| Popis: |
The radiative relaxation of the first excited states, A(π −1 ), of two C 6 H 6 + radical cations in the gaseous phase has been detected following excitation by low energy electron impact. The A 2 E u → X 2 E g emission band system of 2,4-hexadiyne cation, and the O 0 0 band of the corresponding emission of 1,3-hexadiyne cation, which are identified by comparison with their photoelectron spectra are presented and discussed. The decay of the A(π −1 ) excited states of these C 6 H 6 ∓ ions is exceptional as the fragmentation and radiative pathways are competitive and are both detected experimentally. The lifetime of the A 2 E u state of 2,4-hexadiyne radical cation was measured to be 24 ± 2 ns, which considered together with the upper limit of 0.6 for the quantum yield of emission inferred from the cation breakdown diagram of the A 2 E u state, indicates that the radiative and non-radiative pathways deplete the A 2 E u state at approximately the same rate of 2 × 10 7 s −1 . The implications of the observations of the radiative relaxation of these two electronically excited C 6 H 6 ∓ radical cations lying above the fragment ion appearance potentials are considered with respect to the isomerization and fragmentation of C 6 H 6 ∓ isomers. |
