  High-mass stars have an enormous influence on the evolution of the
interstellar medium in galaxies, so it is important that we understand how they
form. We examine the central clumps within a sample of seven infrared-dark
clouds (IRDCs) with a range of masses and morphologies. We use 1 pc-scale
observations from NOEMA and the IRAM 30-m telescope to trace dense cores with
2.8 mm continuum, and gas kinematics in C$^{18}$O, HCO$^+$, HNC, and N$_2$H$^+$
($J$=1$-$0). We supplement our continuum sample with six IRDCs observed at 2.9
mm with ALMA, and examine the relationships between core- and clump-scale
properties. We have developed a fully-automated multiple-velocity component
hyperfine line-fitting code called mwydyn which we employ to trace the dense
gas kinematics in N$_2$H$^+$ (1$-$0), revealing highly complex and dynamic
clump interiors. We find that parsec-scale clump mass is the most important
factor driving the evolution; more massive clumps are able to concentrate more
mass into their most massive cores - with a log-normally distributed efficiency
of around 9% - in addition to containing the most dynamic gas. Distributions of
linewidths within the most massive cores are similar to the ambient gas,
suggesting that they are not dynamically decoupled, but are similarly chaotic.
A number of studies have previously suggested that clumps are globally
collapsing; in such a scenario, the observed kinematics of clump centres would
be the direct result of gravity-driven mass inflows that become ever more
complex as the clumps evolve, which in turn leads to the chaotic mass growth of
their core populations.
