Tandem mass spectrometry has evolved as a routine peptide sequencing technique; however, there are numerous examples where TMS using collision-induced dissociation (CID) does not provide the desired information, including post-translational modifications, sites of disulfide bridges, and site specific glycosylation. UV (193 nm) photodissociation has been shown to provide structural information for such problems. In order to improve the quality of our tandem time-of-flight photodissociation data, we have developed a series of deceleration lenses for focusing peptide ions into a biased activation cell where selected ions are irradiated with 193nm photons. The biased activation cell allows sampling of ‘prompt’ dissociating photoactivated ions, with lifetimes < 1 microsecond. ‘Prompt’ photofragment ion spectra can be compared to spectra that sample photoactivated ions with lifetimes < 10 microseconds. Differences in the relative abundances of fragment ions in each spectrum can lead to conclusions regarding the rates of fragment ion formation. ‘Prompt’ photofragment ion spectra also differ significantly from TOF-TOF CID spectra and such differences can provide another dimension of structural information.