On the use of a Fabry—Perot etalon for the determination of rotational constants of simple molecules—the pure rotational Raman spectra of oxygen and nitrogen

The use of a Fabry-Perot etalon for the study of the pure rotational Raman spectra of oxygen and nitrogen is described. By using an etalon having a plate separation of 12 mm, a resolution of 0.1 cm$^{-1}$ is readily achieved. The use of a Fabry-Perot etalon allows the wavelength of the individual rotational lines to be measured with high accuracy and leads to precise values for the rotational constants of oxygen and nitrogen. The rotational constants obtained are for N$_{2}\ B_{0}$ = 1.98950$_{6}$ $\pm $ 0.00002$_{7}$ cm$^{-1}$, $D_{0}$ = (5.48 $\pm $ 0.05$_{5}$) $\times $ 10$^{-6}$ cm$^{-1}$; for O$_{2}$ $B_{0}$ = 1.437682 $\pm $ 0.000009 cm$^{-1}$, $D_{0}$ = (4.85$_{2}\pm $ 0.01$_{2}$) $\times $ 10$^{-6}$ cm$^{-1}$. The values determined for oxygen are in excellent agreement with recent microwave measurements of these constants.