Rapid HeII->HeI recombination and radiation concerned with this process

Recombination of the primordial helium plasma (HeII->HeI, $z \simeq 1500 - 3000$) is considered. This process has an effect on the CMBR anisotropy and CMBR spectrum distortion. In this work an influence of neutral hydrogen on kinetics of HeII->HeI recombination is investigated in the frame of the standard cosmological model. It is shown that small amount of neutral hydrogen ($10^{-5} - 10^{-2}$ of total number of hydrogen ions and atoms) leads to acceleration of HeII->HeI recombination at $z\lesssim 2000$ and at $z\lesssim 1600$ quasi-equilibrium HeII->HeI recombination (according to the Saha formula) becomes valid.