Non-Empirical Analysis of Isotopic Shifts and Resonance Effects in the Infrared High-Resolution Spectrum of Freon-22 (CHF2Cl), Enriched with 13C

• Published in: Optics and spectroscopy 2023-08, Vol.131 (8), p.688-699
• Main Authors: Krasnoshchekov, S. V., Gainullin, I. K., Laptev, V. B., Klimin, S. A.
• Format: Article
• Language: English
• Subjects: Carbon 12; Chlorine isotopes; Chlorodifluoromethane; Dipole moments; Empirical analysis; Frequency ranges; Infrared analysis; Lasers; Mixtures; Optical Devices; Optics; Perturbation theory; Photonics; Physics; Physics and Astronomy; Potential energy; Resonance; Resonant frequencies; Rotational spectra
• ISSN: 0030-400X; 1562-6911
• DOI: 10.1134/S0030400X23060097

The IR transmittance spectrum of an isotopic mixture of chlorodifluoromethane (CHF 2 Cl, Ereon-22) with a 33% fraction of 13 C and a natural ratio of chlorine isotopes was measured in the frequency range 1400–740 cm –1 with a resolution of 0.001 cm –1 at a temperature of 20°C. An ab initio calculation of the structure and sextic potential energy surface and surfaces of the components of the dipole moment has been carried out by the electronic quantum-mechanical method of Moller–Plesset, MP2/cc-pVTZ. Then the potential was optimized by replacing the harmonic frequencies with the frequencies calculated by the electronic method of coupled clusters, CCSD(T)/aug-cc-pVQZ. The fundamental and combination frequencies were calculated using the operator perturbation theory of Van Vleck (CVPTn) of the second and fourth order ( n = 2, 4). Resonance effects were modeled using an additional variational calculation in the basis up to fourfold VCI excitation (4). The average prediction error for the fundamental frequencies of the 12 C isotopologues was ~1.5 cm –1 . The achieved accuracy made it possible to reliably predict the isotopic frequency shifts of the 13 C isotopologues. It is shown that the strong Fermi resonance ν 4 /2ν 6 dominates in the 12 C isotopologues and is practically absent in 13 C. The literature assumption [Spectrochim. Acta A, 44:553] about the splitting of ν 1 (CH) due to the resonance ν 1 /ν 2 + ν 7 + ν 9 is confirmed. The coefficients of the polyadic quantum number are determined. The analysis made it possible to carry out a preliminary identification of the centers of the vibrational-rotational bands of isotopologues 13 CHF 2 35 Cl and 13 CHF 2 37 Cl in the spectrum of the mixture in preparation for individual analyzes of the vibrational-rotational structures of individual vibrational transitions.