CH2 + O2: reaction mechanism, biradical and zwitterionic character, and formation of CH2OO, the simplest Criegee intermediate. Issue 2 (16th December 2021)

• Record Type: Journal Article
• Authors: Mazarei, Elham; Barker, John R.
• Is Part Of: Physical chemistry chemical physics. Volume 24:Issue 2(2021)
• Page Start: 914
• Page End: 927
• Publication Date: 2021-12-16
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d1cp04372b
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The singlet and triplet potential surfaces for the title reaction were investigated using the CBS-QB3 level of theory. Abstract : The singlet and triplet potential surfaces for the title reaction were investigated using the CBS-QB3 level of theory. The wave functions for some species exhibited multireference character and required the CASPT2/6-31+G(d, p) and CASPT2/aug-cc-pVTZ levels of theory to obtain accurate relative energies. A Natural Bond Orbital Analysis showed that triplet 3 CH2 OO (the simplest Criegee intermediate) and 3 CH2 O2 (dioxirane) have mostly polar biradical character, while singlet 1 CH2 OO has some zwitterionic character and a planar structure. Canonical variational transition state theory (CVTST) and master equation simulations were used to analyze the reaction system. CVTST predicts that the rate constant for reaction of 1 CH2 + 3 O2 is more than ten times as fast as the reaction of 3 CH2 (X 3 B1 ) + 3 O2 and the ratio remains almost independent of temperature from 900 K to 3000 K. The master equation simulations predict that at low pressures the 1 CH2 O + 3 O product set is dominant at all temperatures and the primary yield of OH radicals is negligible below 600 K, due to competition with other primary reactions in this complex system.