The 2p interloper resonances in collisions

Abstract

Ab initio electron scattering calculations using the R-matrix approach have been performed for N + 2 within a three-state valence configuration-interaction model (VCI). The lowest three electronic target states (X 2 + u , A 2 u and the B 2 + u ) of this molecular nitrogen cation are included in the close-coupling method, with each state being represented by a valence CI approximation. From a detailed analysis of the resonance structure found in our work for the 1,3 + g symmetries we find four prominent Rydberg series of the type npπ u , nfπ u , npσ u , nfσ u and a 2pσ u interloper resonance. This 2pσ u interloper molecular resonance associated with the B state of N + 2 is seen to cause distortions of the resulting resonance spectra. A comparison of our total cross sections for the X-B transition shows excellent agreement with the available experimental data.Electron collisions with molecular ions play a fundamental role in laboratory and astrophysical plasmas with the dissociative recombination process being the main mechanism for the removal of ions. The 0-0 band of the first negative system of N + 2 at approximately 391.4 nm (X-B transition) is an extremely intense emission band and is widely used in many diagnostic measurements. It is possible that, during severely disturbed conditions, electron impact excitation of molecular oxygen and nitrogen ions could be important, for example during space vehicle re-entry, but not under normal conditions (Dalgarno 1997). Ionization of the neutral parent is a more likely source of ions as indicated in recent experiments (Doering and Yang 1997a, b). What prompted us to study this system was the fact that the molecular nitrogen ion and its neutral are of importance in the atmosphere of our planet, not least in the study of flow fields surrounding high-velocity space vehicles at re-entry. In this complex, specifically for the X-B transition, there has been early experimental work performed on this system (Crandall et al 1974, Lee and Carleton 1968, Dashchenko et al 1973 and more recently theoretical studies using the complex Kohn method (Orel et al 1990). To the best of our knowledge there has been no detailed study of resonances arising in the case of electron-collisional excitation of this molecular ion complex. Such a study will provide a wealth of electronic and vibrational information which can provide a doorway to other transient molecular processes. Knowledge of the resonance positions and widths, as a function of the internuclear geometry can be used as input to various theories of field-free and laser-assisted, associative (AI) and Penning (PI) ionization. The present work is an initial attempt to provide information and identify the relevant resonant molecular processes and their associated parameters.

An R-matrix study of singlet and triplet continuum states of N2

“…Orel et al (1990) calculated electronic impact cross-sections for the X 2 + g → B 2 + u transition at a single geometry using the complex-Kohn variational method. An R-matrix calculation by Ballance et al (1998) found Rydbergtype resonances of 1,3 + g symmetry, this work was extended by Nagy (Nagy et al 1999, Nagy 2003 to include vibrational motion to determine vibronic electron impact excitation crosssections for the X → B transition. These calculations are in the spirit of a conventional scattering calculation; a single or small number of appropriate geometries are calculated to determine a scattering parameter which, in general, only depends on these internuclear separations.…”

Time-delay matrix analysis of resonances: application to the positronium negative ion

“…On the other hand, results of R-matrix method calculations were analysed recently by taking advantage of the known analytic forms of the R matrix and associated matrices when differentiating with respect to the energy [8][9][10] to find out the maximum of the Lorentzian form. This method was found useful for automatic and fast analysis of the results of R-matrix method calculations.…”

“…When the resonance is narrow or when the background S matrix depends only weakly on the energy, the resonance analysis is fairly simple, the results depending little on the choice of the analysis procedure among the ones mentioned so far. Indeed, the pure Lorentzian form of dδ(E)/dE reduces to a simple expression for the resonance position and width [8][9][10][11]. However, there are cases where the energy dependence of the background S matrix is far from negligible and plays a significant role.…”

Effect of Fluorine on Characteristics of Shallow Trench Isolation Prepared Using High-Density Plasma Chemical Vapor Deposition Including NF3 Chemistry

“…At the valence CI level, an additional check on our results for the 1,3 + g scattering symmetry is a comparison of the lowest R-matrix pole with bound state calculations from closed-channel scattering calculations using the method of Seaton (1985), as implemented for molecules by Sarpal et al (1991) for a range of internuclear geometries which showed excellent agreement (Ballance et al 1998a). Electronic excitation from the ground X 2 + g state to both the A 2 u and B 2 + u states of N + 2 was then investigated within the fixed-nuclei approximation.…”

“…The orbital set (2) yields 778 CSFs for the X state, 1308 CSFs for the A state and 778 CSFs for the B state with an increase in the computational complexity of the problem. To cater for nuclear motion effects in our work, calculations of cross sections for vibrational excitation of the ground state and vibronic excitation of the excited states (X-A, X-B transitions) are currently in progress within a non-adiabatic regime and the results from this work will be available in due course (Ballance et al 1998a).…”