The A 1Π–X 1Σ+ (2,0) transition in 11BH and 10BH observed by (1+2)-photon resonance-enhanced multiphoton ionization spectroscopy

We report the mass-selected resonance-enhanced multiphoton ionization (REMPI) spectrum of photolytically produced diatomic boron hydride over the spectral range from 368 to 372 nm. Features recorded for time-of-flight-resolved cation masses 12, 11 and 10 amu are assigned to the one-photon transition, A 1Π (v′=2)–X 1Σ+ (v″=0), in 11BH and 10BH. Cation production at these wavelengths requires three photons. This signal must therefore reflect resonant one-photon absorption followed by two-photon ionization in a (1+2)-photon process. This work represents the first observation of the well-characterized A 1Π–X 1Σ+ system in ionization spectroscopy and the first measurement of line positions in the A 1Π v=2 state for 10BH.