A surface-enhanced hyper-Raman and surface-enhanced Raman scattering study of trans-1,2-bis(4-pyridyl)ethylene adsorbed onto silver film over nanosphere electrodes. Vibrational assignments: Experiment and theory

Abstract

We present theoretical and experimental studies of the infrared (IR) spectroscopy, normal Raman spectroscopy (NRS), surface-enhanced Raman spectroscopy (SERS), and surface-enhanced hyper-Raman (SEHRS) spectroscopy of trans-1,2-bis(4-pyridyl)ethylene (BPE). This centrosymmetric molecule is expected to have no common Raman and hyper-Raman lines provided that it is not strongly perturbed by adsorption on the surface. The measured SERS spectrum, obtained under electrochemical conditions on Ag film over nanosphere (AgFON) electrodes, shows a well defined C=C stretch band that is not seen in the SEHRS spectrum, but many of the other bands overlap closely. We use ab initio calculations for isolated BPE to assign the spectra, and find excellent agreement between the calculated and measured IR and SERS spectra, and good agreement between the calculated and measured SEHRS spectrum. We find that the apparently overlapping IR, SERS, and SEHRS bands are in fact due to modes that have similar vibrational characteristics but different symmetry. Our results indicate that SEHRS spectra are consistent with the expected (three photon) selection rules and intensities. This rules out an alternative mechanism in which the observed spectrum arises from surface second harmonic generation (SHG) followed by SERS excited at the second harmonic frequency.

Surface-Enhanced Hyper-Raman Scattering: A New Road to the Observation of Low Energy Molecular Vibrations

“…Note that an alternative excitation mechanism, involving SHG followed by SERS, was shown to be inefficient for generating a strong enough signal to compete with the SEHRS signal. 30 The determination of the molecular hyperpolarizability is beyond the scope of the present work, but it is worth mentioning that numerical methods have been specifically developed for its computation, as density-functional theory and Hartree−Fock methods based on Taylor expansion of the hyperpolarizability The Journal of Physical Chemistry C Article and perturbation method.…”

Rapid Detection and Recognition of Organic Pollutants at Trace Levels by Surface-Enhanced Raman Scattering

“…All of them show the three main Raman bands of BPE, Δν = 1639, 1610, and 1200 cm -1 , which can be assigned to the C=C stretching mode, aromatic ring stretching mode and in-plane ring mode, respectively. [38] The SERS intensity of the Ag nanorods grown on thin Ag film are higher than others and the SERS intensity of the Ag nanorods on Al film is larger than that on Ti film. The Ag nanorods on Si film show the smallest SERS intensity.…”

Проявление Сильного Квадрупольного Взаимодействия И Особенности В Спектрах Гигантского Комбинационного Рассеяния И Усиленного Гиперкомбинационного Рассеяния Молекулы 4,4'-Бипиридина

“…В результате в молекуле возникают два типа колеба-тельных состояний: симметричные и антисимметричные с неприводимыми представлениями A и B 1 и очень близкими колебательными частотами. Сходная ситуация описывается в работах [8,14], где подобные пары на-блюдались в молекуле транс-1,2-бис(4-пиридил)этилена (trans-1,2-bis(4-peridyle)ethylene). Эта молекула также состоит из двух бензольных колец, слабо связанных через цепочку атомов углерода, и имеет группу симмет-рии C 2h .…”