(a) Isotropic-sum profile for photofragments at a pump-photolysis delay of . This sum profile is not sensitive to the photofragment angular momentum alignment, and it contains information only about the photofragment recoil spatial distribution. The profile is fitted for the spatial anisotropy parameter, as well as the degree of parent molecule bond alignment as a function of the parameter (see text for details). (b) Isotropic-sum profiles, as in (a), are analyzed for the value of for pump-photolysis delays between 0 and . The shapes of the profiles are shown to vary considerably with the time delay (upper inset), and the measured values of (solid squares) agree well with theory (dashed line).
(Color online) Pairs of time-of-flight profiles of photofragments with the probe laser parallel, (upper line), and perpendicular (lower line), to the TOF axis, for pump-photolysis delays of (a) and (b) . The difference in the and profiles is small for (a), whereas it is considerably larger for (b), showing that the alignment of the ground-state atoms can be controlled optically.
The spatial dependences of the laboratory-frame alignment of the profiles shown in Fig. 3 are calculated using Eq. (16) applied to the and profiles. In both cases, the alignment is approximately constant over the whole profile. For the photofragments with recoils parallel to the TOF axis, we see that for (a) at a pump-photolysis delay of , , whereas for (b) at a pump-photolysis delay of , [the physical range of , for , is from to ].
(Color online) The average value of the photofragment alignment (integrated over all recoil directions) as a function of pump-photolysis delay. The general shape of the time dependence of the experimental points (solid squares) is described well by the model calculations (solid line) as detailed in the text.
(Color online) The Cl-atom alignment is calculated for the (hypothetical) case of the photodissociation of HCl yielding photofragments with electronic angular momentum described by , , after it has coupled with the nuclear spin alignment, which was produced from the polarization transfer from HCl rotation in (a) the state , (black, upper line) and (b) , (red, lower line). This simulation shows that for this favorable case, the atom alignment can be controlled to vary between the large value of for a pump-photolysis delay of (a) and can be reduced to nearly 0 at a pump-photolysis delay of (b) .
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