Oscillator strengths and integral cross sections of the valence-shell excitations of HCl studied by fast electron scattering.

The oscillator strengths and integral cross sections of the valence-shell excitations of HCl have significant applications in the studies of planetary atmospheres and interstellar gases. In the present work, the generalized oscillator strengths of the valence-shell excitations of HCl have been measured at an incident electron energy of 1500 eV and an energy resolution of 70 meV, and their momentum transfer dependence behaviors have been elucidated. It is observed that the generalized oscillator strength ratios of the bΠ(ν' = 0) state to the CΠ(ν' = 0) state are a constant and independent of the squared momentum transfer, and this typical behavior in the momentum space is explained by the intraconfiguration mixing of the bΠ and CΠ states due to the spin-orbital interaction. The optical oscillator strengths of the valence-shell excitations have been obtained by extrapolating the generalized oscillator strengths to the limit of zero squared momentum transfer. The present optical oscillator strengths give an independent cross-check to the previous experimental and theoretical results, and it is found that most of the photoabsorption measurements are limited by the line saturation effect. The integral cross sections of the valence-shell excitations of HCl have been obtained systematically from the threshold to 5000 eV with the aid of the BE-scaling method.