title: Observation of multi-channel non-adiabatic dynamics in aniline derivatives using time-resolved photoelectron imaging.
abstract: We present results from a recent time-resolved photoelectron imaging (TRPEI) study investigating the non-adiabatic relaxation dynamics of N,N-dimethylaniline (N,N-DMA) and 3,5-dimethylaniline (3,5-DMA) following excitation at 240 nm. Analysis of the experimental data is supported by ab initio coupled-cluster calculations evaluating excited state energies and the evolution of several excited state physical properties as a function of N-H/N-CH3bond extension - a critical reaction coordinate. The use of site-selective methylation brings considerable new insight to the existing body of literature concerning photochemical dynamics in the related system aniline at similar excitation wavelengths. The present work also builds on our own previous investigations in the same species at 250 nm. The TRPEI method provides highly differential energy- and angle-resolved data and, in particular, the temporal evolution of the photoelectron angular distributions afforded by the imaging approach offers much of the new dynamical information. In particular, we see no clear evidence of the second excited 2ππ* state non-adiabatically coupling to the lower-lying S1(ππ*) state or the mixed Rydberg/valence S2(3s/πσ*) state. This, in turn, potentially raises some unresolved questions about the overall nature of the dynamics operating in these systems, especially in regard to the 2ππ* state's ultimate fate. More generally, the findings for the aromatic systems N,N-DMA and 3,5-DMA, taken along with our recent TRPEI results for several aliphatic amine species, highlight interesting questions about the nature of electronic character evolution in mixed Rydberg-valence states as a function of certain key bond extensions and the extent of system conjugation. We begin exploring these ideas computationally for a systematically varied series of tertiary amines.
authors.affiliation: Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK. d.townsend@hw.ac.uk.
authors.forename: Magdalena M
authors.initials: MM
authors.lastname: Zawadzki
authors.affiliation: Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK. d.townsend@hw.ac.uk.
authors.forename: Marco
authors.initials: M
authors.lastname: Candelaresi
authors.affiliation: Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK. d.townsend@hw.ac.uk.
authors.forename: Lisa
authors.initials: L
authors.lastname: Saalbach
authors.affiliation: Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK. d.townsend@hw.ac.uk.
authors.forename: Stuart W
authors.initials: SW
authors.lastname: Crane
authors.affiliation: Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Paterson
authors.affiliation: Institute of Photonics & Quantum Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK. d.townsend@hw.ac.uk and Institute of Chemical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK.
authors.forename: Dave
authors.initials: D
authors.lastname: Townsend