Knowledge Bank

Collision-induced transitions between rotational levels of $CH3OH$ and $CH3NH2$ have been studied by microwave double $resonance.1$ For $CH3OH,$ several systems showed small effects, the intensity variations ranging from -3 to 3%. With the use of steady state equations, these effects give rate constants in qualitative agreement with approximate calculated values based on Anderson's $theory.2$ There has been no evidence for selective collision-induced transitions violating dipole-type selection rules. Although similar effects were expected for $CH3NH2$, none were observed. When mixed with He and $H2$ both $CH2OH$ and $CH3NH2$ showed strong effects (the intensity variation was of the order of 6%). Also, collision-induced transitions with $\Delta J>1$ were observed quite strongly, thus showing that dipole-selection rules are violated in $CH3OH-He$ collisions, etc. The occurrence of $\Delta J>1$ transitions has been further evidenced by the method of microwave triple resonance. Mixing of other gases, $O2,CH4,\dots$ etc. was also tried for one system of $CH3OH$. Transitions between the A and E internal rotation states were looked for carefully but not observed.