Theoretical chemical ionization rate constants of the concurrent reactions of hydronium ions (H3O+) and oxygen ions (O2+) with selected organic iodides

Short chain volatile iodinated organic compounds (VIOCs) are of great importance in many fields that include atmospheric chemistry, agriculture, and environmental chemistry related to nuclear power plant safety. Proton-transfer-reaction mass spectrometry (PTR-MS) allows for fast, sensitive, and online quantification of VIOCs if the chemical ionization (CI) reaction rate coefficients are known. In this work, the theoretical CI rate coefficients for the reactions of hydronium ions (H3O+) and oxygen ions (O2+) with selected atmospherically important short chain VIOCs are determined. The neutral CH3I, CH2I2, C2H5I, iso-C3H7I, n-C3H7I, n-C4H9I, 2-C4H9I, n-C5H11I, 2-C5H11I, and 3-C5H11I have been chosen because these compounds are of atmospheric and environmental importance in the field of safety of nuclear plant reactors. Theoretical ion-molecule collision rate coefficients were determined using the Su and Chesnavich theory based on parametrized trajectory calculations. The proton affinity, ionization energy, dipole moment, and polarizability values of the neutral molecules were determined from density functional theory and coupled-cluster calculations. The newly calculated rate constants facilitate the use of the CI mass spectrometry in the atmospheric quantification of selected VIOCs.