GLOBAL FITTING OF (CO2)-C-12-O-16 VIBRATIONAL-ROTATIONAL LINE POSITIONS USING THE EFFECTIVE HAMILTONIAN APPROACH

About 13 000 experimental lines of the principal isotopic species of C O2 selected from the literature have been used to derive about 100 par ameters of a reduced effective Hamiltonian built up to sixth order in the Amat-Nielsen ordering scheme. This Hamiltonian has been obtained f rom an effective Hamiltonian describing all vibrational-rotational ene rgy levels in the ground electronic state and containing in explicit f orm all resonance interaction terms due to the approximate relations b etween harmonic frequencies omega(1)approximate to 2 omega(2), and ome ga(3) approximate to omega(1) + omega(2). An RMS deviation of 0.001 cm (-1) has been achieved in the fitting. In order to test its predictive capabilities, the model has been used to calculate the line positions of six bands: 05511 <-- 05501, 1005(1, 2) <-- 1004(1, 2), 1006(1, 2) <-- 1005(1, 2), and 20033 <-- 00001, which are compared with experimen tal lines not included in the data set. The results are discussed and compared with the predictions of the Direct Numerical Diagonalization technique. Published by Elsevier Science Ltd.