Kinetic energy release distributions in mass spectrometry

Laskin, Julia; Lifshitz, Chava

doi:10.1002/jms.164

Cited by 127 publications

(129 citation statements)

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“…To obtain the energy that is partitioned into the translational and rotational modes of the products (defined in [39] as kinetic energy release, KER), the internal energy and effective temperature of the cluster ions formed upon EC and subsequent sequential loss of water molecules are calculated assuming that the RE is instantaneously deposited into the precursor and is randomized before dissociation, which should occur for the larger clusters. The energy that partitions into the vibrational modes of the lost water molecules should be negligible under these conditions.…”

Section: Recombination Energiesmentioning

confidence: 99%

Measuring the extent and width of internal energy deposition in ion activation using nanocalorimetry

Donald

Williams

2010

J. Am. Soc. Mass Spectrom.

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The recombination energies resulting from electron capture by a positive ion can be accurately measured using hydrated ion nanocalorimetry in which the internal energy deposition is obtained from the number of water molecules lost from the reduced cluster. The width of the product ion distribution in these experiments is predominantly attributable to the distribution of energy that partitions into the translational and rotational modes of the water molecules that are lost. These results are consistent with a singular value for the recombination energy. For large clusters, the width of the energy distribution is consistent with rapid energy partitioning into internal vibrational modes. For some smaller clusters with high recombination energies, the measured product ion distribution is narrower than that calculated with a statistical model. These results indicate that initial water molecule loss occurs on the time scale of, or faster than energy randomization. This could be due to inherently slow internal conversion or it could be due to a multi-step process, such as initial ion-electron pair formation followed by reduction of the ion in the cluster. These results provide additional evidence for the accuracy with which condensed phase thermochemical values can be deduced from gaseous nanocalorimetry experiments. (J Am Soc Mass Spectrom 2010, 21, 615-625) © 2010 American Society for Mass Spectrometry C apture of a low-energy electron by a multiply charged peptide or protein can result in extensive and relatively non-selective fragmentation of the amide backbone, from which information about the amino acid sequence [1-3], post-translational modification sites [3][4][5], and higher-order structure [2,6,7] can be obtained. Similar fragmentation can be obtained by transferring an electron to the peptide or protein cation from a molecular anion [8] or from atoms [9,10]. These methods are being applied to both "bottom up" and "top-down" approaches to protein analysis.An important parameter in understanding how activated ions fragment is the extent of internal energy that is deposited in the activation step. For electron capture dissociation (ECD) [1-6], the recombination energy (RE) resulting from capture of an electron from a multiply charged peptide or protein has been estimated to be between 4 and 7 eV [1,11,12], based in part on known or estimated thermochemical data. Dissociation may occur from excited electronic states or from ground states [13,14], so that the internal energy deposited into an ion may not be a singular value.Some ions have been used as chemical thermometers to measure internal energy deposition [15][16][17][18]. For example, dissociation of the molecular ion of n-butylbenzene results in formation of product ions at m/z 91 and 92, the ratio of which provides information about the average internal energy of the activated precursor [15,16]. Ions that dissociate via sequential fragmentation and that have known threshold dissociation energies and similar dissociation entropies have also been used [18 -...

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Section: Recombination Energiesmentioning

confidence: 99%

Measuring the extent and width of internal energy deposition in ion activation using nanocalorimetry

Donald

Williams

2010

J. Am. Soc. Mass Spectrom.

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“…The study of kinetic energy release distributions (KERDs) offers considerable advantages. As shown by many authors, with Chava Lifshitz at the forefront [1,[6][7][8][9][10][11][12], KERDs are more sensitive than rate constants to deviations from statistical expectations. The reason is easily seen.…”

Section: Of the Importance Of Studying Kerdsmentioning

confidence: 99%

“…The second one, first proposed by Klots [13,14] but mainly developed by Ches-navich and Bowers in an impressive series of papers [15][16][17][18][19], is a variant of phase space theory that studies reactions involving very loose orbiting transition states (OTS). It is hereafter denoted OTST [1,3,10,[15][16][17][18][19][20][21][22]. Each theory is particularly adapted to a specific type of experiment.…”

Section: Of the Importance Of Studying Kerdsmentioning

confidence: 99%

Analysis of kinetic energy release distributions by the maximum entropy method

Leyh¹,

Gridelet²,

Locht³

et al. 2006

International Journal of Mass Spectrometry

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Energy is not always fully randomized in an activated molecule because of the existence of dynamical constraints. An analysis of kinetic energy release distributions (KERDs) of dissociation fragments by the maximum entropy method (MEM) provides information on the efficiency of the energy flow between the reaction coordinate and the remaining degrees of freedom during the fragmentation. For example, for barrierless cleavages, large translational energy releases are disfavoured while energy channeling into the rotational and vibrational degrees of freedom of the pair of fragments is increased with respect to a purely statistical partitioning. Hydrogen atom loss reactions provide an exception to this propensity rule. An ergodicity index, F, can be derived. It represents an upper bound to the ratio between two volumes of phase space: that effectively explored during the reaction and that in principle available at the internal energy E. The function F(E) has been found to initially decrease and to level off at high internal energies.For an atom loss reaction, the orbiting transition state version of phase space theory (OTST) is especially valid for low internal energies, low total angular momentum, large reduced mass of the pair of fragments, large rotational constant of the fragment ion, and large polarizability of the released atom. For barrierless dissociations, the major constraint that results from conservation of angular momentum is a propensity to confine the translational motion to a two-dimensional space. For high rotational quantum numbers, the influence of conservation of angular momentum cannot be separated from effects resulting from the curvature of the reaction path.The nonlinear relationship between the average translational energy and the internal energy E is determined by the density of vibrational-rotational states of the pair of fragments and also by non-statistical effects related to the incompleteness of phase space exploration.The MEM analysis of experimental KERDs suggests that many simple reactions can be described by the reaction path Hamiltonian (RPH) model and provides a criterion for the validity of this method.Chemically oriented problems can also be solved by this approach. A few examples are discussed: determination of branching ratios between competitive channels, reactions involving a reverse activation barrier, nonadiabatic mechanisms, and isolated state decay. Statistical methods in mass spectrometryFor the last 50 years, mass spectrometrists have made great efforts to rationalize fragmentation patterns and breakdown graphs by various statistical models that are all based on a common assumption. The internal energy deposited in a molecular ion is expected to be completely randomized before dissociation [1][2][3][4]. When this is the case, the reaction is declared ergodic.Equivalently, the energetically available phase space is said to be uniformly sampled within the lifetime of the molecular ion. In still more esoteric terms, the molecular ion is said to have reached a stat...

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“…These phenomena have been studied with different experimental techniques, such as ion mass and electron spectroscopies [12][13][14][15][16]. Specific methods such as energy-scanned partial ion yields [17][18][19][20] have been used to observe the fragmentation thresholds and ion production rates, while the nature of dissociation processes has been interpreted, for example, by measuring the kinetic-energy releases (KERs) [21][22][23] of the participating ions. The electron-energy-dependent photoelectron-photoion coincidence (PEPICO) spectroscopy was devised to reveal a more detailed view of the underlying quantum mechanical processes, i.e., to provide a more comprehensive glimpse of the connection between specific electronic states, molecular energetics, and fragments.…”

Section: Introductionmentioning

confidence: 99%

Valence electronic structure and photofragmentation of 1,1,1,2-tetrafluoroethane (CF3-CH2F)

et al. 2012

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The electronic structure and fragmentation of the hydrofluorocarbon compound 1,1,1,2-tetrafluoroethane (CF 3 -CH 2 F) were studied using spectroscopical methods and quantum chemical calculations. Valence photoelectron spectra and the ionic fragmentation products were recorded with synchrotron radiation in the vacuum ultraviolet (VUV) region. The geometric and electronic structures of the CF 3 -CH 2 F molecule were calculated using the complete active space perturbation theory of second order. The calculated vertical ionization energies were used to interpret the experimental photoelectron spectrum. VUV photodissociation of the sample molecule was studied with photoelectron-photoion coincidence spectroscopy. Coincident ion yields are shown for several cations as a function of electron binding energy. The experimental data are discussed in comparison with theory and previous work.

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Kinetic energy release distributions in mass spectrometry

Cited by 127 publications

References 129 publications

Measuring the extent and width of internal energy deposition in ion activation using nanocalorimetry

Measuring the extent and width of internal energy deposition in ion activation using nanocalorimetry

Analysis of kinetic energy release distributions by the maximum entropy method

Valence electronic structure and photofragmentation of 1,1,1,2-tetrafluoroethane (CF3-CH2F)

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