O + C2H4 potential energy surface: lowest-lying singlet at the multireference level

Abstract

In previous studies (West et al. in J Phys Chem A 113(45):12663, 2009; West et al. in Theor Chem Acc 131:1123, 2012), the lowest-lying O(3P) + C2H4 and singlet PES near the ·CH2CH2O· biradical were extensively explored at several levels of theory. In this work, the lowest-lying O(1D) + C2H4 PES is further examined at the multiconfigurational self-consistent field (MCSCF), MRMP2, CR-CC(2,3), GVB-PP, and MR-AQCC levels. This study aims to provide a detailed comparison of these different levels of theory for this particular system. In particular, many reactions for this system involve multiple bond rearrangements and require various degrees of both non-dynamic and dynamic correlation for reasonable energetics. As a result of this variety, coupled cluster results parallel but do not always match up with multireference results as previously anticipated. In the case of the CH2CHOH → oxirane pathway, MCSCF results show the possibility of a two-step mechanism rather than an elementary step, but the case is very difficult to elucidate. In the case of the CH3C:–OH → H2CCO + H2 pathway, a non-traditional NEB MEP at the GVB-PP level and MR-AQCC stationary point determination illustrate the need for a complex treatment of this surface.