ELECTRONIC STRUCTURE OF OXYALLYL DIRADICAL: A PHOTOELECTRON SPECTROSCOPIC STUDY

Abstract

\begin{wrapfigure}[7]{r}{3.0cm} \vspace{-0.3cm} \hspace*{-0.2cm} \epsfig{file=oxy.eps} \end{wrapfigure} The 351 nm photoelectron spectrum of oxyallyl anion has been measured. The anion is synthesized via reaction of atomic oxygen anion with acetone in He buffer gas in a flowing-afterglow tube. Photodetachment leads to the formation of a ``diradical'' species, oxyallyl, which is isoelectronic with trimethylenemethane (TMM). Both CASSCF(4,4) and B3LYP/6-311++G(d,p) electronic structure calculations have been carried out for Franck-Condon simulation of the spectrum. The $^{3}$B$_{2}$ state of oxyallyl appears in the spectrum with a $400\pm40$ $\wn$ vibrational progression of the C-C-C bending motion. Angular distributions of the photoelectrons reveal that the $^{1}$A$_{1}$ state lies very close in energy to the $^{3}$B$_{2}$ state. We tentatively assign the $^{1}$A$_{1}$ state as the ground state, with an electron affinity of $1.945\pm0.010$ eV. The term energy for the $^{3}$B$_{2}$ state is $0.056\pm0.005$ eV. These observations contrast with the photoelectron spectrum of TMM anion. The effects of oxygen substitution on the electronic structure of the diradical are discussed. The photoelectron spectrum of cyclopentanone-2,5-diyl radical anion has also been obtained. The spectrum indicates that the electronic ground state of the diradical, cyclopentanone-2,5-diyl, is $^{1}$A$_{1}$, and the electron affinity is $1.659\pm0.010$ eV. The $^{3}$B$_{2}$ state of the diradical is also observed in the spectrum with a term energy of $0.243\pm0.010$ eV. The constraint on the geometric structure of the diradical due to the five-membered ring perturbs the singlet-triplet energy levels. Supported by the National Science foundation and the Air Force Office of Scientific Research