Hydrogenated amorphous silicon (a-Si:H) thin films deposited by the reactive-sputtering technique and, in some cases, in-situ annealed were subjected to further thermal annealing steps to 600 degrees C. Elastic recoil detection analysis measurements indicate that annealing up to 300 degrees C did not cause a major fraction of bonded hydrogen to evolve. For samples with varying bonded hydrogen contents and structures, bonding configurations, and microstructures, our results show that bonded hydrogen moved and effused from the amorphous network in different ways, depending on particular film structures. Infrared spectroscopy results indicate that bond switching and/or monohydride clustering might have taken place upon thermal annealing, since the 2000 cm(-1) infrared peak (usually assigned to the monohydride vibration) was the first, in almost all cases, to decrease upon heat treatment in the range 200-600 degrees C.