title: Between ethylene and polyenes--the non-adiabatic dynamics of cis-dienes.
abstract: Using Ab Initio Multiple Spawning (AIMS) with a Multi-State Multi-Reference Perturbation theory (MS-MR-CASPT2) treatment of the electronic structure, we have simulated the non-adiabatic excited state dynamics of cyclopentadiene (CPD) and 1,2,3,4-tetramethyl-cyclopentadiene (Me4-CPD) following excitation to S1. It is observed that torsion around the carbon-carbon double bonds is essential in reaching a conical intersection seam connecting S1 and S0. We identify two timescales; the induction time from excitation to the onset of population transfer back to S0 (CPD: -25 fs, Me4-CPD: -71 fs) and the half-life of the subsequent population transfer (CPD: -28 fs, Me4-CPD: -48 fs). The longer timescales for Me4-CPD are a kinematic consequence of the inertia of the substituents impeding the essential out-of-plane motion that leads to the conical intersection seam. A bifurcation is observed on S1 leading to population transfer being attributable, in a 5 : 2 ratio for CPD and 7 : 2 ratio for Me4-CPD, to two closely related conical intersections. Calculated time-resolved photoelectron spectra are in excellent agreement with experimental spectra validating the simulation results.
authors.affiliation: Department of Chemistry, Technical University of Denmark, Kemitorvet 207, DK-2800 Kg, Lyngby, Denmark.
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Kuhlman
authors.forename: William J
authors.initials: WJ
authors.lastname: Glover
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Mori
authors.forename: Klaus B
authors.initials: KB
authors.lastname: Møller
authors.forename: Todd J
authors.initials: TJ
authors.lastname: Martínez