A Gaussian-2 Study of Isomeric C2H2N and C2H2N+

The structures and energetics of the C 2 H 2 N and C 2 H 2 N + isomers have been investigated using a modified Gaussian-2 (G2) method, which takes into account the energy correction due to spin contamination. At the QCISD(Full)/6-31G(d) level, C 2 H 2 N may exist as 12 stable isomers. In the order of decreasing stabilities, they are CH 2 CN ( 1 ), CH 2 NC ( 2 ), CHCNH ( 3 ), c-CH 2 CN ( 4 ), c-NCHCH ( 5 ), CHNCH ( 6 ), NH 2 CC ( 7 ), NHCHC ( 9 ), c-NHCHC ( 10 ), cis -CHCHN ( 12 ), cis -CHNHC ( 13 ), and trans -CHNHC ( 14 ). On the other hand, there are seven C 2 H 2 N + isomers. In the order of decreasing stabilities, they are c-NCHCH + ( 5 + ), CH 2 CN + ( 1 + ), CH 2 NC + ( 2 + ), CHCNH + ( 3 + ), CHNCH + ( 6 + ), c-NHCHC + ( 10 + ), and NH 2 CC + ( 7 + ). The G2 result for the ionization energy of 1 and the Δ H ° f298 values of 1 and 1 + are in good agreement with the available experimental data. However, the G2 results for radicals 2 and 5 as well as cations 2 + and 5 + do not agree with the experimental data in the literature. This calls for a reexamination of the experimental results. Furthermore, in a recent study of the reaction between nitrogen atom and vinyl radical, a C 2 H 2 N radical was formed with an ionization energy < 9.64 eV. On the basis of our calculations and known reactivity of the reactants, it is concluded that the unidentified isomer is likely to be 2 .