FULL DIMENSIONAL ROVIBRATIONAL VARIATIONAL CALCULATIONS OF THE S1 STATE OF C2H2

Changala, Bryan

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https://hdl.handle.net/2142/79461 Copy

Description

Title

FULL DIMENSIONAL ROVIBRATIONAL VARIATIONAL CALCULATIONS OF THE S1 STATE OF C2H2

Author(s)

Changala, Bryan

Contributor(s)

• Stanton, John F.
• Baraban, Joshua H.

Issue Date

26-Jun-15

Keyword(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.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

English

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http://hdl.handle.net/2142/79461

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