Halogen nuclear quadrupole coupling in the rotational spectrum of H₃N···ICl as a probe of inter- and intramolecular charge transfer

Abstract

The ground-state rotational spectra of the three isotopomers H₃¹⁴N···I³⁵Cl, H₃¹⁴N···I³⁷Cl and H₃¹⁵N···I³⁵Cl of a symmetric-top complex formed between ammonia and iodine monochloride were detected and measured by using the pulsed-jet, Fourier-transform microwave technique in combination with a fast-mixing nozzle. The spectroscopic constants B₀, D_J, D_JK, χ(¹⁴N), χ(I), χ(Cl), M_aa(I) and M_bb(I) were determined for each isotopomer. Various of these constants were interpreted with the aid of simple models to give the geometry, the binding strength, and the electric charge redistribution relative to the free molecules NH₃ and ICl. The equilibrium geometry is one of C_3v symmetry, with the nuclei in the order H₃N···ICl and with the distance r(N···I)=2.711(2) Å. The intermolecular stretching force constant k_σ=30.4(3) N m^-1 is large and indicates that the complex is strongly bound. The changes in the halogen nuclear quadrupole coupling constant χ(I) and χ(Cl) from their respective free molecule values lead to the conclusion that the intermolecular electronic charge transfer, δ₁e^-, from N to I on complex formation is 0.078(8) e^-, while the polarization of the ICl subunit can be represented by a transfer, δ₂e^-, of 0.150(3) e^- from I to Cl. The net change at I is -0.073(5) e^-. A comparison of r(N···X), δ₂ and k_σ for the series of complexes H₃N···XY, where XY=Cl₂, Br₂, BrCl, ICl or ClF, is presented and some general conclusions are drawn.

References

1. O. Hassel and Ch. Rømming, Q. Rev., Chem. Soc., 1962, 16, 1.
2. R. S. Mulliken and W. B. Person, Molecular Complexes, A Lecture and Reprint Volume, Wiley-Interscience, New York, 1969 and references cited therein.
3. A. J. Downs and C. J. Adams, in Comprehensive Inorganic Chemistry, ed. A. F. Trotman-Dickenson, Pergamon Press, Oxford, 1973, ch. 26, p. 1214.
4. A. C. Legon and C. A. Rego, J. Chem. Soc., Faraday Trans., 1990, 86, 1915.
5. T. J. Balle and W. H. Flygare, Rev. Sci. Instrum., 1981, 52, 33.
6. A. C. Legon, in Atomic and Molecular Beam Methods, ed. G. Scoles, Oxford University Press, New York, 1992, vol. 2, ch. 9.
7. J. B. Davey, A. C. Legon and E. R. Waclawik, Phys. Chem. Chem. Phys., 1999, 1, 3097.
8. H. M. Pickett, J. Mol. Spectrosc., 1991, 148, 371.
9. A. C. Legon and D. J. Millen, Proc. R. Soc. London, Ser. A, 1988, 417, 21.
10. J. Baker, A. D. Buckingham, P. W. Fowler, P. Lazzeretti, E. Steiner and R. Zanasi, J. Chem. Soc., Faraday Trans. 2, 1989, 58, 201.
11. A. C. Legon, D. G. Lister and J. C. Thorn, J. Chem. Soc., Faraday Trans., 1994, 90, 3205.
12. A. C. Legon, Chem. Phys. Lett., 1995, 237, 291.
13. J. B. Davey, A. C. Legon and E. R. Waclawik, Chem. Phys. Lett., 1999, 306, 133.
14. C. H. Townes and B. P. Dailey, J. Chem. Phys., 1949, 17, 782.
15. C. H. Townes and A. L. Schawlow, Microwave Spectroscopy, McGraw-Hill, New York, 1955, ch. 9.
16. W. Gordy and R. L. Cook, Microwave Molecular Spectra, Techniques of Chemistry, Vol. XV III, Wiley-Interscience, New York 1984 ch. 14.
17. M. D. Marshall and J. S. Muenter, J. Mol. Spectrosc., 1981, 85, 322.
18. G. T. Fraser, K. R. Leopold and W. Klemperer, J. Chem. Phys., 1984, 80, 1423.
19. P. Helminger, F. C. Delucia and W. Gordy, J. Mol. Spectrosc., 1971, 39, 94.
20. C. C. Costain, J. Chem. Phys., 1958, 29, 864.
21. D. J. Millen, Can. J. Chem., 1985, 63, 1477.
22. H. I. Bloemink and A. C. Legon, J. Chem. Phys., 1995, 103, 876.
23. H. I. Bloemink, A. C. Legon and J. C. Thorn, J. Chem. Soc., Faraday Trans., 1995, 91, 781.
24. H. I. Bloemink, C. M. Evans, J. H. Holloway and A. C. Legon, Chem. Phys. Lett., 1996, 248, 260.
25. A. C. Legon, Chem. Phys. Lett., 1997, 279, 55.
26. A. C. Legon, J. Chem. Soc., Faraday Trans., 1995, 91, 1881.
27. A. D. Buckingham, C. Graham and J. H. Williams, Mol. Phys., 1983, 49, 703.
28. S. A. Peebles, P. W. Fowler and A. C. Legon, unpublished calculations.
29. K. P. R. Nair, J. Hoeft and E. Tiemann, Chem. Phys. Lett., 1973, 58, 153.
30. B. Fabricant and J. S. Muenter, J. Chem. Phys., 1977, 66, 5274.
31. E. Herbst and W. E. Steinmetz, J. Chem. Phys., 1972, 56, 5342.
32. L. Pauling, The Nature of the Chemical Bond, Cornell University Press, Ithaca, NY, 3rd edn., 1960, p. 260.
33. S. A. Peebles, P. W. Fowler and A. C. Legon, Chem. Phys. Lett., 1995, 240, 130.