193 nm photodissociation of KI: Branching ratio and collisional mixing rate of K(5 2PJ) doublets

Wang, Kung-Chung; Lin, King-Chuen; Luh, Wei-Tzou
January 1992
Journal of Chemical Physics;1/1/1992, Vol. 96 Issue 1, p349
Academic Journal
Through a three-level kinetic model, the branching ratio of the nascent photofragment K in the 5 2PJ fine-structure states following photodissociation of KI by a 193 nm excimer laser has been experimentally determined to be K(5 2P3/2)=0.791 and K(5 2P1/2)=0.209 with ±1% accuracy. The model has taken into account the rapid energy transfer between the 5 2PJ doublets and the result appears to be more accurate than those fluorescence intensity ratio measurements under low pressure condition. The cross section of fine-structure mixing induced by H2 collisions has also been measured to be 134±6 Å2 for the transition 5 2P3/2←5 2P1/2 and 72±5 Å2 for its reverse process. The ratio 1.86 is consistent with the value 1.89 predicted by principle of detailed balance. Using the Stern–Volmer equation, we have also obtained the radiative lifetime 137±4 ns for the K(5 2PJ) state and its quenching cross section 10.4±1.8 Å2 by collision with H2 molecule. The latter appears much smaller than those of fine-structure energy transfer processes by an order of magnitude.


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