Potential energy surface for the C()/C()+H2O reaction has been studied at various levels of theory including CCSD(T)/6-311+G(3df,2p) at the MP2/6-31G(d,p) and QCISD/6-311G(d,p) optimized geometries. The reaction is shown to proceed by the carbon atom addition to form C–OH2 followed by the H-shift leading to hydroxycarbene (HCOH). Hydroxycarbenes formed at this stage can easily isomerize to formaldehyde or decompose to H2+CO. The triplet C()+H2O reaction exhibits a higher barrier than the singlet one but can also produce the singlet products via a conical intersection in HCOH, as computed at the CASSCF/6-311+G(d,p) level.
