AN ACCURATE AB-INITIO QUARTIC FORCE-FIELD FOR FORMALDEHYDE AND ITS ISOTOPOMERS

The quartic force field of formaldehyde has been computed using large basis sets and augmented coupled cluster methods. A vibrational configuration interaction calculation based on this force field leads to fundamentals in very good agreement with experiment; the largest error (in ν1) is 7 cm-1. It is demonstrated that the vibrational frequencies are stable with respect to improvements in the one-particle basis set (using up to g functions). Computed overtones are of quality comparable to that of previous empirical and/or empirically adjusted force fields: adjustment of the harmonic frequencies leads to a distinctly superior force field. Experimental fundamentals of HDCO and D2CO are reproduced very well; computed overtones and combination bands are presented as assistance to future expcrimental work. © 1993 Academic Press, Inc.