New accurate fit of an extended set of saturation data for the nu(3) band of SF6: Comparison of Hamiltonians in the spherical and cubic tensor formalisms

An extended set of 321 frequencies of vibration-rotation lines of the v(3) band of SF6 has been measured by saturation spectroscopy using various isot opic species of CO2. A least-squares fit of these data has been performed u sing an effective Hamiltonian written either with a spherical tensor or wit h a cubic tensor formalism. We have derived correspondence formulas between the parameters in the two approaches and checked that both formalisms give the same results up to the seventh order. Corrected parameters are given f or the fit with a fifth-order Hamiltonian. An accurate representation of th e band is obtained at the tenth order (standard deviation approximate to 12 kHz) with a remarkable predictive power (better than 40 kHz) for J values less than or equal to 100. The convergence properties of the Hamiltonian po wer expansion are discussed, (C) 2000 Academic Press.