Gas Sensing for Commercial Refrigerants R-134a and R-1234yf Using Rotational Absorption Spectroscopy in the 220–330 GHz Frequency Range

The detection of gaseous refrigerants, necessary for industrial control and environmental monitoring, is explored using rotational spectroscopy in the THz wave region. Rotational absorption spectra for two widely used commercial hydrofluorocarbon (HFC) refrigerants, 1,1,1,2-tetrafluoroethane (R-134a or HFC-134a) and 2,3,3,3-tetrafluoropropene (R-1234yf or HFO-1234yf), are characterized in the 220–330 GHz frequency range at room temperature (297 K) and modest pressures (0.25–8 Torr) using a compact microelectronics-based THz wave spectrometer. The absorption spectra illustrate complex, broad, and repeating structures that result from the blending of hundreds of pressure-broadened rotational lines. The unique and distinct spectra for R-134a illustrate potential for its detection in the present frequency region with estimated detection limits approaching 15 ppm per meter path length in 1 atm of air. The spectra for R-1234yf are less distinct than those for R-134a and illustrate complex structured rotational absorption features in combination with an underlying quasi-continuous absorption that increases in strength to higher frequencies. To our knowledge, this is the first experimental characterization for the spectra of R-134a and R-1234yf in this frequency region.