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UPSC Combined Geo-Scientist

Chemist

  • 3 descriptive papers
  • 200 marks each
  • 3 h per paper

Mains Paper III covers analytical and organic chemistry.

UPSC Combined Geo-Scientist, Mains · 2021 · Mains Paper III

Q2(c). IR spectrophotometer: region, sources, monochromation, detectors

Question

What is the main infrared (IR) region of interest for analytical purposes? Write down the main sources of IR radiation as used in IR spectrophotometers. Which is the main means of monochromation in the IR region and why? Mention the detectors as used in the detection of IR signal.

Answer in brief

Mid IR, mostly 2.5–15 µm (4000–667 cm⁻¹); sources Nernst glower, Globar, nichrome wire; reflection grating for dispersion; thermal detectors (thermocouple, bolometer, Golay, pyroelectric) and photon detectors (MCT).

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Topic notes: spectroscopic instruments (Beer–Lambert law, UV–vis and IR instruments, Job's method, AAS and flame emission), with every Civil Services, IFoS and Geo-Scientist PYQ →

CoversIR spectrophotometerNernst glowerGlobarreflection gratingthermocouple detectorMCT detector

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