n-Vector correlations in collision dynamics with atomic orbital alignment: the importance of coherence denoting azimuthal structure for n .gtoreq. 3

Abstract

An introduction is presented of vector correlations in collision experiments involving atomic orbital alignment or orientation. At present, aligned or oriented species can be prepared (or probed) with "relative" ease using polarized laser beams. First, an extensive expos6 of the necessary mathematical formalisms for two-and three-vector correlations is given, and then experimental examples for atomic Ca are discussed to elucidate the theory. It is demonstrated both theoretically and experimentally that azimuthal structure about the initial relative velocity vector (called coherence) becomes important when three or more vector quantities are controlled in the collision process. I. Ioboduction: Vector CorrelationsCollision processes are very sensitive to vector quantities. The most obvious vector quantity in a collision is the initial relative velocity, vi. With the availability of crossed-beam apparatuses it is possible to have pr& control over the direction of the relative velocity vector. If we consider elastic conditions of structureless species, there is only one additional vector quantity that may be resolved experimentally, the final relative velocity vf. The correlation between the initial and final relative velocity vectors can be determined in a differential scattering experiment, where both velocities are resolved. This correlation can select collision processes within certain well-defined impact parameter ranges. By analyzing the scattering as a function of impact parameter range, one can obtain accurate potential information.I4Atomic collision processes that attract recent interest involve structured states, characterized by the quantum state b,m) for the total electronic angular momentum, j , and magnetic quantum number, m. The potential curves governing the colliiion dynamics are now characterized by a magnetic substate dependence. In most early experimental situations this m dependence is not resolved, because one encounters a statistical average of the varidus substates. The availability of polarized laser beams has made it possible to manipulate the alignment (symmetric m distribution) or orientation (asymmetric m distribution) of these structured species and to study their role in collision dynamics.s-21 For example, a p orbital can be prepared asymptotically parallel (I; state) or perpendicular (n state) in a collision. Interesting magnetic substate dependences can thus be obtained for the collision process, which may reveal important features of the potential cur~es.2~-~ Further possibilities of polarized laser beams may be utilized by preparing two collision partners in an aligned (oriented) state prior to the collision event. Furthermore, it is possible to probe the alignment (orientation) distribution after the collision for either one or both of the structured species. Therefore, it is evident that the number n of relevant vector quantities can easily range from n = 3 to n = 6, or higher if we consider molecular targets.In a Ycompleten scattering experiment all the relevant vector quantitie...

Experimental and theoretical study of the photodissociation reaction of thiophenol at 243nm: Intramolecular orbital alignment of the phenylthiyl radical

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“…For instance, the relative population in ⌳-doublet states of diatomic fragments such as OH͑¯ 2 3 ; X 2 ⌸͒, NO͑¯ 2 1 ; X 2 ⌸͒, and NH * ͑¯ 1 3 ; c 1 ⌸͒ has long been utilized as a clue for determining the planarity of the photodissociation process. [28][29][30][31] This is aided by the fact that the singly occupied electronic orbital, in the classical limit, is either parallel or perpendicular to the rotating plane. The orbital angular momentum may be relatively well defined along the molecular axis for linear polyatomic molecules.…”

Intramolecular Orbital Alignment Observed in the Photodissociation of [D1]Thiophenol

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Effect of Near-Threshold Ionization on Electron Attachment in Gaseous Dielectrics

“…Leone's group performed interesting experiments where the conventional cross-sections for some of the inelastic collisional transitions in the Ca-He complex were determined [18][19][20]. The dependence on the initial orientation of the electronic angular momentum with respect to the initial relative velocity of the collisional partner has proven to reveal many interesting features of the potential curves and collisional dynamics.…”