Resonant Ionization Using IR Light:  A New Tool To Study the Spectroscopy and Dynamics of Gas-Phase Molecules and Clusters

Abstract

Resonant IR excitation of gas-phase molecules and clusters can lead to superhot species that thermally emit an electron. Monitoring the mass selected ion yield as a function of IR laser frequency yields the IR-REMPI (infrared resonance enhanced multiphoton ionization) spectrum of the molecule or cluster. Although this IR-REMPI spectrum is not the same as the linear absorption spectrum, it can be quite similar and it yields valuable information on the IR optical properties of the species investigated. In this article, the method and the necessary tools are presented. Results from experiments on fullerenes, metal carbide, metal oxide, and metal nitride clusters are shown.

Onset of carbon–carbon bonding in the Nb5Cy(y = 0–6) clusters: a threshold photo-ionisation and density functional theory study

“…Nb 8 C 12 has an absorption resonance at 1250 cm À1 . 36,37 This technique could be applied to the clusters mentioned above to provide evidence of the proposed C 2 units. Alternatively, the IR-MPD technique could be applied, which has been successful for rare gas complexes of neutral bare metal clusters.…”

“…intensities of modes can be different due to differing vibrational anharmonicity and internal vibrational redistribution rates), they have been shown to be similar. 36 Fig . 7 shows the experimental and our DFT-calculated IR spectra for Nb 5 C 3 (between 370 and 760 cm À1 with no scaling) for the substituted 2 Â 2 Â 2 cubic isomer (IV A).…”

Formation of polycyclic aromatic hydrocarbons from bimolecular reactions of phenyl radicals at high temperatures

“…The characteristics of the FEL have already been described in the literature. 29,30 It provides a high flux in the fingerprint region that permits to record IR spectra of diluted gaseous samples. The measurements were performed in a differentially pumped molecular beam apparatus.…”

Vibrational spectroscopy of neutral silicon clusters via far-IR-VUV two color ionization

“…This is fulfilled, however, only for a few types of clusters, mainly from refractory materials such as some transition metals, e.g., Nb or W, several metal oxides and carbides, as well as fullerenes. 28 More generally applicable is the combination of IR excitation with near threshold photoionization. This two color ionization scheme relies on the absorption of a single or few IR photons prior to interaction with a UV photon to lift the total internal energy of the species above the ionization threshold.…”