Phase-sensitive sum frequency vibrational spectroscopic study of air/water interfaces: H2O, D2O, and diluted isotopic mixtures

Abstract

Using phase-sensitive sum-frequency vibrational spectroscopy with a carefully chosen phase reference, we revisited the vibrational spectra of vapor/water interfaces of neat H2O and D2O as well as HDO in diluted isotopic mixtures. Using z-cut quartz as the phase reference, with proper frequency scaling, the gross features of the OH and OD stretching spectra from H2O and D2O and from HDO in two isotopic mixtures look similar and agree with those reported earlier, but differences are also apparent. In particular, a weak positive band at low frequencies, which has been asserted by molecular dynamic simulations but not detectable in the experimental OH spectrum with pure H2O, is now visible in the OD spectrum. The differences must arise from the change of intermolecular interaction of water molecules with their surrounding molecules upon exchange of the isotopes.

Interaction of α‐Synuclein with Phospholipids and the Associated Restructuring of Interfacial Lipid Water: An Interface‐Selective Vibrational Spectroscopic Study

“…It is important to note that previous phase‐sensitive/heterodyne‐detected VSFG measurements [20, 27, 37, 38] showed a positive Imχ (2) band around 3200 cm −1 and was assigned to the “ice‐like” or “strongly H‐bonded water pair”. The positive band however is not so prominent in the carefully measured recent Imχ (2) spectra, [35, 36, 39–41] which is in conformity with the present data (black‐dashed curve in Figure 2 a ) measured using high resolution displacement sensor (see the Supporting Information) as well as our previously reported spectra that were phase‐corrected by internal referencing [42–44] . With the addition of 20 μM αS in water, the surface pressure ( π =surface tension of neat water (72.8 mN m −1 )—surface tension of αS solution) becomes ≈20 mN m −1 , indicating adsorption of αS on water surface.…”

Reorientation-induced relaxation of free OH at the air/water interface revealed by ultrafast heterodyne-detected nonlinear spectroscopy

“…In the other two relaxation mechanisms, i.e., the intramolecular energy transfer from the free OH to HB OH stretch and that to the bend overtone, the relaxation is expected to be strongly decelerated in HOD generated with isotopic dilution, because of a large frequency mismatch between the OH and OD stretch vibrations and that between the OH stretch and the HOD bend overtone (Fig. 4b ) 41 – 43 . The present experiment shows that the T 1 time of the excited free OH does not change with the isotopic dilution.…”

Vibrational mode frequency correction of liquid water in density functional theory molecular dynamics simulations with van der Waals correction

“…These correction factors can be also used to predict the vibrational spectra of H 2 O by scaling the vibrational frequency axis with the factor of 1/0.735 in the D 2 O spectra. 89 In fact, the vibrational spectra lineshapes of H 2 O and D 2 O become quite similar after the frequency axis is scaled by this factor. 90 Finally, we note that our correction scheme include a red-shift induced by nuclear quantum effects.…”

“…The free O-D stretch frequency of 2714 cm À1 is obtained from ref. 89, while the simulated free O-D stretch frequencies using DFT-MD simulations were obtained from ref. 34.…”