Interoscillator coupling effects on the OH stretching band of liquid water

Abstract

We have studied the OH stretch spectrum in water to explore the effects of interoscillator coupling. Both H2O, which may have significant intra and intermolecular coupling, and dilute HOD in D2O, which is isotopically decoupled, were studied over a broad range of temperature from −33 °C to 160 °C. By adding a small amount of a calibration dopant, we obtained quantitative spectra. We found interoscillator coupling plays a large role at all temperatures. At high temperature, intramolecular coupling contributes to a downshift in the peak position for H2O as compared to HOD. Intermolecular coupling, however, still has some influence at high temperature. At low temperature, the large excess intensity below 3200 cm−1 in H2O compared to HOD we find is due to an enhanced Raman cross section due to intermolecularly coupled in-phase OH stretch oscillations. We define a degree of delocalization for coupling as the idealized number of perfectly in-phase oscillators that could cause the enhanced scattering and find N≂2 for liquid H2O at −33 °C. An exact isosbestic crossing is not found and this can be understood given the changing line shape that the intermolecular coupling can induce. All the properties of the spectrum approach those found in amorphous solid water or ice near the supercooled water anomalous temperature, Ts≂−45 °C.

Simulations of the infrared, Raman, and 2D-IR photon echo spectra of water in nanoscale silica pores

“…24 They found that the key differences between bulk and confined water are a general blue-shifting of the spectrum along with the appearance of a shoulder on the high-frequency side. They also observed a decrease in the red-shifted shoulder around 3200 cm −1 that appears in the neat H 2 O spectrum, 77,78 but is absent in our simulated spectra for HOD/D 2 O.…”

Hydrogen Bond Network of Water around Protein Investigated with Terahertz and Infrared Spectroscopy

“…Between 18 and 120 THz (600-4000 cm À1 ), pure water exhibits two noticeable dispersions assigned to the H-O-H bending (49 THz) and O-H stretching (~100 THz) (99). Especially, the latter is strongly coupled with intermolecular HB dynamics (49)(50)(51)(52)(55)(56)(57)(58), and in general, the O-H stretching frequency red-shifts as the intermolecular HB becomes stronger (100)(101)(102)(103)(104). On the other hand, the complex dielectric constant of albumin crystal exhibits the several amide bands (66,105,106) between 30 and 50 THz, the C-H stretching (87 THz) (107), and N-H stretching (~100 THz) (66) in the MIR region.…”

“…In addition, an O-H stretching vibration around 100 THz (3330 cm À1 ) has been conventionally used as an index to estimate the HB strength (49)(50)(51)(52)(53)(54)(55)(56)(57)(58). In general, the stronger the HBs that a given water molecule establishes with its neighbors, the more red-shifted is the O-H stretching frequency (49,57,58).…”

Vibrational Line Shapes, Spectral Diffusion, and Hydrogen Bonding in Liquid Water

“…Others have argued that the complications of intramolecular and intermolecular vibrational coupling make simple interpretations of these spectra difficult [7-9, 69, 70, 72]. In fact, many believe that the lower-frequency peak in the VV Raman spectrum arises from a collective mode [7,69,70,72].…”