Photoelectron Spectra of the cis- and trans-Isomers of Some Ethylene Derivatives

The photoelectron spectra of cis- and trans-stilbenes, fumaric acid, dimethyl maleate, and dimethyl fumarate were measured and interpreted, special attention being paid upon their difference between the corresponding trans- and cis-isomers. The two characteristics were found for the photoelectron spectra of cis- and trans-stilbenes: (1) the splitting between the first and fifth bands is smaller for the cis-isomer (steric-hindrance effect); (2) the splitting between the second and third bands is larger for the cis-isomer (through-space interaction). The difference in the carbonyl n orbital ionization potentials between dimethyl maleate and fumarate was interpreted in terms of through-bond interaction.