Photodissociation of the ozone molecule at 193.4 nm (6.41 eV) and 157.6 nm (7.87 eV) is studied by fast-beam translational spectroscopy. Coincident detection of the dissociation products allows direct observation of the 3-fragment channel and determination of its kinematic parameters. The results indicate that at each wavelength, 3-fragment dissociation proceeds through synchronous concerted bond breaking, but the energy partitioning among the fragments is different. The branching fraction of the 3-fragment channel increases from 5.2(6)% at 193.4 nm to 26(4)% at 157.6 nm, in agreement with previous studies. It is shown that vibrational excitation of the symmetric stretch mode in O3 molecules created by photodetachment of O(3)(-) anion enhances the absorption efficiency, especially at 193.4 nm, but does not have a strong effect on the 3-fragment dissociation.

The photodissociation dynamics of the thiophenoxy radical (C 6 H 5 S) have been investigated using fast beam coincidence translational spectroscopy. Thiophenoxy radicals were produced by photodetachment of the thiophenoxide anion followed by photodissociation at 248 nm (5.0 eV), 193 nm (6.4 eV), and 157 nm (7.9 eV). Experimental results indicate two major competing dissociation channels leading to SH + C 6 H 4 (o-benzyne) and CS + C 5 H 5 (cyclopentadienyl) with a minor contribution of S + C 6 H 5 (phenyl). Photofragment mass distributions and translational energy distributions were measured at each dissociation wavelength. Transition states and minima for each reaction pathway were calculated using density functional theory to facilitate experimental interpretation. The proposed dissociation mechanism involves internal conversion from the initially prepared electronic excited state to the ground electronic state followed by statistical dissociation. Calculations show that SH loss involves a single isomerization step followed by simple bond fission. For both SH and S loss, C−S bond cleavage proceeds without an exit barrier. By contrast, the CS loss pathway entails multiple transition states and minima as it undergoes five membered ring formation and presents a small barrier with respect to products. The calculated reaction pathway is consistent with the experimental translational energy distributions in which the CS loss channel has a broader distribution peaking farther away from zero than the corresponding distributions for SH loss.