Photofragment vector correlations measured by sub-doppler 2+1 laser-induced fluorescence spectroscopy

Abstract

The bipolar moment formalism used by Dixon to discuss the measurement of photofragment vector correlations by sub-Doppler 1+1 laser-induced fluorescence spectroscopy is extended to cover measurements using three photons. The 1+1 and 2+1 LIF methods are compared and the 2+1 LIF approach shown to be more sensitive to some of the higher-order bipolar moments. The usefulness of several special geometries is considered and leads to the conclusion that the LIF technique cannot be used to measure the conventional translational anisotropy parameter directly, nor can it be made to yield an isotropic (flat-topped) lineshape for a single experimental geometry. These limitations are contrasted with the advantages offered by the multiphoton ionisation/time-of-flight technique introduced by Mons and Dimicoli which can achieve both of the above simplifications.