Polar di-halogen molecules solvated in bosonic helium clusters: The paradigm ofICl(X)

Abstract

Energies and structures of $^{4}\mathrm{He}_{N}\text{\ensuremath{-}}\mathrm{I}\mathrm{Cl}(X)$ complexes, $N\ensuremath{\leqslant}30$, are determined within the framework of a recently developed Hartree-like approach [Phys. Rev. A 71, 033203 (2005)], in which the He atoms play the role of the electrons and the I and Cl atoms play the role of the nuclei. The potential energy of the system is represented as a sum of the He-ICl triatomic and He-He pair interactions fitted to results of ab initio calculations. The validity of the approach is evaluated through comparisons with the results of ``exact'' variational calculations performed for the cases of $N=1$ and 2. The procedure, which furnishes also the wavefunctions, allows for simulation of the infrared spectra of the ICl molecule embedded in the bath of ${\mathrm{He}}_{N}$ clusters. Similarly to the case of the ``bare'' ICl, when the clusters are formed from bosonic He atoms the absorption selection rules lead only to the $P$ and $R$ branches of the spectra (the $Q$ branches are missing). The spectra exhibit a monotonically increasing blueshift, albeit with a decreasing rate, as the cluster size increases.