Eur. Phys. J. D (2013) 67: 119
https://doi.org/10.1140/epjd/e2013-40139-9

Regular Article

Quantum rotation of Rb₂ (³Σ_u⁺) attached to He_N droplets: a path-integral Monte Carlo study

¹ Inst. de Física Fundamental (CSIC), Serrano 123, 28006 Madrid, Spain
² Dep. de Química-Física I, Universidad Complutense de Madrid, Avda. Complutense s/n, 28040 Madrid, Spain
³ Inst. de Catálisis y Petroleoquímica - CSIC, Marie Curie 2, Cantoblanco, 28049 Madrid, Spain
⁴ Dep. of Chemistry, University of Rome La Sapienza, Piazzale A. Moro 5, 00185 Rome, Italy

^a e-mail: rrcantano@iff.csic.es

Received: 11 March 2013
Received in final form: 26 April 2013
Published online: 25 June 2013

Abstract

Doped He_N Rb₂ (³Σ_u⁺) systems, with N = 20 and 40, have been studied by means of a path integral Monte Carlo method at two different temperatures T = 1 K and 2 K. The impurity, Rb₂, is assumed as a rigid rotor and results are compared with a previous analysis in which no rotational or translational degrees of freedom were taken into account. Quantum effects are observed to play a noticeable role accounting for the extra energy with respect to the fixed Rb₂ case although differences between the two approaches do not seem to be as important as reported for some other dopants attached to helium droplets, such as OCS for example. Probability density distributions exhibit the same overall features as the non-rotating system, predicting the outer location of Rb₂ with respect to the helium atoms. The stability of the two clusters under study at T = 2 K is uncertain: the energy of He₂₀Rb₂ is positive and for He₄₀Rb₂, the observed dependence on the confinements imposed on the system precludes definitive statements regarding its physical existence.