Q9. Force constants of H₂⁺, D₂ and H₂
The vibrational wavenumbers of H₂⁺, D₂ and H₂ are approximately 2322, 3118 and 4400 cm⁻¹, respectively. Calculate the force constants for these molecules and comment on the relative magnitudes of the values you obtain. (H = 1, D = 2)
Answer in brief
k(H₂⁺) = 159, k(D₂) = 573, k(H₂) = 570 N m⁻¹; H₂ and D₂ have the same k (same electronic structure), while H₂⁺, with bond order ½, has a much weaker bond.
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Coversforce constantvibrational spectroscopyisotope effectreduced massbond order