Dissociation dynamics and stability of cyclic alkoxy radicals and alkoxide anions

Photodetachment and dissociative photodetachment processes of cyclopropoxide, c-C₃H₅O^-, and cyclobutoxide have been studied at 532 nm. Photodetachment of c-C₃H₅O^- produces both the ground X(²A″) state and the first excited A(²A′) state of cyclopropoxy radical, c-C₃H₅O. The X(²A″) state is stable at lower levels of excitation, but with increasing internal energy, dissociation into HCO + C₂H₄ is observed. The A(²A′) state completely dissociates into HCO + C₂H₄. Correlated measurements of photoelectron and photofragment kinetic energies provide dissociation energies c-C₃H₅O^- and c-C₃H₅O into HCO^- + C₂H₄ and HCO + C₂H₄ of 0.85 ± 0.07 and -0.26 ± 0.07 eV, respectively. Ab initio calculations have been performed to aid the interpretation of the dissociation mechanism. Cyclobutoxide, c-C₄H₇O^-, undergoes only dissociative photodetachment to ground-state vinoxy radical and ethylene. The adiabatic electron affinity (AEA) of c-C₄H₇O is estimated to be 1.7 ± 0.1 eV. c-C₄H₇O^- and c-C₄H₇O are both found to be thermodynamically unstable relative to dissociation into C₂H₃O^- + C₂H₄ and C₂H₃O + C₂H₄ by -0.52 ± 0.07 and -0.45 ± 0.07 eV, respectively. Factors affecting the relative stability of the c-C₃H₅O and c-C₄H₇O radicals and the corresponding alkoxide anions are discussed on the basis of the observed differences in the dissociative photodetachment dynamics.