Ground state transient linear dichroism for molecules with level-dependent rotational diffusion

Abstract

Transient dichroism for three-level molecules undergoing level-dependent Brownian rotations is discussed. Using the method of expansion of the molecular distribution function on the rotational diffusion operator eigenfunctions, we have derived the expression for the transient dichroism due to the ground state absorption. The linear dichroism evolution is governed by the population kinetics and state-dependent rotational diffusion. This approach includes previously presented results of the transient dichroism theory of von Jena and Lessing and Eisenthal. The relation between the angular distribution function of the molecules in the ground and excited states has been examined. Interesting findings are the anisotropy of the distribution function of the whole system and the predicted “oscillatory” decay of the linear dichroism, even for a spherical rotor, as a consequence of the difference between rotational diffusion rates in the ground and excited states.