Photoelectron and transient absorption spectroscopy on molecular Rydberg states of carbon dioxide

We have used time-resolved differential pump-probe photoelectron spectroscopy to study the competition between autoionization and predissociation dynamics in the Rydberg states of carbon dioxide. An attosecond XUV pulse excites the ground state of the molecule to two overlapping neutral Rydberg series, namely Tanaka-Ogawa and Henning series, converging to A and B continua, respectively. These states, if unperturbed, can undergo spontaneous autoionization and predissociation, where the former depends on the principal quantum number and later depends on the vibrational states and curve crossings. The presence of a conical intersection between these two series makes this system very interesting for the investigation of non-adiabatic dynamics. In our experiment, a time-delayed near infrared probe pulse ionizes the Rydberg states and we study the energy and angular distribution of the photoelectrons emitted. We observe a discrepancy between the photoelectron spectra and the results from transient absorption spectroscopy, as the photoelectron spectra do not contain the expected contributions from the Henning series. We extract previously unknown autoionization and dissociation lifetimes of the Tanaka-Ogawa Rydberg states. These lifetimes show interesting behavior with variation of the probe intensity and frequency which indicates light-induced effects alter the electron dynamics.