Photoelectron spectrum of the vinyl radical: downward revision of the C2H3-ionization potential

The O‐Directed Free Radical Hydrostannation of Propargyloxy Dialkyl Acetylenes with Ph3SnH/cat. Et3B. A Refutal of the Stannylvinyl Cation Mechanism

“…A later Lossing IP determination that used an electron beam on the vinyl radical that they had obtained from the pyrolysis of divinylsulfone yielded a lower value of 8.95 eV, as did a study by Berkowitz (IP=8.43 eV). These lower values are much more in keeping with the later vacuum‐UV photoelectron spectroscopic determination of the IP of the vinyl radical by Chen and Blush, which used a supersonic molecular beam and revealed that the IP was actually even lower 8.25 eV (190.25 kcal mol −1 ) (Scheme ).…”

“… Blush and Chen's experimental determination of the ionisation potential (IP) of a vinyl radical as determined by photoionisation mass spectrometry. Tremendous energy input (190.25 kcal mol −1 /8.25 eV) is required to bring about this ionisation …”

Determination of absolute photoionization cross sections for vinyl and propargyl radicals

“…The most obvious manifestation of this excitation is the observation ͓Figs. 3͑a͒ and 3͑b͔͒ of ion signal at photon energies below the radical ionization potentials, previously found to be 8.25 eV for vinyl 23 and 8.673 eV for propargyl. 24 One must then consider the effect of internal excitation on the value of the photoionization cross section.…”

The ionization energy of the vinyl radical: a Mexican standoff with a happy ending

“…9.20 eV, which is evident in all previously recorded photoionization spectra but not seen in the photoelectron spectrum of Blush and Chen. 29 This indicates a transition to a neutral state, which is only resonant at the corresponding photon energy, and yields photoelectrons by rovibrational autoionization to the electronic ground 1 Aʹ cation state below. Such vibrational progressions are expected for Rydberg manifolds corresponding to ions with a similar geometry to the neutral.…”

“…In fact, the photoelectron spectrum often provides an isomer-specific vibrational fingerprint and can even be used as an analytical tool. 28 But when Blush and Chen pyrolyzed tert-butyl peracrylate and studied the photoelectron spectrum of the vinyl radical, 29 they did not see any vibrational structure. However, on the basis of the onset of the spectrum and surmising that it is only negligibly red-shifted due to hot band transitions, they assigned the IE(C2H3) as 8.25 ± 0.05 eV.…”