Electronic ground state and lowest lying excited singlet species of predominantly valence character of acetylene are studied by means of theab initiomethod. The potential curves are calculated for trans- and cis-bending, symmetric C-H and C-C stretching vibrations at planar molecular geometries and for torsional motion at a number of values of the H-C-C bond angle. It is found that the electronic species studied are contaminated at non-linear and non-planar nuclear arrangements with Rydberg-type configurations. A very simple vibrational analysis of the electronic transitions 11Σ-u← 11Σ+gand 11Δu← 11Σ+g(D∞hnotation), neglecting all types of mode couplings (vibrational and vibronic, i.e. non-adiabatic), is performed. The results obtained are employed for an interpretation of the observedÃ←[Xtilde]and[Btilde]←[Xtilde]spectra of acetylene.