Size dependent reaction kinetics of small gold clusters with carbon monoxide: Influence of internal degrees of freedom and carbonyl complex stability

The reactions of free gold clusters Au^–, , and with carbon monoxide are studied in an rf-octopole ion trap experiment at cryogenic temperatures. While Au^– is unreactive toward CO over the whole temperature range investigated, the two and three atom cluster anions show a maximum adsorption of two CO molecules at temperatures below 250 K. From time resolved trapping experiments the strongly cluster size dependent reaction kinetics are obtained and a distinct reaction mechanism is deduced. The size dependence of the measured rate coefficients reveals the preferred formation and particular stability of the carbonyl complex . Through RRK analysis of the absolute termolecular rate coefficients we are able to estimate the binding energy of CO to and .     

$ {\rm{V}}_2 {\rm{O}}_5^ + $ {\rm{V}}_2 {\rm{O}}_5^ + " border="0"> reaction with C2H4: theoretical considerations of experimental findings

Density functional calculations have been performed for the reactions towards ethylene considering atomic and molecular oxygen loss, oxygen transfer and association reactions. The oxygen transfer channel to ethylene is energetically favourable in contrast to the oxygen loss. This is in agreement with the experimental results [1] which show that does not lose atomic oxygen during the collision induced dissociation at thermal energies. A radical cation mechanism based on structure-reactivity relation of cluster is proposed to explain oxygen transfer channel indicating that this reaction is size selective.     

Theoretical determination of electron binding energy spectra of anionic magnesium clusters

A recently developed accurate scheme for converting the single-particle eigenenergies of the density functional theory into electron binding energies is used to compute the spectra of electron binding energies in and . The computations are performed for different isomeric forms of the clusters using both pseudopotential and all-electron treatments. The results are compared with the data derived from electron photodetachment experiments, and the role of the different isomers in the interpretation of these data is examined.     

Negative-ion photoelectron spectroscopy of acrylonitrile clusters containing a sodium atom

Cluster anions of a sodium atom with acrylonitrile molecules, (n = 0–6), have been studied by negative-ion photoelectron spectroscopy. In addition, theoretical calculations by using density functional theory have been performed to obtain optimized structures and vertical detachment energies. For Na(AN)^–, the spectrum can be explained by excitation of two different isomers of the anion. For , a broad band is found in the photoelectron spectrum, whose profile is almost identical with those of previously reported photoelectron spectra of and a negative ion of chemically synthesized 1,3,5-cyclohexanetricarbonitrile (CHTCN) molecule. From this resemblance of band profiles, we conclude that oligomerization of (AN)₃ takes place in and the CHTCN is formed as the intracluster reaction product.     

A theoretical study on electron transfer in low-energy collisions of a collinear meta-stable with a $ {\rm{Na}}_3^ - $ {\rm{Na}}_3^ - " border="0"> Na

Electron transfer in the collisions of a with a Na is theoretically studied. It is assumed that the target is collinear (D _h ) and that its electronic state is meta-stable triplet state. Adiabatic potential energy surfaces and non-adiabatic couplings of the system are calculated by using a semi-empirical diatomics-in-molecules (DIM) method. The positions of (avoided)-crossings of potential surfaces are investigated and the non-adiabatic couplings between two different electronic states are calculated. An avoided crossing is found in the region where the separation between the target and projectile is relatively large (10–15 bohr). A dynamical calculation demonstrates that this crossing causes charge transfer between the target and projectile. Another intersection at a smaller separation changes the targets spin state (from triplet state to singlet state or vice versa). The cross-sections for charge and spin transfer reaction are estimated at the collision energy of 6.8 keV. It is found that the charge transfer cross-section is extremely enhanced when the target cluster ion is in its meta-stable triplet state comared to the case where the cluster is the ground singlet state.     

Effect of radiation dose on the size of bismuth particles produced by radiolysis

Colloidal bismuth is formed in -irradiated solutions , containing BiO⁺, 0.2 M propanol-2 and 2×10^-2 M of polyacrylic acid. Radiolytic reduction of these solutions produces long-lived bismuth clusters which are stabilized on the polymer chains. The clusters have a distinct absorption band at 350 nm with a tentatively assigned to or structures. With continued irradiation, the clusters coalesce into colloidal particles of 5 nm diameter. The absorption spectra of Bi oligomers and colloidal particles are reported as well as the optical changes accompanying their formation.     

Energetics and dynamics of decaying cluster ions

The recent addition of (i) a third sector field to our two sector field mass spectrometer (resulting in a BE1E2 field configuration) and of (ii) a high performance electron gun enables us now to study in detail the time dependence of the kinetic energy release distribution (KERD) over a relatively wide range of cluster ion lifetimes. Using this newly constructed device we have studied here for the first time KERDs and deduced binding energies BEs (using finite heat bath theory) of large rare gas cluster ions (an upper size limit in earlier studies arose from the fact that different naturally occurring isotopes will contribute to a chosen metastable peak when the size exceeds a certain value) and in addition of fullerene ions smaller and larger than (here again contaminating coincidences did not allow such studies earlier). Moreover, high precision KERD measurements for the decay of rare gas dimer ions in conjunction with model calculations (using recently calculated potential energy curves for the rare gas dimer ions) also enable us to obtain information on the dynamics and the mechanisms of the underlying spontaneous decay reactions . In addition, we are also reporting here a novel method (unified breakdown graph method) to determine cluster ion binding energies using a recently constructed tandem mass spectrometer BESTOF allowing us to measure fragmentation patterns arising from the unimolecular decay of molecular cluster ions induced by surface collisions. The fragmentation and reaction patterns of protonated ethanol cluster ions investigated here clearly demonstrate in contrast to some of the earlier cluster ion studies that unimolecular dissociation kinetics determines the formation of product ions in the surface-induced decomposition.     

Fragmentation of neutral Cn clusters (n = 9): experimental and theoretical investigations

We report on experimental and theoretical efforts designed to understand the fragmentation of small carbon clusters. Experimentally, a new detection system for high velocity fragments has been recently developed allowing the fragmentation of high velocity clusters to be totally recorded [1]. Results for the branching ratios of deexcitation of C₅ and C₉ formed by electron capture in high velocity collisions are presented. Theoretically, the dissociation dynamics of C₅ has been investigated using a kinematical model based on the statistical theory of Weisskopf. In this model various structural quantities (geometries, dissociation energies, harmonic frequencies), are required for both the parent cluster and the fragments. They have been calculated within DFT and coupled-cluster formalisms for C_n up to n = 9. In all cases, a strong correlation between measured branching ratios and calculated dissociation energies is observed.     

Photoemission spectra of deuterated silicon clusters: experiment and theory

We compare experimentally measured and ab initio computed photoelectron spectra of negatively charged deuterated silicon clusters ( , 4m10, 0n2) produced in a plasma environment. Based on this comparison, we discuss the kinetics and thermodynamics of the cluster formation and the effect of deuterium on the geometrical and electronic structure of the clusters.     

Low-energy surface collision induced dissociation of Ge and Sn cluster ions

Fragmentation of germanium and tin cluster ions in the low-energy collisions with a Si surface has been investigated by means of a tandem time-of-flight mass spectrometer. At low incident energies, smaller clusters fragmented by an atom loss process, whereas larger clusters decayed by fission. The favored fragmentation paths for both cluster ions were similar to those for Si cluster ions. The results support the structural similarities among Si, Ge, and Sn clusters in the present size range. For tin cluster ions, low-energy fragmentation patterns were compared with those obtained from theoretical calculations using generalized gradient approximation (GGA) and the B3PW91 exchange-correlation functional. It has been found that the B3PW91 hybrid functional results are consistent with the experimental observations.