A spin–boson model for spectroscopy involving nonadiabatically coupled potential energy surfaces

A spin–boson model, analogous to models commonly used to study multidimensional tunneling, is formulated for the problem of computing optical spectra when nonadiabatically coupled Born–Oppenheimer surfaces are involved. The model is implemented numerically for a one-dimensional prototypical case. It is demonstrated that time kernels associated with low resolution electronic absorption spectra and Raman scattering cross sections can be obtained without excessive effort even in strong coupling regimes where perturbation expansions become inefficient. The outlook for extension to more complicated systems is discussed.