Precision VUV spectroscopy of ArI at 105 nm

The results of a precision measurement of the 3p(6)-3p(5)4s' [1/2](1) (1s(2 ) in Paschen notation) transition in argon by resonance-enhanced 1 VUV + 1 UV photo-ionization spectroscopy at 105 nm are presented. Tunable narrow-ba nd VUV radiation is generated by frequency up-conversion of the powerful ou tput of a pulsed dye amplifier system. A transition frequency of 95 399.833 (3) cm(-1) in Ar-40 is measured, in agreement with (but an order of magnitu de more accurate than) the existing value for this transition. Transition i sotope shifts delta nu(40-38) = 550(10) MHz and delta nu(40-36) = 1036(7) M Hz are obtained, from which specific mass shifts are deduced. An improved v alue for the ionization potential in argon (IP = 127 109.842(4) cm(-1)) is also given.