Towards a quantum mechanical description of the photochemistry of dihalogens in rare gas matrices

Using the semiempirical diatomics-in-molecules method we investigate the nonadiabatically coupled multidimensional potential energy surfaces for Br2 in solid argon. The multidimensional nature of the nuclear motion is accounted for by defining two problem-specific large amplitude coordinates which are coupled to a set of harmonic oscillators in the spirit of a reaction surface model. This not only facilitates a compact description of anharmonicity, but also provides a means for a systematic extension towards more degrees of freedom. Taking the coupled B and C states as an example, two dominant linear vibronic coupling modes are identified giving rise to a minimum four-dimensional model for describing predissociation.