Introduction to infrared spectroscopy

When operating an infrared spectroscopy analysis in a laboratory, we refer to the interaction of infrared light with matter via absorption, emission or reflection. The goal of this analytical technique is to identify the functional groups in a sample via the interpretation of a spectrum. If we consider light a wave, this technique focuses on the principle that different functional groups absorb the radiation at different wavelength values, depending on the structure of the molecules in the sample. Infrared is considered vibrational spectroscopy, as the energy connected to this radiation is not strong enough to break chemical bonds, but produces a vibration with a change in dipole moment. The dipole moment can be described as uneven distribution of electron density in heteronuclear molecules and changes with the expansion and contraction of a bond. When there is a change in dipole moment, the molecule can be considered IR active. When the sample absorbs light from the source, the bonds vibrate in a stretching or bending mode, producing signals that are represented in the spectrum.