Using a home-built time-of-flight mass spectrometer (TOFMS), a research team led by Prof. Haiyang Li from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) has discovered a new competition mechanism in vacuum ultraviolet photoionization of dichloromethane that is useful for studying the stratospheric ozone depletion mechanism and photodegradation of harmful haloalkanes.