Fourier transform spectra of laser-induced fluorescence

A rotationally resolved Fourier Transform laser-induced fluorescence spectrum of the molecular ion from 24400 to 28100 cm−1 is presented, in which gerade ground state vibrational levels up to the 300 polyad can be identified. ions were produced in a stable discharge source and selectively excited at 351 nm in the A2Πu– 2Πg electronic system. The pure laser induced fluorescence signal was obtained by taking the difference between a spectrum recorded with the discharge and laser running and a spectrum obtained from the discharge alone, since the discharge source also produces strong emission. The fluorescence spectrum reveals partially resolved R heads and fully resolved P branches to vibronic levels (100)/(020), (200)/(120), (300)/220 and (002) of the 2Πg1/2 state. Rotational structure for individual (ν1 00)/(ν1 − 1)(20) polyads is analysed in the framework of an effective Hamiltonian, including Fermi resonance and Renner–Teller contributions. An extended set of vibrational energies is also fitted to a set...