Ultrafast dynamics of neutral superexcited Oxygen: A direct measurement of the competition between autoionization and predissociation

TL;DR

This study used ultrafast extreme ultraviolet pulses to directly measure the relaxation dynamics of superexcited neutral oxygen, revealing the competition between autoionization and predissociation with precise lifetime measurements.

Contribution

It provides the first direct measurement of autoionization and dissociation lifetimes for superexcited oxygen states using ultrafast XUV pulses.

Findings

Autoionization dominates for low n Rydberg states.

Autoionization lifetime measured as 92±6 fs and 180±10 fs for specific Rydberg groups.

Neutral dissociation lifetime for vibrational level ν=0 is 1100±100 fs.

Abstract

Using ultrafast extreme ultraviolet pulses, we performed a direct measurement of the relaxation dynamics of neutral superexcited states corresponding to the nl\sigma_g(c^4\Sigma_u^-) Rydberg series of O_2. An XUV attosecond pulse train was used to create a temporally localized Rydberg wavepacket and the ensuing electronic and nuclear dynamics were probed using a time-delayed femtosecond near-infrared pulse. We investigated the competing predissociation and autoionization mechanisms for superexcited molecules and found that autoionization is dominant for the low n Rydberg states. We measured an autoionization lifetime of 92+/-6 fs and 180+/-10 fs for (5s,4d)\sigma_g and (6s,5d)\sigma_g Rydberg state groups respectively. We determine that the disputed neutral dissociation lifetime for the \nu=0 vibrational level of the Rydberg series is 1100+/-100fs.