The rotational spectrum and dynamical structure of LiOH and LiOD: A combined laboratory and ab initio study

Abstract

Millimeter wave rotational spectroscopy and ab initio calculations are used to explore the potential energy surface of LiOH and LiOD with particular emphasis on the bending states and bending potential. New measurements extend the observed rotational lines to J=7<--6 for LiOH and J=8<--7 for LiOD for all bending vibrational states up to (03(3)0). Rotation-vibration energy levels, geometric expectation values, and dipole moments are calculated using extensive high-level ab initio three-dimensional potential energy and dipole moment surfaces. Agreement between calculation and experiment is superb, with predicted Bv values typically within 0.3%, D values within 0.2%, ql values within 0.7%, and dipole moments within 0.9% of experiment. Shifts in Bv values with vibration and isotopic substitution are also well predicted. A combined theoretical and experimental structural analysis establishes the linear equilibrium structure with re(Li-O)=1.5776(4) A and re(O-H)=0.949(2) A. Predicted fundamental vibrational frequencies are v1=923.2, v2=318.3, and v3=3829.8 cm(-1) for LiOH and v1=912.9, v2=245.8, and v3=2824.2 cm(-1) for LiOD. The molecule is extremely nonrigid with respect to angular deformation; the calculated deviation from linearity for the vibrationally averaged structure is 19.0 degrees in the (000) state and 41.9 degrees in the (03(3)0) state. The calculation not only predicts, in agreement with previous work [P. R. Bunker, P. Jensen, A. Karpfen, and H. Lischka, J. Mol. Spectrosc. 135, 89 (1989)], a change from a linear to a bent minimum energy configuration at elongated Li-O distances, but also a similar change from linear to bent at elongated O-H distances.

The equilibrium OH bond length

“…[35] for an extensive literature review). Recently, Higgins et al [35] combined millimeter wave rotational spectroscopy and high level ab initio calculations to explore the potential energy surface of LiOH and LiOD. They found that the molecule is extremely non-rigid and that the structure is linear at equilibrium with r e (OH) ¼ 0.949(2) Å .…”

“…For this reason, it has been the subject of many experimental and theoretical studies (see Ref. [35] for an extensive literature review). Recently, Higgins et al [35] combined millimeter wave rotational spectroscopy and high level ab initio calculations to explore the potential energy surface of LiOH and LiOD.…”

Trends in alkali metal hydrosulfides: A combined Fourier transform microwave/millimeter-wave spectroscopic study of KSH ($\tilde X^1 A^\prime $X̃1A′)

“…Typically, MSH species exhibit bent geometries in their ground electronic states. In contrast, the MOH counterparts are either linear or quasilinear, 16,17 with the exception of CuOH and ZnOH. 18,19 The geometric preference is attributed to the character of the metal-ligand bond.…”

The Fourier transform microwave/millimeter-wave spectrum of YOH and YOD (X̃1Σ+Halfen1, Keogh2, Ziurys3 2015Journal of Molecular Spectroscopy2000View full textAdd to dashboardCite

“…These species have all proved to be linear, with the exception of the indium compound, which is bent with an angle of 132°. Some quasilinear behavior is exhibited by MgOH and LiOH [6,21], as well, which both appear to have very low energy bending potentials. However, very few transition metal hydroxides have been investigated by gas-phase spectroscopic methods.…”

“…High-resolution spectroscopy of alkali and alkaline-earth hydroxide species has been carried out for several decades, beginning with the work of Lide and collaborators [6][7][8][9][10][11][12][13][14][15][16][17][18]. More recently, investigations of aluminum and indium hydroxides have been performed, providing additional insight [19,20].…”