OPTICAL OPTICAL DOUBLE-RESONANCE SPECTROSCOPY OF BR2 THROUGH THE A 3-PI(1U) STATE - ANALYSES OF THE 0+U, 1U, AND 2U(3P2) ION-PAIR STATES

An optical-optical double resonance technique is used to study the ion-pair states of Br2 correlating to Br-(1S) + Br+(3P2). In the (1 + 2) photoexcitation sequence, the pump laser excites the A3-PI(1u)-X1-SIGMA-g+ transition at a fixed frequency for the state selection while the probe laser is scanned to execute the second step by a coherent two-photon transition. The double resonance spectra thus obtained show the transitions terminating on the 1u(3P2) state, because of the DELTA-OMEGA = 0 selection rule for the valence state to ion-pair state transitions. However, the transitions to the 0(u)+ and 2u(3P2) states are also seen as extra lines through the heterogeneous mixing with the 1u(3P2) state, which can be interpreted in terms of the pure-precession approximation. Combined with our previous data obtained through the B3-PI(0u+) state as an intermediate, the energy levels of the 0u+, 1u, and 2u(3P2) states are analyzed by including the heterogeneous interactions, and their potential curves can be elucidated.