Moderator Pressure Research Articles

Effects of translational energy and moderators on vibrational excitation of carbon dioxide by hot hydrogen atoms

The collisional thermalization of hot H atoms produced by the excimer laser photolysis of H2S (193 nm) and HI (193 and 248 nm) has been determined by measuring the decrease in vibrational excitation of CO2 (ν3) as a function of moderator pressure. Cross sections obtained for the rare gases in this way are in reasonable agreement with those calculated for energy loss in hard-sphere collisions. These experiments also indicate that the efficiency of vibrational excitation increases as the relative translational energy increases.

Muonium spin-exchange in low pressure gases: Mu+O2 and Mu+NO

The spin-exchange cross sections σSE for muonium collisions with O2 and NO have been measured in weak transverse magnetic fields in low pressure moderator at 300 K. Average values from runs at 1 and 2.5 atm are σSE(Mu+O2)?1.2)×10−16 cm2 and σSE(Mu+NO) ?1.2)×10−16 cm2. These numbers are in qualitative agreement with those determined earlier by Mobley et al. in ∼40 atm. moderator pressure using a longitudinal field technique. Comparison with recent measurements of the corresponding cross sections for H atom spin exchange at 300 K reveals no isotope effect, consistent with expectations based on a random-phase approximation.