Large-amplitude vibrations and microwave band spectra. Part 1.—Adamantan-1-ol

Abstract

The microwave spectra of adamantan-1-ol and [2H1]adamantan-1-ol have been observed in the frequency range 8–40 GHz at temperatures of 340–350 K. The spectra consist of strong series of µa R-branch bands and in the case of adamantan-1-ol a weaker series of µb Q-branch bands. The separation of the µb 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, v=(A–text-decoration:overlineB+w)(2K+ 1), for the observed µb Q-branch bands. The parameter w arises from the internal rotation part of the Hamiltonian. The barrier to internal rotation in adamantan-1-ol is estimated to be V3= 4.9 (4) kJ mol–1[410 (30) cm–1]. The error in V3 arises largely from the uncertainty in the moment of inertia of the hydroxy group about the internal rotation axis.