Electron attachment and detachment and the electron affinity of cyclo-C4F8.

Abstract

New measurements have been made of rate constants for electron attachment to c-C(4)F(8) (octafluorocyclobutane) and thermal electron detachment from the parent anion, c-C(4)F(8) (-), over the temperature range 298-400 K in 133 Pa of He gas in a flowing-afterglow Langmuir-probe apparatus. From these data the electron affinity for c-C(4)F(8) was determined, EA(c-C(4)F(8))=0.63+/-0.05 eV. The motivation was to resolve a discrepancy between our earlier EA estimate and a higher value (EA=1.05+/-0.10 eV) reported from a recent experiment of Hiraoka et al. [J. Chem. Phys. 116, 7574 (2002)]. The electron attachment rate constant is 9.3+/-3.0x10(-9) cm(3) s(-1) at 298 K. The electron detachment rate constant is negligible at room temperature but climbs to 1945+/-680 s(-1) at 400 K. G3(MP2) calculations were carried out for the neutral (D(2d), (1)A(1)) and anion (D(4h), (2)A(2u)) and yielded EA(c-C(4)F(8) (-))=0.595 eV. Bond energies were also calculated for loss of F from c-C(4)F(8) and loss of F or F(-) from c-C(4)F(8) (-). From these, dissociative electron attachment is found to be endothermic by at least 1.55 eV.