ROTATIONAL BAND CONTOUR ANALYSIS OF NF RYDBERG COMPLEXES OF CO2 AND THE DETERMINATION OF THE FIRST IONIZATION-POTENTIAL

The rotational band contours of CO2 nf Rydberg complexes (n = 4-33) reported in the VUV absorption spectrum are analysed by fitting the calculated contours obtained using a model based on Hund's case (e) representation. The ionization potential, defined as the lowest ionization limit (J(+) = 3/2, Omega(+) = 3/2), is determined to be 111 110 +/- 3 cm(-1). The present value is about 10 cm(-1) less than that reported from a Rydberg series extrapolation, and is in good agreement with a room temperature ZEKE-PE spectrum (111 111 +/- 3 cm(-1)) and a low-temperature high-resolution ZEKE-PFI spectrum (111 113 +/- 3 cm(-1)). Other parameters varied in the calculation are the quantum defects mu in Hund's case (a) representation. Fitted values of mu are found to be about 0 . 01 units greater than those calculated using the frozen-core approximation. Multiphoton (3 + 1) ionization spectra of CO2 are also discussed in the light of the 3-photon excitation band contours obtained for the parameters fitted in the one-photon calculation and using some selected values of the transition tenser components.