Renner-teller effect at the initial acetylene thermal transformation stages

Abstract

It is shown that the vibrational excitation of the acetylene molecule is accompanied by the transformation of its linear structure into a transoid structure because of the Renner-Teller effect. The electron density distribution in transoid acetylene was calculated by nonempirical quantum-chemical methods. It was shown that this structure corresponded to a 1,2-biradicaloid. The intense light absorption in the acetylene spectrum at λmax = 240 nm and temperature above 800 K was found to be related to the S2 ⇃ S0 electron transition. Transoid acetylene 1,2-biradicaloids were shown to participate in the dimerization reaction with the formation of trans-1,4 biradicals. The enthalpies and energy barriers were determined for some elementary stages of the primary thermal transformations of acetylene.