Cross Beam System Research Articles

Reactive scattering of Xe(3P2,0) by Br2, ICl, CH3I, CF3I and CCl4Excitation functions and product rotational alignment

The molecular dynamics of the chemiluminescent reaction of Xe(3 P 2,0) with Br2, ICl, CH3I, CF3I and CCl4 have been studied at collision energies in the range 10–125 kJ mol-1 using a rotor accelerated cross-beam system. Individual measurements include chemiluminescence spectra of the rare gas halide products, their excitation functions and the translational energy dependence of their rotational alignment (obtained from the observed fluorescence polarization). The results correlate closely with the behaviour of the analogous alkali metal atomic reactions despite the opportunity for curve crossings associated with the multiplicity of electronically excited potential surfaces. Simple dynamical models (e.g. the DIPR model) are used to assess the relative importance of kinematic and dynamical factors, particularly in controlling the degree of alignment impressed on the rotating rare gas halide product.

Rotational polarization in the chemiluminescent reaction Xe( 3P 0,2) + Br 2 → XeBr * + Br

A rotor accelerated cross-beam system has been used to record the fluorescence spectrum of XeBr *, produced in the chemiluminescent reaction of Xe( 3P 0,2) with Br 2, and to monitor for the first time, its polarization as a function of reagent energy in the range, thermal ⩽ E t ⩽ 1.25 eV. The results establish (i) that the “primary” and “secondary” bands in the fluorescence spectrum are each associated with parallel polarization (i.e. with ΔΩ = 0); (ii) that the degree of polarization of “primary” band rapidly increases with the collision energy, approaching a limiting value appropriate to spectator stripping dynamics.

Self-aligning comparison beam methods for one-, two- and three-dimensional optical velocity measurements

The automatic beam superposition properties of the Wollaston prism are used to develop comparison beam systems for the simultaneous optical measurement of one, two and three components of the velocity vector in fluids. The systems do not require beam alignment for heterodyning, thus removing a traditional disadvantage of comparison beam systems compared with cross-beam systems and permitting full use of the fact that comparison beam systems are inherently better suited for multidimensional velocity measurement than cross-beam systems. The systems discussed use photodiodes (having one or more photosensitive areas) without preamplification. No electronic or optical high, low or narrow pass filters are used.

Measurements of Wind Speeds with an Optical Crossbeam System

An optical crossbeam technique has been developed for the remote sensing of atmospheric winds. The feasibility tests of a complete system are reported. The initial crossbeam system was found to measure atmospheric winds within ±20 percent of those measured with cup anemometers on a meteorological tower. The system consists of two telescopes (light beams) which collect light along narrow beams. The collected light is measured by photodiodes. The light is found to fluctuate in intensity due mainly to scattering by aerosols. The light source is available skylight only. The fluctuations in light are related to the convective wind velocity by employing space-time correlation techniques.