Chemisorption of Hydrogen Atoms on the Sidewalls of Armchair Single-Walled Carbon\nNanotubes

Abstract

A computational study using the B3LYP/6-31G(d) level of theory shows that the chemisorptions of one and\ntwo hydrogen atoms on the external surface of (3,3), (4,4), (5,5), and (6,6) armchair single-walled carbon\nnanotubes (SWNTs) are exothermic processes. Our results clearly indicate that two hydrogen atoms favor\nbinding at adjacent positions rather than at alternate carbon sites. This is different from the results reported\non zigzag nanotubes (Yang et al. <i>J. Phys. Chem. B</i> <b>2006</b>, <i>110</i>, 6236). In general, the exothermicity of hydrogen\nchemisorption decreases as the diameter of the armchair nanotubes increases, which is in contrast to the\nobservation for zigzag-type structures. The chemisorptions of one and two hydrogen atoms significantly alter\nthe C−C bond lengths of the nanotube in the vicinity of hydrogen addition as a result of a change in\nhybridization of the carbon atom(s) at the chemisorption site(s) from sp² to sp³. The effect of increasing the\nlength of the SWNTs on the geometries and the reaction energies of hydrogen chemisorption has also been\nexplored.