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((2)A ") state and the first excited A((2)A ') state of cyclopropoxy radical, c-C3H5O. The X((2)A ") state is stable at lower levels of excitation, but with increasing internal energy, dissociation into HCO + C2H4 is observed. The A((2)A ') 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 vinery 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.