Paper: CSIR-NET December 2016 · Subject: Physical Chemistry · Chapter: Group Theory · Topic: Group Theory – General · Marks: 2 · Difficulty: Medium
For $\mathrm{H_2O}$ molecule, the electronic transition from the ground state to an excited state of $\mathrm{B_1}$ symmetry is
$\mathrm{C_{2v}}$
E
$\mathrm{C_2}$
$\sigma_v$
$\sigma_v'$
$\mathrm{A_1}$
1
1
1
1
$z, z^2, x^2, y^2$
$\mathrm{A_2}$
1
1
-1
-1
xy
$\mathrm{B_1}$
1
-1
1
-1
x,xz
$\mathrm{B_2}$
1
-1
-1
1
y,yz
(a)not allowed
(b)allowed with $\mathrm{x}$ polarization
(c)allowed with $\mathrm{y}$ polarization
(d)allowed with $\mathrm{z}$ polarization
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
H₂O is C₂v with A₁ ground state; the transition to B₁ is allowed by the B₁ component of the dipole, which is x (with the molecule in the yz plane): x-polarised.