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Introduction to Spectroscopy


Spectroscopy - The study of matter and it’s interaction with light, sound or particles (radiation)

  • Can be through absorption, emission or scattering

What is light?

  • Light is EM radiation, consisting of an electric field and a perpendicular magnetic field
  • Light travels at varying speed through a medium, being energy/wavelength dependent

What is matter?

  • A substance that has inertia and occupies physical space
  • Made up of particles with different mass, charge and size

Postulates of quantum mechanics

  • Particles can only exist in discreet states, determined by their amount of energy
  • Interactions of particles cause energy to be emitted or absorbed
\[ \Delta E=E_{excited}−E_{ground} \]
  • The frequency \(\nu\) and wavelength \(\lambda\) of the radiation is related to its energy
\[ \Delta E=h\nu=\frac{hc}{\lambda} \]

Energy states

  • Energy states arise from molecular/atomic orbitals.
  • The ground state is the lowest energy configuration of the compound
  • As energy is increased, the electrons can jump into a higher orbital with a discreet amount of energy, in what’s called the excited state.
  • Rotational/vibrational states arise from energy in the bonds of the atom itself


Consist of four properties:

  • \(\nu\) frequency
  • \(\lambda\) wavelength
  • \(A\) Amplitude
  • \(T\) Period

Expressed by the formula:

\[ y=A\sin\bigg(\frac{2\pi x}{\lambda} + 2\pi \nu t\bigg) \]

Energy equation


  • \(c=3\times10^8 m\cdot s^{−1}\)
  • \(h=4.135\times 10^{−15} \text{ or } 6.626×\times10^{−34} J\)
\[ \Delta E=h\nu=\frac{hc}{\lambda} \]


\[ \lambda=\frac{c}{n\nu}\approxeq\frac{c}{\nu} \]


\[ \bar{\nu}=\frac{1}{\lambda} \]