Isolated core excitation of (BH)-B-11: Photoabsorption in competition with Rydberg predissociation

The ionization-detected multiresonant absorption spectrum of the high Rydberg states of (BH)-B-11 shows evidence of a valence electronic excitation of the X (2)Sigma(+) (BH+)-B-11 core in which the principal and azimuthal quantum numbers of a bound Rydberg electron are conserved. This phenomenon, known as isolated core excitation (ICE), has been previously reported with Rydberg quantum state specificity only for atoms. In the present triple-resonant photoexcitation experiment, the third laser frequency happens to scan an energy interval of coincidental fourth-photon resonance with transitions in the A (2)Pi-X (2)Sigma(+) system of the (BH+)-B-11 ion core. For a certain range of principal quantum number n, we find that the initially prepared Rydberg electron remains unaffected while the core undergoes an adventitious, strongly allowed valence electron transition, taking the system from a Rydberg level that converges to the X (2)Sigma(+) state of (BH+)-B-11 to a corresponding level converging to excited (BH+)-B-11 A (2)Pi. We denote this absorption as parallel to A (2)Pi >parallel to nl ><-parallel to X (2)Sigma(+)>parallel to nl >. Using a simple mathematical model for which only transitions vertical in n and l are allowed, we show that the interval of principal quantum number over which the rate of adventitious ICE exceeds that of (BH*)-B-11 dissociation depends on the finite linewidths and positions of parallel to A (2)Pi >parallel to nl > features and on the n-dependent predissociative lifetimes of (BH*)-B-11 Rydberg molecules.