Polarization of Fluorescence Following Molecular Photoionization

With use of the B²Σᵤ⁺ state of N₂⁺ as an example, this Letter presents the first measurements demonstrating that fluorescence from molecular ions formed by photoionization is partially polarized. Furthermore, it is shown that the degree of polarization reflects the alignment of the molecular ion and the ratio of the dipole strengths for the degenerate channels producing the ionic state. The wavelength-dependent measurements are compared with both quantum mechanical and classical calculations. Temperature-dependent effects are predicted.