Raman spectra of (He)N-Br2(X) clusters: The role of boson/fermion statistics in a quantum solvent

10 pages, 9 figures, 4 tables.-- PACS: 33.20.Fb; 36.40.Mr; 05.30.Jp; 05.30.Fk; 33.70.Jg; 31.70.Dk; 31.15.Ne; 33.20.VqThe aim of this paper is to elucidate the role played by the bosonic/fermionic character of N He atoms solvating a Br2(X) molecule. To this end, an adiabatic model in the molecular stretching coordinate is assumed and the ground energy levels of the complexes are searched by means of Hartree (or Hartree-Fock) Quantum Chemistry calculations for 4He (or 3He) solvent atoms. Simulations of vib-rotational Raman spectra point at the spin multiplicity as the main feature responsible for the drastic difference in the rotational structures of molecules embedded in boson or fermion helium drops as already observed by the experiments of Grebenev et al. [S. Grebenev, J. P. Toennies, and A. F. Vilesov, Science 279 (1998) 2083].This work has been partially supported by the Italy- Spain Integrated Action Program HI02-74, the DGICYT Spanish Grant No. BFM2001-2179, and the European TMR network Grant No. HPRN-CT-1999-0005. F.A.G. and C.DiP. thank the Research Committee of the University of Rome La Sapienza. M. P. deL.-C. thanks Hendrik J. Monkhorst for useful discussions as well as the Comunidad Autonoma de Madrid (Spain) for the financial support. J.J. was supported by the Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, U.S. Department of Energy under Contract number W-31-109-Eng-38.Peer reviewe