Cosmic ray induced photons in dense interstellar clouds

High-energy particles traversing a medium dissipate their energy through a succession of collisions. Part of the energy deposited by cosmic rays inside dense clouds can be transformed into a chemically significant ultraviolet flux by the impact excitation of molecular hydrogen. Detailed calculations of the collisional coefficients are described and the resulting production of ultraviolet radiation is computed, using various assumptions regarding the dust extinction properties.