title: Singlet and triplet potential surfaces for the O2+C2H4 reaction.
abstract: Electronic structure calculations at the CASSCF and UB3LYP levels of theory with the aug-cc-pVDZ basis set were used to characterize structures, vibrational frequencies, and energies for stationary points on the ground state triplet and singlet O(2)+C(2)H(4) potential energy surfaces (PESs). Spin-orbit couplings between the PESs were calculated using state averaged CASSCF wave functions. More accurate energies were obtained for the CASSCF structures with the MRMP2/aug-cc-pVDZ method. An important and necessary aspect of the calculations was the need to use different CASSCF active spaces for the different reaction paths on the investigated PESs. The CASSCF calculations focused on O(2)+C(2)H(4) addition to form the C(2)H(4)O(2) biradical on the triplet and singlet surfaces, and isomerization reaction paths ensuing from this biradical. The triplet and singlet C(2)H(4)O(2) biradicals are very similar in structure, primarily differing in their C-C-O-O dihedral angles. The MRMP2 values for the O(2)+C(2)H(4)→C(2)H(4)O(2) barrier to form the biradical are 33.8 and 6.1 kcal/mol, respectively, for the triplet and singlet surfaces. On the singlet surface, C(2)H(4)O(2) isomerizes to dioxetane and ethane-peroxide with MRMP2 barriers of 7.8 and 21.3 kcal/mol. A more exhaustive search of reaction paths was made for the singlet surface using the UB3LYP/aug-cc-pVDZ theory. The triplet and singlet surfaces cross between the structures for the O(2)+C(2)H(4) addition transition states and the biradical intermediates. Trapping in the triplet biradical intermediate, following (3)O(2)+C(2)H(4) addition, is expected to enhance triplet→singlet intersystem crossing.
authors.affiliation: Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, USA.
authors.forename: Kyoyeon
authors.initials: K
authors.lastname: Park
authors.forename: Aaron
authors.initials: A
authors.lastname: West
authors.forename: Erica
authors.initials: E
authors.lastname: Raheja
authors.forename: Bernhard
authors.initials: B
authors.lastname: Sellner
authors.forename: Hans
authors.initials: H
authors.lastname: Lischka
authors.forename: Theresa L
authors.initials: TL
authors.lastname: Windus
authors.forename: William L
authors.initials: WL
authors.lastname: Hase
mesh_terms: D004980:Ethane / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D006573:Heterocyclic Compounds, 1-Ring; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry*; D010545:Peroxides / Q000138:chemical synthesis / Q000737:chemistry; D011789:Quantum Theory; D013237:Stereoisomerism; D013499:Surface Properties; D014732:Vibration
chemical_list: D006571:Heterocyclic Compounds; D006573:Heterocyclic Compounds, 1-Ring; D010545:Peroxides; C079142:1,2-dioxetane; D004980:Ethane; D010100:Oxygen