The GATE Grind

GATE 2022 CY – Question 49

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. · 2 marks · Multiple choice

Match rotor types P oblate symmetric, Q prolate symmetric, R spherical, S asymmetric with molecules 1 $SiH_4$, 2 $CH_3Cl$, 3 $C_6H_6$, 4 $CH_3OH$, 5 $CO_2$.

  1. P-1, Q-2, R-3, S-4
  2. P-3, Q-2, R-1, S-4
  3. P-3, Q-5, R-1, S-2
  4. P-5, Q-4, R-3, S-2

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (B) P-3, Q-2, R-1, S-4

Explanation

Planar benzene has oblate symmetric inertia; CH3Cl is prolate symmetric aboutC–Cl. Tetrahedral SiH4 has three equal principal moments and is spherical. Methanol has three unequal moments and is asymmetric.

Thus **P3, Q2, R1, S4, B**; linear CO2 is not one of these four matches.