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Title:FULL DIMENSIONAL ROVIBRATIONAL VARIATIONAL CALCULATIONS OF THE S1 STATE OF C2H2
Author(s):Changala, Bryan
Contributor(s):Stanton, John F.; Baraban, Joshua H
Subject(s):Small molecules
Abstract:Rovibrational variational calculations on global potential energy surfaces are often essential for investigating large amplitude vibrational motion and isomerization between multiple stable conformers, as well as for understanding the spectroscopic signatures of such dynamics. The efficient and accurate representation of high dimensional potential energy surfaces and the diagonalization of large rovibrational Hamiltonians make these calculations a technically non-trivial task. The first excited singlet electronic state of acetylene (chem{C_2H_2}) is an ideal model isomerizing system. The S$_1$ state supports both a emph{trans} conformer and a higher energy emph{cis} conformer ($T_{e}^{cis}-T_{e}^{trans} approx 2700$ wn), separated by a planar near-half-linear transition state ($T_{e}^{TS}-T_{e}^{trans} approx 5000$ wn). The low-energy structure of the emph{trans} well is complicated by strong Coriolis and Darling-Dennison interactions between the near-resonant torsion and asymmetric bending modes. The resulting polyad patterns are eventually broken as the internal vibrational energy approaches that of the barrier to isomerization. In this region, qualitatively new spectroscopic patterns emerge, such as rotational $K$-staggering and vibrational effective frequency dips. We examine these effects with an efficient emph{ab initio} variational treatment. Our global potential energy surface is constructed as a hybrid of a high-level reduced dimension surface, which excludes the two $r_{text{CH}}$ bond lengths, and a lower-level full dimensional surface incorporating the effects of $r_{text{CH}}$ displacement. Diagonalization of the large, sparse Hamiltonian, which contains an exact internal coordinate rovibrational kinetic energy operator, is achieved with an efficient restarted Lanczos algorithm that generates variational energies and wavefunctions. We discuss how our results elucidate the S$_1$ state's rich variety of spectroscopic features and the insights they provide into the isomerization process.
Issue Date:26-Jun-15
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:ACS
Genre:CONFERENCE PAPER/PRESENTATION
Type:Text
Language:English
URI:http://hdl.handle.net/2142/79461
Date Available in IDEALS:2016-01-05


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