Electron collisions with molecular nitrogen in its ground and electronically excited states using the R-matrix method

Abstract

A comprehensive study of electron collisions with the X 1Σg + ground state as well as the metastable A 3Σu + and a 1Πg excited states of the N2 molecule is reported using the fixed-nucleus R-matrix method. Integral elastic scattering and electronic excitation cross sections from the X 1Σg + ground state to the eight lowest electronic states, A 3Σu +, B 3Πg, W 3Δu, B′ 3Σu −, a 1Πg, a′ 1Σu −, w 1Δu and C 3Πu, overall agree well with the available experimental and theoretical results although updates of some recommended values are suggested. Accurate electron impact electronic transition cross sections starting from the A 3Σu + and a 1Πg metastable excited states are reported. The total summed electronic transition cross sections from the a 1Πg state is dominant: an order of magnitude higher than those of the X 1Σg + ground state. The de-excitation cross sections generally show a downward trend with increasing incident electron energy, which is different from the elastic and electronic excitation cross sections which generally increase with collision energy. There is a prominent 2Πu symmetry resonance peak at 2.8 eV for electronic de-excitation scattering of a 1Πg → B 3Πg, which significantly contributes to the total summed cross sections from the a 1Πg excited state. The present results provide a new insight which will aid understanding of electron spectra in the atmosphere of the Earth and Titan.

Electron-impact high-lying N2− resonant states

“…where A is the antisymmetrization operator which accounts for the exchange between the target electrons and the scattering electron, ϕ N i is the wavefunction of the ith target state, and χ N+1 i , called L 2 configurations, are obtained by putting (N + 1) electrons in target molecular orbitals, which are used to represent the short-range polarization and to relax the orthogonality with the continuum functions. These L 2 configurations comprise three configuration classes: (core) 4 (valence) 10 (continuum) 1 , (core) 4 (valence) 11 , and (core) 4 (valence) 10 (virtual) 1 . u i j represent the continuum orbitals of the scattering electron, which are labeled by the target state index i as they depend on the symmetry of the particular target state, since the two couple to give the correct overall spatial and spin symmetry of the total wavefunction N+1 k .…”

“…The radius of the R-matrix sphere a was chosen to be 10a 0 . Compared to our previous study [11] we tested the effect of both increasing the target basis set size (calculations with both cc-pVTZ and cc-pVQZ basis sets are reported below) and increasing the size of the CC expansion. Only results with the largest 41-state CC expansion considered are given below since this expansion was necessary to include the E 3 + g state which Comer and Read [15] suggested was the parent of the 2 + g resonance.…”

“…While there are no bound states of the anionic nitrogen molecule (or atom), there has been considerable work on N 2 − resonance states. The energetically lowest state of N 2 − is the X 2 g shape resonance that dominates the electron-N 2 collision cross section between 1.8 and 3.5 eV; the resonance has become a textbook example of shape resonances which has been well studied both theoretically and experimentally for many years [3][4][5][6][7][8][9][10][11]. As excitation of N 2 − by low-energy electrons is mainly due to resonant scattering processes [12], study of the N 2 − resonance is important for the understanding of nitrogen discharges, plasmas, and surface processes.…”

“…There are very few theoretical studies of high-lying nitrogen resonances. In a recent paper we studied electron-impact excitation of N 2 using the R-matrix method [11] with a particular emphasis on the excitation processes from the two low-lying metastable electronically excited states of N 2 (A 3 + u and a 1 g ). The calculations were shown to give reliable predictions of the electron-impact excitation cross sections [13].…”

Perspectives of Gas Phase Ion Chemistry: Spectroscopy and Modeling

“…This code has proven to be the most versatile tool for calculating both elastic and electronic cross sections from threshold up to about 100 eV in molecules dominated by resonances. Indeed, it has been successfully used to study a large number of molecules, including N 2 and O 2 [160][161][162][163].…”