Strong quantum coupling between O-H+-O stretch and flanking group motions in (CH3OH)2H+ Part I: Unmasking the 800-1200 cm−1peaks

Assigning the vibrational signatures between 800-1200 \wn is not a trivial task for \chem{(CH_3OH)_2H^+}.\footnote{J.R. Roscioli, L.R. McCunn and M.A. Johnson. Science 2007, 316, 249} $^{-}$ \footnote{T.D. Fridgen, L. Macaleese, T.B McMahon, J. Lemaire and P. Maitre. Phys. Chem. Chem. Phys. 2006, 8, 955-966} Such complication in the assignment arises due to the intermode coupling between O-H$^{+}$-O stretch and flanking group motions. In this talk, we will examine the interactions between O-H$^{+}$-O stretch and four flanking group motions: 1) out-of-phase C-O stretch, 2) in-plane \chem{CH_3} rock, 3) out-of-plane \chem{CH_3}, and 4) O-O stretch. Vibrational interactions were investigated by solving a reduced-dimensional Schrödinger equation by means of Discrete Variable Representation (DVR) with harmonic oscillators as basis. Potential and dipole moment surfaces were constructed by scanning along normal mode coordinates using MP2 and CCSD(T) level. It was found out that the O-H$^{+}$-O stretch strongly couples with the four above mentioned flanking motions, leading to intensity redistribution on peaks between 800-1200 \wn.\footnote{J.A. Tan and J.-L. Kuo. J. Phys. Chem. A. 2015, 119, 11320-11328