Frequency resolved interferometric coherent Raman spectroscopy with incoherent light: Raman frequency shifts, dephasing rate constants, and nonresonant hyperpolarizabilities of mixtures of benzene in hexane

Abstract

A newly developed frequency and time resolved coherent anti-Stokes Raman scattering (CARS) technique is used to study properties of the A1g ring breathing mode of benzene in a dilution series of liquid mixtures with n-hexane. Recent advances in the interferometric use of incoherent light in CARS measurements (I(2)CARS) provide excellent precision in the recovered dephasing rate constants, vibrational frequencies, and the ratios of the resonant to non-resonant contributions to the signal. Using this technique we observe a more than two-fold decrease in the dephasing rate constant of the vibration, accompanied by a 0.54 cm−1 increase in the vibrational frequency in the limit of infinite dilution of benzene in n-hexane. These changes in the vibrational spectrum are discussed in terms of the condensed phase dynamics that are responsible. It is also seen how the non-resonant contributions to the signal manifest themselves quantitatively in these frequency and time resolved I(2)CARS measurements.