubly charged rare gas ions and rare gas atoms for primary ion energies below 100 eV
Classified abstracts
214-222
coefficients (~100 1 mole-’ cm-‘) in the spectral range of the excitation source. Signal averaging is accomplished using long lock-in amplifier time constants as well as multichannel scaling. The relative merits of cw photofragment spectroscopy are also discussed with particular reference to the photodissociation of large aromatic molecules. From the angular data, the polarization of the transition dipole relative to the detector axis, the lifetime of the excited molecular state, and the relative ease of fragmentation into different channels can be determined. M J Dzvonik and Sze-cheng Yang, Rev Sci Instrum, 45 (6), 1974, 750-755. 34. HIGH ALTITUDE
AND SPACE TECHNOLOGY
34 214 Reflectance and optical constants of evaporated ruthenium in the vacuum ultraviolet from 300 to 2000 A. (USA) The reflectance and optical constants of evaporated ruthenium films were measured in the wavelength region from 300 to 2000 A. The films were evaporated by electron bombardment in an ion-titaniumpumped vacuum system and were typically deposited at a rate of about 40 A/s onto glass and super-polished fused-quartz substrates which were at 40 and 300°C. Variation of deposition rate from 1 to 80 A/s had very little effect on their reflectance. The optical constants were determined from reflectance measurements made at several angles of incidence. Reflectance losses during extended exposure to air were rather small, indicating that, if oxide films form at room temperature, they are very thin. Films made on substrates at 300°C had slightly higher reflectances than those made at 40°C. Owing to interference effects, semitransparent films 150 to 200 8, thick showed higher reflectances than opaque films at wavelengths in the region of 584 A. At wavelengths near 2000 A, films 300 8, thick had highest reflectances. Ruthenium films prepared under optimum conditions had reflectances of 26% at 584 A. J T Cox et al, J Opt Sot Am, 64 (4), 1974,423-428. 37. METALLURGY INORGANIC ANALYTICAL CHEMISTRY
CHEMISTRY, 37
215. A low noise soft x-ray appearance its application
to chemisorption
potential spectrometer of oxygen on nickel. (USA)
and
A low noise soft x-ray appearance potential spectrometer has been constructed. It consists of a liquid nitrogen-cooled silicon surfacebarrier diode that detects the variations in the emitted photon flux. A 500 8, thick Al window acts as a discriminator for low energy photons (visible light and the tail of the bremsstrahlung). The performance of the detector arrangement has been tested on clean Ni films and chemisorbed 0 on these films. It is shown that the detector behaves ideally, i.e., the signal-to-noise ratio is limited by the shot noise in the photon flux for primary electron beam intensities in the range tested (30-600 PA) and for electron energies, 300-900 eV. (Sweden) S Andersson et al, Rev Scient Instrum, 45 (7), 1974, 877-881. 37 216. The use of a microchannel electron multiplier in spectroscopic instrumentation, involving frequent vacuum breaking. (USA)
The use of microchannel electron multipliers in laboratory instrumentation as a detecting system coupled to an x-uv monochromator or spectrograph, or to a low energy particle spectrometer, corresponds to a particular class of operation in which the detectors are exposed to a very low average input current and to stringent operational conditions, imposed by the instrument concept. It is shown in this paper that frequent vacuum breakings in the system containing the multiplier are not harmful to the stability of its performance. The monitoring of the strip current vs the applied potential is shown to be the simplest and most efficient way of assessing the state of the detector, as, in this particular regime of operation, it is necessary to follow a precise operating procedure to limit spurious secondary effects correlated to the water vapor contamination of its emissive surface. (Italy) J P Rager and J F Renaud, Rev Scient Instrum, 45 (7), 1974, 922-926. 217. The growth and alignment alloys. (GB)
of single crystals of transition
37 metal
A technique based on the Bridgman method of growing metal single crystals is described in some detail. This has been found to
give reliable results for the NiCr and FeCr systems. The method of cutting and aligning the crystals is also described. K J Ftowker et al, JPhys D: AppiPhys, 7 (9), 1974. 1201-1205. 39, MISCELLANEOUS
APPLICATIONS
39 218. An inexpensive vacuum operated tweezer. (USA) The construction of an inexpensive vacuum operated tweezer from a modified aquarium air pump and a disposable syringe is described. R E Hen&&en, Rev Sci Instrum, 45 (6), 1974, 857-858.
IV. Materials and techniques used in vacuum technology 40.GASES AND VAPOURS 40 219. Electron transfer in collisions of doubly charged rare gas ions and rare gas atoms for primary ion energies below 100 eV. (USA) Cross sections for the production of Kr+, Ne+ and Kr2+ in collisions of Kr2+ with Ne and of NeZ+ with Kr were measured for primary ion energies E between 0.5 and 100 eV. For E 2 10 eV, the cross sections all vary rather slowly and are between 1 and 8 A2. As E is decreased below 5-10 eV, the cross sections all increase. A comparison is made between experimental results and theoretically predicted values. The agreement is not too good for the particular reactions discussed. In the apparatus used, primary ions were extracted from an ion source, analyzed in a source mass spectrometer and passed into a reaction chamber. The primary- and secondaryion currents emerging from the reaction chamber were measured with an analysis mass spectrometer. The pressure in the reaction chamber was monitored with a cooled McLeod gauge and was in the range 0.45-l .2 m torr. W B Maier, J Chem Phys, 60 (9), 1974, 3588-3598. 40 220. “He atomic beam scattering from clean surfaces of silicon and germanium. (USA) A modulated, nozzle type “He atomic beam was used to investigate scattering from clean, room temperature surfaces of silicon and germanium. The surfaces were prepared by cleaving in situ under ultrahigh vacuum, with the pressure in the low 10m9 torr range. The beam was operated with the source gas at room temperature or cooled with liquid nitrogen, resulting in a wavelength of -0.57 and -1.07 A, respectively. The scattered beam is subspecularly directed with a maximum intensity less than 1% of the incident beam intensity. The apparatus used has been described previously and appropriate references are given. D E Houston and D R Frank& J Chem Phys, 60 (8), 1974, 3268-3270. 40 221. Negative ion-molecule reactions with atomic hydrogen in the gas phase at 2% K. (USA) The measurements were made in a flowing afterglow (reference given). A buffer gas, He or 02, flow past the electron gun. Negative ions are produced directly from the buffer gas, in the case of 02, or from suitable source gases which are added to the carrier gas stream. Gas phase reaction rates were measured for the reactions of Cl-, I-, OH-, OZ-, SFs- and some hydrates of Cl-, OH- and 02- with atomic hydrogen in the flowing afterglow system at 296 K. In general, the reaction mechanism is associative detachment, X- f H + HX + e, and the rate constants are very large (~10~~ cm3/s). The reactivities of Cl-, OH-, and O,- are reduced by clustering with H,O. The reaction of I- with H is immeasurably slow, and SFh- reacts with H to form SF,- which does not react further. C J Howard et al, J Chem Phys, 60 (12), 1974, 5086-5089. 40 222. Molecular beam scattering from clean and monoxide covered platinum (III) crystal surfaces. (USA) The apparatus used consisted of an ultrahigh vacuum scattering chamber fitted with low energy diffraction (LEED) optics, Auger electron spectrometer (AES), and a rotatable mass spectrometer detector, attached to two diffusion pumped chambers for forming and modulating a molecular beam. Preparation of the crystals is 89
214-222
coefficients (~100 1 mole-’ cm-‘) in the spectral range of the excitation source. Signal averaging is accomplished using long lock-in amplifier time constants as well as multichannel scaling. The relative merits of cw photofragment spectroscopy are also discussed with particular reference to the photodissociation of large aromatic molecules. From the angular data, the polarization of the transition dipole relative to the detector axis, the lifetime of the excited molecular state, and the relative ease of fragmentation into different channels can be determined. M J Dzvonik and Sze-cheng Yang, Rev Sci Instrum, 45 (6), 1974, 750-755. 34. HIGH ALTITUDE
AND SPACE TECHNOLOGY
34 214 Reflectance and optical constants of evaporated ruthenium in the vacuum ultraviolet from 300 to 2000 A. (USA) The reflectance and optical constants of evaporated ruthenium films were measured in the wavelength region from 300 to 2000 A. The films were evaporated by electron bombardment in an ion-titaniumpumped vacuum system and were typically deposited at a rate of about 40 A/s onto glass and super-polished fused-quartz substrates which were at 40 and 300°C. Variation of deposition rate from 1 to 80 A/s had very little effect on their reflectance. The optical constants were determined from reflectance measurements made at several angles of incidence. Reflectance losses during extended exposure to air were rather small, indicating that, if oxide films form at room temperature, they are very thin. Films made on substrates at 300°C had slightly higher reflectances than those made at 40°C. Owing to interference effects, semitransparent films 150 to 200 8, thick showed higher reflectances than opaque films at wavelengths in the region of 584 A. At wavelengths near 2000 A, films 300 8, thick had highest reflectances. Ruthenium films prepared under optimum conditions had reflectances of 26% at 584 A. J T Cox et al, J Opt Sot Am, 64 (4), 1974,423-428. 37. METALLURGY INORGANIC ANALYTICAL CHEMISTRY
CHEMISTRY, 37
215. A low noise soft x-ray appearance its application
to chemisorption
potential spectrometer of oxygen on nickel. (USA)
and
A low noise soft x-ray appearance potential spectrometer has been constructed. It consists of a liquid nitrogen-cooled silicon surfacebarrier diode that detects the variations in the emitted photon flux. A 500 8, thick Al window acts as a discriminator for low energy photons (visible light and the tail of the bremsstrahlung). The performance of the detector arrangement has been tested on clean Ni films and chemisorbed 0 on these films. It is shown that the detector behaves ideally, i.e., the signal-to-noise ratio is limited by the shot noise in the photon flux for primary electron beam intensities in the range tested (30-600 PA) and for electron energies, 300-900 eV. (Sweden) S Andersson et al, Rev Scient Instrum, 45 (7), 1974, 877-881. 37 216. The use of a microchannel electron multiplier in spectroscopic instrumentation, involving frequent vacuum breaking. (USA)
The use of microchannel electron multipliers in laboratory instrumentation as a detecting system coupled to an x-uv monochromator or spectrograph, or to a low energy particle spectrometer, corresponds to a particular class of operation in which the detectors are exposed to a very low average input current and to stringent operational conditions, imposed by the instrument concept. It is shown in this paper that frequent vacuum breakings in the system containing the multiplier are not harmful to the stability of its performance. The monitoring of the strip current vs the applied potential is shown to be the simplest and most efficient way of assessing the state of the detector, as, in this particular regime of operation, it is necessary to follow a precise operating procedure to limit spurious secondary effects correlated to the water vapor contamination of its emissive surface. (Italy) J P Rager and J F Renaud, Rev Scient Instrum, 45 (7), 1974, 922-926. 217. The growth and alignment alloys. (GB)
of single crystals of transition
37 metal
A technique based on the Bridgman method of growing metal single crystals is described in some detail. This has been found to
give reliable results for the NiCr and FeCr systems. The method of cutting and aligning the crystals is also described. K J Ftowker et al, JPhys D: AppiPhys, 7 (9), 1974. 1201-1205. 39, MISCELLANEOUS
APPLICATIONS
39 218. An inexpensive vacuum operated tweezer. (USA) The construction of an inexpensive vacuum operated tweezer from a modified aquarium air pump and a disposable syringe is described. R E Hen&&en, Rev Sci Instrum, 45 (6), 1974, 857-858.
IV. Materials and techniques used in vacuum technology 40.GASES AND VAPOURS 40 219. Electron transfer in collisions of doubly charged rare gas ions and rare gas atoms for primary ion energies below 100 eV. (USA) Cross sections for the production of Kr+, Ne+ and Kr2+ in collisions of Kr2+ with Ne and of NeZ+ with Kr were measured for primary ion energies E between 0.5 and 100 eV. For E 2 10 eV, the cross sections all vary rather slowly and are between 1 and 8 A2. As E is decreased below 5-10 eV, the cross sections all increase. A comparison is made between experimental results and theoretically predicted values. The agreement is not too good for the particular reactions discussed. In the apparatus used, primary ions were extracted from an ion source, analyzed in a source mass spectrometer and passed into a reaction chamber. The primary- and secondaryion currents emerging from the reaction chamber were measured with an analysis mass spectrometer. The pressure in the reaction chamber was monitored with a cooled McLeod gauge and was in the range 0.45-l .2 m torr. W B Maier, J Chem Phys, 60 (9), 1974, 3588-3598. 40 220. “He atomic beam scattering from clean surfaces of silicon and germanium. (USA) A modulated, nozzle type “He atomic beam was used to investigate scattering from clean, room temperature surfaces of silicon and germanium. The surfaces were prepared by cleaving in situ under ultrahigh vacuum, with the pressure in the low 10m9 torr range. The beam was operated with the source gas at room temperature or cooled with liquid nitrogen, resulting in a wavelength of -0.57 and -1.07 A, respectively. The scattered beam is subspecularly directed with a maximum intensity less than 1% of the incident beam intensity. The apparatus used has been described previously and appropriate references are given. D E Houston and D R Frank& J Chem Phys, 60 (8), 1974, 3268-3270. 40 221. Negative ion-molecule reactions with atomic hydrogen in the gas phase at 2% K. (USA) The measurements were made in a flowing afterglow (reference given). A buffer gas, He or 02, flow past the electron gun. Negative ions are produced directly from the buffer gas, in the case of 02, or from suitable source gases which are added to the carrier gas stream. Gas phase reaction rates were measured for the reactions of Cl-, I-, OH-, OZ-, SFs- and some hydrates of Cl-, OH- and 02- with atomic hydrogen in the flowing afterglow system at 296 K. In general, the reaction mechanism is associative detachment, X- f H + HX + e, and the rate constants are very large (~10~~ cm3/s). The reactivities of Cl-, OH-, and O,- are reduced by clustering with H,O. The reaction of I- with H is immeasurably slow, and SFh- reacts with H to form SF,- which does not react further. C J Howard et al, J Chem Phys, 60 (12), 1974, 5086-5089. 40 222. Molecular beam scattering from clean and monoxide covered platinum (III) crystal surfaces. (USA) The apparatus used consisted of an ultrahigh vacuum scattering chamber fitted with low energy diffraction (LEED) optics, Auger electron spectrometer (AES), and a rotatable mass spectrometer detector, attached to two diffusion pumped chambers for forming and modulating a molecular beam. Preparation of the crystals is 89