材料测试分析5.pdf

5 Infrared spectroscopy 1 Spectroscopy “seeing the unseeable” Using electromagnetic radiation as a probe to obtain information about atoms and molecules that are too small to see. Electromagnetic radiation is propagated at the speed of light through a vacuum as an oscillating wave. The entire electromagnetic spectrum is used by chemists Frequency, n in Hz ~1019 ~1017 ~1015 ~1013 ~1010 ~105 Wavelength, l ~.0001 nm ~0.01 nm 10 nm 1000 nm 0.01 cm 100 m Energy (kcal/mol) 300 300-30 300-30 ~10-4 ~10-6 g-rays X-rays UV IR Microwave Radio nuclear core electronic molecular molecular Nuclear Magnetic excitation electron excitation vibration rotation Resonance NMR (PET) excitation (p to p*) (MRI) (X-ray cryst.) Visible Interaction between EM radiation and matter c ___ hc n = E = hn = ___ l l Because the atomic particles in matter also exhibit wave and particle properties (though opposite in how much) EM radiation can interact with matter in two ways: • Collision – particle-to-particle – energy is lost as heat and movement • Coupling – the wave property of the radiation matches the wave property of the particle and “couple” to the next higher q