Vibrationally unusual behaviors predicted for [XeHXe]+: A computational molecular spectroscopy study

To obtain more evidence for our assertion that the ro-vibrationally averaged structure of a linear molecule is to be observed as being “bent,” we here chose a linear molecule X˜Σg+1 [XeHXe]+. Using the basis sets and calculation level checked against the gas-phase spectroscopy data for XeH+, the 3D potential energy surface (PES) of [XeHXe]+ was calculated at the valence CCSD(T)/[5ZP ANO-RCC (Xe), cc-pV5Z-DK (H)] level. Then, ro-vibrational properties were calculated over the DVR3D wavefunctions derived by the Discrete Variable Representation method. The [XeHXe]+ is a covalently bound, stable cation with 110 kcal/mol of the heat of formation, showing a large amplitude bending motion. Three unusual features are noticed and elucidated. (1) Although the [XeHXe]+ is a linear molecule with re(Xe–H) = re(H–Xe) = 1.8682 Å in D∞h symmetry and the PES is symmetric for the two Xe–H bonds, the r0 structure is unsymmetric with 〈r(Xe–H)〉0 = 1.8881 Å, 〈r(H–Xe)〉0 = 1.9028 Å, and 〈∠(Xe–H–Xe)〉0 = 166.6∘. The 〈∠(Xe–H–Xe)〉0 value of 166.6∘ again confirmed our assertion that a linear molecule is to be observed as being bent. (2) The term value ν3 (846 cm−1, antisymmetric stretching mode) is higher than the harmonic frequency ω3 (820 cm−1), which is unusual since in ordinary molecules νi ω3 (820 cm−1).•3) Bending mode is anharmonic, since it is essentially the Xe–H stretching motion.