Christopher D. Cappa

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

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 C2v and D3h 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 D3h structure, while the C2v structure is believed to be a spurious result that is due to symmetry breaking effects. The electron affinity for nCO3 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 nthat CO3−(H2O)n CIMS may be a general and selective method for the detection of atmospherically relevant peroxides.

Computational and experimental studies of chemical ionization mass spectrometric detection techniques for atmospherically relevant peroxides

Abstract We report the results of computational and experimental studies concerning the chemical ionization mass spectrometric detection of hydrogen peroxide (HOOH) and methyl hydroperoxide (CH 3 OOH). GAUSSIAN2 (G2) electronic structure calculations are used to predict structures, natural charges of the atoms and energies for the neutral species, as well as for the cation, anion, and the proton and fluoride adduct species. These calculations are used to predict ion–molecule reaction thermodynamics as a guide to the experimental development of chemical ionization mass spectrometric detection methods. Both HOOH and CH 3 OOH are predicted to react exothermically with O 2 + and F − to yield the cationic and fluoride adduct species, respectively. In addition, CH 3 OOH is predicted to react exothermically with H 3 O + to yield the proton adduct species. The feasibility of F − chemical ionization mass spectrometric detection of peroxides was experimentally explored through kinetic studies. The fluoride adduct formation reactions for both HOOH and CH 3 OOH were found to proceed at or near collision-limited rates.