1. D. Lee andA. C. Albrecht:J. Chem. Phys.,78, 3382 (1983).
2. K.-H. Yang:Ann. Phys. (N.Y.),101, 62 (1976).
3. We limit ourselves to providing a selection of relevant papers:a)C. Cohen-Tannoudji B. Diu andF. Laloe:Quantum Mechanics (J. Wiley and Sons, New York, N.Y., 1977), p. 315;b)J. J. Forney, A. Quattropani andF. Bassani:Nuovo Cimento B,37, 78 (1977);c)D. H. Kobe:Phys. Rev. Lett.,40, 538 (1978);d)D. H. Kobe andA. L. Smirl:Am. J. Phys.,46, 624 (1978);e)C. Leubner andP. Zoller:J. Phys. B,13, 3613 (1980);f)C. Leubner:Am. J. Phys.,49, 738 (1981);g)Y. Aharonov andC. K. Au:Phys. Lett. A,86, 269 (1981);h)J. Bergou:J. Phys. B,16, L647 (1983). A more extensive bibliography can be found in ref. (4).
4. G. P. Arrighini, C. Guidotti andN. Durante: to be published.
5. R. B. Walker andR. K. Preston:J. Chem. Phys.,67, 2017 (1977).