Acetone Clusters Research Articles

Theoretical study on the structure and stability of neutral and cationic butanone clusters

The molecular clusters have attracted increasing attention in recent years due to their applications in areas of laser, synchrotron radiation, molecular beam and time-of-flight mass spectrometry. The cluster structures can be speculated by the mass spectrum measurement and predicted by the quantum chemical methods. It is very important for understanding the solvation kinetics and nucleation to explore the formation and growth of clusters. Meanwhile, it is also beneficial to understanding the atomic or intermolecular interactions in the clusters. The molecular clusters have been studied in our previous work. The acetone clusters (CH3COCH3)n (n 12) were observed by 355 nm pumping laser. The structures of (CH3COCH3)n with n=2-7 were calculated by density functional theory, and some structures of clusters with low energy were given. Subsequently, several butanone cluster fragment ions and protonated butanone (CH3COC2H5, which is formed by taking a methyl change into ethyl from acetone CH3COCH3) clusters were observed by measuring the mass spectra under the irradiations of 355 nm and 118 nm laser lights, respectively. It is important to determine the stable cluster structures and explain the dynamics of the clusters by theoretical calculation. The stable geometric structures of neutral and cationic butanone clusters are optimized at B3LYP/6-31G* and B3LYP/6-311+G** levels based on the density functional theory. The structural characteristics and stabilities of butanone clusters with various sizes are also analyzed. The average binding energy, first-order difference energy, HOMO-LUMO gap and ionized energy are further discussed systematically in the present work. The results show that the structures of (CH3COC2H5)n and (CH3COC2H5)n+ have similar characteristics, single-ring structure is the most stable for them when n=3-7, and the structures also occur in some hydrogen bonded clusters, such as (H2O)n (n=3-6), (NH3)n (n=3-6), (CH3OH)n (n=3-6), and (HCHO)n (n=3-8). Moreover, the stability of double ring structure rises with cluster size increasing. The (CH3COC2H5)3 has the best stability in neutral clusters (CH3COC2H5)n with n=2-7, and it corresponds to the strongest peak in experiment. In addition, the (CH3COC2H5)4+ is the most stable in the cationic clusters with corresponding sizes. Furthermore, the vertical ionization energy of butanone molecule is 9.535 eV via theoretical calculation, which is in agreement with the experimental data. At the same time, the structures of (CH3COC2H5)2+ and (CH3COC2H5)2 are proved to be different by the ionization energy. The results provide a theoretical basis for the formation mechanism of butanone cluster fragment ions in experiment, and it is beneficial to the further study of growing the ketone clusters.

Reactions in acetone, perfluoroacetone and acetylene triggered by low energy (0–15 eV) electrons

Dissociative electron attachment (DEA) to acetone (CH3COCH3), perfluoroacetone (CF3COCF3) and acetylene (HCCH) is studied in the gas phase under collision-free conditions. The results are compared with those recently obtained from a study on electron attachment to homogeneous clusters of acetone and perfluoroacetone (Martin et al., 2009). Gas phase acetone and perfluoroacetone show a series of DEA resonances extending over a wide energy range and leading to various fragment ions. Perfluoroacetone additionally shows a strong signal due to the formation of the parent anion close to zero energy. In strong contrast to that, the cluster analogues exhibit only a low energy resonance while fragmentation is strongly suppressed. Such behaviour mirrors the intrinsic decomposition mechanisms which proceeds rather via predissociation involving a loose transition state than by direct dissociation along repulsive potential energy surfaces. This picture is confirmed by a time-of-flight (TOF) analysis of the fragment ions from the isolated compounds revealing that all fragment ions are formed with only low translational energy. DEA to acetylene leads to C2H− and C2− arising from different resonance regions, with C2H− as the prominent signal at 3eV resulting from predissociation of the π* resonance.

Characteristics of acetone cluster ion beam for surface processing and modification

An acetone cluster ion beam was produced by the adiabatic expansion method without using helium as a support gas. The cluster source for the production of ethanol clusters was replaced with that sealed with metal gaskets. The Laval nozzle for the production of ethanol clusters was also replaced with a stainless steel conical nozzle. The cluster size distributions of the acetone cluster ion beams had mean values approximately at 2 × 10(3) molecules and increased with source pressure. The typical beam current density of the acetone cluster ion beam was approximately 0.5 μA/cm(2).

Interactions of Ionic Liquids and Acetone: Thermodynamic Properties, Quantum-Chemical Calculations, and NMR Analysis

The interactions between ionic liquids (ILs) and acetone have been studied to obtain a further understanding of the behavior of their mixtures, which generally give place to an exothermic process, mutual miscibility, and negative deviation of Raoult's law. COSMO-RS was used as a suitable computational method to systematically analyze the excess enthalpy of IL-acetone systems (>300), in terms of the intermolecular interactions contributing to the mixture behavior. Spectroscopic and COSMO-RS results indicated that acetone, as a polar compound with strong hydrogen bond acceptor character, in most cases, establishes favorable hydrogen bonding with ILs. This interaction is strengthened by the presence of an acidic cation and an anion with dispersed charge and non-HB acceptor character in the IL. COSMO-RS predictions indicated that gas-liquid and vapor-liquid equilibrium data for IL-acetone systems can be finely tuned by the IL selection, that is, acting on the intermolecular interactions between the molecular and ionic species in the liquid phase. NMR measurements for IL-acetone mixtures at different concentrations were also carried out. Quantum-chemical calculations by using molecular clusters of acetone and IL species were finally performed. These results provided additional evidence of the main role played by hydrogen bonding in the behavior of systems containing ILs and HB acceptor compounds, such as acetone.

Acetone cluster ion beam irradiation on solid surfaces

Acetone cluster ions were produced by the adiabatic expansion method without using a support gas. The acceleration voltage of the acetone cluster ion beam was from 3 to 9kV. The sputter depths of silicon irradiated with acetone cluster ion beams increased with acceleration voltage and fluence of the acetone cluster ion beams. The sputter depth was close to that induced by the ethanol cluster ion beam accelerated at the same acceleration voltage. The sputtering yield of silicon by the acetone cluster ion beam at an acceleration voltage of 9kV was approximately 100times larger than that for an argon monomer ion beam at 9keV. The sputter depths of silicon dioxide irradiated with the acetone cluster ion beams were smaller than those of silicon, but larger than those induced by ethanol cluster ion beams. The XPS analysis of silicon surface indicated that the silicon surface was more strongly oxidized by the irradiation of acetone cluster ion beam than ethanol cluster ion beam.

Weak carbonyl-methyl intermolecular interactions in acetone clusters explored by IR plus VUV spectroscopy

Size-selected IR–VUV spectroscopy is employed to detect vibrational characteristics in the region 2850∼3550cm−1 of neutral acetone and its clusters (CH3COCH3)n (n=1–4). Features around 3440cm−1 in the spectra of acetone monomer and its clusters are assigned to the carbonyl stretch (CO) overtone. These features red-shift from 3455 to 3433cm−1 as the size of the clusters increases from the monomer to the tetramer. Based on calculations, the experimental IR spectra in the CO overtone region suggest that the dominant structures for the acetone trimer and tetramer should be cyclic in the supersonic expansion sample. This study also suggests that the carbonyl groups interact with the methyl groups in the acetone clusters. These weak interactions are further confirmed by the use of deuterium substitution.

The influence of alkaline earth ions on the structural organization of acetone probed by the noncoincidence effect of the ν(CO) band: experimental and quantum chemical results

We have investigated the Raman noncoincidence effect (NCE = nu(aniso)-nu(iso), where nu(aniso) and nu(iso) are the anisotropic and the isotropic Raman frequencies) of the nu(C=O) band of acetone arising from the interactions of this solvent with the metal ions in acetone electrolytic solutions of alkaline earth metal (Mg, Ca, Sr, Ba) perchlorates. Assisted by the results of ab initio molecular orbital (MO) calculations carried out at the Hartree-Fock (HF) level with the 6-31+G(2df,p) and LanL2DZ basis sets, we have been able to attribute the anisotropic and isotropic components of this band to the formation of acetone-metal ion clusters, (acetone)(n)M(2+), and to interpret its high and negative NCE, opposed to the positive NCE of the bulk liquid, as the consequence of the large separation between the higher frequency of the in-phase mode (active in the Raman isotropic spectrum) and the lower (average) frequency of the n- 1 out-of-phase modes (predominantly active in the Raman anisotropic spectrum). The negative sign of the NCE is compatible with the transition dipole coupling (TDC) mechanism. The comparison between the observed NCE for each electrolytic solution at the concentrations used in this study and those calculated for the different solvation numbers n of each (acetone)(n)M(2+)cluster gives a clear indication of the highest stability of the hexa-coordinated cluster for the Mg(2+) ion, but leaving uncertain (n = 6 or 8) this conclusion for the acetone clusters of the remaining M(2+) ions. We have interpreted the observed and calculated decrease of the magnitude of NCE with the ion size through the ion polarizing power in the light of the ion effective charge and its distance (M(2+)...O=C) from the C=O oscillators.

Hydrogen bonding in acetone clusters probed by near-edge x-ray absorption fine structure spectroscopy in the carbon and oxygen K-edge regions

Hydrogen bonding in acetone clusters was investigated using near-edge x-ray absorption fine structure (NEXAFS) spectroscopy and density functional theory calculations in the carbon and oxygen K-edge regions. The partial-ion-yield (PIY) curves of the cluster ions were measured as the NEXAFS spectra of acetone clusters. In the carbon K-edge region, the first resonance peak, which was assigned to the C(CO) 1s-->pi( *)(C=O) resonance transition, showed no substantial change in the PIY curves of the acetone clusters, while the C(CH3) 1s-->3ppi(CH(3)) excitation feature was found to be strongly suppressed. The selective suppression of the C(CH3) 1s-->3ppi(CH(3)) resonance transition can be explained by the change in the character of the 3ppi(CH(3)) orbital due to the C=O...H-C type of hydrogen-bonding interaction. On the other hand, the NEXAFS spectra of the acetone molecule and clusters were almost identical in the oxygen K-edge region, except for a small shift in the pi( *)(C=O) resonance of 0.13 eV, because the character of the pi( *)(C=O) orbital remained, regardless of the C=O...H-C hydrogen bonding interaction.

DFT study of the hydrogen bond strength and IR spectra of formic, oxalic, glyoxylic and pyruvic acids in vacuum, acetone and water solution

The molecular geometries of the possible conformations of formic, oxalic, glyoxylic and pyruvic acids have been fully optimized at DFT B3LYP/6-311++G(d,p) levels of calculation in vacuum as well as in water and acetone solution. Solutions were treated according to the SCRF PCM approach but some formic acid–water and formic acid–acetone clusters as well as adducts of oxalic acid with two or four water molecules were also taken into account for testing the importance of specific solute–solvent effects. All the most stable isomers of the title compounds are characterized by weak intramolecular hydrogen bonds, whose strengths (EHB) cannot be correctly estimated as stability difference between the open and chelate forms since the energy of the former isomer is, in turn, stabilized by a weak hydrogen bridge due to the formic acid moiety. Following the Rotation Barrier Method (RBM), proposed some years ago, EHB in the examined molecules (gas phase) falls in the range of 18–22 kJ/mol for oxalic acid (9.6 kJ/mol for the c-C-t isomer), 16.8 kJ/mol for glyoxylic acid and 19.8 kJ/mol for pyruvic acid. Most of them disappear at all, or nearly at all, both in acetone and aqueous solution, in consequence of the solvent effect. The frequencies of the OH and CO stretching modes, calculated according to the anharmonic oscillator model, are in very good agreement with the experimental literature data, where available. Copyright © 2009 John Wiley & Sons, Ltd.

Reactions in clusters of acetone and fluorinated acetones triggered by low energy electrons

Electron attachment to clusters of acetone (A), trifluoroacetone (TFA) and hexafluoroacetone (HFA) is studied in a crossed beam experiment with mass spectrometric detection of the anionic products. We find that the electron attachment properties in A change dramatically on going from isolated molecules to clusters. While single acetone is a very weak electron scavenger (via a dissociative electron attachment (DEA) resonance near 8.5 eV), clusters of A capture electrons at very low energy (close to 0 eV). The final ionic products consist of an ensemble of molecules (M) subjected to the loss of two neutral H 2 molecules ((M n −2H 2) −, n ≥ 2). Their formation at low energies can only be explained by invoking new cyclic structures and polymers. In clusters of TFA, anionic complexes containing non-decomposed molecules (M n −) including the monomer (M −) and ionic products formed by the loss of one and two HF molecules are observed. Loss of HF units is also interpreted by the formation of new cyclic structures in the anionic system. HFA is a comparatively stronger electron scavenger forming a non-decomposed anion via a narrow resonant feature near 0 eV in the gas phase. In HFA clusters, the non-decomposed parent anion is additionally observed at higher electron energies in the range 3–9 eV. The M − signal carries signatures of self-scavenging processes, i.e., inelastic scattering by one molecule and capture of the completely slowed down electron by a second molecule within the same cluster. The scavenging spectrum is hence an image of the electronically excited states of the neutral molecule.

Acetone: isomerization and aggregation

The advanced experimental and theoretical techniques enable us to obtain information on the rearrangement of atoms or molecules in a reaction nowadays. As an example, we report on our research work on acetone isomerization and aggregation to give an insight into the reaction pathways, the products and their structures, and the growth regularity of aggregation. The evidences on the structural change of acetone and the stability of acetone clusters are found by a laser ionization mass spectrometer and the results are interpreted from theoretical analysis based on the DFT/B3LYP method. Various isomerization channels of acetone have been established and the optimal structures of the neutral clusters (CH3COCH3)n and the protonated acetone clusters (CH3COCH3)nH+ for n=1–7 have been determined.

Ultrafast dynamics of acetone–water clusters: the influence of solvation

The ultrafast dynamics of acetone clusters and mixed clusters of acetone and water have been investigated using the pump-probe technique employing a femtosecond laser system coupled to a reflectron time-of-flight mass spectrometer. Studies using an excitation wavelength of 407 nm have revealed that solvation by both acetone and water molecules has a pronounced influence on the dynamics of acetone excited to the 5d Rydberg state. The lifetime of the excited acetone moiety was found to increase substantially from <100 fs in the case of the acetone molecule to a few picoseconds for both pure acetone and mixed acetone–water clusters. The significant slowing of acetone photodissociation is discussed as a possible influence on the lifetime of atmospheric acetone and it is concluded that the number density of acetone water complexes is too low to alter the overall photolysis rate of tropospheric acetone. However, at higher altitudes, where temperatures are lower, complex solvated acetone may become a more significant factor.

Surface-induced dissociations and reactions of acetonitrile monomer, dimer and trimer ions

Dissociations and reactions induced by impact of acetonitrile monomer ions (CH3CN+, CD3CN+), dimer ions [(CH3CN)2+, (CD3CN)2+] and trimer ions [(CD3CN)3+] on a hydrocarbon-covered stainless-steel surface were investigated over the projectile energy range of 3–70 eV. Both simple dissociations of the projectile ion and chemical reactions of H-atom transfer from the surface material (followed by dissociations of the protonated projectile ion formed) were observed for the monomer ions. Results obtained for the dimer ions (CD3CN)2+ indicate the formation of the protonated acetonitrile ions via surface-induced reactions in two ways: (i) an intracluster ion–molecule reaction followed by dissociation to form CD3CND+, and (b) a hydrogen pick-up reaction from the surface material during the interaction of the dimer ion with the surface leading to CD3CNH+. A simple model based on the Brauman double-well potential—suggested earlier to explain the occurrence of analogous reactions in acetone cluster ion/surface interactions—accounts well for the formation of both product ions. Moreover, in adition to these protonated species, considerable amounts of nondissociated dimer ions were observed after acetonitrile dimer cation/surface collisions with energies up to 25 eV. Similarly, both trimer ions (up to 20 eV) and dimer ions (up to 30 eV) were observed in acetonitrile trimer cation/surface interactions. This indicates that unimolecular dissociation kinetics governs the product formation for these cluster ion/surface interactions.

Photoionization and density functional theory study of clusters of acetone containing an alkali metal atom, M((CH 3) 2CO) n (M=Li, Na): intracluster electron transfer from metal to acetone in 1:1 complexes

Ionization threshold energies of clusters of Li and Na atoms solvated by acetone have been determined by laser photoionization. The thresholds for 1:1 complexes agree well with calculated adiabatic ionization potentials based on density functional theory. The structures and charge distributions obtained from the calculation show that electron transfer from the alkali atom to acetone occurs more efficiently in Li((CH 3) 2CO) than in Na((CH 3) 2CO). This difference in the extent of electron transfer can be understood by a consideration of the orbital overlap between the metal np and O2p orbitals and the sp hybridization on the alkali atom.

Surface-induced reactions of acetone cluster cations

The occurrence of two different chemical reactions initiated by the surface impact of acetone dimer, trimer, and tetramer cations (energy 20–70 eV) on a stainless-steel surface (covered with hydrocarbons) was observed. The reaction product is the protonated acetone ion, formed in (i) an intracluster ion–molecule reaction, and in (ii) a hydrogen pickup reaction of the cluster ion with the surface material. Only the monomer product ions (and small amounts of their dissociation products) could be observed; the spectra did not show any presence of clustered product ions. A simple model based on the Brauman double-well potential is suggested to explain the formation of the two product ions. In accordance with predictions from molecular dynamics simulations, this appears to be the first observation of competitive chemical reactions of a cluster ion driven by energy transfer in a surface collision.

Anthropogenic perturbations of tropospheric ion composition

This paper presents a simple model of the vertical distribution of the most abundant positive ions in the troposphere. The model is based on a simple ion chemical scheme, measured rate constants, and observed or calculated atmospheric densities of parent neutral compounds. It suggests that in many cases the most abundant gaseous ions are heavy protonated water cluster ions of pyridine, picoline and lutidine with ammonia molecules attached (pyridinated cluster ions) in the lower troposphere (below 7 km altitude), acetone cluster ions in the upper troposphere (between 7 and 15 km) and methyl cyanide cluster ions above 15 km. The relative abundance of heavy clustered aerosol ions is predicted to be highest near the surface. The model suggests that ion composition could be perturbed as a result of human activities (i.e., increasing emissions of parent neutral species including alkaline compounds), and that in particular, the relative atmospheric abundance of pyridinated water cluster ions is increasing dramatically and should further increase in the future.

Surface-induced reactions of polyatomic ions and cluster ions

We have recently constructed the tandem mass spectrometer set-up BESTOF (consisting of a B-sector field combined with an E-sector field, a surface and a time of-flight mass spectrometer) which allows the investigation of ion/surface reactions with high primary mass and energy resolution, i.e. energy spreads of as low as 80 meV fwhm have been achieved. Using BESTOF we have extended previous investigations in several respects. Firstly, we have revisited previously investigated surface-induced reactions of various polyatomic ions including the acetone ion, the benzene ion and interacting with stainless steel surfaces. In addition, we have started to investigate the reactions of polyatomic hydrocarbon ions with carbon tiles from the Tore Supra tokamak in Cadarache. Thirdly, we have investigated surface-induced reactions (using stainless steel and gold surfaces) of fullerene ions as a function of cluster size n and cluster charge state z (up to z = 5) thereby extending previous measurements of Kappes and co-workers for singly charged fullerene ions to multiply charged fullerene ions. Finally, we have extended these fullerene-cluster ion studies to molecular clusters of benzene and acetone. Here we will first describe the characteristics and the performance of this newly constructed tandem mass spectrometer system BESTOF. We will then discuss in an illustrative manner results obtained with this machine selecting as examples the acetone monomer ion and the acetone dimer ions. Besides demonstrating the capabilities of the newly constructed ion/surface interaction apparatus BESTOF and besides illustrating these capabilities by presenting as an example surface-induced dissociations (SID) and surface-induced (pick-up) reactions (SIR) of the acetone monomer ion impacting on a hydrocarbon-covered stainless steel surface, we have here also extended these studies to surface-induced reactions of the acetone dimer ion. In contrast to several pioneering studies involving surface-induced dissociation of cluster ions, we have been here able for the first time to observe and analyse surface-induced (catalysed) reactions (SIR) of cluster ions. In particular, we have been able - as predicted by Cleveland and Landman using molecular dynamics simulations - to observe for the deuterated acetone dimer ion impact on the one hand `collisions which catalyse chemical reactions between cluster constituents' (intra-cluster ion-molecule reactions) leading to the production of the deuteronated acetone monomer ion and on the other hand `collisions between the cluster ion and the surface material' (hydrogen pick-up reactions) leading to the formation of the protonated acetone monomer ion . In competition with these two reactive SIR channels, also the straightforward fragmentation (SID) of the dimer ion into the two fragments could be observed as a minor reaction channel.

Temperature variation of the evolution of positive small air ions at constant relative humidity

The evolution of positive air ions is mathematically simulated considering 150 trace gases and more than a thousand ion-molecule reactions. The main attention is paid to the evolution of near-ground air ions in the age interval from 10 ms to 3 s where the knowledge about ion evolution is most limited. Recently, detailed experimental data about the time variation of the air ion mobility spectrum became available, and the results of mathematical simulation can be compared with the observed transformations. Unfortunately, the ion mobility measurements have not been accompanied by data about concentrations of the trace gases; therefore the mobilities can be interpreted only ambiguously. Nevertheless, the main features of the measured evolution shape of ions can be explained by the results of simulation, and the best agreement is achieved by the assumption of an enhanced concentration of either acetone or pyridine. In this case, the younger ions should be mainly ions H3O+(H2O)n, while the more aged ions should be either acetone or pyridine family clusters.

Femtosecond excitation dynamics of acetone: Dissociation, ionization, and the evolution of multiply charged elemental species

Recent femtosecond pump–probe experiments have suggested that a stepwise dissociative mechanism is operative for acetone excited to Rydberg states and upper regions of the mixed singlet/triplet state. The present work focuses on the excitation of acetone and acetone clusters to the 3d (or perhaps 4s) electronic intermediate state in order to further explore the operative dissociation mechanisms and the effects of solvation (clustering). As reported herein, results from femtosecond pump–probe experiments suggest that the availability of additional vibrational modes in clusters, where internal energy may be dispersed, increases the fraction of acetyl intermediates which remain behind the barrier to dissociation into methyl and CO fragments. At progressively higher laser fluences, multiply charged elemental carbon and oxygen ions abruptly appear. Interestingly, the extent of their formation is observed to depend on both laser intensity and the relative time delay between the pump and probe laser beams responsible for their occurrence.

Further direct evidence for stepwise dissociation of acetone and acetone clusters

The (pre)dissociation of acetone and acetone clusters after excitation to states corresponding to upper {S1,T1} and 3s Rydberg states of the acetone monomer are investigated through femtosecond pump–probe experiments coupled with molecular beam time-of-flight mass spectrometry techniques. Upon excitation to either state, [(CH3)2CO]n* dissociates rapidly. Acetyl fragments, [(CH3)2CO]n−1CH3CO+ may arise from ionization of an excited species formed by (pre)dissociation of intact precursors or by dissociation after the intact species has been ionized. The method employed to separate these two channels is discussed herein; the resulting transients are fit to a kinetic model to elucidate intermediate lifetimes and dissociation mechanisms. The present experiments establish that a stepwise dissociation mechanism is operative upon excitation to the 3s Rydberg state for the acetone monomer and dimer, with their corresponding acetyl fragments having lifetimes on the order of picoseconds. Larger cluster species, [(CH3)2CO]n (n≳2), do not exhibit the predissociative behavior evident in the monomer and dimer. Conversely, dissociation upon excitation to the {S1,T1} state exhibits an initial loss of a methyl unit, with the acetyl intermediate being considerably more stable than those created by dissociation of acetone from higher lying states. A strong dependence on the internal energy available after the dissociation event is noted.