Excited states of vinylic hydrocarbon radicals

Vinyl radicals are of great practical and theoretical interest. They are important intermediates in high-temperature combustion, photochemistry of interstellar nebulae, and photochemical smog formation in the Earth's atmosphere. Recent experiments done by the Laurie Butler group at Chicago have found that photolysis of halogenated precursors produces these radicals in an electronically excited state.

Vinyl radical

Vinyl radical

1-Buten-2-yl radical

1-Buten-2-yl radical

Our work involved calculating the electronic spectra of several of these radicals and characterizing their excited states.

Vinyl radical molecular orbitals

Relevant molecular orbitals of vinyl

The simplest hydrocarbon radical, vinyl, results from removing one hydrogen off of ethylene, leaving a singly-occupied sp2-orbital, labeled as n. For all the radicals in the group, it was found that the lowest excited state, by about 1 eV, is the valence π→n excitation. Overall, the valence states are rather similar in all these radicals. The spectrum is also dense in Rydberg excitations, particularly those from the occupied n and π orbitals. Unlike the valence states, Rydberg states exhibit systematic changes, which were explained in terms of changes in IP and quantum defects.

Changes in the low-lying Rydberg states of the vinyl radical

Changes in the low-lying n→3pxyz Rydberg states

Related Publications

45. L. Koziol, S. V. Levchenko, and A. I. Krylov
Beyond vinyl: Electronic structure of unsaturated propen-1-yl, propen-2-yl, 1-buten-2-yl, and trans-2-buten-2-yl hydrocarbon radicals
J. Phys. Chem. A 110, 2746 – 2758 (2006) Abstract  PDF (270 kB)