The infrared spectrum of 12C13CH2:: The bending states up to ν4+ν5=4

The vibration-rotation spectra of C-13 monosubstituted acetylene, (CCH2)-C-12-C-13, have been recorded in the region between 450 and 3200 cm(-1) with an effective resolution ranging from 0.004 to 0.006 cm(-1). A total of about 5300 rovibrational transitions have been assigned to 53 bands involving the bending states up to nu(t) = nu(4) + nu(5) = 4, allowing the characterization of the ground state and of 30 vibrationally excited states. All the bands involving states up to nu(t) = 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(t) = 4. These could be satisfactorily reproduced by only adopting, in addition to the previously determined parameters which were constrained in the analysis, a set of effective constants for each vibrational manifold. (C) 2002 Elsevier Science (USA).