Observation of high-lRydberg states of nitric oxide

We report the observation of the 5g-4f Rydberg-Rydberg infrared transition of nitric oxide at 2500 ${\mathrm{cm}}^{\mathrm{-}1}$ using high-resolution (0.03 ${\mathrm{cm}}^{\mathrm{-}1}$) Fourier-transform spectrometry. A rotationally cold (70 K) and resolved spectrum has been obtained in emission from a supersonic jet discharge. A spectrum emanating from hot (850-K) NO gas has also been observed. This spectrum exhibits characteristic spikes reflecting the quantization of the electron angular momentum along the axis of fast core rotation. Both spectra are quantitatively reproduced by theory. The manifestation of ‘‘circular’’ states in the hot spectrum is discussed.