v The infrared spectrum of 13C2H2 in the 60-2600 cm-1 region: bending states up to ν4 + ν5=4

The vibration-rotation spectra of C-13 substituted acetylene, (C2H2)-C-13, 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 nu(tot) = nu(4) + nu(5) = 4, allowing the characterization of the ground state and of 33 vibrationally excited states. All the bands involving states up to nu(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 nu(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. v