Collisional Relaxation Processes for the n=3 States of Helium. II. Associative Ionization

Abstract

Rate constants for the associative ionization reaction He * + He → He 2 + + e have been measured, where He* represents the n=3 states of helium. By line absorption from the metastable 21S and 23S states, the n=3 states in the positive column of a dc discharge in helium were selectively and periodically modulated. Using phase-sensitive detection, the changes in excited-state populations were determined spectroscopically while the corresponding in-phase variations in the concentration of He 2 + were measured with a quadrupole mass filter. The cross sections for associative ionization in units of 10−16 cm2 were determined to be: σ (3 3 P) = 1.6 ± 0.1, σ (3 1 P) = 3.1 ± 1, σ (3 3D) = 4.5 ± 0.5, and σ (3 1D) = 20 ± 4. σ (3 3S) and σ(31S) were apparently zero.

Design of a CO2gasdynamic laser with selective thermal excitation and an unstable resonator

“…An absolute value of cr (v,) is obtained by normalising with the rate coefficient published by Collins et al (1972) k = 8 x cm3 s-'; however, the value of the temperature T required to determine (T from k = (T x fir (fir is the average thermal velocity) is not specified by these authors. A temperature I close to 300 K is assumed in their experiment and a value 6 = 5 x cm2 is deduced which corroborates other absolute values for different levels obtained experimentally (Wellenstein and Robertson 1972, Gauthier et a1 1976, Dubreuil and Catherinot 1980 or theoretically (Cohen 1976a, b).…”

The electronically excited states of helium clusters: an unusual example for the presence of Rydberg states in condensed matter

“…The analyses of energy resolved luminescence spectra of He clusters of various sizes reveal that exceptionally after excitation of the sharp 3p features the energy is transferred strongly from surface atoms into molecular He states. Such an energy transfer has been reported by Wellenstein and Robertson Wellenstein and Robertson (1972) for He in a gas.…”

“…which has been reported by Wellenstein and Robertson Wellenstein and Robertson (1972) is a well-known process in the gas phase. The intensity distribution of the nd 3 D → 2p 3 P lines shows that emissions from lower levels are favoured.…”

Collisional–radiative modelling of a helium microwave plasma in a resonant cavity

“…The present review of elementary processes is made on the basis of a limited number of papers [3,[8][9][10][11][12][13][14][15][16][17][18][19], where coherent sets of data were derived from comparison between experimental and theoretical results available at low temperature. It is completed by specific data for certain processes when it is necessary.…”