Resonance-Mediated Below-Threshold Delayed Photoemission and Non-Franck-Condon Photodissociation of Cold Oxyallyl Anions

Angew Chem Int Ed Engl. 2019 Apr 8;58(16):5312-5315. doi: 10.1002/anie.201900386. Epub 2019 Mar 18.

Abstract

The photoexcitation of cold oxyallyl anions was studied below the adiabatic detachment threshold at a photon energy of 1.60 eV. Photodetachment was observed through two product channels, delayed electron emission from a long-lived anionic state and dissociative photodetachment via absorption of a second photon. The former produced stable neutral C3 H4 O, while the latter resulted in the concerted elimination of CO+C2 H4 products. The neutral oxyallyl singlet state has a barrier-free route to cyclopropanone as well as zwitterionic character with a large charge separation and dipole moment. The role of long-lived dipole-bound resonances built on the singlet state below the detachment threshold is discussed. These results provide one of the first observations of delayed photoemission in a small cold molecular radical anion, a consequence of the complex electronic structure of the neutral diradical, and provide an example of resonance-mediated control of the photodissociation processes.

Keywords: anions; delayed photoemission; dipole-bound states; molecular dynamics; photoelectron spectroscopy.