Chemical reaction within the electronically excited B(2s22D)–H2 complex

Abstract

The reactive decay of electronically excited B(2s22D)–H₂ complexes has been investigated through the detection of chemiluminescence from the formation of electronically excited BH products. Formation of BH in its A¹Π and b³Σ^- electronic states was detected through the observation of emission in the A¹Π→X¹Σ⁺ and b³Σ^-→a³Π band systems. In previous work, the excited electronic states of the B···H₂ complex were probed through fluorescence depletion spectroscopy. The fluorescence depletion spectrum extends to energies both higher and lower than the excitation energy to the B(2s22D)+H₂ asymptote, suggesting that there are both attractive and repulsive excited BH₂ potential energy surfaces in the Franck–Condon region. BH chemiluminescence is observed most strongly with excitation into the lower-energy portion of the electronic transition. This implies that reaction to yield BH(A¹Π, b³Σ^-) occurs mainly on attractive excited BH₂ surfaces. The chemiluminescence spectra have been compared with simulations in order to deduce the degree of vibrational and rotational excitation of the BH products. The products are found to have considerable internal excitation, which depends on the excitation wavenumber. All bound BH(A¹Π) and all energetically allowed BH(b³Σ^-) rovibrational levels were found to be significantly populated. These observations are employed to draw inferences on the reaction dynamics occurring on these excited BH₂ potential energy surfaces. The reactive nature of the B(2s2 ²D)–H₂ surfaces is contrasted with the apparent nonreactivity of the B(23s²S)–H₂ surface.