In an effort to be able to identify the linear and rhombic states of C 4 , Mühlhäuser et al. computed the vertical electronic spectrum of C 4 using MRCI calculations. However, the spectrum was studied only until 6.5 eV whereas in hypersonics, the spectral region of interest lies between 7.0 -8.3 eV. In the calculations presented below, vertical energies upto 11 eV are obtained. At the equilibrium geometry of the excited state, the excited state of interest is characterized by an oscillator strength of 1.6517, thereby denoting a very strong transition. The vertical excitation from the ground state at this geometry is 6.4004 eV. At the equilibrium geometry of ground state, the vertical excitation is 6.8367 eV with an oscillator strength 1.8511. . The blue line represents the optimal geometry plotted in the standard orientation and the orange lines show the bonds are distortion due to vibrations.