Fourier transform infrared (FTIR) spectroscopy has been used to study the nature of the bonding of silicon with hydrogen, oxygen and nitrogen in a-Si networks. The samples of varying hydrogen content were prepared by reactive sputtering under different deposition conditions. The effects of annealing were studied on a-Si:H samples contaminated with trace amounts of oxygen and nitrogen. The FTIR spectra were deconvoluted into their component peaks using the simplex algorithm. The results demonstrate that evolution of hydrogen starts at approximately 200-degrees-C and various silicon -hydrogen moities residing on/near the surface and in the bulk disrupt at different temperatures. The oxygen and nitrogen related groups in the a-Si network change configurations due to annealing.