Knowledge Bank

The strong vibronic interactions between the A and X electronic states lead to a complex structure of the $NO2$ spectrum in the visible and near-IR. The log-wavelength tail of the spectrum is very weak due to small Franck-Condon factors. In 1965, Douglas and $Huberh$ recorded the first low-resolution spectra of the $NO2$ bands in the near infrared. In 1975, Brand {et al}. showed that ``hot” bands are important in this region. In the past, many high-resolution spectra of $NO2$ were recorded, however no rotationally resolved spectra of this important region were reported up to now. We present high-resolution spectra of the first vibronic bands of $NO2$ starting around $9740cm-1$ and discuss vibrational assignments. The dense rotational structure is very difficult to assign although accurate lower-state energies are available from high-resolution infrared spectra.