Crystallization under stringent cylindrical confinement leads to novel quasi-one-dimensional materials. Substances with strong cohesive interactions can eventually preserve the symmetries of their bulk phase compatible with the restricted geometry, while those with weak cohesive interactions develop qualitatively different structures. Frozen molecular deuterium (D2), a solid with a strong quantum character, is structurally held by weak dispersive forces. Here, the formation of one-dimensional D2 crystals under carbon nanotube confinement is reported. In contradiction with its weak cohesive interactions, their structures, scrutinized using neutron scattering, correspond to definite cylindrical sections of the hexagonal close-packed bulk crystal. The results are rationalized on the grounds of numerical calculations, which point towards nuclear quantum delocalization as the physical mechanism responsible for the stabilization of such outstanding structures.

This work has been partly supported by the Spanish Agencia Estatal de Investigación (AEI), Fondo Europeo de Desarrollo Regional (FEDER, EU), Ministerio de Economía y Competitividad (MINECO), Ministerio de Ciencia, Innovación y Universidades (MCIU), under Grants No. MAT2016-75354-P (AEI/FEDER, EU), FIS2015-64654-P (MINECO/FEDER, EU), MAT2015-68394-R (MINECO/FEDER, EU), PGC2018-097018-B-I00 (MCIU/AEI/FEDER, EU), MAT2012-33633 (MINECO/FEDER, EU), MAT2012-39199-C02-02 (MINECO/FEDER, EU), by EU COST Action CM1405 “Molecules in Motion” (MOLIM), and by Spanish Ministerio de Ciencia e Innovación under Grants No. MAT2007-65711-C04-01, MAT2007-65711-C04-05, MAT2002-04540-C05-02, MAT2002-04540-C05-03, and MAT2002-04540-C05-04.

7 figures.-- Supplementary data available.-- © 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

Peer reviewed