Carbon Cluster Anions Research Articles

Cn, CnH and their anions: Quest for linearity with n≤8 even versus odd, and beyond

AbstractUsing the concept of quasi‐molecule (“tile”) and the database of quasi‐molecules embedded on a parent molecule, it is discussed whether the latter can attain linear form or otherwise. Besides anew accurate optimization of all tiles (quasi‐triatomics) at various levels of ab initio theory and basis‐sets, the nature of the predicted stationary points for the title parent molecules is probed through a priori calculations here too reported. Also discussed is the common rule that even‐ anions are linear while odd‐numbered ones tend to have nonlinear isomers. The reported quasi‐molecule approach is general, and allow the prediction of linearity or otherwise of the parent systems prior to calculations on them. When based on an extension of the bisection method (Varandas, Int. J. Quantum Chem. 2023, 123, e27036.), it is easy to use even for large parent molecules, as illustrated for neutral and anionic carbon clusters with .

Probing the stability of metal-organic frameworks by structure-responsive mass spectrometry imaging.

The widespread application of metal-organic frameworks (MOFs) is seriously hindered by their structural instability and it is still very challenging to probe the stability of MOFs during application by current techniques. Here, we report a novel structure-responsive mass spectrometry (SRMS) imaging technique to probe the stability of MOFs. We discovered that intact CuBTC (as a model of MOFs) could generate the characteristic peaks of organic ligands and carbon cluster anions in laser desorption/ionization mass spectrometry, but these peaks were significantly changed when the structure of CuBTC was dissociated, thus enabling a label-free probing of the stability. Furthermore, SRMS can be performed in imaging mode to visualize the degradation kinetics and reveal the spatial heterogeneity of the stability of CuBTC. This technique was successfully applied in different application scenarios (in water, moist air, and CO2) and also validated with different MOFs. It thus provides a versatile new tool for better design and application of environment-sensitive materials.

Evaluation of Molecular Fragmentation in Polycyclic Aromatic Hydrocarbons by Time-of-Flight Secondary Ion Mass Spectrometry

In time-of-flight secondary ion mass spectrometry (TOF-SIMS), ionized molecules and molecular fragments (secondary ions) are generated in collisions of high-energy ions (primary ions) with a solid sample surface. Mass spectra of the emitted secondary ions are typically used to identify molecular species and to determine their spatial distribution on the sample surface. Here, we extend this application in a TOF-SIMS study of a series of polycyclic aromatic hydrocarbons (PAHs) where we focus on the fragmentation of these molecules, with the purpose of better understanding the fragmentation patterns of heavy aromatic molecules in petroleum. For all PAHs, the collision process generated (i) a series of smaller cation fragments and (ii) cations close in size to the original PAH (molecular cations). Stark differences are measured for various PAHs regarding the abundance of smaller fragments versus molecular cations. Observation of hydrogen-deficient (H-deficient) cation fragments indicates the formation of polyynes and allenes. For PAHs producing higher fractions of small cation fragments, these ions are surprisingly hydrogen rich (H-rich). The H/C ratio of fragments does not scale with the fraction of Clar sextet carbon, nor with energies of low-lying electronic transitions. Free radical cation fragments tend to be suppressed. For sufficiently large fragments, aromatic cations appear to be formed and include some free radical aromatics. There is ample production of molecular ions with loss of a single carbon atom or a methine group, which corresponds to the reduction of a 6-membered aromatic ring to a 5-membered ring. There is some enhancement of free radical molecular cations due to the corresponding formation of neutral polyynes. Fragment anions are also produced with a strong preference for very H-deficient carbon clusters, in some cases being the same as carbon cluster anions observed in space. Comparisons of PAH TOF-SIMS spectra with those of asphaltenes are discussed in detail.

About the connection of the electron binding energy of a single carbon anion with binding energies of an electron attached to carbon molecules

We demonstrate that the model of zero-range potentials can be successfully employed for the description of attached electrons in atomic and molecular anions, for example, negatively charged carbon clusters. To illustrate the capability of the model we calculate the energies of the attached electron for the family of carbon cluster anions consisting of two-, three- (equilateral triangle) and four (tetrahedron) carbon atoms equidistant from each other as well as for a C3 molecule having a chain structure. The considered approach can be easily extended to carbon clusters containing an arbitrary number of atoms arranged in an arbitrary configuration.

Identification, Quantification, and Imaging of the Biodistribution of Soot Particles by Mass Spectral Fingerprinting.

Soot is ubiquitous and has large detrimental effects on climate, air quality, and human health. However, identification of soot in carbonaceous media is very challenging due to its nanoscale carbon nature and complex sources. Due to the shortage in the methodology, until now, the fate and health effect of soot particles after inhalation are still poorly understood. Here, we report a new method for label-free identification, quantification, and imaging of soot particles in complex media based on laser desorption/ionization mass spectrometry fingerprinting. We found that soot particles from different origins and with different morphologies showed highly consistent mass spectral fingerprints deriving from peak ratios of small carbon cluster anions (C2--C10-), which enabled both accurate quantification of soot in fine particulate matter (PM2.5) samples and label-free imaging of soot particles in biological media. By using this technique, we tracked and imaged the suborgan distribution of soot particles in mice after exposure to PM2.5. The results showed that the lung is the main target organ for short-term inhalation exposure to soot particles. This study helps to better understand the inhalation toxicology of soot and also provides a practical novel methodological platform for identification, tracing, and toxicological studies of elemental carbon-based nanomaterials.

Radiative cooling of carbon cluster anions C2n+1\u2212 (n\xa0=\xa03\u20135)

Radiative cooling of carbon cluster anions C2n+1− (n = 3–5) is investigated using the cryogenic electrostatic ion storage ring DESIREE. Two different strategies are applied to infer infrared emission on slow (milliseconds to seconds) and ultraslow (seconds to minutes) timescales. Initial cooling of the ions over the millisecond timescale is probed indirectly by monitoring the decay in the yield of spontaneous neutralization by thermionic emission. The observed cooling rates are consistent with a statistical model of thermionic electron emission in competition with infrared photon emission due to vibrational de-excitation. Slower cooling over the seconds to minutes timescale associated with infrared emission from low-frequency vibrational modes is probed using time-dependent action spectroscopy. For C9− and C11−, cooling is evidenced by the time-evolution of the yield of photo-induced neutralization following resonant excitation of electronic transitions near the detachment threshold. The cross-section for resonant photo-excitation is at least two orders of magnitude greater than for direct photodetachment. In contrast, C7− lacks electronic transitions near the detachment threshold.Graphical abstract

Development of a Mass Spectrometry Imaging Method for Detecting and Mapping Graphene Oxide Nanoparticles in Rodent Tissues.

Graphene-based nanoparticles are continuously being developed for biomedical applications, and their use raises concerns about their environmental and biological impact. In the literature, some imaging techniques based on fluorescence and radioimaging have been used to explore their fate in vivo. Here, we report on the use of label-free mass spectrometry and mass spectrometry imaging (MSI) for graphene oxide (GO) and reduced graphene oxide (rGO) analyses in rodent tissues. Thereby, we extend previous work by focusing on practical questions to obtain reliable and meaningful images. Specific radical anionic carbon clusters ranging from C2-• to C9-• were observed for both GO and rGO species, with a base peak at m/z 72 under negative laser desorption ionization mass spectrometry (LDI-MS) conditions. Extension to an LDI-MSI method was then performed, thus enabling the efficient detection of GO nanoparticles in lung tissue sections of previously exposed mice. The possibility of quantifying those nanoparticles on tissue sections has also been investigated. Two different ways of building calibration curves (i.e., GO suspensions spotted on tissue sections, or added to lung tissue homogenates) were evaluated and returned similar results, with linear dynamic concentration ranges over at least 2 orders of magnitude. Moreover, intra- and inter-day precision studies have been assessed, with relative standard deviation below 25% for each concentration point of a calibration curve. In conclusion, our study confirms that LDI-MSI is a relevant approach for biodistribution studies of carbon-based nanoparticles, as quantification can be achieved, provided that nanoparticle suspension and manufacturing are carefully controlled.

Towards investigations of pre-cooled ions stored in the RICE storage ring via action spectroscopy

SynopsisA new cryogenic linear ion trap beamline has been commissioned for use with the RIKEN Cryogenic Electrostatic (RICE) storage ring. Testing of the beamline at room-temperature and cryogenic conditions was conducted using methylene blue cations MB+ and carbon cluster anions Cn −. Action spectroscopy measurements of pre-cooled Cn − anions injected into RICE will help determine the effectiveness of the so-called Pre-Trap Beamline, as well as provide structural and dynamical information on these cluster anions at cryogenic temperatures.

Detection of recurrent fluorescence photons emitted from C4−

SynopsisWe detected recurrent fluorescence (RF) in the region of visible light emitted from small carbon cluster anions C4− and C6− stored in an electrostatic ion storage ring. The observed RF decay profile for C4− is consistent to our simulation under the assignment that the RF is associated with the C2∏g-X2∏u transition. In addition, observation of the RF at two different wavelengths suggests that the RF band is rather broad.

Vibrational radiative cooling of isolated and

SynopsisWe have observed the storage-time dependence of the laser-induced electron detachment yields for the linear carbon cluster anions and stored in an electrostatic ion storage ring (TMU E-ring) with several laser wavelengths. The electron detachment yield reflects the decrease of the internal energy of the stored ions. We succeeded in obtaining the time evolution of the excitation energy distribution below the first dipole-allowed electronic excited energy Eex for and , which was well consistent to the behavior explained by vibrational IR-radiative cooling.

Structural stability and growth mechanism of neutral and anionic small carbon clusters: Density functional study

In this contribution, we propose a systematic and accurate theoretical methodology to describe the elementary physical processes occurring in sputtering discharges, generating a carbon-containing plasma in which medium size clusters are growing (Cn, n<10). At this stage, we performed density functional calculations to analyse the energetics of many neutral and anionic carbon clusters configurations. We use a wide range exchange-correlation functional (PBE, PBE0, B3LYP, CAMB3LYP, M06-2X and HSE06) with aug-cc-PVDZ basis sets to study the relative stability between linear and cyclic structures. These results show that this relative stability between both depends on the exchange-correlation corrections. For neutral carbon cluster size n<10, the most stable structures are linear for odd values of n and cyclic for even values. For anions, the most stable geometries remain linear irrespective of the cluster size. In both cases, the free energy per carbon atom increases in function of the size. The same results were found in the literature using B3LYP functional. According to these preliminary results, the Meta hybrid GGA functional M06-2X is chosen to explore the relative stabilities of different neutral and anion clusters configurations of Cn, for n⩽6. Other stable isomers are found. Otherwise inter conversion between the most stable isomers have been performed and the growing process of carbon clusters by addition of C or C2 are also present here. The results show that the C2 is more favourable for anions while there is a competition between C and C2 for neutral clusters.

Cooling dynamics of carbon cluster anions

A series of ion storage experiments on small carbon cluster anions was conducted to understand size-dependent cooling processes. The laser-induced delayed electron detachment time profile show clear even/odd alternation due to the presence of the electronic cooling. The time evolution of the internal energy distribution was simulated for Cn- (n=4 to 7) with a common procedure taking vibrational and electronic cooling into account.

Observation of recurrent fluorescence photons from small carbon cluster anions

SynopsisWe directly observed recurrent fluorescence from small carbon cluster anions C−6 stored in an electrostatic ion storage ring TMU E-ring. This process, caused by the electronic transitions via low-lying electronic excited states after the inverse internal conversion (IIC), has been recently reported as fast cooling. In the present study, we succeeded in detection of emitted fluorescence. The observed lifetime was consistent with the theoretically estimated lifetime.

Applications of graphene in mass spectrometry.

This paper reviews the up-to-date research about the applications of graphene and its related materials in the field of mass spectrometry (MS). Due to its large surface area, delocalized pi-electrons, thermal conductivity, stability and rich interaction chemistry, graphene has been widely used in MS-based analytical chemistry. Graphene-based materials were applied as very effective matrixes or surfaces for many kinds of organic molecules in laser desorption/ionization (LDI) MS analysis. Many advantages of this novel matrix have been proved, which included: low interference ions from matrix itself, good reproducibility, high salt tolerance and so on. The unique properties of graphene also make it a superior sorbent used in solid-phase extraction (SPE). Further development of online SPE methods based on graphene coupling directly with LDI-MS, GC-MS and LC-MS greatly simplifies the MS-based analytical procedure for complex samples and makes the corresponding high-throughput and automatic analysis performable. Their applications as a platform in proteolysis for the rapid identification of proteins have been also developed. In addition, graphene was found to be a unique precursor for the generation of large-sized carbon cluster anions in the gas phase. Finally, the possible challenges and future perspectives in their applications in MS are discussed too.

Ab initio characterization of size dependence of electronic spectra for linear anionic carbon clusters Cn− (n = 4-17)

In this article, we determine the ground-state equilibrium geometries of the linear anionic carbon clusters C n- (n = 4-17) by means of the density functional theory B3LYP, CAM-B3LYP, and coupled cluster CCSD(T) calculations, as well as their electronic spectra obtained by the multireference second-order perturbation theory CASPT2 method. These studies indicate that these linear anions possess doublet ²∏(g) or ²∏(u) ground state, and the even-numbered clusters are generally acetylenic, whereas the odd-numbered ones are essentially cumulenic. The energy differences, electron affinities, and incremental binding energies of C n- chains all exhibit a notable tread of parity alternation, with n-even chains being more stable than n-odd ones. In addition, the predicted vertical excitation energies from the ground state to four low-lying excited states are in reasonably good agreement with the available experimental observations, and the calculations for the higher excited electronic transitions can provide accurate information for the experimentalists and spectroscopists. Interestingly, the absorption wavelengths of the 1²∏(u/g) ← X²∏(g/u) transitions of the n-even clusters show a nonlinear trend of exponential growth, whereas those of the n-odd counterparts are found to obey a linear relationship as a function of the chain size, as shown experimentally. Moreover, the absorption wavelengths of the transitions to the higher excited states of C n- series have the similar linear size dependence as well.

Large Carbon Cluster Anions Generated by Laser Ablation of Graphene

The formation of large even-numbered carbon cluster anions, C(n)⁻, with n up to 500 were observed in the mass spectra generated by laser ablation of graphene and graphene oxide, and the signal intensity of the latter is much weaker than that of the former. The cluster distributions generated from graphene can be readily altered by changing the laser energy and the accumulation period in the FT-ICR cell. By choosing suitable experimental conditions, weak signals of odd-numbered anions from C₁₂₅⁻ to C₂₁₁⁻, doubly charged anions from C₇₀²⁻ to C₂₃₀²⁻ and triply charged cluster anions from C₈₀³⁻ to C₂₂₄³⁻ can be observed. Tandem MS was applied to some selected cluster anions. Though no fragment anions larger than C₂₀⁻ can be observed by the process of collisional activation with N(2) gas for most cluster ions, several cluster anions can lose units of C(2), C(4), C(6) or C(8) in their collision process. The differences in their dissociation kinetics and structures require further calculations and experimental studies.

Ejection of clusters from solid surface by impact of size-selected cluster ion

Ejection of clusters from a solid surface by impact of size-selected clusters was investigated by mass spectroscopy and molecular dynamics (MD) simulation. It was found experimentally that carbon cluster anions, (m = 1–12), are ejected from a graphite surface by impact of (N = 1–25) at collision energies (E col) of 0.2–14.0 keV per CO2 molecule. A yield, η, of the carbon-atom ejection in the form of C m − was measured to increase with the 4th power of E col as well as the 3.6th power of N, that is, η∼N 3.6 , and levels off as E col increases further. The size distribution of the ejected remains unchanged with E col, while the average size, ⟨m⟩, of increases in proportion to N 0.17. On the other hand, MD simulation showed that C m are produced by recombination of carbon atoms evaporated from a hot surface of a cylindrical crater-shaped defect temporarily formed on the graphite surface by the cluster impact. The E col and N dependences of η and ⟨m⟩ were explained by a thermal desorption model parameterized using the results of the MD simulation. It was concluded that the higher efficiency of the cluster ejection by the larger cluster impact is attained in terms of efficient energy localization in a larger surface area and in a shallower region due to the instantaneous energy deposition by the cluster impact and the fragile nature of graphene sheets.

Polarizability of Small Carbon Cluster Anions from First Principles

We examine the applicability of density functional theory (DFT) to the polarizability of Cn- (n = 3-9) cluster anions. This was achieved by comparing DFT calculations using two different exchange-correlation functionals (the non-empirical local density approximation, LDA, and the semiempirical hybrid functional B97-1) to quantum chemical calculations using the coupled cluster method in the CCSD(T) "gold standard" approximation. We find that, unless the extra electron is not bound at all by DFT, both LDA and B97-1 agree with the CCSD(T) calculation to within 5-10%, allowing for a meaningful qualitative and semiquantitative analysis. Furthermore, the polarizability is found to increase monotonically with chain size, consistent with the trend inferred from electron detachment experiments.

TIME AND ENERGY-RESOLVED THERMIONIC EMISSION IN CARBON CLUSTERS

We present experimental measurements of time-dependent photoelectron spectra observed in thermionic emission of small carbon cluster anions and C 60 fullerenes. The combination of photoelectron velocity-map imaging with time-gated detection allowed to resolve delayed electron emission at different stages of the emission process. This unique capability allows us to analyze pure thermionic energy spectra under well-defined conditions. Experimental spectra are analyzed within the framework of the detailed balance theory.

Efficient Low-Temperature Oxidation of Carbon-Cluster Anions by SO2

Carbon-cluster anions, CN-, are very reactive toward SO2 (sticking probability of 0.012 +/- 0.005 for C27- at 25 degrees C), in contrast to their inertness toward other common atmospheric gases and pollutants. In flow reactor experiments at ambient temperature and near atmospheric pressure, primary adsorption of SO2 by the carbon cluster anions, N = 4-60, yields CNSO2- or CN-1S-. The inferred elimination of neutral CO2 is also detected as meta-stable decay in collision-induced dissociation. At higher temperatures, the reaction of SO2 with nascent carbon clusters yields CN-1SO- as well as undetected CO. The size-dependent initial reactivity reflects the previously established structural transitions (i.e., from chain to cyclic to cage structures). Such carbon clusters are formed in sooting flames and may act as nuclei for the formation of primary soot particles and serve as models for the local structural features of active soot particle sites for black-carbon soot. The facile generation of reactive carbon-sulfide and -sulfinate units may therefore have implications for understanding the health and environmental effects attributed to the coincidence of soot and SO2.