Inner-valence photoionization of O(1D):: Experimental evidence for the 2s22p4(1D)→2s12p5(1P) transition

Photoionization and autoionization of electronically excited atomic oxygen O(D-1) are investigated in the energy range between 12 and 26 eV using tunable laser-produced plasma radiation in combination with time-of-flight mass spectrometry. A broad, asymmetric, and intense feature is observed that is peaking at 20.53 +/- 0.05 eV. It is assigned to the 2s(2)2p(4)(D-1)-> 2s(1)2p(5)(P-1) transition, which subsequently autoionizes by a Coster-Kronig transition, as predicted by the previous theoretical work [K. L. Bell , J. Phys. B 22, 3197 (1989)]. Specifically, the energy of the unperturbed transition occurs at 20.35 +/- 0.07 eV. Its shape is described by a Fano profile revealing a q parameter of 4.25 +/- 0.8 and a width of gamma=2.2 +/- 0.15 eV. Absolute photoionization cross section sigma is derived, yielding sigma=22.5 +/- 2.3 Mb at the maximum of the resonance. In addition, weak contributions to the O(D-1) yield from dissociative ionization originating from molecular singlet oxygen [O-2((1)Delta(g))] are identified as well. Possible applications of the 2s(2)2p(4)(D-1)-> 2s(1)2p(5)(P-1) transition as a state-selective and sensitive probe of excited oxygen in combination with photoionization mass spectrometry are briefly discussed. (C) 2008 American Institute of Physics.