Water Adsorption on Free Cobalt Cluster Cations

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• 作者：Denis M. Kiawi ; Joost M. Bakker ; Jos Oomens ; Wybren Jan Buma ; Zahra Jamshidi ; Lucas Visscher ; L. B. F. M. Waters
• 刊名：Journal of Physical Chemistry A
• 出版年：2015
• 出版时间：November 5, 2015
• 年：2015
• 卷：119
• 期：44
• 页码：10828-10837
• 全文大小：529K
• ISSN：1520-5215

文摘

Cationic cobalt clusters complexed with water Co_n⁺鈥揌₂O (n = 6鈥?0) are produced through laser ablation and investigated via infrared multiple photon dissociation (IR-MPD) spectroscopy in the 200鈥?700 cm^鈥? spectral range. All spectra exhibit a resonance close to the 1595 cm^鈥? frequency of the free water bending vibration, indicating that the water molecule remains intact upon adsorption. For n = 6, the frequency of this band is blue-shifted, but it gradually converges to the free water value with increasing cluster size. In the lower-frequency range (200鈥?50 cm^鈥?) the spectra contain several bands which show a very regular frequency evolution, suggesting that the exact cluster geometry has little effect on the water鈥搒urface interaction. Density functional theory (DFT) calculations are carried out at the OPBE/TZP level for three representative sizes (n = 6, 9, 13) and indicate that the vibrations responsible for the resonances correspond to bending and torsional modes between the cluster and water moieties. The potential energy surfaces describing these interactions are very shallow, making the calculated harmonic frequencies and IR intensities very sensitive to small geometrical perturbations. We conclude that harmonic frequency calculations on (local) minima structures provide insufficient information for these types of cluster complexes and need to be complemented with calculations that provide a more extensive sampling of the potential energy surface.