Lecture Notes: Atomic Spectra and Spectral Analysis

Introduction

• We can determine the composition of stars, nebulas, and distant planets by analyzing their atomic spectra.
• This process involves using spectral analysis to identify elements present in these celestial bodies.

Model of an Atom

• Focus on the hydrogen atom: consists of one proton and one electron.
• Electrons are not particles orbiting like planets; they are quantum objects with wave properties, forming an electron cloud.
• The cloud represents the electron, not a physical path.

Electron Energy Levels

• Electrons can absorb energy, which may allow them to escape the atom or jump to a higher energy state.
• Potential Well Analogy:
  • Electron in a potential well: energy needed to 'escape' the well.
  • Different energy levels exist within the well.

Quantum Mechanical Model

• Electrons have multiple shapes (orbitals) at higher energy levels.
• Energy levels are denoted by the principal quantum number.

Energy Transitions

• Ground state: electron's lowest energy state.
• Excited states: higher energy levels.
• Electrons lose energy when transitioning from excited to lower energy levels, emitting photons.
• Emission of photons corresponds to specific wavelengths (colors).

Emission Spectrum

• Specific wavelengths emitted by electrons transitioning between energy levels.
  • Hydrogen: transitions visible as specific colored lines in the spectrum.
• Each element has a unique emission spectrum, acting as a signature.

Spectral Analysis

• Technique to identify elements based on emitted or absorbed wavelengths.
• Emission Spectrum: Produced by heating elements and observing emitted light.
• Absorption Spectrum: Seen when observing light passing through cooler outer layers of a star.
  • Missing wavelengths indicate absorption by elements.

Practical Application

• Use spectral analysis to identify elements in the atmosphere of exoplanets.

Conclusion

• Whether an absorption or emission spectrum is observed depends on the viewing angle.
• Analysis remains the same, indicating the presence of specific elements based on spectral lines.

Summary

• Continuous spectrum from hot sources, absorption spectrum from cooler gases, and emission spectrum from direct observation of gases.