Photons are scattered inelastically in Raman spectroscopy. It makes use of a monochromatic light source, often a visible, near-infrared, or near-ultraviolet laser, however X-rays can also be employed. The laser causes the energy of the laser photons to change up or down by interacting with phonons, molecular vibrations, or other excitations in the system. The energy shift reveals details about the system's vibrational patterns. The foundation of Raman spectroscopy is the interaction of light and matter's chemical bonds. Making inferences from Raman spectra can provide detailed information on chemical structure, polymorphism, crystallinity, and molecular dynamics.
Applications of Raman Spectroscopy
- When studying chemical and intramolecular interactions and identifying compounds, chemists utilize Raman spectroscopy.
- Raman microscopy can be used in nanotechnology to examine nanowires and learn more about their structure.
- Raman spectroscopy can be utilized in solid state chemistry and the biopharmaceutical sector to identify the active pharmaceutical ingredient (API) as well as its polycrystalline form (if more than one is present).
- Raman spectroscopy is used in a variety of biological and medical processes. The study of low-frequency collective motions in proteins and DNA and their biological activities is made easier by the confirmation of the existence of low-frequency phonons in both DNA and proteins.
- Raman spectroscopy is used in solid state physics to characterize materials, gauge temperatures, and identify sample crystal orientation. Characteristic phonon modes can be used to distinguish solid materials. The ratio of the Stokes and anti-Stokes intensity of the spontaneous Raman signal provides details about the population of phonon modes. Other low-frequency excitations of solids can be seen using Raman spectroscopy.
Fig 1. Experimental IR and Raman spectra compared with the predicted scaled IR spectrum at the B3LYP/cc-pVDZ level of the S-(À)-limonene oxide: (a) experimental Raman spectrum; (b) experimental IR spectrum; (c) sum of the predicted scaled IR spectra of the five most stable conformers. (Moreno J.R.A, et al. 2009)
In order to simulate Raman spectrum, Alfa Chemistry creates and uses computational techniques based on quantum chemistry principles (density general function theory and wave function-based methodologies). These findings aid in understanding the molecular characteristics. Raman scattering simulation techniques can be roughly divided into static and dynamic techniques based on the degree of environment that each one covers. Our quick and effective services include:
- Raman spectrum prediction based on static calculations
We have developed static Raman spectroscopy prediction methods for predicting the chemical structure, crystallinity, and molecular dynamics information of molecules. The static calculations rely on the geometric optimization of the system and are typically performed in the harmonic approximation. Intensity tracking has been used to selectively converge certain bands of interest. The LR-TDDFT method and the (RT)-TDDFT method are widely used by us. In static calculations, we can also include environmental effects by adding some solvent molecules to the simulation or by using non-quantum mechanical approximations of the environment, such as polarization continuum models or QM/MM methods.
- Raman spectrum prediction based on dynamic calculations
At Alfa Chemistry, we perform dynamical methods for vibrational spectroscopy in the framework of DFT-based MD, commonly known as ab initio MD (AIMD), where atomic nuclei move electrons classically on a potential energy surface generated by a quantum mechanical description. . To derive a quantum mechanical description of the system and its surroundings in the condensed phase, we apply periodic boundary conditions. In AIMD, the temporal autocorrelation function of the Placzek polarization rate provides the NR scattering cross-section.
Fig 2. The chemical structures of GQDs with 19, 48 and 79 conjugated rings, respectively, and the UV-Vis-NIR absorption spectra of the GQDs. (Dervishi E, et al. 2019)
Raman spectroscopy predictions provide fluorescence spectra of highly complex molecules using TDDFT computational methods, facilitating further experiments and enhancing the understanding of chemical processes for customers worldwide. Our personalised full service will meet your innovative learning needs. If you are interested in our services, please feel free to contact us. We are happy to work with you and witness your success!
- Moreno J.R.A, et al. (2009). "Conformational Preference of A Chiral Terpene: Vibrational Circular Dichroism (VCD), Infrared and Raman Study of S-(-)-Limonene Oxide." Physical Chemistry Chemical Physics. 11(14): 2459-2467.
- Dervishi E, et al. (2019). "Raman Spectroscopy of Bottom-Up Synthesized Graphene Quantum Dots: Size and Structure Dependence." Nanoscale. 11:16571-16581.