Molecular Beams
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One of the important spectroscopic techniques I use is to take spectra in a molecular beam. This is very simple in concept–simply a jet of gas expanding into a vacuum–but the molecules in the jet have some unusual properties. The molecules all end up with the same velocity and so are moving very slowly with respect to each other. This corresponds to a very low temperature within the jet: 1–2 K is easily achievable. Spectra taken at low temperatures are much simpler than spectra taken at room temperature making them much easier to understand and analyse; low temperatures can also reveal weak features that are obscured at room temperature. |
| To generate unstable species I have developed a special molecular beam source that has a small spark fired within the jet itself which dissociates a suitable precursor to form a free radical. The photograph shows this nozzle in action, taken with a low light camera. The upper section is the (plastic) nozzle body glowing from the discharge inside. The two blobs below is fluorescence from the molecular beam induced by a laser crossing the molecular beam. (The laser does not show on the photograph. Species I have generated include OH (from H2O), ClO (from Cl2 + O2), SO (from H2S + O2) NCO, C3, PF, PH, HCF and CFBr. |  |