Corrections to the Raman fundamental band of N2 and O2 due to molecular non-rigidity: computations and experiment

We present new, highly accurate, measurements of the fundamental band of the roto-vibrational Raman spectrum of molecular nitrogen and oxygen. Experimentally obtained spectra were used as a basis to derive information about the anisotropy of the polarisability tensor, including its dependence on rotational state due to molecular non-rigidity. Third-order perturbative calculations were used to determine corrections to the Raman scattering cross sections as a function of the rotational quantum numbers. Our results for the ratio of polarisability anisotropy at equilibrium divided by its first derivative for nitrogen are in agreement with values reported previously and are significantly different from historical data obtained for oxygen.