Chlorophyll excitation frequency

A dimeric nature of P-700 was first proposed to explain its long wavelength of absorption and its circular dichroism spectrum, which can be attributed to chlorophyll-chlorophyll exciton interaction [15]. When two chlorophylls are close together, excitation by light tends to promote electronic transitions which belong to the pair and not to the individual molecules. In particular for the Qy transition, instead of one transition at the frequency v, an excitonic interaction will create two transitions at v +dv and v-dv. The latter is considered to be the transition at 700 nm, whereas the former could be of low intensity. 

The second volume of Laser Spectroscopy covers the different experimental techniques, necessary for the sensitive detection of small concentrations of atoms or molecules, for Doppler-free spectroscopy, laser-Raman-spectroscopy, doubleresonance techniques, multi-photon spectroscopy, coherent spectroscopy and time-resolved spectroscopy. In these fields the progress of the development of new techniques and improved experimental equipment is remarkable. Many new ideas have enabled spectroscopists to tackle problems which could not be solved before. Examples are the direct measurements of absolute frequencies and phases of optical waves with frequency combs, or time resolution within the attosecond range based on higher harmonics of visible femtosecond lasers. The development of femtosecond non-collinear optical parametric amplifiers (NOPA) has considerably improved time-resolved measurements of fast dynamical processes in excited molecules and has been essential for detailed investigations of important processes, such as the visual process in the retina of the eye or the photosynthesis in chlorophyl molecules. 

PS ll-membranes were prepared from pea leaves Pisum sativum) according to Berthold et al. [1 ] with the modification described in ref. [2]. The membranes were separated by a mild trypsin treatment. For this the membranes were diluted in low salt resuspension medium to a chlorophyll concentration of 100/ig/mi and incubated at room temperature with 2/ig/ml trypsin from bovine pancreas. After 5 min. trypsination was stopped by addition of a 20-fold excess of trypsin inhibitor and the preparation was concentrated by centrifugation. For the measurements the chlorophyll concentration of the sample was adjusted to 2 mg/ml yielding an optical density at 532 nm of 0.1. Photovottage measurements were carried out in a capacitive microcoaxial cell of 3x0.1 mm dimensions [3]. The excitation source was a frequency doubled Nd-YAQ laser delivering flashes at 532 nm of either 12 ns or 30 ps duration. Orientation by an... 

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