| The hydration phenomena of cation, anion, and neutral molecules are of fundamental importance throughout chemistry and biology. The profuse characteristic of noble metal elements result in special properties for hydrated noble metal clusters, and so the hydration of noble metal become the focus of investigations in recent years. However, experimental information on geometric structures and so on of hydrated noble metal clusters is somewhat limited. Along with the rapid development of computational methods and computer technology, theoretical studies on clusters can get more and accurate information. In this paper, Mδ(H2O)1,2 (M = Cu, Ag, Au,δ= 0, -1 and 1),M+(H2O)Rg (Rg = Ne, Ar, Kr),M+(H2O)Ar2 and M+(H2O)2Ar are studied theoretically in detail using MP2 and CCSD(T) of quantum-mechanical ab initio calculation.The structures and binding energies of M+(H2O) (M = Cu, Ag, Au) are studied. The results show that the binding energies of Cu+(H2O),Ag+(H2O) and Au+(H2O) are all higher than single infrared photon energy, and so it is difficult to observe the infrared (IR) spectra of M+(H2O) (M = Cu, Ag, Au). On this basis, hydrated noble metal cation clusters containing Ar atom M+(H2O)Ar are investigated. The Ar atom binding energies can explain the phenomenon in which the infrared spectrum of Ag+(H2O)Ar can be observed using Ar atom tagging technique in the experiment, but only one broad peak was exhibited in the infrared spectrum of Cu+(H2O)Ar. Moreover,it is predicted that the infrared spectrum of Au+(H2O)Ar can't be acquired by the Ar atom tagging method. The interaction between Ar atom and noble metal cation M+ leads to blueshifts for the symmetric and asymmetric OH stretch vibrations of M+(H2O)Ar compared to the corresponding vibrations of M+(H2O), whereas binding argon atom to H atom leads to large red shift in OH stretching vibrations. Moreover, the infrared spectra of M+(H2O) (M = Cu, Ag, Au) can be obtained using Ne atom tagging technique.Geometrical structures and binding energies are calculated and analyzed for Cu+(H2O)Ar2 and Au+(H2O)Ar2. The results indicat that the infrared spectra of Cu+(H2O)Ar2 and Au+(H2O)Ar2 can be obtained by single photon absorb. This paper can supply important foundation to get the infrared spectra of clusters in expetiment. Geometrical structures are optimized for M+(H2O)2 (M = Cu, Ag, Au). The structures of ground state are all with C2 symmetry. It is predicted that single infrared photon can't dissociate M+(H2O)2 to acquire the infrared spectra. Based on this, to explore whether the infrared spectra can be obtained using Ar atom tagging method, ab initio electronic structure calculations are carried out to investigate the geometrical structures, binding energies and infrared spectra of M+(H2O)2Ar (M = Cu, Ag, Au). Theoretical studies predict that for Cu+(H2O)2Ar and Ag+(H2O)2Ar there are two isomeric structures which result from different binding sites of Ar atom, while only one isomer structure with the Ar atom bound to H atom is found for Au+(H2O)2Ar. With regard to Ag+(H2O)2Ar complex, the Ar atom tends to attach to M+, while Cu+(H2O)2Ar prefers the isomer which the Ar atom binds to H atom of the water molecule. Moreover, the calculated binding energies of the Ar atom are smaller than the infrared photon energy, and so it is possible to obtain the infrared spectra for M+(H2O)2Ar (M = Cu, Ag, Au) complexes. Futhermore, tagging Ar atom to metal cation yields a minor perturbation on the infrared spectra, whereas binding Ar atom to an OH site leads to large red shift in OH stretching vibrations.Various possible starting geometries are optimized using MP2 method for Mδ(H2O)1,2 (M = Cu, Ag, Au,δ= 0 and -1). The lowest-energy structures are confirmed, and the vibrational frequencies are calculated. The results show that the ground state structures of M(H2O) (M = Cu, Ag, Au) have Cs symmetry in which the noble mental atoms M (M = Cu, Ag, Au) are bound to O atom. The ground state structures of M(H2O)2 (M = Cu, Ag, Au) are with C1 symmetry. For M(H2O)2 (M = Cu, Ag, Au), the lengths of OH bond elongate, and the bond angles of HOH increase, compared to the correpoding values of (H2O)2. Moreover, in the lowest energy structures of M-(H2O), noble mental anion M- connect to H atom of H2O molecule, and there is a M--H…O hydrogen bond. The global minimum structures of M-(H2O)2 (M = Cu, Ag, Au) have a cyclic structure, with two inequivalent H-bonds and one water-water hydrogen bond. Relative to the OH stretch frequencies of H2O and (H2O)2, the corresponding frequencies of Mδ(H2O)1,2 (M = Cu, Ag, Au,δ= 0 and -1) are shifted to the red.
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