An s.c.f.-l.c.a.o.-m.o. ground state wave function for the lowest 3Σg− and for an excited 1Σg+ state of C4 is reported. All twenty-four electrons are considered in this computation. The internuclear distance assumed for all the states is 1.28 Å. for the three bonds of C4, following some earlier prediction. Diagrams are presented which give a pictorial representation Of the molecular orbitals obtained. An l.c.a.o-m.o. computation was done for the 1Δgand 1Σg+ states and for a second 1Σg+ excited state. A discussion is given on the expected bond variation for the different excited states, as compared with the ground state. Estimates are made of the centers of gravity for the two lowest 3II and 1II states. It is concluded that the 3Σg− should be the ground state as earlier suggested by Pitzer and the author. © 1961, American Chemical Society. All rights reserved.