Journal of Electron Spectroscopy and Related Phenomena 137–140 (2004) 435–439 Ar 2p excited states of argon in non-polar media Takaki Hatsui a,b,∗ , Mitsuru Nagasono c , Nobuhiro Kosugi a,b a Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan b The Graduate University for Advanced Studies, Myodaiji, Okazaki 444-8585, Japan c Department of Materials Science and Engineering, Kyoto University, Kyoto 606-8501, Japan Available online 20 March 2004 Abstract Ar 2p photoabsorption spectra for Ar solid and Ar mixture with Kr, Xe and N 2 have been measured in order to study Ar 2p excited states in solid phase. Based on difference between partial electron yield and fluorescence yield spectra for solid Ar, Ar 2p 3/2 –4s and 2p 3/2 –4p excitations on surface are identified. For Ar:Kr and Ar:Xe mixtures, all bands move to lower energy as the Ar concentration decreases. Compared with solid Ar, Ar:N 2 mixtures show small red shift for the Ar 2p 3/2 –4s excitation and blue shift for broad bands originating from Ar 2p–nd excitations. The spectral differences between the mixtures are discussed in terms of the polarization stabilization of the ionization threshold and the exchange repulsion of the Rydberg electron by the valence electrons of the neighboring atoms/molecules. © 2004 Elsevier B.V. All rights reserved. Keywords: Ar 2p excitation; Surface state; Rydberg state; Exchange interaction; Polarization effect 1. Introduction Rydberg states in condensed phase are sensitive to exter- nal perturbation due to their large orbital radii. Rare gas me- dia have often been used to investigate the Rydberg states of target atoms or molecules. A systematic study of NO molecule in rare gas, N 2 , and H 2 matrices on the first ion- ization threshold has been reported [1–3]. In the core exci- tation region, rare gas cluster and solid have been studied extensively by photoabsorption spectroscopy [4–6] and by resonant photoelectron spectroscopy [7,8]. Early work on Ne 2s, Ar 2p, Kr, 3d, and Xe 4d photoab- sorption for rare gas solid and mixture with another rare gas or with N 2 revealed basic phenomena such as variation of excitation energies upon changing concentration [9]. In the present study, Ar 2p excitations of solid Ar, and Ar:Kr, Ar:Xe and Ar:N 2 mixtures are investigated with high energy reso- lution. Origin of the excitation energy shift is discussed in terms of polarizability stabilization of the ionization thresh- old by the surrounding atoms/molecules and the exchange repulsion of the Rydberg electron by the valence electrons of the neighboring atoms/molecules. Appearance of some weak features in solid phase is also discussed by comparing ∗ Corresponding author. Tel.: +81-564-55-7394; fax: +81-564-55-7394. E-mail address: hatsui@ims.ac.jp (T. Hatsui). partial electron yield and fluorescence yield spectra and by considering local geometric structure around core-excited Ar atoms. 2. Experiment Experiments were carried out at a varied-line-spacing plane grating monochromator beamline BL4B at the UVSOR facility [10]. Photoabsorption spectra with energy resolving power of E/E = 3500 were recorded by using an MCP detector with a retarding mesh. Retarding voltage of -160 V was applied for partial electron yield measure- ments. In order to measure total fluorescence yield, the retarding voltage was set to -400 V to repel all emitted electrons. The photon energy was calibrated before and af- ter every measurement to the Ar 2p 3/2 –4s peak (244.39 eV [11]) of Ar gas by using a gas cell, which was connected downstream to a sample chamber. Relative energies are calibrated within ±0.01eV. Samples were prepared by in- troducing gas mixture of Ar and rare gas (or N 2 ) onto a gold-coated copper plate of a cryostat. In this paper, the molar ratio of the introduced gas mixture is denoted as e.g. Ar:Xe (1:9). The mixed gas was dosed by approximately 30 L. The temperature of the copper plate was below 9 K. Base pressure was less than 1 × 10 -8 Pa. All spectra were taken at the grazing incidence angle of 15 ◦ . The MCP 0368-2048/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.elspec.2004.02.049