Infra-red spectroscopy

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Infra red radiation makes some bonds vibrate more

  • some molecules abosorb energy from IR radiation. Extra energy:covalent bonds: more vibrations
  • Only molecules made of different atoms can absorb IR Radiation, because the bond polarities change as they vibrate - e.g. O2 and N2 don't absorb IR: but CO2, H2O, NO and NH3 do :)
  • Gases that do absorb IR: greenhouse gases because they stop some of IR radiation emitted by Earth from escaping into space.

Different molecules absorb different frequencies

  • Gas molecules' bonds have certain fixed energy levels. They are called 'quantised levels'. So a bond's energy can only jump from one level to another: like moving up a staircase.
  • This means that only frequencies of radiation corresponding to particular amounts of energy: absorbed.
  • Different molecules absorb different frequencies of radiation.

How IR spectroscopy works...

  • A beam of IR radiation is passed through a sample of a chemical.
  • IR radiation: absorbed by the covalent…


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