By Sunil Bhardwaj

9386 Views


Polarisibility in a molecule

Triatomic non-linear H2O molecule makes an angle with oxygen at the centre. Being nonlinear, this molecule possesses oscillating dipole moments so H2O molecule is IR active. and will have, (3n - 6) observed absorption bands.

Where n is the number of atoms.

Thus, water molecule (n = 3 atoms) will have, $$ 3n - 6 = 3(3) - 6 = 9 - 6 = 3 $$ three vibrational degrees of freedom.

Polarisibility in a molecule

All three modes of vibrations involve change in dipole moment as well as change in Polariseability of the molecule i.e. why they are IR active as well as Raman active. The frequencies are 1595cm-1, 3652 cm-1 and 3756 cm-1

Polarisibility in a molecule