Knowledge Bank

The temperature dependence of the cross sections for the vibrational swap process and the intrasymmetry rotational thermalization process has been studied in $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH3F$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CH3F$. This study, Which utilized infrared/millimeter-wave double resonance techniques, was performed to discover more about the collision mechanisms responsible for these processes. The cross section of the vibrational swap process fell smoothly as 1/T for the range of temperatures 120K 10 400K. A variation of Anderson theory applied to resonant vibrational proccsses has been applied to account for this behavior. The theory, which used only well known, physically meaningful parameters, agreed extremely well with the experimental results. The cross section of the intrasymmetry rotational thermalization process (i.e. the recently discovered thermalization process that follows the selection rules $\Delta K=3n$ in $CH3F$) is less well understood. At temperatures below 200K the cross section is very nearly the gas kinetic collision cross section. At temperatures above 200K the cross section rises dramatically to the point where this process appears to be the dominant collisional process at 400K. The implications of these results will be discussed in the context of collisional energy transfer in $CH3F$ and other methyl halides.