Absorption spectrum of carbon nanotubes in the space
Abstract
Graphene C$_{24}$ was recently identified in interstellar space through its characteristic infrared vibrational spectra. As graphene can bend to form carbon nanotubes (CNTs), one of the focuses of ultraviolet and infrared space telescopes is to search for interstellar CNTs. Here, we calculate the absorption spectrum of (5, 0) CNT, the smallest CNT, using the discrete dipole approximation. (5, 0) CNT exhibits four spectral features, peaking at $\sim$0.3, $\sim$0.5, $\sim$0.9, and $\sim$2.9 $\mu$m, with the peak wavelengths shifting toward the red region with the increasing tube length. When the tube length is longer than 23 carbon atoms, the $\sim$2.9 $\mu$m peak becomes quite prominent. Moreover, the absorption spectrum converges if the number of dipoles is at least ten times that of the C–C bonds.
