Comparison of some methods of theoretical photochemistry and spectroscopy

Abstract

We compared two approaches to the mathematical modeling of state population dynamics in a model reaction complex, which is intended for the description of an intramolecular photochemical reaction in a four-level molecule or a secondary photochemical reaction caused by an irreversible transfer of photoexcitation energy from a three-level reagent molecule to one of the states of the product molecule. One approach (used in theoretical photochemistry) involves using the solution of the optical Bloch equations for the complex, while another (used in theoretical spectroscopy) involves the solution of the Schrцdinger equation for a composite system of complex molecules, quantized radiation field, and environment phonon field. The results of these approaches are in agreement in the case of irradiation of the model complex with ultrashort pulses with a resonant carrier frequency, but are considerably different in the case of irradiation with a long pulse. We conclude that when modeling the photoreaction dynamics using a long radiation pulse, the approach based on theoretical spectroscopy formalism should be used. For the considered reactions, the obtained characteristics of the dynamics can serve as a reference point for the choice of photoreaction, the study of which by photochemistry methods will make possible the confirmation of the accuracy of the drawn conclusion and the used concepts on the transformation of light by molecules, accompanied by a photoreaction.