e-m radiation: formation of 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)
–              DE = Efinal - Einitial = hn  (h = Planck’s constant, 6.6 x 10-27 erg sec)
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•types of transition
–collisional excitation/de-excitation  DE = ½mv2 
–radiative absorption  + spontaneous emission; stimulated emission
–           photon energy ΅ radiation frequency (color)
–DE = hn = hc/l
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•e.g. for l = 7000Ε, Ephoton ~ 2 eV (1eV = 1.6 x 10-12 ergs)
•- very low energy
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