Remarks on Experimental Design and Optimization

Easy availability of ultrafast high intensity lasers has fuelled the dream of their use as molecular scissors to cleave selected bonds (1-3). Theoretical approaches to laser assisted control of chemical reactions have kept pace and demonstrated remarkable success (4,5) with experimental results (6-9) buttressing the theoretical claims. The different tablished theoretical approaches to control have been reviewed recently (10). While the focus of these theoretical approaches has been on field design, the photodissociation yield has also been found to be extremely sensitive to the initial vibrational state from which photolysis is induced and results for (11), HI (12,13), HCl (14) and HOD (2,3,15,16) reveal a crucial role for the initial state of the system in product selectivity and enhancement. This critical dependence on initial vibrational state indicates that a suitably optimized linear superposition of the field free vibrational states may be another route to selective control of photodissociation. 

Moreover, the variations in the ratios of these isotopes can be very low (from 1% to 10"%). Thus, it is necessary to use suitable instrumentation and to optimize the procedures in order to reduce the experimental uncertainty to a minimum.The best typical uncertainty that is possible to attain with traditional ICP-Q-MS units is > 0.1 %RSD [99,100], which is often insufficient. This situation seems to further deteriorate if LA is used as the sample introduction technique, most likely because of the transient nature of the signal generated and the sequential nature of this type of mass analyzer. For these reasons, many of the applications listed in Table 39.3 have made use of MC-ICPMS instruments. As discussed in Section 39.2.2, the MC-ICPMS instrument is especially designed to achieve an improved precision for isotope ratios. The performance of this instrument for isotopic analysis is remarkable. On occasion, a precision for archaeometric applications even... 

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