title: Experimental Detection of Branching at a Conical Intersection in a Highly Fluorescent Molecule.
abstract: Conical intersections are molecular configurations at which adiabatic potential-energy surfaces touch. They are predicted to be ubiquitous, yet condensed-phase experiments have focused on the few systems with clear spectroscopic signatures of negligible fluorescence, high photoactivity, or femtosecond electronic kinetics. Although rare, these signatures have become diagnostic for conical intersections. Here we detect a coherent surface-crossing event nearly two picoseconds after optical excitation in a highly fluorescent molecule that has no photoactivity and nanosecond electronic kinetics. Time-frequency analysis of high-sensitivity measurements acquired using sub-8 fs pulses reveals phase shifts of the signal due to branching of the wavepacket through a conical intersection. The time-frequency analysis methodology demonstrated here on a model compound will enable studies of conical intersections in molecules that do not exhibit their diagnostic signatures. Improving the ability to detect conical intersections will enrich the understanding of their mechanistic role in molecular photochemistry.
authors.affiliation: Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
authors.forename: Johanna
authors.initials: J
authors.lastname: Brazard
authors.affiliation: Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
authors.forename: Laurie A
authors.initials: LA
authors.lastname: Bizimana
authors.affiliation: Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
authors.forename: Tobias
authors.initials: T
authors.lastname: Gellen
authors.affiliation: Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
authors.forename: William P
authors.initials: WP
authors.lastname: Carbery
authors.affiliation: Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Turner
keywords: conical intersection; femtosecond transient absorption; oxazine molecules; surface crossing; vibrational wavepacket