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Structures of stoichiometric (La2O3)n (n = 1-6) clusters have been systematically studied by theoretical calculations. Global minimum structures for these clusters are determined by genetic algorithm based global optimizations at density functional level. The ground state structure for La6O9 was found to be highly symmetric with point group Oh and the centered oxygen atom has the coordination number as large as six, which is the same as the highest coordination number of oxygen atoms in bulk La2O3. Analysis of the binding energies shows that La6O9 has a high stability among the studied clusters. The energies of the highest occupied/lowest unoccupied molecular orbitals, vertical ionization energy, and vertical electron affinity of each cluster are provided. Electronic structure of La6O9 is discussed by analysis of the frontier molecular orbitals and unpaired spin density distributions of charged clusters. [ABSTRACT FROM AUTHOR]

The ability to activate methane differs appreciably for different transition metals, and it is attractive to find the most suitable metal for the direct conversion of methane to value-added chemicals. Herein, we performed a comparative study on the reactions of CH4 with Au2+, AuRh+ and Rh2+ cations by mass-spectrometry based experiments and DFT-based theoretical analysis. Different reactivity has been found for these cations: Au2+ has the lowest reactivity, and it can activate methane but only produce H–Au2–CH3+ without H2 release; Rh2+ has the highest reactivity, and it can produce both carbene-type Rh2–CH2+ and carbyne-type H–Rh2–CH+ with H2 release; AuRh+ also has high reactivity to produce only AuRh–CH2+ with H2, avoiding the excessive dehydrogenation of CH4. Our theoretical results demonstrate that Rh is responsible for the high reactivity, while Au leads to selectivity, which may be caused by the unique intrinsic bonding properties of the metals. [ABSTRACT FROM AUTHOR]

The side‐on‐end‐on coordination of N2 can be very important to activate and functionalize this very stable molecule. However, such coordination has rarely been reported. This study reports a gas‐phase species (a polynuclear vanadium nitride cluster anion [V5N5]−) that can capture N2 efficiently (12 %), and the quantum chemistry modelling suggests an unusual side‐on‐end‐on coordination. The cluster anions were generated by laser ablation and the reaction with N2 has been characterized by mass spectrometry, photoelectron imaging spectroscopy, and density functional theory calculations. The back‐donation interactions between the localized d–d bonding orbitals on the low‐coordinated dual metal (V) sites and the antibonding π* orbitals of N2 are the driving forces to adsorb N2 with a high binding energy (about 2.0 eV). [ABSTRACT FROM AUTHOR]

Atomic oxygen radical anion (O⋅−) represents an important type of reactive centre that exists in both chemical and biological systems. Gas‐phase atomic clusters can be studied under isolated and well controlled conditions. Studies of O⋅−‐containing clusters in the gas‐phase provide a unique strategy to interpret the chemistry of O⋅− radicals at a strictly molecular level. This review summarizes the research progresses made since 2013 for the reactivity of O⋅− radicals in the atomically precise metal oxide clusters including negatively charged, nanosized, and neutral heteronuclear metal clusters benefitting from the development of advanced experimental techniques. New electronic and geometric factors to control the reactivity and product selectivity of O⋅− radicals under dark and photo‐irradiation conditions have been revealed. The detailed mechanisms of O⋅− generation have been discussed for the reaction systems of nanosized and heteroatom‐doped metal oxide clusters. The catalytic reactions mediated by the O⋅− radicals in metal clusters have also been successfully established and the microscopic mechanisms about the dynamic generation and depletion of O⋅− radicals have been clearly understood. The studies of O⋅− containing metal oxide clusters in the gas‐phase provided new insights into the chemistry of reactive oxygen species in related condensed‐phase systems. [ABSTRACT FROM AUTHOR]

The selenoketyl (HCCSe) radical has been positively identified for the first time as a product of an electric discharge through selenophene vapor. Laser-induced fluorescence, wavelength resolved emission, and fluorescence decay studies of jet-cooled HCCSe and DCCSe have given a detailed picture of the ground and excited state. The 418–400 nm band system of the HCCSe radical is assigned as à 2Πi-X 2Πi and the available evidence suggests that the radical is linear in the ground state and quasilinear in the excited state. The fluorescence decays of some upper state rotational levels show field-free molecular quantum beats, ascribed to an internal conversion interaction with high vibrational levels of the ground state. A comparison of the molecular structures and bonding in the HCCX (X=O,S,Se) free radicals shows that nonlinear ground state HCCO is best described as the ketenyl radical (H[Single_Bond]C==C==O) with the unpaired electron on the terminal carbon atom, whereas HCCS and HCCSe have linear ground state acetylenic (H[Single_Bond]C=C[Single_Bond]X) structures with the unpaired electron on the heteroatom. On electronic excitation, B 2Π HCCO reverts to the linear acetylenic structure, and à 2Π HCCS and HCCSe become quasilinear with the allenic structure. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The B–X electronic transition of jet-cooled BS[sub 2] has been observed using laser-induced fluorescence techniques. The boron disulfide radical was produced in a pulsed electric discharge jet using a mixture of BCl[sub 3] and CS[sub 2] in high-pressure argon as the precursor. The spectrum consists of a strong 0[sub 0][sup 0] band with the [sup 2]Σ–[sup 2]Π[sub 3/2] component at 24 393.2 cm-1 and short progressions in the symmetric stretching (ν[sub 1][sup ′]=506.7 cm[sup -1]) and bending (ν[sub 2][sup ′]=303.2 cm[sup -1]) modes. A rotational analysis of both spin–orbit components of the 0[sub 0][sup 0] band gave an upper state B value of 0.093 277 9(19) cm-1 and a ground-state spin–orbit coupling constant of A=-405.163(4) cm[sup -1]. The ground-state bond length of 1.6649(2) Å increases to 1.6812(1) Å on σ[sub u]→π[sub g] electronic excitation. The B–X data have been used to further refine the Renner–Teller analysis, which is in good agreement with our previous work [J. Chem. Phys. 119, 2047 (2003)]. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The à ²A' - &Xtilde;²A' electronic spectra of jet-cooled HPCl and DPCl have been obtained for the first time using the pulsed electric discharge technique with a precursor mixture of PCl[sub 3] and H[sub 2] or D[sub 2]. From a combination of laser-induced fluorescence and wavelength resolved emission spectra, all of the vibrational frequencies in the ground and excited states of both isotopomers have been measured and vibrational force fields have been determined. Rotational analyses of the 0[sup 0, sub 0] bands of both isotopomers showed small doublet splittings characteristic of an asymmetric top molecule with a single unpaired electron. From the rotational constants and the force fields, estimated equilibrium structures were derived with r'(PH) = 1.4158(23) Å, r'(PCl) = 2.0388(23) Å, θ' = 95.02(27)°, and r'(PH) = 1.4067(20) Å, r'(PCl) = 2.0050(2) Å, and θ' = 115.53(12)°. The experimental data firmly establish that the observed spectra and those previously obtained by chemiluminescence techniques [Bramwell et al., Chem. Phys. Lett. 331, 483 (2000)] are due to the HPCl free radical. [ABSTRACT FROM AUTHOR]

The à ²Π[sub u] - &Xtilde; ²Π[sub g] electronic band system of jet-cooled boron disulfide (BS[sub 2]) has been recorded in the 760-530 nm region by laser-induced fluorescence (LIF) and wavelength resolved emission techniques. The free radical was produced in a pulsed electric discharge jet using a precursor mixture of BCl[sub 3] and CS[sub 2] in argon. The LIF spectrum consists of a long progression of strong bands involving the ν'[sub 1] (B-S stretching) mode and combinations involving 2ν'[sub 2] and 2ν'[sub 3], as well as many hot bands built on the 2¹[sub 1] band. Detailed analysis of the spectrum shows that the ground state exhibits a substantial Renner-Teller effect with ∈ = -0.2012 and a spin-orbit coupling constant of A = -413.80 cm[sup -1]. Angular momentum coupling is negligible in the excited state, which has a much smaller spin-orbit coupling constant of A = -259.15 cm[sup -1]. The vibrational frequencies of [sup 11]BS[sub 2] are ω'[sub 1] = 542.8, ω'[sub 2] = 285.0, ω'[sub 3] = 1010.5, ω'[sub 1] = 514.1, ω'[sub 2] = 309.7, and ω'[sub 3] = 1543.6 cm[sup -1]. Rotational analysis of the 0[sup 0, sub 0] band allowed a determination of the effective molecular structures as r'[sub 0](BS) = 1.6648(4) Å and r'[sub 0](BS) = 1.7127(5) Å. Ab initio methods have been used to predict the BS[sub 2] spectroscopic parameters and good agreement with experiment was found. Our present understanding of the LIF spectrum is in accord with the pioneering analysis of the absorption spectrum of matrix isolated BS[sub 2] published by Brom and Weltner [J. Mol. Spectrosc. 45, 82 (1973)] three decades ago. [ABSTRACT FROM AUTHOR]

Stretching vibrational band intensities of XH[SUB4] molecules were investigated employing four-dimensional ab initio (X=C and Sn) and effective (X=C and Si) dipole moment surfaces (DMS) in combination with the local mode potential energy surfaces. The ab initio DMS of CH[SUB4] and SnH[SUB4] calculated at the coupled cluster CCSD(T) level of theory reproduced most of the observed intensities within a factor of 1.5. The effective DMS of CH[SUB4] and SiH[SUB4] were obtained by adjusting some selected high-order terms in the ab initio DMS to fit the observed intensities. They were applied to the corresponding deuterated isotopomers yielding better results than the ab initio DMS. The intensities of the combination bands are mainly due to the interbond cross terms in the DMS for SiH[SUB4], GeH[SUB4], and SnH[SUB4], while for CH[SUB4], both diagonal and cross terms are important. The relatively strong combination band that has comparable intensity with the pure overtone was predicted at the fourth local mode manifold for SnH[SUB4]. [ABSTRACT FROM AUTHOR]

The Si–H stretching–bending overtones in SiHCl[sub 3] were investigated employing theoretically calculated potential energy surfaces (PES) and dipole moment surfaces (DMS). The coupled cluster method CCSD(T) was utilized to generate both one-dimensional (1D) and three-dimensional (3D) surfaces. An empirical 3D PES was also taken into consideration. The computed energy levels and band intensities agree reasonably well with observation for most of the bands. Comparison of CCSD(T) and density functional results for the very weak 2ν[sub 1] band shows that it is essential to calculate the DMS at a high level of quantum-chemical theory when cancellation of linear and quadratic contributions to the DMS is significant. The 3D ab initio PES yields more accurate band intensities than the empirical PES and therefore appears to be more realistic.© 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]