Line Shape – Lifetime Relationship and Emission and Scattering of Light by Polyatomic Molecules

Abstract

A unified theory of ordinary Rayleigh scattering, Raman scattering, and the absorption and reemission of light is presented and discussed from an experimental spectroscopist's point of view. Application to polyatomic molecules presents unique problems which are discussed. The theory should be able to account for experimental results off, near, and on resonance, using weak exciting light sources of various band shapes. The evolution of the Franck-Condon envelope on nearing the resonance region is described, and time dependent aspects of the interaction are treated in a general way. The theory in its present form cannot be used when the light source is so intense that population inversion, multiphoton effects, and stimulated processes take place.Une thkorie unifiee de ladiffusion Rayleigh ordinaire, de la diffusion Raman, et de l'absorption et reemission de lurnikre est presentke et discutke d'un point de vue de spectroscopie expkrimentale. L'application aux molCcules polyatomiques presente des problemes specifiques qui sont discutks. La theorie doit itre capable de rendre compte des resultats expkrimentaux loin de, prks de, et a la resonance, en utilisant des sources lumineuses excitatrices faibles de diverses distributions spectrales. L'tvolution de I'enveloppe de Franck-Condon en approchant de la regionde resonance est dCcrite, et les aspects des interactions, dependant du temps sont trait& de maniere genkrale. La thkorie presente ne peut pas Stre utilisee quand la source lumineuse est d'une intensite telle que surviennent: I'inversion de population, les effets a plusieurs photons, et des processus stimulks.[Traduit par le journal]Can. J. Phys., 53,2068 (1975)

On the Mechanism of Light Harvesting in Photosynthetic Purple Bacteria: B800 to B850 Energy Transfer

“…The carotenoid S 2 ← S 0 transition lies at 550 nm, then we have the Q x B850 density of states, then spanning the “hole” between this region and the B800/B850 Q y region is the optically forbidden carotenoid S 1 ← S 0 transition. , Experiments on the B850-only LH2 complex suggest that there is B850 absorption in this 650−720 nm window, which probably accounts for the B670−B850 and B694−B850 energy transfer rates. This contribution to the spectral overlap, presumably arising from various intensity borrowing effects, − was not accounted for in our model. A final observation concerning the spectral funnel in LH2, is the somewhat striking observation that the only real “hole” in the B850 density of states lies at 800 nm (see also Figure ); does this suggest another reason for having the B800 ring?…”