DEUTERIUM-ISOTOPE EFFECTS ON THE CH STRETCHING OVERTONE SPECTRUM OF TOLUENE-ALPHA-D(1)

The room-temperature vapor phase overtone spectrum of toluene-a-dl has been recorded in the CH stretching regions corresponding to Delta ups ilon(CH) = 2-7. The vibrational overtone spectra are recorded by conve ntional near-infrared spectroscopy and by intracavity titanium:sapphir e and dye laser photoacoustic spectroscopy. Absolute oscillator streng ths are obtained from the conventional spectra, and relative oscillato r strengths within a given overtone, from both the conventional and ph otoacoustic spectra. The aryl region of the spectrum is nearly identic al to the aryl region of the spectrum of toluene-d(0) and can be under stood on the basis of two nonequivalent aryl local modes. The methyl b and differs markedly from the methyl band in toluene-d(0) in relative intensity, in line width, and in structure. We use an anharmonic oscil lator local mode model and an nb initio dipole moment function to calc ulate oscillator strengths for the aryl and methyl transitions. As was the case for toluene-d(0), these simple calculations show good agreem ent between observed and calculated intensities both in absolute total intensities and for relative intensities between the two aryl groups and between the aryl and methyl groups. We explain the differences bet ween the methyl bands in the -alpha-d(1) and -d(0) spectra on the basi s of our intensity calculations and on the basis of coupling between C H and CD stretching vibrations and methyl torsions.