Q43 · CSIR-NET Chemistry, December 2011
Paper: CSIR-NET December 2011 · Subject: Inorganic Chemistry · Chapter: Coordination Chemistry · Topic: Electron Transfer Redox · Marks: 2 · Difficulty: Easy
Observe the following electronic transition of a diatomic molecule. (A) $^{1}\Sigma_{g}^{+} \rightarrow {}^{3}\Sigma_{g}^{+}$ (B) $^{1}\Sigma_{u}^{+} \rightarrow {}^{1}\Sigma_{g}^{+}$ (C) $^{1}\Delta_{u} \rightarrow {}^{1}\Sigma_{g}^{+}$ (D) $^{1}\pi_{g} \rightarrow {}^{1}\Sigma_{u}^{+}$ The allowed transitions are
(a)(A) and (C) only
(b)(B) and (D) only
(c)(A), (B) and (C) only
(d)(A), (C) and (D) only
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
Dipole selection rules: ΔS = 0, g↔u, ΔΛ = 0, ±1, Σ⁺↔Σ⁺. ¹Σu⁺→¹Σg⁺ and ¹Πg→¹Σu⁺ are allowed. The others break the spin or ΔΛ rule (b).
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