Probing the Raman Scattering Tensors of Individual Molecules

• Published in: The journal of physical chemistry. B 2006-02, Vol.110 (6), p.2459-2461
• Main Authors: Shegai, Timur O, Haran, Gilad
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp055750f

Single-molecule experiments provide new views into the mechanisms behind surface-enhanced Raman scattering. It was shown previously that spectra of individual rhodamine 6G molecules adsorbed on silver nanocrystal aggregates present stronger fluctuations in two low-frequency bending modes, at 614 and 773 cm-1. Here we use polarization spectroscopy to show that these bands are enhanced by a resonant process whose transition dipole is rotated by 15±10° with respect to the molecular transition dipole. We also show that the polarization function remains stable over the whole time scale of a measurement, indicating that molecular reorientation with respect to the surface is unlikely. Together these findings provide further support to the involvement of a charge-transfer resonance in the enhancement of the low-frequency bands and allow us to suggest a model for the orientation of rhodamine 6G molecules at Raman hot spots.