Fingerprints of microscopic superfluidity in HHen+ clusters.

The structures and the vibrational dynamics of the complexes HHe are investigated experimentally (via mass spectrometry (MS)) and at high levels of electronic-structure theory. The MS measurements reveal interesting trends about the stability of the starting members of the HHe family. The computations establish that the basically linear, strongly bound, symmetric triatomic molecular ion He(H)He, with an equilibrium H–He distance of 0.925 Å and about 2/3 but at least 1/2 of the positive charge on H, is the molecular core of all of the complexes. Definitive quantum-chemical results are obtained for HHe and HHe , including the proton affinity of He (computed to be cm⁻¹ via the focal-point analysis (FPA) scheme), the FPA isomerisation energy between the two linear isomers of HHe (cm⁻¹), and the dissociation energy of the HHe HHe + He reaction, with an FPA estimate of cm⁻¹. The structural isomers of the He-solvated complexes are discussed up to n=18. A useful notation, [k−l−m]-HHe , is introduced to characterise qualitatively the three possible belts around the He–H –He core in HHe (), where l denotes the number of He atoms in the central belt and denote the number of He atoms in the top and bottom belts. Capping He atoms attached to the belts can be indicated by sub- and superscripts. Several possible indicators of microscopic superfluidity are investigated: He evaporation energies, rotational constants, and vibrational fundamentals. [ABSTRACT FROM AUTHOR]