Ab initio and density functional theory (DFT) calculations have been used t
o study the isomerization process in the C-cyanophosphaethyne (NCCP) system
. Minima and transition states have been optimized at the B3LYP/6-311G(2d)
level, and single-point energies have been determined at the CCSD(T)/6-311G
(ld) level. The lowest energy isomer is found to be the N=C-C=P isomer with
C-infinity nu symmetry. The optimized geometry, rotational constant, and d
ipole moment are in good agreement with experiment. The heat of formation (
DeltaH degrees (f,298.15K)) of N=C-C=P has been computed to be 87.1 kcal/mo
l using an isodesmic reaction with G3 theory.