THE NEAR INFRARED ABSORPTION SPECTRUM OF $H_{2}O^{+}$ BY VELOCITY MODULATION

1 H. Lew, Can, J. Phys. 54, 2028 (1976). 2. M. Brommer and M. Vervloet, private communication. 3. M. Brommer, B. Weiss, B. Follmeg, P. Rosmus, S. Carter, N. C. Handy, H-J. Werner, and P.J. Knowles, J. Chem Phys. 98, 5222 (1993) 4. T.R. Huet, C.J. Pursell, W.C. Ho, B.M. Dinelli, and T. Oka, J. Chem. Phys. 97, 5977 (1992). 5. C. Jungen, K.E. Hallin, and A.J. Merer, Mol. Phys 40, 65 (1980) 6. I. Hadj Bachir, T.R. Huet, and J-L Destombes, J. Mol. Spectrosc, accepted for publication (1995).Author Institution: Université des Sciences et Technologies de Lille, F-59655 Villeneuve d'Ascq Cedex(France).; Université de Paris-Sud, F-91405 Orsay Cedex(France)A Titanium-Sapphire laser spectrometer was used to record the absorption spectrum of the $\bar{A}{^{2}}A_{1}-\bar{X}^{2}B_{1}$ electronic transition of $H_{2}O^{+}$ by using the velocity modulation technique $H_{2}O^{+}$ was produced in the positive column of an AC glow discharge with a $He/H_{2}O$ or $He/H_{2}/O_{2}$ gas mixture. Unlike emission spectra, observed only at energy higher than $13000 cm^{-1} 1-2$, this technique allows the expenmental characterization of the Renner-Teller structure closer to the barrier to the linearity. The regions between $12000-12600 cm^{-1}$ and $13200-13500 cm^{-1}$ have already been covered. According to the revised vibrational $numbering^{3}$, the linear levels $\Pi(0,6,0) (T_{\nu} = 12485.3 cm^{-1})$ and $\Sigma(0,7,0) (T_{\nu} = 13409.3 cm^{-1})^{1}$ of the $\bar{A}$ state have been observed. The rotational analysis is carried out by using the combination difference technique in the ground $state^{1,4}$. The model of reference 5 was employed to derive the spectroscopic constants of the upper vibronic states. A good agreement with ab initio $predictions^{3}$ has been found. In addition, strong signals of $N_{2}^{+}$, due to $N_{2}$ impurities, have been observed and $assigned^{6}$. Many lines, most probably due to $H_{2}O^{+}$, still remain unassigned. Any new progress will also be reported