High-resolution synchrotron FTIR spectroscopic analysis of the Coriolis interaction between the v₁₀ = 1 and v₈ = 1 states of ethylene-cis-1,2-d₂

ABSTRACT

The synchrotron Fourier transform infrared (FTIR) spectrum of the b-type ν₁₀ band of ethylene-cis-1,2-d₂ (cis-C₂H₂D₂) was recorded at a resolution of 0.00096 cm⁻¹ in the 550–750 cm⁻¹ region. The measured FWHM of the lines was about 0.002 cm⁻¹. The ν₁₀ band, centred at 662.871885(27) cm⁻¹ was found to be perturbed through a b-type Coriolis resonance with the infrared inactive ν₈ at 759.9582(20) cm⁻¹. In this work, 1989 infrared transitions of ν₁₀ were assigned for the first time. These perturbed and unperturbed infrared transitions were fitted with an rms deviation of 0.00033 cm⁻¹ using the Watson's A-reduced Hamiltonian in the I^r representation with three Coriolis terms to derive the rovibrational constants for v₁₀ = 1 and v₈ = 1 states. Ground state rovibrational constants up to two sextic terms were also derived from a fit of a total of 2532 ground state combination differences with arms deviation of 0.00030 cm⁻¹ from the infrared transitions of the present analysis and those determined previously. The ground state constants compared favourably to the equilibrium state constants from harmonic cc-pVTZ basis set at CCSD(T), MP2 and B3LYP levels. The rotational constants of ν₁₀ and ν₈ from this work agree well with those from anharmonic calculations.

KEYWORDS:

• Ethylene-cis-1,2-d₂
• cis-C₂H₂D₂
• ethylene isotopologue
• high-resolution FTIR spectroscopy
• rovibrational constants

Acknowledgments

The authors are grateful to the Australian Synchrotron, Victoria, Australia for the collection of the ethylene-cis-1,2-d₂ spectra using the THz/far-infrared beamline.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

National Institute of Education, Singapore [grant numbers RS 7/11 TTL and RS 9/15 TTL].