Radiation Physics and Chemistry 70 (2004) 417–433 Structure and photoionization of conﬁned atoms V.K. Dolmatov a, *, A.S. Baltenkov b , J.-P. Connerade c , S.T. Manson d a Department of Physics and Earth Science, University of North Alabama, Florence, AL 35632, USA b Arifov Institute of Electronics, Akademgorodok, Tashkent 700125, Uzbekistan c The Blackett Laboratory, Imperial College, London SW7 2BW, UK d Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, USA Abstract Phenomenologicalapproachesonthebasisofsimplemodelpotentialsforthedescriptionofvarioussituationswhere the atom is spacially conﬁned, such, e.g., as atoms inside a C 60 -like environment or in impenetrable cavities of small radii are reviewed along with the trends in modiﬁcations in structure and photoionization of such conﬁned atoms. r 2003 Elsevier Ltd. All rights reserved. PACS: 31.10.+z; 32.80.Fb Keywords: Compressed atoms; Endohedral atoms; Shell ﬁlling; Photoionization 1. Introduction This paper reviews research activities that branch out from traditional atomic physics in a very signiﬁcant respect:theobjectsofstudyarenolongerfreeatomsbut conﬁned atoms, i.e., atoms which are trapped inside hollow spatial cages whose sizes are commensurable with the sizes of atoms. Obviously, a conﬁned atom behaves differently from the free atom. Therefore, the various properties of conﬁned atoms, such as the modiﬁcation of their atomic orbitals, energy levels, the ﬁlling of electronic shells, polarizability, photoioniza- tion/photoabsorption, hyperﬁne structure, etc., can provide insight into understanding of the phenomenol- ogy of the conﬁned atoms. Examples of situations and phenomena of direct relevance to conﬁned atoms are heliumdroplets(Zicovich-Wilsonetal.,1994), nano-size bubbles formed in liquid helium (Goodfriend, 1990), atoms A encapsulated in hollow cages of carbon based nano-materials, such as endohedral fullerenes A@C 60 (Shinohara, 2000; Moriarty, 2001; Forr ! o and Mih ! aly, 2001), the chemical reactivity and chemical valence of atoms (Lawrence et al., 1981), the reversible storage of ions in certain solids (Connerade, 1997; Connerade and Semaoune, 2000a), the appearance of helium bubbles under high pressure in the walls of nuclear reactors (Walsh et al., 2000), and ESR, NMR and magnetic moments of compressed atoms (Buchachenko, 2001), etc. Conﬁned atoms are also very close in principle to the concepts underpinning conﬁnement within ‘‘quantum dots’’ (Johnson, 1995; Sako and Diercksen, 2003a, b). Thus, the concept of a conﬁned atom provides insight into various problems of interdisciplin- ary signiﬁcance. Thepresentpaperreviewsmanyofresultsonconﬁned atoms obtained after 1996 on the basis of simple phenomenological models where the conﬁnement is imitated by placing an atom inside a model potential (results prior to 1996 were well reviewed by Jask ! olski, 1996). Two different types of conﬁnements are con- sidered, as speciﬁed below. In Section 2, we consider results of latest studies on multielectron atoms conﬁned inside an impenetrable spherical cage of adjustable radius. There is, of course, no actual ionization continuum in a hard-wall cavity. Therefore, this model is appropriate when simulating effects of high pressure on bound energies and wavefunctions of atoms. Correspondingly, herein, we ARTICLE IN PRESS *Corresponding author. Tel.: +1-256-765-4320; fax: +1- 256-765-4795. E-mail address: vkdolmatov@una.edu (V.K. Dolmatov). 0969-806X/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2003.12.024