The basic principle of infrared (IR) spectroscopy is the absorption of infrared light by a sample. Infrared light is a type of electromagnetic radiation with a longer wavelength than visible light. It is absorbed by certain vibrational modes of the bonds between atoms in a molecule. When infrared light is absorbed by a sample, it causes the bonds in the molecule to vibrate at the same frequency as the absorbed light. The absorbed light is then absorbed as energy by the molecule, and the molecule transitions to an excited state. The molecule will eventually return to its ground state, releasing the absorbed energy as heat or light. By measuring the absorption of infrared light at different wavelengths, it is possible to determine the vibrational modes of the bonds in the molecule. Each bond in a molecule has a characteristic vibrational frequency, and the absorption of infrared light at these frequencies can be used to identify the molecular structure of the sample. Infrared spectroscopy is a powerful tool for identifying and analyzing the molecular structure of a wide range of materials, including organic and inorganic compounds, polymers, and biomolecules. It is widely used in a variety of fields, including chemistry, materials science, and biology.