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 aci d (CH3COOH) is reported, which combines older measurements from the literat ure with new measurements from Kharkov, Lille, and NIST, The fit uses a mod el developed initially For acetaldehyde and methanol-type internal rotor mo lecules. 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 tra nsitions 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 a ttempts, it should be cautioned that the present data set is dominated by n u (t) = 0 transitions, and no direct infrared measure of the nu (t) = 1 <-- 0 torsional interval is available. (C) 2001 Academic Press.