The nature of the hydrogen bonding and content and their influence on the film microstructure have been investigated in detail, as a function of the H₂ dilution and the residual pressure, in hydrogenated amorphous silicon (a-Si:H) films prepared by radiofrequency (rf) magnetron sputtering at a common substrate temperature (~ 250 °C) and pressure (5 × 10⁻⁴ torr) and high rates (11−15 Å/s). H₂ percentages in the gas phase mixture (Ar + % H₂) of 5, 10, 15 and 20% have been introduced during growth. For the 20% of H₂, two different pressures of 5 × 10⁻⁴ and 50 × 10⁻⁴ torr were used. A combination of infrared absorption, optical transmission and elastic recoil detection analysis experiments have been carried out to fully characterize the samples in their as-deposited state. The results clearly indicate that for H₂ percentage equal to or lower than 15% , the total bonded H content in the films increases as the H₂ percentage increases, and then reaches a saturation value or even decreases for higher H₂ percentage. Moreover, the microstructure is also found to be deeply affected by the H₂ dilution and pressure. In particular, for high H₂ percentage (20%) and high pressure (50 × 10⁻⁴ torr), unbounded H as well as polyhydride (Si-H₂)_n chains, possibly located in structural inhomogeneities such as voids, are also present in the films in addition to the isolated monohydride Si-H and polyhydride Si-H₂ complexes. As a result, a reduction of the compactness of the film structure associated with a decrease of the refractive index n is observed. The optical gap is found to be rather controlled by the total bonded hydrogen content. The lowest proportion of isolated polyhydride Si-H₂ complexes and the highest density are observed for films deposited with 10% of H₂ in the gas phase and a pressure of 5 × 10⁻⁴ torr.