Low-density flow of molecular hydrogen from a small nozzle is studied using numerical and experimental techniques. The conditions in the nozzle indicate that non-equilibrium effects will significantly influence the flow. Therefore, the numerical analysis is undertaken using a Monte Carlo approach. The experimental studies employ spontaneous Raman scattering. Comparisons of the measured data and computed results are made for total number density, rotational temperature, and for the number density of the first rotational level. The numerical results are found to be quite sensitive to the rotational relaxation rate, and a strong degree of thermal non-equilibrium is observed at the exit plane of the nozzle. Comparisons between experiment and analysis permit estimation of the rotational relaxation rate for hydrogen. Investigations are also conducted for expansion of the supersonic jet into a finite back pressure. The interaction of the plume with the chamber background gas is found to form shock waves in both the simulations and experiments. This phenomenon is investigated further by increasing the background pressure. Direct comparison of the simulation results and experimental measurements is very favourable.