Introduction to Spectroscopy 2004. 4 Yongsik Lee.

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Presentation transcript:

Introduction to Spectroscopy Yongsik Lee

Spectroscopy ► Introduction ► Components of spectrometer ► Atomic spectroscopy ► AA (Atomic Absorption) and AF (Atomic Fluorescence) ► AES (Atomic Emission Spectroscopy) ► Atomic Mass Spectroscopy ► Atomic X-ray Spectroscopy

6A electromagnetic radiation ► ► Electromagnetic radiation (wave) description:   Electric Field Strength   Time t or Distance x   Amplitude A   Velocity v Wavelength l   Period p time for 1 l to pass fixed point   Frequency n # of l passing per s n = 1 ► ► Wavenumber n # of l per cm n = 1 ► ► Velocity v Distance point on wave travels per ► ► second ► ► In a vacuum: ► ► v = n ×l ► ► vvacuum = c ► ► = x108 m / s ► ► A set of waves with identical (a) freqency (b) phase are called ► ► coherent. ► ► CEM 333 page 2.1 ► ► Frequency is always fixed but velocity can vary! ► ► Waves slow down in medium (gas, liquid, solid) so v<c ► ► v = n ×l ► ► Implies l decreases in medium ► ► Refractive index h = c ► ► v ► ► ³ 1.00 ► ► Equation for Wave ► ► E = Asin(wt + f) where w = 2pn ► ► electric field frequency ► ► amplitude phase ► ► angular frequency time ► ► Wave description explains certain EM radiation phenomena: ► ► transmission ► ► reflection and refraction ► ► diffraction ► ► interference ► ► scattering ► ► polarization ► ► CEM 333 page 2.2 ► ► Particle Description of Light: ► ► Based on quantum mechanics ► ► Energy of EM photon: E = hu = hc ► ► l ► ► Planck's Constant=6.626x10-34 J·s ► ► Postulates of QM: ► ► 1. Atoms, ions and molecules exist in discrete energy states ► ► only ► ► E0 = ground state ► ► E1, E2, E3... = excited states ► ► Excitation can be electronic, vibrational or rotational ► ► Energy levels for atoms, ions or molecules different. ► ► Measuring energy levels gives means of identification - ► ► spectroscopy ► ► 2. When an atom, ion or molecule changes energy state, it ► ► absorbs or emits energy equal to the energy difference ► ► DE = E1 - E0 ► ► 3. The wavelength or frequency of radiation absorbed or ► ► emitted during a transition proportional to DE ► ► DE = h ×n = h ×c ► ► l ► ► CEM 333 page 2.3 ► ► Emission Spectra ► ► Plot of emission intensity vs. n or l called emission spectrum ► ► Atom: ► ► E 0 ► ► E 1 ► ► E 2 ► ► DE=202.8 kJ/mol ► ► n=5.08x10 Hz ► ► l=590 nm ► ► 14 ► ► DE=362.5 kJ/mol ► ► n=9.08x10 Hz ► ► l=330 nm ► ► 14 Energy ► ► Atomic ► ► Excitation ► ► Atomic ► ► Emission ► ► Lifetime~1-100 ns ► ► line emission spectra ► ► Inner shell (core) electrons (1s¬2p) - x-rays photons ► ► Outer shell (valence) electrons (3d¬4p) - UV/vis photons ► ► Molecule: ► ► E 0 ► ► E 1 ► ► E 2 ► ► Energy ► ► Molecular ► ► Excitation ► ► Molecular ► ► Emission ► ► V0 ► ► V1 ► ► V2 ► ► V3 ► ► R0 ► ► R10 ► ► Band 1 Band 2 ► ► Lifetime ► ► fs ► ► vibrational and rotational transitions - band emission spectra ► ► CEM 333 page 2.4