Theoretical Study of Raman Spectra of Methanol in Aqueous Solutions: Non-Coincident Effect of the CO Stretch

Abstract

Raman spectra of the CO stretch for liquid methanol and its aqueous solutions were simulated using the combined electronic structure and molecular dynamics simulation method. The instantaneous vibrational frequencies were obtained from an empirical mapping to the electrostatic potentials, while vibrational couplings between different molecules were calculated using the transition dipole coupling model. It is found that noncoincident effects (NCEs) at high concentrations are dominated by the intermolecular couplings of CO stretch and decrease monotonically as the methanol concentration decreases. This behavior is explained as the effect of reduced methanol-methanol hydrogen bonding with the addition of water. A non-monotonic change of the NCEs defined by the peak position of the CO stretch as a function of methanol mole fraction is found, which is ascribed to band asymmetry caused by reorientational dynamics.

SERS and DFT study of 5F‐PB‐22

“…Figure shows the Raman spectral changes obtained when increasing concentrations of 5F‐PB‐22 were added to HPAg in a parallel experiment to that carried out in the UV/visible analysis (Figure b). At concentrations <7.4 × 10 −4 M 5F‐PB‐22, the only peak observed is at ~1,035 cm −1 , which can be assigned to the Raman C–O stretching mode of methanol used here as the solvent for 5F‐PB‐22. Above 7.4 × 10 −4 M and, up to 1.076 × 10 −3 M, a number of new Raman bands appear that show a continuous increase in intensity with increasing concentration.…”

Linear scaling explicitly correlated MP2-F12 and ONIOM methods for the long-range interactions of the nanoscale clusters in methanol aqueous solutions

“…6 The microscopic structures of methanolwater mixtures have been studied by various modern experimental techniques, including x-ray scattering, 7 neutron diffraction, 6,[8][9][10][11] x-ray emission spectroscopy, 12 and other spectroscopic measurements. [13][14][15] The structures, stabilities, interactions, and properties of methanol-water mixtures or clusters have also been theoretically studied by two categories of methods: (1) empirical force field potentials based molecular dynamics (MD) simulation 10,[16][17][18][19][20][21][22][23][24][25] and Monte Carlo simulation; [26][27][28][29][30][31][32][33] (2) quantum mechanics methods, including density functional theory (DFT), [34][35][36][37] high-level ab initio such as second-order Møller-Plesset perturbation (MP2), 34,35,38 a) Author to whom correspondence should be addressed. Electronic mail:…”