The infrared spectrum of ¹³C₂H₂ in the 60–2600 cm⁻¹ region: bending states up to v₄ + v₅ = 4

Abstract

The vibration–rotation spectra of ¹³C substituted acetylene, ¹³C₂H₂, have been recorded in the region between 60 and 2600 cm⁻¹ at an effective resolution ranging from 0.001 to 0.006 cm⁻¹. Three different instruments were used to collect the experimental data in the extended spectral interval investigated. In total 9529 rotation vibration transitions have been assigned to 101 bands involving the bending states up to v _tot = v ₄ + v ₅ = 4, allowing the characterization of the ground state and of 33 vibrationally excited states. All the bands involving states up to v _tot = 3 have been analyzed simultaneously by adopting a model Hamiltonian which takes into account the vibration and rotation l-type resonances. The derived spectroscopic parameters reproduce the transition wavenumbers with a RMS value of the order of the experimental uncertainty. Using the same model, larger discrepancies between observed and calculated values have been obtained for transitions involving states with v _tot = 4. These could be satisfactorily reproduced only by adopting a set of effective constants for each vibrational manifold, in addition to the previously determined parameters, which were constrained in the analysis.

Keywords:

• ¹³C₂H₂
• high-resolution Fourier transform infrared spectroscopy
• fundamental
• combination
• overtone
• hot bands
• global analysis

Acknowledgements

The authors wish to thank Canadian Light Source, which is supported by NSERC, NRC, CIHR and the University of Saskatchewan, where the FIR spectra were recorded, and Dr J.W.C. Johns (NRCC Ottawa) for the recording of the spectra in the 700 cm⁻¹ region. G.D.L. and L.F. acknowledge the financial support of the Ministero dell’Istruzione dell’Università e della Ricerca (PRIN “Spettroscopia molecolare per la Ricerca Atmosferica e Astrochimica: Esperimento, Teoria ed Applicazioni”). M.H. thanks the Action de Recherches Concertées de la Communauté française de Belgique for financial support.