Diode Laser Photochemistry of Biacetyl

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Diode Laser Photochemistry of Biacetyl

• Andrew Chastain
• Reid OBrien Johnson
• Akemi Kunibe

2
Experimental Setup

• 397.5 nm diode laser
• Reaction chamber
• Ocean Optics Spectrometer
• Spex Spectrometer

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Experimental Setup
Fiber Optics Cable
Laser Diode
Reaction Chamber
Output to Computer
Detector
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Laser Calibration

• The laser found to be operating over a range of
  modes when calibrated using a higher resolution
  Spex Spectrometer.

397.0 398.4 nm
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Biacetyl

• IUPAC 2,3-butanedione

Image Source http//en.wikipedia.org/wiki/ImageD
iacetyl-3D-balls.png
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Experimental Results
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Experimental Results
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Results

• Two peaks were noted at 513.31 and 556.28 nm
• These peaks correspond to energy transitions of
  2.41 and 2.22 eV, respectively

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What does this mean?

• Literature values for fluorescent range are given
  as being in the 444.64 - 478.63 nm range. 1
• What else could be happening?

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Photochemistry

• Photochemical cleavage reactions could account
  for shift.
• CH3COCOCH3 hv ? CH3CO CH3CO
• and
• CH3COCOCH3 hv ? CH3COCO CH3

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Expected shift

• Murad, Edmond and Mark G. Inghram calculated the
  bond dissociation energies in Aliphatic carbonyl
  compounds.
• These were found to be 0.49 0.03 eV for the
  CH3-CO bond, and 2.84 0.06 eV for the
  CH3CO-COCH3 bond. 2

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Calculated shift

• The energy shifts associated with the two peaks
  are 0.70 and 0.88 eV at 513.31 and 556.28 nm,
  respectively. The would indicate that the emitted
  energy shift is larger than would be expected
  from a methyl shearing, and much smaller than a
  split down the middle.

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LIF Spectroscopy

• Since the energy of the laser photons exceeds the
  dissociation energy of the bonds, cleave should
  be occurring. But the energy lost from either
  cleavage reaction would not shift the peaks to
  their measured positions.

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LIF Spectroscopy

• What this means is that the additional shift
  might originate from fluorescence of the
  fragments.
• This spectrum could then be used to better
  understand the structural features of the
  cleavage fragments.

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Works Cited

• 1 Brand, J.C.D and A. W.-H. Mau (1974).
  Low-Lying Electronic States of Biacetyl. J. Am.
  Phys. Chem. Soc. 96.144380-4385.
• 2 Murad, Edmond and Mark G. Inghram (1964).
  Thermodynamic Properties of the Acetyl Radical
  and Bond Dissociation Energies in Aliphatic
  Carbonyl Compounds. J. Phys. Chem. 41.2 404-09.