Rotational Intensity Distributions of OH and OD in an Electrodeless Discharge through Water Vapor

The distributions of intensities of the rotational lines of the ${}_{}{}^2{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}-{}_{}{}^2{}_{}{}^{}\Pi$ transition of OH and OD in a high frequency electrodeless discharge through water vapor have been measured. Effects of water vapor pressures from 0.025 to 3.2 mm Hg and added argon, helium, nitrogen, and oxygen to 10 mm Hg have been studied. Two intensity maxima are found at the same energies in both OH and OD, corresponding to total energies in the excited state of 32 950 and 37 400 ${\mathrm{cm}}^{-1\mathrm{}}$. The position of the higher energy maximum is unaffected by pressure or added gas. This is interpreted as indicating that a lower limit of 150 collisions may be set for the collision lifetime for the transfer of rotational energy of the hydroxyl radical. The intensity of the lower energy maximum, which is probably of thermal origin, increases relative to the higher energy maxima with increasing water pressure and with added gas. Argon has the effect of increasing the intensity of the (0, 0) band by more than a factor of ten.