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GATE 2021 CY – Question 28

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 normal mode(s) of vibration of H2O is/are:

Diagram for GATE 2021 CY question 28
  1. Diagram A
  2. Diagram B
  3. Diagram C
  4. Diagram D

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Show answer and explanation

Correct answer: (A) Diagram A; (B) Diagram B; (C) Diagram C

Explanation

A nonlinear three-atom molecule has 3N−6=3 normal vibrations. Water has a symmetric O–H stretch, an H–O–H bend and an asymmetric O–H stretch, represented by A, B and C respectively. D moves all three atoms together in the same direction and is a translation rather than an internal vibration. **A,B,C**.