title: Intramolecular vibrational dynamics in S1 p-fluorotoluene. I. Direct observation of doorway states.
abstract: Picosecond time-resolved photoelectron spectroscopy is used to investigate intramolecular vibrational redistribution (IVR) following excitation of S(1) 18a(1) in p-fluorotoluene (pFT) at an internal energy of 845 cm(-1), where ν(18a) is a ring bending vibrational mode. Characteristic oscillations with periods of 8 ps and 5 ps are observed in the photoelectron signal and attributed to coupling between the initially excited zero-order bright state and two doorway states. Values for the coupling coefficients connecting these three vibrational states have been determined. In addition, an exponential change in photoelectron signal with a lifetime of 17 ps is attributed to weaker couplings with a bath of dark states that play a more significant role during the latter stages of IVR. A tier model has been used to assign the most strongly coupled doorway state to S(1) 17a(1) 6a(2)('), where ν(17a) is a CH out-of-plane vibrational mode and 6a(2)(') is a methyl torsional level. This assignment signifies that a torsion-vibration coupling mechanism mediates the observed dynamics, thus demonstrating the important role played by the methyl torsional mode in accelerating IVR.
authors.affiliation: School of Chemistry, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
authors.forename: Julia A
authors.initials: JA
authors.lastname: Davies
authors.forename: Katharine L
authors.initials: KL
authors.lastname: Reid
mesh_terms: D056951:Photoelectron Spectroscopy; D011789:Quantum Theory; D013997:Time Factors; D014050:Toluene / Q000031:analogs & derivatives / Q000737:chemistry*; D014732:Vibration
chemical_list: D014050:Toluene