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ROBERT J. FOLTYNOWICZ, JASON D. ROBINSON, HARTMUT G. HEDDERICH AND EDWARD R. GRANT, Department of Chemistry, Purdue University, West Lafayette, IN 47907-1393.

We report a harmonic frequency ₂ = 842.464 cm^-1, an anharmonic constant, x₂₂ = -3.15 cm^-1 and a vibrational angular momentum splitting constant g₂₂ = 3.22 cm^-1 for the ground state ^{1 +} for HCO⁺. The constants are calculated based on experimentally measured Rydberg Series from the 3p electronic state which converge to the rovibrational thresholds of the cation (00⁰0), (01¹0), (02⁰0) and (02²0). Along with these thresholds, we use the experimentally measured x₂₃ anharmonic constant from Oka et al. and the theoretical x₁₂ anharmonic constant from Puzzarini et al. and Lee et al. To further characterize the bending coordinate anharmonicity of the potential energy surface of HCO⁺, we assign Rydberg series obtained from the 3p ² (030) ^- N'=0 and 2 converging to rovibrational thresholds (03¹0) and (03³0) in the cation. >From this extrapolation, we refine our anharmonic constants for the ground electronic state for HCO⁺.