  Using ab-initio electronic structure methods we have investigated the ground
state structures and properties of neutral and charged SiH$_{m}$(m=1-4) and
Si$_{2}$H$_{n}$(n=1-6) clusters which are produced in the plasma enhanced
chemical vapor deposition process used in the preparation of hydrogenated
amorphous silicon({\it{a}}-Si:H). Our results show that charging a neutral
cluster distorts it and the distortion mainly occurs through the orientation of
Si-H bond. We attribute structural changes in the charged clusters to
electrostatic repulsion between the bonded and non-bonded electrons. We find
that in addition to the usual Si-H bond, hydrogen atoms form Si-H-H and Si-H-Si
bonds in some clusters. The vibrations of
  Si-H, Si-Si, Si-H-Si bond stretching modes show that the frequencies are
shifted significantly upon charging. The frequency shifts in the charged
clusters are consistent with their bond length variations. We discuss the
fragmentation pathways of silane into binary products and the role of
fragmented silane radicals in the cluster formation and {\it{a}}-Si:H film
deposition process.
