Speaker
Dr
Moncef Bouledroua
(Faculté de Médecine & L.P.R., Badji Mokhtar University, B.P. 205, Annaba 23000, Algeria)
Description
The atmospheric chemistry revealed the importance of the ionic nitrogen in the ionosphere. This is why, over the last few decades, the diffusion and mobility phenomena of this ion have been widely investigated experimentally at different temperatures. More recent experiments of ionic open-shell systems, such as C$^{+}$ and N$^{+}$ ions, evolving in very weakly ionized plasmas have been performed at Tokyo Metropolitan University with flow-drift tubes. In particular, the mobility measurements of ground and metastable-excited nitrogen ions N$^{+}$ diffusing in neutral helium could not be explained theoretically at very low temperatures. The present work suggests improving the above calculations by using a more elaborate gas mobility model for solving the Boltzmann equation, namely, the three-temperature theory, in which full quantal momentum-transfer cross sections are introduced. Indeed, employing the two-temperature theory, most of the previous theoretical works determined, with classical transport cross sections, the reduced mobility coefficients K$_{0}$ of N$^{+}$ ions in terms of the ratio $E/N$ of the electric field strength to He gas number density, although the classical approach should cease to be valid at very low temperatures. To determine the quantum-mechanical cross sections, we first computed with MOLPRO the corresponding NHe$^{+}$ interaction potentials that dissociate into the ground N$^{+}$($^{3}$P)+He and metastable N$^{+}$($^{1}$D)+He asymptotes. The generated potential-energy curves are smoothly connected to specific long- and short-range forms. Higher multipole expansions may be added as temperature goes to ${0}.$ Moreover, the accuracy of the obtained potential curves is verified by looking at their spectroscopic parameters, as the well depths and their minimum positions. Once the NHe$^{+}$ potentials are known, they are used to solve the radial wave equation and, thus, obtain the energy-dependent phase shifts. These phases should therefore allow the computation of the individual full quantum-mechanical cross sections effective in diffusion.
The next step is devoted to the mobility calculations with the average transport cross sections among the triplet states for N$^{+}$ ($^3$P) ions and among the singlet states for N$^{+}$($^{1}$D) ions, both moving in cooled He. To achieve this purpose, we have utilized the Fortran code GC.F of Viehland based on the Gram-Charlier series. The calculations could yield, in particular, the zero-field reduced transport mobility K$_{0}$, which may be considered as a probe for the quality of the NHe$^{+}$ internuclear potentials. The present work produced the value $18.2$ cm$^{2}$V$^{-1}$s$^{-1}$. This value is comparable to $20.0±1.2$ of McFarlan *et al.*, $20.0$ of Fhadil *et al.*, $17.1$ of Sanderson *et al.*, and $17.3$ of Tanuma *et al.* Finally, the computations show the obtained first-set data of the mobility results compare quite well with values from literature.
Primary author
Dr
Moncef Bouledroua
(Faculté de Médecine & L.P.R., Badji Mokhtar University, B.P. 205, Annaba 23000, Algeria)
Co-authors
Dr
Kamel Alioua
(Département des Sciences de la Matière, Chérif Messadia University, B.P. 1553, Souk-Ahras 41000, Algeria)
Mrs
Syhem Lias
(Département des Sciences de la Matière, Chérif Messadia University, B.P. 1553, Souk-Ahras 41000, Algeria)
