Large amplitude bending motion in CsOH, studied through ab initio-based three-dimensional potential energy functions

• Published in: Journal of molecular spectroscopy Vol. 263; no. 2; pp. 150 - 159
• Main Authors: Hirano, Tsuneo, Derpmann, Valerie, Nagashima, Umpei, Jensen, Per
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.10.2010
• Subjects: [formula omitted] CsOH; Ab initio 3D potential energy surface; Molecular constants; MORBID ro-vibrationally averaged structure; Yamada-Winnewisser quasi-linearity parameter; X ˜ 1 Σ + CsOH; Molecular constants; Ab initio 3D potential energy surface; MORBID ro-vibrationally averaged structure; Yamada-Winnewisser quasi-linearity parameter
• ISSN: 0022-2852; 1096-083X
• DOI: 10.1016/j.jms.2010.07.009

The large-amplitude bending motion in CsOH, a ‘classical’ molecule whose microwave spectrum was first recorded in 1967, has been studied ab initio. The three-dimensional potential energy surface has been calculated at the RCCSD(T)_DK3/[QZP + g ANO-RCC (Cs, O, H)] level of theory and employed in MORBID calculations of the rotation–vibration energies and intensities. The ground electronic state is 1 Σ + with the equilibrium structure r e(Cs–O) = 2.3930 Å, r e(O–H) = 0.9587 Å, and ∠ e(Cs–O–H) = 180.0°. The O–H moiety is bound to Cs by an ionic bond and the molecule can be described as Cs δ + ( OH ) δ - . Hence, the bending potential is shallow and gives rise to large-amplitude bending motion. The ro-vibrationally averaged structural parameters, determined as expectation values over MORBID wavefunctions, are 〈 r(Cs–O)〉 0 = 2.3987 Å, 〈 r(O–H)〉 0 = 0.9754 Å, and 〈∠(Cs–O–H)〉 0 = 163°. Although the averaged structure in the vibrational ground state is far from being linear, the Yamada–Winnewissi-linearity parameter for CsOH is γ 0 ≈ - 1.0 , the value characteristic for a linear molecule.