Photodissociation dynamics of superexcited O2: Dissociation channels O(5S) vs. O(3S)

Abstract

The photodissociation dynamics of O2, O2 + hυ → O((3)P) + O(2p(3)((4)S)3s, (3)S/(5)S), has been studied by combining the XUV laser pump / UV laser probe and velocity map imaging methods in the photon energy range 14.64-15.20 eV. The fragment yield spectra of O((3)S) and O((5)S) and their velocity map images have been recorded using the state-selective (1+1) REMPI method to detect the fragments. The fragment yield spectra show resolved fine structure that arises from the predissociated Rydberg states I, I' and I″ ((3)Π(Ω = 0,1,2)). The branching ratios between the two decay channels have been measured by one-photon ionization of the fragments O((3)S) and O((5)S) simultaneously. It is surprising to find that the dissociation cross sections for the production of O((5)S) are larger than, or comparable to, those of O((3)S) for the I and I' states, while the cross sections for the production of O((5)S) are smaller than those of O((3)S) for the I″ state. All fragments O((5)S) arise from perpendicular transitions, which provides direct experimental evidence about the symmetry assignments of the states I, I' and I″ excited in this energy region. Although most of the fragments O((3)S) arise from perpendicular transitions, some of them are from parallel transitions. Based on the calculated ab initio potential energy curves, we propose that the neutral dissociation into O((3)P) + O((3)S) occurs mainly via the interaction of the Rydberg states I, I', and I″ with the vibrational continuum of the diabatic 8(3)Π(u) state (1π(u)⁻¹(a⁴Π(u))3sσ(g), ³Π(u)), while the neutral dissociation into O((3)P) + O((5)S) occurs mainly via the interaction of Rydberg states I, I', and I″ with the diabatic 7(3)Π(u) (1π(g)⁻¹(X²Π(g))3pσ(u), ³Π(u)).

Symmetry of molecular Rydberg states revealed by XUV transient absorption spectroscopy

“…The symmetry assignment for conflicts with most previous studies. A recent photodissociation study of O around 14.6–15.2 eV also discovered some features around vibrational states of 53 . However, the most prominent features of is and 34 , which are beyond the reported spectral range of ref.…”

“…However, the most prominent features of is and 34 , which are beyond the reported spectral range of ref. 53 . The state has much smaller absorption cross section and strongly overlaps with and , which makes the symmetry identification difficult.…”

Division B Commission 14 Working Group: Molecular Data

“…Using a newly developed technique, Ng and colleagues (Gao et al 2011a(Gao et al , 2012(Gao et al , 2013a measured branching fractions for the atomic products arising from dissociation for specific rotational levels. Branching fractions were also obtained for other systems, including CO 2 and N 2 (Gao et al 2011b;Pan et al 2011;Lu et al 2014) as well as O 2 (Holland & Shaw 2012;Zhou et al 2014a). Similar studies involve N 2 photoionization (Holland & Shaw 2012;O'Keeffe et al 2012) and CO 2 photoionization (Furch et al 2013).…”

Multilayer Multiconfiguration Time-Dependent Hartree Theory

“…104 ML-MCTDH theory has been applied by us to the study of m a n y d i ff e r e n t c o m p l e x s y stems. 41,[44][45][46][47][71][72][73][74][75][76][77][78][79][80][81][82][83][84]86,87,[89][90][91][92][93][94][95][96][97][98][99][100][101][102][103][110][111][112][113]123,124 A particularly important area for application of the method is condensed phase problems. Many interesting phenomena in this field require accurate (numerically exact) quantum descriptions across a broad range of physical parameter space and/or with anharmonic potential energy functions, but very often an effective method for such a purpose is lacking.…”