Atomic Spectroscopy | Interaction of Light with Matter

 Electromagnetic Radiation

Electromagnetic radiation consists of waves of the electromagnetic field, propagating through space, carrying electromagnetic radiant energy. It includes radio waves, microwaves, infrared, light, ultraviolet, X-rays, and gamma rays. All of these waves form part of the electromagnetic spectrum.

Interaction of light with matter:

Absorb

Emit

Transmit

 

       Matter              

 

Relationship of frequency, Energy, and wavelength:

Frequency is inversely proportional to Wavelength. Wavelength (ƛ) is defined as the distance between two consecutive crusts and troughs while frequency(f) is defined as the number of waves produced in one second.

ƛ=1/f

ʋ=c/ƛ

Frequency ʋ is directly proportional to Energy E.

E=hʋ=hc/ƛ

Where h is the Planks constant and its value is 6.62607015 × 10−34 Js.

Spectroscopy:

The Study of properties of matter through the interaction of different frequency components with the Electromagnetic spectrum is called spectroscopy.

Spectrum

The wavelengths of electromagnetic radiation that are emitted or absorbed by an object or substance, atom, or molecule are called a spectrum.

Spectral Series:

It is divided into further five classes given below:

      Lyman series

      Balmer series

      Paschen Series

      Brackett Series

      Pfund series

History of Atomic Spectroscopy

·         Jonannes Marcus Marci of Kronland (1595-1667) in Eastern Bonemia can probably be considered the first spectroscopic scientist. He was interested in the phenomenon of the rainbow and performed experiments to explain it.

·         In 1666, Issac Newton perform a solar experiment that didn't conclude anything.

·         Wollaston repeats Newton's experiment in 1802 and reported “The solar spectrum is intersected by dark lines”.

·         Frown Hoffer investigated the dark lines and was able to determine the specific or characteristic wavelength. He reported his experiment in 1823.

·         Atomic emission and Atomic absorption spectroscopy was first observed by Kirchhoff and Frown Hoffer.

·         Atomic absorption spectroscopy was experimentally observed by Elon Walsh in 1955

·         Atomic emission spectroscopy was observed by Bunsen in 1920.

In 1962, Alkemade observed atomic fluorescence.

Principle of Atomic Absorption Spectroscopy

When the beam of EMR of characteristic wavelength is passed through vaporized atom present in a flame of plasma then the atom absorbs these radiations and decreases its intensity which is directly proportional to the atom present in the ground state.

The technique involves the absorption of electromagnetic radiation (UV-Visible) by ground-state neutral atoms in the gas phase of their own specific resonance wavelength.

The sample solution is aspirated into the flame and converted into an atomic vapor. The atoms in the flame are excited thermally by the flame and most of these remain in the ground state.

The degree of absorption is proportional to the ground state population of atoms present in the flame.

The relative population of the ground state and excited state population at a given temperature may be estimated by Maxwell-Boltzmann Equation.

In AAS, the ground state population of atoms is important and is measured.

It is independent of temperature.

Flame photometry and AAS are considered complementary in sensitivity. Their comparative analysis is given below:

Flame Emission spectroscopy atomic	Atomic absorption spectroscopy
Elements with low excitation energies are determined by FES.	Elements with high excitation energies are determined by AAS.
Wavelengths are emitted from atoms.	Wavelengths are absorbed by atoms.
Beer’s Law does not obey.	Beer’s Law is obeyed.
Limited to alkali and alkaline earth metals.	Useful for more than 70 metals.