THE SINGLET-TRIPLET GAP OF THE HALONITRENIUM IONS NHX+, NX2+ AND THE HALOCARBENES CHX, CX2 (X=F, CL, BR, I)

Ab initio studies at the MP4/6-311G(2df)//MP2/6-31G(d) level of theory using effective core potentials for Br and I predict, that halonitrenium ions NX2+ and NHX+ (X = F, Cl, Br, I) have a (1A1) singlet ground state and a singlet-triplet gap between 57-12 for NX2+ and 8-4 kcal mol-1 (1 cal = 4.184 J) for NHX+; a comparison of experimental and theoretical results of the isoelectronic carbenes shows that the theoretical level is quite reliable.