Saint Petersburg State University, Russia
Title: Strong quadrupole light-molecule interaction and surface-enhanced optical processes
Biography: Aleksey Mickhailovich Polubotko
Surface-Enhanced Optical Processes, SERS, SEHRS and SEIRA are of great interest for physics, chemistry and biology since they all allow increasing strongly the sensitivity of these spectroscopic methods and there is a fundamental physical mechanism, which causes the enhancement in these processes. It is so-called strong quadrupole light-molecule interaction, arising in surface electromagnetic fields, strongly varying in space near a rough metal surface. Just this interaction is responsible for the enhancement in SERS 106, in SEIRA 103 -104 and in SEHRS 1012 and significantly higher. Moreover, this interaction is the base for implementation of Single Molecule Detection by SERS, when the enhancement can achieve the value 1014 -1015. This interaction is responsible for appearance of forbidden lines in all these processes on molecules with sufficiently high symmetry. Indeed, these strong lines were observed in ethylene and diprotonated in SEIRA and in pyrazine and phenazine in SEHRS. They are the lines, caused by vibrations with the unit irreducible representation of a molecule symmetry group. Such strong lines are observed in SERS as well. However, they are caused by vibrations with the irreducible representations, which describe transformational properties of the dipole moment component , which is perpendicular to the metal surface. At present the theory of the above mentioned processes, based on this concept is created and explains the most of the observed phenomena, accompanying SERS, SEHRS and SEIRA.