Knowledge Bank

Previous work showed that the shape of the molecular rotational resonance (MRR) intensity law is independent of gas sample $composition.1$ Thus, when measured at a fixed point on the intensity law, the product of the Stark-modulated spectrometer signal amplitude, S, and the square root of the corresponding incident microwave power level, $Po$, is proportional to the product of molecular concentration, N, and the average molecular rotational-relaxation rate, $1/r$, of the absorbing species. In the case of the foreign gas broadening experiments reported here, N is kept constant and the product $APo$ is measured as a function of total sample pressure. This approach to foreign gas relaxation effects offers experimental advantages over line width measurements because one operates exclusively at the absorption line frequency near the maximum available signal amplitude for all measurements. Also, relative relaxation rates are obtained from microwave power differences which are very accurate. This method simplifies data interpretation. For example, Doppler broadening does not effect the measurements and the data readily indicate when other relaxation effects are small compared to those caused by the foreign gas. Several examples will be presented.