Ethylene. Experimental Evidence for New Assignments of Electronic Transitions in the π → π* Energy Region. Absorption and Magnetic Circular Dichroism Measurements with Synchrotron Radiation

Abstract

An exploration of the vacuum ultraviolet magnetic circular dichroism and absorption spectra of propylene and a comparison to ethylene spectra provides new information on the electronic structure of ethylene. Ethylene has three electronic transitions in the energy region previously assigned as two. The presently proposed assignments for these transitions are π → 3s(1Ag → 1B3u), π → π*(1Ag → 1B1u), and π → 3p. The lowest energy transition that was previously assigned as the beginning of the π → π* is assigned as the π → 3s transition. The π → π* and π → 3p transitions are accidentally degenerate in ethylene. The electronic transition with sharp structure doublets which was previously assigned as π → 3s is assigned as one of the π → 3p [π → 3pσ (1Ag → 1B2g), π → 3py (1Ag → 1B1g), or π → 3px (1Ag → 1A1g)] vibronically allowed electronic transitions. A case is presented that it is the π → 3pσ (1Ag → 1B2g) and/or the π → 3py (1Ag → 1B1g) electronic transitions that are responsible for the sharp structured doubl...