Absorbs EM radiation from a source, like a D 2 and Tungsten lamp Electrons relax back to ground...
-
Upload
lesley-goodwin -
Category
Documents
-
view
214 -
download
0
Transcript of Absorbs EM radiation from a source, like a D 2 and Tungsten lamp Electrons relax back to ground...
CHAPTERS 14 & 15
UV-Vis
Nature of Absorption
Absorbs EM radiation from a source, like a D2 and Tungsten lamp
Electrons relax back to ground state
Solvent Effects
Choose solvent based on transparency and effects on the system
Polar solvents tend to mask fine structure
Non-Polar solvents tend to keep the general peak arrangements, and skew the spectra
Analyzing without solvent (Neat) is always the best
Organic Absorption
All organics can absorb EM radiation Chromophores – molecules that contain
such functional groups and are capable of absorbing at UV radiation
Functional groups have pi orbitals that help it absorb
Inorganic Absorption
Absorbing results in exciting non-bonding orbitals into the pi* orbitals
Charge-Transfer Absorption
Leads to a large molar absorptivity Electron donor bonds to electron acceptor Donor loses electron when excited, and
acceptor takes it
Luminescence
Block Diagram
Fluorescence
Excited to singlet state Stabilizes to singlet ground state, then
relaxes down to ground state Relaxation causes emission of radiation Lasts a short time
Phosphorescence
Electrons cross into a triplet state from singlet state
In triplet state electron spins are unpaired, spinning in the same direction
Once stabilized to the triplet ground state, electrons relax back to ground state
This releases radiation, and lasts longer then fluorescence
Chemiluminescence
Luminescence cause by chemical reaction
Not a lot of analytes that do this Emits light when relaxing More common in a biological setting, ex.
fireflies
Selectivity
Rigidity effects how well it absorbs, more rigidity means more fluorescence
Compounds with aromatic functional groups that have low pi to pi* provide intense fluorescence
Components
Sources Lamps Laser
Monochromators Transducers
Photomultiplier tubes Cells
Quartz is best Silica Plastic