A program, called PAM_C2v_2tops, for fitting the high-resolution torsion-rotation spectra of molecules with two equivalent methyl rotors and C2v symmetry at equilibrium is described and applied to the spectrum of acetone [(CH3)2CO]. The G36 permutation-inversion group-theoretical considerations used in the design of the program are presented followed by a description of the structure of the program, which uses the principal axis method and a two-step diagonalization procedure. The program was used to carry out a weighted least-squares fit of 1720 microwave, millimeter-wave, and sub-millimeter-wave line frequencies of acetone that are available in the literature. The weighted root-mean-square deviation of 0.93 obtained here for a joint fit of the microwave lines belonging to the ground, the lower torsional fundamental, and the higher torsional fundamental states of acetone represents significant progress in comparison with previous fitting attempts, especially for the excited torsional states.
Citation: Journal of Molecular Spectroscopy
Pub Type: Journals
acetone, internal rotation, least-squares fitting program, microwave spectrum, torsional excited states, two methyl rotors