Three-dimensional imaging technique for direct observation of the complete velocity distribution of state-selected photodissociation products

Abstract

We report an experimental technique provided to study the full three-dimensional velocity distribution of state-selected products of a chemical process. Time-of-flight mass spectroscopy and resonance enhanced multiphoton ionization combined with a position sensitive detector (delay-line anode) are employed. The technique has a space resolution of 0.4 mm, a time resolution better than 1 ns, and it provides the possibility to detect several products with a minimal difference between arrival times of 17 ns. One major achievement of the new technique is the possibility to determine the full three-dimensional momentum vectors of a chemical reaction product. This is especially valuable for cases where no symmetry is considered in the process. Second, the high sensitivity of the method allowing to observe single ions enables us to study physical and chemical processes at extremely low densities. Three methods for measuring the temperature of a molecular beam with the technique are demonstrated. A novel result of the present work is the study of angular distribution of NO ions due to electron recoil in the ionization of NO(A 2Σ+). Finally the advantages of the method are examined by studying the speed distributions of Cl atoms in the photolysis of Cl2 at 355 nm.