Multiplex spectroscopy of stable and transient species in a molecular beam

A new apparatus is described that uses nonlinear and linear spectroscopic techniques simultaneously for the characterization of stable and transient molecules in a molecular beam environment. Short‐lived species are generated by applying a well‐defined discharge on a suitable precursor prior to supersonic expansion. Femtosecond ionization and mass spectrometry is used to optimize the discharge source. Degenerate and two‐color resonant four‐wave mixing spectroscopy (DFWM and TC‐RFWM, respectively) are used in tandem with laser‐induced fluorescence (LIF) and cavity ring‐down spectroscopy (CRD). We demonstrate initial experiments on the 4051 Å band of C3 ($\tilde{A}^{1}\Pi_{u} - \tilde{X}^{1}\Sigma_{g}^{+}$], 000–000). DFWM, LIF and CRD display similarities in the general shape and position of the rovibronic transitions. A more detailed view, however, reveals the complementary character of the methods and the potential of simultaneously measured spectra. High signal‐to‐noise ratios and well‐structured spectra are obtained by DFWM. LIF is favorable for the observation of weak features but strongly dependent on the relaxation mechanism of the upper excited state. CRD suffers generally from a large background signal but yields quantitative information. By applying the methods in parallel, quantitative measurements of molecular number densities, transitions dipole moments and relaxation rates are accessible. Copyright © 2007 John Wiley & Sons, Ltd.