Hydrogen bond
Hydrogen bonds can vary in strength from weak (1–2 kJ mol) to strong (161.5 kJ mol in the ion ). Typical enthalpies in vapor include:
Staebler–Wronski effect
Historically, the most favored model has been the hydrogen bond switching model. It proposes that an electron-hole pair formed by the incident light may recombine near a weak Si–Si bond, releasing energy sufficient to break the bond. A neighbouring H atom then forms a new bond with one of the Si atoms, leaving a dangling bond. These dangling bonds can trap electron-hole pairs, thus reducing the current that can pass through. However, new experimental evidence is casting doubt on this model. More recently, the "H collision model" proposed that two spatially separated recombination events cause emission of mobile hydrogen from Si–H bonds to form two dangling bonds, with a metastable paired H state binding the hydrogen atoms at a distant site.