Experiments, employing crossed molecular beams, with vibrational state resolution have been performed on the simplest four-atom reaction, OH + D2 --> HOD + D. In good agreement with the most recent quantum scattering predictions, mode-specific reaction dynamics is observed, with vibration in the newly formed oxygen-deuterium bond preferentially excited to v = 2. This demonstrates that quantum theoretical calculations, which in the past decade have achieved remarkable accuracy for three-atom reactions involving three dimensions, have progressed to the point where it is now possible to accurately predict energy disposal in four-atom reactions involving six dimensions.
The Rydberg atom time-of-flight method has been employed for velocity, angular and spin-orbit state-resolved detection of oxygen atoms, O (3 P J). The atoms were ''tagged'' by double-resonance two-photon excitation to high-n Rydberg levels and subsequently field ionized at a detector. The method was characterized by studying a well-known system, the photodissociation of NO 2 at 355 nm. From the O atom time-of-flight spectra, the NO vibrational distribution for different O (3 P J) levels was obtained, with NO (vϭ1͒ rotational structure partially resolved.
The vibrationally inelastic scattering of Rydberg H atoms (n = 30-50) from N2 and O2 at E(coll) = 1.84 eV was studied as a function of laboratory deflection angle. On average, 4 times more vibrational excitation was observed in collisions with O2 than with N2. Vibrational excitation of O2 results largely from collisions in which an electron is briefly transferred from O2 to the proton core, while the Rydberg electron remains a spectator. This provides further evidence that the free electron model applies to low energy collisions involving the ionic core leading to substantial momentum transfer.
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