Isotopic effects in molecular attosecond photoelectron interferometry

TL;DR

This paper demonstrates that attosecond photoelectron interferometry can detect isotopic differences in molecules by analyzing how isotope substitution affects photoelectron oscillations and nuclear dynamics.

Contribution

It introduces the use of attosecond interferometry to observe isotopic effects in molecular photoionization, revealing differences in nuclear autocorrelation functions.

Findings

Isotopic substitution alters photoelectron oscillation amplitude and contrast.

Attosecond interferometry detects isotope-dependent nuclear dynamics.

Differences in nuclear autocorrelation functions explain observed effects.

Abstract

Isotopic substitution in molecular systems can affect fundamental molecular properties including the energy position and spacing of electronic, vibrational and rotational levels, thus modifying the dynamics associated to their coherent superposition. In extreme ultraviolet spectroscopy, the photoelectron leaving the molecule after the absorption of a single photon can trigger an ultrafast nuclear motion in the cation, which can lead, eventually, to molecular fragmentation. This dynamics depends on the mass of the constituents of the cation, thus showing, in general, a significant isotopic dependence. In time-resolved attosecond photoelectron interferometry, the absorption of the extreme ultraviolet photon is accompanied by the exchange of an additional quantum of energy (typically in the infrared spectral range) with the photoelectron-photoion system, offering the opportunity to investigate in time the influence of isotopic substitution on the characteristics of the photoionisation dynamics. Here we show that attosecond photoelectron interferometry is sensitive to isotopic substitution by investigating the two-color photoionisation spectra measured in a mixture of methane (CH$_4$) and deuteromethane (CD$_4$). The isotopic dependence manifests itself in the modification of the amplitude and contrast of the oscillations of the photoelectron peaks generated in the two-color field with the two isotopologues. The observed effects are interpreted considering the differences in the time evolution of the nuclear autocorrelation functions in the two molecules.