Figure 1.

Femtosecond mass spectra of benzyne precursors: 1,4-dibromobenzene (A), 1,3-dibromobenzene (B), and 1,2-dibromobenzene (C). The split peaks are due to bromine isotope composition (see Results). The spectra were obtained at a delay time of ≈50 fs between the pump and probe pulses. The precursors do not absorb a single photon at 307 nm, because the first absorption is typically at 280 nm (26). amu, atomic mass units.