Spectroscopy: Basics

 Introduction

Spectroscopy is an important analytical technique for the measurement and interpretation of the Electromagnetic radiations absorbed or emitted during the course of movement of atoms, molecules or ions from one energy state to the another whether it is from ground level to excited or vice versa.

Read some basics and types of Electromagnetic radiations first 

Theory behind Spectroscopy

As we pass an Electromagnetic radiation through a medium containing atoms molecules or ions, following changes can happen:

1. Intensity of emerged light is less than Intensity of incident light; Absorption of        energy took place.
2. Intensity of emerged light is equal to the incident light; No absorption took place.
3. Refraction, reflection or scattering; Turbidimetric and nephlometric studies can        be   performed.

Ground state refers to the state when species (atoms, molecules or ions) has the lowest energy. This state is stable and preferable state for the species. After absorption of light, the species get excited i.e.  moves from ground state to the excited state having high energy. Excites state is less stable so the species move back again to their ground state loosing the energy.

The process of moving from ground state to the excite state is called Excitation while Relaxation refers to the moving down from excited state to the ground state.

 

The process of relaxation can be executed by one of the following methods:

1.     Collisional Deactivation ( Heat production)
2.     Decomposition into new species
3.     Emission of radiation of:

o   Specific wavelength ( Flame photometry)

o   Longer wavelength instantly ( Flouroscence)

o   Longer wavelength after some lag time (Phosphoroscence)

 

Types of Spectroscopic Techniques

Spectroscopic Techniques can be classified on the following basis;

1.     Whether the study involves absorption or emission of radiations:

a. Absorption Spectroscopy- e.g. Colorimetry, NMR, IR, UV, Atomic absorption spectroscopy

b.     Emission Spectroscopy- e.g. Flourimetry, Flame photometry

2.    Based on the level of energy change:

a. Atomic Spectroscopy- e.g. Atomic absorption spectroscopy, flame photometry

b.     Molecular Spectroscopy- e.g. IR, UV, Colorimetry, Flourimetry

3.     Whether the study is at magnetic or electronic level:

a.     Electronic Spectroscopy- e.g. Flourimetry, UV, Colorimetry

b.     Magnetic Spectroscopy- e.g. NMR, Electron spin resonance spectroscopy.