Spin-changing collisions in the Ca(4s5p 1P1) + He system

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

“…As the so-called "cone of acceptance" is easily visualized for reactive collision experiments in which two reactants are relatively well oriented with respect to each other, the molecular alignment in the laboratory frame has been the subject most intensively investigated. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] In many cases, the alignment of molecules has been achieved by using the interaction of the molecular permanent or transition dipole moments with a strong external electric field, often generated by the optical pumping, [8][9][10][11][12][13][14][15] which then manipulates the nuclear framework in the laboratory-fixed axes. This "laboratory-frame" alignment of the molecule, therefore, enables one to explore stereoselective chemistry in terms of a chemical shape along the direction of approach in bimolecular reactions.…”

“…In the precollision alignment, for example, atomic orbital angular momentum is aligned in the laboratory frame by the polarized laser pulse. [16][17][18][19][20] For in-collision alignment, electronic states of the collision pair prepared in the form of the van der Waals complex is specifically selected. 21,22 In the postcollision alignment, the electronic orbital is aligned either in the laboratory or recoil frame subsequent to the reactive ͑or inelastic͒ collision, photodissociation, or gas-surface collision.…”

Theoretical study of Ca(4s5p 1P)⇄Ca(4s5p 3P) transitions in collision with noble gases: Integral cross sections and alignment effects

“…With the sets of model potentials we have chosen here we were able to reproduce satisfactorily the results ofthe series of experiments of In addition to providing new mechanistic insight into spin-changing transitions in alkaline earth-noble gas collisions, the present calculations can serve as benchmarks to calibrate more approximate treatments of the collision dynamics. 8 Ultimately, it would be interesting to carry out similar fully quantum studies of both spin-changing collisions with molecular partners 6 as well as more complex electronically inelastic processes. 7,10 Thus we believe that the chosen sets of potentials are sufficiently accurate to explain qualitatively those features which are crucial to an overall understanding of the variation with noble gas collision partner of the Ca(4s5p lP)~Ca(4s5p 3p) cross sections, in particular the relative role of the In_3~ and 1~_3n couplings.…”

“…9 However, at closer interparticle separation, Eqs. (8) and (9) show that the transformation to the Fs basis gives rise to off-diagonal terms, arising from the electrostatic interaction, that couple states which correlate to the Ip and 3p asymptotes, It is this coupling which is responsible for the observed Ip_ 3 p transitions. In this close-in, molecular region, it is more appropriate to describe the diatomic system in a Hund's case (a) basis in which the electrostatic Hamiltonian is diagonaL The case (a) wave functions are written as 18 ,29…”

“…It is as yet unclear how to apply this type of simple model to the quantitative prediction of cross sections, given a set of ~ and n potentials. Further, it becomes considerably more difficult to interpret the polarization dependence of the reverse, 3 P -+ I P, cross sections, since in this case the electronic spin couples strongly with the electronic orbital angular momentum L. Devdariani and Zagrebin 8 have used a semiclassical treatment of the collision dynamics based on realistic potentials in order to interpret the spin--changing cross sections determined by In our work,9 we developed the fully quantum framework to describe inelastic I p+-+-3 P processes under Pouilly,Robbe,and Alexander: Ca(4s5p 'P) collisions with noble gases the condition of an initial nonisotropic distribution of M L states. With a choice of reasonable 1.3l: and 1,3n potentials which correlate to the Ca( 4s5p 1,3 P) + M asymptote, one can then carry out exact close-coupled calculations of the relevant cross sections.…”