A molecule is considered to be Ir active it there is change in its dipole moment due to any of the vibrations
Or
A molecule will absrobe IR-radiation in a vibration where there is a change in dipole moment
a) Nâ‚‚: nitrogen is a linear, symmetric and non polar molecule as it is homoatomic. So there will be no vibration where it may show change in dipole, Hence it will not absorb IR radiations
b) CClâ‚‚Fâ‚‚: dichlorodifluoromethane it is asymmetric molecule and will show change in dipole during vibration of bonds and hence will absorb Ir
c) COâ‚‚: it is linear molecule but due to difference in electronegativity of two atoms there will some change in dipole during asymmetric vibrations
Hence will absorb IR radiation
