Spectroscopy and dynamics of excited harpooning reactions: The photodepletion action spectrum of the Ba center dot center dot center dot FCH3 complex

A laser time-of-flight mass spectrometer setup used to investigate the spectroscopy and dynamics of weakly bound complexes is described. Complexes were produced by laser vaporization of metals into a supersonic expansion of helium and a solvent. The first results consisting of laser ionization and photodepletion spectra of Ba ...(FCH3)(n) for 1 less than or equal to n less than or equal to 3 are reported. The measurement of the Ba ... FCH3+ signal as a function of the ionization photon energy allowed estimation of the complex ionization potential, which was found to be 4.5 +/- 0.1 eV. The photodepletion spectrum of the Ba ... FCH3 complex displayed two distinct regions. At longer wavelengths it showed a high cross-section (60-70 Angstrom(2)) and a well-defined vibrational structure, while a much smaller cross-section (2-4 Angstrom(2)), with a more diffuse structure, appeared at shorter wavelengths. In addition, clear resonances were observed at longer wavelengths, indicating a significant coupling between the bound excited potential of the complex and the (open channel) ionic potential leading to BaF* + CH3 reaction products. All of these features are discussed, taking into account the interplay between the spectroscopy and dynamics associated with each electronically excited state of the complex that governs the photoinitiated harpooning reaction.