The ground and first excited torsional states of acetic acid

A global fit of microwave and millimeter-wave rotational transitions in the ground and first excited torsional states (nu (t) = 0 and 1) of acetic acid (CH3COOH) is reported, which combines older measurements from the literature with new measurements from Kharkov, Lille, and NIST, The fit uses a model developed initially For acetaldehyde and methanol-type internal rotor molecules. It requires 34 parameters to achieve a unitless weighted standard deviation of 0.84 for a total of 2518 data and includes A and E-species transitions with J less than or equal to 30 and K-a less than or equal to 15. While these results represent a significant improvement over past fitting attempts, it should be cautioned that the present data set is dominated by nu (t) = 0 transitions, and no direct infrared measure of the nu (t) = 1 <-- 0 torsional interval is available. (C) 2001 Academic Press.