We study the vibrational dynamics of the bending mode at 1730 cm-1 of proton hydration structures in Nafion membranes with polarization-resolved infrared (IR) pump-probe spectroscopy. The bending mode relaxes to an intermediate state with a time constant T1 of 170±30 fs. Subsequently, the dissipated energy equilibrates withTeq of 1.5±0.2 ps. The transient absorption signals show a long-living anisotropy, which indicates that for part of the excited proton hydration clusters the vibrational energy dissipation results in a local structural change, e.g. the breaking of a local hydrogen bond. This structural relaxation relaxes with a time constant of 38±4 ps.

Elsevier B.V.
Chem. Phys. Lett.
Ultrafast Spectroscopy

Liu, L., Lotze, S., & Bakker, H. (2017). Vibrational and Structural Relaxation of Hydrated Protons in Nafion Membranes. Chem. Phys. Lett., 670, 102–108. doi:10.1016/j.cplett.2016.10.062