Rydberg transitions in bis(η⁶-benzene)chromium; a study of isotopic effects and vibronic structures

Abstract

Gas-phase electronic absorption spectra of (η⁶-C₆H₆)₂Cr 1 and (η⁶-C₆D₆)₂Cr 2 have been measured with 30 cm^-1 resolution. Both spectra show 3d(a_1g)→Rnp(e_1u) (n=4–12) and 3d(a_1g)→Rnp(a_2u) (n=5–8) series. The first ionization potentials, determined as a convergence limit of the Rnp(e_1u) series, are 5.459±0.004 and 5.446±0.004 eV for 1 and 2, respectively. The Rydberg np 0₀⁰ bands display a ca. 100 cm^-1 shift on going from 1 to 2. The decreases in ionization potential and Rydberg frequencies have vibrational nature and indicate lower zero-level vibrational energy for bis(η⁶-benzene)chromium in the ground electronic state in comparison with that of the molecule in the Rydberg np states and the ground-state cation. A complete assignment of the vibronic components of the Rydberg transitions in 1 and 2 has been made on the basis of comparison of the spectra. In addition to vibrational progressions on the totally symmetric metal–ring stretching mode, the R4p(e_1u) and R5p(e_1u) transitions show components arising from excitation of CH vibrations. The corresponding absorption features are shifted towards the 0₀⁰ bands on going from 1 to 2.

References

1. S. Yu. Ketkov, G. A. Domrachev and G. A. Razuvaev, Opt. Spectrosc. (USSR), 1987, 63, 167.
2. G. A. Domrachev, S. Yu. Ketkov and G. A. Razuvaev, J. Organomet. Chem., 1987, 328, 341.
3. S. Yu. Ketkov, G. A. Domrachev and G. A. Razuvaev, J. Mol. Struct., 1989, 195, 175.
4. S. Yu. Ketkov and G. A. Domrachev, J. Organomet. Chem., 1990, 389, 187.
5. S. Yu. Ketkov, C. Mehnert and J. C. Green, Chem. Phys., 1996, 203, 245.
6. E. O. Fischer and W. Hafner, Z. Naturforsch., B, 1955, 10, 665.
7. P. L. Timms, Chem. Commun., 1969, 1033.
8. F. G. N. Cloke and M. L. H. Green, J. Chem. Soc., Dalton Trans., 1981, 1938.
9. G. Herzberg, Molecular Spectra and Molecular Structure. III. Electronic Spectra of Polyatomic Molecules, Van Nostrand, New York, 1966.
10. J. Weber, M. Geoffroy, A. Goursot and E. Penigault, J. Am. Chem. Soc., 1978, 100, 3995.
11. D. W. Clack and K. D. Warren, Struct. Bonding (Berlin), 1980, 39, 1.
12. A. Haaland, Acta Chem. Scand., 1965, 19, 41.
13. S. Yu. Ketkov, J. Organomet. Chem., 1992, 429, C38.
14. S. Yu. Ketkov, J. Organomet. Chem., 1994, 465, 225.
15. G. Herzberg, Molecular Spectra and Molecular Structure. II. Infrared and Raman Spectra of Polyatomic Molecules, Van Nostrand, New York, 1945.
16. K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure. IV. Constants of Diatomic Molecules, Van Nostrand, New York, 1979.
17. J. F. Cordes and S. Schreiner, Z. Anorg. Allg. Chem., 1959, 299, 87.
18. E. O. Fischer and S. Schreiner, Chem. Ber., 1958, 91, 2213.
19. E. O. Fischer and H.-P. Fritz, Angew. Chem., 1961, 73, 353.
20. J. T. S. Andrews, E. F. Westrum and N. Bjerrum, J. Organomet. Chem., 1969, 17, 293.
21. R. D. Feltham, J. Inorg. Nucl. Chem., 1961, 16, 197.
22. J. C. Green, M. L. H. Green, C. N. Field, D. K. P. Ng and S. Yu. Ketkov, J. Organomet. Chem., 1995, 501, 107.
23. R. G. Snyder, Spectrochim. Acta, 1959, 15, 807.
24. H.-P. Fritz, W. Lúttke, H. Stammereich and R. Forneris, Spectrochim. Acta, 1961, 17, 1068.
25. L. Schaefer, J. F. Southern and S. J. Cyvin, Spectrochim. Acta, Part A, 1971, 27, 1083.
26. S. J. Cyvin, J. Brunvoll and L. Schaefer, J. Chem. Phys., 1971, 54, 1517.
27. J. Brunvoll, S. J. Cyvin and L. Schaefer, J. Organomet. Chem., 1971, 27, 69.
28. I. I. Greenwald and B. V. Lokshin, J. Mol. Struct., 1990, 218, 255.
29. E. B. Wilson, Phys. Rev., 1934, 45, 706.
30. G. J. Fisanick, A. Gedanken, T. S. Eichelberger IV, N. A. Kuebler and M. B. Robin, J. Chem. Phys., 1981, 75, 5215.
31. P. D. Burrow, A. Modelli, M. Guerra and K. D. Jordan, Chem. Phys. Lett., 1985, 118, 328.
32. M. B. Robin, Higher Excited States of Polyatomic Molecules, Academic Press, Orlando, 1985, vol. 3.