The GATE Grind

GATE 2022 CY – Question 29

Physical Chemistry · Spectroscopy: Atomic spectroscopy; Russell-Saunders coupling; Term symbols and spectral details; origin of selection rules. Rotational, Vibrational, Electronic and Raman spectroscopy of diatomic and simple polyatomic molecules. Line broadening and line widths; simple properties of Gaussian and Lorentzian line shapes. Molecular spectroscopy: Absorbance, Beer- Lambert’s law, Einstein’s coefficient, Jablonski diagram. Relationship of transition moment integral with molar extinction coefficient and oscillator strength. Basic principles of Nuclear Magnetic Resonance: Gyromagnetic ratio; Chemical shift, nuclear coupling. · 1 mark · Multiple select

The CORRECT statement(s) about the spectral line broadening in atomic spectra is(are)

  1. The collision between atoms causes broadening of the spectral line
  2. Shorter the lifetime of the excited state, the broader is the line width
  3. Doppler broadening is more pronounced as the flame temperature increases
  4. In flame and plasma, the natural line broadening exceeds the collisional line broadening

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Show answer and explanation

Correct answer: (A) The collision between atoms causes broadening of the spectral line; (B) Shorter the lifetime of the excited state, the broader is the line width; (C) Doppler broadening is more pronounced as the flame temperature increases

Explanation

Collisions perturb phase and energy, broadening lines, A. The uncertainty relation makes a shorter excited-state lifetime correspond to a larger natural linewidth, B. Thermal velocities increase Doppler broadening with temperature, C. In flames/plasmas, natural broadening is generally smaller than collisional broadening, so D is false. **Select A, B, C**.