Relaxation and Photoionization Dynamics of Autoionizing Resonances in Small Molecules.*

We employed time-resolved photoelectron spectroscopy to study the excitation, decay, and photoionization dynamics of Rydberg states in small molecules like carbon dioxide (CO₂). An XUV attosecond pulse train is used to excite the neutral ground state of the molecule to autoionizing resonances, namely, Henning sharp (ndσ_g) and diffuse (nsσ_g) series. These resonances can decay either by electronic correlation driven autoionization (to  X²Π_g ionic state) or by predissociation to neutral fragments. Using a time-delayed femtosecond NIR probe pulse we photoionized these states to the ionic limit (B²Σ_u⁺). From the delay-dependent photoelectron spectrogram, we obtained the autoionization and predissociation lifetimes of some Henning sharp (ndσ_g) states [1]. In another study, we are investigating the attosecond-resolved photoionization dynamics of these autoionizing Rydberg states using the Rainbow RABBITT technique, where we extract the relative time delays between two-photon ionization channels of different autoionizing resonances.

[1] Biswas, D., Wood, J., Shalaby, I., & Sandhu, A. (2024). Ultrafast dynamics of the Rydberg states of CO 2: Autoionization and dissociation lifetimes. Physical Review A, 110(4), 043106.