The Infrared Spectrum of 13C2H2 : Bending States up to v4 + v5 = 4

The vibration rotation spectra of 13C substituted acetylene, 13C2H2, have been recorded in the region between 60 and 2700 cm1 with an effective resolution ranging from 0.001 to 0.006 cm1. In the FIR range, from 60 to 250 cm1, the Canadian Light Source synchrotron facility was used (resolution = 0.001 cm1). Between 400 and 800 cm1 the modified BOMEM FTIR instrument present in Ottawa was used (resolution = 0.002 – 0.003 cm1) . The spectra above 1000 cm--1 were recorded in Bologna at a resolution of 0.004 – 0.006 cm1. A total of about 9500 rovibrational transitions have been assigned to 101 bands involving the bending states up to vt = v4 + v5 = 4, allowing the characterization of the ground state and of 33 vibrationally excited states. All the bands involving states up to vt = 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 vt = 4. These could be satisfactorily reproduced only adopting, in addition to the previously determined parameters which were constrained in the analysis, a set of effective constants for each vibrational manifold