Ultrafast Dynamics of Neutral Superexcited Oxygen: A Direct Measurement of the Competition between Autoionization and Predissociation

摘要

Using ultrafast extreme ultraviolet pulses, we performed a direct measurement of the relaxation dynamics of neutral superexcited states corresponding to the nlσ_g(c~4Σ_u~-) Rydberg series of O_2 An extreme ultraviolet attosecond pulse train was used to create a temporally localized Rydberg wave packet 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 in superexcited oxygen 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 the (5s, 4d)σ_g and {6s,5d)σ_g Rydberg state groups, respectively. We also determine that the disputed neutral dissociation lifetime for the v = 0 vibrational level of the Rydberg series is 1100 ± 100 fs.