Probing autoionizing states of molecular oxygen with XUV transient absorption: Electronic symmetry dependent lineshapes and laser induced modification

TL;DR

This study investigates autoionizing Rydberg states of molecular oxygen using attosecond transient absorption, revealing symmetry-dependent lineshapes and laser-induced modifications, supported by experimental data and theoretical simulations.

Contribution

It provides new insights into the electronic symmetry effects on autoionizing states and demonstrates the effectiveness of the laser phase shift model in describing NIR perturbations.

Findings

Positive OD change for $ns\sigma_g$ and $nd\pi_g$ states

Negative OD change for $nd\sigma_g$ states

Decay lifetimes depend on effective quantum number

Abstract

The dynamics of autoionizing Rydberg states of oxygen are studied using attosecond transient absorption technique, where extreme ultraviolet (XUV) initiates molecular polarization and near infrared (NIR) pulse perturbs its evolution. Transient absorption spectra show positive optical density (OD) change in the case of $ns\sigma_g$ and $nd\pi_g$ autoionizing states of oxygen and negative OD change for $nd\sigma_g$ states. Multiconfiguration time-dependent Hartree-Fock (MCTDHF) calculation are used to simulate the transient absorption spectra and their results agree with experimental observations. The time evolution of superexcited states is probed in electronically and vibrationally resolved fashion and we observe the dependence of decay lifetimes on effective quantum number of the Rydberg series. We model the effect of near-infrared (NIR) perturbation on molecular polarization and find that the laser induced phase shift model agrees with the experimental and MCTDHF results, while the laser induced attenuation model does not. We relate the electron state symmetry dependent sign of the OD change to the Fano parameters of the static absorption lineshapes.