Rapid Heii→Hei recombination and radiation arising from this process

Recombination of the primordial helium plasma (He II -> He I, z similar or equal to 1500-3000) is considered. This process has an effect on the cosmic microwave background radiation (CMBR) anisotropy and CMBR spectrum distortion. In this work the influence of neutral hydrogen on the kinetics of He II -> He I recombination is investigated in the framework of the standard cosmological model. It is shown that a small amount of neutral hydrogen (a fraction 10(-5)-10(-2) of the total number of hydrogen ions and atoms) leads to the acceleration of He II -> He I recombination at z less than or similar to 2000, and z less than or similar to 1600 quasi-equilibrium He II -> He I recombination (according to the Saha formula) becomes valid.