Optical Absorption of Water: Coulomb Effects versus Hydrogen Bonding

Abstract

The optical spectrum of water is not well understood. For example, the main absorption peak shifts upwards by 1.3 eV upon condensation, which is contrary to the behavior expected from aggregation-induced broadening of molecular levels. We investigate theoretically the effects of electron-electron and electron-hole correlations, finding that condensation leads to delocalization of the exciton onto nearby hydrogen-bonded molecules. This reduces its binding energy and has a dramatic impact on the line shape. The calculated spectrum is in excellent agreement with experiment.

Electronic structure of liquid water from polarization-dependent two-photon absorption spectroscopy

“…This picture of a compressed Rydberg orbital is often used to describe the 0.9 eV shift of the à 1 1 B 1 transition in the 1PA spectrum of water. 30,34 Furthermore, the decreasing experimental 2PA polarization ratio at low energy ͓Fig. 5͑b͔͒ is consistent with the low ratio that we calculate for the à 1 1 B 1 state of the isolated molecule, and supports the notion that the character of that state is not significantly perturbed in the liquid.…”

“…31 An alternate view is one in which the excited molecular orbitals are partially delocalized over one or more neighboring solvent molecules. [32][33][34][35][36] Unfortunately, a clear and consistent theoretical description of the electronically excited states of liquid water is not yet available because accurate electronic structure calculations are extremely difficult for such strongly interacting molecules. [34][35][36][37][38][39][40][41] 2PA spectroscopy provides a new window on the electronic transitions of liquid water because the symmetry selection rules are different than for linear spectroscopy.…”

Optical properties of azobenzene-functionalized self-assembled monolayers: Intermolecular coupling and many-body interactions

“…This behavior is mainly due to LFE, counteracting the red-shift induced by the band-gap narrowing, as an effect of intermolecular electronic interactions. [60][61][62] Moreover, contrary to the case of the d-SAM where the out-of-plane component of Im M dominates the spectrum in the considered frequency range, here Im M and Im ⊥ M show different spectral weights in specific energy regions. This is obviously related to the character of the excitations involved.…”

“…Similar effects, due to the coupling of the electronic wave-functions and to the consequent delocalization of the resulting e-h pairs as an effect of the increased intermolecular interactions, have been discussed already in the context of organic crystals. 39,41,60 When the effects of local fields are accounted for, as in the singlet spectra, they additionally contribute to an overall blue-shift of the oscillator strength and, most importantly, to its redistribution to higher energies.…”

Excitation-energy dependence of the mechanism for two-photon ionization of liquid H2O and D2O from 8.3to12.4eV

“…Recent calculations confirm that the excited state wave functions are indeed diffuse, 49 and that even the first excited state includes delocalized electron density on nearby water molecules in ice. 50 …”