Ab initio determination of quasi-diabatic states for multiple reaction pathways

We have extended our method for the determination of quasi-diabatic states, in order to treat systems with several open reaction channels. The method is based on the unitary transformation of the adiabatic states, obtained with any standard ab initio method, into the quasi-diabatic ones. The transformation is such that the quasi-diabatic wavefunctions exhibit a maximum overlap with a set of diabatic prototypes. In the present work we show how the prototypes can be smoothly adapted to represent diabatic states for different reaction pathways. The new method is applied to a preliminary study of the photochemistry of azomethane, where several reaction channels can be envisaged: dissociation of either one or the other C-N bond, isomerization by rotation, and isomerization by inversion.