A B S T R A C TThe theory of Anstee & O'Mara for the broadening of spectral lines owing to collisions by neutral hydrogen atoms is extended to d-f and f-d transitions of neutral atoms. Width crosssections are tabulated against effective principal quantum numbers for the upper and lower states of the transition, for a relative collision velocity of 10 4 m s ¹1 . The cross-sections are fitted to a variation with velocity of v ¹a , and results for the velocity parameter a are similarly tabulated. The data are tested by application to d-f spectral lines in the solar spectrum. The derived abundances are consistent with those for meteorites.Key words: atomic data -Sun: abundances. I N T R O D U C T I O NPreviously the theory of Anstee & O'Mara (1991, 1995 has been used to produce tables of width cross-sections for s-p and p-s transitions. The theory was recently extended to p-d and d-p transitions by Barklem & O'Mara (1997) and similar tables were presented. In this paper the theory is applied to d-f and f-d transitions.Owing to a lack of strong lines in the solar spectrum corresponding to d-f and f-d transitions, thorough testing of the theory is difficult. However, the tests presented in this paper indicate that the results are consistent with the observed broadening of lines in the solar spectrum. T H E O R YThe theory used in this work has been thoroughly covered by Anstee & O'Mara (1991, 1995 and reviewed by Barklem & O'Mara (1997).For application to d-f and f-d transitions, the theory requires only the following additions: (i) analytic expressions for the I 3jmj functions required to determine the interatomic potentials between a ground-state hydrogen atom perturber and the neutral perturbed atom in an f-state;(ii) an expression for the damping parameter hPðb; vÞi av for the d-f or f-d transition;(iii) the coupled differential equations describing the evolution of the f-state, in the laboratory frame.The I 3jmj analytic expressions were determined, although they are too lengthy to be presented here. They may be obtained on request from the authors. The S-matrix is found using the method first proposed by Roueff (1974), in which the perturber has a classical straight-line path, and the rotation of the system during the collision is included. For f-states the differential equations describing the evolution of the manifold of states are found to be