UV photodissociation of η5-C5H5NiNO: an excited-state Jahn-Teller distortion produces a cartwheeling NO.

The 225 nm photodissociation of cyclopentadienylnickel nitrosyl was studied using velocity-mapped ion imaging with 1 + 1' REMPI detection of the NO (X (2)Π(1/2,3/2), v'' = 0) photofragment. The product recoil energy and angular distributions were measured for selected rotational states of NO. The NO product displays two speeds, a slow product peaked at the center of the ion image and a fast anisotropic product that has an inverted rotational population. In rotational states above J'' = 40.5, an even faster anisotropic NO photofragment appears, most likely because the metal-containing dissociation partner emerges in a lower electronic state, increasing the available energy. The μ-v-j vector correlations were measured and are consistent with the orientation μ∥v⊥ j. The observed vector correlations arise from an excited-state Jahn-Teller distortion of the parent, a distortion that bends the Ni-NO coordinate prior to dissociation.