Unraveling the electronic structure of transition metal dimers using resonant four‐wave mixing

Abstract

The potential of two-color resonant and degenerate four-wave mixing spectroscopy for investigations of the complex spectra of transition metal dimers is explored. Two-color resonant and degenerate four-wave mixing spectroscopy scans of the well-known A-X and B-X transitions in Cu 2 are reported and compared with previous experimental data obtained from standard singleresonance techniques. The selectivity of the method is shown to enable the measurement of isotopologue pure spectra without the need for isotopically enriched metal targets. Specific subsets of the rovibronic structure are separated in a congested spectral region of overlapping transitions. The sensitivity of the method compares satisfactorily with linear spectroscopic methods such as laser-induced fluorescence and cavity ring-down. A new laser vaporization source for the production of transition metal dimers and clusters has been constructed. The new design aims for a high number density and maximum possible shot-to-shot stability. The possibilities of further applications of non-linear four-wave mixing spectroscopy to Cu 2 and other transition metal dimers are discussed.

Observation of a gerade symmetry state of Cu2 using two‐color resonant four‐wave mixing

“…The experimental setup has been described in our previous publications. [15,26] In brief, the copper dimer molecules are produced in a cluster source by laser ablation of a copper target disk. Pure helium gas with a static background pressure of 50 bar is introduced into the source by using a pulsed valve (General valve, series 9), which generates a typical gas pulse of ≈ 250 s width.…”

“…[25] The fully resonant and background-free properties render resonant four-wave mixing spectroscopy a sensitive detection technique that is comparable with laser-induced fluorescence and cavity ring down spectroscopy. [26] So far, resonant four-wave mixing has been used in numerous spectroscopy studies, including stable molecules such as CS 2 , [27] H 2 CO, [28] and Br 2 [29] and free radicals such as C 2 , [30] C 3 , [31] and HC 4 S. [32] Apart from degenerate four-wave mixing that yields an absorption-like spectrum, most of these investigations were performed by using an optical-optical double-resonance scheme. Like other two-photon resonance detection techniques, TC-RFWM can significantly simplify complex spectra.…”

“…The technique has been shown to be favorably suited for the study of small transition metal dimers or clusters, whose electronic spectra are usually very dense and complex due to the high density of states, low vibrational and rotational constants, and the frequent abundance of numerous isotopologues. [14,15,26] Actually, the combination of TC-RFWM and a homemade laser vaporization cluster source yielding internally cold Cu 2 dimers in a molecular beam environment [15] allowed a systematic investigation of the electronic states of dicopper and resulted in the identification of the A ′ 1 u state and the characterization of the I1 u and J0 + u states. [14,15] Furthermore, a recent detailed study of the complex electronic structure of excited "u"-symmetry levels has been performed in this laboratory by applying the same technique.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part XI

“…Visser used resonant four‐wave mixing to unravel the electronic structure of transition metal dimers. A new laser vaporization source for the production of transition metal dimers and clusters was constructed, and the new design aims for a high number density and maximum possible shot‐to‐shot stability . Volkov and co‐workers presented a study of resolving capacity of infrared‐visible sum frequency generation microscopy to address discrete structural realizations of a protein at an interface.…”

Development and applications of nonlinear optical spectroscopy: 14th ECONOS/34th ECW meeting in Leuven (Belgium)

“…The majority of original research papers are concerned with nonlinear optical spectroscopy in gas‐phase systems. Visser et al investigated the potential of using two‐color resonant and degenerate four‐wave mixing spectroscopy to study transition metal dimers. For this purpose, a new laser vaporization source was developed to produce metal dimers and larger clusters in a reproducible manner.…”