Silicon and hydrogen ion implantations have been used to affect the absorption of the infrared stretching modes in hydrogenated amorphous silicon (a-Si:H). Hydrogen ions have been implanted with ion energy of 16 keV and the doses in the range of 2.2 x 10(14) -7.2 x 10(16) cm(-2). Silicon ion implantation has been carried out with the energy of 160 keV and the doses in the range of 9.5 x 10(12) cm(-2) -1.7 x 10(15) cm(-2). The a-Si:H films have been prepared by plasma-enhanced chemical vapor deposition. Nuclear reaction analysis has been used for the determination of the hydrogen concentration in the as-deposited and ion-implanted samples. It has been established that the values of the absorption strengths of stretching modes of the isolated monohydrides, A(2000), and clustered hydrogen forms, A(2100), are not equal and remain constant for all ion implantation doses. A(2100) has been considered as a weighted average of the absorption strengths of polyhydrides and clustered monohydrides, A(2100,SiHx) and A(2100,(SiH)n). It has been established that the ion implantation does not induce any change in the ratio between polyhydrides and clustered monohydrides. It has been suggested that the absorption strengths do not vary when a post-deposition treatment of samples is associated with the introduction of structural defects in the amorphous silicon network. (c) 2007 Elsevier B.V. All rights reserved.