High Rydberg transitions in the principal and intercombination series of mercury

The absorption spectrum of mercury vapour has been recorded at high resolution (+or-0.003 AA) in the 1150-1350 AA region with synchrotron radiation as the background source of the continuum. Observations comprise the principal series: 6s 2 1 S 0 to 6snp 1 P 1 0 (8<n<or=37) and the intercombination series: 6s 2 1 S 0 to 6snp 3 P 1 0 (8<n<or=48). An intensity anomaly occurs at high n values with 3 P 1 0 gaining most of the oscillator strength at the expense of the 1 P 1 0 transitions. Simple intermediate coupling calculations show that this is due to a change from LS to jj coupling with increasing n values. A two-dimensional Lu-Fano plot it is also presented and this exhibits interchannel interactions between the 1 P 1 0 channels. As a result of the new measurements, the previously somewhat uncertain determination of the first ionisation potential is reliably confirmed as 84184.10+or-0.20 cm -1 .