Experimental validation of formaldehyde rotational state selection

We present experimental observations for the rotational state selection of formaldehyde. Data were acquired by using an electrostatic hexapole to focus a supersonic beam of formaldehyde seeded in argon into the ionizer of a quadrupole mass spectrometer. Empirical focusing spectra agree with theoretical predictions when a rigorous quantum mechanical treatment is used to calculate the Stark effect for the rotational states of formaldehyde. These results have implications in the production of beams of cold molecules.