Measurements of relaxation cross sections for NH3 and OCS with a molecular beam maser spectrometer

Scattering cross sections for beams of NH3 and OCS are measured using a molecular beam maser spectrometer. The scattering gases used are NH3, OCS, CF3H, CH3F, N2, and He. In order to determine elastic and inelastic contributions to relaxation cross sections, measurements are made for (I) scattering of pure inversion or rotational state molecules, (II) scattering of molecules in a coherent superposition state, and (III) scattering of the whole beam in a distribution of rotational states. For dipolar scattering gases the cross sections for superposition states (σII) are significantly smaller than cross sections for pure states (σI). A theory of the scattering is presented in terms of phenomenological Redfield parameters and the S matrix. The theoretical description of scattering is used to separate elastic and inelastic contributions to the measured cross sections.