No abstract

The vibrational predissociation dynamics of weakly bound complexes is well known to be highly nonstatistical. In particular, the associated photofragment final state distributions are often far from statistical, consequently reflecting the nature of the dissociation process. For binary complexes consisting of two molecules, a complete description of the final state of the system must include the associated interfragment correlations, specifically between their internal states. Information of this type is imprinted in the translational energies of the fragments, which can be measured using a number of recently developed translational spectroscopy methods. These data can provide detailed insights into the nature of the bond rupture process, as well as accurate values for the dissociation energy of the complexes. The focus of the present review is on experiments that provide correlated final state distributions for weakly bound binary complexes. Where possible, comparisons with theoretical calculations are made.

The laser-based resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS) technique has been applied to the exhaust gas stream of a diesel generator to measure, in real time, concentration levels of aromatic air toxics. Volatile organic compounds, as well as several polycyclic aromatic hydrocarbons were detected in the concentration range of 10-200 ppb in the steady-state diesel generator exhaust. The results were verified and compared with conventional extractive sampling and analytical techniques using gas chromatography/mass spectrometry (GC/MS). The high isomer selectivity of the REMPI-TOFMS instrument provided data for individual xylene isomers that are otherwise (partially) coeluting in standard GC/MS analyses. Good agreement was observed between results for volatile and semivolatile organic compounds obtained with REMPI-TOFMS and conventional extractive sampling. Transient events, such as cold start-ups of the diesel generator, resulted in sharp (less than 15 s) peak emissions that were, for benzene, up to a factor of 90 higher than the predominately constant concentrations observed during steady-state operation; warm restarts resulted in lower peak concentrations by a factor of 2.5. These fast transient emissions are only detectable using a real-time approach (1-s resolution) as demonstrated here using REMPI-TOFMS.