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

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 Ka=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.