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Spectroscopy I



                        PS03CORC01_PS03CIPC01_PS03CINC01_PS03CPHC01_PS03CANC01
                                                          Unit: I


                         A
                         Atomic Absorption Spectroscopytomic Absorption Spectroscopy
                         Atomic Absorption SpectroscopyAtomic Absorption Spectroscopy






               I.1.  Introduction
                       Spectroscopy  is  the  study  of  the  interaction  between  matter  and  electromagnetic

               radiation.
                       Atomic absorption, along with atomic emission, was first used by Guystav  Kirchhoff

               and Robert Bunsen in 1859 and 1860, as a means for the qualitative identification of atoms.
               Although atomic emission continued to develop as an analytical technique, progress in atomic

               absorption  languished  for  almost  a  century.  Modern  atomic  absorption  spectroscopy  was

               introduced in 1955 as a result of the independent work of A. Walsh and C. T. J. Alkemade. 18
               Commercial  instruments  were  in  place  by  the  early  1960s,  and  the  importance  of  atomic

               absorption as an analytical technique was soon evident.


               I.2.  ABSORPTION OF RADIATION BY ATOMS

                       AAS is based on the absorption  of  radiant  energy  by  free  gas  phase  atoms. In the
               process of absorption, an atom changes from a low-energy state to a higher energy state.

                       Gas  phase  atoms  do  not  vibrate  in  the  same  sense  that  molecules  do.  Also,  they  have
               virtually no rotational energy. Hence no vibrational or rotational energy is involved in the

               electronic  excitation  of  atoms.  As  a  result,  atomic  absorption  spectra  consist  of  a  few  very

               narrow  absorption  lines,  in  contrast  to  the  wide  bands  of  energy  absorbed  by  molecules  in
               solution.

                       Each element has a specific number of electrons “located” in an orbital structure that is
               unique  to  each  element.  The  lowest  energy  electronic  configuration  of  an  atom  is  called  the

               ground state.
                       The  ground  state  is  the  most  stable  electronic  state.  If  energy  ∆E  of  exactly  the  right

               magnitude is applied to a free gas phase atom, the energy will be absorbed. An outer electron

               will be promoted to a higher energy, less stable excited state. The frequencies and wavelengths
               of radiant energy capable of being absorbed by an atom are predicted from ∆E = hν = hc/λ. The






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