The reaction of I⁻ ions is often used to titrate ClO⁻, giving deeply coloured I₃⁻ ions, along with Cl⁻ and H₂O. Although never proved, it was once thought that the initial reaction proceeds by O atom transfer from Cl to I. However, it is now believed that the reaction proceeds by Cl atom transfer to give ICl as the intermediate (K. Kumar, R.A. Day, and D.W. Margerum, Inorg. Chem., 1986, 25, 4344). Summarize the evidence for Cl atom transfer.