The asymmetric top–asymmetric frame internal rotation spectrum of ethyl alcohol

Abstract

The rotational–torsional spectrum of ethyl alcohol is presented in the torsional ground state of the OH internal rotation. The spectrum has been investigated in the 12–1650 GHz range. Over 10 000 transitions with quantum numbers through J = 76 and K a = 26 have been assigned and analyzed with a three state Hamiltonian model accounting for the predominately threefold asymmetric internal rotation of the OH group. We believe that this is the first comprehensive analysis of a predominately threefold asymmetric top–asymmetric frame internal rotation problem. The data set includes over 1000 trans to gauche transitions as well as examples of numerous torsion–rotation interactions. The general features of the spectrum are discussed along with a detailed discussion of the Hamiltonian model, its limitations and the prospects for further Hamiltonian development. A complete set of torsion–rotation constants have been determined using an effective Hamiltonian that models the spectrum with a near unity reduced deviation. The comprehensive nature of the data will make ethyl alcohol the prototypical asymmetric top–asymmetric frame internal rotation problem and facilitate the subsequent refinement of the Hamiltonian models.