2003/09/16 by F. Paesani, R. E. Zillich, K. B. Whaley
Physics and Astronomy · #Advanced Chemical Physics Studies #Angular momentum #Delocalized electron #Diffusion Monte Carlo #Energetics #Excited state #Ground state #Molecule #Monte Carlo method #Quantum Monte Carlo #Quantum, superfluid, helium dynamics #Rotational energy #Spectroscopy and Quantum Chemical Studies #physics.atm-clus
paper · pdf · doi:10.1063/1.1624058
26 pages, 11 figures. accepted for publication in the Journal of Chemical Physics
arxiv created 2003/09/16 · openalex publication_date 2003/11/22 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We determine the structure and energetics of complexes of the linear OCS molecule with small numbers of para-hydrogen molecules, N=1–8, using zero temperature quantum Monte Carlo methods. Ground state calculations are carried out with importance-sampled rigid body diffusion Monte Carlo and excited state calculations with the projection operator imaginary time spectral evolution methodology. The ground states are found to be highly structured, with a gradual build up of two axial rings as N increases to 8. Analysis of the azimuthal density correlations around the OCS molecule shows that these rings are quite delocalized for small N values, but become strongly localized for N⩾5. Excited state calculations are made for a range of total cluster angular momentum values and the rotational energy levels fitted to obtain effective rotational and distortion constants of the complexed OCS molecule as a function of cluster size N. Detailed analysis of these spectroscopic constants indicates that the complexes of OCS with para-hydrogen have an unusually rich variation in dynamical behavior, with sizes N=1–2 showing near rigid behavior, sizes N=3–4 showing extremely floppy behavior, and the larger sizes N=5–8 showing more rigid behavior again. The large values of the distortion constant D obtained for N=3–4 are rationalized in terms of the coupling between the OCS rotations and the “breathing” mode of the first, partially filled ring of para-hydrogen molecules.