Nonresonant Photons Catalyze Photodissociation of Phenol

Phenol represents an ideal polyatomic system for demonstrating photon catalysis because of its large polarizability, well-characterized excited-state potential energy surfaces, and nonadiabatic dissociation dynamics. A nonresonant IR pulse (1064 nm) supplies a strong electric field (4 × 10 ⁷ V/cm) during the photolysis of isolated phenol (C ₆ H ₅ OH) molecules to yield C ₆ H ₅ O + H near two known energetic thresholds: the S ₁ /S ₂ conical intersection and the S ₁ - S ₀ origin. H-atom speed distributions show marked changes in the relative contributions of dissociative pathways in both cases, compared to the absence of the nonresonant IR pulse. Results indicate that nonresonant photons lower the activation barrier for some pathways relative to others by dynamically Stark shifting the excited-state potential energy surfaces rather than aligning molecules in the strong electric field. Theoretical calculations offer support for the experimental interpretation.