Relativistic all-electron Dirac-Fock-Breit calculations on xenon fluorides (XeFn,n = 1, 2, 4, 6)

The MOLFDIR package of programs is used to perform fully relativistic all-electron Dirac-Fock and Dirac-Fock-Breit calculations for the the XeF_n (n = 1, 2, 4, 6) molecules assuming experimental symmetries. The Xe-F bound length for XeF₂, XeF₄, and XeF₆ is optimized and the total ground-state energies are reported. The variation of the relativistic energy and the Breit correction with the internuclear distance is plotted. The role of relativistic corrections in the proper prediction of the Xe-F distance and the dissociation energy of the molecule is discussed. The problem of the reduction of the number of scalar two-electron integrals is studied. Our results illustrate the possibilities, difficulties, and limitations of the finite basis Dirac-Fock calculations for polyatomic molecules of different symmetries. © 1997 by John Wiley & Sons, Inc.     

Double ionization of cycloheptatriene and the reactions of the resulting C7H(n)2+ dications (n = 6, 8) with xenon

The formation and fragmentation of the molecular dication C(7)H(8)(2+) from cycloheptatriene (CHT) and the bimolecular reactivities of C(7)H(8)(2+) and C(7)H(6)(2+) are studied using multipole-based tandem mass spectrometers with either electron ionization or photoionization using synchrotron radiation. From the photoionization studies, an apparent double-ionization energy of CHT of (22.67 ± 0.05) eV is derived, and the appearance energy of the most abundant fragment ion C(7)H(6)(2+), formed via H(2) elimination, is determined as (23.62 ± 0.07) eV. Analysis of both the experimental data as well as results of theoretical calculations strongly indicate, however, that an adiabatic transition to the dication state is not possible upon photoionization of neutral CHT and the experimental value is just considered as an upper bound. Instead, an analysis via two different Born-Haber cycles suggests (2)IE(CHT) = (21.6 ± 0.2) eV. Further, the bimolecular reactivities of the C(7)H(n)(2+) dications (n = 6, 8), generated via double ionization of CHT as a precursor, with xenon as well as nitrogen lead, inter alia, to the formation of the organo-xenon dication C(7)H(6)Xe(2+) and the corresponding nitrogen adduct C(7)H(6)N(2)(2+).     

VUV spectra of the xenon fluorides

The absorption spectra of gaseous XeF₂, XeF₄, and XeF₆ have been accurately measured in the photon energy range from 6 to 35 eV with the use of the synchrotron radiation of DESY. The vibrational structure of several Rydberg transitions could be resolved. The spectra are interpreted and most of the structures could be assigned. From these data, information about the ionized species is obtained. The assignment of the first two IP's of XeF₄ is corrected.     

Synthesis, Raman spectra and crystal structures of [Cu(XeF2)n](SbF6)2 (n=2, 4)

Pure [Cu(XeF2)2](SbF6)2 was prepared by the reaction of Cu(SbF 6) 2 with a stoichiometric amount of XeF2 in anhydrous hydrogen fluoride (aHF) at ambient temperature. The reaction between Cu(SbF6)2 and XeF2 (1:4 molar ratio) in aHF yielded [Cu(XeF2)4](SbF6)2 contaminated with traces of Xe 2F 3SbF6 and CuF2. The 6-fold coordination of Cu(2+) in [Cu(XeF2)2](SbF6)2 includes two fluorine atoms from two XeF2 ligands and four fluorine atoms provided by four [SbF6](-) anions. The neighboring [Cu(XeF 2)2](2+) moieties are connected via two [SbF6] units, with the bridging fluorine atoms in cis positions, into infinite [Cu(eta(1)-XeF2)2](cis-eta(2)-SbF 6)2[Cu(eta(1)-XeF 2)2] chains. Because of the high electron affinity of Cu(2+), coordinated XeF2 shows the highest distortion (Xe-Fb=210.2(5) pm, Xe-Ft=190.6(5) pm) observed so far among all known [M(x+)(XeF2)n](A)x (A=BF4, PF6, etc.) complexes. The four equatorial coordination sites of the Cu(2+) ion in [Cu(XeF 2) 4](SbF6)2 are occupied by four XeF 2 ligands. Two fluorine atoms belonging to two [SbF6] units complete the Cu (2+) coordination environment. The neighboring [Cu(XeF2)4](2+) species are linked via one [SbF6] unit, with bridging fluorine atoms in trans positions, into linear infinite [Cu(eta(1)-XeF2)4](trans-eta(2)-SbF6)[Cu(eta(1)-XeF2)4] chains. To compensate for the remaining positive charge, crystallographically independent [SbF6](-) anions are located between the chains and are fixed in the crystal space by weak Xe...F(Sb) interactions.     

Resonant two-photon ionization spectra of o,p, m-xylene...Ar n (n = 1, 2)

The resonant two-photon ionization technique (R2PI) is used to study jet-cooled van der Waals (vdW) complexes o, p, m-xylene...Ar _n (n = 1, 2) through the S ₁ ← S ₀ transition around the origin band. We have tentatively assigned the main spectral features of these vdW complexes. The transitions of these complexes are red-shifted from those of the monomers. The influence of the substituent positions on the vdW vibrations is investigated.     

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.     

Ab initio determination of the ionization potentials of water clusters (H2O)n (n = 2-6)

High-level quantum-chemical ab initio coupled-cluster and multiconfigurational perturbation methods have been used to compute the vertical and adiabatic ionization potentials of several water clusters: dimer, trimer, tetramer, pentamer, hexamer book, hexamer ring, hexamer cage, and hexamer prism. The present results establish reference values at a level not reported before for these systems, calibrating different computational strategies and helping to discard less reliable theoretical and experimental data. The systematic study with the increasing size of the water cluster allows obtaining some clues on the structure and reductive properties of liquid water.     

含BF配体的锇羰基化合物Os(BF)(CO)_n(n=4,3)和Os_2(BF)_2(CO)_n(n=7,6,5,4)稳定性的理论研究

采用MPW1PW91和BP86 2种密度泛函方法对中性单核锇羰基化合物Os(BF)(CO)n(n=4,3)及双核锇羰基化合物Os2(BF)2(CO)n(n=7,6,5,4)进行理论计算研究,优化得到22个低能异构体.研究发现,单核配位饱和Os(BF)(CO)4的能量最低的异构体对称性为C2v,其BF基团在三角双锥赤道面上.该异构体失去1个赤道面上的CO可得到Os(BF)(CO)3的能量最低异构体.单核Os(BF)(CO)n(n=4,3)的能量最低异构体的BF基团都位于配体三角双锥及缺顶点结构的赤道面上.配位饱和双核Os2(BF)2(CO)7有4个能量接近的异构体,其中能量最低的异构体结构中含有2个呈蝶形的桥配位BF基团.配位不饱和的Os2(BF)2(CO)6的2个能量接近的异构体结构相似,2个桥配位BF基团与2个Os原子构成平行四边形结构单元.配位不饱和的Os2(BF)2(CO)5和Os2(BF)2(CO)4的能量最低异构体都含有由2个桥配位BF基团与2个Os原子构成的平行四边形结构单元.双核Os2(BF)2(CO)n(n=7,6,5,4)能量最低异构体的BF基团都以桥配位形式和Os原子相连.离解能研究表明,单核配位饱和的Os(BF)(CO)4具有一定的热力学稳定性.双核的Os2(BF)2(CO)n(n=7,6)失去1个CO或者分裂为单核的Os(BF)(CO)4或Os(BF)(CO)3所需能量较高,表明其具有一定的热力学稳定性.     

Electronic absorption spectra of the protonated polyacetylenes H2CnH+ (n = 4, 6, 8) in neon matrixes

Electronic absorption spectra of the protonated polyacetylenic chains H2CnH+ (n = 4, 6, 8) and the neutral H2C8H have been observed in 6 K neon matrixes after mass selection. The wavelength of the H2CnH+ electronic transitions depends quasi-linearly on n, typical of carbon chains. The origin band is at 286.0, 378.6, and 467.6 nm for n = 4, 6, and 8, respectively. Two ground-state vibrations of H2C4H+ in the IR absorption spectrum were also detected. On the basis of the spectroscopic trends and the assignment of the vibrational frequencies in the ground and excited electronic states, it is concluded that the H2CnH+ species are C(2v) linear carbon chains with one H atom on one end and two on the other.     

DVM-Xα calculations on the electronic structure of the xenon fluorides XeFn : n = 2, 4, 6

The ionization potentials of the XeF₂, XeF₄ and XeF₆ molecules are calculated by the discrete variational Xα-method. The results of the calculations are used for an interpretation of the experitnental PES and XPS of these compounds. Reasonable agreement is found between the theoretical estimates and data obtained from absorption spectroscopy.     

Infrared spectra of the M(NO)n (M = Sn, Pb; n = 1, 2) and PbNO- molecules

Reactions of laser-ablated tin and lead atoms with nitric oxide molecules in solid argon and neon have been investigated using matrix-isolation infrared spectroscopy. In the argon experiments, absorptions at 1560.1, 1625.8, and 1486.7 cm(-1) are assigned to the N-O stretching vibrations of the SnNO and Sn(NO)2 molecules, and absorptions at 1541.9, 1630.0, 1481.8, and 1457.5 cm(-1) are assigned to the N-O stretching vibrations of the PbNO, Pb(NO)2, and PbNO- molecules on the basis of isotopic shifts and splitting patterns. The present neon experiments only produce neutral tin and lead mononitrosyls. Density functional theory calculations have been performed on these tin and lead nitrosyls. The good agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts substantiates the identification of these nitrosyls from the matrix infrared spectra.     

Chemical ionization mass spectra of 2, 4, 6-trinitroaromatic compounds

The methane and isobutane chemical ionization mass spectra of ten 2,4,6-trinitroaromatic compounds have been recorded. The mass spectra contain intense [M + 1]⁺ ions and usually little fragmentation. However, in some cases major fragmentation processes have been observed. Some unusual adduct ions have been found with isobutane as the reagent and their temperature dependence has been studied.     

Infrared spectra of the water-nitrogen complexes (H2O)2-(N2)n(n = 1-4) in argon matrices

The infrared spectra of the water-nitrogen complexes trapped in argon matrices have been studied with Fourier transform infrared absorption spectroscopy. The absorption lines of the H20-N2 1:1, 1:2, 1:n, and 2:1 complexes have been confirmed on the basis of the concentration effects. In addition, we have observed a few lines and propose the assignments for the 2:2, 2:3, and 2:4 complexes in the nu1 symmetric stretching and nu2 bending regions of the proton-acceptor molecule, and in the bonded OH stretching region of the proton-donor molecule. The redshifts in the bonded OH stretching mode and blueshifts in the OH bending mode suggest that the hydrogen bonds in the (H2O)2-(N2)n complexes with n = 1-4 are strengthened by the cooperative effects compared to the pure H2O dimer. Two absorption bands due to the 3:n complexes are also observed near the bonded OH stretching region of the H2O trimer.     

Ab initio investigation of vibrational spectra of water-(CO2)n complexes (n = 1, 2)

In this paper, we have calculated using the ab initio method the IR vibrational spectra of complexes of CO2 formed with water (sp3 O-donating atom). Binding energies and structures of the CO2-H2O and water-(CO2)2 complexes have been determined at the second-order level of the Moller-Plesset perturbation theory (MP2) using Dunning's basis sets. The results are presented and critically discussed in terms of the nature of the water-CO2 interactions, electron donor acceptor (EDA) and weak O...H-O interactions. For water-(CO2)2 trimer, it is also shown that the contribution to the interaction energy of the irreducible three-bodies remains relatively negligible. We have analyzed the frequency shifts and the IR and Raman intensity variations under the complex formation. We have particularly emphasized the splitting of the 2 bending mode of CO2 and stretching modes of water, which have been revealed as the most pertinent probes to assess the nature of the forces involved in the different complexes. Finally, because water can play the role of Lewis base and acid as well, we found that weak O...H-O interactions can cooperate with EDA interactions in trimer, leading to very specific spectral signatures that are further discussed.     

Infrared spectra of the (AgCO)2 and AgnCO (n=2-4) molecules in rare-gas matrices

Reactions of laser-ablated silver atoms with carbon monoxide molecules in solid argon and neon have been investigated using matrix-isolation IR spectroscopy. Small silver cluster carbonyls, (AgCO)2 and AgnCO (n=2-4), as well as mononuclear silver carbonyls, Ag(CO)2 and Ag(CO)3, are generated upon sample annealing in the argon experiments and are characterized on the basis of the isotopic substitution, the CO concentration change, and the comparison with theoretical predictions. However, these polynuclear carbonyls are absent from the neon experiments. Density functional theory calculations have been performed on these silver carbonyls and the corresponding ligand-free silver clusters, which support the identification of these silver carbonyls from the matrix IRspectrum. A terminal CO has been found in the most stable structures of (AgCO)2, Ag2CO, Ag3CO, and Ag4CO. Furthermore, a plausible reaction mechanism has been proposed to account for the formation of the (AgCO)2 and AgnCO (n=2-4) molecules.     

LaC4^n（n=—2,—1,0,＋1,＋2）分子簇的结构与稳定性

本文用密度泛函方法研究了ＬａＣ４ｎ（ｎ＝－２,－１,０,＋１,＋２）分子簇的结构与稳定性。振动频率分析表明,在所提出的九个构型中,当ｎ＝－２,０,＋１,＋２时,稀土位于碳环上最稳定,而当ｎ＝－１时,尽管稀土位于碳环上能量最低,但没有找到稳定的构型,我们的结果还指出,稀土元素是分子簇中对外部环境最敏感的部位,即最具有反应活性     

饱和烷烃分子C_nH_(2n+2)(n=4-6)的电子动量光谱(英文)

使用B3LYP/TZVP//B3LYP/aug-cc-pVTZ方法系统研究了饱和烷烃分子CnH2n+2(n=4-6)的轨道电子动量光谱,比较了同分异构体CnH2n+2(n=4-6)对轨道动量分布的影响.结合二维空间分析方法对电子在坐标空间中的密度分布进行了系统的研究.计算结果表明,最内价壳层电荷分布主要由s电子贡献,第二近邻芯价壳层则主要由p电子贡献,而其余的价壳层则为sp杂化.最内价轨道表现出最大的谱线强度并且远大于其它轨道的谱线强度,而且正烷烃的谱线强度要大于异烷烃等同分异构体的谱线强度,表现出了明显的与甲基移动的个数有关的性质.     

Mg(XeF(2))(n)()](AsF(6))(2) (n = 4, 2): first compounds of magnesium with XeF(2)

The reaction between Mg(AsF(6))(2) and XeF(2) in anhydrous HF (aHF) at room temperature yields two compounds with XeF(2) bonded directly to the Mg(2+) cation: [Mg(XeF(2))(4)](AsF(6))(2); [Mg(XeF(2))(2)](AsF(6))(2). The 1:4 compound is obtained with excess XeF(2) while the 1:2 compound is prepared from stoichiometric amounts of Mg(AsF(6))(2) and XeF(2). [Mg(XeF(2))(4)](AsF(6))(2) crystallizes in an orthorhombic crystal system, space group P2(1)2(1)2(1), with a = 8.698(15) A, b = 14.517(15) A, c = 15.344(16) A, V = 1937(4) A(3), and Z = 4. The octahedral coordination sphere of Mg consists of one fluorine atom from each of the four XeF(2) molecules and two fluorine atoms from the two AsF(6) units. [Mg(XeF(2))(2)](AsF(6))(2) crystallizes in the orthorhombic crystal system, space group Pbam, with a = 8.9767(10) A, b = 15.1687(18) A, c = 5.3202(6) A, V = 724.42(14) A(3), and Z = 2. The octahedral coordination sphere consists of two fluorine atoms, one from each of the two XeF(2) molecules and four fluorine atoms from the four bridging AsF(6) units.     

Selective preparation of macroporous monoliths of conductive titanium oxides Ti(n)O(2n-1) (n = 2, 3, 4, 6)

Monolithic conductive titanium oxides Ti(n)O(2n-1) (n = 2, 3, 4, 6) with well-defined macropores have been successfully prepared as a single phase, via reduction of a macroporous TiO(2) precursor monolith using zirconium getter. Despite substantial removal of oxide ions, all the reduced monoliths retain the macropore properties of the precursor, i.e., uniform pore size distribution and pore volume. Furthermore, compared to commercial porous Ebonex (shaped conductive Ti(n)O(2n-1)), the bulk densities (1.8 g cm(-3)) are half, and the porosities (60%) are about 3 times higher. The obtained Ti(n)O(2n-1) (n = 2, 3, 4, 6) macroporous monoliths could find applications as electrodes for many electrochemical reactions.