Reaction paths for the dissociation a 3A″ CH2CO→X 3B1 CH2 + X 1Σ+ CO

An ab initio investigation of the (CIIs) in-plane bent 3A″ CH2CO→X̃ 3B1 CH2+X̃ 1∑+CO and the (CIs) out-of-plane bent 3A′ CH2CO→X̃ 3B1 CH2+X̃ 1∑+CO dissociation paths has been performed. Geometrical structures, vibrational frequencies, and quadratic force constants have been determined at the DZP SCF and DZP CISD levels of theory for the X̃ 1A1, 3A″, and 3A′ states of ketene and for the 3A″ and 3A′ transition states for dissociation. The DZP CISD structure for à 1A″ ketene is also reported. Final energetic predictions for triplet ketene dissociation have been obtained from large-basis (QZ2P and QZ2P+f) UMP4(SDTQ) calculations at the DZP CISD geometries. The CIIs stationary point for 3A″ ketene dissociation is a true transition state with r(C–C)=2.071 Å at the DZP CISD level of theory. The corresponding CIs stationary point for 3A′ ketene is actually a super transition state for the interconversion of two equivalent 3A″CIIs transition states for dissociation. Final theoretical predictions of Te=19 400 cm−1 and T0=19 150 cm−1 are made for the adiabatic excitation energy of the ã 3A″ state of ketene, and a value of 22.3 kcal/mol is proposed for the 3A″ dissociation energy.