Tert-butyl peroxy radical:ground and first excited state energetics and fundamental frequencies

Bercaw, Ronald M.

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https://hdl.handle.net/2142/107592 Copy

Description

Title

Tert-butyl peroxy radical:ground and first excited state energetics and fundamental frequencies

Author(s)

Bercaw, Ronald M.

Contributor(s)

• Douberly, Gary E.
• Schaefer III, Henry F.
• Moore III, Kevin B.
• Franke, Peter R.

Issue Date

2020-06-23

Keyword(s)

Theory and Computation

Abstract

Alkylperoxy radicals \chem{(RO_2\kern .25ex ^{.})} are key intermediates in combustion and atmospheric oxidation processes. As such, reliable detection and monitoring of these radicals can provide a wealth of information about the underlying chemistry. The tert-butyl peroxy radical is the archetypal tertiary peroxy radical, yet its vibrational spectroscopy is largely unexplored. To aid in future experimental investigations, we have performed high-level theoretical studies of the fundamental vibrational frequencies of the ground- and first excited states. A conformer search on both electronic surfaces reveals single minimum-energy structures. We predict an $\mathrm{\tilde{A}^{2} A' \leftarrow \tilde{X} ^{2} A''}$ adiabatic excitation energy of 7738 \wn via focal point analysis, approximating the CCSDT(Q)/CBS level of theory. This excitation energy agrees to within 17 \wn of the most accurate experimental measurement. We compute CCSD(T) fundamental vibrational frequencies via second-order vibrational perturbation theory (VPT2), using a hybrid force field in which the quadratic (cubic/quartic) force constants are evaluated with the ANO1 (ANO0) basis set. Anharmonic resonance polyads are treated with the VPT2 + K effective Hamiltonian approach. Among the predicted fundamental frequencies, the ground state $\text{O}\!-\!\text{O}$ stretch, excited state $\text{O}\!-\!\text{O}$ stretch, and excited state $\text{C}\!-\!\text{O}\!-\!\text{O}$ bend fundamentals are predicted at 1138, 959, and 490 \wn, respectively. Basis set sensitivity is found to be particularly great for the $\text{O}\!-\!\text{O}$ stretches, similar to what has already been noted in smaller, unbranched peroxy radicals. Exempting these $\text{O}\!-\!\text{O}$ stretches, agreement with the available experimental fundamentals is generally good ($\pm$ 10 \wn).

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

eng

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http://hdl.handle.net/2142/107592

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Copyright 2020 is held by the Author(s)

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