Experimental potential functions for open and closed shell molecular ions: Adiabatic and nonadiabatic corrections in X³Σ^- OH⁺ and X¹Σ⁺ ArH⁺

We have measured 43 transitions in the pure rotational and fundamental vibrational spectra of ¹⁸OH⁺. These data, together with all ground state transitions and combination differences of OH⁺ and ¹⁶OH⁺ available from the literature, have been fit to an explicity internuclear distance dependent rovibrational Hamiltonian to yield several descriptions of the OH⁺ potential function. Significant adiabatic and rotationally and vibrationally nonadiabatic corrections are required to fit all 407 isotopomeric transitions simultaneously. Similar fits are also performed on the closed shell species ArH⁺, yielding an approximate vibrational correction to the recently determined experimental permanent dipole moment of that ion.