Theoretical potential functions and vibrational analysis for halocarbonyl azides CXO-NNN (X=F, Cl and Br)

The structural stability of halocarbonyl azides CXO-NNN (X=F, Cl and Br) was investigated by DFT and MP2 calculations using the 6-311++G** basis set. From the calculations, the molecules were found to have an s-cisdouble left right arrows-trans conformational equilibrium with cis being the lower-energy form. Full energy optimizations were carried out for the transition states and the minima at the B3LYP/6-311++G** and MP2/6-311++G** levels, from which the rotational barriers were calculated to be of the order 8-10 kcal mol(-1). The vibrational frequencies were computed at the DFT-B3LYP level and the vibrational assignments for the normal modes of the stable conformers were made on the basis of normal coordinate calculations.