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We report on the characterisation of the lowest three electronic states of MgKr + , the X + 2 Σ + ground state associated with the Mg + (3s) 2 S 1 / 2 + Kr(4p) 6 1 S 0 dissociation limit and the A + 2 Π Ω (Ω = 1 / 2 , 3 / 2) and B + 2 Σ + excited states associated with the Mg + (3p) 2 P 1 / 2 , 3 / 2 + Kr(4p) 6 1 S 0 dissociation limits. The vibrational structure of the X + ground state was measured by pulsed-field-ionisation zero-kinetic-energy photoelectron spectroscopy starting from the a 3 Π 0 metastable state of MgKr generated by laser ablation of a Mg rod in a Kr supersonic beam. The vibrational assignment was derived from the isotopic structure of the spectra and the adiabatic ionisation energy of the a → X + ionising transition was determined to be 38182.4(2.0) cm − 1 . Partially rotationally resolved spectra of the A + ← X + and B + ← X + transitions were recorded by monitoring the yield of Mg + ions produced by dissociation of MgKr + using the technique of isolated-core Rydberg-dissociation spectroscopy. Analytical potential-energy functions of the X + , A + , and B + states were derived using a global model of these states that includes the spin-orbit interaction. The observation of the highest vibrational levels of the B + state and the onset of the Kr + Mg + (3p) dissociation continuum enabled the precise determination of the dissociation energies of the X + , A + and B + states of MgKr + and of the a state of MgKr. The X + , A + and B + states of MgKr + are important stepping stones to access the Rydberg states of MgKr + and the ground state of MgKr 2 + by resonant multiphoton excitation. [ABSTRACT FROM AUTHOR]

We report on the characterisation of the lowest three electronic states of MgKr + , the X + 2 Σ + ground state associated with the Mg + (3s) 2 S 1 / 2 + Kr(4p) 6 1 S 0 dissociation limit and the A + 2 Π Ω (Ω = 1 / 2 , 3 / 2) and B + 2 Σ + excited states associated with the Mg + (3p) 2 P 1 / 2 , 3 / 2 + Kr(4p) 6 1 S 0 dissociation limits. The vibrational structure of the X + ground state was measured by pulsed-field-ionisation zero-kinetic-energy photoelectron spectroscopy starting from the a 3 Π 0 metastable state of MgKr generated by laser ablation of a Mg rod in a Kr supersonic beam. The vibrational assignment was derived from the isotopic structure of the spectra and the adiabatic ionisation energy of the a → X + ionising transition was determined to be 38182.4(2.0) cm − 1 . Partially rotationally resolved spectra of the A + ← X + and B + ← X + transitions were recorded by monitoring the yield of Mg + ions produced by dissociation of MgKr + using the technique of isolated-core Rydberg-dissociation spectroscopy. Analytical potential-energy functions of the X + , A + , and B + states were derived using a global model of these states that includes the spin-orbit interaction. The observation of the highest vibrational levels of the B + state and the onset of the Kr + Mg + (3p) dissociation continuum enabled the precise determination of the dissociation energies of the X + , A + and B + states of MgKr + and of the a state of MgKr. The X + , A + and B + states of MgKr + are important stepping stones to access the Rydberg states of MgKr + and the ground state of MgKr 2 + by resonant multiphoton excitation. [ABSTRACT FROM AUTHOR]

The ionisation of molecules by attosecond XUV pulses is accompanied by complex correlated dynamics, such as the creation of coherent electron wave packets in the parent ion, their interplay with nuclear wave packets, and a correlated photoelectron moving in a multi-centred potential. Additionally, these processes are influenced by the dynamics prior to and during the ionisation. To fully understand and subsequently control the ionisation process on different time scales, a profound understanding of electron and nuclear correlation is needed. Here, we investigate the effect of nuclear–electron correlation in a correlated two-electron and one-nucleus quantum model system. Solving the time-dependent Schrödinger equation allows to monitor the correlation impact pre, during, and post-XUV ionisation. We show how an initial nuclear wave packet displaced from equilibrium influences the post-ionisation dynamics by means of momentum conservation between the target and parent ion, whilst the attosecond electron population remains largely unaffected. We calculate time-resolved photoelectron spectra and their asymmetries and demonstrate how the coupled electron–nuclear dynamics are imprinted on top of electron–electron correlation on the photoelectron properties. Finally, our findings give guidelines towards when correlation resulting effects have to be incorporated and in which instances the exact correlation treatment can be neglected.

The asymmetric-Lanczos-based equation-of-motion coupled cluster formalism to compute photoabsorption and photoionisation cross-sections of valence excited states [B.N.C. Tenorio, M.A.C. Nascimento, A.B. Rocha, and S. Coriani, J. Chem. Phys. 151 (18), 184106 (2019). doi:] has been adapted to enable the calculation of photoabsorption and photoionisation spectral signatures from inner-shell electrons of such states. Since excited-state properties depend on both the electronic character of the molecular wavefunction and on the nuclear dynamics, we computed the photoionisation spectra using both ground and excited state optimised geometries. The total cross-section profiles were generated for the first two electronically excited states of water, ammonia, ethylene, and uracil by two different methodologies: an analytic continuation procedure based on the Padé approximants and by the Stieltjes imaging procedure. A comparison with literature results, whenever available, is presented. Remarkable differences were observed between the results of the core-ionisation cross-sections of the valence excited states yielded by the two quadrature approaches, at variance from previous studies on the valence photoionisation cross-sections of ground states and of valence excited states. Their origin remains unclear. [ABSTRACT FROM AUTHOR]

The reactions of carbonyl oxide Criegee intermediates with acids proceed predominantly by an insertion mechanism. We characterise the products from one of the simplest reactions of carbonyl oxides with inorganic acids, CH2OO + hydrogen chloride, which occurs via a 1,2-insertion in the H–Cl bond. Reactions of both HCl and DCl isotopologues yield product signal at the mass of the insertion product chloro(hydroperoxy)methane and a dissociative ionisation peak at the mass of the protonated (or deuteronated) Criegee intermediate. The isotopic composition of the insertion product has been measured for reaction mixtures where both HCl isotopologues are present, and the H/D ratio of the product is consistently higher (by a factor of 1.6 ± 0.3) than that of the reactants. This isotope selectivity in the products has smaller uncertainty than the ratio of measured rate coefficients and suggests a normal (kH > kD) kinetic isotope effect in the reaction. Theoretical kinetics calculations predict a small normal kinetic isotope effect for the overall reaction (kH / kD = 1.35 at 20 Torr N2 and kH / kD = 1.2 at 1 atm N2) but predict a substantial inverse kinetic isotope effect (kD > kH) for the stabilisation fraction, in disagreement with the experimental observation. [ABSTRACT FROM AUTHOR]

It is remarkable that time delay is an experimentally measurable quantity, but time itself is not. Time delay in quantum collisions and in photoionisation/photodetachment of atomic and molecular systems is reviewed in this paper. Wigner–Eisenbud formalism of time delay in quantum collision of a wavepacket with a target is discussed. Its equivalence with Smith's formalism of time delay, based on an independent basis for time delay in terms of excess particle density in the collision zone, is demonstrated. Similarity and difference between quantum collision of an electron with a positive atomic/molecular ion and photoionisation/photodetachment of a neutral atom/molecule are discussed, and the underlying quantum dynamics involving the time-reversal symmetry between solutions with outgoing and ingoing wave boundary conditions is pointed out to interpret photoionisation/photodetachment as half-scattering. This relationship is subsequently taken advantage to extend the formalism of Wigner–Eisenbud–Smith time delay in photoionisation/photodetachment. The measurability of time delay is accounted for in terms of a self-adjoint quantum operator that characterises it, even if there is no such operator for time itself. A few illustrative examples of theoretical and experimental studies of time delay are given to indicate outstanding advances made in this field in the last two decades. [ABSTRACT FROM AUTHOR]

Photoionisation in DNA, i. e. the process of photoinduced electron removal from the chromophoric species – the nucleobases – leading to their cationic form, has been scarcely studied despite being considered to be responsible for significant damaging instances in our genetic material. In this contribution we theoretically characterise the electronic ground and excited state decay pathways of cationic DNA nucleobase cytosine+ and its epigenetic derivative 5‐methyl‐cytosine+, including the effects of dynamic electron correlation on energies and geometries of minima and conical intersections. We do this by comparing the results of XMS‐CASPT2 calculations with CASSCF estimates and we find some significant differences between the results of these two methods. In particular, including dynamic electron correlation is found to significantly reduce the barrier to access the (D1/D0) conical intersection. We find notable similarities in both cytosine and 5‐methyl‐cytosine cations, and accessible conical intersections in the vicinity of the Franck‐Condon region are found. This points towards an ultrafast depopulation of their electronic excited states. Moreover, the shape of the ground state potential energy surface strongly directs the decaying excited state population towards the cationic ground state minimum on ultrafast timescales, preventing photo‐fragmentation and thus explaining their photostability. To better compare our calculations with the available experimental data we compute the UV (ground and excited state) and IR absorptions. [ABSTRACT FROM AUTHOR]

It is a particularly challenging task in stereochemistry to determine the absolute configuration of chiral molecules, i.e. to assign to a given sample the microscopic enantiomeric structure. In recent years, Coulomb Explosion Imaging (CEI) has been shown to yield directly the absolute configuration of small molecules in the gas phase. This contribution describes the experimental basics of this approach, highlights the most significant results and discusses limitations. A short discussion on extending Coulomb Explosion Imaging beyond analytic aspects to fundamental questions of molecular chirality concludes this review.

Scientists have been developing sources of light with ever-shorter pulse durations, in order to study motion in systems ranging from a golfer’s swing to the motion of atoms within molecules. The shortest pulses produced to date are under 60 attoseconds, i.e. s. One attosecond is to one second as one second is to the age of the universe. For comparison, the classical orbital period of an electron in a hydrogen atom is 150 attoseconds. Attosecond pulses were first produced in 2001. This article describes how attosecond pulses are generated and how they are measured. Some applications of attosecond pulses are described, such as measuring the delay in photoionisation, or observing molecular dissociation dynamics. [ABSTRACT FROM PUBLISHER]

Methyl iodide (CH 3 I) is one of the most studied molecule in the field of photochemistry. This molecule has been investigated by a variety of light sources including lamps, different lasers as well as synchrotron radiation of varying intensity and wavelength. In this review, photoionisation studies of CH 3 I have been summarised for monomer (CH 3 I) and its aggregates i.e., cluster (CH 3 I) n which were excited with a range of photon energy and intensity using different sources. For the case of monomer, ionisation process follows either ionisation followed by dissociation (ladder climbing mechanism) or dissociation followed by ionisation (ladder switching mechanism) depending upon the wavelength and intensity of ionisation source. In case of CH 3 I ionisation by synchrotron radiation, singly and doubly charged molecular ions were observed depending upon the energy of photon. For ionisation using laser sources, singly and multiply charged ions were observed for laser pulses ranging from femtosecond to nanosecond duration. For the case of cluster (CH 3 I) n ionisation with laser sources, multiply charged ions were observed leading to Coulomb explosion phenomena. Lowest possible laser intensity observed to induce Coulomb explosion in CH 3 I clusters was ∼10 9 W/cm 2 using nanosecond laser pulses. Since observation of multiply charged ion at gigawatt intensity is surprising, a detailed description of experimental results has been summarised. A three stage cluster ionisation model which comprises of multiphoton ionization ignited-inverse Bremsstrahlung heating and electron ionization has been adapted to explain experimental observations and to understand nanosecond laser induced Coulomb explosion of CH 3 I clusters. [ABSTRACT FROM AUTHOR]

In this paper we explore the intermediate line region (ILR) by using the photoionisation simulations of the gas clouds present at different radial distances from the center, corresponding to the locations from BLR out to NLR in four types of AGNs. We let for the presence of dust whenever conditions allow for dust existence. All spectral shapes are taken from the recent multi-wavelength campaigns. The cloud density decreases with distance as a power law. We found that the slope of the power law density profile does not affect the line emissivity radial profiles of major emission lines: Hβ, He II, Mg II, C III, and O III. When the density of the cloud at the sublimation radius is as high as 1011.5 cm−3, the ILR should clearly be seen in the observations independently of the shape of the illuminating radiation. Moreover, our result is valid for low ionization nuclear emission regions of active galaxies.

Photo-thermo-refractive (PTR) glass is an optically transparent photosensitive multicomponent silicate glass. UV-exposure produces silver nanoclusters, and NaF nanocrystals upon heating, giving rise to permanent refractive index changes. This is the basis for the production of Bragg gratings. In this article, we present a comprehensive overview of the photo-thermo-induced effects in PTR glass. We first give a general introduction of PTR glasses and their applications. Then, we perform a thorough analysis of the mechanisms of refractive index changes starting with the photo-induced process followed by the crystal nucleation mechanism and NaF crystallisation kinetics. Finally, we concentrate on the PTR glass nanostructure and its effect on the crystallisation mechanisms and properties, finishing with the kinetics and origin of the refractive index change. Despite the fact that much is known about this septuagenarian glass and that it is already being commercially produced, a number of open problems still exist that warrant further investigation. [ABSTRACT FROM PUBLISHER]

In this study, the propagation mechanism of plasma jet and some bio-medical applications are investigated by two-dimensional numerical model. The key equations of plasma physics and chemistry related with plasma jet are firstly introduced. The simulation results suggest that the sheath forms near the dielectric tube inner surface, which results in the plasma channel to shrink in the radial direction inside the dielectric tube. The photoionisation of air species plays a crucial role in the transition from the localised discharge to streamer. The Penning ionisation increases the electric conductivity of the plasma channel and facilitates the formation of ring-shaped plasma bullet. For the plasma jet in the open air, electron-impact dissociation of H(2)O, electron neutralisation of H(2)O^+, as well as dissociation of H(2)O by O(1D) are found to be the main reactions to produce OH. For micro plasma jet, the higher ignition voltage as the tube diameter decreased is attributed to the deceasing pre-avalanche electron density inside the tube. The simulation of plasma treatment of bacteria biofilm indicates that the mean free path of charged species in µm scale permitted the plasma penetrate into the cavity of the biofilm, and the structure of the biofilm results in the non-uniform distribution of ROS and RNS. The simulation of plasma treatment of cells immersed in liquid suggests that the HO(2) generated by plasma aqueous species is the only way for superoxide to penetrate cell membrane and damage cytosolic fumarase B.

An abundance of absorption and emission lines of iron-peak species such as Fe I and Fe II can be seen in the spectra of many astrophysical objects. Thus, the accurate modelling of such spectra requires sets of high quality atomic data for these species. In this paper, we present preliminary results from the present electron-impact excitation calculations for Fe II and fine-structure resolved photoionisation calculations for Fe I employing the Dirac atomic R-matrix and Breit–Pauli R-matrix methods. For the Fe II excitation, we compare results with all existing calculations, and for the Fe I photoionisation, we present a sample of level-resolved cross-sections. The calculations and results described throughout will be of use to those requiring high quality atomic data for modelling a wide variety of astrophysical objects.

The photoelectron spectrum of water has been recorded in the vicinity of thetransition between 112000 and 116000 cm−1(13.89–14.38 eV). The high resolution allowed the observation of the rotational structure of several bands. Rotational assignments of the transitions involving the Π(080), Σ(070) and Π(060) vibronic states of theelectronic state are deduced from previous studies of theband system of H2O+and photoionisation selection rules. The transition to the Σ(030) vibronic state is tentatively assigned. [ABSTRACT FROM PUBLISHER]

In this study, the positive inception voltage of bare and dielectric‐coated stranded conductors has been researched by numerical calculations and corona cage experiments. The charge simulation method is used to calculate the potential gradient distribution of the coated stranded conductors. Then, based on the positive inception criterion, the photoionisation inception model considering the effective radiation wavelength is proposed and employed to evaluate the inception voltage of the coated stranded conductors. In addition, in the laboratory, the inception voltage test platform is build up to measure the inception voltage. The results reveal that with the increase of the coating layer thickness, the inception voltage increases. For the same thickness, the inception voltage reduces slightly with the increase of relative permittivity. The calculated values are in good agreement with experimental results of the laboratory corona cage. The conclusion lays a foundation for studying the effect of the coating layer on the corona performance. [ABSTRACT FROM AUTHOR]

The fragmentation of free tenfold protonated ubiquitin in intense 70 femtosecond pulses of 90 eV photons from the FLASH facility was investigated. Mass spectrometric investigation of the fragment cations produced after removal of many electrons revealed fragmentation predominantly into immonium ions and related ions, with yields increasing linearly with intensity. Ionization clearly triggers a localized molecular response that occurs before the excitation energy equilibrates. Consistent with this interpretation, the effect is almost unaffected by the charge state, as fragmentation of sixfold deprotonated ubiquitin leads to a very similar fragmentation pattern. Ubiquitin responds to EUV multiphoton ionization as an ensemble of small peptides. [ABSTRACT FROM AUTHOR]

To celebrate 2015 as the 'International Year of Light', this article offers a short survey of the progress made since the award of the Nobel Prize of 1999 to Professor Ahmed Zewail for his pioneering work on taking the timescale for observation of light-induced events down to the femtosecond level. Developments have included the extension of studies (i) to larger molecules, leading up to biological systems; (ii) the increased range of detection methods of transient species from the UV-Vis to the infrared region; (iii) the introduction of Raman spectroscopy to augment IR studies; (iv) examination of combination events to supplement dissociation events; (v) the interrogation of transient structures by X-ray absorption spectroscopy; (vi) the study of reactions taking place at solid surfaces. [ABSTRACT FROM AUTHOR]

On the basis of the microphysical processes of gas discharge, a mathematical physical model of the corona under damped oscillation impulses is proposed in this study. The effects of collision ionisation, drift of the charged particles, space photoionisation, attachment and recombination are all taken into account in the proposed model. The space photoionisation formula is deduced in a coaxial cylindrical geometry. The charge–voltage characteristics under damped oscillation and double exponential impulses can be computed by the proposed model. The computed results are compared with the measured ones and a better agreement is shown between them. The main difference on the charge–voltage characteristics under the two types of impulses is also investigated by the model computation and experimental measurement. [ABSTRACT FROM AUTHOR]

Corona inception can be viewed as the release of capacitive energy stored in the electric field. A new prediction method of the corona onset voltage based on electric field features and support vector machine (SVM) is proposed in this study. This method was used to predict the positive DC corona onset voltage of the rod‐plane air gap. The predicted results were compared with the experimental values and the calculated values of the existing methods. Then, the corona onset voltage of the shielding sphere used in a valve hall of ±660 kV DC converter station was measured and predicted by the SVM model and the photoionisation model. The safe values of corona inception electric field strength were obtained. By comparing the finite element numerical calculation results of the electric field strength with the safe value, it was proved that the corona would not incept on the surface of the shielding sphere under operating voltage. This method provides a new possible way to predict corona onset voltages of valve hall fittings used in HVDC transmission projects. [ABSTRACT FROM AUTHOR]

Slow pyrolysis of different biomasses (miscanthus, douglas fir and oak) was conducted in a U-shape fixed bed reactor combined to (1) on-line analysis of the vapors (primary tar) by soft photoionisation mass spectrometry (single photoionisation time-of-flight mass spectrometer, SPI-TOFMS), (2) quantitative off-line analysis of condensed vapors by GC*GC/MS-FID and (3) permanent gas analysis. The U-shape fixed bed reactor allows controlling external mass transfers, temperature of the bed, quenching char at targeted temperatures and quantifying mass balances. The mass yields in solid, condensable products and gas are studied between 200 °C and 500 °C. The soft on-line photoionisation analysis leads to a more interpretable mass spectra with few fragment ions and gives the evolution of the main markers of volatiles produced in real-time as a function of the temperature. The chemical structure of the markers analyzed on-line by SPI-TOFMS is assigned by GC*GC/FID-MS analysis. The mechanisms of hemicelluloses, cellulose and lignin pyrolysis in the complex network of biomass (including minerals catalytic effect) are discussed. [ABSTRACT FROM AUTHOR]

Helium nanodroplets, commonly regarded as the ‘nearly ideal spectroscopic matrix’, are being actively studied for more than two decades now. While they mostly serve as cold, weakly perturbing and transparent medium for high-resolution spectroscopy of embedded molecules, their intrinsic quantum properties such as microscopic superfluidity still are subject-matter of current research. This article reviews recent work on pure and doped He nanodroplets using photoionisation (PI) spectroscopy, an approach which has greatly advanced in the past years. While the notion of the ideal spectroscopic matrix mostly no longer holds in this context, PI techniques provide detailed insights into the photo-physical properties of pure and doped He nanodroplets and their relaxation dynamics following electronic excitation. Exploiting nowadays available high laser fields, even highly ionised states of matter on the nanoscale can be formed. Our particular focus lies on recent experimental progress including femtosecond time-resolved spectroscopy, photoion and electron imaging, and novel sources of highly energetic radiation. [ABSTRACT FROM PUBLISHER]

The ionisation of molecules by attosecond XUV pulses is accompanied by complex correlated dynamics, such as the creation of coherent electron wave packets in the parent ion, their interplay with nuclear wave packets, and a correlated photoelectron moving in a multi-centred potential. Additionally, these processes are influenced by the dynamics prior to and during the ionisation. To fully understand and subsequently control the ionisation process on different time scales, a profound understanding of electron and nuclear correlation is needed. Here, we investigate the effect of nuclear-electron correlation in a correlated two-electron and one-nucleus quantum model system. Solving the time-dependent Schrödinger equation allows to monitor the correlation impact pre, during, and post-XUV ionisation. We show how an initial nuclear wave packet displaced from equilibrium influences the post-ionisation dynamics by means of momentum conservation between the target and parent ion, whilst the attosecond electron population remains largely unaffected. We calculate time-resolved photoelectron spectra and their asymmetries and demonstrate how the coupled electron-nuclear dynamics are imprinted on top of electron-electron correlation on the photoelectron properties. Finally, our findings give guidelines towards when correlation resulting effects have to be incorporated and in which instances the exact correlation treatment can be neglected., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Ziems, Bruhnke, Engel and Gräfe.)

Pulsed-field-ionisation zero-kinetic-energy (PFI-ZEKE) photoelectron spectra of 132Xe2 have been measured in the range of 90100 to 108400 cm-1, where the lowest electronic states of the cation are located. A (1 + 1') resonance-enhanced two-photon excitation scheme via selected rovibrational levels of the C 0 [image omitted] state of 132Xe2 was used to resolve the rotational structure of several vibrational levels of the I(1/2u), I(3/2g), I(3/2u) and II(1/2u) electronic states. For the ground cationic state even the Ω-doubling was resolved. A vibrational progression belonging to the II(1/2g) electronic state has been observed for the first time proving that the II(1/2g) state is bound. The analysis of the rotational structure, performed in Hund's angular momentum coupling case (c), enabled the determination of the equilibrium internuclear distances and the dissociation energies of the I(1/2u), I(3/2g), I(3/2u) and II(1/2u) states of Xe [image omitted] and the corresponding adiabatic ionisation energies. [ABSTRACT FROM AUTHOR]

Abstract: Polycrystalline Ag, Ag20Au80, Ag40Au60, Ag80Au20 and Au samples were bombarded with 15keV Ar+ at 60° incidence and the resulting secondary neutral yield distribution was studied by non-resonant laser postionisation mass spectrometry. Neutral clusters containing up to 21 atoms were observed for the targets. The yield of neutral clusters, Ag m Au n−m , containing n atoms, Y n , was found to follow a power in n, i.e. Y n ∝ n −δ , where the exponent δ varied from 3.2 to 4.0. For a fixed n, the cluster yields showed a variation with number of gold atoms similar to that expected for a binomial distribution. In addition, the cluster compositions from the sputtered alloys were indicative of sputtering from a gold rich surface. [Copyright &y& Elsevier]

Abstract: Polycrystalline Cu, Cu20Au80, Cu40Au60, Cu80Au20 and Au samples were bombarded with 15keV Ar+, and the resulting secondary neutral yield distribution was studied by non-resonant laser post-ionisation mass spectrometry. Neutral clusters containing up to 15 atoms were observed for the targets. The yield of neutral clusters, Cu m Au n − m , containing n atoms, Yn , was found to follow a power in n, i.e. , where the exponent δ varied from 5.2 to 10.1. For a fixed n, the cluster yields showed a variation with number of copper atoms, m, much greater than expected for a binomial distribution suggesting that the clusters are not formed randomly above the surface and a component of preformed cluster emission occurs. In addition, the cluster compositions from the sputtered alloys were indicative of sputtering from a copper rich surface. [Copyright &y& Elsevier]

This paper describes the combined set-up of on-line chemical analysis of gas phase by single-photon ionisation/resonance enhanced multiphoton ionisation–time-of-flight mass spectrometry (SPI/REMPI-TOFMS) and on-line particle size analysis by differential electrical mobility particle spectrometry (DMS 500) for the investigation of fresh cigarette mainstream smoke. SPI is well suited for the investigation of a great variety of organic species, whereas REMPI is highly sensitive for aromatic compounds. Gas phase measurements of filtered and unfiltered smoke are possible with the SPI/REMPI-TOFMS in order to determine the influence of the presence of particles on the chemical composition of the gas phase. Initial results are shown for the characterisation and comparison of three pure Virginia tobacco research cigarettes having filter ventilations of 0%, i.e. no filter ventilation, 35% and 70% ventilation. The three cigarette types are smoked under two different smoking regimes, a standard regime using puff parameters equivalent to the conventional International Standard Organisation regime and a more intense smoking regime. For the gas phase, qualitative puff-by-puff resolved yields of three selected compounds (acetaldehyde, phenol and styrene) are shown and compared. For particulate matter, particle number, count median diameter and total surface area are illustrated on a puff-by-puff basis. Yields of the chemicals analysed, puff number and surface area are in good agreement with the intensity of the smoking regime and the dilution of smoke by filter ventilation. However, gaseous compounds are influenced differently, depending whether an absolute particle filter is present or not, i.e. they can be totally removed (phenol), partially removed (styrene) or not affected (acetaldehyde). For particle analysis, the count median diameter decreases from puff to puff and is strongly dependent on the smoking regime and ventilation rate. Thereby, 0% ventilated cigarettes smoked under the intense regime result in the smallest count median diameters of ca. 180 nm, whereas 70% ventilated cigarettes smoked with a standard regime lead to the largest values of up to 280 nm. As particle diameter increases, particle number decreases as a consequence of increasing time for particle coagulation. [ABSTRACT FROM AUTHOR]

Abstract: Two-dimensional REMPI data, obtained by recording ion mass spectra for HCl as a function of two-photon wavenumber, revealed a previously unobserved (2+ n) REMPI spectra for H35Cl and H37Cl with band origin for H35Cl at 82521.2cm−1. Analysis of the data, involving simulation calculations, relative ion-yield determinations laser-power-dependence measurements and comparison with earlier experimental and theoretical work allowed the upper state to be assigned as the g3Σ+(1), v′=0 Rydberg state with =10.26cm−1 for H35Cl. [Copyright &y& Elsevier]

The threshold photoelectron, the threshold photoelectron photoion coincidence and ion breakdown spectra of trichloroethene and tetrachloroethene have been recorded from 9-22 eV. Comparisons with the equivalent data for the three dichloroethene molecules and theoretical calculations highlight the nature of the orbitals involved during photoionisation in this energy range. The ground electronic state of [image omitted] ( [image omitted]) is bound, with excited valence states dissociating to [image omitted] ( [image omitted]) and C2HCl+ ( [image omitted]). Appearance energies suggest that C2HCl+ forms from [image omitted] by loss of two chlorine atoms, whereas [image omitted] forms from [image omitted] by loss of a Cl2 molecule. The translational kinetic energy release into [image omitted] ( [image omitted]) + Cl is determined as a function of energy. In both cases, the fraction of the available energy released into translational energy of the two products decreases as the photon energy increases. [ABSTRACT FROM AUTHOR]

Abstract: Spectra of the dications of benzene, naphthalene and azulene produced by double photoionisation of the parent compounds are presented. All the electron distributions show evidence of inner-valence Auger processes, which enhance population of low energy states of the dications. It is confirmed that the ground state of the benzene dication is a triplet, contrary to a recent theoretical prediction. The double ionisation energies of the three title molecules are determined as 24.65±0.03, 21.28±0.03 and 20.2±0.2eV, respectively. [Copyright &y& Elsevier]

Abstract: The photoabsorption spectrum of but-2-yne in the range 5.5–11eV (225–110nm) has been recorded using a synchrotron radiation source. The spectrum is dominated by three d-type Rydberg series, converging to the first ionisation energy (IE) (π−1, 9.562eV). Origins of the π3d members are 7.841, 7.977 and 8.018eV, respectively. Transitions of low intensity, arising from excitation of the π3s state (origin, ∼6.35eV) and two π3p Rydberg states (7.38 and 7.51eV, respectively) have also been identified in the spectrum. Near-threshold electron energy-loss spectra reveal valence excited triplet states at about 5.2 and 5.8eV, respectively. Electronic excitation energies for valence and Rydberg-type states have been computed using ab initio multi-reference multi-root CI methods. These studies used a triple zeta+polarisation basis set, augmented by diffuse (Rydberg) orbitals, to generate the theoretical singlet and triplet energy manifolds. The correlation of theory and experiment shows the nature of the more intense Rydberg state types, and identification of the main valence and Rydberg bands. Calculated energies for Rydberg states are close to those expected, and there is generally a good correlation between the theoretical and experimental envelopes. It was possible to generate singlet Rydberg states which relate to the 5-lowest IEs of but-2-yne; furthermore, the separation of these sequences shows that the IE order (under D3h symmetry) is: , also supported by direct calculation of the IEs by CI. The lowest valence singlet states are ππ∗, optically forbidden, and calculated to lie near 7.3 and 7.6eV. The states which contribute strongly to the observed spectrum are πσ∗ near 7.9eV having excitation, followed by several ππ∗ and πσ∗ states between 10.0 and 10.5eV; an 1E′ antisymmetric combination(2e′2e″−2e′2e″) is by far the strongest in intensity. A further group of symmetry-allowed valence states are calculated to lie near 12.3 and 12.9eV. The two lowest triplet states, both of E′ symmetry (ππ∗), have vertical excitation energies of 5.7 and 6.2eV, but are strongly bent with a trans-CCCC unit (CS and C2h). The theoretical work confirms that, on intensity grounds, valence excited states do not contribute significantly to the spectrum. CI calculations of the ionic states give the ionisation energy sequence : . Adiabatic structures for the first cation, two triplets, and a singlet (C2h) were obtained; these show shortening of C–C, and lengthening of Cce:italic>trans-CCCC, as is found with ethyne. [Copyright &y& Elsevier]

Abstract: The general purpose Monte Carlo code PENELOPE is used to calculate microdosimetric quantities including dose-weighted lineal energy spectra, which can be used to predict relative biological effect (RBE), for binary radiation therapies that utilise the photoabsorption of X-ray of high-Z materials. Spectra are calculated for Gd homogenously distributed at a concentration of 10mg/ml in water and irradiated by 70keV monoenergetic photons, around 20keV above the k-edge of Gd (50.239keV), which has been shown to give optimal dose enhancement, and for a metallic Gd surface in close proximity (within 2μm) to a sensitive component of the nucleosome, modelled as a sphere of water of 1μm diameter, for 60 and 70keV monoenergetic X-rays. X-ray interactions with homogenously distributed Gd lead to a greater population of high lineal energy electrons than in liquid water, probably due to the creation of short range Auger electrons and photoelectrons, whereas interactions with Gd outside of the sensitive volume are longer ranged increasing the population of low lineal energy electrons. The data does not support increased therapeutic advantage through increased RBE in the case of Gd bearing contrast systems where little cellular absorption of Gd occurs. Homogenously distributed Gd leads to higher lineal energies than pure water, probably due to the creation of short range, high LET Auger and photoelectrons, whereas photoelectrons that originate in Gd that are outside the sensitive volume tend to have relatively higher energies and long ranges increasing the population of low LET electrons. [Copyright &y& Elsevier]

Abstract: A complementary study of the interaction of SF5Cl in the gas phase with vacuum-UV photons and low-energy electrons from the onset of ionisation, ca. 12eV, up to 20eV is presented. The photon-induced experiments have used tunable vacuum-UV radiation from a synchrotron and threshold photoelectron photoion coincidence spectroscopy for product ion detection, the electron-induced experiments a trochoidal electron monochromator and a quadrupole mass spectrometer. The strengths and limitations of both experiments are contrasted, the main difference being the absence of state selectivity in the electron-induced study. The parent cation is not observed in either study, suggesting that its ground electronic state is repulsive following Franck–Condon vertical excitation. The fragment cations SF5 +, SF4Cl+, SF4 + and SF3 + have been observed in both studies, with reasonable agreement in their threshold appearance energies. Using a variant of threshold photoelectron photoion coincidence spectroscopy applicable when the ground state of the parent cation is repulsive, the first dissociative ionisation energy of SF5Cl is determined to be 12.3±0.2eV, leading to a value for the adiabatic ionisation energy for the SF5 radical of 9.92±0.28eV. The electron-induced experiment is sensitive to ion-pair production, and onsets for F+ and Cl+ production have been observed which are only possible energetically if the accompanying fragments are the anions SF4Cl− and SF5 −, respectively. A lower limit for the electron affinity of the SF4Cl radical of 4.88eV is determined, a value confirmed by ab initio calculations. The electron-induced experiment is very sensitive to gas impurities, and the effects of minute quantities of SF4, FCl, Cl2 and possibly SF2 in the gas sample are observed. [Copyright &y& Elsevier]

Abstract: The recently discovered emission has been investigated experimentally and theoretically, leading to the identification of two separate fluorescent dicationic transitions ( and 11Δg ←11Δu). The vertical energies of the fluorescent electronic states were directly obtained by detecting photons in coincidence with electron pairs. Their assignment was aided by the use of glass filters to isolate the spectral region of each emission and by performing highly correlated MRCI calculations at a range of geometries. The potential energy curves thus generated predict bound potential energy functions for all linear Σ and Δ states of triplet and singlet spin multiplicities, throughout the energy range studied. Dissociation onsets for different fragmentation pathways are re-evaluated by detecting ions in coincidence with electron pairs. The C+ +S+ onset is revised downwards to 36.8±0.4eV and formation is found to arise from non-statistical dissociation of a limited number of precursor states, which have been identified to be the electronically excited formed in bent structures at these internal energies. Assignments have been attempted for all fragment emissions observed by measuring quantum yields as a function of the selected spectral region. [Copyright &y& Elsevier]

Abstract: The reaction between acetylene ion and ethylene is revisited to investigate possible dynamical effects in one of the reactions, which are considered as benchmark systems for statistical models. Reactant ions are produced by photoionisation with synchrotron radiation and are selected in internal energy by a coincidence method between threshold photoelectrons and photoions. Measured absolute reaction cross-sections decrease with collision energy (0.1–1eV CM), but increase with acetylene ion vibrational energy for the three exothermic channels giving C4H5 +, C3H3 + and C2H4 + ionic products. Even though RRKM calculations are shown to fit rather well experimental results for both the bimolecular (C2H2 + +C2H4) and unimolecular (C4H6 +) systems, some experimental results clearly indicate dynamical effects in this reaction for the C2H4 + production channel, in particular the strongly backward peaked C2H4 + angular distribution. We propose an alternative model combining reaction control both by dynamics and by statistics: the first step in the reactant approach is the capture between reactants, followed by a charge transfer process controlled by dynamics. In a second step, either the two reactants separate leading to C2H4 + ionic products, or there is a rearrangement into 1,3-butadiene (C4H6 +) ion which dissociates statistically into C4H5 + +H and C3H3 + +CH3 products. Charge transfer is shown to be possible at intermediate intermolecular distances, slightly shorter than the capture distance, provided that one takes into account the charge–quadrupole interaction in addition to the ion-induced dipole interaction. This work clearly shows that a good fit of experimental data by RRKM calculations does not prove that the reaction elementary mechanism is controlled by statistics. [Copyright &y& Elsevier]

Abstract: A lamp giving 5ns pulses of 10–50eV photons at 10kHz repetition rate has been developed and used with a magnetic bottle electron time-of-flight (TOF) spectrometer to study double photoionisation of atoms and molecules. In addition to the spectra of the dications and complete electron pair energy distributions, quantum yields of double ionisation, as defined in this paper, can be determined. Electron pair energy distributions in double photoionisation of Hg, N2 and CS2 are presented as representative of results on many other atoms and molecules. Double photoionisation is found to be mainly indirect, dominated by autoionisation of intermediate monocations, for complex atoms, but mainly direct for small molecules in the valence energy range. The difference arises because superexcited states of molecular monocations decay by dissociation to singly charged products. [Copyright &y& Elsevier]

We present the status of optical field ionization soft X-ray lasers. The amplifying medium is generated by focusing a high-energy circularly polarized 30-fs 10-Hz Ti: sapphire laser system in a gaseous medium. Using xenon or krypton, strong laser emission at 41.8 and 32.8 nm, respectively, has been observed. After presenting the basis of the physics, we present recent characterization of the sources as well as dramatic improvement of their performances using the waveguiding technique. [ABSTRACT FROM PUBLISHER]

The L shell X-ray intensity ratios IL1/ILα, ILβ/ILα and ILγ/ILα for W, Au, Hg, Tl, Pb, Bi, Th and U have been measured at excitation energy of 31.635 keV. A comparison is made of the experimental results with calculated values obtained using theoretical X-ray emission rates, subshell ionization cross-sections, subshell fluorescence yields and Coster–Kronig transition probabilities. A good agreement is observed between experimental and theoretical values. [Copyright &y& Elsevier]

The photoionization dynamics of CS have been studied using high-resolution laser photoelectron spectroscopy. The photodissociation of CS2 at ~308 nm results in highly rotationally excited CS in its X1Σ+ singlet ground state, as well as in rotationally cold CS in the excited a3Π triplet state. The ground-state CS fragments are formed together with sulfur in its 3P, 1D, and 1S electronic states; triplet CS is produced in coincidence with ground-state sulfur (3P). In both channels the photoelectron spectra are dominated by Δv = 0 propensity, but transitions involving Δv = 1 and 2 are also observed. [ABSTRACT FROM AUTHOR]

This paper presents pulsed-field ionization, zero electron kinetic energy (ZEKE) photoelectron and threshold photoionization spectra of M-X(CH3)3 (M = Ga, In; X = P, As). The ZEKE spectra exhibit well-resolved vibrational structures. A comparison with B3LYP calculations shows that the spectrum of In-P(CH3)3 arises from the 1A1 ← 2E transition and the spectra of Ga-P(CH3)3 and Ga-As(CH3)3 arise from transitions of a Jahn–Teller distorted doublet state to the 1A1 state. The intensities of the 1A1–2E transition in the indium species are described with the Franck–Condon approximation, while the transitions in the gallium complexes are more complicated due to the dynamic Jahn–Teller effect. The adiabatic ionization potentials of Ga-P(CH3)3, In-P(CH3)3, and Ga-As(CH3)3 are 39 635, 38 930, and 40 322 cm–1, respectively, and the ionization threshold of In-As(CH3)3 is ~39 550 cm–1. The metal–ligand stretching frequencies are 143, 116, and 125 cm–1 for Ga+-P, In+-P, and Ga+-As, respectively, and 96 cm–1 for In-P. The intermolecular bending frequencies are 71, 65, and 42 cm–1 for Ga+-P-C, In+-P-C, and Ga+-As-C, respectively, and 47 cm–1 for In-P-C. In addition, ligand-based vibrational frequencies are determined for the CH3 wag, PC3 and AsC3 umbrella, and P-C stretching vibrations. [ABSTRACT FROM AUTHOR]

Rotationally resolved (1 + 1′), resonance-enhanced, two-photon ionization spectra of the C 0+u ← X 0+g transition of several isotopomers of Xe2 have been recorded. Rotational constants have been determined for the v′ = 14–26 levels of the C 0+u Rydberg state and the v′′ = 0 and 1 levels of the X 0+g ground state, and band origins have been determined with an absolute accuracy of 0.015 cm–1 for the transitions to the v′ = 14–26 levels of the C 0+u state of the 129Xe2, 129Xe–132Xe, and 131Xe–136Xe isotopomers. The equilibrium internuclear separation of the X 0+g ground state (Re = 4.3773(49) Å) was determined from the rotational constants of the v′′ = 0 and 1 levels. The analysis of the isotopic shifts of the band origins enabled the confirmation of the absolute numbering of the vibrational levels of the C 0+u state determined by Lipson et al. (R.H. Lipson, P.E. Larocque, and B.P. Stoicheff. J. Chem. Phys. 82, 4470 (1985)). A semiempirical interaction potential for the X 0+g ground state was derived in a nonlinear fitting procedure using the present spectroscopic results, the positions of the v′′ = 2–9 levels determined by Freeman et al. (D.E. Freeman, K. Yoshino, and Y. Tanaka. J. Chem. Phys. 61, 4880 (1974)) and experimental values for the second virial coefficient. The interaction potential is similar to previous semiempirical potentials but the dissociation energy (De = (196.1 ± 1.1) cm–1) differs from the value of 183.1 cm–1 determined in the latest ab initio calculation (P. Slavíček, R. Kalus, P. Paška, I. Odvárková, P. Hobza, and A. Malijevský. J. Chem. Phys. 119, 2102 (2003)). [ABSTRACT FROM AUTHOR]

We discuss the excitation of forbidden vibrational transitions accompanying photoionization of linear triatomic molecules. Excitation of a single quantum of the antisymmetric stretching vibration is observed for mole cules with inversion symmetry, as is the bending mode. Photoelectron spectra of the N2O+(A2Π), CO2+(C2Σg+), and CS2+(B2Σu+) states obtained over a range of ionization energies exhibit contrasting behavior for the relative intensities of the forbidden vibrations. These energy-dependent vibrational branching ratios are shown to result from an intrachannel vibronic coupling mechanism. Moreover, this intrachannel coupling can be further divided into two cases, one in which the photoionization cross section is sensitive to geometry changes, and a second case in which it is not. These different cases can be distinguished by comparing the experimental and theoretical results for all three molecules. [ABSTRACT FROM AUTHOR]

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The interaction of ionising radiation with atoms and ions is a key fundamental process. This report concentrates on studies of photoexcitation/photoionisation using laser-produced plasmas as continuum sources and synchronised laser plasma plumes to provide the absorbing atom or ion species. Examples from studies of the interaction of ionising radiation with atoms and ions ranging from few-electron atomic and ionic systems to the many-electron high atomic number actinides are reviewed and illustrate the advantages and limitations of the Dual Laser Plasma technique. [Copyright &y& Elsevier]

We present the experimental set-up developed on an undulator beam line of Super-ACO to measure on an absolute scale the photoionisation cross section of multiply-charged ions. Recent results obtained for Ba and Sm ions are presented. [Copyright &y& Elsevier]

The probabilities for transfer of vacancies from K to L shell were measured using intensity ratio of Kα and total Lx X-rays. The Kα and total Lx X-rays yields from the targets excited by 59.5 keV incident photon were obtained using a Si(Li) detector. These experimental results were compared with the theoretically calculated values using radiative and radiationless transitions. The radiative transitions of these elements were observed from the relativistic Hartree–Slater model, which was proposed by Scofield (Atom. Data Nucl. Data Tables 14 (1974) 121). The radiationless transitions were observed from the Dirac–Hartree–Slater model, which was proposed by Chen et al. (Atom. Data Nucl. Data Tables 24 (1979) 13). A fairly good agreement is found between the experimental and calculated values. [Copyright &y& Elsevier]

Aqueous carbaryl is shown to be photolysed with a low quantum yield ((2.1±0.2)×10−3 in air-saturated medium) into 1,2-naphthoquinone, 1,4-naphthoquinone, 2-hydroxy-1,4-naphthoquinone and 7-hydroxy-1,4-naphthoquinone. In acetonitrile and methanol, carbaryl is mostly photoconverted into 1-naphthol. This behaviour contrasts with those of carbamates and aryl esters that generally undergo efficient photo-Fries rearrangement. Several transient species were detected by laser-flash photolysis in water: the triplet–triplet (T–T) absorption (λmax=410 nm, kd=3.5×105 s−1), the solvated electrons (φ=0.022±0.002), the naphthoxyl radicals and a long-lived unassigned species. The mechanism of phototransformation is discussed. [Copyright &y& Elsevier]

The photochemical reactions of the three forms of nicotinic acid (pKa1=2.09 and pKa2=4.85) were studied by laser flash photolysis and product studies. Irradiation at pH=1 yielded a pulse end transient (λmax=310/440 nm) assigned to the protonated triplet. Oxygen quenching experiments showed that this triplet is involved in the formation of 2-hydroxy-nicotinic acid. No transient absorptions were detected at pH=2. Irradiation at pH>2.8 yielded a transient species (λmax=290/375 nm) assigned to the anionic triplet. We demonstrated that this latter yielded bipyridine derivatives by reaction with nicotinic acid. Photoionisation of the anionic singlet excited state was also observed. This reaction is likely to be responsible for the phototransformation occurring in oxygenated basic solutions. [Copyright &y& Elsevier]

A modified atmospheric pressure chemical ionization ion source is applied for direct analysis of volatile or low volatile organic compounds in air. The method is based on the direct introduction of the analytes in the gas phase and/or particle phase into the ion source of a commercial ion-trap mass spectrometer. Two methods are employed for the production of primary ions at atmospheric pressure, photoionization and corona discharge. It is shown that in the presence of a dopant, photoionization can be a highly efficient ionization method also for real-time analysis with detection limits for selected analytes in the lower ppt-range. Using corona discharge for the production of primary ions, which is instrumentally easier since no additional chemicals have to be added to the sample flow, we demonstrate the analytical potential of on-line atmospheric pressure chemical ionization mass spectrometry for reaction monitoring experiments. To do so, an atmospherically relevant gas phase reaction is carried out in a 500 l reaction chamber and gaseous and particulate compounds are monitored in the positive and negative ion mode of the mass spectrometer. [Copyright &y& Elsevier]

In this work, we have investigated the photoionisation of ethylene clusters in the energy range between 17 and 50 eV by following the yield of C3H5+, C4H7+, and C4H8+ product ions. The formation of these stable molecular ions, by conversion into molecular bonds of the weak van der Waals bonds between the ethylene molecules, demonstrates that photoionisation can provide a mechanism for the synthesis of complex molecules from simpler units. The possible role of the ionisation of van der Waals clusters evaporated from dust grains as a complementary mechanism for the synthesis of complex organic molecules in the interstellar medium is discussed. [Copyright &y& Elsevier]