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Measurement of the differential cross section of the photoinitiated reactive collision of using only one molecular beam: A study by three dimensional velocity mapping
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10.1063/1.3427534
/content/aip/journal/jcp/132/24/10.1063/1.3427534
http://aip.metastore.ingenta.com/content/aip/journal/jcp/132/24/10.1063/1.3427534
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

Sketch showing two possible ways to detect forward scattered D atoms with the dye laser (red circle). Here the oxygen precursor is formed by the dissociation laser (blue circle) with a fixed speed and reacts at the time . If the speed is large enough, the ion on path 1 (brown/dashed) can reach the detection laser and will show up in the domain of the forward scattered products.

Image of FIG. 2.
FIG. 2.

Illustration of the relevant coordinate systems. The center of mass system which is defined by the velocity of the atom is transformed into the space fixed laboratory coordinate system by rotating it first about the axis by to coincide z and and then by rotating about the common z-axis by . The axis always lies in the laboratory x,y plane (gray). The measured velocity of a D-atom v is shown as the sum of and u. The components of u in the cm system are constructed by projecting (green dotted lines) u first onto and into the , indicated by the green plane. Finally, is projected onto and .

Image of FIG. 3.
FIG. 3.

Speed distribution and least square fit of the precursor as inferred from Refs. 76 and 77 used in the simulation.

Image of FIG. 4.
FIG. 4.

Forward simulated laboratory velocity distributions of D atoms for different center of mass velocity distributions. (a) Spatially uniform distribution with . (b) Backward scattering, normal speed distribution with mean of 9000 m/s and . (c) Forward scattering, speed distribution as in (b). The ions detected on the two possible paths shown in Fig. 1 are represented by the respective color. Their numbers are olive (desired): 6405; wine (unwanted): 3595. (d) The same point cloud as in (c) but from a different angle. The lines labeled with dissociation and detection shall serve as a help for orientation only. The exact velocity values associated with them have no meaning of their own.

Image of FIG. 5.
FIG. 5.

Reconstruction of the simulated data in Fig. 4. [(a)–(c)] Backward scattered D atoms for different iteration index. (d) Forward scattered D atoms for 150 iterations. (e) Spatially uniform D atom velocity distribution

Image of FIG. 6.
FIG. 6.

Comparison of the DCSs and speed distributions (black, solid) of the simulated distribution in Fig. 4(a) before (left) and after (right) the reconstruction with the ideal functions used in the simulation (red, dashed). One clearly sees that the bias in the speed distribution has been removed successfully and the bias in the DCS was not very large before the reconstruction anyway. This is due to the fact that the biases from forward and backward scattered products cancel each other out. Note that the noise magnification is quite low, too.

Image of FIG. 7.
FIG. 7.

Comparison of the DCSs and speed distributions (black, solid) of the simulated distribution in Fig. 4(c) before (left) and after (right) the reconstruction with the ideal functions used in the simulation (red, dashed). The bias has been removed successfully from both the angular and the speed distribution. The Gaussian fit (blue, dash-dotted) gives a hint of the remaining broadening due to the spread in reactant velocities (see text).

Image of FIG. 8.
FIG. 8.

Doppler sliced 3D velocity map of H atoms emerging from the photodissociation of HBr at 243 nm [two rings with opposite for the and the channel, respectively] and 193 nm shifted perpendicular to the z-axis (dots on the right hand side of the outer ring). The H atoms are detected by at 243 nm. The arrows labeled with the dissociation and detection wavelengths shall serve as a help for orientation only. The exact velocity values associated with them have no meaning of their own.

Image of FIG. 9.
FIG. 9.

Raw data of D atom laboratory velocities and meridian plot of the reconstructed center of mass velocity distribution after background correction. The lines labeled with dissociation and detection in the lower panel shall serve as a help for orientation only. The exact velocity values associated with them have no meaning of their own.

Image of FIG. 10.
FIG. 10.

Upper panel: DCS of the D-atoms emerging from the reaction of ; middle panel: speed distribution; lower panel: speed distribution decomposed into forward and backward scattering (black/solid: backward hemisphere; red/dashed: forward hemisphere).

Image of FIG. 11.
FIG. 11.

Collision energy distribution and O atom precursor velocity distribution from a Monte Carlo simulation assuming a Gaussian center of mass speed distribution of D atoms with 9000 m/s as the center and a standard deviation of 2800 m/s using the experimental parameters and . The lines labeled with dissociation and detection in the lower panel shall serve as a help for orientation only. The exact velocity values associated with them have no meaning of their own.

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/content/aip/journal/jcp/132/24/10.1063/1.3427534
2010-06-25
2014-04-19
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Measurement of the differential cross section of the photoinitiated reactive collision of O(D1)+D2 using only one molecular beam: A study by three dimensional velocity mapping
http://aip.metastore.ingenta.com/content/aip/journal/jcp/132/24/10.1063/1.3427534
10.1063/1.3427534
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