Surface Properties of Ionic Liquids: A Mass Spectrometric View Based on Soft Cluster-Induced Desorption

Abstract

Desorption/ionization induced by neutral clusters (DINeC) in combination with mass spectrometry (MS) was used for the investigation of the molecular composition of the surface of ionic liquids (IL). Based on the surface sensitivity of DINeC-MS, accumulation of either cations or anions was discriminated on the surface of bulk IL depending on the molecular structure of the IL components. In particular, cations with long alkyl chains aggregate on the surface, but this tendency is more reduced the larger the respective anion is; in the case of larger anions and smaller cations, it can be even reversed. For thin layers of IL, the ratio between cations and anions as detected in the mass spectra was found to be further influenced by the substrate surface.

Structure and Surface Behavior of Rh Complexes in Ionic Liquids Studied Using Angle-Resolved X-ray Photoelectron Spectroscopy

“…Interfacial properties of IL-based materials have been intensively studied under ambient conditions by means of various spectroscopic, microscopic, and scattering techniques, such as sum frequency generation (SFG) [31][32][33][34], second harmonic generation (SHG) [35][36][37], atomic force microscopy (AFM) [38][39][40] and spectroscopy (AFS) [41], scanning tunnelling microscopy (STM) [39,40,42], and X-ray reflectivity (XRR) [43,44] tech-Catalysts 2023, 13, 871 2 of 18 niques, to name a few. In addition, owing to the negligible volatility of ILs, ultra-high vacuum (UHV)-based surface science methods have also been successfully applied to access interfacial phenomena, for instance through low-energy ion scattering (LEIS) [45,46], mass spectrometry (MS) [47,48], high resolution electron energy loss spectroscopy (HREELS) [49], ultraviolet photoelectron spectroscopy (UPS) [49][50][51], metastable induced electron spectroscopy (MIES) [49,50], reactive atom scattering (RAS) [52][53][54], and UHV-based STM and AFM techniques [51,[55][56][57][58][59].…”

Soft Deposition of Organic Molecules Based on Cluster-Induced Desorption for the Investigation of On-Surface and Surface-Mediated Reactions

“…The soft desorption of the molecules relies on a dissolution-based mechanism: ,, the impacting clusters do not only provide the energy for desorption but also serve as a transient matrix in which the desorbing molecules are dissolved. − As a result, the effective desorption barrier is reduced which enables soft desorption with low-energy clusters. − As most of the SO 2 molecules are evaporating from the desorbed molecules after cluster-surface impact and desorption, , the bare molecules can be then deposited on a target of choice; as only a minority of the desorbed molecules are ionized, mainly neutral molecules are deposited. Based on the results for DINeC-MS, the DINeC-Depo method can be applied to a broad variety of molecules, e.g., lipids, peptides, proteins, dyes, polymers, and ionic liquids. ,− The coverage of the deposited layers ranges from isolated molecules in the submonolayer regime (Figure b) to films of the thickness of several monolayers. The sample composition was controlled by changing the target material during the deposition process (Figure c).…”

“…Based on the results for DINeC-MS, the DINeC-Depo method can be applied to a broad variety of molecules, e.g., lipids, peptides, proteins, dyes, polymers, and ionic liquids. 20 , 22 − 25 The coverage of the deposited layers ranges from isolated molecules in the submonolayer regime ( Figure 1 b) to films of the thickness of several monolayers. The sample composition was controlled by changing the target material during the deposition process ( Figure 1 c).…”

Bond-specific fragmentation of oligopeptides via electronic stopping of swift heavy ions in molecular films

“…In this contribution, we employ Desorption/Ionization Induced by Neutral SO Clusters (DINeC) in combination with mass spectrometry (MS) for the investigation of SHI-induced fragment formation in oligopeptide films. DINeC is an extremely soft desorption technique which can be applied to various substance classes including peptides, lipids, dyes, and ionic liquids 16 – 19 . In combination with mass spectrometry, it represents an analytical tool with high chemical sensitivity which allows for direct, unambiguous characterization of different types of fragmentation induced in organic molecules 20 , 21 .…”