Anomalous isotopic effect on electron-directed reactivity by a 3-{\mu}m midinfrared pulse

TL;DR

This study reveals an unexpected isotopic effect in electron localization during molecular dissociation under mid-infrared laser pulses, highlighting the role of multi-photon processes and interference effects, especially in heavier isotopes.

Contribution

It uncovers an inverse isotopic trend in electron localization driven by high-order photon coupling and interference, a novel insight for controlling molecular dissociation with mid-infrared lasers.

Findings

Heavier isotopes show higher electron localization in this regime.

Interference through multi-photon channels causes the anomalous isotopic effect.

High-order above-threshold dissociation enhances the effect with increasing mass.

Abstract

We have theoretically studied the effect of nuclear mass on electron localization in dissociating H_2^+ and its isotopes subjected to a few-cycle 3-{\mu}m laser pulse. Compared to the isotopic trend in the near-infrared regime, our results reveal an inverse isotopic effect in which the degree of electron-directed reactivity is even higher for heavier isotopes. With the semi-classical analysis, we find, for the first time, the pronounced electron localization is established by the interferences through different channels of one- and, more importantly, higher-order photon coupling. Interestingly, due to the enhanced high-order above-threshold dissociation of heavier isotopes, the interference maxima gradually become in phase with growing mass and ultimately lead to the anomalous isotopic behavior of the electron localization. This indicates that the multi-photon coupling channels will play an important role in controlling the dissociation of larger molecules with midinfrared pulses.