Theoretical study of the U.V. spectrum of acetylene

Abstract

Electronic ground state and lowest lying excited singlet species of predominantly valence character of acetylene are studied by means of the ab initio method. 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 1 ¹Σ^- _u ← 1 ¹Σ⁺ _g and 1 ¹Δ _u ← 1 ¹Σ⁺ _g (D _∞h notation), 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 observed à ← [Xtilde] and [Btilde] ← [Xtilde] spectra of acetylene.