Knowledge Bank

Ethyl Alcohol offers an outstanding opportunity to study the effects of Asymmetric-Top on an Asymmetric-Frame internal rotation. The ground state spectrum of ethyl alcohol is comprised of three torsional substates; the trans or $e0$, the symmetric gauche ($gauche+$ or $e1$) and the asymmetric gauche (gauche- or $o1$). The interactions and transitions are governed by the $Cs$ group, with all symmetries being either odd or even. Ethyl alcohol is a prolate asymmetric top and the trans substate has slightly larger rotational constants than the two gauche substates. The trans substate is 1185.4 GHz below the $gauche+$ state. As a result of the structure and torsional energy, the energy level structure is rich in strongly avoided crossings and substantial mixing, often of all three substates. The spectrum has been assigned to $J=70$ and $Ka=24$, including multiple avoided crossings between trans and gauche states with $Ka$ differences of less than 3. The ethyl alcohol energy level structure and spectral features unique to the asymmetric internal rotation problem will be described.