Rotational transitions of CH2D+ determined by high-resolution IR spectroscopy

Context. Deuterated forms of CH3+ are responsible for deuterium fractionation in warmer environments. Current searches for CH2D+ are hampered by a lack of accurate laboratory data. Aims. We demonstrate that IR spectroscopy at very high resolution can make accurate rotational predictions. Methods. By combining a low-temperature ion trap with a narrow-bandwidth IR light source, we are able to measure vibrational transitions with high accuracy. A subsequent fit using an asymmetric rotor model allows predictions of MHz accuracy or even better. Results. We predict rotational transitions up to 1.5 THz.