The exothermic formation of  ${\mathrm{CIF}}_3$  is represented by the equation

  ${\mathrm{Cl}}_{2\left(\mathrm{g}\right)} + 3{\mathrm{F}}_{2\left(\mathrm{g}\right)}\rightleftarrows 2{\mathrm{ClF}}_{3\left(\mathrm{g}\right)} ; \mathrm{\Delta }H=-329\mathrm{kJ}$

Which of the following will increase the quantity of ${\mathrm{ClF}}_3$  in an equilibrium mixture of 

 ${\mathrm{Cl}}_2,{\mathrm{F}}_2$  and ${\mathrm{ClF}}_3$