title: Vibrational equilibration in absorption difference spectra of chlorophyll a.
abstract: We describe Franck-Condon simulations of vibrational cooling effects on absorption difference spectra in chlorophyll a (Chl a). The relative contributions of vibrational equilibration in the electronic ground and excited states depend on the pump and probe wavelengths. For Franck-Condon-active vibrational modes exhibiting small Huang-Rhys factors (S < 0.1, characteristic in Chl a pigments), vibrational thermalization causes essentially no spectral changes when the origin band is excited. Significant spectral evolution does occur for S < 0.1 when the 0-1 and 1.0 (hot) vibronic bands are excited. However, vibrational equilibration in these cases causes no spectral shifting in the empirical photobleaching/stimulated emission band maximum. This result bears on the interpretation of time-resolved absorption difference spectra of Chl a-containing antennae such as the Chl a/b light-harvesting peripheral antenna of photosystem II.
authors.affiliation: Ames Laboratory-USDOE, Iowa, USA. wstruve@ameslab.gov
authors.forename: W S
authors.initials: WS
authors.lastname: Struve
mesh_terms: D002734:Chlorophyll / Q000737:chemistry*; D000077194:Chlorophyll A; D003198:Computer Simulation; D008433:Mathematics; D008962:Models, Theoretical; D008968:Molecular Conformation; D013053:Spectrophotometry / Q000379:methods; D014732:Vibration
chemical_list: D002734:Chlorophyll; D000077194:Chlorophyll A