Photodissociation dynamics of ethyl ethynyl ether: A ketenyl radical precursor

We investigate the photodissociation dynamics of ethyl ethynyl ether at 193.3 nm with crossed laser-molecular beam photofragment translational spectroscopy and laser-induced fluorescence. We establish ethyl ethynyl ether as the first clean precursor to the ketenyl radical, a key species in combustion reactions. One major bond fission channel was observed for the system, cleavage along the HCCO-C$_{2}$H$_{5}$ bond, leading to ground state C$_{2}$H$_{5}$ (ethyl) radicals and HCCO (ketenyl) radical products in two distinct electronic states. We observed neither cleavage of the other C-O bond nor molecular elimination to form C$_{2}$H$_{4}$ + CH$_{2}$CO (ketene). Ketenyl radicals formed in the higher recoil kinetic energy channel could be either $\tilde {X}(^{2}$A") or \~{A}($^{2}$A') state ketenyl radical. We assign the lower recoil kinetic energy channel to the spin forbidden \~{a}($^{4}$A") state of the ketenyl radical, reached through intersystem crossing. Laser-induced fluorescence from the ketenyl radical peaks after a 20 $\mu $s delay, indicating that it is formed with a significant amount of internal energy and subsequently relaxes to the lowest vibrational level of the ground electronic state, a result consistent with the product assignment.