Cooling of Pre-Galactic Gas Clouds by Hydrogen Molecule

According to the expanding hot universe model, neutralization of the cosmic plasma ceases at the stage of radiation temperature Tr4000oK. After then, a density contrast in the uniform medium grows into a contracting gas cloud with mass greater than 1056M3· Hydrogen molecule is formed in the cloud after the stage of Tr'300oK, and the thermal evolution is largely affected by the cooling through H 2, whose processes are studied quantitatively in this paper. The present paper is a preliminary one for a more interesting problem of galaxy formation.