INFRARED SPECTRUM OF THE $\nu_{3}$ BAND OF $C_{2}H_{2}^{+}$

$^{1}$ M. W. Crofton, M.-F. Jagod, B. D. Rehfuss, W. A. Kreiner, and T. Oka, J. Chem. Phys., 83, 3702 (1985). $^{2}$ M. W. Crofton, M.-F. Jagod, B. D. Rehfuss, and T. Oka, 42nd Symposium on Molecular Spectroscopy, Columbus, Ohio. $^{3}$ M. W. Crofton, M.-F. Jagod, B. D. Rehfuss, and T. Oka, J. Chem. Phys., 86, (1987), in press.Author Institution: Department of Chemistry and Department of Astronomy and Astrophysics, The University of Chicago; Department of Chemistry and Department of Astronomy and Astrophysics, Lawrence Livermore National LaboratoryWe have observed the $\nu_{3}$ fundamental vibration-rotation band of $C_{2}H_{2}^{+}(^{2}\Pi*)$. This band was among the very rich hydrocarbon spectra in the $3.3 \mu m$ region which also yielded the spectra of $CH_{3}^{+1}$ and $C_{2}H_{3}^{+2}$. It was observed using a difference frequency spectrometer and velocity modulation for detection. This ion was produced in an AC glow discharge with a gas mixture of He:$H_{2}:C_{2}H_{2} (700:20:1)$ with a total pressure of $\approx 6 Torr$. The spectral lines of $C_{2}H_{2}^{+}$ could be discriminated from those of $CH_{3}^{+}$ and $C_{2}H_{3}^{+}$ by their different chemical behavior. We have determined the preliminary molecular constants $as^{3}$ (in $cm^{-1}$):[FIGURE