[4] R. Lisboa, M. Malheiro, A.S. de Castro, P. Alberto and M. Fiolhais, Phys. Rev. C 69 , 024319 (2004). [5] J.N. Ginocchio, Phys. Rep. 414 , 165 (2005). [6] Zhi-Feng Li, Jin-Jin Liu, W. Lucha and F.F. Sch¨ oberl, J. Math. Phys. 46 , 103514 (2005). [7] E.E. Salpeter, Phys. Rev. 87 , 328 (1952). [8] W. Lucha and F.F. Sch¨ oberl, Phys. Rev. D 50 , 5443 (1994). [9] F. Brau, J. Math. Phys. 39 , 2254 (1998). [10] R.L. Hall, W. Lucha and F.F. Sch¨ oberl, J. Phys. A 34 , 5059 (2001), [11] R.L. Hall, W. Lucha and F.F. Sch¨ oberl, J. Math. Phys. 42 , 5228 (2001). [12] R.L. Hall, W. Lucha and F.F. Sch¨ oberl, J. Math. Phys. 43 , 5913 (2002). [13] R.L. Hall, W. Lucha and F.F. Sch¨ oberl, Int. J. Mod. Phys. A, 18 , 2657 (2003). [14] F. Brau, Phys. Lett. A, 313 , 363 (2003). [15] R.L. Hall and W. Lucha, J. Phys. A 38 , 7997 (2005). [16] C. L¨ ammerzahl, J. Math. Phys. 34 , 3918 (1993). [17] F. Gross, Relativistic Quantum Mechanics and Field Theory (Wiley, Weinheim, 1993); M. Srednicki, Quantum Field Theory (Cambridge University Press, Cambridge, 2007). [18] L.D. Landau and E.M. Lifshitz, Mechanics (Pergamon, Oxford, 1976). [19] I.S. Gradshteyn and I.M. Ryzhik, Tables of Integrals, Series, and Products (Elsevier, Amster- dam, 2007). [20] O. Vall´ ee and M. Soares, Airy Functions and Applications to Physics (World Scientific, New Jersey, 2004). [21] L.D. Landau and E.M. Lifshitz, Quantum Mechanics (Nonrelativistic Theory) (Pergamon, Oxford, 1958). [22] L.E. Ballentine, Y. Yang and J.P. Zibin, Phys. Rev. A 50 , 2854 (1994). [23] D.M. Goodmanson, Am. J. Phys. 68 , 866 (2000). 15