The Dissociation Dynamics of Energy‐Selected Ions

Baer, Tomas

doi:10.1002/9780470142882.ch3

Cited by 86 publications

(8 citation statements)

References 194 publications

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“…Along with the related CRUNCH program from Armentrout and co-workers, , L-CID treats the kinetic shift with statistical rate theory. The particular implementation in L-CID corresponds roughly to a phase space theory (PST) treatment, which is the most basic variant of RRKM theory, for which one needs the density-of-states function, ρ( E ), for the starting and the energized complexes. The assumption of statistical behavior in the dissociation of large ions has been tested extensively over several decades, and this assumption can be judged to be good, there being admittedly some rare exceptions. , For statistical rate theory, approximations enter in the calculation of ρ( E ).…”

Section: Discussionmentioning

confidence: 99%

“…The particular implementation in L-CID corresponds roughly to a phase space theory (PST) treatment, which is the most basic variant of RRKM theory, for which one needs the density-of-states function, ρ( E ), for the starting and the energized complexes. The assumption of statistical behavior in the dissociation of large ions has been tested extensively over several decades, and this assumption can be judged to be good, there being admittedly some rare exceptions. , For statistical rate theory, approximations enter in the calculation of ρ( E ). Translational and rotational degrees of freedom can be treated classically, or even altogether neglected (if the moment of inertia of the starting complex and the transition state are sufficiently similar, for example), but vibrational (and librational) degrees of freedom become the principal problem.…”

Section: Discussionmentioning

confidence: 99%

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Bond Dissociation Energies in the Gas Phase for Large Molecular Ions by Threshold Collision-Induced Dissociation Experiments: Stretching the Limits

et al. 2020

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Accurate bond dissociation energies for large molecules are difficult to obtain by either experimental or computational methods. The former methods are hampered by a range of physical and practical limitations in gas-phase measurement techniques, while the latter require incorporation of multiple approximations whose impact on accuracy may not always be clear. When internal benchmarks are not available, one hopes that experiment and theory can mutually support each other. A recent report found, however, a large discrepancy between gas-phase bond dissociation energies, measured mass spectrometrically, and the corresponding quantities computed using density functional theory (DFT)-D3 and DLPNO-CCSD(T) methods. With the widespread application of these computational methods to large molecular systems, the discrepancy needs to be resolved. We report a series of experimental studies that validate the mass spectrometric methods from small to large ions and find that bond dissociation energies extracted from threshold collision-induced dissociation experiments on large ions do indeed behave correctly. The implications for the computational studies are discussed.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Bond Dissociation Energies in the Gas Phase for Large Molecular Ions by Threshold Collision-Induced Dissociation Experiments: Stretching the Limits

et al. 2020

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“…The latter consistently outweighs the former in our systems. Furthermore, their dissociation reactions are amenable to experimental study both in the gas phase (by threshold‐collision induced dissociation) and in solution (by ITC and NMR analysis), making them attractive probes to study dispersion and benchmark computational methods. Notably, we treat proton‐bound dimers as single molecules.…”

Section: Introductionmentioning

confidence: 99%

Compensation of London Dispersion in the Gas Phase and in Aprotic Solvents

et al. 2019

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The importance of London dispersion for structure and stability of molecules with less than about 200 atoms has been established in recent years but the quantitative understanding is still largely based on computations because of apersistent lack of suitable experimental data. We herein report acomprehensive computational and experimental study of the compensation of London dispersion in proton-bound dimer dissociations showing that total compensation is largely invariant in both polar and nonpolar aprotic solvents spanning awide range of bulk polarizabilities.Additionally,wefind that compensation by solvent (which is about 40-80 %) largely dominates over compensation in the gas phase (which is about 0-40 %) for typical experimental temperatures.

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“…A few years later, continuum vacuum UV light sources, dispersed by a monochromator, were utilized by Stockbauer4 and Werner and Baer,9 to collect ions in coincidence with threshold electrons. Although the use of the He(I) lamp for PEPICO studies continued,10, 11 the advantages of higher signal to noise, better electron energy resolution and more readily extractable ions associated with threshold electron detection soon caused the latter approach to dominate the field 12–17. In particular, the threshold PEPICO (TPEPICO) approach has been especially attractive in conjunction with a synchrotron radiation source 5, 16, 18–21.…”

Section: Introductionmentioning

confidence: 99%

Modeling unimolecular reactions in photoelectron photoion coincidence experiments

2010

Self Cite

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A computer program has been developed to model and analyze the data from photoelectron photoion coincidence (PEPICO) spectroscopy experiments. This code has been used during the past 12 years to extract thermochemical and kinetics information for almost a hundred systems, and the results have been published in over forty papers. It models the dissociative photoionization process in the threshold PEPICO experiment by calculating the thermal energy distribution of the neutral molecule, the energy distribution of the molecular ion as a function of the photon energy, and the resolution of the experiment. Parallel or consecutive dissociation paths of the molecular ion and also of the resulting fragment ions are modeled to reproduce the experimental breakdown curves and time-of-flight distributions. The latter are used to extract the experimental dissociation rates. For slow dissociations, either the quasi-exponential fragment peak shapes or, when the mass resolution is insufficient to model the peak shapes explicitly, the center of mass of the peaks can be used to obtain the rate constants. The internal energy distribution of the fragment ions is calculated from the densities of states using the microcanonical formalism to describe consecutive dissociations. Dissociation rates can be calculated by the RRKM, SSACM or VTST rate theories, and can include tunneling effects, as well. Isomerization of the dissociating ions can also be considered using analytical formulae for the dissociation rates either from the original or the isomer ions. The program can optimize the various input parameters to find a good fit to the experimental data, using the downhill simplex algorithm.

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The Dissociation Dynamics of Energy‐Selected Ions

Cited by 86 publications

References 194 publications

Bond Dissociation Energies in the Gas Phase for Large Molecular Ions by Threshold Collision-Induced Dissociation Experiments: Stretching the Limits

Bond Dissociation Energies in the Gas Phase for Large Molecular Ions by Threshold Collision-Induced Dissociation Experiments: Stretching the Limits

Compensation of London Dispersion in the Gas Phase and in Aprotic Solvents

Modeling unimolecular reactions in photoelectron photoion coincidence experiments

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