INFRARED SPECTROSCOPY IN AN $N_{2}$/$H_{2}$/He DISCHARGE : 1) HOT BANDS OF $HN_{2}^{+}$ IN HIGHLY EXCITED STATES.

A new spectrum in the infrared region, between 3500 and $2900 cm^{-1}$, was recorded using a difference frequency laser spectrometer with the velocity modulation technique for detection. Several ions, mainly nitrogen containing ones, were produced in a mixture of $\\sim$0.04 Torr of $N_{2}$, -0.04 Torr of $H_{2}$ and $\\sim$7 Torr of He in an AC glow discharge. In this communication we report the observation of a total of 22 new hot bands of $HN_{2}^{+}$. The position of the lower level of the hot band $v_{1}^{+}v_{3}\\leftarrow 3v_{3}$ ($\\sim7000 cm^{-1}$) above the ground vibrational state indicates the high vibrational temperature of the ions in the discharge. The results of our analysis and those concerning the three fundamental vibration $bands ^{1-4}$ as well as the hot band $4v_{1}+v_{2}\\leftarrow v_{2}$ are fitted together to a global Hamiltonian model. This model takes explicitely into account the degeneracy of $v_{2}$ and the rotational 1-type doubling. The most complete set of molecular constants of $HN_{2}^{+}$ will be presented. Results of the quantitative determination of the vibrational and rotational temperatures will also be reported.