title: MP4 Study of the Anharmonic Coupling of the Shared Proton Stretching Vibration of the Protonated Water Dimer in Equilibrium and Transition States.
abstract: The structure and harmonic and anharmonic IR spectra of the protonated water dimer (PWD) were calculated in C1, C2, and Cssymmetry at the MP4/acc-pVTZ level of theory. We found that structure and IR spectra are practically identical in C2and C1symmetry, demonstrating that an equilibrium C1configuration of the PWD is not realized. Anharmonic coupling of the shared proton stretching vibration with all other modes in the PWD in C2and Cssymmetry was the focus of this investigation. For this purpose, 28 two-dimensional potential energy surfaces (2D PES) were built at the MP4/acc-pVTZ level of theory and the corresponding vibrational Schrödinger equations were solved using the DVR method. Differences in the coupling of the investigated mode with other modes in the C2and Csconfigurations, along with some factors that determine the red- or blue-shift of the stretching vibration frequency, were analyzed. We obtained a rather reasonable value of the stretching frequency of the bridging proton (1058.4 cm-1) unperturbed by Fermi resonance. The Fermi resonance between the fundamental vibration ν7and the combined vibration ν2+ ν6of the same symmetry was analyzed through anharmonic second-order perturbation theory calculations, as well as by 3D PES constructed using Q2, Q6, and Q7as normal coordinates. A significant (up to 50%) transfer of intensity from the fundamental vibration to the combined one was found. We have estimated the frequency of the bridging proton stretching vibration in the Csconfiguration of the PWD based on calculations of the intrinsic anharmonicity and anharmonic double modes interactions at the MP4/acc-pVTZ level of theory (1261 cm-1).
authors.affiliation: Department of Physical Optics, Belarusian State University , Nezavisimosti ave., 4, 220030 Minsk, Belarus.
authors.forename: G
authors.initials: G
authors.lastname: Pitsevich
authors.affiliation: Department of Physical Optics, Belarusian State University , Nezavisimosti ave., 4, 220030 Minsk, Belarus.
authors.forename: A
authors.identifier: http://orcid.org/0000-0001-8716-8655
authors.initials: A
authors.lastname: Malevich
authors.affiliation: Department of Physical Optics, Belarusian State University , Nezavisimosti ave., 4, 220030 Minsk, Belarus.
authors.forename: E
authors.initials: E
authors.lastname: Kozlovskaya
authors.affiliation: Department of Physical Optics, Belarusian State University , Nezavisimosti ave., 4, 220030 Minsk, Belarus.
authors.forename: E
authors.initials: E
authors.lastname: Mahnach
authors.affiliation: Taras Shevchenko National University of Kyiv , Volodymyrska str., 64\13, 01601, Kyiv, Ukraine.
authors.forename: I
authors.initials: I
authors.lastname: Doroshenko
authors.affiliation: Taras Shevchenko National University of Kyiv , Volodymyrska str., 64\13, 01601, Kyiv, Ukraine.
authors.forename: V
authors.initials: V
authors.lastname: Pogorelov
authors.affiliation: Department of Physics, AlbaNova University Center, Stockholm University , S-106 91 Stockholm, Sweden.
authors.forename: Lars G M
authors.initials: LG
authors.lastname: Pettersson
authors.affiliation: Faculty of Physics, Vilnius University , Sauletekio al. 9-3, LT-10222 Vilnius, Lithuania.
authors.forename: V
authors.initials: V
authors.lastname: Sablinskas
authors.affiliation: Faculty of Physics, Vilnius University , Sauletekio al. 9-3, LT-10222 Vilnius, Lithuania.
authors.forename: V
authors.initials: V
authors.lastname: Balevicius