title: Multiple solvation configurations around phthalocyanine in helium droplets.
abstract: Recent measurements of the emission spectrum of phthalocyanine solvated in superfluid helium nanodroplets exhibit a constant 10.3 cm(-1) splitting of each emission line relative to the absorption spectrum. This splitting has been attributed to two distinct helium environments near the surface of the phthalocyanine molecule. Rigid-body path-integral Monte Carlo provides a means of investigating the origin of the splitting on a detailed microscopic level. Path-integral Monte Carlo simulations of 4He(N)-phthalocyanine at 0.625 K with N ranging from 24 to 150 show two distinct helium configurations. One configuration is commensurate with the molecular substrate and the other is a triangular lattice. We investigate the energetics of these two configurations and use a method for calculating electronic spectral shifts for aromatic molecule-rare-gas clusters due to dispersive interactions to estimate the spectral splitting that would arise from the two helium configurations seen for N=150. The results are in reasonable agreement with the experimentally measured splitting, supporting the existence of two distinct local helium environments near the surface of the molecule in the nanodroplets.
authors.affiliation: Department of Chemistry and Kenneth S. Pitzer Center for Theoretical Chemistry, University of California, Berkeley, California 94720, USA. hwhitley@berkeley.edu
authors.forename: Heather D
authors.initials: HD
authors.lastname: Whitley
authors.forename: Patrick
authors.initials: P
authors.lastname: Huang
authors.forename: Yongkyung
authors.initials: Y
authors.lastname: Kwon
authors.forename: K Birgitta
authors.initials: KB
authors.lastname: Whaley