Cage Structure Formation of Singly Doped Aluminum Cluster Cations Al<Subscript><Emphasis Type="BoldItalic">n</Emphasis></Subscript><Emphasis Type="BoldItalic">TM</Emphasis><Superscript>+</Superscript> (<Emphasis Type="BoldItalic">TM</Emphasis> = Ti,V, Cr)

Structural information on free transition metal doped aluminum clusters, Al _n TM ⁺ (TM = Ti, V, Cr), was obtained by studying their ability for argon physisorption. Systematic size (n = 5 – 35) and temperature (T = 145 – 300 K) dependent investigations reveal that bare Al _n ⁺ clusters are inert toward argon, while Al _n TM ⁺ clusters attach one argon atom up to a critical cluster size. This size is interpreted as the geometrical transition from surface-located dopant atoms to endohedrally doped aluminum clusters with the transition metal atom residing in an aluminum cage. The critical size, n _crit , is found to be surprisingly large, namely n _crit = 16 and n _crit = 19 – 21 for TM = V, Cr, and TM = Ti, respectively. Experimental cluster–argon bond dissociation energies have been derived as function of cluster size from equilibrium mass spectra and are in the 0.1–0.3 eV range.     

One-Electron Pseudo-Potential Determination of Stable Isomers of the Li*Ar n Excited Clusters: Absorption Spectra

We present pseudo-potential calculations of geometrical structures of stable isomers of LiAr _n clusters with both an electronic ground state and excited states of the lithium atom. The Li atom is perturbed by argon atoms in LiAr _n clusters. Its electronic structure obtained as the eigenfunctions of a single-electron operator describing the electron in the field of a Li⁺Ar _n core, the Li⁺ and Ar atoms are replaced by pseudo-potentials. These pseudo-potentials include core-polarization operators to account for the polarization and correlation of the inert core with the valence Lithium electron [J Chem Phys 116, 1839 1]. The geometry optimization of the ground and excited states of LiAr _n (n = 1–12) clusters is carried out via the Basin-Hopping method of Wales et al. [J Phys Chem 101, 5111 2; J Chem Phys 285, 1368 3]. The geometries of the ground and ionic states of LiAr _n clusters were used to determine the energy of the high excited states of the neutral LiAr _n clusters. The variation of the excited state energies of LiAr _n clusters as a function of the number of argon atoms shows an approximate Rydberg character, corresponding to the picture of an excited electron surrounding an ionic cluster core, is already reached for the 3s state. The result of optical transitions calculations shows that the absorption spectral features are sensitive to isomer structure. It is clearly the case for transitions close to the 2p levels of Li which are distorted by the cluster environment.     

(Noble Gas)n-NC+ Molecular Ions in Noble Gas Matrices: Matrix Infrared Spectra and Electronic Structure Calculations

An investigation of pulsed-laser-ablated Zn, Cd and Hg metal atom reactions with HCN under excess argon during co-deposition with laser-ablated Hg atoms from a dental amalgam target also provided Hg emissions capable of photoionization of the CN photo-dissociation product. A new band at 1933.4 cm⁻¹ in the region of the CN and CN⁺ gas-phase fundamental absorptions that appeared upon annealing the matrix to 20 K after sample deposition, and disappeared upon UV photolysis is assigned to (Ar)_nCN⁺, our key finding. It is not possible to determine the n coefficient exactly, but structure calculations suggest that one, two, three or four argon atoms can solvate the CN⁺ cation in an argon matrix with C−N absorptions calculated (B3LYP) to be between 2317.2 and 2319.8 cm⁻¹. Similar bands were observed in solid krypton at 1920.5, in solid xenon at 1935.4 and in solid neon at 1947.8 cm⁻¹. H¹³CN reagent gave an 1892.3 absorption with shift instead, and a 12/13 isotopic frequency ratio–nearly the same as found for ¹³CN⁺ itself in the gas phase and in the argon matrix. The CN⁺ molecular ion serves as a useful infrared probe to examine Ng clusters. The following ion reactions are believed to occur here: the first step upon sample deposition is assisted by a focused pulsed YAG laser, and the second step occurs on sample annealing: (Ar)₂⁺+CN→Ar+CN⁺→(Ar)_nCN⁺.     

Fragmentation of size-selected Xe clusters: Why does the monomer ion channel dominate the Xen and ionization?

The fragmentation of the small Xe_n n=2−5 clusters following 70 eV electron impact ionization has been investigated in a size selective experiment and simulated using non-adiabatic dynamics. The experimental results show that the clusters strongly fragment to yield monomer Xe⁺ (more than 90%) and dimer Xe₂⁺ fragments (the remaining few percent). Trimer Xe₃⁺ fragments first occur from the neutral pentamers Xe₅ in a very low yield of approximately 0.3%. The present results are compared with the previous ones for Kr and Ar clusters. It is shown that the Xe and Kr clusters exhibit a qualitatively similar behavior with a strong propensity for monomer fragments, while in the Ar case dimers prevail. The theoretical calculations also reveal a strong fragmentation to the dimer and monomer fragments. However, the dimer Rg₂⁺ is predicted to be the major product for all rare gases (Rg ≡ Ar, Kr, Xe). Possible reasons for the discrepancy between theory and experiment are discussed.     

Fragmentation of sputtered vanadium and niobium cluster ions,kinetic release and dissociation energy

The generation and unimolecular fragmentation of V _n ⁺ and Nb _n ⁺ clusters formed in sputtering vanadium and niobium surfaces by Xe⁺ ions has been studied. The method of measuring the kinetic energy of fragment ions (kinetic energy release distribution) has been used to determine the dissociation energy. Kinetic energy spectra have been measured in the field-free zone (corresponding to a time window of 10⁻⁵–10⁻⁴ sec after emission) of an ion microanalyzer with double focusing in reverse geometry. The results of spectra measurement were treated using the Rice-Ramsperge-Kassel theory of unimolecular reactions and the “evaporative ensemble”, which allowed us to calculate the dissociation energies of homonuclear V _n ¹ (n= 5–11) and Nb _n ¹ (n = 3–8) clusters.     

Cobalt(II) chloro complexation in N-methylformamide–N, N-dimethylformamide mixtures

Cobalt(II) chloro complexation has been studied by titration calorimetry and spectrophotometry in solvent mixtures of N-methylformamide (NMF) and N,N-dimethylformamide (DMF). It revealed that a series of mononuclear CoCln_n ^(2–n)+ (n=1–4) complexes are formed in the mixtures of NMF mole fraction x _NMF=0.05 and 0.25, and the CoCl⁺, CoCl₃ ^– and CoCl₄ ^2– complexes in the mixture of x _NMF=0.5, and their formation constants, enthalpies and entropies were obtained. As compared with DMF, the complexation is markedly suppressed in the mixtures, as well as in NMF. The decreasing formation constant of CoCl⁺ with the NMF content is mainly ascribed to the decreasing formation entropy. DMF is aprotic and thus less-structured, whereas NMF is protic to form hydrogen- bonded clusters. In DMF-NMF mixtures, solvent clusters in neat NMF are ruptured to yield new clusters involving DMF, the structure of which depends on the solvent composition. The entropy of formation of CoCl⁺ will be discussed in relation to the liquid structure of DMF, NMF and their mixtures.     

Thermal characterization of new complexes of Zn(II) and Cd(II) with some bipyridine isomers and propionates

New mixed ligand complexes of the following stoichiometric formulae: M(2-bpy)₂(RCOO)₂·nH₂O, M(4-bpy)(RCOO)₂·H₂O and M(2,4’-bpy)₂(RCOO)₂·H₂O (where M(II)=Zn, Cd; 2-bpy=2,2’-bipyridine, 4-bpy=4,4′-bipyridine, 2,4′-bpy=2,4′-bipyridine; R=C₂H₅; n=2 or 4) were prepared in pure solid-state. These complexes were characterized by chemical and elemental analysis, IR and conductivity studies. Thermal behaviour of compounds was studied by means of DTA, DTG, TG techniques under static conditions in air. The final products of pyrolysis of Cd(II) and Zn(II) compounds were metal oxides MO. A coupled TG/MS system was used to analyse of principal volatile products of thermal decomposition or fragmentation of Zn(4-bpy)(RCOO)2·H2O under dynamic air and argon atmosphere. The principal species correspond to: C⁺, CH⁺, CH₃ ⁺, C₂H₂ ⁺, HCN⁺, C₂H₅ ⁺ or CHO⁺, CH₂O⁺ or NO⁺, CO₂ ⁺, ¹³C¹⁶O₂ ⁺ and ¹²C¹⁶O¹⁸O⁺ and others; additionally CO⁺ in argon atmosphere.     

Theoretical studies on anionic clusters of sulfate anions and carbon dioxide, SO 4?1/?2 (CO2)n, n?=?1?4

Geometry optimizations were performed on monoanionic and dianionic clusters of sulfate anions with carbon dioxide, SO₄^−1/−2(CO₂) _n , for n = 1–4, using the B3PW91 density functional method with the 6-311 + G(3df) basis set. Limited calculations were carried out with the CCSD(T) and MP2 methods. Binding energies, as well as adiabatic and vertical electron detachment energies, were calculated. No covalent bonding is seen for monoanionic clusters, with O₃SO–CO₂ bond distances between 2.8 and 3.0 ?. Dianionic clusters show covalent bonding of type [O₃S–O–CO₂]⁻², [O₃S–O–C(O)O–CO₂]⁻², and [O₂C–O–S(O₂)–O–CO₂]⁻², where one or two oxygens of SO₄⁻² are shared with CO₂. Starting with n = 2, the dianionic clusters become adiabatically more stable than the corresponding monoanionic ones. Comparison with SO₄^−1/−2(SO₂) _n and CO₃^−1/−2(SO₂) _n clusters, the binding energies are smaller for the present SO₄^−1/−2(CO₂) _n systems, while stabilization of the dianion occurs at n = 2 for both SO₄⁻²(CO₂) _n and SO₄⁻²(SO₂) _n , but only at n = 3 for CO₃⁻²(SO₂) _n .     

The effect of basis set superposition error on the convergence of interaction energies

 For the intermolecular interaction energies of ion-water clusters [OH⁻(H₂O) _n (n=1,2), F⁻(H₂O), Cl⁻(H₂O), H₃O⁺(H₂O) _n (n=1,2), and NH₄ ⁺(H₂O) _n (n=1,2)] calculated with correlation-consistent basis sets at MP2, MP4, QCISD(T), and CCSD(T) levels, the basis set superposition error is nearly zero in the complete basis set (CBS) limit. That is, the counterpoise-uncorrected intermolecular interaction energies are nearly equal to the counterpoise-corrected intermolecular interaction energies in the CBS limit. When the basis set is smaller, the counterpoise-uncorrected intermolecular interaction energies are more reliable than the counterpoise-corrected intermolecular interaction energies. The counterpoise-uncorrected intermolecular interaction energies evaluated using the MP2/aug-cc-pVDZ level is reliable. Received: 14 March 2001 / Accepted: 25 April 2001 / Published online: 9 August 2001     

Structural Growth Sequences and Electronic Properties of Lanthanum-Doped-Gold Clusters

The geometries, stabilities, and electronic properties of Au _n La (n = 2–8) clusters have been systematically investigated by using density-functional theory. The results show that the doped La atom prefers to locate at the center site with the number of Au atom increasing from 2 to 8. Furthermore, the Au _n La clusters are more stable than the Au _n+1 clusters. The charges transfer from La atom to Au atoms at n = 2–4, but charge-transferring is reversed at n = 5.     

Collisional fragmentation of Ar@C60

The fragmentation patterns resulting from collisions between (Ar@C₆₀)⁺ or (Ar@C₆₀)⁻ ions and H₂, He, CH₄, Ne, Ar and Kr target gases have been measured. The ion-source material Ar@C₆₀ was synthesized by heating C₆₀ under 3000 atm of argon gas, leading to a 10⁻³ concentration of endohedral fullerenes. The fragmentation spectra (charged molecules only) are dominated by positive ions both when positive or negative endohedrals break up. Endohedral fragment ions Ar@C_n⁺ (48n60) as well as all carbon fragments are observed. For collisions involving (Ar@C₆₀)⁻, ejection of the Ar atom together with two electrons, without permanently damaging the fullerene cage, is a prominent reaction channel, indicating that a ‘window' or a deformation in the form of e.g. a large hole, through which the argon atoms can exit, is opened during the collision.     

Stability and structure of singly-charged xenon-argon clusters [Xe1Arn−1]+,n=3–27

Monte-Carlo calculations have been performed for positively charged xenon-argon clusters in the temperature range between 10K and 40K for cluster sizes up ton=27. The argon-argon interaction potential stems from empirical data, the Xe⁺-Ar potential is determined by ab initio MRD-CI calculations and a semi-empirical treatment of spin-orbit effects. Special stability is found for cluster sizesn=10, 13, 19 and less pronounced forn=23 and 25 fairly independent of the temperature. The geometrical structure of the clusters are given and the construction principle is discussed in light of the interactions among neutral argon atoms and the xenon ion — argon interaction. Comparison with measured mass spectra for mixed rare-gas clusters and [Xe_n]⁺ clusters is made and shows a consistent picture for the building principle.     

Formation and Characterization of Large (Ar) n , (N2) n , and Mixed (Ar) n (N2) m van der Waals Clusters Produced by Supersonic Expansion

This paper reports the formation and characterization of large (Ar) _n , (N₂) _n , and mixed binary (Ar) _n (N₂) _m van der Waals clusters produced at room temperature in the process of supersonic expansion. The average cluster size is determined by the buffer gas induced beam-broadening technique. For both Ar and N₂ clusters, power variations of the average cluster size with the gas stagnation pressure P ₀ give size scaling as . The average cluster sizes of argon vary from 2950 to more than 30900 atoms per cluster with the argon gas stagnation pressures ranging from 4 to 14 bars, and of nitrogen vary from 600 to more than 10400 molecules per cluster with the nitrogen gas stagnation pressures ranging from 8 to 38 bars. The mixed binary (Ar) _n (N₂) _m cluster is produced by supersonic expansion of an Ar–N₂ mixture. The large mixed binary (Ar) _n (N₂) _m clusters with the average sizes n + m between 1000 and 16000 are obtained. In coexpansion of Ar–N₂ mixture, we find that the argon concentration becomes higher in the beam than before the expansion. This finding is discussed and may be helpful for further insight into the phenomenon of clustering.     

The Geometric Structure of Silver‐Doped Silicon Clusters

Cationic silver‐doped silicon clusters, Si_nAg⁺ (n=6–15), are studied using infrared multiple photon dissociation in combination with density functional theory computations. Candidate structures are identified using a basin‐hopping global optimizations method. Based on the comparison of experimental and calculated IR spectra for the identified low‐energy isomers, structures are assigned. It is found that all investigated clusters have exohedral structures, that is, the Ag atom is located at the surface. This is a surprising result because many transition‐metal dopant atoms have been shown to induce the formation of endohedral silicon clusters. The silicon framework of Si_nAg⁺ (n=7–9) has a pentagonal bipyramidal building block, whereas the larger Si_nAg⁺ (n=10–12, 14, 15) clusters have trigonal prism‐based structures. On comparing the structures of Si_nAg⁺ with those of Si_nCu⁺ (for n=6–11) it is found that both Cu and Ag adsorb on a surface site of bare Si_n⁺ clusters. However, the Ag dopant atom takes a lower coordinated site and is more weakly bound to the Si_n⁺ framework than the Cu dopant atom.     

The electronic structure of small sodium clusters

Ab initio molecular orbital calculations using the STO3-21G basis set has been carried out for the cluster series Na _n ⁺ , Na _n , and Na _n ^– (wheren=2–7). The basis set is shown to be reliable compared with more extensive basis sets at the Hartree-Fock level. Thirty-one optimized structures are reported and discussed, many of which (especially for the anions) have not been considered. The STO3-21G//STO3-21G calculations suggest that for most of the species the optimum geometries are planar. In particular, the optimized structures for the anionic species should provide a starting point for more sophisticated configuration interaction calculations.     

High Magnetic Moments in Manganese‐Doped Silicon Clusters

We report on the structural, electronic, and magnetic properties of manganese‐doped silicon clusters cations, Si_nMn⁺ with n=6–10, 12–14, and 16, using mass spectrometry and infrared spectroscopy in combination with density functional theory computations. This combined experimental and theoretical study allows several structures to be identified. All the exohedral Si_nMn⁺ (n=6–10) clusters are found to be substitutive derivatives of the bare Si_n+1⁺ cations, while the endohedral Si_nMn⁺ (n=12–14 and 16) clusters adopt fullerene‐like structures. The hybrid B3P86 functional is shown to be appropriate in predicting the ground electronic states of the clusters and in reproducing their infrared spectra. The clusters turn out to have high magnetic moments localized on Mn. In particular the Mn atoms in the exohedral Si_nMn⁺ (n=6–10) clusters have local magnetic moments of 4 μ_B or 6 μ_B and can be considered as magnetic copies of the silicon atoms. Opposed to other 3d transition‐metal dopants, the local magnetic moment of the Mn atom is not completely quenched when encapsulated in a silicon cage.     

Density functional theory study on (F2AlN3) n (n = 1–4) clusters

Possible geometrical structures and relative stabilities of (F₂AlN₃) _n (n = 1–4) clusters were studied using density functional theory at the B3LYP/6-311+G* level. The optimized clusters (F₂AlN₃) _n (n = 2–4) possess cyclic structure containing Al–N_α–Al linkages, and azido in azides has linear structure. The IR spectra of the optimized (F₂AlN₃) _n (n = 1–4) clusters have three vibrational sections, the whole strongest vibrational peaks lie in 2218–2246 cm⁻¹, and the vibrational modes are N₃ asymmetric stretching vibrations. Trends in thermodynamic properties with temperature and oligomerization degree n are discussed, respectively. A study of their thermodynamic properties suggests that monomer 1A forms the most stable clusters (2A, 3A, and 4B) can occur spontaneously in the gas phase at temperatures up to 800 K.     

Interaction of the Benzenium Ion with Inert Ligands: IR Spectra of C6H7+?Ln Cluster Cations (L=Ar,N2, CH4, H2O)

IR photodissociation spectra of mass‐selected clusters composed of protonated benzene (C₆H₇⁺) and several ligands L are analyzed in the range of the C? H stretch fundamentals. The investigated systems include C₆H₇⁺? Ar, C₆H₇⁺? (N₂)_n (n=1–4), C₆H₇⁺? (CH₄)_n (n=1–4), and C₆H₇⁺? H₂O. The complexes are produced in a supersonic plasma expansion using chemical ionization. The IR spectra display absorptions near 2800 and 3100 cm^?1, which are attributed to the aliphatic and aromatic C? H stretch vibrations, respectively, of the benzenium ion, that is, the σ complex of C₆H₇⁺. The C₆H₇⁺? (CH₄)_n clusters show additional C? H stretch bands of the CH₄ ligands. Both the frequencies and the relative intensities of the C₆H₇⁺ absorptions are nearly independent of the choice and number of ligands, suggesting that the benzenium ion in the detected C₆H₇⁺? L_n clusters is only weakly perturbed by the microsolvation process. Analysis of photofragmentation branching ratios yield estimated ligand binding energies of the order of 800 and 950 cm^?1 (≈9.5 and 11.5 kJ mol^?1) for N₂ and CH₄, respectively. The interpretation of the experimental data is supported by ab initio calculations for C₆H₇⁺? Ar and C₆H₇⁺? N₂ at the MP 2/6‐311 G(2df,2pd) level. Both the calculations and the spectra are consistent with weak intermolecular π bonds of Ar and N₂ to the C₆H₇⁺ ring. The astrophysical implications of the deduced IR spectrum of C₆H₇⁺ are briefly discussed.     

Multiphoton ionization and photodissociation of (NO)mArn clusters

Picosecond multiphoton ionization of (NO)_mAr_n clusters produced in a supersonic expansion of NO/Ar gas mixtures has been studied using time-of-flight mass spectrometry. Two-photon ionization with 266 nm photons show that dilute gas mixtures (1% NO/Ar) yield clusters limited to m≤7, but with as many as 37 argon atoms. Magic numbers are observed for NO⁺Ar₁₂, NO⁺Ar₁₈, (NO) ₂ ⁺ Ar₁₇, NO⁺Ar₂₂, and (NO) ₂ ⁺ Ar₂₁ and are understood in terms of solvation of the NO⁺ and (NO) ₂ ⁺ by argon in icosahedral arrangements. Four-photon ionization with 532 nm light produces dissociation of the clusters to yield only NO⁺Ar_n with n up to 54. This distribution exhibits an additional magic number at n=54, consistent with the completion of a second solvation sphere about the NO⁺. The known wavelength dependence for photodissociation of (NO) ₂ ⁺ and (NO) ₃ ⁺ and comparison of MPI spectra obtained with 266, 355, and 532 nm light indicate that the dissociation is occurring in the cluster ions.     

激光溅射金属等离子体与醇类分子束反应的研究：产物离子对分子束状态的依赖性

The gas phase reactions of metal plasma with alcohol clusters were studied by time of flight mass spectrometry （TOFMS） using laser ablation-molecular beam （LAMB） method. The significant dependence of the product cluster ions on the molecular beam conditions was observed. When the plasma acted on the low density parts of the pulsed molecular beam, the metal-alcohol complexes M^＋An （M=Cu, Al, Mg, Ni and A=C2H5OH, CH3OH） were the dominant products, and the sizes of product ion clusters were smaller. While the plasma acted on the high density part of the beam, however, the main products turned to be protonated alcohol clusters H^＋An and, as the reactions of plasma with methanol were concerned, the protonated water-methanol complexes H3O^＋（CH3OH）n with a larger size （n≤12 for ethanol and n≤24 for methanol）. Similarly, as the pressure of the carrier helium gas was varied from 1 × 10^5 to 5 × 10^5 Pa, the main products were changed from M^＋An to H^＋An and the sizes of the clusters also increased. The changes in the product clusters were attributed to the different formation mechanism of the output ions, that is, the M^＋An ions came from the reaction of metal ion with alcohol clusters, while H^＋An mainly from collisional reaction of electron with alcohol clusters.