Cross sections for rotationally inelastic scattering of H2CO. I. Collisions with polar scattering gases

Rotationally inelastic cross sections for ΔJ=0, ±1, and ±2 transitions in the K_-1=1 ladder of formaldehyde (H₂CO) in collision with CF₃H, CH₃F, and NH₃ are measured in a beam-maser double-resonance (BMDR) experiment. The dependence on detection angle and relative collision velocity is investigated. At least 80% of the integral cross sections is probed. A striking difference in the angular dependence of the differential cross section for ΔJ=0 and ΔJ=±1 transitions is observed. The cross sections are compared with theoretical predictions in modified Anderson theory and adiabatically corrected sudden approximation. Anderson theory predicts very well the K-doublet cross sections and total inelastic cross sections, but fails to reproduce the state-to-state cross sections for ΔJ≠0 transitions. For ΔJ=±1 and ΔJ=±2 transitions corrected sudden approximation shows a much better agreement both with the cross sections determined in this investigation and with the values from other double-resonance experiments.