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The dissociative double ionization of CH3I and CH2I2 irradiated with extreme ultraviolet light at hv = 100 eV is investigated by multi-electron–ion coincidence spectroscopy using a magnetic bottle type electron spectrometer. The spin–orbit state-resolved Auger electron spectra for the I 4d core-hole states, (I 4d3/2)−1 and (I 4d5/2)−1, provide clear identifications of electronic states of CH3I2+ and CH2I22+. The dominant ion species produced after the double ionization correlate with the Auger electron energy, showing that different fragmentation pathways are open depending on the electronic states populated by the Auger decay. Theoretical calculations are performed to understand the fragmentation from the doubly charged states and the observed spin–orbit specificity in the Auger decay. [ABSTRACT FROM AUTHOR]

A method for generating twisted gamma rays utilizing highly accelerated helium‐like ions is presented. These ions are excited to a predetermined state by irradiating two optical lasers and emit a photon with orbital angular momentum in the deexcitation process. Accordingly, its emission rate together with other properties such as background and photo‐ionization processes is studied. [ABSTRACT FROM AUTHOR]

Optically active small organic molecules are computationally designed using the ChemTS python library developed by Tsuda and collaborators, which utilizes a combined Monte Carlo tree search (MCTS) and recurrent neural network model. Geometry optimization and excited‐state calculations are performed for each generated molecule, following which the excitation energy and dissymmetry factors are computed to evaluate the score function in the MCTS process. Using this procedure, molecules not contained in existing databases are generated. Molecules having either high dissymmetry factors or high transition dipole strengths can be generated depending on the choice of the score function. In a single trajectory with 100,000 trials, mutually similar high‐scoring molecules are generated frequently after the initial 15,000–20,000 trials. This indicates that it is better to sample high‐scoring molecules from several trajectories having a modest number of trials each than from a single trajectory having a large number of trials. [ABSTRACT FROM AUTHOR]

Auger decay of the C2H2 double core-hole (DCH) states, including the single-site DCH (C1s-2), two-site DCH (C1s-1C1s-1), and satellite (C1s-2π-1π*+1) states, has been investigated experimentally using synchrotron radiation combined with multi-electron coincidence method, and theoretically with the assumption of the two-step sequential model for Auger decay of the DCH states. The theoretical calculations can reproduce the experimental two-dimensional Auger spectra of the C2H2 single-site DCH and satellite decays, and allow to assign the peaks appearing in the spectra in terms of sequential two-electron vacancy creations in the occupied valence orbitals. In case of the one-dimensional Auger spectrum of the C2H2 two-site DCH decay, the experimental and calculated results agree well, but assignment of peaks is difficult because the first and second Auger components overlap each other. The theoretical calculations on the Auger decay of the N2 single-site DCH state, approximately considering the effect of nuclear motion, suggest that the nuclear motion, together with the highly repulsive potential energy curves of the final states, makes an important effect on the energy distribution of the Auger electrons emitted in the second Auger decay. [ABSTRACT FROM AUTHOR]

Core vacancies created on opposite sides of a molecule operate against each other in polarizing the environment between them. Consequently, the relaxation energy associated with the simultaneous creation of these two core holes turns out to be smaller than the sum of the relaxation energies associated with each individual single core vacancy created independently. The corresponding residual, termed interatomic relaxation energy, is sensitive to the environment. In the present paper we explore how the interatomic relaxation energy depends on the length and type of carbon chains bridging two core ionized nitrile groups (-C≡N). We have uncovered several trends and discuss them with the help of simple electrostatic and quantum mechanical models. Namely, the absolute value of the interatomic relaxation energy depends strongly on the orbital hybridization in carbons being noticeably larger in conjugated chains (sp and sp2 hybridizations) possessing highly mobile electrons in delocalized π-type orbitals than in saturated chains (sp3 hybridization) where only σ bonds are available. The interatomic relaxation energy decreases monotonically with increasing chain length. The corresponding descent is determined by the energetics of the molecular bridge, in particular, by the HOMO-LUMO gap. The smallest HOMO-LUMO gap is found in molecules with the sp2-hybridized backbone. Here, the interatomic relaxation energy decreases slowest with the chain length. [ABSTRACT FROM AUTHOR]

We report on theoretical Auger electron kinetic energy distribution originated from sequential two-step Auger decays of molecular double core-hole (DCH) state, using CH4, NH3, and H2CO molecules as representative examples. For CH4 and NH3 molecules, the DCH state has an empty 1s inner-shell orbital and its Auger spectrum has two well-separated components. One is originated from the 1st Auger transition from the DCH state to the triply ionized states with one core hole and two valence holes (CVV states) and the other is originated from the 2nd Auger transition from the CVV states to quadruply valence ionized (VVVV) states. Our result on the NH3 Auger spectrum is consistent with the experimental spectrum of the DCH Auger decay observed recently [J. H. D. Eland, M. Tashiro, P. Linusson, M. Ehara, K. Ueda, and R. Feifel, Phys. Rev. Lett. 105, 213005 (2010)]. In contrast to CH4 and NH3 molecules, H2CO has four different DCH states with C1s-2, O1s-2, and C1s-1O1s-1 (singlet and triplet) configurations, and its Auger spectrum has more complicated structure compared to the Auger spectra of CH4 and NH3 molecules. In the H2CO Auger spectra, the C1s-1O1s-1 DCH → CVV Auger spectrum and the CVV → VVVV Auger spectrum overlap each other, which suggests that isolation of these Auger components may be difficult in experiment. The C1s-2 and O1s-2 DCH → CVV Auger components are separated from the other components in the H2CO Auger spectra and can be observed in experiment. Two-dimensional Auger spectrum, representing a probability of finding two Auger electrons at specific pair of energies, may be obtained by four-electron coincidence detection technique in experiment. Our calculation shows that this two-dimensional spectrum is useful in understanding contributions of CVV and VVVV states to the Auger decay of molecular DCH states. [ABSTRACT FROM AUTHOR]

We explore the potential of double core hole electron spectroscopy for chemical analysis in terms of x-ray two-photon photoelectron spectroscopy. The creation of deep single and double core vacancies induces significant reorganization of valence electrons. The corresponding relaxation energies and the interatomic relaxation energies are evaluated by complete active space self-consistent field (CASSCF) calculations. We propose a method on how to experimentally extract these quantities by the measurement of single ionization potentials (IPs) and double core hole ionization potentials (DIPs). The influence of the chemical environment on these DIPs is also discussed for states with two holes at the same atomic site and states with two holes at two different atomic sites. Electron density difference between the ground and double core hole states clearly shows the relaxations accompanying the double core hole ionization. The effect is also compared to the sensitivity of single core hole IPs arising in single core hole electron spectroscopy. We have demonstrated the method for a representative set of small molecules LiF, BeO, BF, CO, N2, C2H2, C2H4, C2H6, CO2, and N2O. The scalar relativistic effect on IPs and on DIPs are briefly addressed. [ABSTRACT FROM AUTHOR]

The R-matrix method has been used for theoretical calculation of electron collision with atoms and molecules for long years. The method was also formulated to treat photoionization process, however, its application has been mostly limited to photoionization of atoms. In this work, we implement the R-matrix method to treat molecular photoionization problem based on the UK R-matrix codes. This method can be used for diatomic as well as polyatomic molecules, with multiconfigurational description for electronic states of both target neutral molecule and product molecular ion. Test calculations were performed for valence electron photoionization of nitrogen (N2) as well as nitric oxide (NO) molecules. Calculated photoionization cross sections and asymmetry parameters agree reasonably well with the available experimental results, suggesting usefulness of the method for molecular photoionization. [ABSTRACT FROM AUTHOR]

Low-energy electron collisions with gas-phase glycine molecules have been studied using the fixed-nuclei R-matrix method based on state-averaged complete-active-space self-consistent-field orbitals. A total of 40 electronic states of neutral glycine, including 3s and 3p Rydberg excited states, are included in the R-matrix model. A large peak is observed in the A″ partial elastic cross section around 3.4 eV, which originates from the π* shape resonance. In addition, many sharp narrow peaks coming from core excited resonances are seen in the elastic and inelastic cross sections at energies above 5 eV. Although the effect of the Rydberg orbitals on the elastic cross section is insignificant, these orbitals are crucial to represent core excited resonances in the inelastic cross sections. In previous experiments on dissociative electron attachment to gas-phase glycine, noticeable product ion peaks have been observed at electron collision energies around 1–2 and 5–10 eV. The resonance positions obtained in our calculations are generally close to these experimental results. [ABSTRACT FROM AUTHOR]

The effect of spin–orbit coupling on O([sup 3]P)+O[sub 2]([sup 3]Σ[sub g][sup -]) collisions is investigated for J=0 using time-dependent wave packets. The probability of forming O[sub 3] complexes, which is important for understanding the atom exchange reaction mechanism, is calculated in two different ways. The first approach follows the standard treatment in that only the reactive ground electronic state is included. In the second approach all 27 states correlating with O([sup 3]P)+O[sub 2]([sup 3]Σ[sub g][sup -]) and the nonadiabatic transitions induced by spin–orbit coupling are taken into account; all the excited electronic states are repulsive and thus do not lead to complex formation if nonadiabatic transitions are neglected. The required nine diabatic potential energy surfaces (not including spin–orbit coupling) for the electronic states 1 [sup s]A[sup ′], 2 [sup s]A[sup ′], and [sup s]A[sup ″] (s=1, 3, and 5) are constructed by high-level electronic structure calculations in the asymptotic O+O[sub 2] channel with the O[sub 2] bond length being fixed. The two sets of calculations show that spin–orbit coupling is not an important effect. The probability for forming ozone complexes when the oxygen atom is initially in the excited fine structure state O([sup 3]P[sub j=1]) state is only 10% of that for the lowest state O([sup 3]P[sub j=2]), and it is below 1% for O([sup 3]P[sub j=0]). The single-surface calculation, with the excited states phenomenologically taken into account by a statistical factor, gives a rather accurate value for the thermally averaged complex formation rate coefficient. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Predissociation of H[sub 3] Rydberg states was investigated using the effective Hamiltonian which describes the vibronic transitions among the Rydberg states as well as the predissociation through the vibrationally excited 2s states. The motion of a Rydberg electron and the vibrations of the H[sup +][sub 3] ion core was treated simultaneously without assuming the Born-Oppenheimer approximation. We developed the effective potential for a Rydberg electron, which contains the Coulomb potential and the exchange effect. The energies and predissociation lifetimes of H[sub 3] Rydberg states were obtained by analyzing the effective Hamiltonian and compared with the available experimental values. The s and p Rydberg states with lower vibrational excitation have lifetimes between a few ps to 1 ns and show an irregular lifetime distribution with respect to the principal quantum number. In contrast, d and ƒ Rydberg states have longer lifetime, 10 ns for example. The energy level spacings of the Rydberg states obey the distribution close to the Poisson one and thus indicates these states being regular. The route of predissociation was investigated by propagating a wave packet as well as analyzing the eigenvectors of the effective Hamiltonian. We found that the energy level matching between nearby states play an important role for efficient predissociation. The present results suggest that the predissociation of the H[sub 3] molecule and the dissociative recombination of the H[sup +][sub 3] ion might be efficient under rotational excitation through inclusion of additional energy levels. [ABSTRACT FROM AUTHOR]

Abstract: We have theoretically investigated the correlation satellite spectra associated with the single-site (ss) and two-site (ts) double core–hole (DCH) states. The calculated ssDCH satellite spectra of N2 (N 1s−2) and CO (O 1s−2) reproduced the observed experimental spectra satisfactorily and provided the first detailed assignments. DCH spectroscopy using X-ray two-photon photoelectron spectroscopy (XTPPS) was examined taking account of the single core–hole (SCH) and DCH satellite spectra. The results demonstrate that in XTPPS the ssDCH satellite spectrum is separated from other SCH/tsDCH spectra, while the tsDCH states and their satellite states may be overlapped with the SCH satellite spectrum. [Copyright &y& Elsevier]

Double-core-hole (DCH) spectra have been investigated for pyrimidine, purine, the RNA/DNA nucleobases, and formamide, using the density functional theory (DFT) method. DCH spectra of formamide were also examined by the complete-active-space self-consistent-field (CASSCF) method. All possible single- and two-site DCH (ssDCH and tsDCH) states of the nucleobases were calculated. The generalized relaxation energy and interatomic generalized relaxation energy were evaluated from the energy differences between ssDCH and single-core-hole (SCH) states and between tsDCH and SCH states, respectively. The generalized relaxation energy is correlated to natural bond orbital charge, whereas the interatomic generalized relaxation energy is correlated to the interatomic distance between the core holes at two sites. The present analysis using DCH spectroscopy demonstrates that the method is useful for the chemical analysis of large molecular systems. [ABSTRACT FROM AUTHOR]

Abstract: We have investigated the K –2, K –1 L –1, and L –2 double core hole (DCH) states of the SiX4 (X=H, F, Cl, and CH3) molecules using the CASSCF and DFT methods aiming at the DCH electron spectroscopy. The Si 1s IPs and DIPs of the present molecules and the generalized relaxation energies are compared and analyzed. The values extracted from the excess relaxation energy agree well with the generalized relaxation energy. The effect of the substituents (H, F, Cl, and CH3) surrounding the central Si atom is examined. The present results illustrate that the DCH electron spectroscopy for K –2, K –1 L –1, and L –2 DCH states is useful for the chemical analysis. [Copyright &y& Elsevier]

Abstract: We have theoretically investigated the double core–hole (DCH) states of the open-shell molecules and examined the possibility of DCH spectroscopy by means of X-ray two-photon photoelectron spectroscopy (XTPPS). Energies of many DCH states were obtained by the CASSCF calculations and the generalized intra- and inter-atomic relaxation energies were evaluated. We show that XTPPS can extract these quantities by the measurement of single and double core–hole ionization potentials. We discuss the influence of chemical environment on the DCH states with two holes at the same atomic site and at two different atomic sites. [ABSTRACT FROM AUTHOR]

Abstract: Low-energy electron impact excitations of S2 molecules are studied using the fixed-nuclei R-matrix method based on state-averaged complete active space SCF orbitals. Integral cross sections are calculated for elastic electron collision as well as impact excitation of the 7 lowest excited electronic states. Also, differential cross sections are obtained for elastic collision and excitation of the and states. The integrated cross section of optically allowed excitation of the state agrees reasonably well with the available theoretical result. [Copyright &y& Elsevier]

The predissociation rates of 600 vibrationally excited H3 2sA1′ states were obtained by three-dimensional wave packet calculations. Ab initio calculations were carried out for the nonadiabatic coupling matrix elements as well as a quantum defect surface of the H3 2sA1′ state, which were represented in terms of the hyperspherical coordinates to be utilized in the wave packet study. For the 2sA1′ ground vibrational level, the estimated rate agrees well with the experimental value. The mean decay rate increases with vibrational energy, but the distribution largely scatters around the mean rate. An implication of the experiments for higher Rydberg states is given based on the analysis of the present results. [Copyright &y& Elsevier]

The Huggins band of ozone is investigated by means of exact dynamics calculations using a new (diabatic) potential energy surface for the 1B2 state. The remarkable agreement with the measured spectrum strongly suggests that the Huggins band is due to the two Cs potential wells of the 1B2 state. The vibrational assignment, based on the nodal structure of wave functions, supports the most recent experimental assignment. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This study has proposed a Hückel theory-based extrapolation scheme for estimating the highest occupied molecular orbital (HOMO)-the lowest unoccupied molecular orbital (LUMO) gap of polymers without resorting to periodic boundary condition calculations using plane wave functions with hybrid functionals. The extrapolation scheme similar to ONIOM combines pure density functional theory (DFT) using plane wave functions for polymers and hybrid DFT using Gaussian functions for oligomers. We numerically assessed the scheme for polythiophene and 380 polymers and confirmed its accuracy and efficiency for polymer screening. Therefore, this scheme can be a screening methodology to estimate HOMO-LUMO energy gaps. [ABSTRACT FROM AUTHOR]

We have calculated one-dimensional potential cuts of twenty-five singlet/triplet A′/A″ states of ozone. The calculations are performed at the multi-reference configuration interaction level of electronic structure theory with the aug-cc-pVTZ set of atomic basis functions. It is found that many triplet potentials cross the 31A′(1B2) potential, on which the fragmentation after excitation in the Huggins–Hartley band system primarily proceeds. These crossings allow the population of the three spin-forbidden product channels O(3P)+O2(a1Δg), O(3P)+O2(b1Σg+) and O(1D)+O2(X3Σg−). Possible consequences of singlet–triplet crossings for the Wulf band are also briefly discussed. [Copyright &y& Elsevier]

Elastic organic crystals have attracted considerable attention as next‐generation flexible smart materials. However, the detailed information on both molecular packing change and macroscopic mechanical crystal deformations upon applied stress is still insufficient. Herein, we report that fluorescent single crystals of 9,10‐dibromoanthracene are elastically bendable and stretchable, which allows a detailed investigation of the deformation behavior. We clearly observed a Poisson effect for the crystal, where the short axes (b and c‐axes) of the crystal are contracted upon elongation along the long axis (a‐axis). Moreover, we found that the Poisson's ratios along the b‐axis and c‐axis are largely different. Theoretical molecular simulation suggests that the tilting motion of the anthracene may be responsible for the large deformation along the c‐axis. Spatially resolved photoluminescence (PL) measurement of the bent elastic crystals reveals that the PL spectra at the outer (elongated), central (neutral), and inner (contracted) sides are different from each other. [ABSTRACT FROM AUTHOR]

Elastic organic crystals have attracted considerable attention as next‐generation flexible smart materials. However, the detailed information on both molecular packing change and macroscopic mechanical crystal deformations upon applied stress is still insufficient. Herein, we report that fluorescent single crystals of 9,10‐dibromoanthracene are elastically bendable and stretchable, which allows a detailed investigation of the deformation behavior. We clearly observed a Poisson effect for the crystal, where the short axes (b and c‐axes) of the crystal are contracted upon elongation along the long axis (a‐axis). Moreover, we found that the Poisson's ratios along the b‐axis and c‐axis are largely different. Theoretical molecular simulation suggests that the tilting motion of the anthracene may be responsible for the large deformation along the c‐axis. Spatially resolved photoluminescence (PL) measurement of the bent elastic crystals reveals that the PL spectra at the outer (elongated), central (neutral), and inner (contracted) sides are different from each other. [ABSTRACT FROM AUTHOR]

Abstract: Optical activity in inorganic colloidal materials was controlled through interactions of chiral molecules with the nanoparticle (NP) surface. An inversion of optical activity in the synthesis of mercury sulfide (HgS) NPs was demonstrated with an intrinsically chiral crystalline system in the presence of an identical chiral capping ligand. A continuous decrease in the positive first Cotton effect and an eventual reversal of CD profile were observed upon heating the aqueous solution of HgS NPs capped with N‐acetyl‐ l‐cysteine (Ac‐ l‐Cys) at 80 °C. Ac‐ l‐Cys afforded two bidentate coordination configurations with an almost mirror image of each other using the thiolate and either of carboxylate or acetyl–carbonyl groups on the HgS core. Experiment and calculation suggest that a shift in the distribution of the NP formation with energy in response to the combinations of ligand coordination structure and chiral crystalline surface is responsible for the inversion of optical activity. [ABSTRACT FROM AUTHOR]

Abstract: Optical activity in inorganic colloidal materials was controlled through interactions of chiral molecules with the nanoparticle (NP) surface. An inversion of optical activity in the synthesis of mercury sulfide (HgS) NPs was demonstrated with an intrinsically chiral crystalline system in the presence of an identical chiral capping ligand. A continuous decrease in the positive first Cotton effect and an eventual reversal of CD profile were observed upon heating the aqueous solution of HgS NPs capped with N‐acetyl‐ l‐cysteine (Ac‐ l‐Cys) at 80 °C. Ac‐ l‐Cys afforded two bidentate coordination configurations with an almost mirror image of each other using the thiolate and either of carboxylate or acetyl–carbonyl groups on the HgS core. Experiment and calculation suggest that a shift in the distribution of the NP formation with energy in response to the combinations of ligand coordination structure and chiral crystalline surface is responsible for the inversion of optical activity. [ABSTRACT FROM AUTHOR]

Theory predicts that double-core-hole (DCH) spectroscopy can provide a new powerful means of differentiating between similar chemical systems with a sensitivity not hitherto possible. Although DCH ionization on a single site in molecules was recently measured with double- and single-photon absorption, double-core holes with single vacancies on two different sites, allowing unambiguous chemical analysis, have remained elusive. Here we report that direct observation of double-core holes with single vacancies on two different sites produced via sequential two-photon absorption, using short, intense X-ray pulses from the Linac Coherent Light Source free-electron laser and compare it with theoretical modeling. The observation of DCH states, which exhibit a unique signature, and agreement with theory proves the feasibility of the method. Our findings exploit the ultrashort pulse duration of the free-electron laser to eject two core electrons on a time scale comparable to that of Auger decay and demonstrate possible future X-ray control of physical inner-shell processes. [ABSTRACT FROM AUTHOR]

We present the results of an experimental and theoretical investigation of vibrationally resolved valence shell photoionization of BF3 leading to the [image omitted] state of [image omitted], where vibronic coupling and shape resonances are known to be important. The experimental vibrational branching ratios for multiple quantum excitations of the symmetric stretching mode of the ion [image omitted] as well as for the single vibrational excitation of the asymmetric stretching mode [image omitted] are compared with the predictions of single-channel Schwinger variational calculations performed within the Chase adiabatic approximation to obtain vibrational-state specific cross sections. The presence of a shape resonance in the continuum of [image omitted] symmetry is seen to lead to significant non-Franck-Condon intrachannel vibronic coupling effects. The breakdown in the Franck-Condon approximation is due to the sensitivity to the asymmetric stretching mode of the energy of the resonance and the magnitude of the transition moment for exciting the resonance. However, there are indications that interchannel vibronic coupling effects may also be significant in this system. [ABSTRACT FROM AUTHOR]