Study of gas‐phase reactions of NO2+ with aromatic compounds using proton transfer reaction time‐of‐flight mass spectrometry

The study of ion chemistry involving the NO2+ is currently the focus of considerable fundamental interest and is relevant in diverse fields ranging from mechanistic organic chemistry to atmospheric chemistry. A very intense source of NO2+ was generated by injecting the products from the dielectric barrier discharge of a nitrogen and oxygen mixture upstream into the drift tube of a proton transfer reaction time‐of‐flight mass spectrometry (PTR‐TOF‐MS) apparatus with H3O+ as the reagent ion. The NO2+ intensity is controllable and related to the dielectric barrier discharge operation conditions and ratio of oxygen to nitrogen. The purity of NO2+ can reach more than 99% after optimization. Using NO2+ as the chemical reagent ion, the gas‐phase reactions of NO2+ with 11 aromatic compounds were studied by PTR‐TOF‐MS. The reaction rate coefficients for these reactions were measured, and the product ions and their formation mechanisms were analyzed. All the samples reacted with NO2+ rapidly with reaction rate coefficients being close to the corresponding capture ones. In addition to electron transfer producing [M]+, oxygen ion transfer forming [MO]+, and 3‐body association forming [M·NO2]+, a new product ion [M−C]+ was also formed owing to the loss of C═O from [MO]+.This work not only developed a new chemical reagent ion NO2+ based on PTR‐MS but also provided significant interesting fundamental data on reactions involving aromatic compounds, which will probably broaden the applications of PTR‐MS to measure these compounds in the atmosphere in real time.