Multiplex spectroscopy of stable and transient species in a molecular beam

Abstract

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 4051Å band of C 3 (Ã 1 5 u −X 1 6 + 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.

Recent advances in linear and nonlinear Raman spectroscopy II

“…Tulej et al 74 described a new apparatus that uses nonlinear and linear spectroscopic techniques simultaneously for the characterization of stable and transient molecules in a molecular beam environment. Degenerate and two-color resonant four-wave mixing spectroscopies were used in tandem with laser-induced fluorescence and cavity ring-down spectroscopy for a high spectral resolution study of C 3 thus allowing quantitative measurements of molecular number densities, transitions dipole moments and relaxation rates.…”

Degenerate and two‐color resonant four‐wave mixing of C2− in a molecular beam environment

“…[32 -52] The nonlinear methods are often complementary to the more conventional linear spectroscopic techniques and offer sometimes additional capabilities. [51,53] Because four-wave mixing is based on absorption, the signal intensity is insensitive to the lifetime of the upper level. [54] As a consequence, the large and important category of molecules exhibiting nonfluorescing [55] or predissociative states are accessible.…”

“…For example, an SNR of up to 50 000 for the rotationally resolvedà 1 u −X 1 + g transition of C 3 has been obtained by discharging an acetylene/argon mixture. [53] The latter experiment has been performed by using a cylindrical nozzle assembly. By introducing a discharge assembly designed to provide a two-dimensional slit expansion that increases the interaction volume of the four-wave mixing beams with the molecular beam, a further increase in sensitivity could be achieved.…”

“…[65] In the following, we take four-wave mixing spectroscopy one step further and demonstrate its excellent sensitivity by applying the method to an anion, C − 2 , emerging from a supersonic slit discharge. [59] Experimental We briefly outline the DFWM and TC-RFWM experiments in our laboratory in the following; a detailed description of the molecular beam apparatus [53] and the slit-jet discharge source [65] has been published elsewhere.…”

ECONOS in the epoch of CARS renaissance

“…Tulej et al 17 describe a new apparatus that simultaneously employs nonlinear and linear spectroscopic techniques for the characterization of stable and transient molecules in a molecular beam. In the approach developed in this work, short-lived species are generated by applying a welldefined discharge on a suitable precursor prior to supersonic expansion.…”