Photolysis and radiolysis of cyclopentane in the liquid phase

The liquid-phase photolysis of cyclopentane has been investigated at energies below (7.6, 8.4 eV) and above (10.0, 11.6 eV) the ionization threshold (8.7 eV). The molecules excited by photon absorption and by charge recombination undergo four major dissociation processes: c-C/sub 5/H/sub 10/ ..-->.. H + c-C/sub 5/H/sub 9/ (I); c-C/sub 5/H/sub 10/ ..-->.. H/sub 2/ + c-C/sub 5/H/sub 8/ (II); c-C/sub 5/H/sub 10/ ..-->.. 1-C/sub 5/H/sub 10/ (III); and c-C/sub 5/H/sub 10/ ..-->.. C/sub 2/H/sub 4/ + C/sub 3/H/sub 6/ (IV). The quantum yields of processes I and IV increase drastically with increasing energy at the expense of process II. The ioniztion quantum yield was estimated to be 0.26 +- 0.05 and 0.4 +- 0.1 at 10.0 and 11.6 eV, respectively, based on chemical scavenging of the parent cyclopentane ions. Electron-scavenging experiments show that, in the radiolysis, neutralization (mainly geminate) of the parent ion leads to the formation of electronically excited molecules which dissociated according to processes I-IV. By comparing the relative abundances of these fragmentation channels with their quantum yields in the photolysis experiments at different energies, it is found that the average excitation energy of the cyclopentane molecules formed by charge recombination is in excess of 10 eV. Partial retention of the internal energy of the parent ions at the time of return of the geminate electron is suggested.