The spatial part of an excited state $\mathrm{b}^{3} \Sigma_{\mathrm{u}}^{+}$of hydrogen molecule is proportional to $\left[1 \sigma_{\mathrm{g}}(1) \sigma_{\mathrm{u}}(2)-1 \sigma_{\mathrm{g}}(2) \sigma_{\mathrm{u}}(1)\right]$. Using LCAO-MO expansion of $1 \sigma_{\mathrm{g}}$ and $1 \sigma_{\mathrm{u}}$ in terms of 1s-atomic orbitals, one can infer that this wavefunction has
(a)only ionic parts
(b)only covalent parts
(c)both ionic and covalent parts
(d)neither ionic nor covalent parts
Answer
Answer: B ✓ checked by 4AB · confidence high
The source book printed no answer; this one was worked out and checked — see the explanation.
Explanation
With σ_g = a + b and σ_u = a − b: σ_g(1)σ_u(2) − σ_g(2)σ_u(1) = 2[b(1)a(2) − a(1)b(2)]; the ionic terms a(1)a(2) and b(1)b(2) cancel, so the triplet is purely covalent.