Thermal lens technique for sensitive kinetic determinations of fast chemical reactions. Part I. Theory

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Abstract
The thermal lens effect can be successfully explained by use of the presently available theories. However, the existing theories fail for cases where the sample concentration changes with time, i.e., when the sample undergoes a chemical reaction. The objective of this work is to demonstrate that the thermal lens technique can be used for the sensitive kinetic determination of fast chemical reactions. It is systematically approached from two different directions: the theoretical aspect which is described in this paper and the experimental section which will be reported in the following paper. Specifically, novel theories which are based on the parabolic as well as the aberrant model have been derived to describe the thermal lens signal for cases where the sample concentration changes with time. Based on the developed theories, computer calculations were then performed to simulate conditions for various chemical reactions. It was found that in all cases, both of the developed (parabolic and aberrant based) theories can be used successfully to determine not only the order of the reaction but also the reaction rate constant.