The near-infrared bands of NO2 observed by high-resolution Fourier-transform spectroscopy

Fourier-transform absorption spectra of ${\mathrm{NO}}_{\mathrm{2}}$ at 298 K were recorded between $\text{9000–15\hspace{0.17em}000\hspace{0.5em}}{\mathrm{cm}}^{\text{−1}}$ at Doppler-limited resolution $\text{(0.012\hspace{0.5em}}{\mathrm{cm}}^{\text{−1}}\mathrm{),}$ in the region near the ${\mathrm{Ã\hspace{0.17em}}}^2{B}_2{\mathrm{–X̃\hspace{0.17em}}}^2{A}_1$ conical intersection. The strong rovibronic bands are rather isolated and organized into polyads which can be assigned by the number of bending quanta of the ${\mathrm{Ã\hspace{0.17em}}}^2{B}_2$ state, corresponding to the transitions with the largest Franck–Condon factors. Around $9735{\mathrm{cm}}^{\text{−1}},$ where the origin of the ${\mathrm{Ã\hspace{0.17em}}}^2{B}_2{\mathrm{–X̃\hspace{0.17em}}}^2{A}_1$ vibronic band system is located and up to about $\text{11\hspace{0.17em}200\hspace{0.5em}}{\mathrm{cm}}^{\text{−1}},$ hot bands dominate the spectrum. The complexity of the spectrum increases with energy due to an increasing density of ${\mathrm{Ã\hspace{0.17em}}}^2{B}_2$ and ${\mathrm{X̃\hspace{0.17em}}}^2{A}_1$ vibrational levels. The rotational structure is dense and irregular as already observed for higher bands.