The electron impact spectra of some mono-olefinic hydrocarbonsa)

Abstract

Electron impact spectra of ethylene, propylene, isobutene, trans-butene, cis-butene, trimethylethylene, and tetramethylethylene have been obtained at scattering angles of 0° and 90° and at impact energies from ?20 to 150 eV. The spectra scan an energy-loss region from 2.5–15 eV. All of the observed Rydberg transitions of the methyl derivatives are correlated to corresponding Rydberg transitions of ethylene. The missing π→3p transitions of ethylene are tentatively located via this correlation. Evidence is also presented for assigning the N→3R′ system of ethylene (at 8.26 eV) to a π→3px transition. Possible assignments of some broad continua above ?8–9eV as σ→π* and σ→σ* transitions are considered. In agreement with other reported large-angle electron impact spectra, no evidence is obtained for transitions that could be assigned to triplet Rydberg states. However the π→π* triplet transitions are all clearly located with transition energies in good agreement with those obtained by a variety of other techniques.

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

“…The electronic excited states of propylene have been previously investigated using absorption spectroscopy, electron impact spectroscopy and theoretical calculations. 1,17,39,52,[62][63][64][65][66][67] The magnetic circular dichroism results are consistent with what was expected from these previous results; however, it also gives new information about the electronic structure. The magnetic circular dichroism spectrum shows unequivocally that there are at least three electronic transitions in this energy region and also shows the energy of these transitions.…”

Implications Concerning the Electronic States of Ethylene and Other Olefins from Magnetic Circular Dichroism Measurements of Tetramethylethylene

“…These results are consistent with electron impact measurements on tetramethylethylene which showed two transitions in this region in addition to the π f 3s and π f π* transitions. 29 These two transitions occurred at about 205 and 196 nm. This compares well with our proposed π f 3p σ at 204.5 nm and π f 3p y in the 195 nm region.…”

A theoretical study of the diffuseness of the V(1B1u) state of planar ethylene

“…It differs by 0.28 eV from the experimental value for the maximum of the absorbtion band [26]. However, this energy difference can be explained easily by the nonvertical nature of the excitation, where the band maximum corresponds to a slightly twisted molecule [ 101.…”

“…The excitation energy, which is experimentally found to be 7.66 eV [26], has never been reproduced by an ab initio method to the level of accuracy expected. The best theoretical result could be argued to be that of Sunil et al [21] of 8.09 eV, which is 0.4 eV larger than the experimental result.…”