The infrared vibration–rotation spectrum of the molecular ion: extension to higher vibrational and rotational quantum numbers

The assigned infrared spectrum of the [Formula: see text] molecular ion is extended from 84 to 529 lines by three types of spectroscopic measurements on hollow-cathode electrical discharges through deuterium gas: (i) emission from a small hollow cathode, in which the [Formula: see text] lines were distinguished from the electronic transitions of D2 by the pressure dependence of their intensities; (ii) absorption in the same hollow cathode with discharge amplitude modulation; and (iii) absorption in a larger hollow cathode cell with discharge amplitude modulation. The observed lines belong mainly to the [Formula: see text] fundamental and its hot bands [Formula: see text], [Formula: see text] and [Formula: see text] in the 1330–2530 cm−1 region in experiments (i) and (ii), and to the first overtone band [Formula: see text] in the 3160–4000 cm−1 region in experiment (iii). The lines were assigned by means of calculations with a large vibration–rotation basis, using a Morse-based discrete variable representation for the vibrations. This method overcomes the convergence problems for the centrifugal terms in the effective Hamiltonian approach. Six coefficients in the Meyer–Botschwina–Burton ab initio potential were adjusted in order to fit these data with a standard deviation of 0.059 cm−1.