Fingerprints in IR OH vibrational spectra of H2O clusters from different H-bond conformations by means of quantum-chemical computations

Abstract

Abstract:The thermodynamic stabilities and IR spectra of the three water clusters (H 2 O) 20, (H 2 O) 54, and (H 2 O) 100 are studied by quantum-chemical computations. After full optimization of (H 2 O) 20,54,100 structures using the hybrid density functional B3LYP together with the 6-31+G(d, p) basis set, the electronic energies, zero-point energies, internal energies, enthalpies, entropies, and Gibbs free energies of the water clusters at 298 K are investigated. Furthermore, the OH stretching vibrational IR spectra of water molecules in (H 2 O) 20,54,100 are simulated and split into sub-spectra for different H-bond groups depending on the conformations of the hydrogen bonds. From the computed spectra the different spectroscopic fingerprint features of water molecules in different H-bond conformations in the water clusters are inferred.2

Evaluation of Thiol Raman Activities and pKa Values Using Internally Referenced Raman-Based pH Titration

“…32 This conclusion is also consistent with the observation that hydrogen bonding induces a red-shift of the O-H stretch in water. [40][41] The two thiols in 1,2-BDT are both deprotonated in the 1 M NaOH solution ( water have, to our knowledge not been reported before. Only one 1,2-BDT thiol pKa value (6.8) was reported and that is for 1,2-BDT dissolved in dimethyl sulfoxide.…”

Raman and IR Spectra of Ice Ih and Ice XI with an Assessment of DFT Methods

“…In Figure 6, the IR spectra of stretching vibrations in 16 different isomers of ice Ih are shown in the range of 3090 -3460 cm -1 . Unlike the distinct distribution of the sub-spectra of each proton group in water clusters, 75,77 the sub-spectra in ice overlap in all the 16 cases. This is also observed for the Raman spectra, shown in Figure 7.…”

“…No obvious difference between ice Ih and XI is found for the OH stretching part of the spectrum, which might suggest that the intramolecular vibrations are little affected by the proton-ordering. Figure S6) as in previous studies, [75][76][77][78] and the contribution from each group to the total spectra was projected out (in accordance with the number of H atoms of the group and their vibrational amplitudes squared [75][76][77][78] ). In Figure 6, the IR spectra of stretching vibrations in 16 different isomers of ice Ih are shown in the range of 3090 -3460 cm -1 .…”

“…In addition, the OH stretching vibrations are projected into different categories based on the contributions from different H-bond configurations as in previous studies. [75][76][77][78]  RESULTS AND DISCUSSION Assessment of DFT Methods. H-bonding between water molecules is the dominating interaction in ice.…”

“…This is also observed for the Raman spectra, shown in Figure 7. The OH stretching vibration is very sensitive to the strength of the H-bond 75,77 (the Badger-Bauer rule). [94][95][96] We see that in ice each of the H-bonded pair configuration essentially contributes to all the peaks in the OH stretching region.…”