Ethylene.: Experimental evidence for new assignments of electronic transitions in the π → π* energy region.: Absorption and magnetic circular dichroism measurements with synchrotron radiation

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 pi --> 3s((1)A(g) --> B-1(3u)), pi --> pi*(1A(g) --> B-1(1u)), and pi --> 3p. The lowest energy transition that was previously assigned as the beginning of the pi --> pi* is assigned as the pi --> 3s transition. The pi --> pi* and pi --> 3p transitions are accidentally degenerate in ethylene. The electronic transition with sharp structure doublets which was previously assigned as pi --> 3s is assigned as one of the pi --> 3p [pi --> 3p(sigma) ((1)A(g) --> B-1(2g)), pi --> 3p(y) ((1)A(g) --> B-1(1g)), or pi --> 3p(x) ((1)A(g) --> (1)A(1g))] vibronically allowed electronic transitions. A case is presented that it is the pi --> 3p(sigma) (1A(g) --> B-1(2g)) and/or the pi --> 3p(y) ((1)A(g) --> B-1(1g)) electronic transitions that are responsible for the sharp structured doublets in ethylene.