UC Irvine

Ambient ionization processes are becoming more widely used for the measurement of atmospherically relevant particles and gases. We report here ambient ionization mass spectra utilizing a commercial tincture of iodine and a piezoelectric discharge gun (PDG) to generate the ionizing reagents. Analytes include Cl2, Br2, HNO3, the C1–C9 series of saturated monocarboxylic acids, benzoic acid, 2,2-dimethylpropanoic acid, 9-decenoic acid, and trichloroacetic acid. While Cl2 and Br2 form the [M + I]− iodide adducts, HNO3 and the organic acids show unexpected peaks corresponding to [2M – 2H + I]−. For HNO3, the new ion formed is interpreted as the [NO3 –···IONO2] complex, where IONO2 is likely formed upon reaction of HOI with gaseous NO3 –. Similarly, for the organic acids, the [2M – 2H + I]− peaks are interpreted as [RC­(O)­O–···IOC­(O)­R] complexes formed by association of RC­(O)­O– with acyl hypoiodites [RC­(O)­OI]. It is proposed that the association of (1) Cl2 and Br2 with I–, (2) IONO2 with NO3 – ions, and (3) RC­(O)­OI with carboxylate ions occurs via non-covalent halogen bonding. The results suggest the possibility that halogen bonding may play a role in chemical transformations in the atmosphere, particularly in particles where concentrations of iodinated species may be significant.