Infrared Spectroscopy—Mid-infrared, Near-infrared, and Far-infrared/Terahertz Spectroscopy

This article aims to overview infrared (IR) spectroscopy. Simultaneously, it outlines mid-infrared (MIR), near-infrared (NIR), and far-infrared (FIR) or terahertz (THz) spectroscopy separately, compares them in terms of principles, characteristics, advantages, applications. MIR is the central spectroscopic technique IR region, mainly concerned with fundamentals molecular vibrations. NIR incorporates both electronic vibrational spectroscopy; however, this review, I have chiefly discussed spectroscopy, where bands due overtones combination modes appear. FIR THz contains rotational However, only has been review. These three cover wide areas their applications, making rather difficult describe these various topics simultaneously. Hence, selected key topics: hydrogen bond studies, applications quantum chemical calculations, imaging. The perspective last section.