Water Adsorption on Free Cobalt Cluster Cations
Denis M Kiawi1, Joost M Bakker1, Jos Oomens1
1Radboud University , Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7, 6525 ED Nijmegen, The Netherlands.
The Journal of Physical Chemistry. A
|October 9, 2015
Summary
Cationic cobalt clusters with water show distinct vibrational modes. Water molecules remain intact, with bending vibrations converging to free water values as cluster size increases.
Area of Science:
- Physical Chemistry
- Spectroscopy
- Computational Chemistry
Background:
- Cationic metal clusters are crucial in catalysis and atmospheric chemistry.
- Understanding water-metal cluster interactions provides insights into solvation and adsorption.
Purpose of the Study:
- To investigate the structural and vibrational properties of cationic cobalt-water clusters (Con(+)-H2O, n=6-20).
- To explore the nature of water-cluster interactions using experimental and computational methods.
Main Methods:
- Laser ablation was used to generate Con(+)-H2O clusters.
- Infrared multiple photon dissociation (IR-MPD) spectroscopy was employed to analyze vibrational frequencies.
- Density functional theory (DFT) calculations were performed to interpret spectral data and explore potential energy surfaces.
Main Results:
- IR-MPD spectra revealed a water bending resonance near 1595 cm(-1), indicating intact water molecules.
- The frequency of this band blue-shifted for smaller clusters (n=6) and converged with increasing size.
- Low-frequency bands (200-650 cm(-1)) showed regular evolution, suggesting geometry-independent water-surface interactions.
- DFT calculations identified bending and torsional modes between cobalt clusters and water, sensitive to geometric perturbations.
Conclusions:
- Water molecules remain intact in cationic cobalt clusters.
- Water-cluster interactions are characterized by low-frequency bending and torsional modes.
- Harmonic frequency calculations require extensive potential energy surface sampling for accurate interpretation of these cluster complexes.
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