Gas-phase spectroscopy of the unstable acetonitrile N-oxide molecule, CH3CNO

The unstable acetonitrile N-oxide molecule, CH3CNO, has been thermolyticall y generated in very high yield in the gas phase from its stable ring dimer, dimethylfuroxan, and studied by ultraviolet photoelectron spectroscopy, ph otoionization mass spectroscopy, and mid-infrared spectroscopy. The individ ual spectroscopies provide a detailed investigation into the vibrational an d electronic character of the molecule, and are supported by both conventio nal ab initio calculations and density functional theory. The ground-state structure is also investigated by theory at the B3-LYP, MPn (n = 2-4), QCIS D, and QCISD(T) levels with medium to large basis sets, and illustrates the need for a precise description of electron correlation. Given that both is omerization and dimerization are feasible loss processes for this unstable molecule, the relative stability of CH3CNO with respect to the known cyanat e (CH3OCN), isocyanate (CH3NCO), and fulminate (CH3ONC) isomers and the mec hanism of the dimerization processes were studied with density functional t heory.