On the spin-rotation contribution to nuclear spin conversion in C3v-symmetry molecules. Application to CH3F

The symmetrized contribution of E -type spin-rotation interaction to conversion between spin modifications of E - and A 1 -types in molecules with C 3v -symmetry is considered. Using the high- J descending of collisional broadening for accidental rotational resonances between these spin modifications, it was possible to co-ordinate the theoretical description of the conversion with (updated) experimental data for two carbon-substituted isotopes of fluoromethane. As a result, both E -type spin-rotation constants are obtained. They are roughly one and a half times more than the corresponding constants for (deutero)methane.