Microscopic mechanisms for the reaction of H2 with divalent Ge defects in H-loaded germanosilicate optical fibers were studied by using  ab initio  quantum-chemical techniques. The reaction with the lowest energy barrier corresponded to H2 breaking a Ge-O bond, at the divalent Ge site, to form a -Ge-H bond. However, H2 addition to yield a dihydride, followed by H migration from Ge to an adjacent O atom, also led to this -Ge-H defect. The vibrational frequency which corresponded to this -Ge-H defect was attributed to a previously observed Raman mode at 1875/cm. The reverse reaction barrier was very small; thus indicating that this -Ge-H defect was likely to be easily bleached at higher temperatures.

B.Zhang, K.Raghavachari: Applied Physics Letters, 1995, 66[20], 2658-60