F‐to‐HF reactions. VIII. Nonthermal complications for the CHF₃/C₃F₆/C₂F₆ moderated nuclear recoil system

Abstract

Results are reported from moderated nuclear recoil I8F experiments with the 273 K CHF:+/C:,F~/CZF~ system. Although the measurement sensitivity is only about f12%, there is no evidence to support the occurrence of nonthermal F-to-HF reactions at 95 mol % CzFe moderator concentration.

Chemical Kinetics and Hot Atom Chemistry — Present Status and Future Perspectives

“…The early 18 [132,133,135] led to relative Arrhenius parameters exhibiting good agreement with literature data [137,139,[229][230][231][232], However, the subsequent attempts to develop absolute scaling relations based upon these results have been disappointing, probably in part because of previously unanticipated 18 F loss unimolecular decomposition complications associated with the thermal 18 F + C 3 F 6 reaction at 1.32 atm [234], Although the moderated nuclear recoil method is applicable for this type of study, further 18 F experiments are needed at enhanced moderator concentrations and total pressures.…”

F‐to‐HF reactions. IX. Nonthermal complications for the CH4/C3F6/C2F6 moderated nuclear recoil system

“…The O2 concentration in each sample must either be reduced to the sub-parts-per-million level or be consistently maintained in excess of 2.0 mol-%. The fluorocarbon and CH4 reagents have been purified from impurity 0 2 using repeated 77 K freeze-pump-thaw cycles and Cs gettering, respectively Kinetic complications resulting from the presence of reactive impurities in the C2F6 become important in 18F MNR experiments at large moderator concentrations [17]. Because C2F6 concentrations as large as 99.95 mol-% have been used in this study, several precautions in addition to routine vacuum degassing have been observed to ensure the quality of the C2F6 reagent.…”

“…Because our measurement techniques have been described in companion papers [4,17,18], the following account has been limited to the preparation of high-pressure samples containing CH4 thermal competitor.…”

“…Manipulations with high-pressure samples are extremely hazardous. The safety procedures described in the companion paper should be carefully followed [17]. Table 11.…”

“…With a kgW value of (1.1 f 0.1) X 1013 cm3/mol-s reaction (2) is about 100-fold faster than the 300 K thermal 18F + CHF3 process. As shown in the companion paper [17], the precision of the CHF3/C3F&$6 18F MNR system is thus only N f12%. However, our experiments with CHFB did not yield evidence for kinetic complications due to nonthermal F-to-HF reactions.…”