Heating of primordial gas by the background radiation in the presence of heavy elements

A study is made of the influence of an admixture of the elements C, O, Si, and S in the primordial gas on the thermal regime of the matter during cosmological expansion in the epoch of z value lower than 150. It is shown than an admixture of these elements at the level of a few percent of their contemporary abundance can lead to appreciable heating of the gas. The corresponding distortions in the spectrum of the background radiation are estimated.