METHANOL DIMER - THE EXPERIMENTAL RESULTS ON THE $\Delta K = 1$ SPECTRUM AND CONSISTENT ASSIGNMENTS OF K = 0 AND K = 1

Abstract

Previously at this meeting we reported on the K = 0 spectrum of methanol $dimer^{1}$. In essence the theoretical model of Ohashi and $Hougen^{2}$ indicates that 16 tunneling-rotational states should occur for each rigid rotor rotational level; 4 nondegenerate A levels, 4 fourfold degenerate G levels, and 8 doubly degenerate E levels. The internal motions which give rise to these tunneling states are: methyl internal rotation of two inequivalent tops, hydrogen bond interchange between donor and acceptor sub-units, and interchange of the lone-pair orbital of the acceptor oxygen atom. Two years ago we reported observation of 15 of the expected 16 states for $K_{a} = 0$ manifold and intensity measurements showed one transition in the E state appears to be a degenerate pair since it is twice the twice the intensity of the other E state lines. Based on a two-top $model^{3}$ for the internal rotation splittings from the two inequivalent methyl groups, we searched for b-and c-type transitions with $\Delta K = 1$ in order to aid the assignment of the $K_{a} = 1$ manifold observed previously. Three and four level connections (loops) of K = 0 and $K_{a} = 1$ have been obtained for the four A states, four G states and four of the eight E states. The assignments and analysis with the two-top approach will be described.