State-to-state reaction dynamics in crossed supersonic jets: threshold evidence for non-adiabatic channels in F+H₂

Abstract

The reaction of F+n-H₂ to form HF(v,J)+H is studied in a crossed jet apparatus under single collision conditions, using high-resolution direct absorption spectroscopy to probe the nascent rotational HF distributions. The J-dependent reactive cross-sections into HF(v=3,J) are investigated over a range of center-of-mass collision energies well below the 1.9 kcal mol^-1 barrier for adiabatic chemical reactions with groundstate F(²P_3/2) atoms. The energy dependent reaction cross-sections decrease much more slowly with E_com than predicted by exact quantum calculations on the adiabatic F(²P_3/2)+H₂ surface (K. Stark and H. Werner, J. Chem. Phys., 1996, 104, 6515). In addition, product states in the HF(v=3) manifold are observed that are energetically accessible only to the excitedspin–orbit state F*(P_1/2)+H₂(j=0,1) channel. These observations strongly suggest that non-adiabatic reactions with spin–orbit excited F^*(P_1/2) contribute significantly in the near threshold region, in good agreement with recent calculations by M. Alexander, H. Werner and D. Manolopoulos (J. Chem. Phys., 1998, 109, 5710). Finally, the feasibility of high-resolution IR laser Dopplerimetry on the nascent products is illustrated on collision free HF(v,J) distributions formed from reactions of F+CH₄.

References

1. H. Shaefer III, J. Phys. Chem., 1985, 89, 5336.
2. J. C. Polanyi and J. L. Schreiber, Faraday Discuss. Chem. Soc., 1977, 62, 267.
3. D. Manolopoulos, J. Chem. Soc., Faraday Trans., 1997, 93, 673.
4. J. Anderson, Adv. Chem. Phys., 1980, 41, 229.
5. L. J. Butler, Annu. Rev. Phys. Chem., 1998, 49, 125.
6. W. B. Chapman, Jr., B. W. Blackmon, S. Nizkorodov and D. J. Nesbitt, J. Chem. Phys., 1998, 109, 9306.
7. K. Stark and H. Werner, J. Chem. Phys., 1996, 104, 6515.
8. R. D. Coombe and G. C. Pimentel, J. Chem. Phys., 1973, 59, 251.
9. S. Lu, C. Liu, X. Yang, K. Li, Y. Gu and Y. Tao, J. Chem. Phys., 1988, 88, 2379.
10. D. M. Neumark, A. M. Wodtke, G. N. Robinson, C. C. Hayden and Y. T. Lee, J. Chem. Phys., 1985, 82, 3045.
11. N. Jonathan, C. M. Mellier-Smith and D. H. Slater, Mol. Phys., 1971, 20, 93.
12. D. Truhlar, J. Chem. Phys., 1972, 56, 3189.
13. J. T. Muckerman and M. D. Newton, J. Chem. Phys., 1972, 56, 3191.
14. B. Hartke and H. Werner, Chem. Phys. Lett., 1997, 280, 430.
15. G. Dharmasena, K. Copeland, J. Young, R. Lasell, T. Phillips, G. Parker and M. Keil, J. Phys. Chem. A, 1997, 101, 6429.
16. F. Aoiz, L. Banares, B. MartinezHaya, J. Castillo, D. Manolopoulos, K. Stark and H. Werner, J. Phys. Chem. A, 1997, 101, 6403.
17. J. F. Castillo, B. Hartke, H. J. Werner, F. J. Aoiz, L. Banares and B. Martinez-Haya, J. Chem. Phys., 1998, 109, 7224.
18. J. Castillo, D. Manolopoulos, K. Stark and H. Werner, J. Chem. Phys., 1996, 104, 6531.
19. E. Rosenman and A. Persky, Chem. Phys., 1995, 195, 291.
20. F. Aoiz, L. Banares, V. Herrero, K. Stark and H. Werner, Chem. Phys. Lett., 1996, 254, 341.
21. J. Castillo and D. Manolopoulos, personal communications.
22. JANAF Thermochemical Tables, NSRDS-NBS 37, 2nd edn., 1971.
23. W. C. Stwalley, Chem. Phys. Lett., 1970, 6, 241.
24. W. T. Zemke, W. C. Stwalley, J. A. Coxon and P. G. Hajigeorgiou, Chem. Phys. Lett., 1991, 177, 412.
25. S. A. Nizkorodov, W. W. Harper, W. B. Chapman, Jr., B. W. Blackmon and D. J. Nesbitt, J. Chem. Phys., submitted.
26. E. Arunan, D. W. Setset and J. F. Ogilvie, J. Chem. Phys., 1992, 97, 1734.
27. M. Alexander, H. Werner and D. Manolopoulos, J. Chem. Phys., 1998, 109, 5710.
28. J. E. Pollard, D. J. Trevor, T. T. Lee and D. A. Shirley, J. Chem. Phys., 1982, 77, 4818.
29. P. Huber-Walchli and J. W. Nibler, J. Chem. Phys., 1982, 76, 273.
30. R. J. Gallagher and J. B. Fenn, J. Chem. Phys., 1974, 60, 3492.
31. K. Dharmasena, J. Jefferies, G. Mu, J. Young, B. Bergeron, R. Littell and N. Shafer-Ray, Rev. Sci. Instrum., 1998, 69, 2888.
32. M. Baer, M. Faubel, B. Martinez-Haya, L. Rusin, U. Tappe and J. Toennies, J. Chem. Phys., 1998, 108, 9694.
33. J. Harrison, L. Isakson and H. Mayne, J. Chem. Phys., 1989, 91, 6906.
34. J. B. Song and E. A. Gislason, J. Chem. Phys., 1995, 103, 8884.
35. M. Faubel, B. Martinezhaya, L. Rusin, U. Tappe and J. Toennies, Z. Phys. Chem., 1995, 188, 197.
36. M. Faubel, L. Rusin, S. Schlemmer, F. Sondermann, U. Tappe and J. Toennies, J. Chem. Soc., Faraday Trans., 1993, 89, 1475.
37. W. Chapman, M. Weida and D. Nesbitt, J. Chem. Phys., 1997, 106, 2248.
38. W. W. Harper, S. A. Nizkorodov and D. J. Nesbitt, J. Chem. Phys., in preparation.
39. K. Sugawara, F. Ito, T. Nakanaga, H. Takeo and C. Matsumura, J. Chem. Phys., 1990, 92, 5328.
40. A. Gauss, Jr., J. Chem. Phys., 1976, 65, 4365.
41. J. C. Corchado and J. S. Espinosa-Garcia, J. Chem. Phys., 1996, 105, 3160.
42. H. Kornweitz, A. Persky and R. D. Levine, Chem. Phys. Lett., 1998, 289, 125.