In the electronic absorption spectrum of an aqueous solution of $\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}$, a very weak band is observed between the bands due to the transitions ${ }^{3} \mathrm{A}_{2 \mathrm{g}} \rightarrow{ }^{3} \mathrm{T}_{2 \mathrm{g}} \rightarrow$ and ${ }^{3} \mathrm{A}_{2 \mathrm{g}} \rightarrow{ }^{3} \mathrm{T}_{1 \mathrm{g}}(\mathrm{F})$. The transition responsible for the very weak band is (Given: atomic number of Ni is 28 )