STATE-RESOLVED PREDISSOCIATION DYNAMICS OF THE FORMYLOXYL RADICAL BY DISSOCIATIVE PHOTODETACHMENT OF HCO$_2^-$ / DCO$_2^-$

Author Institution: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093Near threshold dissociative photodetachment dynamics of HCO$_2^-$ and DCO$_2^-$ were studied using photoelectron-photofragment coincidence spectroscopy in a cryogenically cooled ion beam trap. The combination of colder precursor ions and lower kinetic energy electrons has enabled us to record higher resolution state-resolved dissociation dynamics for the HCO$_2^-$/DCO$_2^-$ + h$\nu$ $\rightarrow$ H/D + CO$_2$ + e$^-$ reaction, complementing and extending our earlier study of this system. For h$\nu=4.27$\,eV, photodetachment accesses the three lowest-lying electronic states ($^2$B$_2$, $^2$A$_1$, and $^2$A$_2$) of the formyloxyl radical, with the resulting vibrational features dominated by the OCO bending mode. Excitation of this OCO bend in the transient formyloxyl neutral couples to the bending excitation observed in the state-resolved translational energy distribution for the CO$_2$ product. Each vibrational state of the nascent neutral is observed to predissociate to several CO$_2$ product states leading to pronounced vibrational predissociation sequence bands in the photoelectron-photofragment coincidence spectra for both HCO$_2^-$ and DCO$_2^-$