Pulsed I*(5(2)P(1/2)) --> I(5(2)P(3/2)) lasing pumped by energy transfer from excited NCl(a(1) Delta) was observed in experiments in which iodine atoms and NCl were produced by photodissociation of CH2I2 and ClN3, respectively. The inversion among the iodine atoms is pumped by NCl(a(1) Delta) generated in the chain decomposition of ClN3, rather than by excited NCl produced in the initial photodissociation. A kinetic model for the system which includes the energy transfer process, the chain decomposition of the azide, and I* loss processes is in qualitative accord with the observed I* chemiluminescence time profiles and the threshold times of the pulsed lasing.