CROSSED-BEAM STUDIES OF NEUTRAL REACTIONS: State-Specific DifferentialCross Sections

Crossed-molecular-beam and laser techniques have enabled experimentalists to measure the state-resolved differential cross sections of elementary chemical reactions. This article reviews recent progress in this area. Particular emphasis is placed on some intriguing physical phenomena associated with a few benchmark reactions and how these measurements help in answering fundamental questions about reaction dynamics. We examine specifically the geometric phase effects in the reaction H + D2, the dynamical resonance phenomenon in F + HD, the unusually large spin-orbit reactivity in Cl(2P) + H2, the insertion reaction O(1D) + H2, and the modespecific reactivity in Cl + CH4(º). The give-and-take between experiment and theoryin unraveling the physical picture of the dynamics is illustrated throughout this review.