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

It is shown that the

λ 2300

carbon band analyzed by Landsverk belongs very probably to the transition

{σ_{g}}^{2} σ_{u} {π_{u}}^{4} σ_{g}

{}^{1}{Σ_{u}}^{+} \to {σ_{g}}^{2} {σ_{u}}^{2} {π_{u}}^{4}

{}^{1}{Σ_{g}}^{+}

. The

{}^{1}{Σ_{g}}^{+}

state should lie not far above the normal state of

C_{2}

, or possibly be the normal state. Approximate energies and internuclear distances (

r_{0}

) are predicted and tabulated for all low-energy states of

C_{2}

and

C_{2}^{+}

; an equation for predicting

r_{0}' s

is given. Carbon-carbon bond distances in polyatomic carbon compounds are compared with those in

C_{2}

. Apparently bonding to other atoms helps to shorten C—C and C=C bonds in polyatomic compounds as compared with

C_{2}

. The same effect is noted in nitrogen compounds.

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