A Vacuum Ultraviolet Photoionization Time-of-Flight Mass Spectrometer for Investigation of Free Radical Reaction

Abstract

Abstract A home-made vacuum ultraviolet (VUV) photoionization linear time-of-flight mass spectrometer (VUVPI-LTOFMS) was utilized to study atmospheric radical reactions. A commercial krypton discharge lamp with photon energy at 10.6 eV was installed as VUV light source and combined with a cage-shape photoionization source to efficiently extract and focus ions. A limit of detection (LOD) of 0.03 μg/L (S/N = 3) for benzene was achieved. A microwave discharge fast flow tube was employed as chemical reactor to produce free radicals and initiate their atmospheric reactions. The concentration of methyl radical was measured with its self-reaction kinetics and the available rate constant. As a representative example, the reaction of the methyl radical with nitric oxide was studied. Both the stable species and radicals involved in the reaction were probed, and the reaction rate constant at room temperature and pressure of 300 Pa was measured to be k(CH3 + NO) = 1.2 × 10−12 cm3/(molecule·s).