| Tóm tắt: | <p>Cyclo[18]carbon (C<sub>18</sub>, a molecular carbon allotrope) can be synthesized by dehalogenation of a bromocyclocarbon precursor, C<sub>18</sub>Br<sub>6</sub>, in 64% yield, by atomic manipulation on a sodium chloride bilayer on Cu(111) at 5 K, and imaged by high-resolution atomic force microscopy. This method of generating C<sub>18</sub> gives a higher yield than that reported previously from the cyclocarbon oxide C<sub>24</sub>O<sub>6</sub>. The experimental images of C<sub>18</sub> were compared with simulated images for four theoretical model geometries, including possible bond-angle alternation: <em>D</em><sub>18<em>h</em></sub> cumulene, <em>D</em><sub>9<em>h</em></sub> polyyne, <em>D</em><sub>9<em>h</em></sub> cumulene, and <em>C</em><sub>9<em>h</em></sub> polyyne. Cumulenic structures, with (<em>D</em><sub>9<em>h</em></sub>) and without (<em>D</em><sub>18<em>h</em></sub>) bond-angle alternation, can be excluded. Polyynic structures, with (<em>C</em><sub>9<em>h</em></sub>) and without (<em>D</em><sub>9<em>h</em></sub>) bond-angle alternation, both show a good agreement with the experiment and are challenging to differentiate.</p>
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