Angular distribution direction

It is advantageous if the laser system pemiits rotation of the optical polarization. Detached electrons correlated witii different final electronic states of the neutral molecule will generally be emitted with different angular distributions about the direction of polarization. Measurement of the angular distribution helps in the interpretation of complex photoelectron spectra. The angular distribution/(0) of photoelectrons is [50]... 

The most important observable is the angular distribution of the scattered products with respect to the initial approach direction of the reagents, which is called the state-to-state differential cross-section (DCS). The DCS can be written [57-61]... 

While it is clear that a direct measurement of the angular distribution, Eq. (4), with a given hehcity of hght should be capable of yielding the h angular parameter, it is often more convenient to examine the dichroism, or difference, obtained with opposite helicities of the light (or, possibly, of the enantiomer). From Eq. (4) and the antisymmetry property Eq. (6) one obtains an expression for the PECD ... 

The PECD measurement clearly takes the form of a cosine function with an amplitude given entirely in terms of the single chiral parameter, b. It therefore provides exactly the same information content as the y asymmetry factor dehned above [Eq. (8)]. Experimental advantages of examining the PECD rather than the single angular distribution /p(0) are likely to include some cancellation of purely instrumental asymmetries (e.g., varying detection efficiency in the forward-backward directions) and consequent improvements in sensitivity. 

We consider the expression of the lab frame photoelectron angular distribution for a randomly oriented molecular sample. The frozen core, electric dipole approximation for the differential cross-section for electron emission into a solid angle about a direction k can be written as... 

Fig. 21. The product D-atom velocity-flux contour map, d

Time-of-fhght spectra of the D atom products have been measured at many laboratory angles at both collision energies. Translational energy distributions can be derived by direct conversion of these TOF spectra. For the experiment carried out at 2.0 kcal/mol, Fig. 28(a) shows the total product angular distribution from 0 = —60° to 117.5°, which correspond to the forward (—60°), the sideward (30°) and the backward (117.5°) scattering directions. The direction of the D2 beam is at 0 = 0°, while the direction of the 0(XD) beam is at 0/. 90°. By definition, the forwardness and back-... 

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