Study of gas-phase reactions of NO 2 + 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 H3 O+ 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.