UV/VIS Review

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UV/VIS Review
2012-12-01 16:12:55
Inst390 sait clt2

Main terms and acronyms related to spectroscopy
Show Answers:

  1. A tungsten source produces light in the _____ range
  2. A deuterium source produces light in the _____ range
  3. Is the intensity of the light produced by a light source the same for each wavelength region it covers?
    No. The intensity varies with wavelength
  4. The cathode of a PMT is coated with a _____ material which emits electrons when struck by a photon
  5. What kind of electrons does UV light interact with?
    bonding electrons
  6. MO
  7. Which has higher energy: bonding or anti bonding molecular orbitals?
    Anti bondingĀ 
  8. MO with single bondsĀ 
  9. MO with double bonds
  10. An asterisk * is used to denote
    Anti bonding orbitals
  11. N electrons
    Non bonding electrons
  12. Which type of transition tends to have smaller epsilon values?
    N transitions (non bonding electrons jumping up)
  13. HOMO
    Highest occupied molecular orbital
  14. LUMO
    Lowest Unoccupied Molecular Orbital
  15. The most important transition is typically the one with the (highest/lowest) energy
  16. What are the characteristics of molecules that can have an n to pi* transition?
    They all have pi bonds and non-bonding electrons (ex. C=N, C=O, C=S)
  17. A functional group that absorbs light and contributes to a molecule's color
  18. A group which affects how a chromophore absorbs (give the name and an example of one)
    • auxochrome
    • Ex: OH, halogens
  19. The shift of absorption to a longer wavelength (red shift)
  20. The shift of absorption to a shorter wavelength (blue shift)
  21. When an auxochrome increases absorbance, this is called
    hyperchromic behavior
  22. When an auxochrome decreases absorbance, this is called
    hypochromic behavior
  23. Choose your solvent carefully because it can affect:
    • The sharpness of peaks (polar solvents cause band broadening)
    • The wavelength of maximum absorbance
  24. Charge Transfer Complex is another name for
    A coordinate covalent compound
  25. If you have two species that absorb at the same wavelength, what are two options for analysis?
    • Use a masking agent
    • Use simultaneous equations
  26. A name for a double beam technique where you measure the difference in absorbance between two samples
    Difference Spectrometry (see slide 55)
  27. The name for titrations using spectrophotometry to detect the endpoint
    photometric titrations
  28. When the actual absorbance is less than that predicted by Beer's law, this is called
    negative deviation
  29. Random thermal motion of electrons in the detector is called
    Johnson's noise
  30. Johnson's noise is typically more of a problem with
    older PMT's
  31. Movement of electrons in detector between anode and cathode without any incoming stimulation
    Signal shot noise
  32. The term for noise that occurs when the light source fluctuates
    Flicker noise
  33. Two options to improve signal-noise ratio
    • Increase signal
    • Decrease noise