Intermolecular interaction in carbon nanotube ropes

Using Raman spectroscopy we determined the van-der-Waals component of the l ow-frequency vibration in ropes of single-walled nanotubes at 171 cm(-1). W hile Raman peaks in this frequency range are commonly believed to correspon d to the pure radial breathing mode of a single tube, our pressure and temp erature-dependent measurements show that van-der-Waals contribution of the peak observed at 514.5 nm excitation is necessary to explain its large pres sure coefficient of 9.7 cm(-1)/GPa. Our results are consistent with the sma ll elastic modulus predicted for nanotube ropes.