Modeling of Photochemical Reactions in a Focused Laser Beam, II

Published

September 1, 2008

Author(s)

Adolfas K. Gaigalas, Fern Y. Hunt, Lili Wang

Abstract

A method is described for obtaining rate constants of photodegradation process of fluorophores illuminated by a focused laser beam. The explicit kinetic equations, describing the population dynamics of excited singlet and triplet states, are averaged over the illuminated volume to describe the resulting fluorescence signal. The illumination is modulated at frequencies 1 Hz to 100 Hz. Synchronous detection of the resulting fluorescence yields in- phase and quadrature components. The measurement of the ratio of quadrature to in-phase components at several power levels yields information on the photodegradation rate. Specifically it is shown that the data can be interpreted in a manner which yields the value of the photodegradation rate independently of other parameters entering the model. Experiments are performed with erythrosine B which has a large intersystem crossing rate to the triplet state. Measurements in solutions with different viscosities shows that the photodegradation rate depends on the viscosity. This is interpreted as evidence for an intermolecular interaction mechanism. We explore the uncertainty of the estimated photodegradation constant taking into account the uncertainties of the measurements used in the synchronous detection technique.

Citation

Journal of Research of the National Institute of Standards and Technology

Volume

113

Issue

5

Pub Type

Journals

Citation

Gaigalas, A. , Hunt, F. and Wang, L. (2008), Modeling of Photochemical Reactions in a Focused Laser Beam, II, Journal of Research of the National Institute of Standards and Technology (Accessed April 26, 2024)