Environmentally Applied Refrigerant Technology Hub
(EARTH)

The chemistry of the refrigerants on ice surfaces and within ices is not well known. After the Montreal protocol, the ozone depleting cholorofluoro carbons (CFC) were replaced by more environment friendly hydrofluoro carbons (HFC). But the understanding of the refrigerant chemistry in upper troposphere and of their degradation products is still in its infancy. New-generation HFCs, mainly hydrofluoroolefins (HFOs) like 2,3,3,3-tetrafluoropropene are widely utilized in household and automotive industries for cooling systems. However, there is a significant knowledge gap with respect to the fate of these new refrigerants under tropospheric conditions with concerns that they may form persistent chemicals like trifluoroacetic acid. Once released into the troposphere, it is speculated that these refrigerants are degraded eventually to trifluoroacetyl fluoride (CF₃CFO), trifluoro acetaldehyde (CF₃CHO), and ultimately trifluoro acetic acid (CF₃COOH). In the presence of water crystals and in particular on water surfaces, these degradation processes are unknown. These processes are simulated and explored under matrix isolation conditions and on surfaces of water ices in an ultrahigh vacuum vessel.

Hydroxyl (OH) radicals play a central role in the atmospheric chemistry of the degradation of hydrofluorocarbons (HFCs). Due to their high reactivity, they initiate a complex chain of gas phase reaction, and hence, there is a concern on how the can affect the chemistry of the troposphere. On the one hand, HFCs have been exploited as refrigerants in air conditioning and refrigeration systems, but key refrigerants represent potent greenhouse gases. On the other hand, new refrigerants are being developed as a more environmentally friendly alternative to HFCs, but laboratory data are needed to investigate the effect of these refrigerants on the atmospheric chemistry. Therefore, it is essential to study in the laboratory the intermediates and products of reactions of refrigerants with hydroxyl radicals, since they are unknown and can lead to the formation of environmentally harmful species. The crossed molecular beams apparatus offers a highly detailed view of the reaction dynamics of these bimolecular processes, allowing to elucidate their entrance and exit barriers, and reaction intermediates, critical for understanding the atmospheric fate of the investigated refrigerants, such as 1,1,1,2-tetrafluoroethane (CF₃CH₂F) or trifluoropropene (C₃F₃H₃). In these experiments, a primary supersonic beam of hydroxyl radicals interacts with a second supersonic beam containing the refrigerant under single collision conditions. The reactively scattered products are monitored by a triply differentially pumped mass spectrometric detector, rotatable in the scattering plane defined by the primary and secondary beams. At the entrance of the detector the neutral products are ionized by electron impact ionization and filtered according to their mass to charge ratio by a quadrupole mass spectrometer.