The (3)Sigma(-)(u)<-X(3)Sigma(-)(g) electronic absorption spectrum of linear C-4 in a neon matrix

The electronic absorption spectrum of linear C-4 in a neon matrix has been detected. This was achieved by codepositing mass selected C-4(-) ions with an excess of neon and UV irradiation of the matrix during or after deposition. Mass selection, experimental and spectroscopic evidence, available ab initio calculations and comparison with the spectra of C-2n (n = 3-7) chains lead to the conclusion that the observed band system with origin at approximate to 380 nm is due to the 3 Sigma(u)(-) <-- X(3) Sigma(g)(-) transition of linear C-4. Vibrational frequencies of C-4 in the excited electronic state have been inferred.