Using block diagonalization to determine dissociating autoionizing states: Application to N2H, and the outlook for SH

D.O Kashinski,A.P Hickman,D Talbi

doi:10.1051/epjconf/20158403003

Abstract

We describe our implementation of the block diagonalization method for calculating the potential surfaces necessary to treat dissociative recombination (DR) of electrons with N2H+. Using the methodology we have developed over the past few years, we performed multi-reference, configuration interaction calculations for N2H+ and N2H with a large active space using the GAMESS electronic structure code. We treated both linear and bent geometries of the molecules, with N2 fixed at its equilibrium separation. Because of the strong Rydberg-valence coupling in N2H, it is essential to isolate the appropriate dissociating, autoionizing states. Our procedure requires only modest additional effort beyond the standard methodology. The results indicate that the crossing between the dissociating neutral curve and the initial ion potential is not favorably located for DR, even if the molecule bends. The present calculations thereby confirm our earlier results for linear N2H and reinforce the conclusion that the direct mechanism for DR is likely to be inefficient. We also describe interesting features of our preliminary calculations on SH.

Highlights

In recent work [1,2,3] we have shown that the powerful techniques of quantum chemistry can be adapted to the calculation of dissociating, autoionizing states by implementing the block diagonalization method
We describe our implementation of the block diagonalization method for calculating the potential surfaces necessary to treat dissociative recombination (DR) of electrons with N2H+
Our work has revealed that a thorough treatment of the DR processes of ground state SH+ and a diabatization of the states concerned will require the consideration of additional higher Rydberg states, such as the 3d series and the Rydberg series converging to the first excited 1 state of the ion

Summary

Introduction

In recent work [1,2,3] we have shown that the powerful techniques of quantum chemistry can be adapted to the calculation of dissociating, autoionizing states by implementing the block diagonalization method. This manuscript describes calculations that address the dissociative recombination (DR) of N2H+, a process thought to be quite important in the interstellar medium: e− + N2H+ →. In 2007, Talbi [7] reported a theoretical investigation of the potential surfaces for linear N2H and N2H+ She concluded that the likely outcome of dissociative recombination would be the N2 + H channel, with N2 in the first electronically excited state. This manuscript investigates this issue further by considering bent geometries of N2H

Determination of autoionizing states using block diagonalization

Electronic structure calculations for N2H

2.86 Å sin2θ

Findings

Concluding remarks