Electronic properties and vibrationally averaged structures of X̃ Σ MgOH: a computational molecular spectroscopy study.

For X̃ Σ MgOH, we have calculated the 3D potential energy surface (PES) at the MR-SDCI+/[cc-pCV5Z (Mg), aug-cc-pV5Z (O), cc-pV5Z (H)] level and derived the vibrational properties from there using the discrete variable representation (DVR) method. The PES minimum is at the linear structure; hence, MgOH is a "linear molecule." The 3D PES is shallow, and MgOH tends to bend in the region immediately when either or both Mg-O and O-H bonds become longer than those of the equilibrium structure ((Mg-O) = 1.7614 Å, (O-H) = 0.9453 Å, and ∠(Mg-O-H) = 180°). The zero-point structure, determined as the expectation values over the DVR3D wavefunctions, has 〈(Mg-O)〉 = 1.7837 Å and 〈(O-H)〉 = 0.9948 Å, and the deviation angle from linearity 〈〉 = 26.4°. The harmonic frequencies for the Mg-O stretching, bending, and O-H stretching modes are 768, 142, and 4060 cm, respectively, and the corresponding term values , , and are 752, 156, and 3867 cm. All the vibrational behaviors, such as quasi-linear features, unusual relationship > , a large amplitude bending motion, , are elucidated in terms of the electronic wavefunctions and the DVR3D vibrational wavefunctions. We have another piece of evidence to support our postulation that a linear molecule is observed as being bent.