Electronic properties and vibrationally averaged structures of X̃ 2 Σ + MgOH: a computational molecular spectroscopy study.

For X̃ 2 Σ + MgOH, we have calculated the 3D potential energy surface (PES) at the MR-SDCI+ Q /[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 ( r e (Mg-O) = 1.7614 Å, r e (O-H) = 0.9453 Å, and ∠ e (Mg-O-H) = 180°). The zero-point structure, determined as the expectation values over the DVR3D wavefunctions, has 〈 r (Mg-O)〉 0 = 1.7837 Å and 〈 r (O-H)〉 0 = 0.9948 Å, and the deviation angle from linearity 〈  〉 0 = 26.4°. The harmonic frequencies ω e for the Mg-O stretching, bending, and O-H stretching modes are 768, 142, and 4060 cm -1 , respectively, and the corresponding term values ν 1 , ν 2 , and ν 3 are 752, 156, and 3867 cm -1 . All the vibrational behaviors, such as quasi-linear features, unusual relationship ν 2 > ω 2 , a large amplitude bending motion, etc. , are elucidated in terms of the ab initio 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.