화학공학소재연구정보센터
Journal of Physical Chemistry B, Vol.110, No.6, 2459-2461, 2006
Probing the Raman scattering tensors of individual molecules
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 degrees 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.