星际碳纳米管的吸收光谱

Absorption spectrum of carbon nanotubes in the space

近年来,石墨烯C_(24)在星际空间中通过其红外振动光谱而得以证认.因为石墨烯片卷曲可能形成碳纳米管(Carbon Nanotube,CNT),搜寻星际碳纳米管成为空间紫外和红外望远镜的重要关注点.本文采用离散偶极子近似方法计算最小的CNT—(5,0)CNT—在紫外、可见光和近红外波长范围内的吸收光谱.结果显示有四个比较明显的特征峰,它们的波长分别为∼0.3,∼0.5,∼0.9和∼2.9μm.随着CNT的增长,峰值吸收光谱的波长向红端移动.当管长达到23个或更多碳原子后,∼2.9μm特征峰变得异常的强.计算表明,为确保计算精度,偶极子数目应不少于C–C键数的10倍.

Graphene Cwas 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 ~0.3, ~0.5, ~0.9, and ~2.9 μm, with the peak wavelengths shifting toward the red region with the increasing tube length. When the tube length is longer than23 carbon atoms, the ~2.9 μm 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.