Photofragment translational spectroscopy

Ashfold M N R, Mordaunt D H and WIson S H S 1996 Photodissociation dynamics of hydride molecules H atom photofragment translational spectroscopy Adv. Photochem. 21 217-95... 

J. Helpburn, Photofragment translational spectroscopy, Atomic and Molecular Beam Methods, ed. G. Scoles (Cambridge Press). 

The photodissociation dynamics of jet-cooled methyl radical produced in a pyrolysis radical beam have been investigated at 193.3 nm using photofragment translational spectroscopy by North and co-workers.112 Only... 

Photodissociation Dynamics of Hydride Molecules H Atom Photofragment Translational Spectroscopy (Ashfold, Mordaunt, and Wilson) Photo-Fries Rearrangement and Related Photochemical (l.j) Shifts of... 

While one might expect that the techniques developed for photodissociation studies of closed-shell molecules would be readily adaptable to free radicals, this is not the case. A successful photodissociation experiment often requires a very clean source for the radical of interest in order to minimize background problems associated with photodissociating other species in the experiment. Thus, molecular beam photofragment translation spectroscopy, which has been applied to innumerable closed-shell species, has been used successfully on only a handful of free radicals. With this problem in mind, we have developed a conceptually different experiment [4] in which a fast beam of radicals is generated by laser photodetachment of mass-selected negative ions. The radicals are photodissociated with a second laser, and the fragments are detected in coinci-... 

The qualitative picture suggested by these calculations has recently been confirmed by new experiments on the UV photochemistry of phenol. Lee and collaborators have shown that loss of H atoms is the major process in phenol at 248 nm excitation [36], Ashfold and co-workers have applied high-resolution photofragment translational spectroscopy to obtain uniquely detailed insight into the photodissociation dynamics of phenol [37], The phenoxy radical is produced in a surprisingly limited subset of its available vibrational states [37], Such vibrational mode-specific dynamics is a signature of ultrafast radiationless decay through directly accessible conical intersections. Similar results have been obtained for pyrrole, imidazole and indole [38 10],... 

The UV photochemistry of phenol and related systems (such as indole, pyrrole, imidazole) is dominated by a hydrogen detachment reaction which is driven by repulsive 1ira states [33,35 10], For the isolated chromophores, the 1 mr -driven photodissociation has been explored in unprecedented detail by high-resolution photofragment translational spectroscopy [40], The OH (or NH) bond is broken homolytically, resulting in the formation of two radical species, the hydrogen atom and the phenoxy (or indolyl, etc.) radical. Ion pair formation (abstraction of protons) is energetically not feasible for isolated photoacids. 

The photodissociation cross sections and angular distributions can be obtained experimentally by different methods for example, time of flight (TOF) photofragment translational spectroscopy (Busch, et al., 1969), Doppler analysis (Xu, et al., 1986), and ion imaging. 

Similar information can also be provided by fast beam photofragment translational spectroscopy where the two photofragments from the same fragmentation event are detected in coincidence (Leahy, et al., 1995). 

In an important variation of this experiment, one of the reactant beams is replaced by a pulsed laser which photodissociates molecules in the remaining reactant beam. Use of a pulsed laser makes it straightforward to determine the product translational energy distribution by time of flight. This experiment, photofragment translational spectroscopy, was first demonstrated by Wilson [20. 21] in and is now used in many laboratories... 

PHOTODISSOCIATION DYNAMICS OF HYDRIDE MOLECULES H ATOM PHOTOFRAGMENT TRANSLATIONAL SPECTROSCOPY... 

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