Coupled-Channel Studies of Rotational and Vibrational Energy Transfer by Collision

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Publisher Summary The chapter discusses the coupled-channel studies of rotational and vibrational energy transfer by collision. For nonreactive collisions of closed-shell molecules at energies below the threshold of electronic excitation, nuclear motion is determined by a single potential energy surface. Under these conditions, the physical processes possible are elastic scattering and energy exchange between the translational (T), rotational (R), and vibrational (V) degrees of freedom. Almost all non-empirical potential energy surfaces determined over a range of coordinate space to be usable for scattering applications have been computed following the Hartree-Fock (HF) and configuration interaction (CI) models. A method that, in principle, can yield the exact solution of the collision dynamics on a specified potential energy surface is the ‘coupled channel’ or ‘close-coupling’ (CC) method. Applications of CC methods have been restricted almost exclusively to collisions of H, He, and Li + with H 2 because of the lack of availability of accurate ab initio and reliable semi-empirical potential energy surfaces for larger systems. The H 2 molecule provides a particularly useful scattering target because of its large energy level spacing, which greatly reduces the range of excitations possible at specified collision energy. This chapter examines the dependence of computed cross sections on selected computational and physical parameters.