Choosing Between Vibrational Methods: Infrared, Raman and Resonance Raman · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Picking the vibration watcher

Science · Chemistry · ages 22-24
Name ______________________   Date ____________

  1. A motion changes polarizability but leaves the dipole fixed. Which method sees it?

    • Infrared absorption
    • Raman scattering
    • Neither method

  2. Why does an infrared absorption appear as a band of close lines?

    • Each vibration carries rotation companions along
    • The light source emits many colors at once
    • The molecule jumps two rungs at a time

  3. The symmetric stretch of carbon dioxide is strong in Raman and absent in infrared.

    Circle one:   True   False

  4. You must follow one metal-ligand stretch in a dilute water solution of a colored complex. Which technique fits?

    • Resonance Raman with the laser on the color band
    • Plain infrared absorption of the whole solution
    • Raman with the laser far from every electronic band

  5. When does Raman scattering grow enormously stronger?

    • When the sample is frozen before the run
    • When the spectrum is recorded twice as long
    • When the laser lands on an electronic absorption band

  6. Why does the resonance choice beat plain infrared for that colored water solution?

    • It heats the sample until the band glows
    • It shrinks the spectrum to the vibrations tied to the transition
    • It shifts every band to a clearer region

  7. Two analysts argue. One wants infrared for a polar stretch, the other resonance Raman for a colored impurity band. How do you settle it?

    • Match each band to its motion: dipole change goes infrared, color-tied goes resonance Raman
    • Pick infrared for both, since one instrument is simpler
    • Pick resonance Raman for both, since boosting always helps

  8. A student picks infrared to chase a symmetric stretch. What is the flaw, and what is the fix?

    • The band is too weak; record the infrared trace for longer
    • The sample is too pure; dilute it before measuring
    • The motion lacks a dipole change; switch to Raman
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Picking the vibration watcher W1-mt_YxLAvBIBAR-s1

  1. Raman scattering · Polarizability change is the Raman condition; infrared needs a dipole change.
  2. Each vibration carries rotation companions along · Rotation changes ride on the vibration, bunching lines into a band.
  3. True · The motion shifts polarizability without shifting charge to one side.
  4. Resonance Raman with the laser on the color band · Resonance suits water, needs little material, and lifts exactly the tied stretch.
  5. When the laser lands on an electronic absorption band · Resonance with the electronic transition boosts tied vibrations up to a millionfold.
  6. It shrinks the spectrum to the vibrations tied to the transition · A short list with the wanted band standing out beats a crowded trace.
  7. Match each band to its motion: dipole change goes infrared, color-tied goes resonance Raman · Each choice must name its motion and survive its rival.
  8. The motion lacks a dipole change; switch to Raman · No dipole change means infrared stays dark whatever the recording time.
Worksheet · LightMySky