Direct measurement of fine structure changing collisional losses in cold trapped Rb-85

Using a technique that consists in ionizing atoms out of the 5P(1/2) fragme nts originated in the cold collision process, we have measured the contribu tion of the fine structure changing collision (FS) to the total trap loss r ate of cold Rb-85. Our results show that FS contribution is responsible for about 4% of the total trap loss. This result should stimulate new theoreti cal discussions involving exoergic cold collisions.