Gas-phase ion/molecule reactions in octafluorocyclobutane

Abstract

Ion/molecule reactions in octafluorocyclobutane (c-C4F8) were studied using a high-pressure mass spectrometer. The thermochemical stabilities of the cluster ions of halide ions (X−) with c-C4F8 were measured. While the F− ion forms a covalent bond with c-C4F8, the interaction between other halide ions with c-C4F8 is mainly electrostatic. Theoretical calculation revealed that the halide ions interact not with the lowest unoccupied molecular orbital but with the next lowest unoccupied molecular orbital of the c-C4F8 molecule in the most stable cluster ions X−(c-C4F8). The electron affinity of c-C4F8 was measured to be 24.2±2.3 kcal/mol (1.05±0.10 eV) by observing the equilibria for reaction of SF6−+c-C4F8=c-C4F8−+SF6. While the sound equilibrium for that reaction was established in the temperature region from ∼350 K down to the lowest temperature measured (∼150 K), that was not established in the higher temperature region above 350 K. This was attributed to the existence of an isomer for c-C4F8− whose electron detachment energy is smaller than 1.05±0.10 eV. By the measurement of thermochemical stabilities of [(O2)m(c-C4F8)n]− (m+n=1–3), the lower electron affinity of c-C4F8 was determined to be 12.0±1.2 kcal/mol (0.52±0.05 eV). The lower limit of the proton affinity of c-C4F8 was estimated to be 130 kcal/mol.