Microwave Studies of Collision-Induced Transitions between Rotational Levels. VI CH3OH and CH3NH2

Abstract

The techniques of high‐power microwave double and triple resonance have been applied to the study of collision‐induced transitions between rotational levels of CH₃OH and CH₃NH₂. Experiments have been carried out both for the pure gases and for mixtures with excesses of foreign gases, in particular He and H₂. The results of the experiments and their quantitative analysis are summarized as follows: (i) Collision‐induced transitions in pure CH₃OH were observed between rotational levels connected by ${\mu }_a$ and ${\mu }_b$ dipole selection rules $\text{ΔJ\hspace{0.17em}=\hspace{0.17em}0, ±1, ΔK\hspace{0.17em}=\hspace{0.17em}0, ±1}$ . No collision‐induced transitions were observed in pure CH₃NH₂. (ii) In CH₃OH–He, CH₃OH–H₂, and CH₃NH₂–He mixtures collision‐induced transitions with $\text{ΔJ>1}$ have been observed strongly. This result was interpreted as showing that for collision‐induced transitions in these mixtures the value of $\mathrm{\Delta J}$ is rather arbitrary while $\text{ΔK\hspace{0.17em}=\hspace{0.17em}0}$ is preferred. (iii) Collision‐induced transitions between different torsional levels ${\mathrm{A\leftrightarrow E,\; A}}_{+}{\mathrm{\leftrightarrow A}}_{-}$ , and $\text{υ\hspace{0.17em}=\hspace{0.17em}1↔0}$ were searched but never found. This result shows that these transitions are orders of magnitude smaller than transitions in a single torsional level not only in pure sample but also in mixtures. For several four‐level systems in pure CH₃OH, observed results are compared with values derived from resistance network analogs to the four‐level systems and dipolar rate constants calculated using Anderson's theory.