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Photoionization of CO₂ (ARPES)

Vibrational branching ratios and asymmetry parameters in the photoionization of CO₂ in the region between 650 Å and 840 Å

A.C. Parr,¹  J.B. West,²  M.R.F. King,²  K. Ueda,³  P.M. Dehmer,⁴  J.L. Dehmer,⁵  D.J. Schwab,⁶  A.M. Sansonetti,⁶  K. Olsen,⁶  and R.A. Dragoset⁶

¹Sensor Science Division, NIST, Gaithersburg, MD 20899, USA
²Daresbury Laboratory, Warrington, WA4 4AD, UK
³Research Institute for Scientific Measurements, Tohoku University, Sendai 980, Japan
⁴Office of Basic Energy Science, U.S. Department of Energy, Germantown, MD 20874, USA
⁵National Science Foundation, 4201 Wilson Blvd., Arlington, VA 22230, USA
⁶Physical Measurement Laboratory, NIST, Gaithersburg, MD 20899, USA

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Abstract

The vibrational branching ratios and asymmetry parameters for CO₂ have been determined in the wavelength region of 650 Å to near the ionization onset at about 840 Å. The study was performed using synchrotron radiation from the Daresbury storage ring that was dispersed with a 5 m grating monochromator that afforded resolution of 0.1 Å to 0.2 Å. This resolution allowed the study of the branching ratios and asymmetry parameters with enough detail to see the changes in the parameters within the pronounced autoionization structure in CO₂ in this wavelength region. While the electron spectrometer resolution was not sufficient to resolve the spin orbit and Renner-Teller splitting in the photoelectron spectra, we are able to fit the data with a model that identifies the major structure in terms of the symmetric stretch and elements of the asymmetric stretch and bending modes. A calculation of the expected relative vibrational excitations based upon the Franck-Condon principle clearly showed non-Franck-Condon behavior in some of the vibrational-electronic transitions.

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Table of Contents

1. Introduction
2. Experimental Procedure
3. Analysis of the Data
4. Discussion
5. References
6. List of Figures