The dephasing dynamics of a vibrational coherence can reveal the interactions of chemical functional groups with their environment.  To investigate such processes at a surface, we employ free-induction decay sum-frequency generation (FID-SFG) to measure the time it takes for free OH stretch oscillators at the mineral/water interfaces to loose their collective coherence.  By employing non-collinear optical parametric amplification (NOPA) technology and FID-SFG, we showed that the single free OH peak observed in non-linear vibrational SFG spectroscopy of an alumina/water (Al2O3/H2O) interface actually corresponds to two distinct oscillators oriented opposite to each other. The total dephasing time, T2, of the free OH stretch modes at the Al2O3/H2O interface (pH~13, KOH) was measured with sub-40 fs temporal resolution.  Our results revealed that the free OH oscillators associated with interfacial water dephase on the time-scale of ~90 fs, whereas the dephasing of interfacial alumina hydroxyls is an order of magnitude slower.

Ultrafast vibrational sum-frequency spectroscopy and dynamics of OH groups at mineral/aqueous interfaces

247th National Meeting (2014)

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