Slit-Source Supersonic Jet Expansion
Outlined in Figure 1 is our research strategy, employing the combination of three experimental techniques. The first is a pulsed supersonic jet coupled with IR CRDS, for the observation of spectroscopic signatures of weakly-bound complexes and short-lived intermediates. There exists considerable theoretical evidence, based on ab initio calculations and kinetic modeling [e.g., Zhu and Lin, 2002], that weakly-bound bimolecular complexes may be significant precursors to atmospheric reactions. Such complexes may have a notable influence on the kinetics of associated reactions by affecting barrier heights and/or energy partitioning of reaction products. However, detection of such complexes, as well as short-lived reaction intermediates, can be difficult under thermal conditions, a consequence of low concentrations and weak intensities due to broadly distributed partition functions.
A pulsed supersonic expansion will allow us to produce vibrationally and rotationally cold species for spectroscopic observation; with spectra uncluttered by rotational fine structure, species will be significantly easier to identify than under thermal conditions. A slit-source jet will be employed, providing long path length and hence high sensitivity. The sample pulses will be synchronized with our laser system, a doubled Nd:YAG-pumped dye laser, driving a H2 Raman shifter, producing tunable IR light in the range of 1-8 microns. This allows for studies over an extremely wide spectral range. The advantage of CRDS is extremely high sensitivity, enabling the observation of small signals from weakly-bound complexes or short-lived intermediates. Once characteristic features have been identified in a jet, they may then be studied under thermal conditions, such as in an HPF system, and their importance in reactive systems may be assessed.