Inelastic Atom-atom Collisions Research Articles

Dissociative recombination of molecular ions in noble-gas plasmas

This review treats the process of dissociative recombination of molecular ions with electrons and its role in shaping the properties of a weakly-ionized plasma of the inert gases and mixtures of them. Data are presented on the rate constants of the process and the efficiency of recombination with formation of excited atoms in various states. We discuss experimental methods that enable study of recombination processes over a wide range of variation of the electron temperature. We analyze the competition of dissociative recombination with alternative mechanisms of formation of excited atoms in recombinatively nonequilibrium plasmas, the manifestation of heteronuclear ions in the kinetics of excited and charged particles, and the mechanisms of relaxation of the energy of vibrational motion in collisions of molecular ions with atoms and dissociation in collisions with electrons. The results are discussed of experiments to study the role of inelastic atom-atom collisions in the formation of the emission spectrum of the plasma with molecular ions.

A collisional-radiative model applicable to argon discharge over a wide range of conditions. IV. Application to inductively coupled plasmas

For pt.III see ibid., vol.23, p.526 (1990). The extensive collisional-radiative model is applied to plasmas generated by a RF coil in an atmospheric argon flow in order to investigate excitation mechanisms and departures from local thermodynamic equilibrium in several spatial positions in these discharges. Computations are carried out for various sets of input parameters, such as the electron kinetic temperature Te, the atom temperature Ta, the electron number density ne, the ground-state atom population n1, the plasma column radius R and the escape factors Lambda mn and Lambda m, characterizing the non-equilibrium plasmas under consideration. The numerical modelling presented yields reliable information on the populations in the excited levels and on the validity of the so-called 'close to LTE concept' and the occurrence of an ionizing or a recombining regime in the locations investigated. The effect of the changes in the discharge parameters Te, Ta, ne, R and Lambda 1n on the excitation mechanisms, together with the role played by the inelastic atom-atom collisions and by the recombination flow of electrons from a continuum, are also shown.

Quantum-Mechanical Calculation of Cross Sections for Inelastic Atom-Atom Collisions. I. Inelastic2S3→2P3Collisions between Metastable and Ground-State Helium Atoms

A quantum-mechanical two-state close-coupling calculation of the inelastic cross section for the $2^{3}S\ensuremath{\rightarrow}2^{3}P$ excitation has been carried out for collisions between $2^{3}S$ metastable and ground-state helium atoms in the center-of-mass (c.m.) energy range 5-500 eV. The calculations were carried out in both the diabatic and adiabatic representations using two single-configuration valence-bond molecular wave functions and the corresponding adiabatic linear combinations, respectively. Both representations, as expected, gave identical results. In the diabatic representation, the coupling matrix element was found to be extremely large, resulting in a strong avoided crossing of the corresponding adiabatic potential curves and very small inelastic cross sections for energies $E\ensuremath{\lesssim}100$ eV (c.m.), but increasing to a value of about 4 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at 500 eV (c.m.), The semiclassical Stueckelberg-Landau-Zener approximation was found to be very poor at all energies considered. The JWKB distorted-wave approximation was found to be fairly good at energies $E\ensuremath{\gtrsim}400$ eV (c.m.).