First-principles molecular dynamics study of the stretching frequencies of hydrogen molecules in carbon nanotubes

Abstract

We present a study of the vibrational frequencies of hydrogen molecules adsorbed in bundles of single wall carbon nanotubes. The frequencies are extracted from the analysis of first-principlesmolecular dynamics trajectories. We study the case of molecules inside the nanotubes (endohedral) and in the interstitial pores between the nanotubes (exohedral). We find that, in both configurations, the stretching frequencies are redshifted with respect to the free H2 molecule. However, whereas all the exohedral molecules exhibit a redshift of around 45 cm-1, the endohedral molecules show two frequencies, one close to that of the exohedral molecules and the other similar to that of free H2.