e-m radiation: spectral lines
•Quantum transitions
– energy levels within atomic and molecular systems quantized
– only discrete orbits/energies permitted
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•when atom makes a transition between 2 states, gives  up energy corresponding to the difference
–discrete amounts of energy only (photons)
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•types of transition
–collisional excitation/deexcitation
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•radiative absorption  + spontaneous emission; stimulated emission
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•Photon energy µ radiation frequency (color)
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•DE = Efinal - Einitial = hn (radiation) or œmv2 (collisional)
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