Velocity map ion imaging and velocity-resolved action spectroscopy of H atom photofragments via Doppler-free multiphoton ionization

Hydrogen atom photofragments with high velocities in the laboratory frame lead to strong Doppler broadening of the (2 + 1) resonance-enhanced multiphoton ionization transition. Here, an alternative setup for Doppler-free ion imaging is demonstrated and explored for predissociation of methylamine and probing of H photofragments, at close wavelengths. This approach enables measurement of the entire velocity distributions in each laser pulse, enhances sensitivity and consequently provides acquisition of high quality H images and action spectra. These results shed light on dissociation dynamics and can be foreseen to be useful in revealing the dynamics in other molecular systems.