Results of the experiment are shown in Figure . In this experiment, CO and Cl2 were mixed with no catalyst applied, thus eliminating any possibility of producing the molecules at M63 and M65 mentioned in Table 1 via electrocatalytic or even thermal catalytic reactions. When comparing mass spectra of external CClF (i.e., direct CO and Cl2 gas mixing, Figure ) and internal CClF (Cl2 formation in CO atmosphere, Figure ), all m/z showing a peak in internal CClF showed up in external CClF as well. These results indicate that the observed IMX increase was not induced by electrochemical reactions, but either from a non-catalyzed thermal reaction between CO and Cl2, or from chemical ionization in the MS ionization chamber. Cl2 would not react with CO2 because it is uphill thermodynamically and Cl2 is unlikely to react with CO to form phosgene without the presence of both an activated carbon catalyst and elevated temperatures . Thus, this would suggest that the increased IM63 and IM65 in external CClF were the results of Chem-I. Note that although the absolute Cl2 concentration was different in internal and external CClF, it does not influence our argument on the inadvertent occurrence and involvement of Chem-I in the EI chamber.