An Experimental and Theoretical Investigation of the Excited States of Isobutene

Vacuum ultraviolet magnetic circular dichroism (MCD)
and absorption spectra of isobutene were obtained
experimentally and compared to theoretical data
(DFT calculation with Gaussian software) with the
goal of better understanding the electronic structure
of simple olefins. MCD is the differential absorption of
left and right circular polarized light in the presence
of an external magnetic field. This means that a MCD
spectrum contains both positive and negative peaks
while an absorbance spectrum contains only positive
peaks. MCD is useful when used in conjunction
with a corresponding absorbance spectrum to assign
spectral bands that may have been hidden by overlap
in the absorbance spectrum. The experimental and
theoretical results coincide with the two lowest energy
transitions of isobutene being assigned as [...]. This is also consistent with what has been observed
in ethylene and propylene, π→π^* is not the
lowest transition in mono-olefins.