Structures and energies of low-lying doublet excited states of N₃ from accurate configuration interaction calculations

Abstract

The low-lying doublet excited states of the azide radical (N₃) have been studied at a highly multireference ab initio level of theory including basis sets up to augmented quadruple-ζ quality. A full hypersurface scan under C_2v restrictions for five low-lying bent N₃ states (²A₂, ²A₁, ²B₁, and two ²B₂) revealed a highly complex potential surface manifold with many stationary points, conical intersections and multiple surface crossings, all of which have been characterized at a high level of theory. The behavior of these states is discussed, especially as a function of the NNN angle. At least two new low-lying pathways on the excited surfaces leading from the linear to the cyclic-N₃ region were found, both involving the components of the degenerate excited ²∏_u state of linear N₃.

Keywords:

• azide radical
• low-lying doublet excited states
• configuration interaction
• conical intersection
• cyclic-N₃

Acknowledgements

The present research is supported, in part, by grants from AFOSR (FA9550-04-1-0080 and FA9550-07-1-0395). Computer time was provided by a grant under the DoD-High Performance Computing Program and by the Research Center for Computational Science, Okazaki, Japan, as well as by the Cherry Emerson Center for Scientific Computation.