Both Inter- and Intramolecular Coupling of O–H Groups Determine the Vibrational Response of the Water/Air Interface

Abstract

Vibrational coupling is relevant not only for dissipation of excess energy after chemical reactions but also for elucidating molecular structure and dynamics. It is particularly important for O-H stretch vibrational spectra of water, for which it is known that in bulk both intra- and intermolecular coupling alter the intensity and line shape of the spectra. In contrast with bulk, the unified picture of the inter/intra-molecular coupling of O-H groups at the water-air interface has been lacking. Here, combining sum-frequency generation experiments and simulation for isotopically diluted water and alcohols, we unveil effects of inter- and intramolecular coupling on the vibrational spectra of interfacial water. Our results show that both inter- and intramolecular coupling contribute to the O-H stretch vibrational response of the neat HO surface, with intramolecular coupling generating a double-peak feature, while the intermolecular coupling induces a significant red shift in the O-H stretch response.

Temperature and polarization dependent Raman spectra of liquid H2O and D2O

“…Moreover, open questions remain regarding the influence of both intermolecular and intramolecular OH⋯OH resonance coupling on the spectral shape and intensity of the OH stretch band of H 2 O (and the OD band of D 2 O). [17,42,43] The likely importance of Fermi resonance coupling is evidenced, for example, by recent 2D-IR experiments that have confirmed the facile energy exchange between the bend and stretch modes of water. [44,45] Furthermore, twice the observed frequency of the HOH (or DOD) bend of water overlaps with the broad OH (or OD) stretch band; thus, Fermi resonance is expected to significantly influence the shape of the coupled bend overtone and OH stretch band.…”

“…This discrepancy is likely due, at least in part, to the fact that most of the theoretical predictions of water spectra incorporate the effects of Fermi resonance coupling between the OH stretch fundamental and HOH bend overtone. Moreover, open questions remain regarding the influence of both intermolecular and intramolecular OH⋯OH resonance coupling on the spectral shape and intensity of the OH stretch band of H 2 O (and the OD band of D 2 O) . The likely importance of Fermi resonance coupling is evidenced, for example, by recent 2D‐IR experiments that have confirmed the facile energy exchange between the bend and stretch modes of water .…”

Structure from Dynamics: Vibrational Dynamics of Interfacial Water as a Probe of Aqueous Heterogeneity

“…Isotopic dilution of water can exclude the contribution of the energy splitting of the two identical O–H groups, the Fermi resonance, and the intermolecular coupling, differentiating the spectra of the O–H stretch modes at the water–air and isotopically diluted water–air interface. 8,62,63 This allows us to determine if the two peaks in the hydrogen-bonded water region are from two different types of water or two coupled vibrational modes. 11,64 Transitioning from H 2 O to HDO can also be used to differentiate between relaxation pathways.…”

Contribution of Fermi and Darling–Dennison resonances to the formation of Raman spectra of water and water–ethanol solutions

“…However, the studies, in which the role of DDR in the formation of the band 5900–7450 cm −1 was studied experimentally, are unknown for the authors of this paper. The spectra of the stretching vibrations overtone of H 2 O and D 2 O were studied in papers . The authors noted a shift of the band towards high frequencies with increasing temperature (similarly to the corresponding shift of the band of stretching vibrations of fundamental tone), but they did not connect the process of formation of the band of overtones with resonance of Darling–Dennison.…”

“…The spectra of the stretching vibrations overtone of H 2 O and D 2 O were studied in papers. [35][36][37][38][39][40][41][42][43][44] The authors noted a shift of the band towards high frequencies with increasing temperature (similarly to the corresponding shift of the band of stretching vibrations of fundamental tone), but they did not connect the process of formation of the band of overtones with resonance of Darling-Dennison.…”