Theoretical insights into interaction energy, IR intensity and Raman activity enhancements of H2O adsorbed on Mg containing Zn3O3 nanoclusters: A computational study

Theoretical insights into H2O detection ability of Zn3O3 and Mg containing Zn3O3 nanoclusters are provided using density functional theory (DFT) based calculations. For this, the IR and Raman spectral properties of H2O adsorbed on Zn3O3, Zn2MgO3 (Mg as substituent) and Zn3O3Mg (Mg as interstitial atom) nanoclusters are investigated. All the species in study are optimized at B3LYP/6-31G(d,p) computational model. While Zn site of Zn3O3 is favorable for interaction of the water molecule, the site of Mg in both the Zn2MgO3 and Zn3O3Mg is preferential for interaction of H2O molecule. The complex geometry formed by H2O interacting with Mg site of Zn2MgO3 shows highest interaction energy and significant magnitudes of molecular orbital interactions. The IR intensity calculations on the stable geometries show that the symmetric mode of vibration of water molecule enhances significantly, and the predicted IR enhancement agrees with an experimental finding. The Raman activity enhancement for the symmetric vibrational mode of H2O is notable, when H2O interacts with Zn(3)O3Mg at Mg site. The observed IR and Raman enhancements are substantiated by the calculations on dipole moment and polarizability components of the complex geometries distorted along normal coordinates of H2O vibrational modes. The time dependent (TD) DFT calculations carried out at B3LYP/6-31G(d,p) computational model, envisages that Zn3O3Mg is a good SERS substrate for amplification of Raman spectral lines of H2O by surface plasmon resonance.