Higher rotational lines in the ν2 fundamental of the H 3+ molecular ion

Abstract

By use of a new high-pressure hollow-cathode discharge cell and a Fourier transform spectrometer, many lines of the ν 2 fundamental band of H 3 + are observed in emission. These lines are discriminated from those of other species by pressure labeling, in which the relative intensities are studied as functions of the H 2 gas pressure in the cell. The H 3 + lines are found to persist to higher pressures than those of H atoms or H 2 or H 3 molecules. Practically all of the previously known lines of H 3 + are observed with this cell, and the measurements are extended to higher J because of the high rotational temperature of the H 3 +. Absorption measurements of some high- J lines were also performed in this new cell. Altogether 113 lines of the ν 2 band of H 3 + with J′ max = 10 have been assigned, and 111 of them are fitted to 0.0654 cm −1 with a 29-parameter effective Hamiltonian that uses a Padé formulation of the centrifugal distortion effects. Many of the higher rotational levels of ν 2 are affected by a Birss resonance with levels of ν 1. The fitted values ν 1 = 3175.0 cm −1 and α 12 = 1.377 cm −1 for the vibrational frequency and perturbation parameter are in reasonable agreement with ab initio values. Alternative fits using a vibration-rotation supermatrix model with a limited number of independent matrix elements are consistent with these assignments, but the quality of these fits degrades rapidly with increasing J′ max because the model does not describe centrifugal effects accurately.