Probing alkenoxy radical electronic structure using anion PEI spectroscopy

Photoelectron imaging spectra of three alkenoxide radical anions (3-buten-1-oxide, 3-buten-2-oxide, and 2-propenoxide) are presented and analyzed with supporting results of density functional theory calculations. In all spectra, intense detachment features are observed at approximately 2 eV electron binding energy, which is similar to the electron affinities of saturated neutral alkoxy radicals [Ramond et al., J. Chem. Phys. 112, 1158 (2000)]. Photoelectron angular distributions suggest the presence of several overlapping transitions which are assigned to the X̃ and à states of multiple energetically competitive conformers. The term energy of the à state of the 2-propenoxy radical, 0.17 eV, is higher than that of 3-buten-2-oxy (0.13 eV) and 3-buten-1-oxy (0.05 eV) radicals. Comparing the butenoxy radicals, we infer that stronger interactions between the non-bonding O 2p orbitals and the π bond increase the splitting between the ground and the first excited state in the 3-buten-2-oxy radical relative to the 3-buten-1-oxy radical.