W2013CHM2311 Part 4b Notes

Phys leipzig 1905 17 132 148 e e e h eh

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Unformatted text preview: that visible light can be absorbed, these molecules coloured. The energy gap is lowest for I2 then increases from Br2 to Cl2 to F2. As a result the colours go from dark purple for I2 to red brown for Br2 to yellow for Cl2. Fluorine absorbs light in the UV region and so is colourless. Photoelectric Effect & Photoelectron Spectroscopy Ioniza0on occurs when macer interacts with light of sufficient energy (Heinrich Hertz, 1886) (Einstein, A. Ann. Phys. Leipzig 1905, 17, 132- 148.) e- e- e- hν Ehν = electron kine0c energy + electron binding energy Photoelectron spectroscopy uses this phenomenon to probe the electronic structure of ma4er. It is par7cularly powerful for probing the (molecular orbital) energy levels in molecules Photoelectron Spectroscopy A7er Before hν FÖRE EFTER A A+ e - (E kin ) Ekin = hνh ν IEE → E + + E - + A A kin + Kai Siegbahn et al., Uppsala University Experimental Determina0on of Orbital Energies The energy of an orbital can be determined by ejec0ng an electron from the orbital using a light of specific wavelength. O2 + hv O2+ + e- The kine0c energy of the electron is measured. IE = photon energy – KE of electron The ioniza0on energy gives the energy of the orbital from which the electron was expelled. In photoelectron spectroscopy, two types of wavelengths are used: Molecular Spectroscopy mol + hν → mol* Photoelectron Spectroscopy mol + hν → [mol]+ ejected e Binding Energy 0 KE = ½ mv2 = hv – hv0 IP reflects calculated orbital Energy (Koopmans’ Thm) -5 Shape of band indicates bonding properties of orbital - 10 Intensity IP1 Intensity ν1 ν2 Frequency IP2 IP3 ν3 KE of ejected electron Interstate...
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