Knowledge Bank

A Titanium-Sapphire laser spectrometer was used to record the absorption spectrum of the $A¯\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}A1-X¯2B1$ electronic transition of $H2O+$ by using the velocity modulation technique $H2O+$ was produced in the positive column of an AC glow discharge with a $He/H2O$ or $He/H2/O2$ gas mixture. Unlike emission spectra, observed only at energy higher than $13000cm-11-2$, this technique allows the expenmental characterization of the Renner-Teller structure closer to the barrier to the linearity. The regions between $12000-12600cm-1$ and $13200-13500cm-1$ have already been covered. According to the revised vibrational $numbering3$, the linear levels $\Pi (0,6,0)(T\nu =12485.3cm-1)$ and $\Sigma (0,7,0)(T\nu =13409.3cm-1)1$ of the $A¯$ state have been observed. The rotational analysis is carried out by using the combination difference technique in the ground $state1,4$. The model of reference 5 was employed to derive the spectroscopic constants of the upper vibronic states. A good agreement with ab initio $predictions3$ has been found. In addition, strong signals of $N2+$, due to $N2$ impurities, have been observed and $assigned6$. Many lines, most probably due to $H2O+$, still remain unassigned. Any new progress will also be reported.