The photoelectron spectrum of the oxyallyl (OXA) radical anion has been measured. The radical anion has been generated in the reaction of the atomic oxygen radical anion (O¿-) with acetone. Three low-lying electronic states of OXA have been observed in the spectrum. Electronic structure calculations have been performed for the triplet states ( 3B 2 and 3B 1) of OXA and the ground doublet state ( 2A 2) of the radical anion using density functional theory (DFT). Spectral simulations have been carried out for the triplet states based on the results of the DFT calculations. The simulation identifies a vibrational progression of the CCC bending mode of the 3B 2 state of OXA in the lower electron binding energy (eBE) portion of the spectrum. On top of the 3B 2 feature, however, the experimental spectrum exhibits additional photoelectron peaks whose angular distribution is distinct from that for the vibronic peaks of the 3B 2 state. Complete active space self-consistent field (CASSCF) method and second-order perturbation theory based on the CASSCF wave function (CASPT2) have been employed to study the lowest singlet state ( 1A 1) of OXA. The simulation based on the results of these electronic structure calculations establishes that the overlapping peaks represent the vibrational ground level of the 1A 1 state and its vibrational progression of the CO stretching mode. The 1A 1 state is the lowest electronic state of OXA, and the electron affinity (EA) of OXA is 1.940 + 0.010 eV. The 3B 2 state is the first excited state with an electronic term energy of 55 + 2 meV. The widths of the vibronic peaks of the X¿ 1A 1 state are much broader than those of the 3B 2 state, implying that the 1A 1 state is indeed a transition state. The CASSCF and CASPT2 calculations suggest that the 1A 1 state is at a potential maximum along the nuclear coordinate representing disrotatory motion of the two methylene groups, which leads to three-membered-ring formation, i.e., cyclopropanone. The simulation of b¿ 3B 1 OXA reproduces the higher eBE portion of the spectrum very well. The term energy of the 3B 1 state is 0.883 + 0.012 eV. Photoelectron spectroscopic measurements have also been conducted for the other ion products of the O¿- reaction with acetone. The photoelectron imaging spectrum of the acetylcarbene (AC) radical anion exhibits a broad, structureless feature, which is assigned to the X¿ 3A¿ state of AC. The ground ( 2A¿) and first excited ( 2A¿) states of the 1-methylvinoxy (1-MVO) radical have been observed in the photoelectron spectrum of the 1-MVO ion, and their vibronic structure has been analyzed. C 2011 American Chemical Society.
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