Using a three-photon (2 + 1) resonance-enhanced multiphoton ionization (REMPI) technique, we have demonstrated that 193 nm photodissociation of KI should lead to the predominant channel of K(52PJ) and I(52P3/2) states. The quantum yield of the ground state I(52P3/2) amounts to (97 +/- 3)%. In terms of a three-level kinetic model, we have furthermore determined the fine-structure branching ratio of the resultant nascent K 52PJ doublets in the presence of Ar, He, H2, CH4, and CO2 to be 0.800, 0.798, 0.791, 0.797, and 0.785, respectively, with +/- 1% accuracy. This model takes into account the rapid energy transfer between the 52PJ doublets and the relevant collisional quenching, thereby leading to a more accurate value than the measurement of fluorescence intensity at low pressure. Since a variety of foreign gases that cause different energy transfers and quenching capabilities have been considered in the system, the resulting branching ratios derived at the zero-pressure are identical, thus confirming reliability of our kinetic model. The relevant fine-structure mixing rate coefficients and the collisional quenching rate coefficients are also evaluated. In addition, the kinetic model has been extended to the case of photodissociation at 248 nm; given the appropriate mixing rate coefficients reported elsewhere, the average branching ratio of K(42P3/2) photofragment are then determined to be 0.610 in the presence of Ar, H2, and N2. It is advantageous to find that the model can also be used to inspect the evaluation of fine- structure mixing rate caused by various foreign gases.