Red-shift Of Vibrational Frequency Research Articles

Ab Initio Investigation of the Micro-species and Raman Spectra in Ca(NO3)2 Solution

In this work, the structural details and Raman spectra of the Ca(NO3)2(H2O) n=0–10 clusters were studied by using ab initio method. The results show that the main species in the cluster is the contact ion pair (CIP) when n = 1–7. When n = 8–10, the main species changes into solvent shared ion pair (SIP) CaNO3(H2O) n …NO3 − in the bidentate form. One of the r Ca–N distances remains unchanged at ~2.95 A, while the other one increases to more than 4.8 A. The hydration distance r Ca–O remains at 2.42 A. The contact between Ca2+ and NO3 leads to a red shift of the v 1–NO3 − band while the polarization of water by Ca2+ leads to a blue shift. The vibrational frequency of water molecules remains unchanged for the same types of water molecules. Hydrogen bonds are the main reason for the red shift of vibrational frequency of water molecules.

Pentagonal dodecahedron methane hydrate cage and methanol system — An ab initio study

Density functional theory based studies have been performed to elucidate the role of methanol as an methane hydrate inhibitor. A methane hydrate pentagonal dodecahedron cage’s geometry optimization, natural bond orbital (NBO) analysis, Mullikan charge determination, electrostatic potential evaluation and vibrational frequency calculation with and without the presence of methanol using WB97XD/6-31+ +G(d,p) have been carried out. Calculated geometrical parameters and interaction energies indicate that methanol destabilizes pentagonal dodecahedron methane hydrate cage (1CH4@512) with and without the presence of sodium ion. NBO analysis and red shift of vibrational frequency reveal that hydrogen bond formation between methanol and water molecules of 1CH4@512 cage is favourable subsequently after breaking its original hydrogen bonded network.

Beyond the Gold–Hydrogen Analogy: Doping Gold Cluster with H-atom–O2 Activation and Reduction of the Reaction Barrier for CO Oxidation

The gold–hydrogen analogy is well established in terms of analogous chemistry exhibited by gold and hydrogen atoms. A step beyond this analogy is demonstrated here by showing that the replacement of a Au atom with a H-atom in a gold cluster can lead to considerable enhancement in its reactivity. The present computational study reveals that while the closed-shell neutral pristine gold cluster Au8 can bind only weakly with an O2 molecule, its doped counterpart Au7H shows remarkable enhancement in its binding with molecular oxygen. It also shows an increment in O–O bond length and a red shift in vibrational frequency, indicating the activation of the O2 molecule. Furthermore, the H-doped gold cluster reduces the barrier height for the environmentally important CO oxidation reaction as compared to the pristine cluster. These observations may spur further studies in the design of a cost-effective and efficient catalyst by doping gold clusters with a cheaper element like hydrogen.

DFT calculations of vibrational spectra and nonlinear optical properties for MgO nanotube clusters

The IR and Raman spectra, nonlinear optical properties of MgO nanotube clusters are studied by density-functional theory at B3LYP/6-31G(d) level. The IR spectra are match closely to those in the corresponding MgO cluster and bulk materials. The strongest peaks of the IR spectra are located in the range from 650 to 750 cm −1. The Raman spectra are very sensitive to structural variations in MgO clusters, and redshift of vibrational frequency is observed in Raman spectra as increasing cluster length. The motion of the strongest peaks in spectra is discussed. The total dipole moment and the first hyperpolarizabilities oscillate between zero and a constant when the layer is grown for the layer dependence of symmetry in MgO nanotube clusters.