Global effective Hamiltonians of 16O13C17O and 16O13C18O improved from CW-CRDS observations in the 5900-7000 cm−1 region

The parameters of the polyad models of the effective Hamiltonian of the 16O13C17O and 16O13C18O isotopologues of carbon dioxide have been refined by the least-squares fittings to the line positions collected from the literature. Such refinement has become necessary as the observed dataset has been significantly extended by our CW-CRDS observations in the 5900-7000 cm−1 region. In the case of the 16O13C17O isotopologue, 1151 line positions of 11 bands have been used to refine the effective Hamiltonian parameters published by Chédin [A. Chédin, J. Mol. Spectrosc. 76 (1979) 430-491]. With the obtained set of parameters, the collected line positions are reproduced with a RMS (root mean squares of the residuals) equal to 0.0013 cm−1. In the case of the 16O13C18O isotopologue, 61 parameters of the effective Hamiltonian were fitted to more than 6410 line positions. A weighted standard deviation of χ = 1.77 and a global RMS of 0.0017 cm−1, close to the experimental accuracy, were achieved. However, several rotational levels of the 31113 state (P = 10) could not be reproduced in the frame of this polyad model and were then excluded from the fit. We found that these levels are affected by an anharmonic resonance interaction with the 51106 vibrational state (P = 11) leading to energy shifts up to 0.060 cm−1 and significant intensity transfer to several extra lines which could be detected. The coupling matrix element has been estimated to 0.11 cm−1 from the detailed analysis of the experimental spectrum. This is the first evidence of an interpolyad resonance interaction in the case of the carbon dioxide molecule. In order to extend the input spectroscopic information, the weak lines left unassigned in our previous analysis of the CW-CRDS spectrum of the 13C enriched carbon dioxide [Y. Ding, P. Macko, D. Romanini, V.I. Perevalov, S.A. Tashkun, J.-L. Teffo, S.-M. Hu, A. Campargue, J. Mol. Spectrosc. 226 (2004) 146-160.] have been revisited. Thirteen 13C16O2 bands, one 16O13C17O band and two 16O13C18O bands could be newly assigned together with a number of transitions corresponding to high J values of previously observed bands. The spectroscopic constants Gv, Bv, and Dv for the unperturbed bands have been fitted to the observed line positions.