Vibrational and rotational bound states in floppy triatomic systems: The distributed Gaussian functions approach

32 pages, 12 figures, 2 tables.-- PACS nrs.: 03.65.Ge; 21.45.-v; 21.60.Gx; 36.40.-c.-- Printed version published Oct 2007.A variational method based on the use of bond coordinates and of a basis set expansion described by distributed Gaussian functions (DGF) is reviewed for its applications to the study of weakly bound triatomic clusters. This approach will be shown to be particularly well suited to treat very diffuse states as those presented by Noble gas (Ng) containing systems like the Ng3, and Ng2X, with X being also a very weakly bound atomic impurity. Several statistical properties such as radial distributions, sizes and dominance of triangular configurations for the corresponding bound states are shown to be directly obtained with this method over the whole spectrum of the floppy cluster bound states, in both the rotationless case and also when special care is taken to define rotational constants to yield rovibrational states and their energy levels.The financial support of the Italian Ministry of University (MIUR), of the University of Rome ‘La Sapienza’ Research Committee and of the INTAS Project no. 03-51-6170 is gratefully acknowledged. We also thank the Italy–Spain Collaborative Integrated Action for support during the period 2002–2006 and the DGICYT (Spain) under contract FIS2004-02461. The computational help of the CASPUR Consortium is also gratefully acknowledged. One of the authors, T.G.L., would also like to thank support from the CSIC-MEC 200650I134 project.Peer reviewe