Quantum-mechanical transport properties of N+ (3P) and N+ (1D) ions in a neutral gas made of helium.

The difficulty to reproduce the measured data by a classic-theoretical calculations of mobility of nitrogen ions N + in dilute atom-gas of helium He at low temperatures T = 4.3 and 77 K mentioned in the work of Tanuma group [H. Tanuma, S. Matoba and K. Ohtsuki, Mobility of Ions in Gases, presented at the Atomic and Molecular Data Application Forum Seminar Aiming at 'Matching the Needs and Seeds of Atomic and Molecular Data' held in National Institute for Fusion Science 17–18 December 2008. <>], prompted us to try quantum calculations to minimise this failure. To do this, we have carried out the calculations of the potential-energy curves of the low lying states corresponding to the N + + He ion-atom system using the SA-CASSCF with MRCI ab initio methods including the Davidson and BSSE corrections. The transport coefficients of the N + ( 3 P) and N + ( 1 D) ions in He atom are then carefully determined with special emphasis on the behaviour of the reduced mobility with the ratio E/N of the electric field and the gas density and try to explain its observed decrease near the value E / N ∼ 10 Td. [ABSTRACT FROM AUTHOR]