Optical Properties of Mass Selected Clusters 1

The photofragmentation spectra of the size-selected Sr+X (X=Ne, Ar, Kr, Xe, CO2, N2, CO) complexes are measured over the  400 - 650 nm wavelength region1-7. In the most of the spectra, vibrational progressions are observed and are attributed to dipole transitions from vibrational levels v’’ of the electronic ground state X2Ó to vibrational levels v’ of the electronic excited states 2Ð or 2Ó. These excited states correlate to the Sr+ atomic states 52P or 42D. Isotope-resolved measurements of several of the observed transitions are performed to obtain the absolute vibrational numbering. From these assignments, the vibrational  frequency ùe, the anharmonicity ùe÷e and the binding energy De of the involved states are deduced. The results are analyzed and compared in the framework of an electrostatic potential model.

Photofragmentation spectroscopy of mass selected clusters



 Accurate spectroscopic constants for a series of prototype weakly bonded diatomic complexes have been obtained and the data have been used to prove theoretical models of electrostatic interactions.

 The optical absorption of the clusters as a function of their size has been studied and the absorption spectra have been explained by applying theoretical models.



Ch. Lüder and M. Velegrakis, “Photofragmentation spectrum of the Sr+Ar complex”  J. Chem. Phys. 105, 2167 (1996)


Ch. Lüder, D. Prekas, A. Vourliotaki, and  M. Velegrakis, “ Photodissociation spectrum of Sr+Ne”, Chem. Phys. Lett. 267, 149 (1997)


S. Xantheas, G.S. Fanourgakis, S.C. Farantos and M. Velegrakis, “ Spectroscopic constants of the X-2S and A-2Ð states of Sr+Ar from first principles: Comparison with experiment”, J. Chem. Phys. 108, 46 (1998)


D. Prekas, B.H. Feng,  and  M. Velegrakis , “Vibrational constants and binding energies for the A 2P and X 2S states of Sr+Kr from photodissociation spectroscopy”, J. Chem. Phys. 108, 2712 (1998)


G. Fanourgakis, Ch. Lüder,  S.C.Farantos,  S.S. Xantheas and M. Velegrakis, “ Optical absorption of  Sr+Arn (n=2-8) clusters: Experiment and theory”,  J. Chem. Phys. 109, 108 (1998)


G.S  Fanourgakis, S.C.Farantos,  S.S. Xantheas and M. Velegrakis, “Photofragmentation Spectra and Potential Energy  Surfaces of  Sr+Ar2”, Phys. Chem. Chem. Phys. (PCCP)  1, 977 (1999)


M. Velegrakis, “Stability, structure and optical properties of metal ion-doped noble gas clusters”, in : Advances in metal and semiconductor clusters, Chapter 7, Vol. V, ed. M.A. Duncan (JAI Press, Greenwich), June 2001


M. Massaouti, A. Sfounis, M. Velegrakis, “ The photofragmentation of Sr+Xe”, Chem. Phys. Lett., 348, 47 (2001)


S. C. Farantos, E.Filippou, S. Stamatiadis, G. E. Froudakis, M. Muehlhaeuser, M. Massaouti,  A. Sfounis and M. Velegrakis, “Photofragmentation Spectra of Sr+CO Complex: experiment and ab initio calculations” Chem. Phys. Lett. 366, 231 (2002)


S. C. Farantos, E.Filippou, S. Stamatiadis, G. E. Froudakis, M. Mühlhäuser, M. Massaouti,  A. Sfounis and M. Velegrakis, “The excited states of Sr+CO: Photofragmentation Spectra and ab initio calculations”, Chem. Phys. Lett. 379, 242 (2003)


M. Massaouti,  M. Velegrakis, “ Vibrational constants and binding energies for the low-lying electronic states of  Sr+CO2 from photodissociation spectroscopy”, J. Phys. Chem. A, 109, 6860 (2005)


Michalis Velegrakis and Antonis Sfounis “Formation and photodecomposition of cationic titanium oxide Clusters” Applied Physics A 97, 765 (2009)


M. Massaouti,  George Fanourgakis, M. VelegrakisPhotodissociation spectroscopy and ab initio calculations for the Sr+N2 complex “ Chem. Phys. Lett. 490, 138 (2010)







Linear complexes


Experiment Theory





Sr+Arn (n=2-8) CLUSTERS


The total photofragmentation cross section is displayed as a function of the photon energy. The points are the experimental results and the solid blue lines are the calculations using the perturbation model. A global agreement is obtained for a cluster temperature of 30±5 K. (Individual temperature adjustments for each cluster size give better agreement).


Probing the interaction forces


Laser frequency [cm-1]