HYPERFINE-RESOLVED ROVIBRATIONAL SPECTRUM OF THE X(2)PI STATE OF HI+

A high resolution spectroscopic study of HI+ has been carried out for the first time. The absorption spectrum in the inverted 2Π ground electronic state has been measured with a linewidth of 0.004 cm -1 between 1995 and 2245 cm-1. A total of 117 vibration-rotation transitions were observed with a tunable diode laser spectrometer coupled to an ac glow discharge cell employing velocity modulation. Lines were measured in the vibrational fundamental of the 2Π 1/2 spin substate and in the three lowest (υ + 1 ← υ) bands of the 2Π3/2 spin substate. A good fit to the data was obtained using a standard vibration-rotation, fine structure Hamiltonian. Equilibrium values were determined for 16 molecular parameters including the harmonic vibrational frequency ωe, the rotational constant Be, and the A-doubling constants pe and q e. A review of the ground state properties of the hydrogen halide ions HX+ (X=F, C1, Br, I) shows that the harmonic force constant is, to excellent approximation, a linear function of the internuclear spacing. In ten different vibration-rotation transitions of the two spin substates of HI+ , hyperfine splittings were observed. A total of 58 relative splittings of hyperfine components were analyzed to determine the iodine quadrupole coupling constant eQq0 as well as the Frosch-Foley magnetic hyperfine constants a, (b + c), and d. The results have been used to investigate the electronic properties of the ion. © 1995 American Institute of Physics.