Construction and calibration of an instrument for three-dimensional ion imaging

摘要

We describe a new instrument based on a delay-line detector for imaging the complete three-dimensional velocity distribution of photoionized products from photoinitiated reactions.Doppler-free [2+1] resonantly enhanced multiphoton ionization (REMPI) of H and D atoms formed upon photolysis of HBr and DBr in the range 203 nm<=lambda_(photolysis)<=243 nm yields radial speeds measured to be accurate within 1% of those calculated.The relative speed resolution is about 5% and limited by photoionization recoil broadening.A relative speed resolution of 3.4% is obtained for [3+1] REMPI,which minimizes the ionization recoil.We also determine the branching ratio between ground-state and spin-orbit-excited product channels and their associated anisotropies.We find that DBr photolysis dynamics differs slightly from its HBr counterpart.