LARGE-AMPLITUDE VIBRATIONS AND MICROWAVE BAND SPECTRA .1. ADAMANTAN-1-OL

The microwave spectra of adamantan-1-01 and [2Ht]adamantan-l-ol have been observed in the frequency range 8-40GHz at temperatures of 40-350 K. The spectra consist of strong series of pa R-branch bands and in the case of adamantan-1-01 a weaker series of ,ub Q-branch bands. The separation of the pb Q-branch bands is almost twice that expected for a rigid rotor.
An analysis using the internal axis method to treat the internal rotation of the hydroxy group and which assumes the molecule to be a symmetric rotor gives the approximate formula Y=(A-B+w)(~K+~) for the observed Q-branch bands. The parameter w arises from the
internal rotation part of the Hamiltonian. The barrier to internal rotation in adamantan-1-01 is estimated to be V, = 4.9 (4) kJ mol-' [410 (30) cm-'I. The error in V, arises largely from the uncertainty in the moment of inertia of the hydroxy group about the internal rotation axis.