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45236-AC6
New Theoretical Methods for Reaction Dynamics
The work sponsored by my Petroleum Research Fund type-AC award is progressing well. We have completed approximately half of the proposed research. In the following paragraphs, I shall briefly review the work that has been completed so far.
(1) The State-to-State-to-State view of Chemical Reactions
We had proposed to investigate the utility of a new view of bimolecular reaction dynamics based on the use of the quantum bottleneck states associated with the transition state (TS) of the reaction. By decomposing the S-matrix into factors representing the passage into and out of the TS, we hoped to glean physical insight the product state distribution and DCS of some A+BC type chemical reactions. The method has proven to work quite well. We have found that the product state distribution for the D+H2 reaction could be understood in detail using our approach. A new Franck-Condon like approximation was introduced to further reveal the underlying within the state-to-state-to-state picture. The model was particularly useful in understanding the reactivity of different helicity state of the reagents. It was found that some anomalous molecular beam scattering results of XM Yang and coworkers could be perfectly rationalized using our approach. We have found that helicity selected differential cross sections along the collision axis could be inferred from unpolarized beam scattering experiments using an approach based on our methods. Recently, we have discovered that some rather mysterious vibrational branching observed for F+HDàHF(v')+D could be understood using our model.
(2) The F+HClà HF+Cl Reaction
We proposed to study the detailed reaction dynamics of this reaction using a newly developed potential energy surface. It was found that the huge disagreement between molecular beam scattering and thermal reaction dynamics could be traced to the rotational enhancement of the reaction probability. Higher rotational states of the HCl reagent were found to be vastly more reactive than the lower rotational states. A simple physical picture of this enhancement was developed. Furthermore, we have found that 2/3 of the reaction proceeds through reactive resonance states at room temperature. This resonant mechanism is likely the cause of the pronounced curvature observed in the Arrhenius plot of the rate constant. The resonance states have been studied in detail and assigned quantum numbers using a full calculation of Smith Q-matrix (i.e. the lifetime matrix).
(3) Reaction Dynamics of Rydberg Atoms
We proposed to study the reaction dynamics of highly excited (n~50) Rydberg atoms with neutral molecules. We have investigated in detail the reaction D*+H2(0,0)àHD(v',j')+H*, that has been studied by Yang and coworkers in the laboratory. We have found that the state resolved differential cross section (DCS) for this process is closely related to that of the ion-molecule reaction D++H2(0,0)àHD(v',j')+H+. This is highly significant since the Rydberg atom reaction is much easier to experimentally study that the ion-molecular reaction since it avoids well known problems with space charge repulsion. However, we have discovered some systematic and important differences between the DCS of the two problems. We have found that the Rydberg electron is actually not an ideal (in the sense of the Fermi model) spectator to the reaction, and in reality exhibits some very interesting dynamics. We have found that collision induced ionization and spontaneous emission are important and depend on the scattering angle and final state of the products. We have developed an “instrument function” to account for the differences in DCS of the Rydberg and ionic reactions.
(1) J. Zhang, D. X. Dai, S. A. Harich, C. C. Wang, S. A. Harich, X. Wang, X. M. Yang, M. Gustafsson, and R. T. Skodje, Phys. Rev. Lett. 96, 93201 (2006).
(2) M. Gustafsson and R. T. Skodje, J. Chem. Phys. 124, 144311 (2006).
(3) M. Gustafsson, R. T. Skodje, J. Zhang, D. Dai, S. A. Harich, X. Wang, and X. Yang, J. Chem. Phys. 124, 241105 (2006).
(4) M. Gustafsson and R. T. Skodje, Chem. Phys. Lett. 434, 20-24 (2007).
(5) M. Gustafsson and R. T. Skodje, to be published.
(6) M. P. Deskevich, M. Y. Hayes, K. Takahashi, R. T. Skodje, and D. J. Nesbitt, J. Chem. Phys. 124, 224303 (2006).
(7) M. Y. Hayes, M. P. Deskevich, D. J. Nesbitt, K. Takahashi, and R. T. Skodje. Phys. Chem. A 110, 436-444 (2006).
(8) M. Y. Hayes, K. Takehashi, and R. T. Skodje, to be published.
(9) H. Song, D. Dai, G. Wu, C. C. Wang, S. A. Harich, M. Y. Hayes, X. Wang, D. Gerlich, X. Yang, and R. T. Skodje, J. Chem. Phys. 123, 074314 (2005).
(10) D. Dai, C. C. Wang, G. Wu, S. A. Harich, H. Song, M. Y. Hayes, R. T. Skodje, X. Wang, D. Gerlich, and X. Yang, Phys. Rev. Lett. 95, 013201 (2005).
(11) M. Y. Hayes and R. T. Skodje, J. Chem. Phys. 126, 104306 (2007).
