Laser induced fluorescence spectroscopy of the jet cooled SiNSi radical: Rotational analysis of the Ẽ 2

We have generated SiNSi in supersonic free jet expansions, and have measured laser induced fluorescence (LIF) spectra in the ultra-violet (UV) region. On the basis of rotational analyses, four vibronic bands in the LIF spectra have been attributed to those of the Ẽ 2Σu+ – X̃ 2Πg electronic transition of SiNSi. The two bands at 32918 and 33059 cm−1 have been assigned to the two spin–orbit components of the 000 band. The other two bands at 34173 and 34314 cm−1 have been attributed to two subbands of a vibronic band, although no conclusive vibrational assignment have been obtained yet. All of the rotational line widths, ∼ 0.10 cm−1, of the four bands are significantly wider than that of the instrumental resolution, ∼ 0.03 cm−1. The widths have been interpreted as coupling of the rotational levels of the Ẽ 2Σu+ state with quasi-continuum background levels consisting of low-lying electronic states. For the upper vibronic levels of the 34173 and 34314 cm−1 subbands, a very local perturbation has been found only at the f rotational level, J′=16.5.