| Autor: |
Fukuzawa, Kaori, Matsushita, Toshio, Morokuma, Keiji, Levandier, Dale J., Chiu, Yu-hui, Dressler, Rainer A., Murad, Edmond, Midey, Anthony, Williams, Skip, Viggiano, Albert A. |
| Předmět: |
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| Zdroj: |
Journal of Chemical Physics; 8/15/2001, Vol. 115 Issue 7, p3184, 11p, 1 Diagram, 2 Charts, 5 Graphs |
| Abstrakt: |
Theoretical and experimental studies are performed to elucidate the low energy charge-transfer dynamics of the reaction, O[sup +]([sup 4]S)+C[sub 2]H[sub 2](X [sup 1]Σ[sub g][sup +])→O+C[sub 2]H[sub 2][sup +]. In particular, the role of the low-frequency acetylene bending modes (612 and 730 cm-1) in promoting charge transfer was examined. High-temperature guided-ion beam measurements are carried out over the energy range from near-thermal to 3 eV at 310 and 610 K. The charge-transfer cross sections are found to decrease up to 0.5 eV, to have a constant value at intermediate energies between 0.5 and 1.5 eV, and then to dramatically increase above a threshold of a spin-allowed process determined to be at 1.7 eV. A bending vibrational enhancement of ∼8 is observed at intermediate energies. Thermal energy rate co-efficients are measured in a variable temperature-selected ion flow drift tube apparatus from 193 to 500 K. At each temperature, a negative energy dependence is observed. In order to elucidate the reaction mechanism in detail, high level ab initio calculations using Complete Active Space Self-Consistent Field and Multi-Reference Single- and Double-excitation Configuration Interaction methods have been performed. The results indicate that the charge transfer reaction occurs at an early stage via nonadiabatic transition between quartet and doublet states. There is a weak van der Waals minimum at the entrance channel between O[sup +]([sup 4]S) and C[sub 2]H[sub 2] with the relative energy of -1.51 kcal/mol. The minimum of the quartet/doublet crossing seam (Q/D MSX), where the spin-forbidden nonadiabatic transition is most likely to take place, lies very near this minimum at R[sub CO]=4.06 Å, R[sub CC]=1.20 Å, and / CCH=166.6° with a relative energy of -1.48 kcal/mol. After the nonadiabatic transition, the system propagates on the doublet surface to reach the exothermic O([sup 1]D)+C[sub 2]H[sub 2][sup +](X˜ [sup 2]... [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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