Ian A. Finneran, Ralph Welsch, Marco A. Allodi, Thomas Francis Miller, and Geoffrey A. Blake
http://pubs.acs.org/doi/abs/10.1021/acs.jpclett.7b02106
Fundamental properties of molecular liquids are governed by long range interactions that most prominently manifest at terahertz (THz) frequencies. Here we report the detection of nonlinear THz photon-echo (rephasing) signals in liquid bromoform, using THz-THz-Raman spectroscopy. Together, the many observed signatures span frequencies from 0.5-8.5 THz, and result from couplings between thermally populated ladders of vibrational states. The strongest peaks in the spectrum are found to be electric dipole-forbidden and polarizability-allowed and may arise from nonlinearities in the intramolecular dipole moment surface driven by intermolecular interactions.
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