Absorption Spectra

Absorption Spectra

Introduction

• Absorption spectra are patterns of light produced when photons pass through a gas, and certain photons are absorbed by atoms.
• These spectra provide valuable information about the energy levels and composition of atoms and molecules.

Absorption Process

• When photons of light pass through a gas, some photons have energy that matches the energy gaps between an atom's energy levels.
• These specific photons are absorbed by the atoms, leading to the creation of absorption lines in the spectrum.

Absorption Spectra

• Absorption spectra are characterised by dark lines or bands on a continuous spectrum.
• The dark lines represent the specific wavelengths of light that have been absorbed by the gas.
• The positions of these lines are indicative of the energy levels within the gas's atoms.

Relationship with Emission Spectra

• The lines in the absorption spectra of an element are in the same positions as the lines in the emission spectra of that element.
• This correspondence allows scientists to identify elements based on their unique absorption and emission patterns.

Observing Absorption in the Sun

• While sunlight appears as a continuous spectrum, closer inspection using a spectroscope reveals dark, narrow lines known as Fraunhofer lines.
• These lines are caused by specific frequencies of sunlight being absorbed by gases in the sun's upper atmosphere.

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Absorption Spectra

Significance

• Absorption spectra help scientists identify the chemical composition of substances by analysing the specific wavelengths of absorbed light.
• These spectra play a crucial role in various fields, including astronomy, chemistry, and environmental science.

Summary

• Absorption spectra result from the absorption of specific wavelengths of light by atoms or molecules.
• Dark lines or bands on a continuous spectrum represent the absorbed wavelengths.
• Absorption and emission spectra of the same element have corresponding lines.
• Fraunhofer lines in sunlight are due to the absorption of specific frequencies by gases in the sun's atmosphere.
• Absorption spectra aid in identifying the composition of substances and have diverse applications in scientific research.