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Molecules E&R Chapter 12
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Outline Bonding 12-1 Molecular Excitations 12-4 Ionic 12-2
Covalent 12-3 Molecular Excitations 12-4 Rotation 12-5 Vibration 12-6 Electronic Electronic + Vibration + Rotation 12-7
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Bonding R Nave, Georgia State Univ
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Chemical Bonding R Nave, Georgia State Univ
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Ionic Bonds RNave, GSU at
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Ionic Bonds
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Ionic Bonding RNave, Georgia State Univ at hyperphysics.phy-astr.gsu.edu/hbase/molecule
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Ionic Bonding a.u. = atomic energy unit = 2*(13.6eV) Brandsen&Joachim
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E&R
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Covalent Bonds RNave, GSU at
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Covalent Bonding SYM ASYM spatial spin ASYM SYM spatial spin
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Covalent Bonding not really parallel, but spin-symmetric Stot = 1
not really anti, but spin-asym
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Covalent Bonding Bransden&Joachin
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Ionic vs Covalent Bond Properties
Ionic Characteristics Crystalline solids High melting & boiling point Conduct electricity when melted Many soluble in water, but not in non-polar liquids Covalent Characteristics Gases, liquids, non-crystalline solids Low melting & boiling point Poor conductors in all phases Many soluble in non-polar liquids but not water
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Rotational Spectra w rotational A.M. moment of inertia
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Rotation
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Rotation
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Rotational Spectra
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Ocean Optics: Nitrogen N2
~ 0.3 eV ~ 0.4 eV
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Vibration HF 970 HCl 480 HBr 410 Hi 320 CO 1860 NO 1530 “Spring Const”
Molecule “Spring Const” ( N/m ) HF 970 HCl 480 HBr 410 Hi 320 CO 1860 NO 1530
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Vibration (in an Electronic state)
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Electronic + Vibration
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Electronic + Vibration + Rotation
2.550 eV 2.656 eV electronic excitation gap vibrational excitation gaps
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Electronic + Vibration + Rotation
Vibrational Well Vibrational Well 2.656 eV depth ~ eV electronic excitation gap vibrational excitation gaps
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Electronic, Vibration, Rotation
Electronic ~ optical & UV ~ 1 – 3 eV Vibration ~ IR ~ 10ths of eV Rotation ~ microwave ~ 1000ths of eV
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Electronic + Vibration + Rotation
2.550 eV 2.656 eV electronic excitation gap vibrational excitation gaps
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** + Vibration + Rotation
IN A DIATOMIC MOLECULE because a photon has one unit of angular momentum, the rotational quantum number must change (vib is not angular motion) Dr = 0 not allowed
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** + Vibration + Rotation
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Ocean Optics: Nitrogen N2
~ 0.3 eV ~ 0.4 eV
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Some Molecular Constants
Molecule Equilibrium Distance Ro (Å) Dissociation NRG Do (eV) Vibrational freq v a (cm-1) Moment of Inertia Bb (cm-1) H2+ 1.06 2.65 2297 29.8 H2 0.742 4.48 4395 60.8 O2 1.21 5.08 1580 1.45 N2 1.09 9.75 2360 2.01 CO 1.13 9.60 2170 1.93 NO 1.15 5.3 1904 1.70 HCl 1.28 4.43 2990 10.6 NaCl 2.36 4.22 365 0.190 Notes: a) vibrational frequency in table is given as f / c b) moment of inertia in table is given as hbar2/(2I) / hc
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Fluorescence absorb at one wavelength, emit at another
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Phosphorescence tunneling slows the decay process
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