六氢吡啶和氨形成的氢键团簇C5H10NH(NH3)n(n=1～3)结构的从头算研究

在RHF/6-31G(d)水平下,对C5H10NH(NH3)n(n=1～3)氢键团簇的平衡构型进行了从头算研究,优化得到各种可能的平衡构型.C5H10NH(NH3)为线型氢键结构,而C5H10NH(NH3)2为三元环结构,C5H10NH(NH3)3为四元环结构.在MP2/6-31G(d)//B3LYP/6-31G(d)水平下,对最稳定构型C5H10NH(NH3)n(Ⅰ)(n=1～3)的分子轨道进行布居分析,并且对相应的占据轨道进行指认.C5H10NH(NH3)n(Ⅰ)(n=1～3)垂直电离势的计算结果表明,形成氢键团簇后,分子的垂直电离势降低.     

Fragmentation of Na(NH3) n + cluster ions

Photoionization and -fragmentation of Na(NH₃)_n clusters by 170 fs and 8 ns laser pulses are studied with photon energies of 2.98 eV to 3.46 eV. In the reflectron timeof- flight mass spectra a strong metastable loss of NH₃ is observed independent of the laser pulse length. From the fragmentation rate constants the internal energy of the cluster ions prior to the fragmentation process is determined by an RRK approach.     

Structures of small Li(NH3)n and Li(NH3)n+ clusters (n = 1-5): evidence from combined photoionization efficiency measurements and ab initio calculations

Photoionization threshold measurements have been carried out for small Li(NH3)n clusters (n = 1-5) and have been combined with ab initio calculations to determine structural information. The calculated adiabatic ionization energy for the lowest-energy isomer of each cluster is found to be in excellent agreement with the corresponding experimental photoionization threshold, providing evidence that the calculated structures are correct. The combination of the photoionization efficiency curve and the calculated adiabatic ionization energies also confirms the tentative assignment of the infrared spectrum of Li(NH3)4 reported by Salter and co-workers (J. Chem. Phys. 2006, 125, 34302); i.e., the 3 + 1 isomer does not contribute and the spectrum is due solely to the 4 + 0 isomer. The findings are consistent with an inner solvation shell that can hold a maximum of four ammonia molecules around the central lithium atom.     

Electronic states of sodium dimer in ammonia clusters: theoretical study of photoelectron spectra for Na2-(NH3)n (n = 0-6)

The geometries, energetics, and vertical detachment energies of Na2-(NH3)n (n = 0-6) were examined by ab initio molecular orbital methods in connection with their photoelectron spectra. One of the Na atoms is selectively solvated in the most stable structures for each n. The solvated Na is spontaneously ionized and the formation of a solvated electron occurs with increasing n, giving rise to the Na-Na+(NH3)n(e-)-type state. The ground and two lowest-lying excited states derived from the 11Sigma g+, 13Sigma u+, and 13Pi u states of Na2, respectively, are of ion-pair character though the 13Sigma u+-type state has an intermediate nature slowly changing to the radical-pair state with increasing n. On the other hand, the higher states stemming from the 11Sigma u+, 13Sigma g+, and 11Pi u states of Na2 show a developing radical-pair nature as n increases. The size dependences of the photoelectron spectra such as the near parallel shifts of the first and second bands, as well as the rapid red shifts of the higher bands, are studied on the basis of the electronic change of the neutrals by solvation.     

Ionization induced relaxation in solvation structure: a comparison between Na(H2O)n and Na(NH3)n

The constant ionization potential for hydrated sodium clusters Na(H2O)n just beyond n=4, as observed in photoionization experiments, has long been a puzzle in violation of the well-known (n+1)(-1/3) rule that governs the gradual transition in properties from clusters to the bulk. Based on first principles calculations, a link is identified between this puzzle and an important process in solution: the reorganization of the solvation structure after the removal of a charged particle. Na(H2O)n is a prototypical system with a solvated electron coexisting with a solvated sodium ion, and the cluster structure is determined by a balance among three factors: solute-solvent (Na+-H2O), solvent-solvent (H2O-H2O), and electron-solvent (OH{e}HO) interactions. Upon the removal of an electron by photoionization, extensive structural reorganization is induced to reorient OH{e}HO features in the neutral Na(H2O)n for better Na+-H2O and H2O-H2O interactions in the cationic Na+(H2O)n. The large amount of energy released, often reaching 1 eV or more, indicates that experimentally measured ion signals actually come from autoionization via vertical excitation to high Rydberg states below the vertical ionization potential, which induces extensive structural reorganization and the loss of a few solvent molecules. It provides a coherent explanation for all the peculiar features in the ionization experiments, not only for Na(H2O)n but also for Li(H2O)n and Cs(H2O)n. In addition, the contrast between Na(H2O)n and Na(NH3)n experiments is accounted for by the much smaller relaxation energy for Na(NH3)n, for which the structures and energetics are also elucidated.     

Infrared spectroscopy of Li(NH3)n clusters for n=4-7

Infrared spectra of Li(NH3)(n) clusters as a function of size are reported for the first time. Spectra have been recorded in the N-H stretching region for n=4-->7 using a mass-selective photodissociation technique. For the n=4 cluster, three distinct IR absorption bands are seen over a relatively narrow region, whereas the larger clusters yield additional features at higher frequencies. Ab initio calculations have been carried out in support of these experiments for the specific cases of n=4 and 5 for various isomers of these clusters. The bands observed in the spectrum for Li(NH3)(4) can all be attributed to N-H stretching vibrations from solvent molecules in the first solvation shell. The appearance of higher frequency N-H stretching bands for n > or =5 is assigned to the presence of ammonia molecules located in a second solvent shell. These data provide strong support for previous suggestions, based on gas phase photoionization measurements, that the first solvation shell for Li(NH3)(n) is complete at n=4. They are also consistent with neutron diffraction studies of concentrated lithium/liquid ammonia solutions, where Li(NH3)(4) is found to be the basic structural motif.     

Molecular structure and infrared spectra of (HXeCN)n (n=2, 3 or 4)

The structure, energetics, and vibrational spectra of the (HXeCN)2 dimer were investigated at the CCSD(T), MP2 and B3LYP levels. Such properties of the (HXeCN)3 trimer and (HXeCN)4 tetramer were investigated at the B3LYP level. The dimer, trimer, and tetramer were predicted to have a C2h, C2v, and D2d structure, respectively. In all of these oligomers, the N?Xe intermonomeric interaction is the most important one for holding the monomers together. Included with the ZPVE and BSSE, the stabilization energy of the dimer is 12.36 kcal/mol at the CCSD(T) level, while those of the dimer, trimer, and tetramer are 10.42, 18.23, and 31.34 kcal/mol, respectively, at the B3LYP level. At the B3LYP level, with respect to those of the isolated monomer, the C-Xe and Xe-H asymmetric stretching frequencies are shifted by -11.2 and +128.0 cm(-1) for the dimer, -51.6, +220.7 and -11.5, +96.6 cm(-1) for the trimer, and -14.1 and +201.8 cm(-1) for the tetramer.     

Theoretical study on the structures and electronic spectra of C120On (n=1,2)

ZINDO series calculations have been carried out to study the double‐cage oxides C₁₂₀O_n (n=1,2). The results show that the formation of a furan ring by the bridge‐bond between the two cages connected the two C₆₀ fullerene units and formed the C₁₂₀O with C_2v symmetry. C₁₂₀O₂ has two isomers with C_2v symmetry depending on either 6–6 or 6–5 connection between the two cages. Two furan rings and a pure four‐member ring form in this molecule. The formation of C₁₂₀O assuages the constraint of epoxide structure in C₆₀O, shortens the distance of the monomers, and produces some finite interaction between the two balls. More bonding in C₁₂₀O₂ shortens the distance of the two cages further and brings about stronger interaction. However, the two cages in C₁₂₀O_n (n=1,2) behave somehow independently that the electronic spectra of C₁₂₀O_n (n=1,2) are similar to those of C₆₀. The 6–6 connection isomer of C₁₂₀O₂ is more stable; its spectra are in good agreement with those of the experiment. The calculated electronic spectra of C₁₂₀O not only are in good agreement with the experiment in the ultraviolet region but also get some weak peaks in the visible region (>400 nm) not observed in experiment. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 291–307, 2000     

Vibrational spectra and structure of AlCl3NH3 and molten mixtures with MCl-AlCl3 (M = Li,Na, K OR Cs)

Raman and IR spectra were obtained of molten AlCl₃NH₃, AlCl₃ND₃ and AlBr₃NH₃ in addition to chloroaluminate mixtures of the AlCl₃NH₃. The main spectral features of the gaseous AlCl₃NH₃ molecules having a C_3v-symmetry are retained in the molten and glassy states. Some additional bands were observed both in the pure liquid and in mixtures with chloroaluminate melts. The spectra indicated that the discussion reaction 2AlCl₃NH₃ = AlCl⁻₄ + [AlCl₂(NH₃)₂]⁺ occurs with K ⋍ 3 × 10⁻³ (mole fraction basis). Frequency shifts found on liquefaction demonstrate that extensive hydrogen bonding takes place between AlCl₃NH₃ molecules. This observation is supported by the glass-forming nature of AlCl₃NH₃. The molecule Al₂Cl₆NH₃ seems to exist in binary AlCl₃-AlCl₃NH₃ melts.     

ChemInform Abstract: Vibrational Spectroscopy of the Ammoniated Ammonium Ions NH+ 4(NH3)n ( n = 1-10)

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Temperature dependence of nqr spectra in MSbBrF3 (M=Na,Cs, NH4) and Cs3Sb2Br9

Conclusions We have studied the temperature dependence of the NQR parameters of¹²³Sb and⁸¹Br in the range 77–360 K for the complexes of MSbBrF₃ (M=Na, Cs, NH₄) and Cs₃Sb₂Br₉. We have established the temperature regions for which piezoelectric properties appear in the crystal hydrate NaSbBrF₃.H₂O, and in the compounds MSbBrF₃ (M=Na, NH₄) and Cs₃Sb₂Br₉ anomalous changes appear in the dependences of the quadrupole coupling constant, the asymmetry parameter of the electric field gradient for the antimony atoms and the resonance frequency of the bromine atoms.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1501–1504, July, 1987.     

Collision energy transfer in collision of NH(4) (+)(NH(3))(n-1) (n=3-9) with ND(3)

An incorporation of ND(3) into protonated ammonia cluster ions NH(4)(+)(NH(3))(n-1) (n=3-9), together with a dissociation of the cluster ions, was observed in the collision of the cluster with ND(3) at collision energies ranging from 0.04 to 1.4 eV in the center-of-mass frame. The branching fractions of the cluster ion species produced in the reactions were obtained as a function of the collision energy. The branching fractions of the incorporation products were successfully explained in terms of the Rice-Ramsperger-Kassel (RRK) theory at collision energies lower than the binding energy of the cluster ion. In addition, the internal energy distributions of the parent cluster ions were determined, and found to be in good agreement with those predicted using the evaporative ensemble model. In incorporations at collision energies lower than the binding energy of the cluster ion, all of the collision energy was transferred to the internal energy of the cluster ions; subsequently, an evaporation of ammonia molecules occurred in an equilibrium process after a complete energy redistribution in the clusters. In contrast, at collision energies higher than the binding energy of the cluster ion, a release of an ammonia molecule from the incorporation products occurred in a nonequilibrium process. The transition from the complex mode to the direct mode in the incorporation was observed at collision energies approximately equal to the binding energy. On the other hand, the collision energy dependence of the cross sections for the dissociation and for a nonreactive collision were estimated by a RRK simulation in which the collision energy transfer was interpreted by using the classical hard-sphere collision model. A relationship between reactivity and reaction modes in the collision of NH(4)(+)(NH(3))(4) with ND(3) is discussed via a comparison of the experimental results with the RRK simulation.     

Infrared photodissociation spectroscopy of Na(NH3)n clusters: probing the solvent coordination

The first mass-selective vibrational spectra have been recorded for Na(NH3)n clusters. Infrared spectra have been obtained for n = 3-8 in the N-H stretching region. The spectroscopic work has been supported by ab initio calculations carried out at both the DFT(B3LYP) and MP2 levels, using a 6-311++G(d,p) basis set. The calculations reveal that the lowest energy isomer for n or= 7 is indicative of molecules entering a second solvation shell, i.e., the inner solvation shell around the sodium atom can accommodate a maximum of six NH3 molecules.     

Geometry, chemical bonding, and electronic spectra of Si(n) and Si(n)-glycine (n = 3-5) complexes

Structures and spectra are calculated for Si(n) and Si(n)-Gly (n = 3-5) complexes. Relative stability differences of Gly conformers are magnified by interactions with the Si(n) cluster, so that one conformer of Si(n)-Gly is stabilized. Significant charge transfer occurs from the amino group in Gly to a Si atom in the cluster. Interactions with Gly are predicted to shift the excitation energies of Si(n) significantly to the blue to 2.1-2.7 eV, although they are still lower than in a Si cluster passivated by hydrogen.     

Systematic study of (Na n )2 dimer transient state in Na n +Na n collisions (n=8, 9, 19, and 20)

From distance dependent tight-binding molecular dynamics simulations, we systematically study the Na _n +Na _n collision dynamics around the first two closed shells (n=8 and 20). We investigate the stability of sodium cluster dimers (Na _n )₂, for many events with random relative orientation at finite temperature, various impact parameters and incident energies. We find that (Na₈)₂, (Na₉)₂, (Na₁₉)₂ and (Na₂₀)₂ can exist during about 3000 fs in central collisions while they can exist up to about ten thousands fs in peripheral collisions with larger impact parameters in fusion mechanism at c.o.m energy per atomE _cm/n=0.025 eV. We observe that the lower the incident energy, the longer the lifetime of the cluster dimers in both central and peripheral collisions. There is no apparent difference in the dynamical stability of (Na₈)₂ and (Na₉)₂, (Na₁₉)₂ and (Na₂₀)₂ although (Na₈)₂ and (Na₂₀)₂ are respectively slightly colder than (Na₉)₂ and (Na₁₉)₂ for the same incident energy per atom and the same impact parameter.     

The solvation of two electrons in the gaseous clusters of Na- (NH3)n and Li- (NH3)n

Alkali metal ammonia clusters, in their cationic, neutral, and anionic form, are molecular models for the alkali-ammonia solutions, which have rich variation of phases with the solvated electrons playing an important role. With two s electrons, the Na(-)(NH(3))(n) and Li(-)(NH(3))(n) clusters are unique in that they capture the important aspect of the coupling between two solvated electrons. By first principles calculations, we demonstrate that the two electrons are detached from the metal by n = 10, which produces a cluster with a solvated electron pair in the vicinity of a solvated alkali cation. The coupling of the two electrons leads to either the singlet or triplet state, both of which are stable. They are also quite distinct from the hydrated anionic clusters Na(-)(H(2)O)(n) and Li(-)(H(2)O)(n), in that the solvated electrons are delocalized and widely distributed among the solvent ammonia molecules. The Na(-)(NH(3))(n) and Li(-)(NH(3))(n) series, therefore, provide another interesting type of molecular model for the investigation of solvated electron pairs.     

Coordination and solvation of copper ion: infrared photodissociation spectroscopy of Cu(+)(NH(3))(n) (n = 3-8)

Coordination and solvation structures of the Cu(+)(NH(3))(n) ions with n = 3-8 are studied by infrared photodissociation spectroscopy in the NH-stretch region with the aid of density functional theory calculations. Hydrogen bonding between NH(3) molecules is absent for n = 3, indicating that all NH(3) molecules are bonded directly to Cu(+) in a tri-coordinated form. The first sign of hydrogen bonding is detected at n = 4 through frequency reduction and intensity enhancement of the infrared transitions, implying that at least one NH(3) molecule is placed in the second solvation shell. The spectra of n = 4 and 5 suggest the coexistence of multiple isomers, which have different coordination numbers (2, 3, and 4) or different types of hydrogen-bonding configurations. With increasing n, however, the di-coordinated isomer is of growing importance until becoming predominant at n = 8. These results signify a strong tendency of Cu(+) to adopt the twofold linear coordination, as in the case of Cu(+)(H(2)O)(n).     

纳米尺寸团簇NinZrn(n=3～5)的几何结构与成键规律研究

根据化学键理论与拓扑原理，设计了团簇NinZrn(n=3-5)的可能几何构型，并用从头算方法进行构型优化，结果表明，由NiZr组成的团簇原子间的Zr-Zr和Zr-Ni键明显较强，而Ni-Ni的成键较弱，并发与NinZrn(n=3-5)团簇电子性质与有机烯烃分子等瓣相似，原子之间的成键按照强弱相间的规则分布。     

Structures and energetics of Be(n)Si(n) and Be(2n)Si(n) (n = 1-4) clusters

The structures and energies of Be(n)Si(n) and Be(2n)Si(n) (n = 1-4) clusters have been examined in ab initio theoretical electronic structure calculations. Cluster geometries have been established in B3LYP/6-31G(2df) calculations and accurate relative energies determined by the G3XMP2 method. The two atoms readily bond to each other and to other atoms of their own kind. The result is a great variety of low-energy clusters in a variety of structural types.     

Infrared spectra of the Li+-(H2)n (n=1-3) cation complexes

The Li+-(H2)n n=1-3 complexes are investigated through infrared spectra recorded in the H-H stretch region (3980-4120 cm-1) and through ab initio calculations at the MP2/aug-cc-pVQZ level. The rotationally resolved H-H stretch band of Li+-H2 is centered at 4053.4 cm-1 [a -108 cm-1 shift from the Q1(0) transition of H2]. The spectrum exhibits rotational substructure consistent with the complex possessing a T-shaped equilibrium geometry, with the Li+ ion attached to a slightly perturbed H2 molecule. Around 100 rovibrational transitions belonging to parallel Ka=0-0, 1-1, 2-2, and 3-3 subbands are observed. The Ka=0-0 and 1-1 transitions are fitted by a Watson A-reduced Hamiltonian yielding effective molecular parameters. The vibrationally averaged intermolecular separation in the ground vibrational state is estimated as 2.056 A increasing by 0.004 A when the H2 subunit is vibrationally excited. The spectroscopic data are compared to results from rovibrational calculations using recent three dimensional Li+-H2 potential energy surfaces [Martinazzo et al., J. Chem. Phys. 119, 11241 (2003); Kraemer and Spirko, Chem. Phys. 330, 190 (2006)]. The H-H stretch band of Li+-(H2)2, which is centered at 4055.5 cm-1 also exhibits resolved rovibrational structure. The spectroscopic data along with ab initio calculations support a H2-Li+-H2 geometry, in which the two H2 molecules are disposed on opposite sides of the central Li+ ion. The two equivalent Li+...H2 bonds have approximately the same length as the intermolecular bond in Li+-H2. The Li+-(H2)3 cluster is predicted to possess a trigonal structure in which a central Li+ ion is surrounded by three equivalent H2 molecules. Its infrared spectrum features a broad unresolved band centered at 4060 cm-1.