Zero-kinetic-energy photoelectron spectrum of carbon dioxide

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Abstract
The zero‐kinetic‐energy (ZEKE) photoelectron spectrum of carbon dioxide has been measured between 111 000 and 112 000 cm−1 at a resolution of 1.5 cm−1 using a coherent source of XUV radiation based on four‐wave mixing in krypton. The spectrum consists of six bands corresponding to transitions from the ground X 1Σ+g(v1,v2,v3=000) state of the neutral to the two spin–orbit components of the (000) vibrational level and the four Renner–Teller states associated with the (010) vibrational level of the ground electronic state (X 2Πg) of the ion. The analysis of the partially resolved rotational structure of the various bands leads to a detailed picture of the photoionization process. The propensity rules for angular momentum transfer during photoionization are strongly dependent on the symmetry (2Πg,3/2, 2Πg,1/2, 2Δu,5/2, 2Δu,3/2, 2Σ+u, and 2Σ−u) of the different ionic states probed and on the Hund’s coupling case they follow [case (a) for the Π and Δ states and case (b) for the Σ states]. A comparison of the experimental ZEKE line intensities with theoretical predictions and conventional photoelectron spectra reveals a series of anomalies which are discussed in terms of final state interactions. The ionization potential of CO2 is estimated to be 111 111.0±3 cm−1, somewhat lower than the value of 111 121±2 cm−1 determined from extrapolation of the Rydberg series by Cossart‐Magos et al. [Mol. Phys. 61, 1077 (1987)].