Ab initio potential energy surface and vibration-rotation energy levels of magnesium monohydroxide revisited

The accurate potential energy surface of magnesium monohydroxide, MgOH, in its ground electronic state $\tilde{X}{}^2{\Sigma }^{+}$ has been determined from ab initio calculations using the coupled-cluster approach in conjunction with the correlation-consistent basis sets up to septuple-zeta quality. The core-electron correlation, higher-order electron correlation, scalar relativistic, and adiabatic effects were taken into account. The equilibrium configuration of the MgOH molecule was confirmed to be linear, although with the bending potential energy function being very flat near the minimum. The vibration–rotation-spin energy levels of the MgOH, MgOD, ²⁵MgOH, and ²⁶MgOH isotopologues were predicted using a variational approach. The spectroscopic constants of these isotopologues were determined to high accuracy.