Gas-phase ion/molecular reactions in octafluorocyclobutane

摘要

Ion/molecule reactions in octafluorocyclobutane (c-C_4F_8) were studied using a high-pressure mass spectrometer. The thermochemical stabilities of the cluster ions of halide ions (X~-) with c-C-4F_8 were measured. While the F~- ion forms a covalent bond with c-C_4F_8, the interaction between other halide ions with c-C_4F_8 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-C_4F_8 molecule in the most stable cluster ions X~- (c-C_4F_8). The electron affinity of c-C_4F_8 was measured to be 24.2 (+-) 2.3 kcal/mol (1.05 (+-) 0.10 eV) by observing the equilibria for reaction of SF_6~- + c-C_4F_8~- = c-C_4F_8~- + SF_6. While the sound equilibrium for that reaction was established in the temperature region from approx 350 K down to the lowest temperature measured (approx 150 K), that was not established in in the higher temperature region above 350 K. This was attributed to the existence of an isomer for c-C_4F_8~- whose electron detachment energy is smaller than 1.05 (+-) 0.10 eV. By the measurement of thermochemical stabilities of [(O_2)_m(c-C_4F_8)_n]~- (m + n = 1-3), the lower electron affinity of c-C_4F_8 was determined to be 12.0 (+-) 1.2 kcal/mol (0.52 (+-) 0.05 eV). The lower limit of the proton affinity of c-C_4F_8 was estimated to be 130 kcal/mol.