We study the ultrafast relaxation dynamics of hydrated proton clusters in acetonitrile using femtosecond mid-infrared pump-probe spectroscopy. We observe a strong dependence of transient absorption dynamics on the frequency of excitation. When we excite the OH vibrations with frequencies ≤3100 cm-1 we observe an ultrafast energy relaxation that leads to heating of the local environment of proton. This response is assigned to the OH vibrations of the water molecules in the core of the hydrated proton cluster. When we excite with frequencies ≥3200 cm-1 we observe a relatively slow vibrational relaxation with a T1 time constant ranging from 0.22±0.04 ps at νex=3200 cm-1 to 0.37±0.02 ps at νex=3520 cm-1. We assign this response to water molecules in the outer part of the hydrated proton cluster.

Additional Metadata
Keywords Physical and Theoretical Chemistry, Materials Chemistry, Surfaces, Coatings and Films
Publisher ACS
Funder NWO , ERC
Persistent URL dx.doi.org/10.1021/acs.jpcb.9b02067
Journal J. Phys. Chem. B
Citation
Sofronov, O.O, & Bakker, H.J. (2019). Vibrational Relaxation Dynamics of the Core and Outer Part of Proton-Hydration Clusters. J. Phys. Chem. B, 123(29), 6222–6228. doi:10.1021/acs.jpcb.9b02067


Additional Files
16539M_H.Bakker.pdf Author Manuscript , 720kb
16539ESI.pdf Author Manuscript , 1mb