The 1E″ state of NH3: the Jahn-Teller effect revealed by infrared-optical double resonance

Several new vibronic levels of the 1 E″ state of NH 3 have been measured using infrared-optical double resonance and supersonic jet spectroscopy. Rotational analyses of these bands are presented and an analysis of the overall vibronic structure is also given. A small but significant Jahn-Teller distortion is found to be present (less than the zero point motion). Vibronic interactions with nearby electronic states are required to explain the observed pattern of fibronic energy levels.