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Third Report of the Committee on Photochemistry Reprint and Circular Series of the National Research Council (1938) / Chapter Skim
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The Primary Absorption Process in Photochemistry
Pages 35-40

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From page 35...
... , that the molecule in the activated state produced by the absorption of these diffuse bands undergoes a radiationless transfer to another electronic state and dissociates in a time which is short compared to the period of rotation. Such changes have been expressed graphically by Herzberg (6)
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From page 36...
... Hence we should expect, other things being equal, that molecules represented by diagrams similar to figure lb will show predissociation over a wider range and more frequently than those corresponding to the other diagrams. At the present time we do not know enough about these potential curves to make any quantitative calculations concerning predissociation.
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From page 37...
... The interpretation of the spectra of polyatomic molecules has not progressed to the point where we can say whether an analogous set of rules applies or not. However, we may say that we can expect to find the probabilities of radiationless transfers occurring ranging from practically every time the molecule reaches the state represented by the intersection of the potential energy curves to practically complete prohibition of the change.
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From page 38...
... Turner (15) found that, if iodine vapor were illuminated with light absorbed in the band region in the presence of a magnetic field or inert gases, there was a marked absorption of the spectrum lines characteristic of iodine atoms.
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From page 39...
... Hence, the possibility of dissociation in the primary step of a photochemical reaction cannot be excluded on the basis of welldefined lines in the absorption bands nor even on the basis of fluorescence observations. Another interesting example is furnished by tellurium vapor, Tee.
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Key Terms

  • inert gases
  • photochemical reactions
  • potential energy
  • primary process
  • excited state

  • diffuse bands
  • energy diagrams
  • activated molecules
  • energy curves
  • activated molecule

  • state represented
  • hundred times
  • radiationless transfer
  • low pressures
  • magnetic field

  • light absorption
  • total angular
  • spectrum line
  • quantum yield
  • lying level

  • considerable detail
  • modified considerably
  • sensitive indicator
  • molecule vibrates
  • rates using

  • eff ect
  • radiationless transfers
  • state produced
  • practically complete
  • rollefson department


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