AN AB INITIO MOLECULAR ORBITAL STUDY OF THE VIBRATIONAL FREQUENCIES OF ONF AND NOF

The optimized geometries and vibrational frequencies of ONF and NOF are determined using second order Moller Plesset perturbation theory with the 6-31$G^{*}$ basis set. The geometry and frequencies of ONF are in good agreement with $experiment,^{1}$ whereas the vibrational frequencies of NOF are in poor agreement with the observed $frequencies.^{2,3}$ The theoretical predictions support the contention of $Jacox^{3}$ that the band observed by Smardzewski and $Fox^{2}$ at $1886 cm^{-1}$ is not the NO-stretching fundamental of NOF. Also, the predicted shifts in frequencies of the $\\nu_{2}$ and $\\nu_{3}$ bands upon isotopic substitution are in sharp disagreement with experimental $shifts,^{2}$ raising the question of whether NOF has actually been observed in low temperature matrices. The NOF isomer is calculated to be 40 keal/mol less stable than ONF with a barrier of 13 keal/mole for conversion of NOF to ONF. The possibility that the ground state of NOF is a triplet was also investigated.