Ion recoil following (2+1) REMPI of nascent atoms - The effect on nascent velocity distributions in velocity map imaging

Velocity map imaging has achieved thus far a resolution at 1 eV kinetic ene rgy release of similar to 30 meV, thus 3% DeltaE/E. In order to further imp rove the resolution we need to look more critically at one of the assumptio ns in the imaging method - that the conversion of neutral fragments to ioni c fragments using the standard REMPI technique does not significantly chang e the nascent velocity distribution of the neutral species. This is shown i n this paper to be a questionable assumption in many cases. The effects of ion recoil due to the detection process in the photo dissociation of HI and O-2 are predicted to fall in the 2-3% range for normal conditions in veloc ity map imaging. Recoil effects are illustrated for REMPI of D atoms cooled in a supersonic discharge expansion. Dramatic effects of recoil are also i llustrated here for the photodissociation of I-H. Recoil effects are shown to play a role in the final resolution of many types of velocity mapping ex periments.