Chemistry in one dimension offers surprising result: The nanotube walls will then protect the encapsulated molecules from outer space and make reactions with molecules and atoms outside the tube impossible. Once the SWNTs are filled with C60 molecules there is not enough space for hydrogen molecules to go in. That was the common opinion when the research groups started their experiments a few years ago.
But their experiments leave no doubt, hydrogen does actually penetrate into peapods and react with fullerenes. The evidence is rather direct, when the temperature and pressure of hydrogenation is taken to extreme values the fullerene cage collapses completely and large hydrogen molecules are formed. This was confirmed both by Raman spectroscopy and high resolution TEM.