Resonance absorption and fluorescence in argon

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Abstract
Absorption cross sections of argon for argon resonance radiation have been measured by several techniques. The apparent cross sections are small (0·1 to 1·6 × 10-18 cm2) for resonance absorption and the values depend on the technique used for measurement. These observations are interpreted in terms of extensive reversal and broadening in the source. The excitation and quenching of resonance fluorescence was studied to provide information about the rates of the processes The rate constants were estimated relative to k r, the rate constant for radiation. Radiation imprisonment leads to a reduction of k r from its natural value and observations of the decay of resonance fluorescence suggest that k r ∼ 1·5 × 105 s-1 in our system at [Ar] = 2 × 1017 atom cm-3. Combining this value with the relative values for the quenching rate constants gives k 1 < 1·5 × 10-13, k 1′(M = N2) ∼ 6 × 10-12, k 1′(M = NO) ∼ 4 × 10-10, in units of cm3 s-1 molecule-1.