Knowledge Bank

The 0$\mathrm{00}$, 4$\mathrm{01}$, 4$\mathrm{02}$ and 2$\mathrm{01}$ vibronic bands of the $A~$ state NO$3$ absorption spectrum has been successfully observed with our high-resolution, jet-cooled cavity ring-down apparatus. Ground state combination differences, nderline{\textbf{93}}, 951 (1990)}}, nderline{\textbf{231}}, 193 (1998)}} are used to analyze all four vibronic bands. Rotational transitions of the 4$\mathrm{01}$ band (parallel band) band are assigned including some levels that appear to be doubled. The 4$\mathrm{02}$ band verifies the existence of anomalous doublets in both the 4$\mathrm{01}$ and 4$\mathrm{02}$ bands. The 2$\mathrm{01}$ band is a perpendicular band which has a different band type. Preliminary assignments of this band are utilized for the comprehensive understanding of the structure of NO$3$ in the $A~$ state. Besides the $\nu 2$ and $\nu 4$ vibronic bands, the vibronically forbidden origin band (0$\mathrm{00}$ band) has also been recorded. The weakly observed $A~$-$X~$ origin band structure appears to be different from either the parallel or perpendicular band type and is likely a magnetic dipole transition.