Specific rate constants for the fragmentation of vibrationally excited benzyl radicals

Abstract

The competition between collisional deactivation and fragmentation of vibrationally highly excited benzyl radicals in the ground electronic state has been investigated. Vibrationally highly excited benzyl radicals have been prepared from the dissociation of ethylbenzene after UV photon excitation followed by rapid internal conversion. Subsequently, the benzyl radicals are collisionally deactivated in collisions with the bath gas, argon. After selected delay times the benzyl radicals were excited again by absorption of another UV-photon, followed by fast internal conversion. A certain fraction of the reexcited benzyl radicals decomposes while the rest is collisionally stabilized. The total loss of benzyl radicals due to reexcitation has been monitored by UV absorption spectroscopy. Absolute values of the specific rate coefficients for fragmentation have been derived for excitation energies between 47000 and 53000 cm^-1. These specific rate constants agree well with a deconvolution of the thermal high pressure rate constant obtained from previous shock wave experiments.

References

1. M. Szwarc, J. Chem. Phys., 1948, 16, 128.
2. R. D. Smith, J. Phys. Chem., 1979, 83, 1553.
3. V. S. Rao and G. B. Skinner, 21st International Symposium on Combustion. The Combustion Institute, Pittsburgh, 1986, p. 809.
4. K. M. Pamidimukkala, R. D. Kern, M. R. Patel, H. C. Wei and J. H. Kiefer, 21st International Symposium on Combustion, The Combustion Institute, Pittsburgh, 1986, p. 585.
5. L. D. Brouwer, W. Müller-Markgraf and J. Troe, J. Phys. Chem., 1988, 92, 4905.
6. M. Braun-Unkhoff, P. Frank and Th. Just, 22nd International Symposium on Combustion, The Combustion Institute, Pittsburgh, 1988, p. 1053.
7. H. Hippler, C. Reihs and J. Troe, Z. Phys. Chem., 1990, 167, 1.
8. M. B. Colket and D. J. Seery, 25th International Symposium on Combustion, The Combustion Institute, Pittsburgh, 1994, p. 883.
9. W. Müller-Markgraf and J. Troe, J. Phys. Chem., 1988, 92, 4914; W. Müller-Markgraf, PhD Thesis, University of Göttingen, 1987.
10. U. Brand, H. Hippler, L. Lindemann and J. Troe, J. Phys. Chem., 1990, 94, 6305; L. Lindemann, PhD Thesis, University of Göttingen, 1987.
11. M. Braun-Unkhofff, P. Frank and Th. Just, Ber. Bunsen-Ges. Phys. Chem., 1990, 94, 1417.
12. R. Fröchtenicht, H. Hippler, J. Troe and J. P. Toennies, J. Photochem. Photobiol. A: Chem., 1994, 80, 33.
13. J. Jones, G. B. Bacskay and J. C. Mackie, J. Phys. Chem. A., 1997, 101, 7105.
14. H. Hippler, L. Lindemann and J. Troe, Ber. Bunsen-Ges. Phys. Chem., 1988, 92, 440.
15. M. Damm, F. Deckert and H. Hippler, Ber. Bunsen-Ges. Phys. Chem., 1997, 101, 1901.
16. G. Porter and B. Ward, J. Chim. Phys., 1964, 61, 1517.
17. C. Cossart-Magos and S. Leach, J. Chem. Phys., 1972, 56, 1534; J. Chem. Phys., 1976, 64, 4006.
18. D. M. Brenner, G. P. Smith and R. N. Zare, J. Am. Chem. Soc., 1976, 98, 6707.
19. T. Okamura, T. R. Charlton and B. A. Thrush, Chem. Phys. Lett., 1982, 88, 369.
20. H. H. Nelson and J. R. McDonald, J. Phys. Chem., 1982, 86, 1242.
21. M. Heaven, L. Dimauro and T. A. Miller, Chem. Phys. Lett., 1983, 95, 347.
22. C. Cossart-Magos and W. Goetz, J. Mol. Spectrosc., 1986, 115, 366.
23. J. I. Selco and P. G. Carrick, J. Mol. Spectrosc., 1989, 137, 13.
24. J. I. Selco and P. G. Carrick, J. Mol. Spectrosc., 1990, 139, 449.
25. M. F. Cai, T. A. Miller and V. E. Bondybey, Chem. Phys. Lett., 1989, 158, 475.
26. P. K. Chowdhury, Ber. Bunsen-Ges. Phys. Chem., 1990, 94, 474.
27. G. Porter and M. I. Savadatti, Spectrochim. Acta, 1966, 22, 803.
28. B. Ward, Spectrochim. Acta A, 1968, 24, 813.
29. F. Bayrakceken and J. E. Nicholas, J. Chem. Soc. B, 1970, 691.
30. N. Ikeda, N. Nakashima and K. Yoshihara, J. Phys. Chem., 1984, 88, 5803.
31. H. R. Wendt and H. E. Hunziker, J. Chem. Phys., 1984, 81, 717.
32. H. Hippler, J. Troe and H. J. Wendelken, J. Chem. Phys., 1983, 78, 5351.
33. M. Damm, H. Hippler, H. A. Olschewski, J. Troe and J. Willner, Z. Phys. Chem., 1990, 166, 129.
34. H. Hippler, J. Troe and H. J. Wendelken, J. Chem. Phys., 1983, 78, 6709.
35. H. Hippler, Ber. Bunsen-Ges. Phys. Chem., 1985, 89, 303.
36. N. Ikeda, N. Nakashima and K. Yoshihara, J. Phys. Chem., 1984, 88, 5803.
37. L. Ackermann, H. Hippler, P. Pagsberg, C. Reihs and J. Troe, J. Phys. Chem., 1990, 94, 5247.
38. D. L. Baulch, C. J. Cobos, R. A. Cox, C. Esser, P. Frank, Th. Just, J. A. Kerr, M. J. Pilling, J. Troe, R. W. Walker and J. Warnatz, J. Phys. Chem. Ref. Data, 1992, 21, 411.
39. C. Reihs, PhD Thesis, University of Göttingen, 1989.
40. J. B. Pedley and J. Rylance, in Computer Analysed Thermochemical Data: Organic and Organometallic Compounds, University of Sussex, Brighton, UK, 1997, p. 1.
41. H. Hippler and J. Troe, J. Phys. Chem., 1990, 94, 3803.
42. M. W. Chase Jr., C. A. Davies, J. R. Downey, Jr., D. J. Frurip, D. A. McDonald and A. N. Syverud, JANAF Thermochemical Tables (Third Edition), J. Phys. Ref. Data, 1985, 14, Suppl. 1.
43. H. Hippler and J. Troe, in Bimolecular Collisions, eds. J. E. Bagott and M. N. R. Ashfold, The Royal Society of Chemistry, London 1989.
44. G. Rink, PhD Thesis, University of Karlsruhe, 1997.
45. H. Hippler and G. Rink, Ber. Bunsen-Ges. Phys. Chem., 1998, in preparation.
46. K. Reihs, PhD Thesis, University of Göttingen, 1989; K. Luther and K. Reihs, Ber. Bunsen-Ges. Phys. Chem., 1988, 92, 442.
47. T. Lenzer, PhD, Thesis, University of Göttingen, 1995.
48. T. Beyer and D. F. Swinehart, Commun. Assoc. Comput. Machines, 1973, 16, 379; S. E. Stein and B. S. Rabinovitch, J. Chem. Phys., 1973, 58, 2438.
49. G. Z. Whitten and B. S. Rabinovitch, J. Chem. Phys., 1963, 38, 2466; G. Z. Whitten and B. S. Rabinovitch, J. Chem. Phys., 1964, 41, 1883.
50. L. D. Brouwer, H. Hippler, L. Lindemann and J. Troe, J. Phys. Chem., 1985, 89, 4608.
51. H. Hippler, J. Troe and H. J. Wendelken, J. Chem. Phys., 1983, 78, 5351.
52. W. Forst, Theory of Unimolecular Reactions, Academic Press, New York, London, 1973.
53. T. Baer and W. Hase, in Unimolecular Reactions Dynamics, Theory and Experiments, Oxford University Press, Oxford, 1996.
54. M. Damm, F. Deckert, H. Hippler and J. Troe, J. Phys. Chem., 1991, 95, 2005.
55. J. Troe, J. Phys. Chem., 1983, 87, 1800.