1. ■ The inelastic scattering of light was predicted by Smekal in 1923, it was not until 1928 that it was observed in practice. ■ The Raman effect was named after one of its discoverers, the Indian scientist Sir C. V. Raman who observed the effect by means of sunlight. ■ Raman won the Nobel Prize in Physics in 1930 for this discovery accomplished using sunlight, a narrow band photographic filter to create monochromatic light and a "crossed" filter to block this monochromatic light. He found that light of changed frequency passed through the "crossed" filter. History and Background What is Raman Spectroscopy? Beyond Just Vibrational Spectroscopy Conclusion References ■ Silverstein, R. "Spectrometric Identification of Organic Compounds" 6th Edition. ■ NIST Chemistry WebBook: http://srdata.nist.gov/gateway. ■ Application of Raman Spectroscopy and Sequential Injection Analysis for pH Measurements with Water Dispersion of Polyaniline Nanoparticles Lindfors, T.; Ivaska, A. Anal. Chem.; (Article); 2007; 79(2); 608-611. DOI: 10.1021/ac061069d . ■ S ilica-Immobilized Zinc β-Diiminate Catalysts for the Copolymerization of Epoxides and Carbon Dioxide Kunquan Yu; Christopher W. Jones, Organometallics (Article); 2003, 22,2571-2580 ■ Complete Refrence in Presentation Portfolio….. Raman Spectroscopy BY: MARIAM ISRAIEL CHEM 405/ Fall 2007 Instructor: Dr. Hanae Haouari Chemistry Department (NJCU) Raman scattering of light by molecules may be used to provide information on a sample's chemical composition and molecular structure. It is used to study: 1. Vibrational 2. Rotational 3. Other low-frequency modes in a system It relies on Raman scattering of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range. 1- The Raman effect occurs when light impinges upon a molecule and interacts with the electron cloud of the bonds of that molecule. 2- The incident photon excites one of the electrons into a virtual state. 3- For the spontaneous Raman effect, the molecule will be excited from the ground state to a virtual energy state, and relax into a vibrational excited state, which generates Stokes Raman scattering or anti-Stokes Raman scattering if it was already in an elevated vibrational energy state. 4- A molecular polarizability change with respect to the vibrational coordinate as a result the molecule exhibits the Raman effect. 5- Finally, the amount of the polarizability change will determine the intensity, whereas the Raman shift is equal to the vibrational level that is involved. Basic Theory ► Application of Raman Spectroscopy and Sequential Injection Analysis for pH Measurements with Water Dispersion of Polyaniline Nanoparticles Based on this article Raman Spectroscopy was used to conduct pH measurements from 1800 to 1000 cm-1at 633-nm laser excitation wavelength. In this study, the pH-sensitive CH ═ CH stretching band at 1422 cm-1 and C — H in-plane bending band of the quinoid form at 1163 cm-1 were chosen as the primary wavenumbers. Raman spectra of the water dispersion of polyaniline (PANI) nanoparticles (1:10) measured at 1422 cm-1. The measurements were done between pH 7.0 and 10.4 using the Raman techniques. CH ═ CH and C ═ N stretching bands of the quinoid form at 1420 and 1443 cm-1 are well separated at higher pH values. ► Silica-Immobilized Zinc β -Diiminate Catalysts for the Copolymerization of Epoxides and Carbon Dioxide Raman Spectra of species: (A) SBA-15-SH-Capped (B) [(BDI-1)ZnOMe] 2 (C) species after [(BDI-1)ZnOMe] 2 ● The infrared spectra will be collected using a liquid cell and the FTIR spectrometer. ● Liquid samples are placed in a fluorescence cell and in the sample compartment for the Raman experiments. Applications and Experimental procedures of Raman Spectroscopy Raman Instrumentation and Basic Experimental Procedures Raman Spectroscopy showing sensitivity to phonon modes in a solid Raman Spectroscopy showing sensitivity to size of particles The Raman Effect Stokes versus Anti-Stokes Results Comparing IR and Raman Spectra Some vibrational modes will either be Raman or IR active. ■ Raman spectroscopy is useful for analyzing molecules without a permanent dipole moment which would not show up on an IR spectrum. ■ A useful 'exclusion rule' states that for molecules with an inversion centre, no modes can be both IR and Raman active. ■ It can be used to determine bond lengths in non-polar molecules. ■ It is useful for determining the identity of organic and inorganic species in solution