Knowledge Bank

Electronic emission from the SiN radical, produced by the addition of $SiCl4$ to active nitrogen, has been known for many years. The spectrum is dominated by a strong $B2\Sigma \to X2\Sigma$ system, but also contains weaker $D2\Pi \to A2\Pi ,K2\Sigma \to A2\Pi$ and $L2\Pi \to A2\Pi$ band systems. However, no $B\to A$ or $A\to X$ system has been reported and consequently the locations of the A, D, K and L states with respect to the ground state are unknown. Results will be presented which demonstrate that the weak 440 nm violet degraded bands previously assigned to a are part of the $B2\Sigma \to A2\Pi$ system of SiN. The analysis of these bands shows that $T(A2\Pi )=994.4cm-1$. This very small $Te$ value places the $A\leftrightarrow X$ system in the mid infrared and explains the lack of observation of this system by photographic techniques.