Molecular Spectroscopy

Spectroscopy and Electromagnetic Radiation

• Spectroscopy is the interaction between electromagnetic radiation and matter, giving rise to electromagnetic spectra.
• Analysis of these spectra provides valuable information about the atomic structure and molecular bonding of organic and inorganic compounds.
• Electromagnetic radiation has two models: wave and corpuscular.
• Electromagnetic waves consist of two waves oscillating perpendicular to one another and transmitted through space.
• Light is a part of electromagnetic radiation, and its speed is similar to that of electromagnetic disturbances.

Properties of Electromagnetic Waves

• Electromagnetic waves are simple harmonic motion and have properties of sine waves.
• They have a displacement (y), amplitude (A), angular velocity (ω), and frequency (ν).
• The wave number (ν) is equal to 1/λ, and ν = C/λ.
• The energy of electromagnetic radiation (E) is related to frequency (ν) and wavelength (λ) by E = hν = hC/λ.

Quantization of Energy

• Planck's experiment showed that energy emitted by a hot black body is quantized, meaning it only occurs in discrete energies.
• The energy of an oscillator is discontinuous, and only certain discrete energies are allowed.
• The energy of electromagnetic radiation is related to the frequency and wavelength by E = hν = hC/λ.

Effects of Electromagnetic Radiation on Atoms

• Electromagnetic radiation can cause elevation of electrons from lower to higher energy levels, leading to molecular vibrations, rotations, and spin of nuclei or electrons.
• The energy required to free an electron from an atom is called the work function.

Atomic Spectra

• Atomic spectra are the result of absorption or emission of radiation by atoms.
• The absorption or emission of radiation always occurs in energy quanta of a definite size (hν).
• Quanta can only be absorbed by matter if their size exactly equals the energy change in some possible atomic or molecular process.
• Each type of physical process is associated with a particular frequency (ν) of the spectra.

Types of Atomic Spectra

• Continuous spectrum (Thermal spectra): comes from hot, dense objects like the sun, stars, and any body above 0 K.
• Line spectra:
  • Emission line spectra: occur when electrons return to the ground state, producing photons of different energies.
  • Absorption line spectra: occur when electrons absorb energy, jumping to higher energy levels.