  The possibility to detect cosmological signals from the post-recombination
Universe is one of the main aims of modern cosmology. In a previous paper we
emphasized the role that elastic resonant scattering through LiH molecules can
have in dumping primary CBR anisotropies and raising secondary signals. Here we
extend our analysis to all the evolutionary stages of a primordial cloud,
starting with the linear phase, through the turn-around and to the non linear
collapse. We have done calculations for proto-clouds in a CDM scenario and,
more generally, for a set of clouds with various masses and various turn-around
redshifts, in this case without referring to any particular structure formation
scenario. We found that the first phase of collapse, for
$t/t_{free-fall}=0.05\div 0.2$ is the best one for simultaneous detection of
the first two LiH rotational lines. The observational frequency falls between
30 and 250 GHz and the line width ${\Delta \nu\over \nu}$ is between $10^{-5}$
and $10^{-4}$. As far as we know this is the most favourable process to detect
primordial clouds before they start star formation processes.
