Photoassociation of cold Ca atoms

We present the first measurement of a photoassociative spectrum of an alkal ine earth element near the dissociation limit. The observed spectrum of Ca- 2 formed from cold atoms shows the regular vibrational series with the char acteristic spacing of the 1/R-3 asymptotic potential. The interpretation is in principle simplified compared to previous measurements on alkali metals by the nondegenerate ground state and the missing hyperfine structure of C a-40. As an example, we derive the natural decay rate of the excited atomic 4p P-1(1) state from the positions of the observed vibrational and rotatio nal resonances with reduced uncertainty compared to previous measurements.