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This paper briefly reviews recent progress in product imaging studies of photodissociation and bimolecularreaction dynamics. The SO2 + hv SO(3Σ−) + O(3P2) channel in the ultraviolet photodissociation of sulfur dioxide at photolysis wave lengths between 202 and 207 nm has been studied using resonance-enhanced multiphoton ionization with time-of-flight product imaging. These imaging experiments allowed the determination of the vibrational populations of the SO(3Σ−) fragment at several wave lengths. A change in the vibrational populations occurs from a distribution where most of the population is inv = 0 for wave lengths shorter than 203.0 nm to one where the population is more evenly distributed for longer wavelength dissociation. The changes in the internal energy distribution are attributed to participation of two different predissociation mechanisms. Our data suggest that the predissociation mechanism below 203.0 nm involves an avoided crossing with the repulsive singlet state.1A1. The O3(X 1A1) +hv 0(2p3PJ) + O2(X3Σg−) product channel in the UV photodissociation of ozone has been investigated at photolysis wave lengths of 226, 230, 233, 234, 240, and 266 nm. At 226, 230, 233, 234, and 240 nm, the yield of the O2 product in vibrational states greater than or equal to 26 was 11.8 ± 1.9%, 11.5 ± 1.2%, 8.2 ± 2.0, 4.7 ± 1.8, and 0.6 ± 0.1%, respectively. Two-dimensional ion counting product imaging has also been used to determine the bond energy for the dissociation of jet-cooled O3 into O(1D) + O2(1Δ). The bond dissociation energy into O(1D) + O2(1Δ) was found to be 386.59 ± 0.04 kJ/mol. The standard heat of formation of O3 is calculated to be −144.31 ± 0.14 kJ/mol. State-selective differential cross sections for rotationally in elastic scattering of NO (Ji = 0.5, 1.5, F1 Jf = 2.5–12.5, F1 and Jf=1.5–9.5, F2) from He and D2 measured by crossed molecular beam ion imaging are reported. The images typically exhibit a single broad rotational rain bow maximum that shifts from the forward to the back ward scattering direction with in creasing ΔJ. The angle of the rain bow maximum was lower at a given ΔJ for D2 than for He as a collision partner. At a collision energy of ∼500 cm−1, primarily the repulsive part of the potential surface is probed, which can be modeled with a 2-D hard ellipse potential. This model for rotationally in elastic scattering is shown to qualitatively match the experimental differential cross sections. A more advanced CEPAPES for NO + He does not give substantially better agreement with the experiment. |
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