CH STRETCHING OVERTONE INVESTIGATION OF RELATIVE CH BOND LENGTHS IN PYRIDINE

We have recorded the room temperature CH stretching overtone spectra o f pyridine, both in the vapor and in the liquid phase. We have used in tracavity laser photoacoustic as well as conventional near-infrared ab sorption spectroscopy to measure these overtone transitions. Peaks cor responding to three nonequivalent CH stretching local modes are assign ed in the high-energy vapor phase spectrum, as opposed to previous inv estigations which assigned only two. Absolute oscillator strengths are obtained from the conventional spectra and relative oscillator streng ths between the observed peaks within a given overtone from the photoa coustic spectra. Oscillator strengths are calculated with an anharmoni c oscillator local mode model and ab initio dipole moment functions. I n the high-energy vapor phase spectrum, we have assigned the three pea ks based on comparisons with ab initio calculated bond lengths and acc urate overtone intensity calculations. Our simple calculations, which contain no adjustable parameters, are in very good agreement with both the absolute and relative observed intensities.