Velocity distribution of the pulsed ND3 molecular beam selected by a quadrupole Stark velocity filter

We selected the slow velocity components from the ND3 molecules with Maxwell–Boltzmann distribution at room temperature by using a pulsed nozzle and a quadrupole Stark guide. The velocity distribution after the filtering system shows good agreement with theory based on the Stark energy shift in molecular rotational states. We can detect the component of 60 m/s as the slowest column, which corresponds to 4 K of the thermal energy. This result promises that molecules in the mK region would be obtainable by combining this technique with a pre-cooling process like He buffer gas cooling.