The absorption spectrum studies light and electromagnetic radiation at different wavelengths.
The absorption spectrum is a graph that shows how a substance absorbs light or electromagnetic radiation at different wavelengths. It is generated when radiation energy is absorbed by the electrons of the atoms or molecules of a substance, causing transitions between different energy levels. This spectrum is unique for each material and is useful for identifying and studying the composition of substances in fields such as chemistry, astronomy, and biology.
Examples of absorption spectrum
The absorption spectrum has key applications in various scientific disciplines. A classic example is the absorption spectrum of hydrogen , which shows dark lines corresponding to the wavelength of light absorbed by each electron as it jumps between specific energy levels. This has been fundamental for the development of quantum theory and for understanding atomic structure.
In the field of biology, the absorption spectrum of chlorophyll is an emblematic case. This pigment, responsible for photosynthesis in plants, mainly absorbs light in the blue and red regions of the visible spectrum, which explains its green color. This phenomenon is crucial for the conversion of solar energy into chemical energy.
In analytical chemistry , atomic absorption spectroscopy is used to detect and quantify elements in samples. For example, the analysis of heavy metals such as lead or mercury in solutions is based on their specific absorption spectra.
In astronomy , absorption spectra play an important role in studying the composition of stars and galaxies. By observing light passing through a stellar atmosphere, scientists can identify which elements are present and in what quantities, through characteristic absorption lines.
Theoretical foundations
The absorption spectrum is based on the nature of light as a form of electromagnetic radiation that propagates in the form of waves. The electromagnetic spectrum encompasses different types of radiation, from radio waves to gamma rays, and each type is characterized by a specific wavelength and frequency.
When light interacts with matter, molecules and atoms can absorb energy at certain wavelengths. This absorption causes an electronic transition , where electrons jump from a lower energy level to a higher one. Each atom or molecule has a specific pattern of energy levels, so it absorbs light at characteristic wavelengths, forming a unique absorption spectrum.
These transitions occur both in individual atoms and in more complex molecules, and are fundamental to understanding processes such as photosynthesis, spectroscopy, and the identification of elements in space.
UV-Vis spectroscopy is useful for identifying organic compounds and analyzing the concentration of solutions.
Spectroscopy techniques: applications and principles
Spectroscopy is a fundamental tool for analyzing the interaction of light with matter, providing detailed information about the molecular and atomic structure of substances. There are several spectroscopy techniques, each with specific applications in science and technology.
UV-Vis Spectroscopy
It is used to study the absorption of ultraviolet and visible light of the electromagnetic spectrum, being useful in the identification of organic compounds and the analysis of the concentration of solutions.
Infrared (IR) spectroscopy
It is based on the absorption of infrared light by molecules, which causes characteristic molecular vibrations. It is a key technique for the identification of functional groups in organic molecules and in the analysis of chemical substances.
Fluorescence spectroscopy
It measures the emission of light by a substance after having absorbed radiation, and is widely used in biochemistry to study proteins and nucleic acids, due to its high sensitivity.
Raman spectroscopy
It explores changes in light scattering when it interacts with molecular vibrations, allowing molecular structures to be analyzed without the need for complex sample preparation.
Nuclear Magnetic Resonance (NMR) Spectroscopy
It is crucial to study the three-dimensional structure of molecules through the interaction of atomic nuclei with magnetic fields, being an essential tool in organic chemistry and biomedicine.
Mass spectroscopy
It analyzes ions generated by molecules in the gas phase to determine their mass and molecular structure, with applications ranging from compound identification to protein analysis.
Flame emission spectroscopy
It is used to detect metallic elements from the light emitted when a sample is introduced into a flame, being useful in analysis of metals and inorganic chemistry.
Types of spectra and their analysis
The study of spectra is essential to understand the properties of light emitted or absorbed by different sources. The spectrometer is the key device used to break down light into its different wavelengths and analyze the type of spectrum generated.
One of the most common types is the emission spectrum , which occurs when an object emits light by releasing energy. This can occur in different forms, such as the continuous spectrum , which shows an uninterrupted range of wavelengths, as occurs in the light emitted by hot bodies, such as the sun or stars.
In contrast, the discrete spectrum is characterized by the appearance of specific emission or absorption lines, each corresponding to a particular electronic transition. This type of spectrum is typical of gases in an excited state, such as in neon lamps or in the analysis of specific chemical elements.
The band spectrum is a variation that appears in more complex molecules, where electronic transitions combine with molecular vibrations, generating absorption or emission bands that span a range of wavelengths.
Finally, the stellar spectrum is a continuous emission and absorption spectrum observed in light from stars. This spectrum allows us to study the chemical composition, temperature and motion of stars by identifying specific absorption lines in their spectrum.
Flame emission spectroscopy detects metal elements.
Absorption spectrum modifications
The absorption spectrum can be affected by various physical phenomena, which modify the position or shape of the spectral lines.
Zeeman effect
It refers to the decomposition of a spectral line into several components in the presence of a magnetic field. This occurs due to the interaction between the external magnetic field and the electronic energy levels of the atoms or molecules, causing the displacement of the absorption lines.
Stark Effect
It occurs when an external electric field alters the energy levels of electrons. This effect generates the displacement or division of the absorption spectral lines, being very useful for studying electric fields in plasmas and other environments.
Doppler effect
It is related to the relative movement between the light source and the observer. When a light-emitting or light-absorbing object moves toward or away from the observer, the spectral lines shift toward blue (higher frequency) or red (lower frequency), respectively. This effect is crucial in astronomy to measure stellar velocities and displacements in galaxies.