Helmholtz Gemeinschaft and GSI under the project VH–NG–421. The work of D.A.G. is supported by the grant of the President of Russian Federation, the Saint-Petersburg Gov- ernment, and the FAIR–Russia Research Center. V.M.S. acknowledges the support by the Alexander von Humboldt Foundation. 35 [1] S. A. Blundell, Phys. Rev. A 47 , 1790 (1993). [2] I. Lindgren, H. Persson, S. Salomonson, and A. Ynnerman, Phys. Rev. A 47 , R4555 (1993). [3] M. H. Chen, K. T. Cheng, W. R. Johnson, and J. Sapirstein, Phys. Rev. A 52 , 266 (1995). [4] V. A. Yerokhin, A. N. Artemyev, T. Beier, G. Plunien, V. M. Shabaev, and G. Soff, Phys. Rev. A 60 , 3522 (1999). [5] A. N. Artemyev, T. Beier, G. Plunien, V. M. Shabaev, G. Soff, and V. A. Yerokhin, Phys. Rev. A 60 , 45 (1999). [6] V. A. Yerokhin, A. N. Artemyev, V. M. Shabaev, M. M. Sysak, O. M. Zherebtsov, and G. Soff, Phys. Rev. Lett. 85 , 4699 (2000). [7] O. M. Zherebtsov, V. M. Shabaev, and V. A. Yerokhin, Phys. Lett. A 277 , 227 (2000). [8] V. A. Yerokhin, A. N. Artemyev, V. M. Shabaev, M. M. Sysak, O. M. Zherebtsov, and G. Soff, Phys. Rev. A 64 , 032109 (2001). [9] J. Sapirstein and K. T. Cheng, Phys. Rev. A 64 , 022502 (2001). [10] O. Y. Andreev, L. N. Labzowsky, G. Plunien, and G. Soff, Phys. Rev. A 64 , 042513 (2001). [11] A. N. Artemyev, V. M. Shabaev, M. M. Sysak, V. A. Yerokhin, T. Beier, G. Plunien, and G. Soff, Phys. Rev. A 67 , 062506 (2003). [12] V. A. Yerokhin, P. Indelicato, and V. M. Shabaev, Phys. Rev. Lett. 97 , 253004 (2006). [13] V. A. Yerokhin, A. N. Artemyev, and V. M. Shabaev, Phys. Rev. A 75 , 062501 (2007). [14] Y. S. Kozhedub, D. A. Glazov, A. N. Artemyev, N. S. Oreshkina, V. M. Shabaev, I. I. Tupitsyn, A. V. Volotka, and G. Plunien, Phys. Rev. A 76 , 012511 (2007). [15] V. A. Yerokhin, P. Indelicato, and V. M. Shabaev, Phys. Rev. A 77 , 062510 (2008). [16] Y. S. Kozhedub, O. V. Andreev, V. M. Shabaev, I. I. Tupitsyn, C. Brandau, C. Kozhuharov, G. Plunien, and T. St¨ ohlker, Phys. Rev. A 77 , 032501 (2008). [17] B. Edlen, Phys. Scr. 28 , 51 (1983).