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

ABSTRACT

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 d_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.

KEYWORDS:

• CHF₃
• fluoroform
• high-resolution infrared spectroscopy
• greenhouse gas absorption
• intramolecular quantum dynamics
• FTIR
• THz

Acknowledgment

Substantial help from and many discussions with Ziqiu Chen, Csaba Fábri, Ľuboš Horný, Carine Manca Tanner and Georg Seyfang are gratefully acknowledged. Our work is supported financially by ETH Zürich in particular the Laboratory of Physical Chemistry, the Swiss National Science Foundation and an ERC advanced grant. We also enjoyed discussion with and support from Frédéric Merkt and Alexander Wokaun. Hospitality for our project at the Swiss Light Source is acknowledged as well as also support from COST MOLIM. Part of the research was funded from Tomsk Polytechnic University Competitiveness Enhancement Program grant, project TPU CEP-PTI-72/2017.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

European Research Council [project number 290925]; Tomsk Polytechnic University Competitiveness Enhancement Program [grant number TPU CEP-PTI-72/2017]; Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung [grant number 200020-153057].