Explore advanced spectroscopic techniques such as infrared spectroscopy, UV-Visible spectroscopy, atomic absorption spectroscopy, and mass spectrometry used in analytical chemistry for qualitative and quantitative analysis.
Spectroscopic Techniques – Quick Reference Notes
| Domain | Technique | Typical Wavelength Range | Primary Information |
|---|---|---|---|
| Electronic | UV‑Vis Absorption, Fluorescence, Phosphorescence | 200 nm – 800 nm | Electronic transitions, conjugation, band gaps |
| Vibrational | Infrared (IR), Raman, FT‑IR, Near‑IR | 2.5 µm – 25 µm (IR), 0.78 µm – 2 µm (NIR) | Bond types, functional groups, molecular symmetry |
| Rotational | Microwave, Millimeter‑wave | 0.3 mm – 10 mm | Gas‑phase molecular geometry, bond lengths |
| Nuclear | Nuclear Magnetic Resonance (NMR) | Radiofrequency (≈ 10 MHz – 1 GHz) | Chemical environment of nuclei, connectivity |
| Mass‑Based | Mass Spectrometry (MS) (often coupled with spectroscopy) | N/A (ion detection) | Molecular weight, fragmentation pattern, isotopic composition |
| Surface‑Specific | X‑ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) | Soft X‑ray (≈ 0.1–10 keV) | Elemental composition, oxidation states, surface chemistry |
| Time‑Resolved | Pump‑probe, Transient Absorption, Fluorescence Lifetime | Variable (depends on pump & probe) | Dynamics of excited states, reaction kinetics |
| Phenomenon | Physical Basis | Observed Signal |
|---|---|---|
| Absorption | Photon energy matches a transition → population moves to higher level | Decrease in transmitted intensity (Beer‑Lambert law) |
| Emission | Excited species relax → photon emitted | Fluorescence, phosphorescence, Raman scattering |
| Scattering | Incident photons interact with molecular polarizability | Raman shift (inelastic) or Rayleigh (elastic) |
| Resonance | Matching of photon energy with natural frequency of a system | Enhanced intensity (e.g., resonance Raman, ESR) |
| Relaxation | Non‑radiative processes (vibrational cooling, intersystem crossing) | Affects line shape, quantum yield, lifetimes |