LAB angular distribution

Using a forward-convolution program131 with instrumental and experimental parameter inputs (aperture sizes, flight distances, beam velocities, etc.), along with two center-of-mass (CM) input functions (the translational energy release distribution, P(E), and the CM angular distribution, T(0)), TOF spectra and lab angular distributions were calculated and compared... 

Fig. 10. (a) Lab angular distribution for non-reactively scattered yttrium atoms from... 

A second feature of the Y + CH3OH reaction that is common to many metal reactions is the presence of competing reaction channels, in this case YH2+H2CO and YOCH3+H. Time-of-flight spectra for both these products are shown in Fig. 11. The corresponding lab angular distributions and CM distributions used to fit the TOF spectra are shown in Fig. 12. 

The lab angular distributions shown in Fig. 12 contain information about the cross-section for each reaction. In practice, extraction of an absolute cross-section is difficult because of uncertainties in the number densities of the reactant beams and the ionization efficiencies of the products.130,135 However, in the determination of the product branching ratio, many of... 

Fig. 15. Newton diagram in velocity space for Y+cyclopropane at Eco = 18.5 kcal/mol. Larger solid circle corresponds to maximum velocities for YCH2 products, while smaller solid circle and smaller dotted circle correspond to maximum velocities for Y-propyne and Y-allene products, respectively. Lab angular distributions for YCH2 (open squares) and YC3H4 (open circles) recorded under identical collision conditions. Solid-line fits to lab angular distributions generated using CM distributions in Fig. 17.

For the reaction with propene, the YCH2 product signal was clearly observed at Econ > 15.8 kcal/mol. The complete set of lab angular distributions recorded for reactions of Y + propene at different collision energies is shown in Fig. 25. Although an increase in the relative amount of YCH2 formed was observed as Eco increased (Fig. 26), YC3H4 formation was always the dominant process. 

Fig. 25. Lab angular distributions for YC3H4 (open circles) and YCH2 (open squares) from collisions of Y + propene at con = (a) 43.2, (b) 28.8, (c) 25.2, (d) 15.8, and (e) 12.3kcal/mol. Product branching ratio, cf>ych2 included in top right...

Fig. 37. Lab angular distributions for all reactive products from reactions of Y with four butene isomers at con = 26.6 kcal/mol. Products are YC4H6 (open circles), YH2 (open triangles), and YCH2 (open squares). Solid-line fits generated using CM distributions shown in Fig. 38. Corresponding product yields given in the upper right corner of each graph. Each distribution is scaled to the same number of scans (2).

Fig. 9. HCCO and CH2 product lab angular distributions from the 0(3P) + C2H2 reaction at Ec = 9.5kcalmol 1. Solid lines are best-fit curves obtained from the best-fit product angular and translational energy distributions (adapted from Ref. 33). The Newton diagram of the experiment is also shown there the Newton circles delimit the maximum velocity that the indicated products can attain assuming that all the available energy is channelled into translation.

Fig. 12. Comparison of HCCO product lab angular distributions and TOF spectra at = 22° from the 0(3P) + C2H2 reaction for a beam crossing angle of 7 = 90° (Ec = 9.5 kcal mol 1, setup of Fig. 1) and of 7 = 135° (Ec = 12.6 kcal mol l, setup of Fig. 7). The corresponding Newton diagrams are also shown. Note the higher angular and TOF resolution obtained when 7 = 135°, as witnessed by the wider HCCO lab angular distribution and slower (and wider) TOF spectrum.

Figure 1.7 The in-plane lab angular distribution of KBr from K + Br2 [2]. The Newton diagram is given for the most probable beam velocities (both beams are unselected and their temperature is given), and the circles indicate the length of u Br vectors corresponding to various values of E (kcal/mole). The simple interpretation of these results is to equate the lab peak at 0 = 17° with a c.m. peak at 0 = 0° (direct forward scattering) and hence estimate 1.2 kcal/mole.

Figure 3. LAB angular distribution for F + p-H2, 1.84 kcal/mol, and Newton diagram. Both the data and calculated LAB distributions are shown (e data, total calculated,...

Figure 9. LAB angular distributions for F + H2(J=0) and J=l. The innermost and next smallest Newton circles are for HF(v= 3) product from H2(J=0) and J l, respectively.

LAB angular distributions for F H2(J=0) and F H2(J°1) at 1.84 kcal/mol in Figure 9 show that there is considerably less forward peaking of the HF(v 3) product from H2(J 1) than from H2(J 0). It appears that resonance effects are less pronounced... 

The final result for the LAB angular distribution of the product for Tq = 0.081 eV (Fat = 0-61 eV) is shown in Fig. 14, together with the experimental results [103]. It is seen that while there is some disagreement on the width at half-height, the agreement on the peak position and the total width is excellent. 

The LAB angular distribution of ArD+ at the lowest collision energy is shown in Fig. 8.7. All the ArD+ is scattered at angles close to the direction of the incident Ar+ beam, which is expected since the center-of-mass momentum does not differ greatly from the momentum of the heavy incident (Ar+) or scattered (ArD+) particles. By transforming these data to CM a portrait of the reaction dynamics can be constructed. 

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