Fast beam experiments

All previous 2S Lamb shift measurements for medium-Z hydrogen-like ions have been carried out using fast ion beams, and uncertainties associated with Doppler shifts form a significant source of error in all these experiments. Various methods have been employed or suggested for reducing the sensitivity of fast beam experiments to Doppler corrections [22]—[24]. A measurement of the 2S1/2-2P3/2 transition frequency in N6+ using a fast ion beam is currently under way at Florida State University [25]. Our approach, however, is to reduce such... 

The condition on the temperature may be relaxed if the SSE system is irradiated with microwave pulses of short duration only. In this case we may work at considerably higher temperatures, arguing that, owing to the short interaction times, the thermal radiation does not have enough time to destroy quantum coherence. This argument is used and found to be valid in atomic fast beam experiments (see, e.g., Moorman and Koch (1992)) that are conducted at room temperature. 

Still, many collinear fast-beam experiments have been performed on neutral atoms. For this purpose, the ions are neutralized by charge transfer, preferably in passing them through an alkali vapor cell. The charge-transfer cross sections for the reaction... 

Before discussing the various features observable in three-level laser spectroscopy, with particular emphasis on fast beam experiments, the kinematics will be dealt with. 

Fast beam experiments using laser excitation... 

Temporal analysis of products (TAP) reactor systems enable fast transient experiments in the millisecond time regime and include mass spectrometer sampling ability. In a typical TAP experiment, sharp pulses shorter than 2 milliseconds, e.g. a Dirac Pulse, are used to study reactions of a catalyst in its working state and elucidate information on surface reactions. The TAP set-up uses quadrupole mass spectrometers without a separation capillary to provide fast quantitative analysis of the effluent. TAP experiments are considered the link between high vacuum molecular beam investigations and atmospheric pressure packed bed kinetic studies. The TAP reactor was developed by John T. Gleaves and co-workers at Monsanto in the mid 1980 s. The first version had the entire system under vacuum conditions and a schematic is shown in Fig. 3. The first review of TAP reactors systems was published in 1988. 

While one might expect that the techniques developed for photodissociation studies of closed-shell molecules would be readily adaptable to free radicals, this is not the case. A successful photodissociation experiment often requires a very clean source for the radical of interest in order to minimize background problems associated with photodissociating other species in the experiment. Thus, molecular beam photofragment translation spectroscopy, which has been applied to innumerable closed-shell species, has been used successfully on only a handful of free radicals. With this problem in mind, we have developed a conceptually different experiment [4] in which a fast beam of radicals is generated by laser photodetachment of mass-selected negative ions. The radicals are photodissociated with a second laser, and the fragments are detected in coinci-... 

To reduce sensitivity to the Doppler shift further the experiment can be carried out using a transverse geometry on a fast beam, or on a slow beam, or... 

A third possibility of obtaining narrow microwave pulses is to use a fast beam of Csl molecules that is passed between a periodic array of sharp edges, as shown in Fig. 5.14. If the edges are spaced at a distance d and the molecules fly with a velocity v, then the molecule experiences microwave pulses of frequency v = v/dm its rest-frame. If 10 GHz pulses are desired, and the edges are spaced a distance d = 1mm apart, then V = 10 m/s is required. This is on the order of 10% of the speed of light, but should be technically feasible. 

Fast Neutral Collisions Involving Metallic Species 3.4.1. Overview of Fast Neutral Beam Experiments... 

A common drawback of all fast neutral beam experiments is the difficulty in determining absolute cross sections. This can be primarily attributed to problems in deriving the neutral beam intensity in the interaction region and product detection efficiencies. As will be discussed in the following section, estimated cross sections for examined processes have been reported, but they can differ by orders of magnitude from one fast neutral beam experiment to another. 

Fig. 3.12. Principle of the measurement of the global adsorption probability in a molecular beam experiment. The desorption pulse is composed by a fast component ( S fast) corresponding to molecules reflected or desorbing from the substrate and a slow component (5siow) corresponding to (chemisorbed) molecules desorbing from the metal clusters. The relative amplitude of the slow component gives the global adsorption probability...

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