GAUCHE ETHYL ALCOHOL: LABORATORY ASSIGNMENTS AND INTERSTELLAR IDENTIFICATION

摘要

Ethyl alcohol (ethanol) is known to possess a pair of closely spaced excited torsional substates (gauche +, gauche-) at an energy of approximately 57 K above the ground (trans) torsional substate. We report an extended analysis of some gauche-gauche + Q-branch (ΔJ = 0) transitions with a three-substate fixed frame axis method (FFAM) Hamiltonian. Our approach accounts for complex trans-gauche interactions for the first time. In addition, we are able to obtain intensities for perturbed rotational transitions, and to determine the trans to gauche + separation to be 1185399.1 MHz. A complete ground state rotational-torsional partition function accounting for the previously neglected gauche substates is presented. Based on our analysis, a total of 14 U lines obtained towards Orion KL can now be assigned to gauche substates of ethanol. Analysis of these lines yields a rotational temperature of 223 K and a total (trans + gauche) column density of 7.0 x 10~(15) cm~(-2). The column- density is in reasonable agreement with the recent value of 2-3 x 10~(15) cm~(-2) based on observations of trans-ethanol by Ohishi et al., although there is some disparity in the rotational temperatures. Eight additional U lines in the literature are assigned to transitions of gauche ethanol.