Nonadiabatic effects in the photodetachment of ClH2(-)

The photoelectron spectra of the ClH2(-) and ClD2(-) anions have been simulated using a Franck-Condon model involving vertical excitation to the four coupled quasidiabatic potential energy surfaces that correlate with Cl(2P)+H2(1 Sigma g +). A careful analysis of the excitation process is presented. All electrostatic, spin-orbit, and Coriolis couplings in the photodetached ClH2 (ClD2) neutral are included. At a resolution of 1 meV, the resulting spectra are dominated by the bound and resonant states of the Cl...H2 and Cl...D2 van der Waals complexes, along with contributions from the associated continua. Only small differences occur between these spectra and those simulated under the assumption that each of the three electronically adiabatic Cl(2P)+H2 states can be treated separately. In particular, photodetachment to form the Cl*(2P 1/2)H2 complex leads to very low intensity of spectral features associated with Cl(2P 3/2)H2. This clearly implies that, while nonadiabatic effects do have some influence on the bound and resonance state energies of both complexes as shown recently by Garand et al. [Science 319, 72 (2008)], nonadiabatic transitions between the two complexes are extremely rare.     

Photoelectron spectroscopy and the electronic structure of the uranyl tetrachloride dianion: UO(2)Cl(4) (2-)

The uranyl tetrachloride dianion (UO(2)Cl(4) (2-)) is observed in the gas phase using electrospray ionization and investigated by photoelectron spectroscopy and relativistic quantum chemical calculations. Photoelectron spectra of UO(2)Cl(4) (2-) are obtained at various photon energies and congested spectral features are observed. The free UO(2)Cl(4) (2-) dianion is found to be highly stable with an adiabatic electron binding energy of 2.40 eV. Ab initio calculations are carried out and used to interpret the photoelectron spectra and elucidate the electronic structure of UO(2)Cl(4) (2-). The calculations show that the frontier molecular orbitals in UO(2)Cl(4) (2-) are dominated by the ligand Cl 3p orbitals, while the U-O bonding orbitals are much more stable. The electronic structure of UO(2)Cl(4) (2-) is compared with that of the recently reported UO(2)F(4) (2-) [P. D. Dau, J. Su, H. T. Liu, J. B. Liu, D. L. Huang, J. Li, and L. S. Wang, Chem. Sci. 3 1137 (2012)]. The electron binding energy of UO(2)Cl(4) (2-) is found to be 1.3 eV greater than that of UO(2)F(4) (2-). The differences in the electronic stability and electronic structure between UO(2)Cl(4) (2-) and UO(2)F(4) (2-) are discussed.     

The totally symmetric Raman stretching vibration v(Mo-Mo) of quadruple molybdenum–molybdenum bonds varies linearly with the mass of molybdenum and its ligands

The electronic (400-800nm), i.r. and Raman (20-400cm-1) spectra of several hexahalo-di(aquo)dimolybdate(II) anions, Mo2X6(H2O)22− (X=Cl, Cl/Br, Br and I) containing quadruple metal-metal bonds have been investigated. The electronic spectra of the solid compounds at 300K show intense bands in the visible region (510-580nm) assigned to the expected delta delta transitions. From the i.r. and Raman spectra the skeletal and stretching modes in these binuclear anions have been identified. The metal-metal v(MoMo) stretching vibrational wavenumbers vary linearly as a function of the total mass, including molybdenum and its ligands. From this relationship, the mass of the ligands and that of the unknown material have been determined and compared with analytical results. In conclusion, the results are in very good agreement. This revised version was published online in June 2006 with corrections to the Cover Date.     

Photoelectron imaging of Ag(-)(H2O)x and AgOH(-)(H2O)y (x=1,2, y=0-4)

The photoelectron images of Ag(-)(H(2)O)(x) (x=1,2) and AgOH(-)(H(2)O)(y) (y=0-4) are reported. The Ag(-)(H(2)O)(1,2) anionic complexes have similar characteristics to the other two coinage metal-water complexes that can be characterized as metal atomic anion solvated by water molecules with the electron mainly localized on the metal. The vibrationally well-resolved photoelectron spectrum allows the adiabatic detachment energy (ADE) and vertical detachment energy (VDE) of AgOH(-) to be determined as 1.18(2) and 1.24(2) eV, respectively. The AgOH(-) anion interacts more strongly with water molecules than the Ag(-) anion. The photoelectron spectra of Ag(-)(H(2)O)(x) and AgOH(-)(H(2)O)(y) show a gradual increase in ADE and VDE with increasing x and y due to the solvent stabilization.     

Spectroscopy of UO(2)Cl(4)(2)(-) in basic aluminum chloride-1-ethyl-3-methylimidazolium chloride

The optical absorption, emission, FT Raman, one-photon excitation, two-photon excitation, and luminescence lifetime measurements are reported for UO(2)Cl(4)(2)(-) in 40:60 AlCl(3)-EMIC (where EMIC identical with 1-ethyl-3-methylimidazolium chloride), a room-temperature ionic liquid. Comparison of the spectra with previous results from single crystals containing UO(2)Cl(4)(2)(-) allowed the characterization of four ground-state vibrational frequencies, two excited-state vibrational frequencies, and the location of eight electronic excited-state energy levels. The vibrational frequencies and electronic energy levels are found to be consistent with the UO(2)Cl(4)(2)(-) ion. Comparison of the one-photon and two-photon excitation spectra, and the relative intensities of the transitions in the emission spectrum indicate that the center of symmetry is perturbed by an interaction with the solvent.     

含有金属-金属键的双核原子簇离子体系[Mo~2Sn]^2-(n=6~9)的电子结构与电子光谱

使用SCF-CI方法研究了含有Mo-Mo单键的原子簇离子体系[Mo~2Sn](n=6~9)的电子结构及电子光谱。讨论了随n增加, 配体S, S~2, S~4对Mo-Mo键序、原子电荷的影响及其变化规律。分析了原子簇离子中的d-d相互作用能级次序及Mo-Mo, Mo-S'~t等键的性质, CI计算得到的谱带波数及强度次序与实验符合。指认分析表明, 谱带的跃迁性质是有趣的, 如第一吸收带为成键轨道之间的跃迁σ~x^2-y^2→σ~x~2(n=6~8), 同时, 对电子跃迁的性质进行了分类, 对谱带的电荷转移性质也进行了讨论。     

Near threshold Cl(-)·CH3I photodetachment: apparent 2P1/2 channel suppression and enhanced 2P3/2 channel vibrational excitation

Cl(-)·CH(3)I cluster anion photoelectron images are recorded over a range of detachment wavelengths in the immediate post threshold region. The photoelectron spectral features fall into two categories. A number of weak, photon energy dependent transitions are observed and attributed to atomic anion fragmentation products. Several more intense, higher electron binding energy transitions result from single photon cluster anion detachment. Comparison with I(-)·CH(3)I suggests that the detachment process is more complicated for Cl(-)·CH(3)I. The single photon transition spacing is consistent with CH(3)I ν(3) mode excitation, but the two distinct vibronic bands of I(-)·CH(3)I detachment are not easily distinguished in the Cl(-)·CH(3)I spectra. Similarly, while the spectral intensities for both cluster anions show non-Franck Condon behavior, the level of vibrational excitation appears greater for Cl(-)·CH(3)I detachment. These observations are discussed in terms of low lying electronic states of CH(3)I along the C-I coordinate, and the influence of the CH(3)I moiety on the neutral halogen atom states.     

PFI-ZEKE photoelectron spectra of the methane cation and the dynamic Jahn-Teller effect

High resolution pulsed-field-ionization (PFI) zero-kinetic-energy (ZEKE) photoelectron spectroscopy has been used to record the photoelectron spectra of CH4, CDH3, CD2H2 and CD4. The observed extensive progression of rotationally resolved transitions between 100,800 cm-1 and 104,100 cm-1 reveals for the first time the complex energy level structure of the methane cation. The high resolution enabled the determination of accurate values for the adiabatic ionization potentials of the different isotopomers. Based on a simple one-dimensional model for the pseudorotation in the different isotopomers, progress has been made towards the understanding of the Jahn-Teller effect at low energies. The static Jahn-Teller distortion in the ion could be determined directly from the vibrationless photoelectron transition in CD2H2. The analysis of the rotational structure in this spectrum with a rigid rotor model leads to an approximate experimental C2v structure. The dynamics of the other methane isotopomers near the adiabatic ionization potentials is dominated by large amplitude vibrational motions between equivalent structures. The corresponding ground state tunneling motions takes place on a picosecond time scale.     

Crystal structure and physical properties of conducting molecular antiferromagnets with a halogen-substituted donor: (EDO-TTFBr2)2FeX4 (X = Cl, Br)

The crystal structure and physical properties of radical ion salts (EDO-TTFBr2)2FeX4 (X = Cl, Br) based on halogen-substituted organic donor and magnetic anions are investigated, including the comparison with the isomorphous compounds (EDO-TTFBr2)2GaX4 with nonmagnetic anions. The crystal structure of these four salts consists of uniformly stacked donor molecules and tetrahedral counter anions, and the Br substituents of the donor molecules are connected to halide ligands of anions with remarkably short intermolecular atomic distances. These salts show metallic behavior around room temperature and undergo a spin-density-wave transition in the low-temperature range, as confirmed with the divergence of the electron spin resonance (ESR) line width. Although close anion-anion contacts are absent in these salts, the FeCl4 salt undergoes an antiferromagnetic transition at TN = 4.2 K, and the FeBr4 salt shows successive magnetic transitions at TN = 13.5 K and TC2 = 8.5 K with a helical spin structure as a candidate for the ground state of the d-electron spins. The magnetoresistance of the FeCl4 salt shows stepwise anomalies, which are explained qualitatively using a pi-d interaction-based frustrated spin system model composed of the donor pi-electron and the anion d-electron spins. Although on the ESR spectra of the FeX4 salts signals from the pi- and d-electron spins are separately observed, the line width of the pi-electron spins broadens under the temperature where the susceptibility deviates from the Curie-Weiss behavior, showing the presence of the pi-d interaction.     

链状三核异金属簇阴离子［Cl_2FeS_2M＇（PPh_3）_2］~－（M＝Mo

在５５０～９０ｃｍ~（－１）波数范围内，测量簇阴离子［Ｃｌ_２ＦｅＳ_２ＭＳ_２Ｍ′（ＰＰｈ_３）_２］~－（Ｍ＝Ｍｏ，Ｍ′＝Ａｇ；Ｍ＝Ｗ，Ｍ′＝Ｃｕ，Ａｇ）的付里叶变换红外光谱，并对标题簇阴离子［Ｃｌ_２ＦｅＳ_２ＷＳ_２Ｃｕ（ＰＰｈ_３）_２］~－，［Ｃｌ_２ＦｅＳ_２ＭｏＳ_２Ａｇ（ＰＰｈ_３）_２］~－和［Ｃｌ_２ＦｅＳ_２ＷＳ_２Ａｇ（ＰＰｈ_３）_２］~－骨架的振动光谱给予经验指认。同时采用＂诱导自洽方法计算振动力常数＂程序，对簇骨架［Ｃｌ_２ＦｅＳ_２ＭＳ_２Ｍ~′Ｐ_２］进行简正坐标分析。振动频率的计算值与观测值符合良好，两者平均偏差小于１．０％，计算结果支持了振动谱带的归属并表明计算力常数的合理性。文中还讨论了主要价键振动频率的变化规律。     

Probing the structural and electronic properties of Ag(n)H(-) (n = 1-3) using photoelectron imaging and theoretical calculations

Structural and electronic properties of silver hydride cluster anions (Ag(n)H(-); n = 1-3) have been explored by combining the negative ion photoelectron imaging spectroscopy and theoretical calculations. The photoelectron spectrum of AgH(-) exhibits transitions from AgH(- 2)Σ(+) to AgH (1)Σ(+) and AgH (3)Σ(+), with the electron affinity (EA) 0.57(3) eV. For Ag(2)H(-), the only observed transition is from Ag(2)H(-) (C(∞v)) (1)Σ(+) to Ag(2)H (C(2v)) (2)A(') and the electron affinity is 2.56(5) eV. Two obvious electron bands are observed in photoelectron imaging of Ag(3)H(-), which are assigned to the transitions from Ag(3)H(-) (C(2v)-T, which means C(2v) geometry with top site hydrogen) (2)B(2) to Ag(3)H (C(2v)-T) (1)A(1) and Ag(3)H (C(2v)-T) (3)B(2). The electron affinity is determined to be 1.61(9) eV. The Ag-H stretching modes in the ground states of AgH and Ag(2)H are experimentally resolved and their frequencies are measured to be 1710(80) and 1650(100) cm(-1), respectively. Aside from the above EAs and the vibrational frequencies, the vertical detachment energies to all ground states and some excited states of Ag(n)H (n = 1-3) are also obtained. Theoretical calculations reproduce the experimental energies quite well, and the results are used to assign the geometries and electronic states for all related species.     

On the origins of core-electron chemical shifts of small biomolecules in aqueous solution: insights from photoemission and ab initio calculations of glycine(aq)

The local electronic structure of glycine in neutral, basic, and acidic aqueous solution is studied experimentally by X-ray photoelectron spectroscopy and theoretically by molecular dynamics simulations accompanied by first-principle electronic structure and spectrum calculations. Measured and computed nitrogen and carbon 1s binding energies are assigned to different local atomic environments, which are shown to be sensitive to the protonation/deprotonation of the amino and carboxyl functional groups at different pH values. We report the first accurate computation of core-level chemical shifts of an aqueous solute in various protonation states and explicitly show how the distributions of photoelectron binding energies (core-level peak widths) are related to the details of the hydrogen bond configurations, i.e. the geometries of the water solvation shell and the associated electronic screening. The comparison between the experiments and calculations further enables the separation of protonation-induced (covalent) and solvent-induced (electrostatic) screening contributions to the chemical shifts in the aqueous phase. The present core-level line shape analysis facilitates an accurate interpretation of photoelectron spectra from larger biomolecular solutes than glycine.     

Relaxation of (CS2)2(-) to its global minimum mediated by water molecules: photoelectron imaging study

The coexistence of several isomers of (CS 2) 2 (-) is examined via photoelectron imaging at 355 and 266 nm. Assisted by theoretical calculations, the bands in the photoelectron spectra are assigned to the CS 2 (-).CS 2 ion-molecule complex ( C s symmetry, (2)A' electronic state) and two covalently bound dimer-anion structures: C 2 v ( (2)B 1) and D 2 h ( (2)B 3g). The isomer distribution depends sensitively on the ion source conditions, particularly the presence of water in the precursor gas mixture. The intensity variation of the photoelectron bands suggests that the presence of water enhances the formation of the global-minimum C 2 v ( (2)B 1) structure, particularly relative to the metastable (local-minimum) ion-molecule complex. This trend is rationalized with two assumptions. The first is that the presence of H 2O at the cluster formation stage facilitates the nonadiabatic transitions necessary for reaching the global-minimum dimer-anion equilibrium when starting from the CS 2 (-) + CS 2 asymptote. The second is that the initial clusters formed in the presence of water tend to have, on average, more internal energy, which is needed for overcoming the potential energy barriers separating the metastable equilibria from the global-minimum structure. As the covalent bonds are formed, excess solvent molecules are evaporated from the cluster, giving rise to stable (CS 2) 2 (-) dimer anions. In the (CS 2) n (-), n >or= 3, and (CS 2) 2 (-)(H 2O) m , m > 0, clusters, the population of the covalent-dimer core structures diminishes drastically due to more favorable solvent interactions with the monomer-anion (i.e., CS 2 (-)) core.     

Photoelectron imaging and theoretical studies of silver monohalides AgX- (X = Cl, Br, I) and AuCl-

Photodetachment of AgX(-) (X = Cl, Br, I) and AuCl(-) is studied by a photoelectron velocity map imaging technique and theoretical calculations. Photoelectron spectra (PES) and photoelectron angular distributions (PADs) were obtained. The vibrationally resolved spectra provided approximately equal electron affinities (EAs) for AgX: 1.593(22) eV for AgCl, 1.623(21) eV for AgBr, and 1.603(22) eV for AgI, respectively. Franck-Condon simulations of these spectra gave the equilibrium bond lengths and vibrational frequencies of the title anions. Relativistic density functional theory (DFT) calculations using BLYP, PW91, PBE, and BP86 functionals have been performed to predict the EAs of the AgX (X = Cl, Br, I) molecules. The computed EAs at the BP86 level of theory are in good agreement with the experimental values. Energy partitioning analyses (EPA) at the BP86(ZORA)/QZ4P level of theory of both anions and their neutrals were reported.     

Effects of solvation and core switching on the photoelectron angular distributions from (CO2)n(-) and (CO2)(n)(-).H2O

Photoelectron images are recorded in the photodetachment of two series of cluster anions, (CO(2))(n)(-), n=4-9 and (CO(2))(n)(-).H(2)O, n=2-7, with linearly polarized 400 nm light. The energetics of the observed photodetachment bands compare well with previous studies, showing evidence for switching between two anionic core structures: The CO(2)(-) monomer and covalent (CO(2))(2)(-) dimer anions. The systematic study of photoelectron angular distributions (PADs) sheds light on the electronic structure of the different core anions and indicates that solvation by several CO(2) molecules and/or one water molecule has only moderate effect on the excess-electron orbitals. The observed PAD character is reconciled with the symmetry properties of the parent molecular orbitals. The most intriguing result concerns the PADs showing remarkable similarities between the monomer and dimer anion cluster-core types. This observation is explained by treating the highest-occupied molecular orbital of the covalent dimer anion as a linear combination of two spatially separated monomeric orbitals.     

Ab initio study of the spectroscopy of (CH3)(3)CN and (CH3)(2)CHN

Using the complete active space self-consistent field (CASSCF) method with 6-311++g(3df,3pd) basis sets, a few electronic states of nitrenes (CH3)3CN and (CH3)2CHN and their positive ions are calculated. All calculated states are valence states, and their characteristics are discussed in detail. In order to investigate the Jahn-Teller effect on (CH3)3CN radical, Cs symmetry was used for (CH3)3CN and (CH3)2CHN in the calculations. The results of our calculations (CASPT2 adiabatic excitation energies and RASSI oscillator strengths) suggest that the calculated transitions of (CH3)3CN at 27,710 cm(-1) and (CH3)2CHN at 28,110 cm(-1) are attributed to 23A' --> 13A', while those of (CH3)3CN at 28,916 cm(-1) and (CH3)2CHN at 29,316 cm(-1) are attributed to 13A' --> 13A'. The vertical and adiabatic ionization energies were obtained to compare with the photoelectron spectroscopic data. These results are in agreement with previous experimental data. Also, we present a comprehensive review on the CAS calculation results for (CH3)nCH(3-n)N (n = 0-3) presented in our previous and present papers.     

Low energy electron energy-loss spectroscopy of CF3X (X=Cl,Br)

We report threshold electron energy-loss spectra for the fluorohalomethanes CF3X (X=Cl,Br). Measurements were made at incident electron energies of 30 and 100 eV in energy-loss range of 4-14 eV, and at scattering angles of 4 degrees and 15 degrees. Several new electronic transitions are observed which are ascribable to excitation of low-lying states as well as are intrinsically overlapped in the molecules themselves. Assignments of these electronic transitions are suggested. These assignments are based on present spectroscopic and cross-section measurements, high-energy scattering spectra, and ab initio molecular orbital calculations. The calculated potential curves along the C-X bond show repulsive nature, suggesting that these transitions may lead to dissociation of the C-X bond. The present results are also compared with the previous ones for CF3H, CF4, and CF3I.     

Outermost and inner-shell electronic properties of ClC(O)SCH2CH3 studied using HeI photoelectron spectroscopy and synchrotron radiation

A study of valence electronic properties of S-ethyl chlorothioformate (S-ethyl chloromethanethioate), ClC(O)SCH(2)CH(3), using HeI photoelectron spectra (PES) and synchrotron radiation is presented. Moreover, the photon impact excitation and dissociation dynamics of ClC(O)SCH(2)CH(3) excited at the S 2p and Cl 2p levels are elucidated by analyzing the total ion yield (TIY) spectra and time-of-flight mass spectra acquired in multicoincidence mode [photoelectron-photoion coincidence (PEPICO) and photoelectron-photoion-photoion coincidence (PEPIPICO)]. The HeI photoelectron spectrum is dominated by features associated with lone-pair electrons from the ClC(O)S- group, the HOMO at 9.84 eV being assigned to the n(π)(S) sulfur lone-pair orbital. Whereas the formation of C(2)H(5)(+) ion dominates the fragmentation in the valence energy region, the most abundant ion formed in both the S and Cl 2p energy ranges is C(2)H(3)(+). Comparison with related XC(O)SR (X = H, F, Cl and R = -CH(3), -C(2)H(5)) species reveals the impact of the alkyl chain on the photodissociation behavior of S-alkyl (halo)thioformates.