Sum Frequency Generation Spectrum of a Self-Assembled Monolayer Containing Two Different Methyl Group Orientations

作者：Kett P J N; Casford M T L; Davies P B^*

来源：Journal of Physical Chemistry Letters, 2012, 3(22): 3276-3280.

DOI：10.1021/jz301363k

The theory of sum frequency generation (SFG) has recently been extended to monolayers where the SFG active functional group can adopt two different orientations [Kett, P. J. N.; Casford, M. T. L.; Davies, P. B. Mol. Phys. 2012, DOI: 10.1080/00268976.2012.711492]. This Letter compares the SFG spectra for the C-H stretching vibrations of the methyl group in a model test molecule, 2,4-dimethylbenzenethiol (DMBT), self-assembled on a gold substrate, with theoretical predictions. The spectrum in the PPP polarization combination and counterpropagating beam geometry is comprised of peaks for the two symmetric stretching bands (r(+) resonances) and a dip for the asymmetric stretching mode (r(-) resonance). This spectrum agrees with theory for the case where the methyl groups are assumed to orientate in opposite directions with respect to the surface normal. Calculated topographical plots show that the r resonances appear with the same phases as the experimental spectrum when the tilt angle of the DMBT lies between 0 and 48 degrees and the twist angle between -22 and 30 degrees.

• 出版日期2012-11-15