Laser-induced fluorescence excitation spectroscopy of N₂⁺ produced by VUV photoionization of N₂ and N₂O

Synchrotron radiation emitted from the UVSOR storage ring is monochromated by a grazing-incidence monochromator and introduced coaxially with the second harmonic of a mode-locked Ti:sapphire laser. Sample gases, N₂ and N₂O, are photoionized into vibronically ground N₂⁺ with the fundamental light of the undulator radiation at 18.0 and 18.6 eV, respectively. Laser-induced fluorescence (LIF) excitation spectra of N₂⁺ from N₂ and N₂O are measured in the laser wavelength region of the (B ²∑_u⁺, v′ = 0) ← (X ²∑_g⁺, v″ = 0) transition at 389-392 nm. The LIF excitation spectra of N₂⁺ exhibit two maxima due to the P and R branches in which rotational bands are heavily overlapped. The rotational temperature is determined by simulating an LIF excitation spectrum by using the theoretical intensity distribution of rotation bands convoluted with the spectral width of the laser.