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Zero-point vibrational corrections to isotropic hyperfine coupling constants in polyatomic molecules
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).ORCID iD: 0000-0003-2729-0290
Department of Chemistry and State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, China .
Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsö, Norway.
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2011 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 2, 696-707 p.Article in journal (Refereed) Published
Abstract [en]

The present work addresses isotropic hyperfine coupling constants in polyatomic systems with a particular emphasis on a largely neglected, but a posteriori significant, effect, namely zero-point vibrational corrections. Using the density functional restricted-unrestricted approach, the zero-point vibrational corrections are evaluated for the allyl radical and four of its derivatives. In addition for establishing the numerical size of the zero-point vibrational corrections to the isotropic hyperfine coupling constants, we present simple guidelines useful for identifying hydrogens for which such corrections are significant. Based on our findings, we critically re-examine the computational procedures used for the determination of hyperfine coupling constants in general as well as the practice of using experimental hyperfine coupling constants as reference data when benchmarking and optimizing exchange-correlation functionals and basis sets for such calculations.

Place, publisher, year, edition, pages
RSC Publishing, 2011. Vol. 13, no 2, 696-707 p.
National Category
Physical Chemistry Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-25886DOI: 10.1039/c0cp01443eISI: 000285390400041PubMedID: 21063618Scopus ID: 2-s2.0-79953248258OAI: oai:DiVA.org:kth-25886DiVA: diva2:360464
Funder
Swedish e‐Science Research Center
Note
QC 20101103. Updated from manuscript to article in journal. 20111220 The published version of this article is deposited in DiVA by permission of the publisher. The pdf may however by no means be further made available or distributed.Available from: 2010-11-03 Created: 2010-11-03 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Theoretical studies on molecular magnetic properties
Open this publication in new window or tab >>Theoretical studies on molecular magnetic properties
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: US-AB, 2010. 39 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2010.16
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-25887 (URN)978-91-7415-718-5 (ISBN)
Presentation
2010-09-17, RB15 AlbaNova, Stockholm, 12:50 (English)
Opponent
Supervisors
Note
QC 20101103Available from: 2010-11-03 Created: 2010-11-03 Last updated: 2011-11-23Bibliographically approved
2. Theoretical Studies on Magnetic and Photochemical Properties of Organic Molecules
Open this publication in new window or tab >>Theoretical Studies on Magnetic and Photochemical Properties of Organic Molecules
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The present thesis is concerned with the theoretical studies on magnetic and photochemical properties of organic molecules. The ab initio and first principles theories were employed to investigate the vibrational effects on the isotropic hyperfine coupling constant (HFCC) known as the critical parameter in electron paramagnetic resonance spectrum, the theoretical simulations of the vibronically resolved molecular spectra, the photo-induced reaction mechanism of α-santonin and the spin-forbidden reaction of triplet-state dioxygen with cofactor-free enzyme. The theoretical predictions shed light on the interpretation of experimental observations, the understanding of reaction mechanism, and importantly the guideline and perspective in respect of the popularized applications.

We focused on the vibrational corrections to the isotropic HFCCs of hydrogen and carbon atoms in organic radicals. The calculations indicate that the vibrational contributions induce or enhance the effect of spin polarization. A set of rules were stated to guide experimentalist and theoretician in identification of the contributions from the molecular vibrations to HFCCs. And the coupling of spin density with vibrational modes in the backbone is significant and provides the insight into the spin density transfer mechanism in organic π radicals.

The spectral characters of the intermediates in solid-state photoarrangement of α-santonin were investigated in order to well understand the underlying experimental spectra. The molecular spectra simulated with Franck-Condon principle show that the positions of the absorption and emission bands of photosantonic acid well match with the experimental observations and the absorption spectrum has a vibrationally resolved character.

α-Santonin is the first found organic molecule that has the photoreaction activities. The photorearrangement mechanism is theoretically predicted that the low-lying excited state 1(nπ*) undergoing an intersystem crossing process decays to 3(ππ*) state in the Franck-Condon region. A pathway which is favored in the solid-state reaction requires less space and dynamic advantage on the excited-state potential energy surface (PES). And the other pathway is predominant in the weak polar solvent due to the thermodynamical and dynamical preferences. Lumisantonin is a critical intermediate derived from α-santonin photoreaction. The 3(ππ*) state plays a key role in lumisantonin photolysis. The photolytic pathway is in advantage of dynamics and thermodynamics on the triplet-state PES. In contrast, the other reaction pathway is facile for pyrolysis ascribed to a stable intermediate formed on the ground-state PES.

 The mechanism of the oxidation reaction involving cofactor-free enzyme and triplet-state dioxygen were studied. The theoretical calculations show that the charge-transfer mechanism is not a sole way to make a spin-forbidden oxidation allowed. It is more likely to take place in the reactant consisting of a non-conjugated substrate. The other mechanism involving the surface hopping between the triplet- and singlet-state PESs via a minimum energy crossing point (MECP) without a significant charge migration. The electronic state of MECP exhibits a mixed characteristic of the singlet and triplet states. The enhanced conjugation of the substrate slows down the spin-flip rate, and this step can in fact control the rate of the reaction that a dioxygen attaches to a substrate.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. xvi, 62 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2012:2
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-52818 (URN)978-91-7501-227-8 (ISBN)
Public defence
2012-01-18, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20111220Available from: 2011-12-20 Created: 2011-12-19 Last updated: 2012-01-20Bibliographically approved

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