Mid-infrared spectroscopy (MIR) covers a wavelength range between 2.5 and 25 μm and is commonly referred to as infrared spectroscopy (IR). Since most mid-infrared spectrometers are Fourier transform-based, the wavelength range is usually expressed in wavenumbers, spanning from 4000 to 400 cm−1. The energy of mid-infrared light is lower than that of near-infrared light, and mid-infrared spectroscopy reflects the fundamental frequency information of the vibrations and deformation movements (also known as bending vibrations) of chemical bonds within molecules. While molecules undergo vibrational movements, they also experience rotational movements. Although the energy changes involved in rotational movements are small and occur in the far-infrared region, these movements influence the changes in dipole moments during vibrational movements. As a result, the spectra obtained in the infrared region represent a combination of molecular vibrational and rotational movements.