VIBRATIONAL-SPECTRUM AND HARMONIC FORCE-FIELD OF TRIMETHYLAMINE

Infrared and Raman spectra are reported for the isotopic species trimethylamine-d0, -d3, -d6, -d8, and -d9. Revised assignments are presented for several bands, in particular in the methyl deformation region. Estimates of the harmonic vibrational frequencies have been made with an empirical procedure based on Dennison's rule. The molecular structure and harmonic force field were calculated at the ab initio MP2/6-3 IG* level of theory, and the force field was fit to the harmonized experimental frequencies by use of eight independent scale factors. The quality of the fit is excellent (standard deviation: 2.4 cm-1), and the results are notable in that the largest variation between the various scale factors is about 1%. The latter result implies that, for this molecule, the vibrational coordinates are accurately described by the unscaled ab initio calculation.