Near infrared transitions between Rydberg states of nitric oxide: The 4f-F2Δ band at 1.71 μm

Several near infrared transitions between highly excited Rydberg (R) states of nitric oxide have been recorded at high resolution (0.15 cm−1) with a SISAM interferometer. The spectra all show a simple rotational structure, characteristic of R-R transitions. A full analysis has been performed of the previously unobserved 4f(v = 0) → F2Δ(v = 0) band at 1.71 μm. The band shows a peculiar structure, characteristic of Hund's Case (d) behaviour for one of the states. The relative branch intensities are calculated from first principles, and the agreement with the observed spectrum is excellent. This work shows the potential of interferometers for studying excited electronic states of simple molecules at high resolution.