Initial-site characterization of hydrogen migration following strong-field double-ionization of ethanol

Hydrogen migration in ethanol (CH₃CH₂OH) can originate from each of the three non-equivalent initial sites of the molecule, leading to hydrogen-rich fragments such as H₃⁺, H₂O⁺, H₃O⁺, and CH₄⁺. Following photofragmentation by intense ultrashort pulses, we measure the momenta of the dissociating fragments using a COLTRIMS technique. By combining measurements of a few different deuterium-tagged isotopologues of ethanol, we determine all the site-specific probabilities for H₃⁺, H₂O⁺, H₃O⁺, and CH₄⁺ ion compositions. The technique can be extended to other dynamical variables, such as the kinetic energy release, and to larger molecules. These measurements provide a new benchmark for molecular dynamics calculations.