Quantitative results on photodissociation of CH 2 (X 3 B 1 ) through the coupled 2 A and 3 A states are presented. A three-dimensional, hybrid time-dependent quantum dynamical method was used, employing diabatic potential energy surfaces taken from ab initio calculations. In agreement with experiment and recent approximate dynamical calculations, a small product fraction (2.7%) was computed for the CH(A 2 Δ) + H channel. The dissociation proceeds mostly on an A 2 -like diabatic surface, into CH (a 4 Σ - ) + H (93.3%) and C( 3 P) + H 2 (4.0%). Model calculations show that the initial motion on the bright B 1 -like surface biases the outcome of the dissociation in favour of CH + H.