A neutral C 60 effusive source was assembled in a crossed molecular-beam apparatus in order to perform atom-molecule electron transfer collisions and its calibration by time-of-flight mass spectrometry. This source consists of a stainless-steel oven where the C 60 sublimation takes place. Typical operation temperatures are in the range of 723 up to 888 K. Through this setup the study of the ion pair formation process KϩC 60 →K ϩ ϩC 60 Ϫ ͑where K is a potassium atom͒ can be performed in a wide range of collision energies ͑10 up to 500 eV͒. The results show evidence of negative ion formation ͑being the ratio of intensities between the parent ion and fragment ions͒ clearly dependent on the collision energy used.

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