ABSTRACT
As a useful working denition, spectroscopy can be dened as the interaction of electromagnetic radiation (EM) with matter, although this does not include mass spectroscopy. Several factors have led to the branching of spectroscopy in different directions. Most signicant is the order of magnitude of the energies involved, but additional factors such as the presence of a magnetic eld and instrumentation considerations have led to the techniques of ultraviolet (UV), infrared (IR), nuclear magnetic resonance (NMR), and electron spin resonance (ESR) spectroscopy. Breakup and analysis of the above denition will be useful before delving into the details of the different spectroscopic techniques mentioned. The denition includes
1. Electromagnetic radiation 2. Interaction of EM with matter 3. Matter
EM radiation consists of an electric eld perpendicular to a magnetic eld and both at right angles to the direction of propagation of light (Figure 5.1). A fundamental property of EM radiation is that it can behave as though it exists as discrete quanta or packets of energy:
E h= υ
where E = energy h = Planck’s constant = 6.63 × 10−34 J·s υ = frequency of radiation in Hertz
There are two ways in which EM radiation interacts with matter: absorption and emission. Absorption occurs when incident radiation increases the energy of a system. An increase in energy is manifested as a decrease in intensity of emergent radiation. Emission occurs when there is a decrease in the energy of a system. Decrease in energy may be due to
1. Thermal energy loss: Energy loss by molecular or submolecular motion like a collision, vibration, or rotation.
