Observation of Electronic Structure Change at the First-Order Phase Transition in Quasi-Two-Dimensional Squaric Acid ( $H_{2}$ $C_{4}$ $O_{4}$ ) by ${}^{13}C$ NMR

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3 August 1981

journal article
research article
Published by American Physical Society (APS) in Physical Review Letters

Vol. 47 (5) , 366-370
https://doi.org/10.1103/physrevlett.47.366

Abstract

A direct relation between Feder's normal mode coordinate for solid squaric acid (

H_{2}

C_{4}

O_{4}

) and the line separation

Δ σ

in high-resolution

{}^{13}C

NMR is established. The temperature variation of

Δ σ

fits to a first-order phase transition. At the phase transition the

C_{4}

O_{4}

unit is shown to undergo a change in its electronic structure.

Keywords

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