Microwave Double Resonance Studies of Collision-Induced Transitions in C2H5OH, CH2DCH2OH, and C2H5OH–He

The technique of modulated microwave double resonance spectroscopy has been used to investigate rotational relaxation in ethyl alcohol. For both pure C₂H₅OH and pure CH₂DCH₂OH, b‐dipole collision‐induced transitions have been observed for the trans‐OH configuration. Weak b‐dipole collision‐induced transitions have also been observed for a mixture of C₂H₅OH and He. Collision‐induced transitions obeying a‐dipole ``selection rules'' have been searched for, but not observed, in pure C₂H₅OH and in ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH–He}$ . From the data, it may be inferred that for pure C₂H₅OH, collision‐induced transitions for which ΔJ=2 are much slower than b‐dipole transitions. Collision‐induced transitions for the gauche‐OH configuration of C₂H₅OH have also been searched for but not observed. Based on the assumption of dipole‐dipole interactions, approximate calculations of R_fi have been performed for one series of transitions in pure C₂H₅OH. These results are in fair agreement with the experimental results, and they support the conclusion that dipole‐dipole interactions are the principle mechanism responsible for the collisional transfer of rotational energy in ethyl alcohol. In addition to the double resonance measurements, the linewidths have also been measured for one series of signal transitions in C₂H₅OH. These data are consistent with those obtained in the double resonance experiments.