A study of the structure and dynamics of the hydronium ion by high resolution infrared laser spectroscopy. II. The v₄ perpendicular bending mode of H₃¹⁶O⁺

Sixty-six lines in the v₄ band of H₃O⁺ have been measured using diode laser velocity modulation spectroscopy. 36 have been assigned to the a-a component of the spectrum and 30 to the s-s component. The observed spectra were fit to a standard symmetric top Hamiltonian including the effects of l-type doubling. The band origin of the s-s transitions is at 1625.947(5) cm^-1, whereas that of the a-a component lies at 1638.533(3) cm^-1. The effect of the asymmetric bending vibration on the inversion splitting is in qualitative agreement with previous theoretical results, but the experimental band origins deviate by about 60 cm^-1 from calculated values. Coriolis perturbations are found to have an important effect on the rotational constants of the v₄ and v₂ levels.