PHOTOCHEMICAL THERMAL LENS SPECTROSCOPY .1. SINGLE-QUANTUM NON-CHAIN REACTION

The paper deals with photochemical thermal lens spectroscopy being a new hybrid trend in thermal lens spectroscopy having been achieved the most acknowledgement among the photothermal methods of the small absorption measurement. The general manner of dual-laser thermal lens measurement was considered. For kinetic measurement the analytical signal expression, i. e. the intensity at the laser beam center passing through the absorbing medium, was concluded. The manner of the most complete explotation of a laser irradiation used in measurement was discussed in detail, namely the simultaneous use of that to induce the photoreaction followed by the absorption alteration. The possible ways of absorbed energy conversion were considerated. The general equation for analytical signal was suggested in the most common case of single-quantum photochemical reaction of the first order and considering photochemical reaction locality determined by the laser irradiated cell volume. The total and three partial cases were examined. Photochemical thermal lens spectroscopy was shown to permit the quantum yield, the reaction heat and also an unknown impurity concentration to be recognized. The measurement of thermal lens signal from two samples (the solution of non-fluorescent dye taking no part in photoconversions and that with well-known content of an impurity under analysis) is need carry out with focused and disfocused excite laser beam to receive the previously mentioned information. Further the influence of more difficult photoprocess on an analytical signal will be discussed too.