A velocity map imaging mass spectrometer for photofragments of fast ion beams

We present the details of a fast ion velocity map imaging mass spectrometer that is capable of imaging the photofragments of trap-cooled (>= 7 K) ions produced in a versatile ion source. The new instrument has been used to study the predissociation of N2O+ produced by electric discharge and the direct dissociation of Al-2(+) formed by laser ablation. The instrument's resolution is currently limited by the diameter of the collimating iris to a value of Delta v/v = 7.6%. Photofragment images of N2O+ show that when the predissociative state is changed from (2)Sigma(+)(200) to (2)Sigma(+)(300) the dominant product channel shifts from a spin-forbidden ground state, N (S-4) + NO+(v = 5), to a spin-allowed pathway, N*(D-2) + NO+. The first photofragment images of Al-2(+) confirm the existence of a directly dissociative parallel transition ((2)Sigma(+)(u) -> (2)Sigma(+)(g)) that yields products with a large amount of kinetic energy. D-0 of ground state Al-2(+) ((2)Sigma(+)(g)) measured from these images is 138 +/- 5 kJ/mol, which is consistent with the published literature. Published by AIP Publishing.