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The ultrafast dynamics of unsubstituted spironaphthopyran (SNP) were investigated using femtosecond transient UV and visible absorption spectroscopy in three different solvents and by semi-classical nuclear dynamics simulations. The primary ring-opening of the pyran unit was found to occur in 300 fs yielding a non-planar intermediate in the first singlet excited state (S-1). Subsequent planarisation and relaxation to the product ground state proceed through barrier crossing on the S-1 potential energy surface (PES) and take place within 1.1 ps after excitation. Simulations show that more than 90% of the trajectories involving C-O bond elongation lead to the planar, open-ring product, while relaxation back to the S-0 of the closed-ring form is accompanied by C-N elongation. All ensuing spectral dynamics are ascribed to vibrational relaxation and thermalisation of the product with a time constant of 13 ps. The latter shows dependency on characteristics of the solvent with solvent relaxation kinetics playing a role. Funding Agencies|Max Planck Society

Recent advances in ultrafast electron and X-ray diffraction have pushed imaging of structural dynamics into the femtosecond time domain, that is, the fundamental time scale of atomic motion. New physics can be reached beyond the scope of traditional diffraction or reciprocal space imaging. By exploiting the high time resolution, it has been possible to directly observe the collapse of nearly innumerable possible nuclear motions to a few key reaction modes that direct chemistry. It is this reduction in dimensionality in the transition state region that makes chemistry a transferable concept, with the same class of reactions being applicable to synthetic strategies to nearly arbitrary levels of complexity. The ability to image the underlying key reaction modes has been achieved with resolution to relative changes in atomic positions to better than 0.01 Å, that is, comparable to thermal motions. We have effectively reached the fundamental space-time limit with respect to the reaction energetics and imaging the acting forces. In the process of ensemble measured structural changes, we have missed the quantum aspects of chemistry. This perspective reviews the current state of the art in imaging chemistry in action and poses the challenge to access quantum information on the dynamics. There is the possibility with the present ultrabright electron and X-ray sources, at least in principle, to do tomographic reconstruction of quantum states in the form of a Wigner function and density matrix for the vibrational, rotational, and electronic degrees of freedom. Accessing this quantum information constitutes the ultimate demand on the spatial and temporal resolution of reciprocal space imaging of chemistry. Given the much shorter wavelength and corresponding intrinsically higher spatial resolution of current electron sources over X-rays, this Perspective will focus on electrons to provide an overview of the challenge on both the theory and the experimental fronts to extract the quantum aspects of molecular dynamics.

The photochemistry of the triiodide anion has been investigated by femtosecond electron diffraction. The time-resolved signal indicates the presence of reaction products and large-amplitude coherent motion produced by participating species. To reconstruct the atomic detail of the reaction and identify the major contributors to the detected signal, we outline the approach for atomic-level reconstruction.

Because of the comparable electron scattering abilities of carbon and boron, the electron diffraction structure of the C2v-symmetric molecule closo-1,2-C2B10H12 (1), one of the building blocks of boron cluster chemistry, is not as accurate as it could be. On that basis, we have prepared the known diiodo derivative of 1, 9,12-I2-closo-1,2-C2B10H10 (2), which has the same point-group symmetry as 1 but in which the presence of iodine atoms, with their much stronger ability to scatter electrons, ensures much better structural characterization of the C2B10 icosahedral core. Furthermore, the influence on the C2B10 geometry in 2 of the antipodally positioned iodine substituents with respect to both carbon atoms has been examined using the concerted application of gas electron diffraction and quantum chemical calculations at the MP2 and density functional theory (DFT) levels. The experimental and computed molecular geometries are in good overall agreement. Molecular dynamics simulations used to obtain vibrational parameters, which are needed for analyzing the electron diffraction data, have been performed for the first time for this class of compound. According to DFT calculations at the ZORA-SO/BP86 level, the (11)B chemical shifts of the boron atoms to which the iodine substituents are bonded are dominated by spin-orbit coupling. Magnetically induced currents within 2 have been calculated and compared to those for [B12H12](2-), the latter adopting a regular icosahedral structure with Ih point-group symmetry. Similar total current strengths are found but with a certain anisotropy, suggesting that spherical aromaticity is present; electron delocalization in the plane of the hetero atoms in 2 is slightly hindered compared to that for [B12H12](2-), presumably because of the departure from ideal icosahedral symmetry.

Solid-state reactions are influenced by the spatial arrangement of the reactants and the electrostatic environment of the lattice, which may enable lattice-directed chemical dynamics. Unlike the caging imposed by an inert matrix, an active lattice participates in the reaction, however, little evidence of such lattice participation has been gathered on ultrafast timescales due to the irreversibility of solid-state chemical systems. Here, by lowering the temperature to 80 K, we have been able to study the dissociative photochemistry of the triiodide anion (I3−) in single-crystal tetra-n-butylammonium triiodide using broadband transient absorption spectroscopy. We identified the coherently formed tetraiodide radical anion (I4•−) as a reaction intermediate. Its delayed appearance after that of the primary photoproduct, diiodide radical I2•−, indicates that I4•− was formed via a secondary reaction between a dissociated iodine radical (I•) and an adjacent I3−. This chemistry occurs as a result of the intermolecular interaction determined by the crystalline arrangement and is in stark contrast with previous solution studies. Dissociative reactions in the solid state are prone to sample damage. Now, improved sample handling and measurement conditions enable the study of the dissociative reaction of a model triatomic system in the solid state on ultrafast timescales, revealing the significant impact of lattice coordination on the reaction pathway.

The molecular structures and relative ratios of the two conformers (anti and gauche) of HCCCH2ONO2 detected in the gas phase at room temperature have been determined by electron diffraction. The results are discussed on the basis of quantum chemical calculations. The molecular structures of (NO2)3CCH2C≡CCH2C(NO2)3 and (NO2)3CCH3 have been determined by X-ray diffraction. A109Ag NMR study was performed for silver trinitromethanide Ag[C(NO2)3] in various polar solvents.

Azido(difluoro)phosphane, F2PN3, is a colorless gas, which freezes to a glassy solid at ca. -120 degrees C, and the boiling point obtained by extrapolating the vapor-pressure curve is 8 degrees C. It has been characterized by IR (gas phase, Ar matrix), Raman (liquid, amorphous, and crystalline solid), and F-19, P-31, N-14, and N-15 NMR spectroscopy. The conformational properties of F2PN3 have been studied by vibrational spectroscopy, gas electron diffraction (GED), and quantum chemical calculations. An almost equimolar mixture of two conformers was identified in the gas and neat liquid phases, as well as in Ar matrix, for which the N-3 group adopts a syn and anti orientation with respect to the bisector of the FPF angle. The syn conformer was found to be slightly more stable than the anti conformer by 2.4 +/- 0.6 kJ mol(-1) (Delta H degrees) determined by gas-phase temperature-dependent IR spectroscopy, but in the crystalline state at low-temperature only the anti form is observed. The very different conformational properties of F2PN3 relative to that of the previously investigated F2PNCO are discussed, guided by a natural bond orbital (NBO) analysis of electron delocalizations and steric exchange repulsions.

The molecular and electronic structures of AsP(3) and P(4) have been investigated. Gas-phase electron diffraction studies of AsP(3) have provided r(g) bond lengths of 2.3041(12) and 2.1949(28) A for the As-P interatomic distances and the P-P interatomic distances, respectively. The gas-phase electron diffraction structure of P(4) has been redetermined and provides an updated value of 2.1994(3) A for the P-P interatomic distances, reconciling conflicting literature values. Gas-phase photoelectron spectroscopy provides experimental values for the energies of ionizations from the valence molecular orbitals of AsP(3) and P(4) and shows that electronically AsP(3) and P(4) are quite similar. Solid-state (75)As and (31)P NMR spectroscopy demonstrate the plastic nature of AsP(3) and P(4) as solids, and an extreme upfield (75)As chemical shift has been confirmed for the As atom in AsP(3). Finally, quantum chemical gauge-including magnetically induced current calculations show that AsP(3) and P(4) can accurately be described as strongly aromatic. Together these data provide a cohesive description of the molecular and electronic properties of these two tetraatomic molecules.

The improvement of a Balzers Eldigraph KD-G2 gas-phase electron diffractometer, previously operated at the University of Tubingen, is reported. The diffractometer was equipped with a state-of-the-art telefocus electron gun, and high-energy radiation-sensitive imaging plates were introduced as detector system. A differential vacuum pumping system separating the diffraction chamber from the electron source was installed. A nozzle for the evaporation of compounds in a temperature range from 25 to 400 degrees C was constructed and its functionality proven by the structure determination of quinoline. Calibration, data reduction and structure refinement using standard procedures in connection with a selection of literature-known programs are described. The gas-phase structure of quinoline was determined, discussed and compared with ab initio and solid-state X-ray diffraction results.

N,N-Dimethylaminopropylsilane H 3 Si(CH 2 ) 3 NMe 2 was synthesised by the reaction of (MeO) 3 Si(CH 2 ) 3 NMe 2 with lithium aluminium hydride. Its solid-state structure was determined by X-ray diffraction, which revealed a five-membered ring with an Si···N distance of 2.712(2) A. Investigation of the structure by gas-phase electron diffraction (GED), ab initio and density functional calculations and IR spectroscopy revealed that the situation in the gas phase is more complicated, with at least four conformers present in appreciable quantities. Infrared spectra indicated a possible Si···N interaction in the Si-H stretching region (20002200 cm -1 ), as the approach of the nitrogen atom in the five-membered ring weakens the bond to the hydrogen atom in the trans position. Simulated gas-phase IR spectra generated from ab initio calculations (MP2/TZVPP) exhibited good agreement with the experimental spectrum. A method is proposed by which the fraction of the conformer with a five-membered ring can be determined by a least-squares fit of the calculated to experimental absorption intensities. The abundance of this conformer was determined as 23.7(6)%, in good agreement with the GED value of 24(6)%. The equilibrium Si···N distance predicted by theory for the gas-phase structure was highly variable, ranging from 2.73 (MP2) to 3.15 A (HF). The value obtained by GED is 2.91(4) A, which could be confirmed by a scan of the potential-energy surface at the DF-LCCSD[T] level of theory. The nature of the weak dative bond in H 3 Si-(CH 2 ) 3 NMe 2 can be described in terms of attractive inter-electronic correlation forces (dispersion) and is also interpreted in terms of the topology of the electron density.

Joint investigation of the photo-initiated geminate recombination of triiodide in solid state using transient absorption spectroscopy and ultrafast electron diffraction provides evidence of the atomic origins of the coherent modes driven by the reaction.

CrystEngComm 18(38), 7212 - 7216(2016). doi:10.1039/C6CE01049K, Reversibility is an important issue that prevents ultrafast studies of chemical reactions in solid state due to product accumulation. Here we present an approach that makes use of spectrally-selected, post-excitation, ultrashort laser pulses to minimise photoproduct build-up, i.e. recover before destroy. We demonstrate that this method enabled us to probe the ultrafast dynamics of the ring opening reaction of spironaphthooxazine thin crystals by means of transient absorption spectroscopy. By extension, this approach should be amenable to other photochromic systems and use with structural probes., Published by RSC, London

Trifluoromethyl trifluoromethanesulfonate, CF3SO2OCF3, has been synthesised and its gas-phase structure determined from electron-diffraction data. This structural study was supported by HF, MP2 and DFT (B3LYP and B1B95) calculations, which revealed a strong dependence of the theoretical structure on the polarisation of the basis set. Infrared spectra for the gas and solid and a Raman spectrum for the liquid were obtained, and the observed bands were assigned. The experimental vibrational data, along with theoretical (B3LYP) force constants, were used to define a scaled quantum mechanical force field, which enabled reproduction of the measured frequencies with a final root-mean-square deviation of 6 cm–1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The gas-phase structure of 6,9-CSB8H12 has been determined by electron diffraction and ab initio calculations, and that of 6,9-CNB8H13 has also been calculated. The accuracy of each structure has been confirmed by 11B NMR calculations. The position of the sulfur atom is very close to that of the boron atom occupying the equivalent position in the parent molecule [B10H14](2-), reflecting the similarity of sizes of sulfur and boron atoms. The nitrogen and carbon atoms, on the other hand, lie much closer to the centers of the cages. The B8-X9-B10 angles increase from 98.7 degrees for X = S to 122.8 degrees for X = N. There are also large changes in relative lengths of bonds, with some bonds lengthening by up to 14.6 pm on introduction of a sulfur atom.

Femtosecond electron diffraction has been used to probe the photoinduced phase transition in the strongly-correlated system, Me4P[Pt(dmit)2]2, revealing molecular motions involved in this process and breaking new ground in terms of chemical complexity.

We review our work on the photoinduced dynamics of X[M(dmit)2]2 salts in the charge-separated (CS) phase from the viewpoints of both electronic structural change and lattice or molecular structural change. The driving force for the CS phase formation is a strong correlation among the charge distribution, orbital energies, and the molecular structure; this is in contrast to frequently studied charge-ordered systems such as EDOTTF2PF6, whose formation is mainly driven by the intersite Coulomb repulsion. Despite the localized nature of the structural component, the cooperativity inherent to the crystal is likely to play an important role in photoinduced phenomena. In this review, we summarize the results obtained by a series of optical pump-probe experiments on this class of materials. We have also recently extended these studies using ultrafast electron diffraction to follow the nuclear motion in one of these systems. Such information is crucial for a full understanding of the photoinduced phenomena and it is anticipated that combining the results of the optical and diffraction studies will lead to more fruitful insight than either technique can offer in isolation.

The title compound is characterized by IR (gas phase, Ar matrix), Raman (liquid, amorphous, and crystalline solid), and 19F, 31P, 14N and 15N NMR spectroscopy, as well as by quantum chemical DFT calculations.

(C(2)F(5))(2)PCl is now accessible through a significantly improved synthesis protocol starting from the technical product (C(2)F(5))(3)PF(2). (C(2)F(5))(3)PF(2) was reduced in the first step with NaBH(4) in a solvent-free reaction at 120 °C. The product, P(C(2)F(5))(3), was treated with an excess of an aqueous sodium hydroxide solution to afford the corresponding phosphinite salt Na(+)(C(2)F(5))(2)PO(-) selectively under liberation of pentafluoroethane. Subsequent chlorination with PhPCl(4) resulted in the selective formation of (C(2)F(5))(2)PCl, which was isolated by fractional condensation in an overall yield of 66 %. The gas electron diffraction (GED) pattern for (C(2)F(5))(2)PCl was recorded and found to be described by a two-conformer model. A quantum chemical investigation of the potential-energy surface revealed the possible existence of many low-energy conformers, each with a number of low-frequency vibrational modes and therefore large-amplitude motions. The conformer calculated to be most stable was also found to be most abundant by GED and comprised 61(5) % of the total. The molecular structure parameters determined by GED were in good agreement with those calculated at the MP2/TZVPP level of theory; the only significant difference was a discrepancy of about 3° in the C-P-C angle, which, for the lowest-energy conformer, was refined to 98.2(4)° and was calculated to be 94.9°.

Tautomeric properties of acetoacetyl fluoride, CH3-C(O)-CH2-C(O)-F, were studied by IR (gas phase), Raman (liquid and solid), and NMR spectroscopy (neat liquid), gas electron diffraction (GED), X-ray crystallography, and quantum chemical calculations. The keto-enol tautomer possesses a much higher vapour pressure than the diketo form and therefore the keto-enol form strongly predominates in the gas phase. In the neat liquid state the thermally unstable compound tautomerizes at low temperatures slowly to yield the diketo form. Raman and NMR spectra show equilibrium with strong predominance of the diketo tautomer (>90%) in the liquid phase. Single crystals, grown at 90 degrees C from the gas phase, contain exclusively acetoacetyl fluoride in the keto-enol form and the molecules possess a planar skeleton with overall C-S symmetry and with the O-H bond adjacent to the methyl group.

The structures of free molecules of the title compounds in the gas phase are determined by gas phase electron diffraction, photoelectron spectroscopy, and quantum chemical DFT calculations.

A series of analogous nitratomethyl compounds of carbon and silicon of the formula types Me(3)ElCH(2)ONO(2) (1a/1b), Me(2)El(CH(2)ONO(2))(2) (2a/2b), MeEl(CH(2)ONO(2))(3) (3a/3b), (CH(2))(4)El(CH(2)ONO(2))(2) (4a/4b), and (CH(2))(5)El(CH(2)ONO(2))(2) (5a/5b) were synthesized [El = C (a), Si (b); (CH(2))(4)El = (sila)cyclopentane-1,1-diyl; (CH(2))(5)El = (sila)cyclohexane-1,1-diyl]. All compounds were characterized by using NMR, IR, and Raman spectroscopy and mass spectrometry. In addition, the crystal structures of Me(2)C(CH(2)ONO(2))(2) (2a), (CH(2))(4)C(CH(2)ONO(2))(2) (4a), Me(2)Si(CH(2)ONO(2))(2) (2b), and (CH(2))(5)Si(CH(2)ONO(2))(2) (5b) were determined by single-crystal X-ray diffraction. The gas-phase structures of the C/Si analogues 1a and 1b were determined by electron diffraction and compared with the results of quantum chemical calculations at different levels of theory. The thermal stabilities of the C/Si pairs 1a/1b-5a/5b were investigated by using DSC. In addition, their friction and impact sensitivities were measured with standard BAM methods. The extreme sensitivities of the silicon compounds 1b-5b compared to those of the corresponding carbon analogues 1a-5a were discussed in terms of the structures of the C/Si analogues and possible geminal Si...O interactions.

The molecular structure of methyl methanethiosulfonate, CH 3 SO 2 SCH 3 , has been determined in the gas phase from electron-diffraction data supplemented by ab initio (HF, MP2) and density functional theory (DFT) calculations using 6-31G(d), 6-311++G(d,p), and 6-31 lG(3df,3pd) basis sets. Both experimental and theoretical data indicate that although both anti and gauche conformers are possible by rotating about the S-S bond, the preferred conformation is gauche. The barrier to internal rotation in the CSSC skeleton has been calculated using the RHF/6-31G(d), MP2/6-31G(d), and B3LYP/6-31G(d) methods as well as MP2 with a 6-31G(3df) basis set on sulfur and 6-31G(d) on C, H, and O. A 6-fold decomposition of the rotational barrier has been performed in terms of a Fourier-type expansion, enabling us to analyze the nature of the potential function, showing that the coefficients V 1 and V 2 are the dominant terms; V 1 is associated with nonbonding interactions, and V 2 is associated with hyperconjugative interactions. A natural bond orbital analysis showed that the lone pair → σ* hyperconjugative interactions favor the gauche conformation. Furthermore, the infrared spectra for the liquid and solid phases and the Raman spectrum for the liquid have been recorded, and the observed bands have been assigned to the vibrational normal modes. The experimental vibrational data, along with calculated theoretical force constants, were used to define a scaled quantum mechanical force field for the target system that enabled us to estimate the measured frequencies with a final root-mean-square deviation of 6 cm -1 .

The molecular structures of the three heterodecaboranes arachno-6,9-C2B8H14, arachno-6,9-N2B8H12, and arachno-6,9-Se2B8H10 have been determined by ab initio MO theory. In addition, the structure of arachno-6,9-C2B8H14 was experimentally determined using gas-phase electron diffraction (GED). The accuracy of all four of these structures has been confirmed by the good agreement of the (11)B chemical shifts calculated at the GIAO-MP2 level with the experimental values. A comparison of the GIAO-HF and GIAO-MP2 methods shows that for these heteroborane clusters, electron correlation effects on the computed delta((11)B) values are quite substantial and that it is necessary to go beyond the HF level in the NMR computation.

Several recent resources affirm the importance of culturally sensitive family practice and training. Two multidisciplinary anthologies are reviewed and their applications to family and couples counseling are discussed.

The syntheses of the perfluorinated alcohols (F5C6)(F3C)(2)COH (1) and (F5C6)(C5F10)COH (2) are described. Both compounds were prepared in reasonable yields (1: 65%, 2: 85%) by reacting the corresponding ketone with C6F5MgBr, followed by acidic work-up. The alcohols were characterized by NMR, vibrational spectroscopy, single-crystal X-ray diffraction, acidity measurements and gas-phase electron diffraction. A combination of appropriate 2D NMR experiments allowed the unambiguous assignment of all signals in the F-19 spin systems, of which that of 2 was especially complex. High acidity of the alcohols is indicated by acidity measurements as well as the calculated gas phase acidities. It is also supported by the crystal structure of 2, which exhibits only a single weak intermolecular hydrogen bridge with an O center dot center dot center dot O distance of 301 pm. This shows the low donor strength of the oxygen atom in the compound, which is partly compensated through formation of two intramolecular CF center dot center dot center dot H contacts of 220 and 232 pm length to the proton not involved in the hydrogen bridge. The pK(a) values in acetonitrile are 22.2 for 1 and 22.0 for 2; their calculated gas phase acidities are 1367 and 1343 kJ mol(-1) (MP2/TZVPP level).

The structure of tris(pentafluoroethyl)phosphane, P(C(2)F(5))(3), has been determined in the solid state by in situ single crystal growth and subsequent X-ray diffraction and in the gas phase by electron diffraction. The experimental structure determinations have been supported by and compared to quantum chemical calculations at different levels of theory. P(C(2)F(5))(3) prefers a conformation of C(3) symmetry with the CF(3) groups of the three C(2)F(5) units oriented to the same side of the molecule as the phosphorus lone pair of electrons, leading to an estimated Tolman cone angle of 193 degrees (solid) and 191 degrees (gas), whereas a second stable conformer of C(3) symmetry, (only 5 kJ mol(-1) higher in energy) has a smaller Tolman cone angle of 171 degrees . The structures are discussed in context with related molecules E(CF(3))(3) (E = N, P, As, Sb) as well as N(C(2)F(5))(3) and P(C(2)H(5))(3).

Eight simple models of H2 in the ground state are examined through use of Dunham's formulas, numerical integration of the vibrational Schrodinger equation, and the WBK energy condition. These models provide four examples for studying the effects of variable screening and four examples for the effects of polarization on vibration‐rotation properties. At small v, variability of the screening parameter α correlates with positive curvatures of the ΔG and Bv curves; i.e., for the four models with α =1 both curvatures are negative, while both curvatures are positive for the four cases with α variable. The dominance of the quartic potential coefficient a2 in determining near‐equilibrium ΔG and Bv curvatures is pointed out. Near dissociation, the presence of polarization causes positive curvature of these two curves. In showing this, large fictitious values of the reduced mass are employed to provide several vibrational levels very close to the dissociation limit. The Dv curves have a pronounced minimum, similar ...