On external edges of cold molecular clouds the regions of transition from atomic to molecular hydrogen are observed. In these transition regions the distribution functions of hydrogen molecules by kinetic energy are characterized by excess populations at suprathermal energies in comparison with local equilibrium Maxwellian distribution. Really, the hydrogen molecules, formed on the surfaces of interstellar grains and ejected into a gas-phase, have an excess of kinetic energy in comparison with surrounding cold interstellar gas. The numerical method for calculation of kinetics and relaxation of superthermal hydrogen molecules was proposed. The calculated non-equilibrium distribution functions of “hot” (or translationally excited) hydrogen molecules are used to estimate the kinetic rate coefficients of a lot of endothermic chemical reactions playing the important role in chemical synthesis of complex prebiotic molecules in the interstellar matter.