Ramanspektroskopian

Raman spectroscopy is a spectroscopic technique based on inelastic scattering of photons by molecular vibrations. When light interacts with a sample, most photons are elastically scattered (Rayleigh), but a small fraction undergoes inelastic scattering, gaining or losing energy corresponding to vibrational transitions. The energy shifts, expressed as Raman shifts in wavenumbers (cm^-1), create a spectrum that serves as a molecular fingerprint. The phenomenon was discovered by C. V. Raman in 1928, earning him the Nobel Prize in Physics in 1930.

Instrumentation: Modern Raman systems use a monochromatic light source, typically a laser, to illuminate the sample. Scattered light is collected and filtered to remove the dominant Rayleigh line, then dispersed in a spectrograph and detected by a CCD. The resulting spectrum plots intensity versus Raman shift. Different configurations exist, including resonant enhancement, surface-enhanced Raman spectroscopy (SERS) on metallic substrates, and tip-enhanced Raman spectroscopy (TERS) for nanoscale spatial resolution.

Types and variants: Spontaneous Raman spectroscopy is the standard form; resonance Raman occurs when the excitation coincides with an electronic transition, enhancing particular vibrations; SERS increases sensitivity by several orders of magnitude via plasmonic effects; TERS combines Raman with scanning probe techniques.

Applications: It is widely used for chemical identification, material characterization, pharmaceutical analysis, biology and medical diagnostics, environmental monitoring, and art conservation. Advantages include non-destructive analysis with minimal sample preparation and compatibility with liquids; limitations include inherently weak signals, fluorescence background, and the need for careful calibration and interpretation.

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