The angular dependence of the sum-frequency signal radiated in a total internal reflection geometry is studied both theoretically and experimentally for a monolayer of octadecyl trichlorosilane chemisorbed upon CaF<sub>2</sub>. A predicted signal enhancement of 2 orders of magnitude is verified experimentally. The line amplitudes ofthe CH-stretching modes of the terminal methyl group depend strongly on the polarization geometry, the molecular hyperpolarizability, and the angles of incidence of the fundamental waves. By exploiting both the angular and the polarization dependence of the line amplitudes, one can obtain the molecularproperties unambiguously. The hyperpolarizability tensor elements of the terminalmethyl group are determined directly from the sum-frequency spectra.
© 1997 Optical Society of America
J. Löbau and K. Wolfrum, "Sum-frequency spectroscopy in total internal reflection geometry: signal enhancement and access to molecular properties," J. Opt. Soc. Am. B 14, 2505-2512 (1997)