An accurate ion lens was simulated using a 3D ion trajectory simulation package (Simion 7.0). The simulation got an effect that all particles with the same initial velocity vector were mapped onto the same point on the detector. A high-resolution apparatus of ion velocity mapping was built by using the simulating result. The photodissociation dynamics of the Cl₃Br was studied at 267 nm. The three dimensional velocity and angular distributions of Br(²P_3/2) and Br^*(²P_1/2) were determined. The values of anisotropy parameter β were β(Br)=-0.48 and β(Br^*)=1.44, respectively. A qualitative model of the photodissociation dynamics of Cl₃Br was suggested.

Key words: ion velocity mapping, ion lens, CCl₃Br, photodissociation dynamics