The feasibility of standardless molecular spectral analysis of mixtures under conditions of photochemical transformations of molecules

The problem of standardless molecular spectral analysis of multicomponent mixtures with allowance for photochemical reactions of their molecules has been formulated and its formal procedure has been developed. The case when the time dependence of the spectrum of the mixture is determined only by the change in the concentrations of the components with time and the spectra of the individual components remain constant has been considered. The corresponding requirements for the physicochemical properties of the molecules have been identified and shown to be met for quite a wide range of polyatomic molecules and their reactions. The exception is molecules with metastable excited electronic states. A large set of model calculations relevant to the actual molecular entities and their experimentally observed photochemical transformations have shown the practicability of the approach. The solution of the problem converges to exact values and is resistant to uncertainty in setting the initial spectral data due to the peculiarities of the experimental procedure, the choice of theoretical models, and other factors. The resulting theoretical values of the concentrations meet the least squares test and their errors are measured by the variance per unit weight. The variance makes it possible to evaluate the noise level of the spectral data used in the analysis and reliability of the result and can serve as a criterion for the correctness of the initial hypotheses about the qualitative composition of a multicomponent mixture.