Thorsten Klüner

Periodic density functional embedding theory for complete active space self-consistent field and configuration interaction calculations: Ground and excited states

We extend our recently reported embedding theory [J. Chem. Phys. 110, 7677 (1999)] to calculate not only improved descriptions of ground states, but now also localized excited states in a periodically infinite condensed phase. A local region of the solid is represented by a small cluster for which high quality quantum chemical calculations are performed. The interaction of the cluster with the extended condensed phase is taken into account by an effective embedding potential. This potential is calculated by periodic density functional theory (DFT) and is used as a one-electron operator in subsequent cluster calculations. Among a variety of benchmark calculations, we investigate a CO molecule adsorbed on a Pd(111) surface. By performing complete active space self-consistent field, configuration interaction (CI), and Moller–Plesset perturbation theory of order n (MP-n), we not only were able to obtain accurate adsorption energies via local corrections to DFT, but also vertical excitation energies for an int...

LASER-INDUCED DESORPTION OF NO FROM NIO(100) : AB INITIO CALCULATIONS OF POTENTIAL SURFACES FOR INTERMEDIATE EXCITED STATES

In order to interpret the experimental results of the state resolved UV‐laser‐induced desorption of NO from NiO(100) (rotational and vibrational populations, velocity distributions of the desorbing NO molecules, etc.), we have performed ab initio complete active space self‐consistent field (CASSCF) and configuration interaction (CI) calculations for the interaction potential between NO and the NiO(100) surface in the electronic ground state and for those excited states which are involved in the desorption process. The NiO(100)–NO distance and the tilt angle between the NO axis and the surface normal have been varied. A cluster model containing a NiO8−5‐cluster embedded in a Madelung potential has been used for representing the NiO(100) surface. The excited states which are important for the desorption process, are charge transfer states of the substrate–adsorbate system, in which one electron is transferred from the surface into the NO‐2π‐orbital. The potential curves of these excited charge transfer stat...

A complete quantum description of an ultrafast pump-probe charge transfer event in condensed phase

An ultrafast photoinduced charge transfer event in condensed phase is simulated. The interaction with the field is treated explicitly within a time-dependent framework. The description of the interaction of the system with its environment is based on the surrogate Hamiltonian method where the infinite number of degrees of freedom of the environment is approximated by a finite set of two-level modes for a limited time. This method is well suited to ultrafast events, since it is not limited by weak coupling between system and environment. Moreover, the influence of the external field on the system-bath coupling is included naturally. The surrogate Hamiltonian method is generalized to incorporate two electronic states including all possible system-bath interactions. The method is applied to a description of a pump-probe experiment where every step of the cycle is treated consistently. Dynamical variables are considered which go beyond rates of charge transfer such as the transient absorption spectrum. The pa...

ESIMS Studies and Calculations on Alkali‐Metal Adduct Ions of Ruthenium Olefin Metathesis Catalysts and Their Catalytic Activity in Metathesis Reactions

Electrospray ionization mass spectrometry (ESIMS) and subsequent tandem mass spectrometry (MS/MS) analyses were used to study some important metathesis reactions with the first-generation ruthenium catalyst 1, focusing on the ruthenium complex intermediates in the catalytic cycle. In situ cationization with alkali cations (Li(+), Na(+), K(+), and Cs(+)) using a microreactor coupled directly to the ESI ion source allowed mass spectrometric detection and characterization of the ruthenium species present in solution and particularly the catalytically active monophosphine-ruthenium intermediates present in equilibrium with the respective bisphosphine-ruthenium species in solution. Moreover, the intrinsic catalytic activity of the cationized monophosphine-ruthenium complex 1 aK(+) was directly demonstrated by gas-phase reactions with 1-butene or ethene to give the propylidene Ru species 3 aK(+) and the methylidene Ru species 4 aK(+), respectively. Ring-closing metathesis (RCM) reactions of 1,6-heptadiene (5), 1,7-octadiene (6) and 1,8-nonadiene (7) were studied in the presence of KCl and the ruthenium alkylidene intermediates 8, 9, and 10, respectively, were detected as cationized monophosphine and bisphosphine ruthenium complexes. Acyclic diene metathesis (ADMET) polymerization of 1,9-decadiene (14) and ring-opening metathesis polymerization (ROMP) of cyclooctene (18) were studied analogously, and the expected ruthenium alkylidene intermediates were directly intercepted from reaction solution and characterized unambiguously by their isotopic patterns and ESIMS/MS. ADMET polymerization was not observed for 1,5-hexadiene (22), but the formation of the intramolecularly stabilized monophosphine ruthenium complex 23 a was seen. The ratio of the signal intensities of the respective with potassium cationized monophosphine and bisphosphine alkylidene Ru species varied from [I(4a)]/[I(4)]=0.02 to [I(23a)]/[I(23)]=10.2 and proved to be a sensitive and quantitative probe for intramolecular pi-complex formation of the monophosphine-ruthenium species and of double bonds in the alkylidene chain. MS/MS spectra revealed the intrinsic metathesis catalytic activity of the potassium adduct ions of the ruthenium alkylidene intermediates 8 a, 9 a, 10 a, 15 a, and 19 a, but not 23 a by elimination of the respective cycloalkene in the second step of RCM. Computations were performed to provide information about the structures of the alkali metal adduct ions of catalyst 1 and the influence of the alkali metal ions on the energy profile in the catalytic cycle of the metathesis reaction.

The [Si(S2O7)3]2− Anion: A First Example of Octahedral Silicon Coordination by Three Chelating Inorganic Ligands

Tetravalent silicon surrounded in an octahedral environment by oxygen atoms is not frequently observed, but several compounds have been reported nevertheless. The typical textbook example is the complex [Si ACHTUNGTRENNUNG(cat.)3]2 in which cat. is 1,2-dihydroxybenzene (catechol). The complex forms when 1,2-dihydroxybenzene reacts with SiO2. [1] The silicon atom is coordinated by three chelating diolate ligands; this motif has varied with several derivatives of 1,2-dihydroxybenzene. Subsequently, octahedral oxygen coordination has also been achieved with carboxylic acids, for example, citric acid, malic acid, and salicylic acid. Furthermore, mixedligand complexes and neutral species exhibiting the [SiO6] skeleton have been reported. Compared with these numerous examples of organic ligands, the reports on purely inorganic compounds with octahedral silicon coordination are scarce. Most of the examples are complex silicates that originate from high-pressure, solid-state reactions. A remarkable example is the sodium silicate Na2[SiACHTUNGTRENNUNG(Si2O7)] with part of the silicon atoms surrounded by six monodentate disilicate groups. According to the formulation 3 1[SiACHTUNGTRENNUNG(Si2O7)6/6]2 , the [SiO6] octahedra and the disilicate anions are linked to a three-dimensional network. A similar structural feature is found for the hydrogenphosphate complex Cs2[SiACHTUNGTRENNUNG(HP2O7)2].[7] However, this compound has been prepared under ambient conditions and exhibits silicon atoms surrounded by two chelating and two monodentate HP2O7 3 ions leading to a one-dimensional heteropolyanion according to 1 1 [P ACHTUNGTRENNUNG(Si2O7)4/2]2 . Herein, we present the first example of a complex silicate anion with octahedral silicon coordination by three chelating inorganic ligands, namely, three disulfate groups (Figure 1). The tris(disulfato)silicate anion [Si ACHTUNGTRENNUNG(S2O7)3]2 is observed in the crystal structures of A2[Si ACHTUNGTRENNUNG(S2O7)3] (A=Na, Cs), which are formed in the reaction of SiCl4 with oleum at elevated temperatures in the presence of A2SO4 (A=Na, Cs). A potassium compound of the same composition was reported by Thilo and Winkler in 1969. The compound was obtained by the reaction of K2SiO3 with SO3, but unfortunately no structure determination was performed. However, the authors suggested that a complex anion with octahedrally coordinated silicon may have formed. It is very likely that this compound adopts one of the structures presented herein. In the crystal structure of Na2[SiACHTUNGTRENNUNG(S2O7)3] the silicon atom is situated at the Wyckoff site 4a of space group P212121 leading to C1 symmetry for the complex [Si ACHTUNGTRENNUNG(S2O7)3]2 anion, whereas in Cs2[Si ACHTUNGTRENNUNG(S2O7)3] all of the three crystallographically different silicon atoms are located at 2d sites of space group P3̄, so that the [Si ACHTUNGTRENNUNG(S2O7)3]2 anions have C3 symmetry in this compound. The observed O-Si-O angles do not indicate strong deviation from octahedral symmetry in either of the compounds. The Si O distances range from 175.8 to 177.4 pm (av 176.7 pm) for Na2[Si ACHTUNGTRENNUNG(S2O7)3] and from 175.8 to 176.8 pm (av 176.2 pm) for Cs2[Si ACHTUNGTRENNUNG(S2O7)3]. The mean distances of Cs2[Si ACHTUNGTRENNUNG(HP2O7)2] (av 177.1 pm) are slightly shorter than those observed for Na2[SiACHTUNGTRENNUNG(Si2O7)] (av 178.9 pm). Within the S2O7 2 groups those oxygen atoms that are [a] Dipl.-Chem. C. Logemann, Prof. Dr. T. Kl ner, Prof. Dr. M. S. Wickleder Universit t Oldenburg Institut f r Reine und Angewandte Chemie Carl von Ossietzky-Str. 9-11, 26111 Oldenburg (Germany) Fax: (+49) 441-798-3352< E-mail : mathias.wickleder@uni-oldenburg.de Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem201002619. Figure 1. Structure of the [Si ACHTUNGTRENNUNG(S2O7)3]2 ion. Selected bond lengths [pm] and angles [8] within the [SiO6] octahedron of Na2[Si ACHTUNGTRENNUNG(S2O7)3]: Si O 175.81(7), 176.61(7), 176.64(7), 176.66(7), 177.06(7), 177.40(7); O-Si-O 85.54(4)–92.68(4), 176.51(4)–177.60(4) and Cs2[Si ACHTUNGTRENNUNG(S2O7)3]: Si O 175.9(3) (3 ), 176.5(3) (3 ), 176.2(3) (3 ), 176.2(3) (3 ), 175.5(3) (3 ), 176.8(3) (3 ); O-Si-O 86.44(9)–93.41(9), 177.79(9)–178.16(9).

Surrogate Hamiltonian study of electronic relaxation in the femtosecond laser induced desorption of NO/NiO(100)

A microscopic model for electronic quenching in the photodesorption of NO from NiO(100) is developed. The quenching is caused by the interaction of the excited adsorbate–substrate complex with electron hole pairs (O 2p→Ni 3d states) in the surface. The electron hole pairs are described as a bath of two level systems which are characterized by an excitation energy and a dipole charge. The parameters are connected to estimates from photoemission spectroscopy and configuration interaction calculations. Due to the localized electronic structure of NiO a direct optical excitation mechanism can be assumed, and a reliable potential energy surface for the excited state is available. Thus a treatment of all steps in the photodesorption event from first principles becomes possible for the first time. The surrogate Hamiltonian method, which allows one to monitor convergence, is employed to calculate the desorption dynamics. Desorption probabilities of the right order of magnitude and velocities in the experimentally...

The vibrational excitation of NO desorbing from NiO(100) after UV laser irradiation: is NO− a possible intermediate species?

Abstract We report on ab initio and wave packet calculations with the intention of simulating the vibrational excitation of NO desorbing from a NiO(100) surface after laser irradiation. The influence of the electrostatic field above the singly positively charged surface on the N–O equilibrium distance of the NO − -like intermediate is investigated by Hartree–Fock calculations. It is shown that the field leads to a considerable shortening of the equilibrium bond length of NO − , whereas the equilibrium distance of the neutral NO molecule is only slightly modified. Taking this field effect into account, we are able to obtain quantitative agreement between experimental and theoretical vibrational state populations.

Laser induced desorption of NO from NiO(100): Characterization of potential energy surfaces of excited states

Abstract In order to interpret experimental results such as velocity flux distributions and rotational/vibrational populations of the state resolved UV-laser induced desorption of NO from NiO(100) ab initio calculations at the configuration interaction (CI) and complete active space self consistent field (CASSCF) levels have been performed for the electronic ground state and those excited states which are important for the desorption process. The NO NiO(100) system was described by a NiO8−5-cluster embedded in a Madelung field of point charges with NO adsorbed in the on-top position on the central Ni2+ ion. Two-dimensional potential energy surfaces for several electronic states have been calculated as a function of the NNi distance and the tilt angle of NO towards the surface normal. The excited states involved in the desorption process are charge transfer states in which one electron is transferred from the oxygen 2p-shell into the NO 2π-orbitals. The dependence of the potential energy surfaces on the NNi distance is dominated by a strong Coulomb attraction between the NO− ion formed as an intermediate and the hole created within the cluster. The angular dependence of the potentials favours an upright adsorption geometry if NO− is approaching the surface. This offers an explanation of the strong coupling between translation and rotation, which has been observed experimentally for the system NO NiO(100) , as well as the absence of such a coupling in the system NO NiO(111) .

The elusive tetrasulfate anion [S4O13](2-).

Sulfates united: the unique tetrasulfate S(4)O(13)(2-) anion was observed in the structure of (NO(2))(2)[S(4)O(13)] that forms in the reaction of N(2)O(5) with SO(3). Theoretical investigations show that the anion is a stable member of the polysulfate series [S(n)O(3n+1)](2-), which was investigated up to n=11.

Reactions with oleum under harsh conditions: characterization of the unique [M(S2O7)3]2- ions (M=Si, Ge, Sn) in A2[M(S2O7)3] (A=NH4, Ag).

The reactions of group 14 tetrachlorides MCl(4) (M=Si, Ge, Sn) with oleum (65% SO(3)) at elevated temperatures lead to the unique complex ions [M(S(2)O(7))(3)](2-), which show the central M atoms in coordination with three chelating S(2)O(7)(2-) groups. The mean distances M-O within the anions increase from 175.6(2)-177.5(2) pm (M=Si) to 186.4(4)-187.7(4) pm (M=Ge) to 201.9(2)-203.5(2) pm (M=Sn). These distances are reproduced well by DFT calculations. The same calculations show an increasing positive charge for the central M atom in the row Si, Ge, Sn, which can be interpreted as the decreasing covalency of the M-O bonds. For the silicon compound (NH(4))(2)[Si(S(2)O(7))(3)], (29)Si solid-state NMR measurements have been performed, with the results showing a signal at -215.5 ppm for (NH(4))(2)[Si(S(2)O(7))(3)], which is in very good agreement with theoretical estimations. In addition, the vibrational modes within the [MO(6)] skeleton have been monitored by Raman spectroscopy for selected examples, and are well reproduced by theory. The charge balance for the [M(S(2)O(7))(3)](2-) ions is achieved by monovalent A(+) counter ions (A=NH(4), Ag), which are implemented in the syntheses in the form of their sulfates. The sizes of the A(+) ions, that is, their coordination requirements, cause the crystallographic differences in the crystal structures, although the complex [M(S(2)O(7))(3)](2-) ions remain essentially unaffected with the different A(+) ions. Furthermore, the nature of the A(+) ions influences the thermal behavior of the compounds, which has been monitored for selected examples by thermogravimetric differential thermal analysis (DTA/TG) and XRD measurements.