Determination of population, orientation and alignment of symmetric top molecule using laser-induced fluorescence

Abstract

General expressions used for transforming the laser-induced fluorescence (LIF) intensity into the population, orientation and alignment parameters of a symmetric top molecule are derived by employing the density matrix approach. The molecular population, orientation and alignment are described by molecular state multipoles. Both excitation and detection are circularly polarized lights. The problem on how to extract the initial molecular state multipoles from the resolved LIF intensity is discussed in detail. In general cases, the LIF intensity is a complex function of the initial molecular state multipoles, the dynamic factors and the excitation–detection geometrical factors. It contains a population, 10 orientation and 14 alignment multipoles. The theoretical results show that it is possible for experimentalists to determine all these state multipoles by controlling the propagation directions of excitation and detection light beams.