Temperature dependence of collisional broadening and shift for the Kr 4p⁶S01→5p[3/2]₂ electronic transition

Temperature scaling of collisional broadening parameters for krypton (absorber) 4p⁶S01→5p[3/2]₂ electronic transition centered at 107.3 nm in the presence of major combustion species (perturber) is investigated. The absorption spectrum in the vicinity of the transition is obtained from the fluorescence due to the two-photon excitation scan of krypton. Krypton was added in small amounts to major combustion species such as CH₄, CO₂, N₂, and air, which then heated to elevated temperatures when flowed through a set of heated coils. In a separate experimental campaign, laminar premixed flat flame product mixtures of methane combustion were employed to extend the investigations to higher temperature ranges relevant to combustion. Collisional full width half maximum (FWHM) (w_C) and shift (δ_C) were computed from the absorption spectrum by synthetically fitting Voigt profiles to the excitation scans, and their corresponding temperature scaling was determined by fitting power-law temperature dependencies to the w_C and δ_C data for each perturber species. The temperature exponents of w_C and δ_C for all considered combustion species (perturbers) were -0.73 and -0.6, respectively. Whereas the temperature exponents of w_C are closer to the value (-0.7) predicted by the dispersive interaction collision theory, the corresponding exponents of δ_C are in between the dispersive interaction theory and the kinetic theory of hard-sphere collisions. Comparison with existing literature on broadening parameters of NO, OH, and CO laser-induced fluorescence spectra reveal interesting contributions from non-dispersive interactions on the temperature exponent.