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

Abstract

Abstract. We describe our implementation of the block diagonalization method for calculating the potential surfaces necessary to treat dissociative recombination (DR) of electrons with N 2 H + . Using the methodology we have developed over the past few years, we performed multi-reference, configuration interaction calculations for N 2 H + and N 2 H with a large active space using the GAMESS electronic structure code. We treated both linear and bent geometries of the molecules, with N 2 fixed at its equilibrium separation. Because of the strong Rydberg-valence coupling in N 2 H, 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 N 2 H 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.

Dissociative recombination ofN2H+

“…These limits are identified by analyzing the configurations of the electronic states and the calculated energies. In agreement with what was found by the group of Talbi [18], the lowest resonant state of 2 A ′ is quasidiabatically dissociating into N 2 3 Σ + u +H. The next 2 A ′ and 2 A ′′ are both associated with the N 2 3 Π g +H limit.…”

“…The potential energy surfaces and autoionization widths of quasidiabatic resonant states driving the direct DR of N 2 H + will be presented. These are compared with the resonant state potentials calculated by the group of Talbi and Hickman [14][15][16]18]. The electron scattering calculation carried out to study the indirect mechanism is slightly different than the one described above.…”

“…where all nitrogen is recycled. This reaction has gained substantial attention both experimentally [7][8][9][10][11][12][13] and theoretically [14][15][16][17][18]. DR measurements of this reaction have been performed using both the Flowing Afterglow Langmuir Probe technique [7,8,[10][11][12] and ion-storage ring experiments [9,13].…”

“…Extensive theoretical studies of the potential energy surfaces of electronic states of 2 A ′ symmetry important for the DR reaction have been carried out by the group of D. Talbi and A. P. Hickman [14][15][16]18]. In [14] structure calculations were performed at linear geometries with the * Electronic address: aasal@fysik.su.se NN distance frozen, using the multi-reference configuration interaction (MRCI) method with orbitals of localized character.…”

“…In the following publications [15,16,18], the block diagonalization method [19] was used to generate slices of potential energy surfaces of diabatic resonant states. In [15], the NN distance was frozen at the equilibrium value of the N 2 H + ion, while the potential energy surface of the lowest electronic resonant state was computed as a function of the other two Jacobi coordinates.…”