  In previous studies we identified two classes of starless cores, thermally
subcritical and supercritical, distinguished by different dynamical behavior
and internal structure. Here we study the evolution of the
dynamically-unstable, thermally-supercritical cores by means of a numerical
hydrodynamic simulation that includes radiative equilibrium and simple
molecular chemistry. We use our non-LTE radiative transfer code MOLLIE to
predict observable CO and N2H+ line spectra, including the non-LTE hyperfine
ratios of N2H+, during the contraction. These are compared against observations
of the starless core L1544.
