Jheng-Wei Li, Kaito Takahashi and Jer-Lai Kuo Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan Vibrational Coupling in Solvated form of H 3 O + : A case study on H 3 O +... Ar 1, 2 & 3 70 th OSU Int. Symp. on Mol. Spectroscopy, University of Illinois Urbana-Champaign, USA, June/26/2015

Solvation of Excess Protons The Spectral Signatures of H 5 O 2 + (FC02 = H 4 O 2 + ) Eigen H 3 O + Zundel H 5 O 2 +

Vibrational Modes of H 3 O + Vibration-Inversion-Rotation A portion of observed spectrum umbrella 762 cm -1 bend 1666 cm -1 symm. 3573cm -1 asym. 3695cm -1 B3LYP/6-31+G(d,p)

Solvated H 3 O + 4

Outline Quick review on theoretical works Methodology Results Summary 5

O-H stretch by AIMD M. H. Begemann, R. J. Saykally, J. Chem. Phys. 1985, 82, 3570 – 3579 M. Okumura, L. I. Yeh, J. D. Myers, Y. T. Lee, J. Phys. Chem. 1990, 94,3416 – Marcel Baer, Dominik Marx, and Gerald Mathias BOMD at 150K with CP2K BLYP with dispersion correction & TZV2P basis set Chem Phys Chem 2011, 12, 1906 – 1915 AIMD approximately reproduces the relative peak heights and also the widths of the experimental bands. ….. one cannot expect to compute IR spectra classically in the sense of a “black-box” approach, but one rather has to carefully probe, crosscheck, and consider their temperature dependence when comparing to experiment and assigning bands; we note in passing that failing to do so is probably a major reason why previous studies fall short in explaining complex vibrational spectra.

Association motion (bending + hinder rot) Mechanical or Electronic anharmonicity ? J. Phys. Chem. B 2014, 118, 8286−8294Phys. Chem. Chem. Phys., 2012, 14, 7205–7214 Local or Normal modes?

Normal Mode Approx. (NMA) A simple DVR along normal mode direction (approx.) PES obtained from ab initio cal. (no approx.) Diagonalize the (no approx.) Intensities were calculated via Fermi Golden Rule (no approx.) We use harmonic grids

Benchmark Cal. 1 (Reduced Dimension) H3O+H3O+ bend 1666 cm -1 sym. 3573cm -1 asym. 3695cm -1 B3LYP/6-31+G(d,p) Bends Sym. Asym

Benchmark Cal. 2 (E xc /basis set) Vib. modes B3LYP/6- 31+G** MP2/aDZMM/PES-2 a Exp a 5D Centroid b HOH Bending Sym. OH Stretching Asymm. OH Stretching Huang, X.; Carter, S.; Bowman, J. M. J. Phys. Chem. B 2002, 106, 8182–8188. CCSD(T)/aTZ B3LYP/6-31+G(d,p), MP2/aDZ & CCSD(T)/aTZ

Free OH 3D (stretch) The Ar induced Change on OH stretch On the Stretches (3D) Largely Red-Shifting of OH…Ar Stretch H3O+H3O+ OH…Ar stretches H 3 O + Ar 1

H 3 O + Ar 2 H 3 O + Ar 3 OH…Ar stretches Free OH H 3 O + Ar 1 Total Binding = kcal/mol -3.89/1 = D (stretch) Anti-cooperative Effect The Ar induced Change on OH stretch On the Stretches (3D) Largely Red-Shifting of OH…Ar Stretch H3O+H3O+ Total Binding = kcal/mol -7.39/2 = Total Binding = kcal/mol /3 = Gradually Blue-Shifting with the addition of Ar

Splitting between sym and asym modes H 3 O + Ar 2 Sym. & Asym. nearly degenerate.

The Coupling between 2bends & 3stretches H 3 O + Ar 1 H 3 O + Ar 3 H 3 O + Ar 2 3D (stretch)

5D (bend & stretch) The Coupling between 2bends & 3stretches On the Bend-Stretch (5D) H 3 O + Ar 1 H 3 O + Ar 3 H 3 O + Ar 2 Fermi-Resonance (0,1 stretch ) GS (2 bend,0) (1 bend,0) (0,0) (n b1,n b2,n s1,n s2,n s3 ) (2,0,0,0,0) (0,0,1,0,0) (0,2,0,0,0) (0,0,0,1,0) (1,1,0,0,0) (0,0,0,0,1) ~3000cm cm cm -1 Anti-cooperative effect tunes the F-R strength !

Comparing theory and xxperiment Doublet ? association band 5D (bend & stretch) Exp. J. Phys. Chem. B 2014, 118, 8286−8294

Adding Hindered Rotation 5D (bend & stretch) 249cm cm cm cm cm cm -1 Fund.=229cm -1 Fund.=305cm -1 Fund.=368cm -1 (0,0)

Summary: comparing theory and experiment) 218cm cm cm -1 Exp. Bend overtone + hind. rot. Anti-cooperative effect tunes the F-R strength !Assoc. band (freq. & intensity)