Resonance Raman spectroscopy
Resonance Raman spectroscopy (RR spectroscopy or RRS) is a variant of
Resonance Raman spectroscopy has much greater sensitivity than non-resonance Raman spectroscopy, allowing for the analysis of compounds with inherently weak Raman scattering intensities, or at very low concentrations.
Theory
In Raman scattering, photons collide with a sample and are scattered with a difference in energy: The scattered photons may be higher or lower in energy (have a shorter or longer wavelength) than the incident photons. This difference in energy is caused by excitation of the sample to a higher or lower vibrational energy level: if the sample was initially in an excited vibrational state, the scattered photon may be higher in energy than the incident photon (anti-Stokes Raman scattering). Otherwise, the scattered photon has a lower module of energy than the incoming photon (Stokes Raman scattering). Among the two phenomena, Stokes shift and anti-Stokes shift, the former is the most likely to occur. As a consequence, the relative intensity of Raman spectra acquired in Stokes mode is more intense than the other. For most materials, Raman scattering is extremely weak compared to Rayleigh scattering, in which light is scattered without loss of energy.[9] Raman-scattered light, which contains information about vibrational transitions, is therefore difficult to observe for many substances.
Resonance Raman spectroscopy takes advantage of an increase in the intensity of Raman scattering when the incident photons match the energy of an
Resonance Raman scattering differs from fluorescence in that it occurs without vibrational relaxation during the lifetime of the excited electronic state. It thus exhibits much narrower line widths than fluorescence.[11] However, fluorescence and resonance Raman scattering co-occur in many materials, and interference from fluorescence may complicate the collection of resonance Raman spectra.[3]
Variants
Typically, resonance Raman spectroscopy is performed in the same manner as ordinary Raman spectroscopy, using a single
- Time-resolved resonance Raman spectroscopy: By using pulsed lasers with a controllable delay between pulses, resonance Raman spectroscopy can be used to monitor changes in the sample over time, following a laser-induced photochemical change or temperature increase.[12] This method has been used to examine the dynamics of excited electronic states,[13] binding of oxygen or other gases to heme-containing proteins,[14] and protein dynamics.[12][15]
- Resonance hyper-Raman spectroscopy: Excitation of the sample occurs by forbidden in ordinary resonance Raman spectroscopy, with intensity enhancement due to resonance, and also simplifies collection of scattered light. It is especially useful for molecules that are both polar and polarizable.[16]
- Surface-enhanced resonance Raman spectroscopy: A hybrid of RRS and nanoparticles and a laser matching the surface plasmon resonance of the nanoparticles is used for excitation. If the wavelength of the surface plasmon matches that of an electronic transition in the sample, the Raman scattering will be greatly enhanced compared to ordinary RRS.[17]
- Resonance Raman microscopy: A microscope is used to focus the excitation laser onto a particular point in the sample, and spectra are collected for many such points. The Raman intensity at different points can then be assembled into a microscopic image of the sample. By appropriate choice of excitation wavelength, a microscopic map of the distribution only of a component of interest can be made.[18]
Applications
Because of its selectivity and sensitivity, resonance Raman spectroscopy is typically used to study molecular vibrations in compounds that would have very weak and/or complex Raman spectra in the absence of resonance enhancement. Like ordinary Raman spectroscopy, resonance Raman is compatible with samples in water, which has a very weak scattering intensity and little contribution to spectra. However, the need for an excitation laser with a wavelength matching that of an electronic transition in the analyte of interest somewhat limits the applicability of the method.[8]
Pigments and Dyes
Dyes and pigments, all of which exhibit electronic transitions in the visible part of the electromagnetic spectrum, were among the first substances to be studied by resonance Raman spectroscopy. Resonance Raman spectra of
Proteins
Proteins have been widely examined by resonance Raman spectroscopy. Protein-bound
Nucleic acids and viruses
Resonance Raman spectroscopy with ultraviolet excitation can be used to examine the chemistry, structure, and intermolecular interactions of
Nanomaterials
Resonance Raman spectroscopy has also been used to characterize the structure and photophysical properties of
See also
- Scattering
- Rayleigh scattering
- X-ray Raman spectroscopy
- Coherent anti-Stokes Raman spectroscopy
- Tip-enhanced Raman spectroscopy
- Vibronic spectroscopy
- Depolarization ratio
References
- ISSN 0021-9584.
- ^ Drago, R.S. (1977). Physical Methods in Chemistry. Saunders. p. 152.
- ^ ISSN 0003-2700.
- .
- ^ ISSN 0570-0833.
- PMID 8277873.
- ^ PMID 7752933.
- ^ PMID 18082644.
- .
- S2CID 7686714.
- ^ .
- ^ S2CID 208954659.
- S2CID 20448809.
- PMID 2998161.
- ISSN 0009-2673.
- PMID 20055673.
- PMID 18443681.
- PMID 24050305.
- PMID 23351238.
- ISSN 1075-4261.
- PMID 21604722.
- PMID 11761332.
- ISSN 0002-7863.
- PMID 34604840.
- ^ PMID 22335827.
- PMID 10410793.
- PMID 25163005.
- S2CID 93629086.
Further reading
- Long, Derek A (2002). The Raman Effect: A Unified Treatment of the Theory of Raman Scattering by Molecules. Wiley. ISBN 978-0471490289.
- Que, Lawrence Jr., ed. (2000). Physical Methods in Bioinorganic Chemistry: Spectroscopy and Magnetism. Sausalito, CA: University Science Books. pp. 59–120. ISBN 978-1-891389-02-3.
- Raman, C.V.; Krishnan, K.S. (1928). "A Change of Wave-Length in Light Scattering". Nature. 121 (3051): 619. doi:10.1038/121619b0.
- Raman, C.V.; Krishnan, K.S. (1928). "A New Type of Secondary Radiation". Nature. 121 (3048): 501–502. S2CID 4128161.
- Skoog, Douglas A.; Holler, James F.; Nieman, Timothy A. (1998). Principles of Instrumental Analysis (5th ed.). Saunders. pp. 429–443. ISBN 978-0-03-002078-0.
- Landsberg, G.S; Mandelshtam, L.I. (1928). "Novoye yavlenie pri rasseyanii sveta. (New phenomenon in light scattering)". Zhurnal Russkogo Fiziko-khimicheskogo Obschestva, Chast Fizicheskaya (Journal of Russian Physico-Chemical Society, Physics Division: 60–4.
- Chao, R.S.; Khanna, R.K.; Lippincott, E.R. (1975). "Theoretical and experimental resonance Raman intensities for the manganate ion". Journal of Raman Spectroscopy. 3 (2–3): 121–131. .
External links
- https://www.spectroscopyonline.com/view/exploring-resonance-raman-spectroscopy
- http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Vibrational_Spectroscopy/Raman_Spectroscopy/Raman%3A_Interpretation
- http://www.horiba.com/us/en/scientific/products/Raman-spectroscopy/Raman-academy/Raman-faqs/what-is-polarised-Raman-spectroscopy/
- Kelley, A.M. "Resonance hyper-Raman spectroscopy". University of California, Merced.