Beam-foil spectroscopy of As III, IV and V

The beam-foil technique is applied to study the spectra of As III-V in the wavelength range 300 to 2000 AA. Fifteen new transitions are assigned to As V, involving the classification of eight new levels. From the 4s, 5s, 6s and 4p, 5p, 6p levels the As V ionisation potential is found to be 62.76+or-0.06 eV. Lifetimes and multiplet f values are reported from transitions from the 4s 2 4d and 4s4p 2 2 D terms of As III, the 4s5s and 4p 2 1 S, 4p 2 1 D, 4s4p 1 P 0 and 4s4d 3 D terms of As IV, and the 4p 2 P 0 , 4d 2 D and 5s 2 S terms of As V. Arbitrarily normalised decay curve (ANDC) analyses were used to overcome the problems associated with cascade repopulation in the cases of the 4s4p 1 P 0 (As IV) and 4p 2 P 0 (As V) terms. The resulting multiplet f value for the As V resonance transition is in good agreement with theory, but that for the As IV resonance transition is about 20% below theory, possibly due to omission from the ANDC analysis of the cascade from 4s4d 1 D, which is yet to be assigned.