A computational investigation of the electron affinity of CO3 and the thermodynamic feasibility of CO3−(H2O)n + ROOH reactions

Abstract

The results of electronic structure studies aimed at establishing an accurate theoretical value for the electron affinity of CO₃ are reported. The minimum energy structures for CO₃ and CO₃⁻ are found to be influenced by the same symmetry breaking effects that have plagued the structure determination of the isoelectronic NO₃⁺ and NO₃ species. Although both the planar C_2v and D_3h minimum energy structures are found for both CO₃ and CO₃⁻, and the difference in energy between these two structures is highly dependent on the theoretical method, it is proposed that the true minimum energy structure for each species is the D_3h structure, while the C_2v structure is believed to be a spurious result that is due to symmetry breaking effects. The electron affinity for CO₃ was calculated with a number of high accuracy methods, resulting in electron affinities ranging between 3.85 to 4.08 eV. These values are significantly higher than some experimental estimates but are in better agreement with more recent experimental results. The thermodynamic feasibility of potential chemical ionization mass spectrometric (CIMS) detection schemes for hydrogen peroxide (H₂O₂) and methyl hydroperoxide (CH₃OOH) using CO₃⁻ and CO₃⁻(H₂O) ionization schemes is also evaluated. An adapted version of G2MS theory was used for calculation of structures and thermodynamic properties of all relevant species for the study of the CIMS schemes. Several thermodynamically feasible CO₃⁻(H₂O)_n chemical ionization schemes for the detection of H₂O₂ and CH₃OOH are identified thus indicating that CO₃⁻(H₂O)_n CIMS may be a general and selective method for the detection of atmospherically relevant peroxides.