TY - JOUR
T1 - Resonance Raman and Temperature-Dependent Electronic Absorption Spectra of Cavity and Noncavity Models of the Hydrated Electron
AU - Casey, Jennifer R.
AU - Larsen, Ross E.
AU - Schwartz, Benjamin J.
PY - 2013/2/19
Y1 - 2013/2/19
N2 - Most of what is known about the structure of the hydrated electron comes from mixed quantum/classical simulations, which depend on the pseudopotential that couples the quantum electron to the classical water molecules. These potentials usually are highly repulsive, producing cavity-bound hydrated electrons that break the local water H-bonding structure. However, we recently developed a more attractive potential, which produces a hydrated electron that encompasses a region of enhanced water density. Both our noncavity and the various cavity models predict similar experimental observables. In this paper, we work to distinguish between these models by studying both the temperature dependence of the optical absorption spectrum, which provides insight into the balance of the attractive and repulsive terms in the potential, and the resonance Raman spectrum, which provides a direct measure of the local H-bonding environment near the electron. We find that only our noncavity model can capture the experimental red shift of the hydrated electron's absorption spectrum with increasing temperature at constant density. Cavity models of the hydrated electron predict a solvation structure similar to that of the larger aqueous halides, leading to a Raman O-H stretching band that is blue-shifted and narrower than that of bulk water. In contrast, experiments show the hydrated electron has a broader and red-shifted O-H stretching band compared with bulk water, a feature recovered by our noncavity model. We conclude that although our noncavity model does not provide perfect quantitative agreement with experiment, the hydrated electron must have a significant degree of noncavity character.
AB - Most of what is known about the structure of the hydrated electron comes from mixed quantum/classical simulations, which depend on the pseudopotential that couples the quantum electron to the classical water molecules. These potentials usually are highly repulsive, producing cavity-bound hydrated electrons that break the local water H-bonding structure. However, we recently developed a more attractive potential, which produces a hydrated electron that encompasses a region of enhanced water density. Both our noncavity and the various cavity models predict similar experimental observables. In this paper, we work to distinguish between these models by studying both the temperature dependence of the optical absorption spectrum, which provides insight into the balance of the attractive and repulsive terms in the potential, and the resonance Raman spectrum, which provides a direct measure of the local H-bonding environment near the electron. We find that only our noncavity model can capture the experimental red shift of the hydrated electron's absorption spectrum with increasing temperature at constant density. Cavity models of the hydrated electron predict a solvation structure similar to that of the larger aqueous halides, leading to a Raman O-H stretching band that is blue-shifted and narrower than that of bulk water. In contrast, experiments show the hydrated electron has a broader and red-shifted O-H stretching band compared with bulk water, a feature recovered by our noncavity model. We conclude that although our noncavity model does not provide perfect quantitative agreement with experiment, the hydrated electron must have a significant degree of noncavity character.
KW - Optical spectroscopy
KW - Quantum simulation
KW - Raman spectroscopy
KW - Solvated electron
UR - http://www.scopus.com/inward/record.url?scp=84874259850&partnerID=8YFLogxK
U2 - 10.1073/pnas.1219438110
DO - 10.1073/pnas.1219438110
M3 - Article
C2 - 23382233
AN - SCOPUS:84874259850
SN - 0027-8424
VL - 110
SP - 2712
EP - 2717
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 8
ER -