Abstract: A combination of flash photolysis reactor tube and synchrotron radiation photoionization mass spectrometer has been constructed for the study of the gas phase chemical kinetics. The radical-molecule chemical reactions in a side-sampled flow tubular reactor are initiated by a pulsed photolysis laser. Then the gas mixture is sampled via a pinpole and photoionized by tunable synchrotron radiation VUV photons. The constant flux ions are detected by the subsequent time-of-flight mass spectrometer. At the same time, pulsed generator generates a burst of pulses with duration of 40-50 s, which initiate the collection of mass spectrometer. The continuous collection covers the overall reaction time. The time resolution of mass spectrometer is 40 s, fulfilling the detection of transient or stable species on a millisecond time scale. In addition, the reaction products are directly detected by mass spectrometer and different structural isomers can be distinguished by photoionization efficiency curves. The experiment utilizing Cl radical reaction with 1-butene and isobutene obtains the addition and abstraction products as well as their photoionization energies.