  Infrared Dark Clouds (IRDCs) are very dense and highly extincted regions that
host the initial conditions of star and stellar cluster formation. It is
crucial to study the kinematics and molecular content of IRDCs to test their
formation mechanism and ultimately characterise these initial conditions. We
have obtained high-sensitivity Silicon Monoxide, SiO(2-1), emission maps toward
the six IRDCs, G018.82$-$00.28, G019.27+00.07, G028.53$-$00.25, G028.67+00.13,
G038.95$-$00.47 and G053.11+00.05 (cloud A, B, D, E, I and J, respectively),
using the 30-m antenna at the Instituto de Radioastronom\'{i}a Millim\'{e}trica
(IRAM30m). We have investigated the SiO spatial distribution and kinematic
structure across the six clouds to look for signatures of cloud-cloud collision
events that may have formed the IRDCs and triggered star formation within them.
Toward clouds A, B, D, I and J we detect spatially compact SiO emission with
broad line profiles which are spatially coincident with massive cores. Toward
the IRDCs A and I, we report an additional SiO component that shows narrow line
profiles and that is widespread across quiescent regions. Finally, we do not
detect any significant SiO emission toward cloud E. We suggest that the broad
and compact SiO emission detected toward the clouds is likely associated with
ongoing star formation activity within the IRDCs. However, the additional
narrow and widespread SiO emission detected toward cloud A and I may have
originated from the collision between the IRDCs and flows of molecular gas
pushed toward the clouds by nearby HII regions.
