Dipole oscillator strengths, dipole properties and dispersion energies for SiF 4 ASHOK KUMAR 1,3 y, MUKESH KUMAR 2 and WILLIAM J. MEATH 3 y* 1 Department of Physics, Ch. Charan Singh University, Meerut, 250004, India 2 S. V. College, Aligarh, 202001, India 3 Department of Chemistry, University of Western Ontario, London, Ontario, N6H 5B7, Canada (Received 14 January 2003; revised version accepted 15 January 2003) A recommended isotropic dipole oscillator strength distribution (DOSD) has been constructed for the silicon tetrafluoride (SiF 4 ) molecule through the use of quantum mechanical constraint techniques and experimental dipole oscillator strength data. The constraints are furnished by experimental molar refractivity data and the Thomas–Reiche–Kuhn sum rule. The DOSD is used to evaluate a variety of isotropic dipole oscillator strength sums, logarithmic dipole oscillator strength sums and mean excitation energies for the molecule. A pseudo-DOSD for SiF 4 is also presented which is used to obtain reliable results for the isotropic dipole–dipole dispersion energy coefficients C 6 , for the interaction of SiF 4 with itself and with 43 other species and the triple-dipole dispersion energy coefficient C 9 for (SiF 4 ) 3 . 1. Introduction The main purpose of this paper is to present reliable results for a wide variety of the isotropic dipole proper- ties of the ground state silicon tetrafluoride (SiF 4 ) molecule and for the isotropic dipole–dipole dispersion energies for the interaction of SiF 4 with itself and with a variety of other species. A discrete pseudo-state repre- sentation of the recommended constrained dipole oscillator strength distribution for SiF 4 is constructed which is useful for the efficient evaluation of the dipolar dispersion energies, particularly the triple-dipole dispersion energies, for interactions involving this molecule. The relationship between molecular dipole oscillator strength distributions (DOSDs) and the isotropic dipole properties of molecules, and the dipole–dipole and the triple-dipole dispersion energies for interactions involv- ing the molecules of interest, are reviewed in } 2. The moleculardipolepropertiesexplicitlyconsideredhereare the dipole oscillator strength sums S k , the logarithmic dipole sums L k , the mean excitation energies I k and the molar refractivity R ! as a function of wavelength !. The properties S k , L k and I k whichdependonthevalueofthe index k, and the dipolar dispersion energies find application in many research areas [1–15]. The construction of the recommended DOSD for SiF 4 is discussed in } 3 and the evaluation of the dipole properties and dispersion energies in } 4. A quantum mechanical constraint technique [3–6, 16, 17] is used to construct the DOSD from a base of experimental dipole oscillator strength input data [18–24] using constraints comprised of the experimental molar refractivity [25] of the molecule for two well-separated wavelengths and the Thomas–Reiche–Kuhn sum rule [2, 26] for the DOSD. Specific results for integrated dipole oscillator strengths for SiF 4 , over various energy regions, are given in } 3 where they are compared with literature results. The discussion includes examples of the need for using appropriate constraints, which are sensitive to a wide range of excitation energies, when normalizing dipole oscillator strength data. Recommended values for the dipole sums, S k ,k ¼ 10(2)  6(1)  3(1/2)0, 1, 2, the logarithmic dipole sums L k and mean excitation energies I k , k ¼ 2(1)2, and the molar refractivity of SiF 4 , are tabulated in } 4. A 10 pseudo-state representation of the recommended DOSD for silicon tetrafluoride is also presented in } 4 where it is used to evaluate reliable results for the dipole–dipole dispersion energy coeffi- cientsforavarietyofinteractionsinvolvingSiF 4 ,andthe tripole-dipole dispersion energy coefficient for (SiF 4 ) 3 . The estimated uncertainties in our results for the dipole properties and dispersion energies, and a comparison with available literature values, are included in } 4. Often the values obtained from the present constrained DOSD approach are either the only values, or the only *Author for correspondence. yAssociated with the Center for Interdisciplinary Studies in Chemical Physics, University of Western Ontario. MOLECULAR PHYSICS, 20 May 2003, VOL. 101, NO. 10, 1535–1543 Molecular Physics ISSN 0026–8976 print/ISSN 1362–3028 online # 2003 Taylor & Francis Ltd http://www.tandf.co.uk/journals DOI: 10.1080/0026897031000092986