Vibration–internal rotation–overall rotation interactions in CH3OH. II. Vibration introduced τ-dependence to the reduced kinetic energy coefficient for internal rotation

Abstract Vibration–internal rotation–rotation interaction theory has been used to calculate the τ -dependence of F , the reduced kinetic energy coefficient for internal rotation for CH 3 OH from molecular structure. The leading term is −3.2×10 −5 cos 3τ as a fraction of F 0 . Smaller terms are 1.5×10 −7 cos 6τ and then −0.82×10 −7 cos 2τ and 5.0×10 −10 cos 4τ for the symmetry breaking terms of the vibrationally distorted molecule. These terms have not been included previously in torsion–rotation anaylses for CH 3 OH but should be compared with the fractional uncertainty in F 0 of ±7×10 −7 . A rough estimate of the τ -independent vibrational contributions to F 0 is of the order 4% with the largest contributors being the COH bend and OH stretch.