INTENSITY OF CH-STRETCHING AND NH-STRETCHING TRANSITIONS IN THE OVERTONE SPECTRA OF CYCLOPROPYLAMINE

Vapor phase room temperature overtone spectra of cyclopropylamine are measured both with conventional absorption spectroscopy for the lower overtones and with intracavity laser photoacoustic spectroscopy for th e higher overtones. Spectra are recorded in both the CH-stretching (DE LTAv(CH)=2-7) and NH-stretching (DELTAv(NH)=2-6) regions. The relative intensities of XH-stretching peaks are explained in terms of the loca l mode model of harmonically coupled anharmonic oscillators, where all modes but the XH-stretching modes are neglected. The dipole moment fu nction is expanded in the XH-stretching coordinates, with the expansio n coefficients determined from ab initio molecular orbital calculation s. The high number of peaks throughout the spectra makes assignment di fficult, but allows the overlap of spectra from different experimental conditions. Thus it is possible to approximately determine the absolu te intensities for the higher overtone spectra that are obtained from the laser experiments. The simple intensity calculation, which contain s no adjustable parameters, can account very well for the magnitude of the intensities and for the relative intensities of the pure local mo de peaks for all XH oscillators in the overtone spectral region from D ELTAv(CH)=3 to 7.