Notes. Columns 1 and 2 give the transition wavelength and labels for the states involved. Columns 3 and 4 give the adopted oscillator strength, in the form log (gf), and the source of these data (see notes). Columns 5−8 give collisional broadening data (see text and notes). Columns 9−12 show, for each line of Mg i, the collision process most responsible for the changes between model B and model F, and thus indicates the most important contributor of the new collision data introduced in this work (see Sect. 5 for more details). Results are given for the four test atmospheric models described in Sect. 5: Dr = Dwarf, metal-rich; Dp = Dwarf, metal-poor; Gr = Giant, metal-rich; Gp = Giant, metal-poor. The collisional processes are labelled (see Sect. 5) H when the line has a sensitivity similar to charge transfer with H  and CH0; collisional excitation with H , CH, and CE indicates the line is sensitive mostly to the electron collision rates. For Mg ii lines there are non-LTE effects in some lines, but the non-LTE abundance corrections are not sensitive to any particular collisional process. Oscillator strengths (f-values) were collected mostly from the NIST database (Ralchenko et al. 2010). The original sources of the NIST data are Froese Fischer & Tachiev (2010) [Fro], Chang & Tang (1990) [C-T] Butler et al. (1993) [But], Siegel et al. (1998) [Sie]. Other sources are Aldenius et al. (2007) [Ald], Civiš, S. et al. (2013) [Civ] and Kurucz & Peytremann (1975) [K-P]. For the Mg i IR lines with no data found in the literature we calculated the f-values using the hydrogenic formula from Guseinov & Mamedov (2012) [Hydro]. To calculate the van der Waals line widths Γ₆ we used data in the ABO theory format where σ is the broadening cross-section in atomic units and α is the velocity parameter. These were calculated with the ABO theory except for those marked with an asterisks, which were calculated in this work (see Table 3 for the IR lines). Stark broadening line widths, Γ₄, were taken from Dimitrijevic & Sahal-Bréchot (1996) [D-SB], van Regemorter & Hoang Binh (1993) [vR-HB] and Mashonkina (2013, including only electrons) [Mas].