New rovibrational data for MgOH and MgOD and the internuclear potential function of the ground electronic state

Using millimeter wave absorption spectroscopy we have recorded pure rotation spectra of MgOH in its ground vibrational state and in six excited vibrational states. We have also determined a large number of bending vibrational energies, and the MgO stretching frequency, using dispersed fluorescence studies of both MgOH and MgOD. By a weighted least-squares optimized fitting to this data, using the vibrational approach MORBID (Morse oscillator rigid bender for internal dynamics), we have derived the full ground state potential surface in an analytical form. The equilibrium structure is determined to be linear but with a flat predominantly quartic bending potential.