The infrared spectrum of the ν2 fundamental band of the molecular ion

Abstract

Measurements of 60 infrared lines of the molecular ion [Formula: see text] in the region 1810–2180 cm−1 are reported. These lines are observed in a hollow-cathode discharge through deuterium gas as absorptions of tunable diode-laser radiation. The present data are combined with 45 lines (five in common) from laser ion-beam experiments of Wing and colleagues in a detailed analysis of the ν2(e′) band of [Formula: see text]. Altogether, 84 lines are fitted with a standard deviation of 0.0024 cm−1, employing a 25-parameter effective Hamiltonian that uses a Padé representation of the centrifugal distortion effects. Five other lines assigned to specific transitions have larger residuals, while 11 lines that may be rotationally or vibrationally hotter remain unassigned. The value obtained for ν2 is 1834.669 cm−1, and both it and the observed ground-state combination differences and principal molecular parameters agree well with ab initio calculations. The values of the higher order parameters in the effective Hamiltonian do not agree well with theoretical perturbation formulas because of the slow convergence of perturbation series for this light molecule.