Broad spectral feature at ~3300cm

Problem: Broad spectral feature at 3300 cm-1/ Short hold time for liquid nitrogen cooled detector

Example data:

Notice the growth of the broad spectral feature at about 3,300 cm-1. This spectral ice band is growing as ice accumulates on the cold detector surface within the dewar assembly.

Common causes:
  • Insufficient or complete loss of vacuum in liquid nitrogen cooled detector.

Example data:

Notice that unlike the “ice” growth in the detector with poor vacuum, these bands are more broad. Also, the water condenses (you see the increase) and then evaporates (see the decrease). Repeatedly doing this will lead to poor vacuum because of the freeze/shrink/thaw/expand cycle on the O-ring caused by the liquid nitrogen spillage.

Common causes:
  • Overfilling of the detector.
  • Insufficient dewar vacuum for liquid nitrogen cooled detector.
  • Condensation on the detector window.

  • Contact Madison Instruments, Inc. for detector re-evacuation.

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