Molecules in the postrecombination universe and microwave background anisotropies

We consider the effects of the elastic Thomson scattering between cosmic background radiation (CBR) and primordial molecules, like H2, H2(+), HeH(+), HD, HD(+), LiH, LiH(+): primary CBR anisotropies may be erased or attenuated for angular scales is less than or equal to 10 deg up to 50 deg and frequencies nu is 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 abundance of primordial elements. Already available data on CBR anisotropies at various frequencies impose primordial LiH abundance to be not larger than 2 x 10-9(H). Secondary anisotropies are expected at arcsecond-arcminute angular scales, due to the anisotropic scattering by moving molecular clouds: they are stronger in the millimetric region and close to be detected in IRAM 200 GHz observations.