AB initio calculation of vertical transition energies of the C2H2 molecule

Various ab initio SCF and Cl treatments are reported for the acetylene molecule in ground and excited states at its fixed linear equilibrium geometry. The results speak in favor of the former analysis of the vacuum UV absorption spectra of C₂H₂ given by Wilkinson according to which above the X?C state an allowed transition to a linear upper state (X?D) and two allowed transitions with broad bands (X?E and X?F) to non-linear upper states are present. The calculated order and spacing of the excited states does not support the new analysis given by Jungen according to which only one allowed transition (X?F) and a forbidden one to a linear upper state (X?D) should appear between 1250 and 1360 A.