O + C2H4 Potential Energy Surface: Lowest-Lying Singlet at the Multireference Level

Aaron C. West, Iowa State University
Joseph D. Lynch, Robert C. Byrd Health Sciences Center, School of Medicine
Bernhard Sellner, University of Vienna
Hans Lischka, University of Vienna
William L. Hase, Texas Tech University
Theresa Lynn Windus, Iowa State University

This article is from Theoretical Chemistry Accounts 131 (2012): 1279, doi:10.1007/s00214-012-1279-7.

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) + C2H4PES 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.