Isotope effect in tunnelling ionization of neutral hydrogen molecules

TL;DR

This study experimentally investigates the isotope effect in tunneling ionization of hydrogen molecules, confirming theoretical predictions that nuclear motion significantly influences ionization rates under strong laser fields.

Contribution

The paper provides the first experimental validation of theoretical predictions on isotope effects in tunneling ionization, challenging the frozen-nuclei approximation.

Findings

Measured ionization yield ratio matches theoretical predictions

Nuclear motion significantly affects tunneling ionization rates

Results challenge the frozen-nuclei approximation in strong-field ionization

Abstract

It has been recently predicted theoretically that due to nuclear motion light and heavy hydrogen molecules exposed to strong electric field should exhibit substantially different tunneling ionization rates (O.I. Tolstikhin, H.J. Worner and T. Morishita, Phys. Rev. A 87, 041401(R) (2013) [1]). We studied that isotope effect experimentally by measuring relative ionization yields for each species in a mixed H2/D2 gas jet interacting with intense femtosecond laser pulses. In a reaction microscope apparatus we detected ionic fragments from all contributing channels (single ionization, dissociation, and sequential double ionization) and determined the ratio of total single ionization yields for H2 and D2. The measured ratio agrees quantitatively with the prediction of the generalized weak-field asymptotic theory in an apparent failure of the frozen-nuclei approximation.