Alignment and orientation effects in Sr energy pooling

Alignment and orientation effects in the energy pooling process, Sr(5s5p P- 3(1)) + Sr(5s5p P-3(1)) --> Sr(5s5p P-1(1)) + Sr(5s(2) S-1(0)), are studied in a single atomic beam. The Sr atoms are prepared in an aligned initial s tate with a polarized laser, and alignment information is extracted by obse rving the fluorescence from the final Sr(5s5p P-1(1)) state as the atoms pr ecess in an applied magnetic field. This allows the dependence of the total energy pooling cross section (integrated over the final state alignment) o n the initial state alignment to be almost completely described. A prominen t alignment effect is observed. If m(j) represents the component of total e lectronic angular momentum of a Sr(5s5p P-3(1)) atom along the relative vel ocity vector of the collision, then the total energy transfer cross section for a particular initial state alignment can be expressed as a sum of the so-called fundamental cross sections, sigma(m1m2) and sigma(m1m2;m'm2'), th at describe collisions between the various m(j) states. Here sigma(m1m2) re presents the cross section for energy transfer when an atom in state m(1) c ollides with an atom in state m(2). The cross section sigma(m1m2;m1'm2') re presents the contribution to the total cross section from interference when the colliding system is in a superposition of the state m(1) colliding wit h m(2) and the state m(1)' colliding with m(2)'. It is found that the cross sections sigma(1-1), sigma(00), and sigma(10) as well as the interference terms Re(sigma(00;1-1)) and sigma(01;10) have relatively large values while sigma(11) and sigma(1-1;-11) are small. Coupled with future theoretical wo rk, these results may provide new insights into the dynamics of the curve c rossings that lead to energy transfer.