3. Infrared Spectroscopy

• Infrared spectroscopy, beam of IR radiation is passed through a sample of chemical. IR radiation is absorbed by covalent bonds in molecules, increasing their vibrational energy. Bonds between different atoms absorb different frequencies of IR radiation. Bonds in different places in molecule absorb different frequencies too - so O-H bond in alcohol shows what frequencies different bonds absorb
• Wave number = 1/ wavelength
• Region between 1000cm-1 and 1550 cm-1 on spectrum is called fingerprint region. Unique to particular compound.
• Sun emits mainly UV / visible radiation which is absorbed by Earths surface and re-emitted as IR radiation. Molecules of greenhouse gases, like carbon dioxide, methane and water vapour, have bonds that are really good at absorbing IR energy - so if amounts of these gases in atmosphere increase, more IR radiation is another which leads to global warming. More IR radiation a Molecule absorbs, more effective the are as greenhouse gases