Rotational Spectrum
The water molecule is an asymmetric top, that is, it has three independent moments of inertia. Consequently the rotational spectrum has no obvious structure A large number of transitions can be observed; lines due to atmospheric water vapor can easily be observed from about 50 μm (200 cm−1) to longer wavelengths. Measurements of microwave spectra have provided a very precise value for the O-H bond length, 95.84 ± 0.05 pm and H-O-H bond angle, 104.5 ± 0.3°.
Read more about this topic: Electromagnetic Absorption By Water