Polarization effects on rotational line strengths in collision-free polyatomic fluorescence spectra

Abstract

Methods are given to calculate rotational line strengths in collision-free polyatomic electronic fluorescence spectra after single rotational levels are pumped with polarized (laser) excitation. Such fluorescence retains substantial polarization so that attempts to calculate line strengths with standard Hönl–London formulas or related procedures give significant errors. Illustrations with glyoxal S1→S0 fluorescence show good agreement between observed and calculated line strengths when polarization is accounted for. Specific formulas are given for the separate polarization components when partial depolarization of such fluorescence also occurs on account of external magnetic fields. Comparisons of field-free calculations with experimental data show that cross sections for collisional fluorescence depolarization (ΔM changes) in S1–S0 glyoxal collisions do not exceed those known for ΔJ, ΔK changes (about five times gas kinetic).