MOLECULES IN THE POSTRECOMBINATION UNIVERSE AND MICROWAVE BACKGROUND ANISOTROPIES

We consider the effects of the elastic Thomson scattering between cosm ic background radiation (CBR) and primordial molecules, like H2(,) H-2 (+), HeH+, HD, HD+, LiH, LiH+ : primary CBR anisotropies may be erased or attenuated for angular scales less than or equal to 10 degrees dou ble left right arrow 50 degrees and frequencies nu less than or equal to 50 GHz, if LiH primordial abundance exceed 10(-10)[H]. Conversely, CBR anisotropy data may be used to put stringent upper limits on the a bundance of primordial elements. Already available data on CBR anisotr opies at various frequencies impose primordial LiH abundance to be not larger than 2 x 10(-9)[H]. Secondary anisotropies are expected at arc second-arcminute angular scales, due to the anisotropic scattering by moving molecular clouds: they are stronger in the millimetric region a nd close to be detected in IRAM 200 GHz observations.