Double optical resonance mass selective detection of aromatic molecules in a supersonic molecular beam.

Optical excitation followed by ion mass detection in a supersonic molecular beam can offer unusually high levels of selectivity for detection of trace concentrations of material in the atmosphere. We describe recent work involving two-color excitation of aromatic molecules in a supersonic molecular beam, time-of-flight mass spectrometer. It is shown how double resonance excitation in cold molecules can provide two very selective stages of optical selectivity, further augmented by single mass detection. Three applications are described: (1) Two-color excitation to higher excited electronic states is illustrated for final states above and below the ionization potential. (2) Stimulated emission pumping is shown to allow selective identification using ion dip detection. (3) Resonance ion dissociation is demonstrated as a means for obtaining double optical and double mass selectivity.