Rotational energy transfer in pure HCN and in HCN-rare gas mixtures by microwave double resonance and pressure broadening

Microwave double resonance studies have been made of collision‐induced rotational transitions occurring in pure HCN and in HCN in the presence of He, Ar, or Xe. Double resonance intensities and phase shifts have been determined as a function of pressure for HCN l doublets up to $\text{Δ J= +3}$ from the pumped transition. The effects of Ar and Xe are similar and quite distinct from those of He. In the latter case the $\text{Δ J= 2}$ , $\mathrm{\pm \; \leftrightarrow \; \pm }$ transition is strongly preferred while in the former case no preferences are observed. Collision broadening linewidth parameters have been determined for the J=6, 7, 8, and 10 HCN l doublets for the pure gas and for the three rare gas collision partners. Experimental evidence is presented that indicates that quantum coherence effects are being observed in both Stark and double resonance absorption spectroscopy. An analysis is presented that utilizes the experimental total cross sections (linewidths) in a linear kinetic model of the energy transfer processes to determine partial cross sections (rates of collision induced transitions) that reproduce the double resonance data. General consideration of the atom‐dipole collision dynamics allows a preferred set of rates to be selected for each collision partner from several sets that are found to reproduce the data.