2-STEP LASER EXCITATION OF THE EVEN-PARITY RYDBERG LEVELS OF LEAD

We report new data for the even-parity, J = 0, 1 and 2 levels of neutr al lead using a two-step laser excitation technique in conjunction wit h a thermionic diode detector. The Rydberg series 6pnp(1/2, 3/2)(2), ( 10 less than or equal to n less than or equal to 56); 6pnp(1/2, 3/2)(1 ), (10 less than or equal to n less than or equal to 25); 6pnp(1/2, 1/ 2)(0), (10 less than or equal to n less than or equal to 36) and 6pnf( 1/2, 5/2)(2), (7 less than or equal to n less than or equal to 29) as well as four perturbing levels, 6p7p(3/2, 1/2)(1,2) and 6p7p(3/2, 3/2) (1,2) have been identified. The 6pnp(1/2, 1/2)(0) series possesses a c onstant quantum defect implying its unperturbed behaviour. For the par ametrization of the perturbed Rydberg series, the multichannel quantum -defect theory analysis has been performed using three channels for th e J = 1 levels and four channels for the J = 2 levels.