Time-resolved spectroscopy for kinetics

17 A configuration used for time-resolved absorption spectroscopy, in which an intense laser pulse is used to generate a monochromatic pump pulse and a second laser pulse, the probe, arrives at the sample some time later to measure a spectroscopic feature of the reaction mixture. 

The rates of appearance and disappearance of the various species are determined by observing time-dependent changes in the spectrum of the sample during the course of the reaction. This monitoring may be done by passing a second, weaker laser pulse, the probe, through the sample at different times after the laser pulse. For example, the wavelength of the probe pulse maybe set at an absorption of an intermediate (to probe its formation and decay) or a product (to probe the rate of its formation). 

Biological processes that are open to study by time-resolved spectroscopy include the energy-converting processes of photosynthesis (Section 5.11 and Case study 12.3) and the light-induced processes of vision Case study 12.2). In other experiments, the laser-induced ejection of carbon monoxide from myoglobin and the attachment of O2 to the exposed heme site have been studied to obtain rate constants for the two processes. 

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