The adiabatic global potential energy surface of the CH 2 system for the first singlet state of
A′ symmetry (ã 1 A′) has been computed. Ab initio, multireference, single and double
configuration interaction calculations have been used to characterize this state. This
potential energy surface has a calculated well depth of 99.7 kcal/mol relative to the C (1 D)+
H 2 asymptote. The surface has no barrier for the perpendicular C 2v geometry, but presents
a large barrier (12.35 kcal/mol) for the collinear C∞ v geometry. The ab initio calculations …