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The ground-state dissociation energy, D0(S0), of isolated intermolecular complexes in the gas phase is a fundamental measure of the interaction strength between the molecules. We have developed a three-laser, triply resonant pump-dump-probe technique to measure dissociation energies of jet-cooled M•S complexes, where M is an aromatic chromophore and S is a closed-shell 'solvent' molecule. Stimulated emission pumping (SEP) via the S0?S1 electronic transition is used to precisely 'warm' the complex by populating high vibrational levels v" of the S0 state. If the deposited energy E(v") is less than D0(S0), the complex remains intact, and is then mass- and isomer-selectively detected by resonant two-photon ionization (R2PI) with a third (probe) laser. If the pumped level is above D0(S0), the hot complex dissociates and the probe signal disappears. Combining the fluorescence or SEP spectrum of the cold complex with the SEP breakoff of the hot complex brackets D0(S0). The UV chromophores 1-naphthol and carbazole were employed; these bind either dispersively via the aromatic rings, or form a hydrogen bond via the -OH or -NH group. Dissociation energies have been measured for dispersively bound complexes with noble gases (Ne, Kr, Ar, Xe), diatomics (N2, CO), alkanes (methane to n-butane), cycloalkanes (cyclopropane to cycloheptane), and unsaturated compounds (ethene, benzene). Hydrogen-bond dissociation energies have been measured for H2O, D2O, methanol, ethanol, ethers (oxirane, oxetane), NH3 and ND3.

Recent experiments are reviewed which have led to the determination of the ionization and dissociation energies of molecular hydrogen with a precision of 0.0007 cm–1 (8 mJ/mol or 20 MHz) using a procedure based on high-resolution spectroscopic measurements of high Rydberg states and the extrapolation of the Rydberg series to the ionization thresholds. Molecular hydrogen, with only two protons and two electrons, is the simplest molecule with which all aspects of a chemical bond, including electron correlation effects, can be studied. Highly precise values of its ionization and dissociation energies provide stringent tests of the precision of molecular quantum mechanics and of quantum-electrodynamics calculations in molecules. The comparison of experimental and theoretical values for these quantities enable one to quantify the contributions to a chemical bond that are neglected when making the Born-Oppenheimer approximation, i.e. adiabatic, nonadiabatic, relativistic, and radiative corrections. Ionization energies of a broad range of molecules can now be determined experimentally with high accuracy ( i.e. about 0.01 cm–1). Calculations at similar accuracies are extremely challenging for systems containing more than two electrons. The combination of precision measurements of molecular ionization energies with highly accurate ab initio calculations has the potential to provide, in future, fully reliable sets of thermochemical quantities for gas-phase reactions.

We present the adaptation of the sectional model approach to the pyrolysis of cellulose, (C6H10O5)n. Cellulose is the major component of lignocellulosic biomass. Due to its longitudinal structure, cellulose is characterised by one-dimensional chains composed of a varying number of cellobiose molecules, C12H22O11. Fragments of those chains with similar mass are grouped into size classes (BINs) determined by characteristic numbers of cellobiose units. During the pyrolysis of cellulose, reaction temperatures of more than 500 K (depending on the heating rate) initiate bond dissociation between cellobiose units. We have developed a new reaction scheme for the pyrolysis of cellulose based on literature models. However, we present the sectional approach as a new concept for modelling the degradation of cellulose. We propose a kinetic data set of A = 2.2 ∙ 1013 s−1 and EA = 225.9 kJ/mol for the dissociation of a single glycosidic bond. Additionally, our model includes the cellobiose devolatilisation to glucose or tars (levoglucosan) including primary gaseous products, the formation of char and water, and secondary gas-phase reactions. Our reactor simulations of cellulose pyrolysis at constant heating rates of 1, 10, 15, and 150 K/min show good agreement with two different experimental data sets.

Expanding research in the field of modified oligonucleotides demands suitable analytical tools for size and purity verification of known compounds and accurate structure elucidation of unknowns. There is a need for characterization of the types and sites of modifications in oligonucleotides and to identify and sequence selected candidates originating from synthesis. The potential of electrospray tandem mass spectrometry (ESI-MS/MS) for structural characterization and sequencing of oligonucleotides is demonstrated. The fundamental behavior of DNA, RNA, and selected modified oligonucleotides in gas-phase is shown. Since gas-phase dissociation does not demand specific structural prerequisites, the method bears a great potential for rapid and most accurate characterization of modified oligonucleotides, e.g. from combinatorial libraries.

Kordes und Nolte sind der Meinung, das Na2W2O7 beim Schmelzen dissoziiert gemas wahrend Gelsing et al. annehmen, das im gleichen Fall Dissoziation in Na+-Ionen und ein Gemisch aus Ketten von WO4-Tetraedern (WO, W2O, W3O usw.) auftritt. Im nachstehenden Artikel wird nachgewiesen, das das Dissoziationsschema nach Gelsing et al. die von Kordes und Nolte selbst gefundenen kryometrischen Resultate hervorragend erklaren kann. Das Dissoziationsschema nach Gelsing et al. ist sogar wahrscheinlicher als das nach Kordes und Nolte, wenn auch die Resultate von Oberflachenspannungsmessungen, berichtet von Gossink und Stevels, in die Betrachtungen einbezogen werden. Kordes and Nolte are of the opinion that, on melting, Na2W2O7 dissociates according to the reaction whereas Gelsing et al. assume a dissociation into Na+ ions and a mixture of chains of WO4 tetrahedra (WO, W2O, W3O, etc.). In the present paper it is demonstrated that a dissociation according to the ideas of Gelsing et al. can excellently explain the cryometric results found by Kordes and Nolte themselves. The dissociation scheme proposed by Gelsing et al., is even more likely than that proposed by Kordes and Nolte when the results of surface tension measurements reported by Gossink and Stevels are taken into account.