Observation of the ν1 fundamental band of H2D+

The ν1 fundamental band of H2D+ has been observed in absorption in a discharge with a difference frequency laser spectrometer in the range 2830–3200 cm−1. The 27 observed lines are assigned and the transition wave numbers are fit to an effective Hamiltonian to determine the molecular constants. The band origin (2992.488±0.016 cm−1) and the rotational constants are in good agreement with those from ab initio calculations. The dependence of the concentration of H2D+ on the D2/H2 mixing ratio, which can be used to identify absorption lines of this ion, is discussed.