Ab Initio Frequency Calculations of Pyridine Adsorbed on an Adatom Model of a SERS Active Site of a Silver Surface

Abstract

Ab initio and Urey−Bradley calculations of normal modes were carried out to analyze the frequency shifts observed on the SERS spectrum of pyridine obtained on a Ag surface. A molecular model with a Ag atom attached to the pyridine nitrogen was used in the Urey−Bradley calculation. The frequency shifts in the SERS spectrum were calculated by adding K(Ag−N) and F(Ag· · ·Cα) force constants and by adjusting the ring stretches according to how their bond lengths changed in an ab initio calculation with a (Ag−Py)+ model. The ab initio calculations were done with the HF, MP2, and B3LYP methods using the 3-21G, 6-31G, 6-31G*, 6-31G**, and LanL2DZ basis sets. The surface active site was modeled in the calculation by means of Ag0, Ag+ atoms, and a Ag4 + pyramidal cluster structure. The calculations were evaluated on how well they matched the observed frequencies, the ν(Ag−N) stretch, and the frequency shifts for the SERS spectrum in an electrochemical environment. The calculation with the Ag4 + model yielded the best results although the (Ag−Py)+ model also gives reasonable results. All calculations were consistent with an edge-on interaction between pyridine and the electrode surface and a Ag+ species as part of the surface active site.

Binding Interactions and Raman Spectral Properties of Pyridine Interacting with Bimetallic Silver–Gold Clusters

“…Electrostatic interactions enhances the NÀ Ag bond in PyÀAg 4 + and PyÀAg 5 + . [43,46] Similar results were also obtained in the pyridine-bimetallic cluster complexes.…”

“…Although interactions between pyridine and homogeneous metallic clusters (such as Ag, [31,33,43,44] Ag + , [31,45,46] Au, [31,33] Ag 2 , [32,47,48] Au 2 , [32,47,48] Ag 4 , [32,47] Ag 4 + , [43] Ag 5 + , [48] and Ag 6 [49] ) have been investigated theoretically, no investigation has been reported on pyridine interacting with a mixed AgAu cluster.…”

“…[47] For the Py/Ag system, Vivoni et al suggested that the NÀAg bond length is close to about 2.32 . [43] Bilic et al reported the shortest NÀAu bond length of 2.43 for pyridine at the top site of Au(111) at a low coverage. [52] The NÀAg (Au) bond distances coincide with our values calculated using the B3LYP method for chemisorbed pyridine on metal clusters.…”

Surface-enhanced Raman Scattering Study of the Binding Modes of a Dibenzotetraaza[14]annulene Derivative with DNA/RNA Polynucleotides

“…26,27 The latter causes the charge redistribution in the nitrogen consisting moieties, responsible for the observed band shifts. 28,29 Apart from chemisorption, electrostatic interactions between the positive charge in the side substituents and the negatively charged citrate ions on the silver surface enable placement of the DBTAAbpp molecules in close vicinity to the metal nanoparticles.…”

Nanoscale Insights into Enhanced Raman Spectroscopy

“…Among them is the formation of a metal-molecule complex, anion and field gradient effects [8,[13][14][15][16]. CE can be separated into a resonant and nonresonant mechanism.…”