The kinetics of the two-photon ionization of N,N,N′,N′-tetramethylbenzidine (TMB) in dichloromethane (CH2Cl2)-doped solid argon using 254 nm high-pressure Hg-lamp radiation is investigated by means of UV/VIS absorption spectroscopy. The experimental findings, especially the incomplete running of the ionization reaction, can be quantitatively understood on the basis of a kinetic model which includes dissociative electron attachment to CH2Cl2 and associative photodetachment of the corresponding radical anion. The model implies that the underlying electron transfer reactions reach the photoequilibrium TMB+CH2Cl2⇌hν2hνTMB•++ClHCH•⋯Cl−. The ionization cross-section of TMB in the lowest triplet state, the cross-section of associative photodetachment and the rate constant of cation electron recombination are obtained by adapting calculated to measured irradiation time dependent concentrations of the radical cation.

The kinetics of the two-photon ionization (TPI) of N,N,N′,N′-tetramethylbenzidine (TMB) in CH2Cl2-doped solid argon using 313 nm Hg lamp radiation is investigated by means of ultraviolet/visible (UV/VIS) absorption spectroscopy. The experimental findings can be quantitatively understood on the basis of a rate equation model. The ionization cross-section of TMB in the lowest triplet state and the rate constant of cation–electron recombination are obtained by adapting calculated to measured irradiation time-dependent concentrations of the cation.

Persistent contact ion pairs (CIPs) have been obtained by one-photon-induced electron transfer from N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) to tetrachloromethane (CCl4) in solid argon, in addition to TMPD⋅+ free radical cations (FRCs) generated by two-photon ionization of TMPD as the primary process. The first UV/VIS absorption band of the CIPs is tentatively explained on the basis of the corresponding band of the FRCs.

A preceding study on persistent contact ion pairs (CIPs) which had been produced by Hg lamp irradiation of solid argon doped with N,N,N′,N′-tetramethyl-p-phenylenediamine and tetrachloromethane is extended to N,N,N′,N′-tetramethylbenzidine as a further donor and xenon as an additional solid medium. Experimental and theoretical ultraviolet/visible absorption spectroscopic and photokinetic investigations as well as energetic considerations lead to a more detailed understanding of the formation and properties of the CIPs.

Fluorescence spectroscopic studies have been performed on the radical cations of tetrathiafulvalene (TTF), 4,4′-dimethyl-5,5′-diphenyltetrathiafulvalene (DMDP–TTF), bis-(4,5-dihydronaphtho-[1,2d]-tetrathiafulvalene) (BDHN–TTF) and bis-(ethylenedithio)-tetrathiafulvalene (BEDT–TTF) in low-temperature organic glasses. For the first time emission and excitation spectra have been obtained for radical cations of this class of compounds. Only in the case of BEDT–TTF·+ fluorescence could not be detected. The luminescence spectra have been related to the corresponding UV/Vis/NIR absorption spectra and absorption data obtained using the LNDO/S PERTCI method. For DMDP–TTF·+ the fluorescence lifetime (1.09 ns) has been measured and the fluorescence quantum yield (5×10−3) has been estimated.

The fluorescence and fluorescence excitation spectra of the radical cation of 5,10-dihydro-5,10-dimethylphenazine (DHDMP⋅+) have been recorded in liquid solution at room temperature. The fluorescence lifetime (0.47 ns) has been measured in an organic glass at 77K and the fluorescence quantum yield (1×10−3) has been estimated. This is virtually the only organic radical cation for which all the above-mentioned photophysical properties have been obtained in an organic solvent and the only system for which the spectra are available at room temperature. This is due to the unusually high stability of the DHDMP⋅+ radical cation and is an important step forward with regard to practical applications using radical cations.

Photoionization of N,N,N′,N′-tetramethyl-p-phenylenediamine in CCl4- and CH2Cl2-doped solid argon using 313 (3.96) and 254 nm (4.88 eV) Hg lamp radiation, respectively, has been studied by UV/Vis absorption spectroscopy. According to the observed relation between the radical cation production and applied light intensity, the ionization proceeds as a sequential two-photon process.

The nature and structure of electron attachment products in the photoinduced electron transfer reaction DMA + CH2Cl2→hvDMA+ + (electron attachment products) in solid argon has been studied by FTIR spectroscopy (DMA = N,N-dimethylaniline, hν = 4.88 eV Hg lamp radiation) along with extensive ab initio calculations. Two attachment products have been identified: the radical anion of CH2Cl2 and the dichloromethane anion (HCCl2−. The radical anion turns out to have a C1 hydrogen bridged structure (ClHCH…Cl−1). This structure as well as the species of HCCl2− have not been detected before.

Electron correlation effects on the electronic structure of atoms were investigated by means of a variety of position and momentum space related properties such as radial one-electron densities and radial electron momentum densities, Compton profiles and radial electron pair distributions. The results were obtained from MR-SDCI wavefunctions utilizing very large basis sets and are discussed in a comparative manner, analysing characteristic features and trends.

Inelastic (or X-ray incoherent) scattering factors for Li to Ar are presented which take into account electron correlation to a large extent. The scattering factors were derived from MR-SDCI (multi-reference singly and doubly excited configuration interaction) calculations which recover between 90 and 99% of the estimated total correlation energy. Experimental high-energy electron and X-ray scattering cross sections available for Ne and Ar are compared with the corresponding calculated results.

The kinetics of the photobleaching process o-thiobenzoquinone methide (1) → benzo[b]thiete (2), i.e. the forward reaction of the optically switchable 1⇌2 system, in a solid argon layer has been investigated experimentally by measuring the time-dependent photon flux density (photon irradiance) of the transmitted photolysis light. A kinetic model is presented which simultaneously accounts for both the anisotropy of the light absorption and variation of the photon flux density in the layer with position and time. Good agreement between theory and experiment is achieved.

High-energy electron and X-ray scattering cross-sections of O2, F2, CO and CO2 have been calculated within the framework of the first Born approximation from MR-SDCI wavefunctions recovering up to 92% of the estimated correlation energy. In contrast to the fair agreement found for X-ray scattering cross-sections, comparison with available experimental data shows large deviations in the case of electron scattering. Possible causes for the observed discrepancies are discussed.

Photoelectron angular distribution parameters for the X2E ionization of allene and, for the first time, for ionizations of reaction intermediates, namely the K2B1 ionization of ketene and the K2B1, Ã2B2 and K2B1 ionizations of thioketene have been measured using synchrotron radiation up to photon energies of 23.0, 20.0 and 19.5 eV, respectively. The β curves exhibit several structures which could stem from resonance phenomena. Indications of an autoionization resonance were found in the X2E ionization of allene and for a shape resonance in the K2B1 ionization of thioketene.

The LNDO/S PERTCI method for treating vertical valence electronic transitions and ionizations of chiefly organic molecules has been reparametrized for molecules containing N and O atoms and extended to systems containing F and S atoms including d AOs for sulfur. The quality of results is statistically judged on utilizing appropriate groupings of the transitions and ionizations considered.

Using the technique of photochemically generating benzocyclopropenone in solid solutions (solid argon or an organic glass (freons-acetone-d6)) and then transferring the solid product into a solvent (solid argon case) or the solid solution into the liquid state (organic glass case) the elusive benzocyclopropenone is amenable to spectroscopic studies in solution (e.g., by NMR spectroscopy) or studies of thermally activated uni- and bi-molecular chemical reactions.

A detailed spectroscopic study of the elusive benzocyclopropenone obtained on photoactivation of benzocyclobutenedione is presented. The UV/VIS and IR absorption spectra are interpreted on the base of semi-empirical valence electron (UV/VIS) and ab initio (IR) calculations. Agreement between theory and experiment is surprisingly good. Owing to this work benzocyclopropenone is established for the first time.

Using a specially constructed thermal flow reactor in conjunction with a newly designed ionization cell for our UPG 200 photoelectron spectrometer the thermal decomposition of benzocyclobutenedione is studied as a function of reaction temperature and pressure. From the results three band systems in the photoelectron spectrum of the thermoproducts are clearly established to belong to o-benzyne. Assignments of the band systems to ion states are based on quantum chemical data (both semi empirical and ab initio).

Resonant two-photon ionization (TPI) of phenol (PhOH) has been successfully achieved in methylene chloride (CH2Cl2) doped solid argon using a KrF laser and a Hg resonance lamp. The result constitutes the first-time TPI of a typically organic molecule in this medium using an excimer laser as well as the first-time spectroscopic identification of PhOH+•. A qualitative model is proposed which is consistent with both the unexpected photostability of PhOH+• and the incomplete running of the TPI process in the applied medium.

Photoelectron angular distribution parameters for the first three valence-shell photoionizations of cyanoacetylene, for the first one also vibrationally resolved, were measured using synchrotron radiation in the photon energy range from 13.5 to 28.0 eV. LCAO (linear combination of atomic orbitals)/MS Xα MO (multiple scattering Xα molecular orbital) photoelectron angular distribution parameters and photoionization cross sections were computed for photon energies up to 28.0 eV. The comparison between theory and experiment revealed the presence of shape resonances in the first two ionization processes.

A newly constructed angle-resolving photoelectron spectrometer and an appropriate computer-based spectrometer control and data-acquisition system, both specifically designed for photoionisation studies of free atoms and molecules using monochromatised synchrotron radiation from the electron storage ring BESSY, are described. Details of an experimental procedure for the determination of high-precision photoelectron angular-distribution parameters β are specified. To illustrate the performance of the described apparatus and procedure, β values for the Kr+ (4p)−1 spin—orbit components 2P32 and 2P12, measured using synchrotron radiation in the photon energy range 15–24.8 eV, are presented and compared with available experimental and theoretical literature data. The uncertainties of the reported angular-distribution parameters are considerably smaller than those of earlier data. Hence the angular-distribution parameters of the present study can be very useful for future accurate polarisation determinations of monochromatised synchrotron radiation and for calibration procedures of other angle-resolving photoelectron spectrometers.