Stereochemical effects of laser-aligned atoms in energy transfer and reactive collisions

In crossed beam experiments collisional energy transfer and reactive processes are studied to examine the effects of Ca* orbital geometry on the reaction rate, electronic branching and final state orbital alignment. The collisional energy transfer experiments use Ca* + rare gas systems and are either two- or three-vector correlation studies. The reactive systems involve electronically excited Ca* with SF{dollar}sb6{dollar}, N{dollar}sb2{dollar}O and O{dollar}sb2{dollar}.; To control the initial orbital alignment of the excited Ca, polarized lasers are used in the excitation. This produces an aligned state with respect to the relative velocity of the colliding partners. In the two-vector studies of Ca(4s4f{dollar}sp1Fsb3{dollar}) + rare gas {dollar}to{dollar} Ca(4p{dollar}sp2{dollar} {dollar}sp1Ssb0{dollar}) + rare gas, six-fold oscillations are observed in the initial state alignment dependence. With each rare gas the magnetic sublevel cross sections leading to formation of Ca(4p{dollar}sp2 sp1Ssb0{dollar}) show a large preference for the m = 0 initial state sublevel.; A laser pump-probe technique is used to investigate the spin-changing Ca(4s5p {dollar}sp1Psb1{dollar} {dollar}to{dollar} {dollar}sp3Psb2{dollar}) and intramultiplet mixing Ca(4s4p {dollar}sp3Psb1{dollar} {dollar}to{dollar} {dollar}sp3Psb{lcub}2,0{rcub}{dollar}) energy transfer with He. These three-vector experiments make use of a newly developed theory to obtain highly state resolved m-sublevel to m-sublevel cross sections and coherence effects in the collision process. For parallel preparation of the Ca* state with respect to the relative velocity, both systems produce highly aligned distributions in the final magnetic substates. In the perpendicular configuration, orientation information is obtained by breaking the azimuthal symmetry of the collision. When introduced by this lower symmetry, coherence effects contribute significantly to the observed alignment data.; Reactive systems of aligned Ca* with SF{dollar}sb6{dollar}, N{dollar}sb2{dollar}O and O{dollar}sb2{dollar} show a wide range of alignment dependencies. These are examined in the chemiluminescence of the products and chemiionization of the reactants. While these results are considered preliminary, they include alignment dependent electronic branching into CaF* and Ca ionization by O{dollar}sb2{dollar}. No observable alignment effect is found for the reaction with N{dollar}sb2{dollar}O to form CaO*.