Infra-red (IR) spectroscopy is an essential tool in the analysis of molecules of forensic significance. IR can help in unambiguous identification of molecules. Regions of IR-Spectrum
1. Near IR: From 12,820—4000 cm-1
2. Mid-IR: from 4000 cm-I to 400 cm-1
3. Far-IR: from 400—10 cm-1
For most forensic purposes, the mid-IR region is commonly used for identification purposes.
The Mid-IR region can be further divided into 3 main regions:
(a) from 4000 to 1400 cm-1 (b) from 1400 to 900 cm-1 (c) from 900 to 400 cm-1
Some of the common vibrations associated with the groups in organic molecules are given below.