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Structure and dynamics of S3- radicals in ultramarine-type pigment based on zeolite A: Electron spin resonance and electron spin echo studies.
- Source :
- Journal of Chemical Physics; 5/28/2009, Vol. 130 Issue 20, p204504, 11p, 2 Diagrams, 3 Charts, 12 Graphs
- Publication Year :
- 2009
-
Abstract
- X-band electron spin resonance (ESR) spectra of S<subscript>3</subscript><superscript>-</superscript> radicals in ultramarine analog (pigment) prepared from zeolite A and maintaining the original structure of parent zeolite were recorded in the temperature range of 4.2–380 K. Electron spin echo experiments (echo detected ESR, electron spin-lattice relaxation, and spin echo dephasing) were performed in the temperature range of 4.2–50 K. The rigid lattice g factors are g<subscript>x</subscript>=2.0016, g<subscript>y</subscript>=2.0505, and g<subscript>z</subscript>=2.0355, and they are gradually averaged with temperature to the final collapse into a single line with g=2.028 above 300 K. This is due to reorientations of S<subscript>3</subscript><superscript>-</superscript> molecule between 12 possible orientations in the sodalite cage through the energy barrier of 2.4 kJ/mol. The low-lying orbital states of the open form of S<subscript>3</subscript><superscript>-</superscript> molecule having C<subscript>2v</subscript> symmetry are considered and molecular orbital (MO) theory of the g factors is presented. The orbital mixing coefficients were calculated from experimental g factors and available theoretical orbital splitting. They indicate that the unpaired electron spin density in the ground state is localized mainly (about 50%) on the central sulfur atom of S<subscript>3</subscript><superscript>-</superscript> anion radical, whereas in the excited electronic state the density is localized mainly on the lateral sulfur atoms (90%). A strong broadening of the ESR lines in directions around the twofold symmetry axis of the radical S<subscript>3</subscript><superscript>-</superscript> molecule (z-axis) is discovered below 10 K. It is due to a distribution of the S–S–S bond angle value influencing mainly the energy of the <superscript>2</superscript>B<subscript>2</subscript>-symmetry MO. This effect is smeared out by molecular dynamics at higher temperatures. A distribution of the g factors is confirmed by the recovery of the spin system magnetization during spin-lattice relaxation measurements, which is described by a stretched exponential function. Both the spin-lattice relaxation and electron spin echo dephasing are governed by localized phonon mode of energy of about 40 cm<superscript>-1</superscript>. Thus, the anion-radical S<subscript>3</subscript><superscript>-</superscript> molecules are weakly bonded to the zeolite framework, and they do not participate in the phonon motion of the host lattice because of their own local dynamics. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00219606
- Volume :
- 130
- Issue :
- 20
- Database :
- Complementary Index
- Journal :
- Journal of Chemical Physics
- Publication Type :
- Academic Journal
- Accession number :
- 40638001
- Full Text :
- https://doi.org/10.1063/1.3124551