A b i n i t i o multiple reference double-excitation configuration-interaction ground and excited state potential curves for nitromethane decomposition

Abstract

Reliable ab initio quantum chemical calculations for the ground and electronically excited potential energy surfaces for C–NO2 bond dissociation pathways in addition to the bond dissociation energy from the ground electronic state are crucial to evaluating energetic materials. The excited electronic state potential energy surfaces are important especially for laser induced decomposition. The curve crossings and avoided crossings are important since they determine the electronic states of the resulting fragments which influences their subsequent reactivities. We have carried out large basis set multiple reference double-excitation configuration-interaction (MRD-CI) calculations for the lowest several singlet and triplet potential curves for the H3C – NO2 decomposition of nitromethane. The proper ground state decomposition should lead to two radicals. The self-consistent-field (SCF) treatment (for the ground electronic state) was found to be satisfactory around the equilibrium structure (except for the ever-present ππ* transition of the electrons in the NO2 group) while failing completely to predict the proper dissociation limit. The analysis of the MRD-CI wave function allows distinguishing of two regions which can be interpreted as interaction within bonded molecule and interaction between species of already dissociated molecule.