Valence photoionization and resonant core excitation of ozone – experimental and theoretical study of the ~ C-state of O þ 3 K. Wiesner a, * , R.F. Fink b , S.L. Sorensen c , M. Andersson a , R. Feifel a , I. Hjelte a , C. Miron a , A. Naves de Brito d,e , L. Rosenqvist a , H. Wang a , S. Svensson a , O. Bj € orneholm a a Department of Physics, Uppsala University, Box 530, Uppsala 751 21, Sweden b Institut f€ ur Physiologie MA 2/149, Ruhr Universit€ at Bochum, Bochum D-44780, Germany c Department of Synchrotron Radiation Research, Institute of Physics, University of Lund, Box 118, Lund 221 00, Sweden d Laborat orio Nacional de Luz S  ıncrotron (LNLS), Box 6192, CEP:13084-971 Campinas -SP, Brazil e Institute of Physics, University of Brasilia, Brazil Received 26 February 2003; in final form 8 May 2003 Abstract ResonantAugerelectronspectraofcoreexcitedO 3 (O T 1s 1 2b 1 1 )arepresentedforthefirsttime.Thephotoionization valence spectrum with sample purity and resolution superior to those published is presented. The first direct experi- mental evidence for the ~ C 2 B 1 state of O þ 3 is found. Ab initio calculations of the resonant Auger electron (RAE) spectrum have been performed supporting the assignment of the ~ C-state. Ó 2003 Elsevier Science B.V. All rights reserved. 1. Introduction The strong absorption of radiation by ozone through a dissociative reaction in the stratosphere is the primary absorption mechanism for harmful ultraviolet solar radiation on earth. The fourth ionized state ( ~ C-state) of O þ 3 was found to be re- sponsible for the photofragmentation of O þ 3 toO 2 and O þ by visible light [1]. However, no trace of this state has so far been seen in the direct photoionization spectrum at the predicted ioniza- tion energy of around 14 eV [2,3]. The geometry of O 3 in the ground state has C 2v symmetry with a bond angle of 117.4° and a bond length of 1.19  A [4]. The electronic configuration in the ground state is: core: 1a 2 1 2a 2 1 1b 2 2 ; valence: ð3a 2 1 2b 2 2 4a 2 1 5a 2 1 1b 2 1 3b 2 2 Þ 1a 2 2 4b 2 2 6a 2 1 2b 0 1 7a 0 1 5b 0 2 ; mixing with: ð3a 2 1 2b 2 2 4a 2 1 5a 2 1 1b 2 1 3b 2 2 Þ 1a 0 2 4b 2 2 6a 2 1 2b 2 1 7a 0 1 5b 0 2 . The core molecular orbitals are associated with the central oxygen (O C ) 1s orbital 1a 1 and the symmetric and antisymmetric linear combinations Chemical Physics Letters 375 (2003) 76–83 www.elsevier.com/locate/cplett * Corresponding author. Fax: +46-18-471-3524. E-mail address: karoline.wiesner@fysik.uu.se (K. Wiesner). 0009-2614/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0009-2614(03)00818-2