  Tungsten and cobalt carbonyls adsorbed on a substrate are typical starting
points for the electron beam induced deposition of tungsten or cobalt based
metallic nanostructures. We employ first principles molecular dynamics
simulations to investigate the dynamics and vibrational spectra of W(CO)6 and
W(CO)5 as well as Co2(CO)8 and Co(CO)4 precursor molecules on fully and
partially hydroxylated silica surfaces. Such surfaces resemble the initial
conditions of electron beam induced growth processes. We find that both W(CO)6
and Co2(CO)8 are stable at room temperature and mobile on a silica surface
saturated with hydroxyl groups (OH), moving up to half an Angstr\"om per
picosecond. In contrast, chemisorbed W(CO)5 or Co(CO)4 ions at room temperature
do not change their binding site. These results contribute to gaining
fundamental insight into how the molecules behave in the simulated time window
of 20ps and our determined vibrational spectra of all species provide
signatures for experimentally distinguishing the form in which precursors cover
a substrate.
