Vibrationally excited molecular beam scattering

SURFACE EFFECTS IN VIBRATIONALLY EXCITED MOLECULAR BEAM SCATTERING... 

Since the critical configuration is reached when P is far from M, then the reaction will have a large cross section. The velocity of the products will be low, and the products will initially be in excited vibrational levels. The molecular beam contour diagram will show predominantly forward scattering typical of a stripping mechanism. 

The more exoergic reaction Ba + NzO has a smaller reaction cross section ( 90 A2 or 27 A2) [347, 351] and crossed-molecular beams studies [349] show that the BaO product is backward-scattered with a large amount of internal excitation ((Fr) < 0.20). Laser-fluorescence measurements [348] of the BaO(X Z+) product for the reaction in the presence of an argon buffer gas, find population of vibrational states up to v = 32. The relative populations have a characteristic temperature of 600 K for v = 0—4 and 3600 K for v = 5—32 with evidence of non-thermal population of v — 13—16. This study also observes population of A n and a 3II states of BaO with v = 0—4. A molecular beam study of Ba + N20 with laser-induced fluorescence detection indicates that the BaO( X) product is formed with a very high rotational temperature. 

The H2 + OH H -I- H2O reaction is a prototype reaction for H atom abstraction by an OH radical to form water as a product. Moreover, it is important in combustion chemistry and interstellar chemistry [85,142]. Consequently, it has attracted extensive experimental and theoretical studies. Crossed-molecular beam experiments on the isotopically substituted D2-I-OH D- -HOD reaction revealed that the product was strongly backward-scattered, with the majority of the available energy channeled into HOD internal excitation and the newly formed OD bond in the HOD molecule preferentially excited to the v = 2 state [123]. The reverse reaction has also been studied widely as a prototype system for mode specific chemistry, in which different vibrational modes in the reactants can play an important role in the reaction dynamic. As three of the four atoms in this system are hydrogen isotopes, it has been straightforward to pursue both high-quality ab initio calculation of a PES and accurate quantum dynamics calculations. As a result, this reaction has become a benchmark system for four-atom reactions, in much the same role that the H -I- H2 reaction played for three-atom reactions. 

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