Interference effects in the predissociation of the Cs2C 1Πu and (2)3Πu states through the dissociative (2)3Σu+ state

The excitation spectrum of the Cs-2 molecule monitoring the emission from the dissociated Cs(6p(2)P(3/2)) atoms was measured by employing a pulsed supersonic molecular beam crossed with a laser beam. Strong predissociation was found in the 16 600-17 200 cm(-1) region. Vibrational progressions with broad asymmetric profiles, which were found via the ionization of dissociated Cs(6p(2)P(3/2)) atoms by Kim and Yoshihara, were observed. Transitions from the ground state X (1)Sigma (+)(g) to the dissociative state (2)(3)Sigma (+)(u) are allowed by the spin-orbit interaction between the (2)(3)Sigma (+)(u) and B (1)Pi (u) states. The (2)(3)Sigma (+)(u), (2)(3)Pi (u), and C (1)Pi (u) states are mixed by the spin-orbit interaction. By solving the coupled differential equations using the three-channel model, the transition probability to the mixed levels, (2)(3)Pi (u)(upsilon) and C (1)Pi (u)(upsilon') was calculated. The coupling between the (2)(3)Sigma (+)(u) and (2)(3)Pi (u) states is larger than that between the (2)(3)Sigma (+)(u) and C (1)Pi (u) states. Accordingly, the linewidth of the (2)(3)Pi (u)<--X (1)Sigma (+)(g) transition is observed to be wider than that of the C (1)Pi (u)<--X (1)Sigma (+)(g) transition. The sign of the Fano shape index q was shown to coincide with the sign of the vibrational overlap integral between the discrete level and the continuum. (C) 2000 American Institute of Physics. [S0021-9606(00)01443-4].