Quantum state specific detector

The technique is illustrated by Fig. 8.29. A collimated supersonic beam of argon, which contains Na atoms and Na2 molecules, is crossed perpendicularly with a noble gas beam [1077]. Molecules of Na2 in the level W J ) that have been scattered by the angle d- are monitored by a quantum-state-specific detector. It consists of a cw dye laser focused into a spot behind the aperture A and tuned to the transition, 7 v p 7j>, and an optical system of a mirror and lens, which collects the LIF through an optical fiber bundle onto a photomultiplier. The entire detector can be turned around the scattering center. 

The applications of lasers in kinetic studies are essentially twofold. Firstly, they can be used to produce a particular species. This might be a vibration—rotationally defined quantum state of a molecule [21], or it could be an ion [22—24] or fragment [25—28] produced by photoionization or photodissociation [29, 30] of some parent. The combination of specific frequency, short pulse duration and high powers makes selective control of chemical reactions possible. Secondly, they can be used as detectors of specific species and quantum states [31, 32]. There are a number of different methods of using lasers to detect small concentrations of a species in a chemical reaction. Lin and McDonald [33] have broadly reviewed the generation and detection of reactive species in static systems with particular emphasis on the use of lasers for this purpose. 

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