Microwave detection of direct <i>g</i> <i>a</i> <i>u</i> <i>c</i> <i>h</i> <i>e</i> to <i>t</i> <i>r</i> <i>a</i> <i>n</i> <i>s</i> transitions in CHD2OH

Abstract

A portion of the microwave torsional–rotational spectrum of CHD2OH has been assigned between 12.4 and 41.3 GHz. Of particular interest is the detection and identification of direct gauche to trans transitions from both gauche states as well as gauche to gauche transitions. The energy level system has three substates in the torsional motion with a rotational manifold for each torsional substate. In terms of torsional substate, ten Q-type and three R-type transitions have been assigned for e0 (gauche) to o1(gauche); 13 Q-type for o1(gauche) to e1(trans); and four R-type for e0(gauche) to e1(trans). Additional lines have been assigned within each torsional substate. Spectral analysis has been made using a phenomenological rotational Hamiltonian plus an internal axis torsion–rotation Hamiltonian in zeroth order. The approximate torsional energy level differences are gauche–gauche=184.7 GHz, gauche(upper)–trans=202.5 GHz, and gauche(lower)–trans=387.2 GHz. Two sets of potential energy coefficients, one with positive V2 and the other with negative V2, have been determined that give essentially equivalent fit in the spectral analysis.