The Methyl Alcohol Molecule and Its Microwave Spectrum

Publisher Website
Google Scholar
Abstract
The theory of hindered rotation in methyl alcohol developed by Burkhard and Dennison has been extended to include the second-order Stark effect as well as a detailed discussion of K-type doubling. It has been applied to an interpretation of the microwave spectrum of normal methanol and of two isotopic molecules, C13H3O16H and C12H3O18H3 recently measured by Hughes, Good, and Coles. A very convincing fit between the predicted and observed lines is obtained which serves to determine many of the molecular constants, as well as providing a substantial number of self-consistency checks. The height of the potential barrier (on the assumption of a sinusoidal potential) is found to be 374.8 cm−1. The CH distance in the methyl group cannot be obtained with any accuracy from the present data but is consistent with the CH distance in methane, namely, 1.093A, and has been taken to have this value. The remaining dimensions are, however, well determined and are: OH distance=0.937A, CO distance=1.434A, COH angle=105°56′, HCH angle=109°30′. The symmetry axis of the methyl group passes between the H and O of the hydroxyl group and lies at a distance of 0.079A from the oxygen. The above values for the barrier height and molecular dimensions do not differ much from those found by Burkhard and Dennison but are believed to be considerably more accurate. Using the molecular constants, the positions of all the observed microwave lines which can be identified have been calculated. In every case the agreement is good. Those discrepancies which do exist are of an order of magnitude which can be ascribed to higher-order effects not included in the present theory. The Stark effect, both first and second order, has been computed for all identified lines. In all but one or two cases the agreement with experiment is found to be very satisfactory.