Near infrared second overtone cw-cavity ringdown spectroscopy of D2H+ ions

A study of D2H+ ions in their lowest rotational states is presented. The ions are generated in pulsed discharge in liquid N2 cooled He/Ar/H2/D2 gas mixture. Near infrared (NIR) second overtone transitions in the 6534–6536 cm−1 (1.529–1.530 μm) region are used to identify the ions and determine their degree of rotational excitation. The data were obtained using NIR cavity ringdown absorption spectroscopy (NIR-CRDS). The sensitivity obtained was typically 5 × 10−9 cm−1. The measured second overtone transition frequencies are in very good agreement (better than 0.02 cm−1) with ab initio predictions. From the Doppler broadening the kinetic temperature of ions is estimated to be (220 ± 50) K. The absolute number density of D2H+ as a function of H2/D2 mixing ratio and time is measured.