An experimental methodology is described for the realhyphen;time clocking of elementary bimolecular reactions, i.e., timing the process of formation and decay of the collision complex. The method takes advantage of the propinquity of the potential reagents in a binary van der Waals (vdW) lsquo;lsquo;precursorrsquo;rsquo; molecule. An ultrashort pump laser pulse initiates the reaction, establishing the zerohyphen;ofhyphen;time (e.g., by photodissociating one of the component molecules in the vdW precursor, liberating a lsquo;lsquo;hotrsquo;rsquo; atom that attacks the nearby coreagent). A second ultrashort, suitably tuned, variably delayed probe laser pulse detects either the intermediate complex or the newly born product. From an analysis of this temporal data as a function of pump and probe wavelengths, the realhyphen;time dynamics of such a lsquo;lsquo;van der Waalshyphen;impacted bimolecular (VIB)rsquo;rsquo; reaction can be determined. Chosen as a demonstration example is the VIB reaction H+CO2rarr;HOCODagger;rarr;HO+CO, using the HIsdot;CO2vdW precursor. The pump laser wavelength was varied over the range 231ndash;263 nm; the probe laser detected OH in two different quantum states. The measured rates of formation and decay of the HOCODagger;complex are characterized by time constants tgr;1and tgr;2; tgr;2spanned the range 0.4ndash;4.7 ps, varying with the available energy. The dynamics of the HOCODagger;decay are discussed.
展开▼
