The deexcitation of the Ar (3P2, 3p1 and 1P1) states as measured by absorption both in pure argon and in the presence of additives

The de-excitation of the 3P2, 3p1 and 1P1 states of argon was studied in pure argon between 10 and 200 torr and in Ar + CO and Ar + H2 mixtures. These states are populated after excitation of the gas by a short (20 ns) pulse of 500 keV electrons (FEBETRON). Under our experimental conditions, the relation between the measured optical density of the lines studied and the concentration of absorbing species was found to be: DO = log I0/I ∝ (lC)n with n = 0,4. The three body rate constants k2 were measured for the two resonant states 3p1 (k2 = (1,65 ± 0,3) x 10-32 cm6 s-1) and 1P1 (k2 = (1,0 ± 0,2) x 10-32 cm6 s-1); they had not been considered in previous low pressure studies. For the metastable state 3P2, the measured value of k2 ((1,6 ± 0,3) x 10-32 cm6 s-1) is in good agreement with those found in the literature. However, our two body rate constant k1 is about ten times higher than that found in measurements at low pressure. This difference could be due to a collision-induced emission process at high pressure. The rate constants for the quenching by CO and H2 were measured for the metastable state 3P2 (1,85 and 10,5 x 10-11 cm3 s-1) and for the resonant states 3P1 (4,5 and 20 x 10-11 cm3 s-1) and 1P1 (8,5 and 33 X 10-11 cm3 s-1). Comparison of the de-excitation cross sections of resonant and metastable states should lead to a better understanding of energy transfer processes from these latter. (author)