Types of Spectroscopy
Because different molecules and characteristics of molecules absorb at different energies of light, there is a need for different forms of spectroscopy. The types are:
Absorption spectroscopy is a technique in which the power of a beam of light measured before and after interaction with a sample is compared.
Fluorescence spectroscopy uses higher energy photons to excite a sample, which will then emit lower energy photons.
When X-rays of sufficient frequency (energy) interact with a substance, inner shell electrons in the atom are excited to outer empty orbitals, or they may be removed completely, ionizing the atom. The inner shell "hole" will then be filled by electrons from outer orbitals. The energy available in this de-excitation process is emitted as radiation.
Liquid solution samples are aspirated into a burner or nebulizer/burner combination, dissolved, atomized, and sometimes excited to a higher energy electronic state. This change in state will be measured as either emission or absorption.
- Plasma Emission Spectroscopy
Similar to flame atomic emission spectroscopy, plasma emission spectroscopy uses a plasma flame and has largely replaced it.
Many atoms emit or absorb visible light. In order to obtain a fine line spectrum, the atoms must be in a gas phase. This means that the substance has to be vaporised. The spectrum is studied in absorption or emission. Visible absorption spectroscopy is often combined with UV absorption spectroscopy.
All atoms absorb in the ultraviolet region, because these photons are energetic enough to excite outer electrons. This is measured in UV spectroscopy.
Infrared spectroscopy offers the possibility to measure different types of inter atomic bond vibrations at different frequencies.
Raman spectroscopy uses the inelastic scattering of light to analyse vibrational and rotational modes of molecules. The resulting 'fingerprints' are an aid to analysis.
- Nuclear Magnetic Resonance (NMR)
Nuclear magnetic resonance spectroscopy analyzes the magnetic properties of certain atomic nuclei to determine different electronic environments of hydrogen, carbon, or other atoms in an organic compound. This is used to help determine the structure of the compound.
Photoemission spectroscopy measures the electron emission from matter after the absorption of energetic photons.
Used to examine the properties of specific isotope nuclei in different atomic environments, Mossbauer spectroscopy is named after the Mossbauer effect, which is based on the resonant absorption of characteristic gamma rays.