SPECTROSCOPIC INVESTIGATION OF SUBTLE CH-BOND CHANGES BETWEEN SOLID AND VAPOR-PHASE NAPHTHALENE

We have recorded CH-stretching overtone spectra of naphthalene-d(0) (N -d(0)) and selectively deuterated naphthalene-2,3,6,7-d(4) (N-beta d(4 )) both in the vapor and in the solid phase. We have used intracavity and extracavity laser photoacoustic as well as conventional absorption spectroscopy to measure these overtone transitions. The N-d(0) spectr a can be unequivocally assigned on the basis of comparison of the N-d( 0) and N-beta d(4) spectra. Subtle changes of the two nonequivalent CH -stretching oscillators are observed from the vapor to the solid phase . The peaks assigned to CHbeta experience a red shift whereas peaks as signed to CHalpha are blue shifted. These changes are explained on the basis of a condensed phase red shift and a selective blue shift due t o repulsive intermolecular steric crowding of CHalpha in the naphthale ne crystal structure.