Spectrometry Techniques

Spectroscopic Techniques

Energy States of Matter

• Energy States: Various energy states associated with molecules/atoms of matter.
  • At any given moment, particles of matter possess different energy states.
  • Energy states can be changed when particles interact with photons of electromagnetic radiation.
• Types of Energy States:
  1. Rotational Energy States: Smallest differences in energy change.
  2. Vibrational Energy States: Greater energy differences than rotational states.
  3. Electronic Transition Energy States: Highest energy differences.
  • Ground State: The state with the lowest possible energy, also the state of highest probability at room temperature.

Interaction of Radiation with Matter

• Photon Interaction: When radiation interacts with a substance, energy states of its particles may change through energy absorption or emission.
• Quantised Energy States: The energy differences between energy states and the energy of photons are both quantised.
• Energy Absorption Example: For an electron to move from ground electronic state $S<em>0$ to the first electronic excited state $S</em>1$, it must absorb a photon with energy:
  • $E = hV$ (where $h$ is Planck's constant and $V$ is the frequency of the radiation).
• Key Points:
  • Changes in energy states require a quantised amount of energy.
  • Electromagnetic radiation of appropriate photon energy is necessary for energy state transitions.
  • Transition from higher to lower energy states results in radiation emission.

Spectroscopic Techniques Overview

• Spectroscopy: The field that employs radiations that contain the right amount of energy to instigate changes in energy states.
• Applications: Various spectrometry techniques utilize these transitions (e.g., UV-visible spectrometry).

Types of Transitions and Related Techniques

1. Electronic Transitions:
   • Require photons from the UV and visible regions.
   • Only UV and visible photons have enough energy for electronic transitions.
   • UV-visible spectrometry techniques utilize these transitions.
2. Vibrational Transitions:
   • Require photons from the Infra-red region.
   • Infra-red photons match the energy difference between vibrational states.
   • Infra-red and Raman spectrometry techniques utilize these transitions.
3. Rotational Transitions:
   • Require photons from microwave radiation.
   • Microwave photon energies match the differences in energy of rotational states.
   • Rotational spectroscopies employ these transitions.

UV-Visible Spectrometry

• Definition: The use of photons from UV and visible regions to study the qualitative and quantitative compositions of chemical compounds.
• Wavelength Range: 200 nm to 800 nm is used in this technique.
• Mechanism: UV-visible radiation causes transitions of electrons from low-energy molecular orbitals to high-energy molecular orbitals.
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