Solid Infrared Spectra, Assignment and Vibrational Potential Function of Diazomethane

Infrared spectra of pure solid diazomethane and diazomethane in nitrogen or argon are given here for the molecules CH2N2, CD2N2, CHDN2, and CH2N15N. These data combined with the gas-phase spectra reported earlier provide a basis for a reassignment of the vibrational spectrum. The vibrational potential function, centrifugal distortion constants, Coriolis coupling constants, and thermodynamic functions of diazomethane have been calculated. The out-of-plane hydrogen bending force constant is found to be unusually low, 0.045×10—11 erg rad—2. This is about one-fifth of that for ethylene and about one-half of that for ketene. The observed divergence of the energy levels of the out-of-plane hydrogen bending mode shows that there must be a large positive quartic contribution to the potential function for this motion.