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 ${}^4\mathrm{He}$ 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.