Photolysis of Cyclopentane at 1470, 1236, and 1048–1067 Å

Abstract

The photolysis of cyclopentane has been investigated at 1470, 1236, and 1048–1067 Å. The primary process, cyclo-C5H10+hv→C5H8+H2 is of major importance at 1470 Å, but its quantum yield diminishes at shorter wavelengths where processes involving C–C cleavage become more predominant. The products formed in the gas-phase photolysis of cyclo-C5D10—H2S mixtures and in the solid-phase photolysis of cyclo-C5H10 indicate that the excited cyclopentane molecule undergoes ring opening to form a 1-pentene molecule. In the gas phase, the internally excited 1-pentene decomposes to form methyl and ethyl radicals. Evidence is also obtained for the occurrence of the dissociative process: C5H10*→C2H4+C3H6 where C3H6 consists of cyclopropane and propylene. At 1048–1067 Å (11.6–11.8 eV), ionization is extensive (ionization potential of cyclo-C5H10=10.5 V). Saturation current measurements yielded a value of 0.64 for ηC5H10/ηNO. On the basis of an isotopic analysis of the propane formed in the photoionization of C5D10–C5H10–O2 mixtures it is shown that the parent ion dissociates as follows: C5H10+→C3H6++C2H4 and that the C3H6+ ions participate in an H2− transfer reaction: C3H6++C5H10→C3H8+C5H8+. Fragmentation of the parent ion diminishes with an increase in pressure. The collisional deactivation process is more pronounced for the perdeuterated than for the perprotonated cyclopentane ion. The data also indicate that a fraction of the parent ions undergoes ring opening to form cis- or trans−2-pentene as a final product.