  The stellar Initial Mass Function (IMF) seems to be close to universal in the
local star-forming regions. However, this quantity of a newborn stellar
population responds differently at gas metallicities $Z \sim$ $Z_\odot$ than
$Z$ = 0. A view on the cosmic star formation history suggests that the cooling
agents in the gas vary both in their types and molecular abundances. For
instance, in the primordial gas environment, the gas temperature can be higher
by a factor of 30 as compared to the present day. Stellar radiation feedback
and cosmic microwave background (CMB) radiation may even contribute towards
increasing the floor temperature of the star-forming gas which subsequently can
leave profound impacts on the IMF. We present the contribution of the radiation
sources towards the thermodynamical evolution of the Jeans unstable gas cloud
which experiences fragmentation and mass accretion. We find evidence which
suggests that the latter becomes the dominant process for star formation
efficiencies (SFE) above 5 - 7 %, thus increasing the average mass of the
stars. We focus on the isolated and binary stellar configurations emerging
during the gas collapse. The binary fraction on average remains 0.476 and
contributes significantly towards the total SFE of 15 %.
