Probing nanoscopic droplet interfaces in aqueous solution with vibrational sum-frequency scattering: A study of the effects of path length, droplet density and pulse energy

We present a description of sum frequency scattering experiments to probe the interfacial vibrational spectrum of nanoscopic oil droplets dispersed in water. SF scattering measurements as a function of optical path length, infrared (IR) pulse energy and particle density show that for different IR excitation wavelengths a different optimum experimental geometry exists. The optimum optical path length matches roughly the 1/e absorbance length in D2O of the used IR frequency. The intensity depends linearly on the particle density. The SF intensity also scales linearly with the IR pulse energy, whereas no changes are observed in the spectral shape.