Asymmetric line shapes in the indirect predissociation of the <i>f</i> 1Σ<i>u</i>+ Rydberg state of O2

Abstract

Rotationally-resolved Beutler–Fano line shapes observed in the photoabsorption spectrum of the (2,0) band of the 3pπuf 1Σu+←X 3Σg− Rydberg system of O2 are interpreted using a coupled-channel Schrödinger equations model. It is found that the f 1Σu+ state is indirectly predissociated by the B 3Σu− continuum, and that the f←X transition borrows oscillator strength primarily from dipole-allowed transitions into the mixed Rydberg-valence states of 3Σu− symmetry. Both the predissociation linewidth and oscillator strength of the (2,0) resonance are controlled by the spin-orbit interaction between the 1Σu+ and 3Σu− components of the 3p-complex. There is some evidence for a destructive quantum interference between the transition amplitude borrowed from the 3pπuE 3Σu−←X 3Σg− transition and that borrowed weakly from the f 1Σu+←b 1Σg+ transition through spin-orbit mixing between the b 1Σg+ and X 3Σg− states.