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Measurements have been made of the spectral distribution of continuum radiation arising from collisions of low energy electrons and of metastable (3P0,2) argon atoms with hydrogen and deuterium molecules. The electron impact spectra, a(3Σ+g, v′=0) → b(3Σ+u)+hν, are in good agreement with the calculations of James and Coolidge. The spectra originating from Ar*+H2, D2 were obtained using crossed supersonic beams. In both cases, an onset at 0.065 ± 0.009 eV relative collision energy was observed. For deuterium, this onset occurs below the energy required to produce D2(a 3Σ+g) . Calculations of the spectral distributions when compared to experiment showed that, at 0.07 eV, the observed radiation arises from the first two vibrational levels of ArD* in the ratio (v′=0)/(v′=1)=4. For hydrogen at this energy, both product channels are present in the ratio ArH*/H*2=2 . At higher energy, both product channels are found in both systems with D*2 predominating in the case of D2 and ArH* in the case of H2.

Measurements of the velocity dependence of the absolute cross sections for the chemi-ionization of Ar, Kr, and Xe on impact of thermal energy metastable helium atoms in the relative velocity range 1–3 km sec−1 have been made using a single velocity-selected beam, collision-chamber method. Separate measurements for both 23S and 21S helium atoms are obtained through the use of a He discharge lamp to quench the singlets from the beam. The metastable atom electron ejection efficiencies are separately measured in the same apparatus. The results are compared with the relative measurements of other workers. The constants are evaluated in a two-parameter exponential function representing the coupling width for decay of the discrete electronic state of the incoming channel into the continuum electronic state of the outgoing channel, which give the best fit to the experimental data for the He* (23S) –Ar and He* (23S) –Kr systems.

Ionization cross sections for collisions of metastable 23S and 21S He atoms in Ar, Kr, Xe, H2, O2, N2, and CO have been measured using a thermal-energy atomic beam in which a fraction of the helium atoms are excited by electron bombardment. Ions produced in these gases by inelastic collisions were detected at a metal electrode, and unscattered or elastically scattered metastable atoms were detected by observing the electrons they ejected from metal surfaces. Within the experimental error of the measurements, the cross sections for the triplet and singlet states of helium were the same in all cases except that of H2. For the rare gases, the results indicated that the size of the struck particle is the primary factor in determining the cross section for ionization, rather than the energy excess. In the case of the diatomic molecules an additional consideration, that of the number and type of ionization processes possible, was also found to be important.