Ly α generation in intermediate velocity shock waves

We update the Paris-Durham shock model, a state-of-the-art magnetohydrodynamic (MHD) shock code developed with a focus on molecular chemistry, in order to account for the self-generated UV field produced in shocks at velocities in the range 25-50 km/s. In these shocks there is significant excitation of atomic Hydrogen, with a large flux of Ly α photons escaping ahead of the shock to heat, ionize and drive molecular chemistry in a large slab of preshock gas.