High resolution FTIR spectroscopy of fluoroform ¹²CHF₃ and critical analysis of the infrared spectrum from 25 to 1500 cm⁻¹

We report high-resolution ( 0.001 cm⁻¹) Fourier Transform Infrared spectra of fluoroform (CHF₃) including the pure rotational (far infrared or THz) range (28–65 cm⁻¹), the ν₃ fundamental ( = 700.099 cm⁻¹), as well as the associated “hot’ band 2ν₃ − ν₃ ( = 699.295 cm⁻¹) and the ‘atmospheric window’ range 1100–1250 cm⁻¹ containing the strongly coupled polyad of the levels ν₂, ν₅ and ν₃ + ν₆, at room temperature and at 120 K using the collisional cooling cell coupled to our Bruker IFS 125 HR prototype (ZP2001) spectrometer and Bruker IFS 125 HR ETH-SLS prototype at the Swiss Light Source providing intense synchrotron radiation. The pure rotational spectra provide new information about the vibrational ground state of CHF₃, which is useful for further analysis of excited vibrational states. The ν₃ fundamental band is re-investigated together with the corresponding ‘hot’ band 2ν₃ − ν₃ leading to an extension of the existing line lists up to 4430 transitions with = 66 for ν₃ and 1040 transitions with = 43 for 2ν₃ − ν₃. About 6000 transitions were assigned to rovibrational levels in the polyad ν₂/ν₅/ν₃ + ν₆ with = 63 for ν₂ ( = 1141.457 cm⁻¹), = 63 for ν₅ ( = 1157.335 cm⁻¹) and = 59 for ν₃ + ν₆ ( = 1208.771 cm⁻¹)( = in each case). The resonance interactions between the ν₂, ν₅ and ν₃ + ν₆ states have been taken into account providing an accurate set of effective hamiltonian parameters, which reproduce the experimental results with an accuracy close to the experimental uncertainties (with a root mean square deviation <i>d</i>_rms = 0.00025 cm⁻¹). The analysis is further extended to the ν₄ fundamental ( = 1377.847 cm⁻¹) interacting with 2ν₃ ( = 1399.394 cm⁻¹). The results are discussed in relation to the importance of understanding the spectra of CHF₃ as a greenhouse gas and as part of our large effort to measure and understand the complete spectrum of CHF₃ from the far-infrared to the near-infrared as a prototype for intramolecular quantum dynamics and rovibrational energy redistribution.