IR SPECTROSCOPYPresented by

Arunkumar rengaraj

Seo-Young OhNano-Bio Analysis lab

Inha university

IR RADIATION

• Infrared radiation is popularly known as heat radiation.

• Infrared light from the Sun accounts for 49% of the heating of Earth

• It is electromagnetic radiation with longer wavelengths than those of visible light.

Infrared spectroscopy

Molecules absorb specific frequencies that are characteristic of their structure.

Absorbed radiation matches the transition energy of the bond or group that vibrates.

Transition energy calculated by

• Shape of the molecular (potential energy surfaces)

• Masses of the atoms

• Vibronic coupling

causing a change in the amplitude of molecular vibration

Energy Levels: Basic Ideas

About 15 micron radiationBasic Global Warming: The C02 dance …

Scanning monochromator method

where one wavelength at a time passes through the sample

Fourier transform infrared (FTIR) spectroscopy

It is a measurement technique that allows one to record infrared spectra.

Infrared light is guided through an interferometer and then through the sample (or vice versa).

Interferometry makes use of the principle of superposition

A moving mirror inside the apparatus alters the distribution of infrared light that passes through the interferometer. The signal

directly recorded, called an "interferogram", represents light output as a function of mirror position.

A data-processing technique called Fourier transform turns this raw data into the desired result (the sample's

spectrum.

Fourier transform

It is a mathematical transformation employed to transform signals between time (or spatial) domain and frequency

domain.

Fourier transform can be simplified to the calculation of a discrete set of complex amplitudes

FTIR improving both speed and signal-to-noise ratio.

A dispersive measurement requires detecting much lower light levels than an FTIR measurement. [3] 

1-Hexene

CH2 CH CH2 CH2 CH2 CH3

sp2

C-H

sp3

C-H stretch

C=C stretch

out of planebendings (oops)

Toluene

CH3

sp2

C-Hsp3

C-H aromatic C=C

aromatic oops

Cyclohexanol

OHO-Hstretch

bending

C-Ostretch

sp3 C-H stretch