IMPLICATIONS CONCERNING THE ELECTRONIC STATES OF ETHYLENE AND OTHER OLEFINS FROM MAGNETIC CIRCULAR-DICHROISM MEASUREMENTS OF TETRAMETHYLETHYLENE

An investigation of the electronic excited states of tetramethylethyle ne in the 240-160 nm region has been carried out using synchrotron rad iation for magnetic circular dichroism and absorption spectroscopy. Th ese studies show that there are at least six and probably nine electro nic transitions in the region once considered to be the sole domain of the pi --> pi(B-1(1u)) and pi - 3s(B-1(3u)) transitions. The most li kely assignments for the additional four transitions are pi --> 3p(sig ma)(B-1(2g)), pi --> 3p(gamma)(B-1(1g)), pi --> 3d(delta)(B-1(2u)), pi --> 3d(delta)(B-1(3u)), or sigma - sigma. The other three possible e lectronic transitions are discussed in the paper. These studies also i ndicate that the positive magnetic circular dichroism bands observed i n ethylene are due to an additional electronic transition in the pi -- > pi and pi --> 3s region and not a vibronically induced part of the pi --> 3s transition.