Knowledge Bank

The $H2O+$ optical spectrum was detected first in the laboratory by $Lew1$ and later in the tail of comet $Kohoutec2$. We have previously reported the observation by difference freqnency spectrometer of the vibration-rotation infrared spectrum of $H2O+$ in the region $3100-3400cm-1$ using an A.C. glow discharge through He, $H2$ and $O2$ (100:1:1). The observed lines were assigned to the $\nu 3$ vibration-rotation band of that molecular ion. The $\nu 1$ band was not observable unlike the case of isoelectronic $NH2$ radical for which the $\nu 1$ transitions were reported to be much stronger than the $\nu 3$ transitions. The ground state molecular constants of Lew have been improved by including ground state combination differences from our data in the fit. A Watson reduced asymmetric rotor Hamiltonian, including the spin rotation interaction was used. The Coriolis interaction between the $\nu 1$ and $\nu 3$ vibrations has been included in the Hamiltonian to determine the excited state molecular constants for the first time.