Doppler-selected TOF technique

Fig. 1. Schematic illustration of the basic concept of the Doppler-selected TOF technique. The hatched slice on the left represents a Doppler-selection of a given vz- The strip on the Doppler slice (the middle figure) is the ID Vy-distribution measured under the -restriction of a slit in front of the TOF spectrometer. The combination of many Doppler-selected TOF measurements yields the result shown on the right. The lower figures are the corresponding actual data at each stage for the reaction of S(1D) + H2.

Fig. 4. A quantitative analysis of velocity selectivies in Doppler-selected TOF technique. Shown here is for a single value of the product velocity v. The left panel corresponds to the Doppler selection along the z-axis, and the right panel shows the TOF measurement of the v -component for all possible vx at a selected r>z-slice.

To sum up, the basic idea of the Doppler-selected TOF technique is to cast the differential cross-section S ajdv3 in a Cartesian coordinate, and to combine three dispersion techniques with each independently applied along one of the three Cartesian axes. As both the Doppler-shift (vz) and ion velocity (vy) measurements are essentially in the center-of-mass frame, and the (i j-componcnl, associated with the center-of-mass velocity vector can be made small and be largely compensated for by a slight shift in the location of the slit, the measured quantity in the Doppler-selected TOF approach represents directly the center-of-mass differential cross-section in terms of per velocity volume element in a Cartesian coordinate, d3a/dvxdvydvz. As such, the transformation of the raw data to the desired doubly differential cross-section becomes exceedingly simple and direct, Eq. (11). 

The title reaction was studied by the Doppler-selected TOF technique to be compared with Schnieder s results65 recorded by the Rydberg tagging... 

The Doppler-selected TOF technique is one of the laser-based techniques for measuring state-specific DCSs.30 It combines two popular methods, the optical Doppler-shift and the ion TOF, in an orthogonal manner such that in conjunction with the slit restriction to the third dimension, the desired center-of-mass three-dimensional velocity distribution of the reaction product is directly mapped out. Using a commercial pulsed dye laser, a resolution of T% has been achieved. As demonstrated in this review, such a resolution is often sufficient to reveal state-resolved DCSs. 

---