THE JET-COOLED HIGH RESOLUTION $\tilde{A} ^2E^{\prime\prime}$-$\tilde{X} ^2A_2^{\prime}$ VIBRONIC BANDS OF NO$_3$

Abstract

The 0$^0_0$, 4$^1_0$, 4$^2_0$ and 2$^1_0$ vibronic bands of the $\tilde{A}$ 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$^1_0$ band (parallel band) band are assigned including some levels that appear to be doubled. The 4$^2_0$ band verifies the existence of anomalous doublets in both the 4$^1_0$ and 4$^2_0$ bands. The 2$^1_0$ 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 $\tilde{A}$ state. Besides the $\nu_2$ and $\nu_4$ vibronic bands, the vibronically forbidden origin band (0$^0_0$ band) has also been recorded. The weakly observed $\tilde{A}$-$\tilde{X}$ origin band structure appears to be different from either the parallel or perpendicular band type and is likely a magnetic dipole transition.