The unstable ground-state potential surface of triatomic hydrogen has served as prototype for the development of bimolecular reaction-rate theory, and is still largely territory only of theoretical chemistry. While the ground electronic state of H/sub 3/ is dissociative, electronically excited states of this molecule are tightly bound. These states are described in terms of a Rydberg electron bound by the field of the stable, triangular H/sub 3/(+) core. The authors report the first observation of photodissociation of H/sub 3/. Predissociation of the optically prepared 3s(2) A1 and 3d(2)E states by the X(2)E' ground state is detected by monitoring of the production of vibrationally excited diatomic hydrogen molecules and H atoms. Product excitation is found to be highly dependent on H/sub 3/ electronic and nuclear configuration.