Spectrochimica Acta Part A 56 (2000) 2107 – 2115 Surface enhanced Raman scattering of 2,2 biquinoline adsorbed on colloidal silver particles Joydeep Chowdhury, Manash Ghosh, T.N. Misra * Department of Spectroscopy, Indian Association for the Cultiation of Science, Calcutta 700 032, India Received 21 January 2000; received in revised form 9 March 2000; accepted 9 March 2000 Abstract Surface enhanced Raman scattering (SERS) in silver sol and normal Raman spectra in the bulk and in solution of 2,2 biquinoline (BQ) molecule have been investigated. The observed Raman bands along with their corresponding FTIR bands have been assigned based on the established assignments of the vibrational bands of the parent napthalene and quinoline molecules. Existence of both the cis and trans form of the BQ molecule in solution and in the bulk are inferred from the normal Raman and FTIR spectra, whereas SERS study reveal that in the surface adsorbed state the molecule exists in the cis form. Definite evidence of the charge transfer interaction to the overall contribution in the SER enhancement have been reported. The excitation profile also supports the CT interaction. Estimated enhancement factor of the principal SERS bands indicate that the molecule is adsorbed on the silver surface through both the nitrogen atoms with the molecular plane almost perpendicular to the surface. This preferred orientation of the molecule is in conformity with its existence in the cis form in the surface adsorbed state. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Raman scattering; SERS; Biquinoline; Silver colloids; Charge transfer www.elsevier.nl/locate/saa 1. Introduction Surface enhanced Raman scattering (SERS) has opened up wide research fields in Raman spec- troscopy and in physics and chemistry of inter- faces [1–3]. It is an established technique to study the physical and chemical interactions between the adsorbate molecule and the metal surface. It is now established that there are two main contribu- tions to the overall SERS effect [4]. One is the electromagnetic contribution which is generally attributed to the increase in the local field of the adsorbate because of the excitation of the surface plasmons on the metal surface [2] and the other is the chemisorption [5 – 8], attributed to short dis- tance chemical effects due to the charge transfer between the metal and the adsorbed molecule. Quinoline and its various derivatives form sta- ble complexes with metal cations [9,10] and these metal chelates find extensive applications in ana- lytical chemistry and in hydrometallurgy [11,12]. Such applications of these quinoline molecules * Corresponding author. Tel.: +91-33-4734971; fax: +91- 33-4732805. E-mail address: sptnm@mahendra.iacs.res.in (T.N. Misra). 1386-1425/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S1386-1425(00)00263-8