Distributions translational energy

This rate coefficient can be averaged in a fifth step over a translational energy distribution P (E ) appropriate for the bulk experiment. In principle, any distribution P (E ) as applicable in tire experiment can be introduced at this point. If this distribution is a thennal Maxwell-Boltzmann distribution one obtains a partially state-selected themial rate coefficient... 

Figure B2.5.12 shows the energy-level scheme of the fine structure and hyperfme structure levels of iodine. The corresponding absorption spectrum shows six sharp hyperfme structure transitions. The experimental resolution is sufficient to detennine the Doppler line shape associated with the velocity distribution of the I atoms produced in the reaction. In this way, one can detennine either the temperature in an oven—as shown in Figure B2.5.12 —or the primary translational energy distribution of I atoms produced in photolysis, equation B2.5.35.

Figure 8. Translational energy distributions of CO(v = 0) after dissociation of H2CO at hv = 30,340.1 cm for the CO product rotational levels (a) Jco = 40, (b) 7co = 28, and (c) Jco = 15. The internal energy of the correlated H2 fragment increases from right to left. Dashed lines are translational energy distributions obtained from the trajectory calculations. Markers indicate H2 vibrational thresholds up to v = 4, and in addition odd rotational levels for v = 5—7. Reprinted from [8] with permission from the American Association for the Advancement of science.

The combined experimental and theoretical investigation of Dixon et al. [75] applied the H-atom Rydberg time-of-flight method to measure the translational energy distribution of H atoms from the photodissociation... 

Fig. 8. Photofragment center-of-mass translational energy distribution P(Et) and anisotropy distribution 0 Et) for the photolysis of C2H2. The arrows mark the energetic thresholds for the corresponding electronic states of the fragment C2H. The out-of-phase correlation between the mild oscillations of 0 and the structures in P(Et) is indicated by vertical dashed lines.

Fig. 9. Partitioned P(Et) for the photolysis of C2H2 under the assumption that f = 0 and 02 = —0.8. The upper panel shows the resulting branching fraction, while the lower panel displays the fragment translational energy distributions of the two corresponding pathways.

Fig. 11. Photofragment translational energy distribution (upper panel) and anisotropy distribution (lower panel) for the photolysis of H2S. The arrow in the upper panel marks the energetic onset for the generation of SH(A2S+, 1/) + H.

Fig. 12. Partitionings of hydrogen fragment translational energy distribution into three components. The solid line denotes the contribution from H2S — 8H(,4 "S+ ) + H which yields a resolved structure with a rovibrational state assignment on the top. The dotted line denotes the contribution of hydrogen from the SH(442 +) —> S(3P) + H reaction, which is a reflection of the solid curve but the structure is smeared out. The corresponding rotational quantum numbers of the parent molecule SI I (A 2>l 1 ) l =0 is marked on the bottom. The remaining part of the P(E) spectrum is represented by the square-like dashed curve.

Fig. 15. (a) Product translational energy distributions, (b) product center-of-mass... 

Since H-atom products from chemical reactions normally do not carry any internal energy excitation with its first excited state at 10.2 eV, which is out of reach for most chemical activations, the high-resolution translational energy distribution of the H-atom products directly reflects the quantum state distribution of its partner product. For example, in the photodissociation of H2O in a molecular beam condition,... 

Fig. 5. The total translational energy distribution of H2O photodissociation at 157 nm. The peaks correspond to the different rovibrationally excited OH products.

Fig. 7. The total translational energy distribution of the H-atom product from (a) the mixed sample using 1 18 mass ratio, (b) pure H2O sample using 1 18 mass ratio.

Similarly, the TOF spectrum of the D-atom product from the mixed sample has also been measured. Figure 8(a) shows the translational energy distribution for the D-atom product from the mixed sample. In order to show the contribution from the D20 photodissociation, Fig. 8(b) also shows the translational energy distribution for the photodissociation of the pure D20 sample converted from the D-atom TOF spectrum using a mass ratio... 

From the translational energy distributions obtained above, the quantum state distributions and the quantum state-specific anisotropy parameters can be determined. In a molecular photodissociation process, the photodissociation product detected at an angle in the center-of-mass... 

Fig. 9. The translational energy distributions of H2O photodissociation at 121 nm obtained with photolysis laser polarization parallel to the detection direction, (a) The upper trace was acquired experimentally, (b) The lower trace is the simulated distribution.

Fig. 14. The product translational energy distributions at very low translational energy region. The solid lines are the experimental results while the dotted lines are the simulated distributions, (a) The photolysis laser polarization is perpendicular to the detection axis, (b) the photolysis laser polarization is parallel to the detection axis.

Fig. 15. The product translational energy distributions for the OH + D channel from the HOD photodissociation at 121.6 nm with the photolysis laser polarization parallel as well as perpendicular to the detection direction.

---