1. N.G. Gotts, D.G. Lethbridge, and A.J. Stase, J. Chem. Phys. 96, 408 (1962).
2. J. Purnell, E.M. Snyder, S. Wei, and A.W. Caslemand, Chem. Phys. Lett. 229, 33e(1994).
3. T. Ditmire, T. Donnelley, R.W. Falcone, and M.D. Perry, Phys. Rev. Lett. 75, 3122(1995).
4. Y.L. Shao, et al., Phys. Rev. Lett. 77, 3343 (1996).
5. T. Ditmire, et al., Nature 386, 54 (1997).