Collisional effects in Stark spectroscopy of molecules in 1Π electronic states

We present the theoretical framework necessary to describe inelastic collisions between Stark mixed Λ-doublet levels of a molecule in a 1Π electronic state, and the subsequent effect on fluorescence intensities. It is convenient to work with the spherical tensor moments of the excited state density matrix. For weak fields and short times after excitation the ratio of the fluorescence intensities for emission on ‘‘forbidden’’ and allowed 1Σ+←1Π lines is predicted to vary linearly with time and quadratically with field strength. Simulation studies are presented, based on collisional parameters suggested by previous theoretical studies of inelastic collisions of molecules in Π electronic states. The present article provides the foundation for the accurate interpretation of laser diagnostic studies in plasma environments, such as those described by Mandich, Gaebe, and Gottscho in the accompanying article.