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 Title: STUDYING ROTATION/TORSION COUPLING IN H5+ USING DIFFUSION MONTE CARLO Author(s): Marlett, Melanie L. Contributor(s): McCoy, Anne B; Lin, Zhou Subject(s): Ions Abstract: H$_{5}^{+}$ is a highly fluxional intermediate found in interstellar clouds. The rotational/torsional couplings in this molecule are of great interest due to the unusually large coupling between these modes. However, theoretical studies of highly fluxional molecules like H$_{5}^{+}$ are challenging due to the lack of a good zero-order model. In order to better understand the rotation/vibration interaction, a method has been developed to model the rotational/torsional motions. This method is based upon diffusion Monte Carlo (DMC). In this approach, the vibrational contribution to the wavefunction is modeled using standard DMC approaches, while the rotational/torsional contribution is treated as a set of coefficients that are assigned to the various rotational/torsional state vectors. The potential portion of the Hamiltonian is expressed as a low-order expansion in terms of the torsion angle between the two outer H$_{2}$ units. The expansion coefficients are evaluated at each time step for each walker and depend on the $3N-7$ other internal coordinates. The transition frequencies obtained from this method for $J leq 1$ agree well with results obtained using other methods such as fixed-node diffusion Monte Carlo.footnote{Sarka, J.; F'abri, C.; Szidarovszky, T.; Cs'asz'ar, A.G.; Lin Z.; McCoy, A.B., �Modeling Rotations, Vibrations, and Rovibrational Couplings in Astructural Molecules - A Case Study Based on the H$_{5}^{+}$ Molecular Ion.�, accepted by Mol. Phys.} This new method is advantageous over the fixed-node approach because it allows for multiple state calculations at once which saves on computation time. Issue Date: 22-Jun-15 Publisher: International Symposium on Molecular Spectroscopy Citation Info: ACS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/79474 Date Available in IDEALS: 2016-01-05
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