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Raman Microscopy
Published in John Girkin, A Practical Guide to Optical Microscopy, 2019
The Raman effect is a light scattering phenomenon in which the electromagnetic field associated with light interacts with the electric field of the molecule, and in particular with the localized electric field around each molecular bond. The effects of light interacting with a molecule can be seen in Figure 10.1. When light interacts with a molecule most of the time it will be elastically scattered, with the result that the emerging light has the same wavelength as the incoming beam and there is no exchange of energy with the sample. This type of inelastic scattering is known as Rayleigh scattering. If the light is in the near, or mid, infrared there is a possibility that the photon will be absorbed to alter the vibrational levels of the molecule, leading to a transfer of energy to the molecule, in effect heating the sample. If the photon has sufficient energy it can also be absorbed causing an electron to be excited to a higher electron energy level, leading to fluorescence. This is not a scattering event as was discussed in Chapters 2 and 6. However, around 1 photon in 107 can be scattered by the molecule and emerge from this encounter with a change in wavelength.
Review of Nanoscale Spectroscopy in Medicine
Published in Sarhan M. Musa, Nanoscale Spectroscopy with Applications, 2018
Chintha C. Handapangoda, Saeid Nahavandi, Malin Premaratne
Raman scattering is the inelastic scattering of a photon that results in a frequency change in the emitted photon. Stokes Raman scattering produces a photon whose energy (hence frequency) is less than that of the absorbed photon, whereas anti-Stokes Raman scattering produces a photon whose energy (hence frequency) is greater than that of the absorbed photon. Figure 11.11 shows the energy level diagram for elastic Rayleigh scattering and Stokes and anti-Stokes Raman scattering. Approximately 1 in 10s photons that are incident on a given bond vibration are Raman scattered (Talley et al. 2005). The low sensitivity of Raman spectroscopy due to the inherent low probability of a photon being Raman scattered has made its applications limited (Talley et al. 2005). Due to this extremely low cross-section, Raman spectroscopy is generally limited to samples that are relatively concentrated and requires high incident power and long integration times to generate Raman spectra of detectable signals (Talley et al. 2005). Biological systems generally involve low concentrations of chemicals such that conventional Raman scattering cannot be used. However, surface-enhanced Raman scattering (SERS) can be used to dramatically increase the Raman scattering cross-section (Talley et al. 2005).
Optical Studies of Carrier Dynamics and Non-Equilibrium Optical Phonons in Nitride-Based Semiconductors
Published in Kong-Thon Tsen, and Nanostructures, 2018
Consider an incident laser beam of angular frequency ωi that is scattered by a semiconductor and the scattered radiation is analyzed spectroscopically, as shown in Figure 7.3. In general, the scattered radiation consists of a laser beam of angular frequency ωi accompanied by weaker lines of angular frequencies ωi ± ω. The line at an angular frequency ωi – ω is called a Stokes line; whereas, at an angular frequency, ωi + ω is usually referred to as an anti-Stokes line. The important aspect is that the angular frequency shifts co are independent of ωi. In this way, this phenomenon differs from that of luminescence, in which it is the angular frequency of the emitted light that is independent of ωi. The effect just described is called the Raman effect. It was predicted by Smekal48 and is implicit in the radiation theory of Kramers and Heisenburg.49 It was discovered experimentally by Raman50 and by Lansberg and Mandel’shtam 51 in 1928. It can be understood as an inelastic scattering of light in which an internal form of motion of the scattering system is either excited or absorbed during the process.
Theoretical study on spectral differences of polypeptides constituted by L- and D-amino acids
Published in Molecular Physics, 2021
Ren-Hui Zheng, Wen-Mei Wei, Yan-Ying Liu
Raman is an inelastic scattering process, which detects the frequency difference between the incident light and the scattering light. We present non-resonant Raman in Figure 4. The difference between LKα14 and D-LKα14 is little, which is similar to the IR spectra. In the range of 1000–2000 cm−1, the intensest peak with a value of 1.1 × 10−31 cm2/sr is at 1520 cm−1 from the CH3 bending vibration of the Leu side chain. The Raman intensity of the amide I vibration with a value of 1.8 × 10−32 cm2/sr at 1777 cm−1 is smaller than that of the amide III vibration with a value of 7.1 × 10−32 cm2/sr at 1368 cm−1. Generally, Raman intensity is weak when the corresponding IR intensity is large. This rule can also be applied to the 2539 cm−1 intramolecular hydrogen bond vibrational mode and its Raman intensity is 5.7 × 10−33 cm2/sr, which is about one order of magnitude smaller than that of the amide III vibration. The 2540 cm−1 mode is a non-symmetric vibration with a strong IR intensity and a weak Raman intensity.
Quantification of anhydrous ethanol and detection of adulterants in commercial Brazilian gasoline by Raman spectroscopy
Published in Instrumentation Science & Technology, 2019
Andressa Cristina de Mattos Bezerra, Danieli de Oliveira Silva, Gustavo Henrique Machado de Matos, Josuel Pereira dos Santos, Claudio Neves Borges, Landulfo Silveira, Marcos Tadeu Tavares Pacheco
Raman spectroscopy is based on the inelastic scattering of the incident light through the molecule, involving the changes in the polarizability of the irradiated molecule and the emission of a photon, carrying information of the energy vibrational bonds of the molecule. The emission spectrum is characterized by bands at frequencies referred to the energy levels of the molecule. Since the vibrational energy levels are unique to each molecule, the Raman spectrum provides a fingerprint of a particular molecule. The spectra may provide information on molecular structure, dynamics, and environment.[14]
Concentrated Nonequilibrium HD for the Cross Calibration of Hydrogen Isotopologue Analytics
Published in Fusion Science and Technology, 2020
Sebastian Mirz, Tim Brunst, Robin Größle, Bennet Krasch
Raman spectroscopy uses the Raman effect, the inelastic scattering of (laser) light on molecules, in order to probe molecular rotational and vibrational energy levels. Since these energy levels depend on the reduced mass of the molecule, this method can distinguish between different molecules and even isotopologues. The measured signal is the intensity of the scattered light depending on the wavelength. The intensity of the scattered light depends on the number of molecules in the observed volume and therefore on the concentration.