Periodische Anregung und Messung schneller chemischer Reaktionen

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Abstract
Relaxation methods have been developed for the study of fast chemical reactions. With these methods chemical equilibrium is disturbed by a rapid change of temperature, pressure, intensity of light or radiation etc. The following equilibration process is observed by changes of absorption, fluorescence, conductivity etc. The feasibility of relaxation measurements depends on the signal‐to‐noise‐ratio s/n of the signal by which the course of reaction is recorded. The large bandwidth which is necessary to record fast reaction signals causes a high noise level i.e. a poor s/n‐ratio. This disadvantage may be avoided if the perturbation is periodically performed by a rapid change of temperature, pressure, intensity of light or radiation. Thus, the high contents of information contained in periodic signals may be evaluated to increase s/n‐ratio.Owing to this enhancement in s/n‐ratio reactions are measurable which are not detectable at all with a single process. On the other hand, at small excitation energies the relaxation method can be applied also to sensitive biological systems. Furthermore, the time resolution can be improved, too. The periodic chemical relaxation method was developed first for the study of fast photochemical reactions 10−5…10−1 sec) which were excited by short flashes of light and measured by absorption changes. The periodic measuring signal (exciting frequency νa = 2 … 100 c/s) is slowly sampled and recorded in the time T5 (min … h). The gain in s/n‐ratio is given by the expression νa·Ts. An improvement of 200 in s/n‐ratio was attained.—The periodic relaxation method was used to study photochemical reactions which occur during the primary process of photosynthesis.

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