Practical FTIR analysis Introduction - PlasTEP（PlasTEP实际红外光谱分析介绍）.pdf

Practical FTIR analysis Introduction David Cameron Professor of Material Technology Advanced Surface technology Research Laboratory (ASTRaL) University of Lappeenranta Finland Part-financed by the European Union (European Regional Development Fund Outline • Basics of FTIR spectroscopy • Identification of structural features • Some practical examples • Exercises PlasTEP Summer School, Warsaw 29.07.2011 1 IR absorption • Change in molecule dipole moment during vibration can absorb energy from an incident electromagnetic wave. • Only certain vibrations able to absorb energy, depends on selection rules • Selection rules depend on molecule symmetry - shape of molecule • Vibrational frequency can be approximated by ball and spring model mass of mass of atom 1 atom 2 m1 m2 interatomic bond PlasTEP Summer School, Warsaw 29.07.2011 2 Vibrational frequency • Simply, vibration frequency of molecule depends on Hooke’s Law 1   2  ν= fundamental vibrational frequency κ= force constant m m μ = reduced mass  1 2 m m 1 2 • Weak bonds = lower frequency • Heavier atoms = lower frequency • Frequency is also affected by the adjacent atoms PlasTEP Summer School, Warsaw 29.07.2011 3 Vibrational modes • Number of vibrational modes for a molecule with N atoms = 3N –6 (non-linear mol