Extended Measurement of the V(2)(1(-)<- 0(+)) Band of H3o+ by Mid-Infrared Diode Laser Spectroscopy

Twenty-five new R-branch lines of the V-2 (1(-) <- 0(+)) band of H3O+ are measured using diode laser velocity modulation spectroscopy between 1070 and 1230 cm(-1). The H3O+ ions are produced in a high voltage ac discharge with water diluted in helium. The observed lines together with all the previously published measurements are lit to the standard vibration-rotational Hamiltonian of an oblate symmetric top, yielding a set of improved molecular constants. All the sextic centrifugal distortion constants for both 0(+) and 1(-) states are determined precisely. The observed R(13, 0) transition is shifted about -0.129 cm(-1) from its calculated value, indicating that a near degeneracy exists between the (13, 0)(+) and (13, 3) (-) ground-state rotation-inversion levels.