Precision VUV spectroscopy of Ar I at 105 nm

Abstract
The results of a precision measurement of the 3p6-3p54s´[½]1 (1s2 in Paschen notation) transition in argon by resonance-enhanced 1 VUV+1 UV photo-ionization spectroscopy at 105 nm are presented. Tunable narrow-band VUV radiation is generated by frequency up-conversion of the powerful output of a pulsed dye amplifier system. A transition frequency of 95 399.833(3) cm-1 in 40Ar is measured, in agreement with (but an order of magnitude more accurate than) the existing value for this transition. Transition isotope shifts 40-38 = 550(10) MHz and 40-36 = 1036(7) MHz are obtained, from which specific mass shifts are deduced. An improved value for the ionization potential in argon (IP = 127 109.842(4) cm-1) is also given.