Knowledge Bank

The l-type doubling in the $\nu 2$ and $\nu 1+\nu 2$ states of the $HN2+$ molecular ion has been studied using infrared microwave double resonance spectroscopy. The molecular constants q and $q1$ were determined for both states from our observed transition frequencies. This work is a continuation of our application of this sensitive technique to molecular ions and represents the first observation of centimeter wave transitions of a molecular ion. The $HN2+$ ion was produced in a hollow cathode discharge at a pressure of 50 mTorr. Microwave transitions for $J=6,7$, and 8 in the $\nu 2$ state and $J=6$ and 7 in the $\nu 1+\nu 2$ state were pumped with 6 Watts of radiation produced by a centimeter wave synthesizer and amplified by a traveling wave tube amplifier. This radiaiton was introduced into the hollow cathode cell via an X-band waveguide soldered to the hollow cathode. A color center laser served both to saturate the infrared transition and as a probe of the microwave transition. Similar l-type doubling transition were first observed for the isoelectronic neutral HCN. In addition, many collision-induced transitions were observed for HCN.