Knowledge Bank

“The absorption spectrum of $NO2$ in the visible and photographic infrared has been studied at moderately high resolution. The principal feature of the spectrum from about 4500A to the origin near 9000A is a progression of bands with an average $\Delta$ G of $700cm-1$. The complexity of these bands increases rapidly towards shorter wave lengths where the widths of the bands become of the same magnitude as the distance between them. The gross structure can be explained on the basis of a linear or near linear equilibrium structure in the excited electronic state. Transitions occur from rotational sub-levels in the ground state to $v2$ vibrational levels in the excited state. Because of the strong Franck-Condon effect, the bands near the origin are extremely weak, long path length techniques being required to avoid excessive pressure broadening of the rotational structure.”