Precision measurement of the absolute energy of the 2s3s 1S0 state in neutral 9Be

We report on the absolute energy of the 2s3s S-1(0) state in neutral 9Be. In doing so, we measure the transition frequencies of the 2s(2) S-1(0) -> 2s2p(1)P(1)(degrees) and 2s2p(1)P(1)(degrees)-> 2s3s(1)S0 transitions, also determining the absolute energy of the 2s2p(1)P(1)(degrees) state. The results are obtained from a home-built hollow cathode discharge lamp using saturated absorption spectroscopy with laser frequencies referenced to a frequency comb. The transition frequencies are determined to be 1276080080(50) and 363105650(130) MHz for the 2s2 S-1(0)-> 2s2p(1)P(1)(degrees) and 2s2p(1)P(1)(degrees) -> 2s3s S-1(0) transitions, respectively. The absolute energies are determined to be 42565.4498(17) and 54677.350(5) cm(-1) for the 2s2p(1)P(1)(degrees) and 2s3s S-1(0) states, respectively. The results confirm recent theoretical calculations that included 6 (QED) corrections. All experimental results are limited by unresolved hyperfine structure.