Note on Electronic States of Diatomic Carbon, and the Carbon-Carbon Bond

It is shown that the λ2300 carbon band analyzed by Landsverk belongs very probably to the transition σg²σᵤπᵤ⁴σg, ¹Σᵤ⁺→σg²σᵤ²πᵤ⁴, ¹Σg⁺. The ¹Σg⁺ state should lie not far above the normal state of C₂, or possibly be the normal state. Approximate energies and internuclear distances (r₀) are predicted and tabulated for all low-energy states of C₂ and C₂^_⁺; an equation for predicting r₀'s is given. Carbon-carbon bond distances in polyatomic carbon compounds are compared with those in C₂. Apparently bonding to other atoms helps to shorten C---C and C=C bonds in polyatomic compounds as compared with C₂. The same effect is noted in nitrogen compounds.