1. Association Reaction Studies of Alkali Metal Ions and Dimethoxy ethane (DXE) Hideya Koizumi and P. B. Armentrout University of Utah +

2. Objectives R. Dunbar has measured BDEs by association reactions in an FT-ICR Here, we investigate the kinetic energy dependence of association reaction by GIBMS Alkali metal cation and DXE association reaction is chosen because the only product is the long- lived association complex We want to develop methods to obtain the BDE for the association reaction cross section The results test our use of statistical theory

3. Potential Energy Surface M + DXE * M + + DXE Association Unimolecular Dissociation C I D

4. Guided Ion Beam Mass Spectrospcopy(Efrim)

5. Schematics Association Reaction M + + DXE Association M + (DXE) * Long lived Complex Dissociation The lifetime of the complex can be calculated from the energy dependent unimolecular decay rate constant k Required conditions for obtaining good experimental data 1)Complex has to be long lived (more than flight time  ) to be detected 2)No collisional stabilization by multiple collisions (pressure dependence) Basically,  M+DXE (E) =  LGS (E) exp[-k(E)  ]

6. Pressure Dependence

7. 2.50 (0.19) 1.64 (0.04) 1.23 (0.04) BDEs (eV) from CID values and theory (More et al.) 1.35 1.79 2.65

8. Modeling the cross sections In all models, the only adjustable parameter is E 0 Statistical distribution of total angular momentum (AM) (by Rodgers, Ervin, Armentrout) Usual method used for CID (Fix n and  0 to give  LGS ) Problem:AM is not conserved 2)Explicit conservation of orbital AM Use impact parameter distribution It conserves AM for the complex (w/ stationary target approx.) Approximation L ’ = L ’’ (No Coupling to rotations); |J | << |L | 3) Rigorous Statistical Theory (Phase Space Theory) (by Chesnavich, Bowers) Explicitly conserve angular momentum (Coupling allowed)

9. Distribution of Total Angular Momentum of the Energized Molecule J J Distribution Statistical Orbital AM Conservation & PST Centrifugal acceleration J max Deceleration

10. CID 1.64 (0.04) eV Statistical 1.78 ± 0.12 Orbital AM conservation 1.75 ± 0.11 PST 2.20 ± 0.17 ! ! Means work in progress

11. Very conservative Error chosen for time being Model Orbital AM conservation

12. CID 1.23 (0.04) eV Statistical 1.28 ± 0.10 Orbital AM Conservation 1.28 ± 0.10 PST 1.62 ± 0.08 !

13. CID 2.50 (0.19) eV Statistical 2.45 ± 0.35 Orbital AM conservation 2.40 ± 0.3 PST 3.00 ± 0.4 !

14. CIDTheory StatisticalOrbital AM conservation Phase Space Theory (!) Li + + DXE 2.50 (0.19) 2.652.45 (0.35) 2.40 (0.3) 3.00 (0.4) Na + + DXE 1.64 (0.04) 1.791.78 (0.12) 1.75 (0.11) 2.20 (0.17) K + + DXE 1.23 (0.04) 1.391.28 (0.10) 1.28 (0.10) 1.62 (0.08)

15. Summary Energy dependence of the cross section is well charactorized with all model The association reaction analysis (Statistical and Orbital AM conservation) nearly reproduce the bond dissociation energy obtained by CID The dynamic range of this analysis is established to be fairly large Work In Progress Better implementation of Statistically rigorous PST in this example. Oblate & TS switching & etc

16. Acknowledgement Group Members Prof. P. B. Armentrout Prof. K. M. Ervin Thank you for listening!! This work is supported by NSF#

17. One Possible reason of poor performance of statistically rigorous PST Maybe the complex rotating fast Fragments of TS (large |L |) stop rotating Better approximated by TTS 1)Barrierless TS switching (K dependent) ( Chesnavitch & Bowers) 1)Note (Tightness of TS is depend on |L |) Allow TS switch for even small K but large L K J L |L | large enough that TS is better considered to be Tight TS

18. What about Sphere approximation? Sphere is very good approximation! (Chesnavich&Bowers) atom-oblate atom-prolate What about Centrifugel distortion of M + DXE complex? Our calculation shows that change of rotational energy is much less than 5% in all case [Li < Na < K]

19. Question Does rotational phase space dynamically restricted? PST always prefer to dissociate with low value of orbital angular momentum no matter how fast the complex rotate.