Laser induced fluorescence spectroscopy of the jet cooled SiNSi radical: Rotational analysis of the E 2??+-X2?g transition

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 + - 2 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, similar to 0.10 cm(-1), of the four bands are significantly wider than that of the instrumental resolution, similar to 0.03 cm(-1). The widths have been interpreted as coupling of the rotational levels of the 2+ 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 rotational level, '=16.5.