Investigation of the 6p 2(3 P 0)n p Rydberg series of bismuth by multiphoton excitation

Rydberg states of the odd-parity series 6p ²(³ p ₀)n p of BiI are excited by a three-photon process. A two-photon dissociation of Bi₂ into excited atomic states followed by a one-photon absorption leads to highly excited atomic Rydberg states up ton = 32. States of the even-parity Rydberg series 6p ²(³ p ₀)nsJ=1/2,ndJ=3/2 andndJ=5/2 are also observed. In order to avoid the background caused by ionization of the bismuth molecules we performed a two-color excitation with pulsed dye lasers. With this experiment the 6p ²(³ p ₀)npJ=3/2 Rydberg series could be resolved up ton=75. The increasing quantum defect of this series is due to a perturbing state close to the first ionization limit. By a MQDT analysis we obtain the energy of the perturbing state and a value of 58,761.68±0.1 cm^?1 for the first ionization limit of atomic bismuth.