Study of the OH^- + CH₂F₂ Reaction by Selected Ion Flow Tube Experiments and ab Initio Calculations

Abstract

The reaction OH -+ CH 2 F 2 f products has been investigated by both selected ion flow tube (SIFT) experiments and ab initio molecular calculations. The SIFT experiments showed that a bimolecular process, leading to two major anionic products, CHF 2 -(86%) and F -(11%), and one minor anionic product, HF 2 -(3%), is in competition with a three-body association leading to OH -‚CH 2 F 2 (where values in parentheses are the relative values of the detected anionic products at 300 K). From a pressure dependence study, an upper limit of the bimolecular reaction rate coefficient at 300 K is determined to be (2.4 ( 1.4) × 10 -12 cm 3 molecule -1 s -1 . This shows a small negative temperature dependence, suggesting that the reaction proceeds via an ion-complex intermediate. These experimental results were rationalized using ab initio molecular orbital calculations. Stationary points on the reaction paths of the two main reaction channels were located at both the HF/6-31++G ** and MP2/6-31++G ** levels. The relative energies of the located stationary points were calculated at up to the CCSD(T)/6-311++G 3df,2p //MP2/6-31++G ** level. The CHF 2 -+ H 2 O channel was found to be endothermic by 7.5 kcal mol -1 and the F -+ CH 2 (OH)F channel was found to be exothermic by 20.4 kcal mol -1 . It was found that both reaction channels proceed via the reactant-like ion-molecule complex intermediate, OH -‚CH 2 F 2 , in agreement with the conclusion drawn from the experimental negative temperature dependence of the overall rate coefficient. The fact that the product anion yields show that [CHF 2 -] > [F -], despite the fact that the CHF 2 -+ H 2 O channel is endothermic whereas the F -+ CH 2 (OH)F channel is exothermic, has been rationalized using transition-state theory.

Nature of the transition state in gas phase SN2 identity reactions: correlation between nucleophilicity and proton affinity

“…pioneering work in the field of gas phase negative ion-molecule chemistry. [13][14][15][16][17][18][19][20][21][22] On the other hand, the cationic subclass [eqn. (3)]…”

Oxygen anion (O−) and hydroxide anion (HO−) reactivity with a series of old and new refrigerants

“…The latter result is closer to the capture rate coefficient k c = 2.4 10 −9 cm 3 .s −1 calculated for the reaction. Lee et al studied the reactivity of a similar molecule CH 2 F 2 with hydroxide . Three products were observed: CHF 2 − , F − , and HFF − .…”

“…Lee et al studied the reactivity of a similar molecule CH 2 F 2 with hydroxide. 76 Three products were observed: CHF 2 − , F − , and HFF − . They noticed that despite the fact that the proton transfer pathway was slightly endothermic compared to the highly exothermic S N 2 reaction, the major product was CHF 2 − .…”

Theoretical Insight into the Kinetics of H‐Abstraction Reaction of CHF2CH2OH with OH Radical, Atmospheric Lifetime and Global Warming Potential

“…For the reaction CH 2 F 2 +OH, we have obtained a barrier height of 12.26 kJ/mol and for CH 2 F 2 +Cl, a barrier height of 53.09 kJ/mol has been obtained. Lee et al . reported a rate coefficient of (2.4± 1.4)×10 −12 cm 3 molecule −1 s −1 at 300 K for the reaction CH 2 F 2 +OH.…”