Gas-Phase Ion/Molecule Reactions in C₅F₈

Abstract

Gas-phase ion-molecule reactions in octafluorocyclopentene (C5F8) were studied with a pulsed electron beam mass spectrometer. When a few Torr of major gas, CH4, Ar, or N2, containing approximately 10 mTorr C5F8 was ionized by 2 keV electrons, C5F8+, C5F7+, C4F6+, C4F5+, and C3F3+ were formed as major fragment ions. The interaction between those ions and C5F8 is found to be a weak electrostatic interaction. The cation...C5F8 bonding energies are around 10 kcal/mol, which were reproduced well by (U)B3LYP/6-311+G(d) calculations. The proton affinity of C5F8 (=148.6 kcal/mol by B3LYP/6-311+G(d)) was found to be smaller than that of C2H4 (=162.8 kcal/mol). In the negative mode of operation, the intense signal of C5F8- was observed during the electron pulse. This indicates that C5F8 has a positive electron affinity (1.27 eV by (U)B3LYP/6-311+G(d)). The C5F8- ion was quickly converted to a complex C10F16-. This complex did not react further with C5F8 down to 170 K. The theoretical calculation revealed that a C5F7-F-...C5F8 interaction mode in (C5F8)2- was converted to a C5F7*...C5F9- one via fluoride-ion transfer. The F- ion was found to form a strong covalent bond with C5F8, but the interaction in F-(C5F8)- - -C5F8 is a weak electrostatic interaction due to the charge dispersal in F-(C5F8). The halide ions except F- interact with C5F8 only weakly. Thermochemical stabilities for the cluster ions I-(CH3I)n (n = 1, 2) were also determined.

Selected ion flow tube cation–molecule reaction studies and threshold photoelectron photoion coincidence spectroscopy of cyclic-C5F8

“…± 0.7 eV, while Hiraoka et al 12 calculated the IE to be 11.2 eV using B3LYP methods. To verify these values, we have performed a new electron ionisation study at the Institut für Ionenphysik in Innsbruck, 34 and a He(I) photoelectron spectrum has been recorded at the University of Southampton.…”

“…The second study investigated cation and anion molecule reactions in a high pressure environment. 12 One aim of this work is to gain insight into how electron transfer occurs in bimolecular reactions.…”

Positive Ion/Molecule Reactions in Tetrafluoroethylene

“…1. Figure 2 shows the temperature dependence of the rate constants for reaction (5) measured in the temperature range of 180῎310 K. Although the data points are rather scattered due to the di$culty in maintaining the steady-state experimental conditions (charging of the ion source), the rate constants for reaction (5) are found to be independent on the ion source temperature in the range of 180῎310 K. It was confirmed that the second-order rate constants for reaction (5) were independent on the change of the C 2 F 4 pressure in the range of 1 to 13 mTorr, i.e., reaction (5) is first-order with the C 2 F 4 pressure. The average value of the rate constants in the range of 180῎310 K in Fig.…”

“…The formation of CF 3 ῌ as one of the major ions is a very important information in the plasma chemistry because this ion is known to act as a very e$cient etchant in the semiconductor fabrication. (5). That is, reactions (4) and (5) are highly exothermic.…”

“…These plasma process technologies with fluorocarbon gases require a deeper understanding of the chemical reactivities of these fluorocarbons. In our previous work, gas-phase ion/molecule reactions in CF 4 , 1), 2) C 3 F 6 , 3) c-C 4 F 8 , 4) and C 5 F 8 , 5) were studied in detail. The interactions between positive ions and C 3 F 6 or C 5 F 8 are weak and mainly electrostatic.…”