Adsorption of He atoms in external grooves of single wall carbon   nanotube bundles
  I calculate the quantum states for He atom in the potential of an external groove of the single wall carbon nanotube bundle. The calculated ground state energy is found to be in fair agreement with the experimental estimate which suggests that the outer groove site is a preferential site for the adsorption of He gas in the samples studied experimentally. I also calculate the specific heat of low-density $^4$He atom gas adsorbed in groove positions. The specific geometry of the groove and its influence on the adsorbate quantum states and specific heat are discussed. 
Antonio Siber