UV Photodissociation of Pyrroles: Symmetry and Substituent Effects

摘要: H (Rydberg) atom photofragment translational spectroscopy and ab initio electronic structure calculations are used to explore ways in which ring substituents affect the photofragmentation dynamics of gas phase pyrroles. S1 ← S0 (σ* π) excitation bare pyrrole is electric dipole forbidden but gains transition probability by vibronic mixing with higher states. The state dissociative respect N–H bond extension, resulting pyrrolyl radicals formed a limited number (nontotally symmetric) vibrational levels (Cronin et al. Phys. Chem. 2004, 6, 5031–5041). Introducing σ-perturbing groups (e.g., an ethyl group 2-position or methyl 2- 4-positions) lowers molecular symmetry (to Cs), renders S1–S0 (weakly) allowed, causes some reduction strength; radical products again select subset many possible all involve in-plane (a′) ring-breathing motions as expe...