Theoretical Studies Of Collision-induced Energy Transfer Within Diatomic Molecules In Excited States

Collision-induced quantum interference(CQI) effects within singlet-triplet mixed states were demonstrated in the energy transfer processes of CO(A1,v=0~e3∑-,v=1) + M (M= He, Ne, Ar or HCl) and Na2 (A1∑u+, v=8 ~ b3 0u, v=14) +Na(3s). For these systems, interference phase angles (0st) were also measured experimentally. The present dissertation reports our theoretical studies on the above described processes based on the quantum inelastic scattering theory. The results are as follows:1. θST for Na2+Na collision system was calculated by using the first order Born approximation of time dependent perturbation theory. Two different intramolecular interaction potentials, long range attractive and Lennard-Jones interactions, were utilized to simulate θst and gave θst of 67.0° for the former potential and 67.7° for the latter under the temperature 750K. These results are quite in agreement with the experimental result 71°. Further more, various factors that influence CQI in Na2+Na system were discussed and the temperature dependence of θst was analyzed.2. A theoretical model, based on the quantum inelastic scattering and angular momentum theory, was presented for collision-induced energy transfer within singlet-triplet mixed states diatom-diatom system and was applied to CO(A1,v=0~e3∑-,v=1)+HCl(X1∑+) system. Both the transfer cross sections and θST for CO(-/F2)(?) CO(-/F2), Ja=122, 13, △Ha =±1 transition process were computed. The theoretical results, θst=99° for Ja=12 and θSt=109° for Ja=13, were in good agreement with the experimental θst of 101° for Ja=12 and 110° for Ja=13. Obviously, θSt for CO(A/e)-HCl system is much greater than that forCO(A/e)-He system where θst is about 58°~65°. Our calculations gave the effective collision times to be ~1.5×10-12 and ~0.3×l0-12 s, respectively, for CO-HCl and CO-He. This well explained the fact θsT(CO-HCl)>θST(CO-He).3. A further study on the temporal behavior of collision-induced transition amplitude and phase angle within CO(A~e) mixed states is carried out with a view to elucidating the role of a polar collision partner, HCl, as compared to a rare gas, He. The calculation shows that the transition amplitudes display some damped oscillation with a period inversely proportional to the energy gap between the initial and final states and a damping time determined by the inter-molecular potential of the collision system. It is interesting to note that in the system of CO+He, all the transition amplitude vectors are located in the 1st quadrant of the complex plane both for singlet and triplet channels, whereas for CO+HCl system the transition vectors of singlet and triplet channels are located respectively in the 4th and 1st quadrants. These results explain satisfactorily the experimental fact that θst is smaller than 90° for CO+He, whereas θst is larger than 90° for CO+HCl.4. In a gas cell experiment, 9st measured experimentally represent some average for collisions with different impact parameter b and molecular velocity v. Based on the quantum inelastic scattering theory, the influences of b and v on θst were analyzed both for CO+He system and CO+HCl system. The computation shows that within the physically reasonable scope of b and v, θst of CO-He system is in the range of 30°~70°, while θST of CO-HCl system is in the range of 93°-116°. These results demonstrate that there is no problem of cancellation among positive and negative interferences, the "average" effect of θst for collision with different b and v in cell experiment is not very serious.