Selected ion flow tube studies of the reactions of HO, NO, O˙ and O˙ ions with alkanes in He and N carrier gases at different temperatures.

The kinetics of the reactions of HO, NO, O˙ and O˙ with -hexane, 3-methylpentane, 2,5-dimethylhexane and 2,3-dimethylheptane were studied experimentally under several selected ion flow tube (SIFT) conditions: in a Profile 3 instrument in He and N carrier gases at 300 K and in the Voice200 instrument in N carrier gas at 300 and 393 K - where the effect of the extraction lens voltage was also assessed. It was found that HO ions react differently than expected, with reaction rates slower than collisional. Instead of transferring a proton, they associate and form fragment product ions [M-H]. NO ions react hydride ion transfer. O˙ ions react charge transfer followed by fragmentation that is highly sensitive to the temperature and the ion extraction lens voltage. Negative ions did not react, except for the O˙ ion, which reacted an associative detachment process. Computational analysis using Density Functional Theory (DFT) provided insights into the exothermicities and exergodicities of these reactions. A notable result is that proton transfer from HO does not take place despite its potential exothermicity; this is important for the interpretation of proton transfer reaction (PTR) and SIFT mass spectrometry data.