Quantum Chemical Modeling of the Adsorption of Chloride Ion and Water Molecule on Group 1B Metals

I. V. Nechaev and A. V. Vvedenskii

Voronezh State University, Universitetskaya pl. 1, Voronezh, 394006 Russia

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Received July 7, 2008

Abstract — Quantum chemical modeling (at DFT-B3LYP level) of the adsorption of Cl and H₂O particles on top and into hollow sites of defect-free low index faces of copper, silver, and gold simulated by n-atomic clusters with n = 9 to 17 is carried out. The validity of simulations is confirmed by the comparison to the available literature data on the work function of the metals and the calculated gas-phase adsorption of chlorine. Relative effects of the chemical (metal nature), macrostructural (crystal face), and coordination (adsorption site) factors on the parameters of the chemisorption bond and molecular characteristics of the adsorbate and adsorbent, namely, the _ads adsorption energy at = 0K, R(MeCl) and R(Me–O) adsorption bond lengths, Q effective charges of chlorine atom and water molecule, O–H distance and angle in ₂ molecule, deviation of the H₂O dipole moment vector from normal orientation to the cluster surface, and energies of the highest occupied molecular orbital of _n, [Me_nCl], Me_nH₂O, and [Me_nClH₂O] clusters, are considered. The inner hydration shell of Cl is shown to involve six water molecules, the most stable configuration of (₂)₆ cluster being prism-like. An electron density shift from chlorine and water molecule to the metal cluster is found to accompany the adsorption and be more pronounced in the case of anion. The character of differences in the hydrophilicity of the group 1B metals and their diverse crystal faces is discussed. The role of hydration effects in the chemisorption of chloride ion on copper, silver, and gold is analyzed in terms of the continuum, molecular, and combined molecular–continuum models.