GLOBAL FIT OF ROTATIONAL TRANSITIONS IN THE GROUND TORSIONAL STATE OFMETHANOL

We have carried out a global fit of a v(1) = 0 and J less than or equa l to 20 methanol data set containing some 730 microwave lines (K less than or equal to 12) and 1320 Fourier-transform far-infrared transitio ns (K less than or equal to 14), using a theoretical model and compute r program successfully applied previously to acetaldehyde torsion-rota tion levels below the barrier. Microwave lines were assigned a measure ment uncertainty of either 4 kHz (supersonic jet Fourier-transform mea surements) or 50 kHz. Far-infrared lines were assigned a measurement u ncertainty of 0.0002 cm(-1). A very satisfactory fit was obtained with 43 adjusted usted and 3 fixed parameters, yielding an overall weighte d standard deviation of 1.04. (It must be noted, however, that microwa ve measurements with K greater than or equal to 13 had to be excluded from the fit.) We conclude that the existing model is capable of fitti ng v(t) = 0 methanol rotational transitions to experimental accuracy, provided that K values are restricted as stated above. We believe that interactions of high-K v(t) = 0 levels with low-K v(t) = I levels, le ading to level shifts on the order of a few MHz, is the cause of our h igh-K fitting difficulties. (C) 1995 Academic Press, Inc.