We consider a possibility to explain the observed suppression of the second acoustic peak in the anisotropy spectrum of the Cosmic Microwave Background ( CMB ) by interaction between a fraction of non-baryonic Cold Dark Matter ( CDM ) and normal baryonic matter .
This scenario does not require any modifications in the standard Big Bang Nucleosynthesis ( BBN ) .
We estimate the required values of the cross-section-to-mass ratio for elastic scattering of CDM particles off baryons .
In case of velocity-independent elastic scattering ( in the velocity interval \upsilon \sim 10 ^ { -5 } \div 10 ^ { -3 } ) we find that such particles do not contradict observational limits if they are heavier than \sim 10 ^ { 5 } GeV or lighter than \sim 0.5 GeV .
Another candidate , which may appear in the models with infinite extra dimensions , is a quasistable charged particle decaying through tunneling into extra dimensions .
Finally a millicharged particle with the electric charge ranging from \sim 10 ^ { -4 } to \sim 10 ^ { -1 } and with mass M \sim 0.1 \mbox { ~ { } GeV } \div 1 \mbox { ~ { } TeV } also may be responsible for the suppression of the second acoustic peak .
As a byproduct we point out that CMB measurements set new limits on the allowed parameter space for the millicharged particles .