The fluorescence intensity ratios of (OClO)-Cl-37/(OClO)-Cl-35 excited to the (A) over tilde (2)A(2) state have been found to be much larger than that expected from the Cl-37/Cl-35 natural abundance ratio for several low-energy vibrational levels. For instance, the (OClO)-Cl-37/(OClO)-Cl-35 ratios are 1.67 and >10 for the (0,0,0) and (1,1,0) bands, respectively, which are 5 and 30 times larger than those expected from the natural abundance ratio. These unusual isotope effects are observed in a narrow energy region within similar to 1000 cm(-1) above the electronic origin. It is likely that the isotopomer-selective, near-resonant spin-orbit coupling of the low-energy vibrational levels of the (2)A(2) state with those of the (2)A(1) state, which provides a decay channel for the (2)A(2) state via spin-orbit coupling, is responsible for the unusual isotope effect.