Structure of nitrilimine: allenic or propargylic?

High-level ab initio molecular orbital calculations, using basis sets up to 6-311+G(2df,2p), with electron correlation incorporated at the quadratic configuration interaction (QCISD) level, have been used to examine the structure of formonitrilimine (HCNNH). In contrast to previous theoretical findings, the lowest energy structure of nitrilimine is predicted to have a nonplanar, allenic geometry. The planar, propargylic structure is not a stable local minimum on the HCNNH potential energy surface at higher levels of theory. On the other hand, the nitrilimine radical cation (HCNNH.+) is predicted to have a planar, propargylic structure. The ionization energy and heat of formation (DELTAH(f)degrees298) of nitrilimine are predicted to be 9.15 eV and 370 kJ mol-1, respectively. Calculated IR and UV spectra are also reported.