Related Experiment Video
Updated: May 19, 2026

Photoelectron Imaging of Anions Illustrated by 310 Nm Detachment of F−
Published on: July 27, 2018
Direct experimental evidence for dissociative photoionization of oxygen molecule via 2Σ(u)(-) ionic "optical dark"
Xiaofeng Tang1, Xiaoguo Zhou, Manman Wu
1Hefei National Laboratory for Physical Sciences at the Microscale, Department of Chemical Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.
Abstract:
Direct experimental evidence for dissociative photoionization of oxygen molecule via the (2)Σ(u)(-) ionic optical dark state is presented by an investigation using the method of threshold photoelectron-photoion coincidence (TPEPICO) velocity imaging. Besides vibrational progress of the B(2)Σ(g)(-) state, several weak vibrational bands of the (2)Σ(u)(-) ionic optical dark state are observed concomitantly in an excitation energy range of 20.2-21.1 eV. Only O(+) fragments are detected in the whole excitation energy range; therefore, all vibrational bands are completely predissociative. TPEPICO three-dimensional time-sliced velocity images of O(+) fragments dissociated from vibrational state-selected O(2)(+)((2)Σ(u)(-),v(+)) ions are recorded. For the (2)Σ(u)(-)(v(+)=0-3) vibrational states, only the lowest dissociation channel of O(+)((4)S) + O((3)P) is observed. Once the photon energy is slightly increased to the (2)Σ(u)(-)(v(+)=4) level, a new concentric doughnut appears in the image, indicating that the second dissociation channel of O(+)((4)S) + O((1)D) is identified indeed. With the aid of potential energy curves, the dissociative mechanism of O(2)(+) in the (2)Σ(u)(-)(v(+)) state is proposed.
Related Concept Videos
UV–Vis Spectroscopy: Molecular Electronic Transitions
Deactivation Processes: Jablonski Diagram
Photoelectric Effect
Molecular Orbital Theory II
Molecular Spectroscopy: Absorption and Emission
Photochemical Electrocyclic Reactions: Stereochemistry
Selection Rules: Photochemical Activation

