Thermal diffusion factors for the 4He-2 0Ne system have been measured in a low temperature region previously unexplored (down to 31 K) using a trennschaukel. Both quantum and classical transport collision integrals were evaluated for a recently proposed helium-neon intermolecular potential of the Hartree-Fock dispersion (HFD) type which has been shown to correlate cross section and transport property data quite well. The present data agree extremely well with the quantum mechanically calculated thermal diffusion factors. The classically calculated values fall considerably lower.

No abstract

A velocity selector wheel of novel spiral groove design was constructed and successfully tested.The wheel can be used to select a narrow band (~ ± 1.2%) of vela cities from a molecular beam while presenting an effective open time of38%. No velocity sidebands are transmitted and alignment is relatively simple. Experimental measurements verified performance essentially as predicted.

The thermal-diffusion factor, αT, for the neon–xenon system has been measured from 328°–873°K at seven compositions ranging from 5%–95% neon. These measurements were made with a 20-tube trennschaukel where the pumping rate, the quantity of gas pumped, the duration of the experiments, and the temperature gradient could be varied over a wide range. This flexibility allowed the operating conditions to be chosen so that the theoretical corrections for trennschaukel operation were small and therefore could be applied to the measured separations with confidence. The present corrected data have been compared with theoretical calculations based on the Lennard-Jones (12–6) potential and the modified Buckingham (exp-6) potential. Both the experimental data and the theory indicate that the reciprocal of αT is a linear function of the composition. The present data agree well with the results of Grew and of Heymann and Kistemaker, but do not agree with that of Saxena and co-workers nor with the results of Atkins, Bastick, and Ibbs. The mutual diffusion coefficient for neon–xenon, which was derived from the measured composition dependence of αT, agrees well with experimental diffusion coefficients reported in the literature and also with values calculated from experimental viscosity and thermal conductivity data. Although the values of αT are in disagreement with the present work, the composition dependence of αT reported by Saxena, Nain, and Saxena also appears to be consistent with the values of the diffusion coefficient; however, that reported by Atkins et al. and Mathur and Saxena are not.

Absolute vibrational and electronic cross sections for low-energy electron (2-12 eV) scattering from condensed pyrimidine Absolute total cross sections for He-Ar were measured in the relative velocity range of -800-2000 mls by passing a supersonic nozzle beam through a cell containing the target gas. The beam attenuation was determined by passing the unscattered beam particles into a quadrupole detector. The absolute number density of target gas particles in the target cell was obtained by a calibrated-flow method of introducing gas into the cell during an experiment. A correction was applied for the angular resolution of the apparatus. The average experimental uncertainty was estimated to be -3% to 3.5%. The present results, as well as other available data, were deconvoluted in a two-step process to yield QI and QU, the first and second approximations to the total cross section, as a function of the relative velocity. The composite results of all experimental data were compared to seven interatomic potentials and the Hartree-Fock-dispersion (HFD) potential represented the data best.