A theoretical investigation of chlorine-oxygen compounds. Part 1. G2 and G2(MP2) energies of ClO, Cl 2O, ClO 2 and Cl 2O 2

Abstract

The energies of ClO, two isomers of Cl 2O, two isomers of ClO 2 and three isomers of Cl 2O 2 have been determined at the G2 and G2(MP2) levels of theory. The purpose of this paper is three-fold. The first is to determine the energies of these atmospherically important molecules at a consistent and accurate level of theory. Previously determined G2 and G2(MP2) energies are used to study bond strengths (dissociation energies), and an increasing body of G2 and G2(MP2) energies allows for future use of these results in other studies. The second goal is to determine the accuracy of these energies. This is done by comparing these results with previous theoretical and experimental studies. In agreement with earlier theoretical results, OClO is 2.0 and 3.0 kcal mol −1 more stable than ClOO at the G2 and G2(MP2) levels. In addition, for Cl 2O, the ClOCl isomer is found to be 17.0 and 16.2 kcal mol −1 more stable than the ClClO structure at the G2 and G2(MP2) levels, respectively. Also, for the three structural isomers of Cl 2O 2, both levels of calculation predict the ClOOCl isomer to be the most stable. The (O) 2ClCl structure is the next highest in energy (by 6.9 and 4.3 kcal mol −1 at the G2 and G2(MP2) levels, respectively), while the ClOClO structure is 11.7 and 11.1 kcal mol −1 above the ClOOCl conformation at the G2 and G2(MP2) levels, respectively. The final purpose of this study is to critically compare the results obtained at the G2 and G2(MP2) levels. It is found that the G2(MP2) results for relative energies and dissociation energies are in good agreement with the G2 values. This strongly suggests that the computationally less-intensive G2(MP2) method can be used in larger studies of chlorine oxides without a significant loss of accuracy.