Beam maser investigation of inelastic scattering of NH3. III. Cross sections for rotational transitions induced by CO2, N2, and H2

Abstract

Cross sections for rotational transitions between various low-lying inversion doublets of NH3 in collisions with CO2, N2, and H2 are measured in a double-resonance beam maser setup. A modification of Anderson’s theory [D. B. M. Klaassen, J. J. ter Meulen, and A. Dymanus, J. Chem. Phys. 77, 4972 (1982)] yields values for the cross sections that are in good agreement with the experimental results for CO2 and N2. For the system NH3–H2, transition probabilities are evaluated in Anderson’s theory using ‘‘bent’’ trajectories. Induction and dispersion terms up to R−7 are considered in the long-range intermolecular potential. For the short-range repulsive part, two empirical potentials are proposed with parameters that are fitted to the experimental results. Integral cross sections for rotational transitions calculated with these potentials are also presented.