High-order harmonic generation from polyatomic molecules including nuclear motion and a nuclear modes analysis

TL;DR

This paper introduces a method to incorporate nuclear motion effects into high-order harmonic generation modeling for polyatomic molecules, enabling mode analysis and supporting experimental nuclear dynamics studies.

Contribution

It presents a generic approach combining electronic and nuclear dynamics, using Franck-Condon factors to analyze nuclear mode contributions in harmonic generation.

Findings

Nuclear motion significantly influences high-order harmonic spectra.

The method successfully decomposes nuclear modes affecting harmonic generation.

Results support experimental observations of nuclear rearrangement in methane.

Abstract

We present a generic approach for treating the effect of nuclear motion in the high-order harmonic generation from polyatomic molecules. Our procedure relies on a separation of nuclear and electron dynamics where we account for the electronic part using the Lewenstein model and nuclear motion enters as a nuclear correlation function. We express the nuclear correlation function in terms of Franck-Condon factors which allows us to decompose nuclear motion into modes and identify the modes that are dominant in the high-order harmonic generation process. We show results for the isotopes CH$_4$ and CD$_4$ and thereby provide direct theoretical support for a recent experiment [Baker {\it et al.}, Science {\bf 312}, 424 (2006)] that uses high-order harmonic generation to probe the ultra-fast structural nuclear rearrangement of ionized methane.