Nonexponential temperature dependence of the rate of threshold inelastic processes in dense media

The influence of the density of the medium on the temperature dependence of the rate constants of inelastic processes is investigated. It is shown that besides the effects like lowering of the ionization potential, which accelerate excitation and ionization processes in a nonideal plasma, there is a stronger mechanism for such acceleration, which is associated with the high frequency of collisions between particles and leads to destruction of the one-to-one relation between the energy and momentum of the particles in a dense medium. It is manifested by the presence of power-law tails in the equilibrium momentum distribution of the particles, which leads to a nonexponential temperature dependence of the rates of inelastic reactions in dense gases and nonideal plasmas. A kinetic equation for the generalized energy and momentum distribution function of electrons in an external electric field, which permits investigation of the effect under consideration under nonequilibrium conditions, is presented.