Identification of the X state in Ca and a new Rydberg series

The X state in Ca is identified as 4s5g 1 G 4 at 44874.5+or-0.2 cm -1 , and the upper states in the observed transitions are reassigned to the 4snh 1 H 5 series. The simple polarisation theory gives surprisingly good agreement with experiment for all the observed transitions. The extracted polarisability of 75.3+or-0.4 a 0 3 is in excellent agreement with values calculated from oscillator strengths.