Measurement of Three-Dimensional Velocity Distributions of the Products of Cl2, NO, and HCl Photodissociation or Photoionization
| Autor: | A. I. Chichinin, T. Einfeld, C. Maul, K. H. Gericke |
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| Rok vydání: | 2005 |
| Předmět: | |
| Zdroj: | Doklady Physical Chemistry. 402:96-100 |
| ISSN: | 1608-3121 0012-5016 |
| Popis: | Not long ago, it seemed unrealistic for molecular dynamics of photodissociation processes that the escape velocity and direction of photoproducts could be directly measured given an exact knowledge of the quantum states of these photoproducts and of the initial molecule. However, a breakthrough was made in 1987 with the advent of an imaging technique that made it possible to determine the three-dimensional spatial distribution of charged particles [1]. In this technique, resonance-enhanced multiphonon ionization (REMPI) is used for ionizing photofragments and the nascent fragment ions are accelerated by an electric field and detected as scintillations on a phosphorescent screen. Recently (1997), an improved version of this method— velocity map imaging [2, 3]—was suggested. In this method, due to the application of electrostatic lenses, all ions with the same initial velocity vector are mapped onto the same point on the detector irrespective of their initial positions. In this paper, we describe a new version of the imaging technique, an alternative to velocity map imaging, in which a homogeneous electric field is used and a phosphorescent screen is exchanged for a delay-line detector (DLD) with high time resolution. This new method makes it possible to measure all three components of the velocity of a photodissociation or photoionization product. A setup consists of a time-of-flight mass spectrometer, a chamber for creating a molecular beam, and a laser system (Fig. 1). The mass spectrometer consists of a chamber with a homogeneous electric field, in which a molecular beam (the Y axis) and a laser beam (the X axis) intersect. Positive photoions created by laser radiation are accelerated by the electric field (along the Z axis) and are detected by means of the DLD. The ion detecting system is a multichannel plate 8 cm in diameter, each channel of which is a photoelectron multiplier; the DLD is located behind this plate. In principle, such detectors have been known for half a century, but they have heretofore been used only in nuclear physics [4, 5]. The detector used in this work |
| Databáze: | OpenAIRE |
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