The characterization of the complete set of bound vibronic states of HNO in its excited Ã1A″ electronic state

Laser-induced fluorescence excitation spectra of the HNO $\text{A}\text{?}{}^1\text{A″-}\text{X}\text{?}{}^1\text{A′}$ band system have been recorded with high sensitivity. This has enabled detection of the Franck-Condon unfavored vibronic bands (002)-(000) and (003)-(000), thereby completing the set of fully bound vibronic levels in the $\text{A}\text{?}$ state. Extensions have also been made to other bands. A strong Coriolis resonance between the K_a¹ = 8 levels of the excited (010) vibronic state and the K_a¹ = 9 levels of the (001) state leads to rotational perturbations of up to 9 cm^?1. The (100-000) band includes weak axis-tilting branches. It is concluded from the vibrational energy level spacings that vibronic interaction makes an important contribution to the energies of the higher bending levels, consistent with the correlation of the $\text{A}\text{?}{}^1\text{A″}$ state with a component of a ¹Δ state for linear HNO.