Infrared spectroscopy is carried out using somewhat higher energy electromagnetic radiation (300 GHz to 400 THz) than microwave spectroscopy. The infrared region of the spectrum is usually a good match for the vibrational energy-level spacing in molecules, so infrared spectroscopy is typically used to study the vibrational energy levels of molecules. Vibrational spectroscopy can be used to study molecules in the gas, liquid, and solid phases, as well as molecules on surfaces.