Infrared Response of H 2 to X-Rays

The rates of population of the rovibrational levels of H2 by the impact of energetic photoelectrons produced by the absorption of X-rays are calculated. Population occurs by excitation of electronically excited states of H2 followed by cascading and by direct impact excitation of the lowest vibrational level. The resulting infrared spectra are presented. The emission from high vibrational levels is similar to that from ultraviolet pumping. Emission from the v = 1 and 2 vibrational levels in a gas of low fractional ionization is dominated by direct electron impact excitation. The intensity ratio of the S(1)(2-1) and S(1)(1-0) lines is 0.06 in a gas of low fractional ionization and 0.54 in a gas of high fractional ionization.