Knowledge Bank

Rotational structure is assigned for the $(000),(010),(0200),(0220),(100),(0310)$ and $(0330)$ vibrational levels of the $3p\sigma$ Rydberg state of $NO2$ by ionization-detected two-photon and double resonance electronic spectroscopy in transitions from the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}A1$ ground state. Accurate positions established for these fundamentals determine the vibrational constants $\omega 2$, $X22$ and $g22$, and characterize the Fermi resonance that couples $(0200)$ with (100) in the $NO2+$ cation core. Results are compared with isoelectronic $CO2$.