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  Section: Practical Skills in Chemistry » Instrumental techniques
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Introduction to spectroscopy

Instrumental techniques
  Basic spectroscopy
    Introduction to spectroscopy
    UV Ivisible spectrophotometry
    Fluorescence spectrophotometry
    Phosphorescence and luminescence
    Atomic spectroscopy
  Atomic spectroscopy
    Atomic Absorption Spectroscopy
    Atomic Emission Spectroscopy
    Inductively coupled plasma
    Decomposition techniques for solid inorganic samples
  Infrared spectroscopy
  Nuclear magnetic resonance spectrometry
    1H-NMR spectra
    13C-NMR spectra
  Mass spectrometry
    Interfacing mass spectrometry
  Chromatography ~ introduction
    The chromatogram
  Gas and liquid chromatography
    Gas chromatography
    Liquid chromatography
    High-performance liquid chromatography
    Interpreting chromatograms
    Optimizing chromatographic separations
    Quantitative analysis
    The supporting medium
    Capillary electrophoresis
    Capillary zone electrophoresis (CZE)
    Micellar electrokinetic chromatography (MEKC)
  Electroanalytical techniques
    Potentiometry and ion-selective electrodes
    Voltammetric methods
    Oxygen electrodes
    Coulometric methods
    Cyclic voltammetry
  Radioactive isotopes and their uses
    Radioactive decay
    Measuring radioactivity
    Chemical applications for radioactive isotopes
    Working practices when using radioactive isotopes
  Thermal analysis

The absorption and emission of electromagnetic radiation of specific energy (wavelength) is a characteristic feature of many molecules, involving the movement of electrons between different energy states, in accordance with the laws of quantum mechanics. Electrons in atoms or molecules are distributed at various energy levels, but are mainly at the lowest energy level, usually termed the ground state. When exposed to energy (e.g. from electromagnetic radiation), electrons may be excited to higher energy levels (excited states), with the associated absorption of energy at specific wavelengths giving rise to an absorption spectrum. One quantum of energy is absorbed for a single electron transition from the ground state to an excited state. On the other hand, when an electron returns to its ground state, one quantum of energy is released; this may be dissipated to the surrounding molecules (as heat) or may give rise to an emission spectrum. The energy change (ΔE) for an electron moving between two energy states, E1 and E2, is given by the equation:
⇒ Equation [26.3] ΔE = E1E2 =

where h is the Planck constant and ν is the frequency of the electromagnetic radiation (expressed in Hz or s−1). By substituting for frequency in [26.3J it IS possible to rearrange this equation to give the expression:

⇒ Equation [26.4] ΔE = hc


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