What is the chlorination of methane in the presence of $hv$?

The chlorination of methane is a free radical substitution reaction that occurs in the presence of ultraviolet light $(hv)$ or at high temperatures $(573-773 \ K)$. The hydrogen atoms of methane are successively replaced by chlorine atoms.
$(i) \ CH_4 + Cl_2 \xrightarrow{hv \text{ or } 573-773 \ K} CH_3Cl + HCl$
$(ii) \ CH_3Cl + Cl_2 \xrightarrow{hv} CH_2Cl_2 + HCl$
$(iii) \ CH_2Cl_2 + Cl_2 \xrightarrow{hv} CHCl_3 + HCl$
$(iv) \ CHCl_3 + Cl_2 \xrightarrow{hv} CCl_4 + HCl$
The overall reaction is: $CH_4$ $\xrightarrow{Cl_2, hv, -HCl} CH_3Cl$ $\xrightarrow{Cl_2, hv, -HCl} CH_2Cl_2$ $\xrightarrow{Cl_2, hv, -HCl} CHCl_3$ $\xrightarrow{Cl_2, hv, -HCl} CCl_4$.