Heating of primordial gas by relict radiation in the presence of hydrogen

Small impurity of molecular hydrogen can exist in primoprdial gas in the cosmological epochs z approximately equal to 1000. The effect of heating of the gas by relict radiation in the epochs z < or approximately 150 is considered. The processing of radiation energy to thermal energy of the gas takes place at transitions between low rotational levels of H2 molecules. This process leads to the increase of gas temperature to about some tens of Kelvins. The possibility of observational test for this effect is discussed