Competition between autoionization and dissociation in the [O₂⁺(B² _g )]nland [O₂⁺(c⁴ _u )]nlRydberg states investigated by photon-induced dissociation to neutral fragments

Abstract

Formation of fluorescing and metastable fragments from photon-induced dissociation of O2 has been investigated in the 20.2–21.2 eV and 22.5–25.0 eV photon energy regions under high resolution. The neutral particles are detected using a microchannel plate stack, where electric potentials prevent charged particles from reaching the detector. Yield curves of excited neutral particles exhibit peaks at Rydberg states converging to O2+(B 2Σg−) and O2+(c 4Σu−). Furthermore, these yields are strongly enhanced at high-n, enabling the measurement of their energy location and width. A simple model for the decay of the Rydberg states converging to O2+(c 4Σu−) based on the competition between autoionization and neutral dissociation is used to describe qualitatively the observed spectrum. The results indicate that the lifetime of the O2+(c 4Σu−)v = 0 level is two orders of magnitude longer than that of the O2+(c 4Σu−)v = 1 level.

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

“…We note this agreement also justifies the Rydberg state groupings that we had introduced in our model. The measured value for predissociation lifetime τ d is also in agreement with the experimental lower bounds measured by Hikosaka et al [22] and Padmanabhan et al [24] who argued τ d > 600 fs and τ d ≥ 1 ps respectively. In summary, we were able to disentangle and measure the competing autoionizaton and neutral dissociation lifetimes of the (5s, 4d)σ g and (6s, 5d)σ g Rydberg states of O * * 2 , formed through the XUV excitation of a 2sσ u electron.…”

“…2(a)). The nlσ g (c 4 Σ − u ) Rydberg state assignments for the ν = 0 vibrational level obtained from prior synchrotron work [22] are shown in Fig. 2(b) along with our excitation spectrum.…”

An angle-resolved dissociative photoionization study of the c4Σ−ustate in O+2using the TPEPICO technique

“…c Single and double excitation configuration interaction (SDCI). d 1.1 meV is their upper limit from experimental observation, corresponding to a lower limit on τ 0 ; 0.05 is an estimate from the model presented in [18]. They support [16] in their value for τ 1 .…”

“…The PFI-PE study of Evans et al [16], mentioned above, determined τ 0 to be 2.7 ± 0.3 × 10 −13 s, four orders of magnitude smaller than that from [23]. Although the subsequent theoretical study by Liebel et al [24] generally favoured 'fast' dissociation over 'slow' dissociation of [23], the τ 0 value from [16] was criticized in the study by Hikosaka et al [18] as being too prompt. From their experimental data they place a lower limit on τ 0 as 6 × 10 −13 s and introduce a qualitative theoretical model resulting in a τ 0 value of ∼1.3 × 10 −11 s, which they caution should be viewed as a 'very rough estimate'.…”

Probing autoionizing states of molecular oxygen with XUV transient absorption: Electronic-symmetry-dependent line shapes and laser-induced modifications

“…(2) of low quantum number Rydberg states that do not follow core-ion approximation [57], with few-cycle NIR pulses, will enable us to study the non-adiabatic effects associated with fast autoionization and dissociation in O 2 . The relationship between the static properties and transient absorption line shapes explored here leads us to propose that finer features of ATAS spectra in molecules could be used to characterize the undetermined electronic properties of dynamically evolving systems and test the theoretical models of the strong-field modification of the correlated electron dynamics, including recently proposed interference stabilization of autoionizing states [67].…”