How ergodic is the fragmentation of the pyridine cation?

Gridelet, E.; Locht, Robert; Lorquet, Andrée; Lorquet, Jean-Claude; Leyh, Bernard

doi:10.1016/s1387-3806(03)00132-5

Cited by 15 publications

(42 citation statements)

References 71 publications

(109 reference statements)

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“…At still higher internal energies, F keeps on decreasing but is found to level off or even re-increase, say at E ≈ 2.5 eV, where it reaches its lowest value, which is roughly of the order of 50% for the investigated reactions. This behaviour has been observed in a number of cases: loss of a Br atom from C 2 H 3 Br + [40], loss of I from C 2 H 5 I + [48], HCN loss from the pyridine ion [42] and, very recently, loss of an acetylene molecule from C 6 H 6 + ions. 1 As the internal energy increases, the lifetime decreases whereas the volume of phase space to be sampled increases enormously.…”

Section: A Very Interesting Question Concerns the Energy-dependence Omentioning

confidence: 84%

“…In many cases [22,[37][38][39][40][41][42][43][44], the very simple expression (10) is found to provide a very good approximation to P(ε|E) if the value of the exponent k is adequately chosen. A value of k equal to 1/2 or to 1 is usually found.…”

Section: Mem Expression Of the Actual Kerdsmentioning

confidence: 99%

“…In addition to techniques like MIKES (mass-analyzed ion kinetic energy spectrometry), which analyze the KERD on the microsecond time scale, two experimental approaches are available to measure KERDs at higher values of the internal energy E: PEPICO [11,47], and retarding field methods [21,40,42,44]. The KERD measured with the MIKES and retarding field techniques is actually an average over an internal energy distribution D(E): it will be denoted as P (ε).…”

Section: Energy Dependencementioning

confidence: 99%

“…(17) are introduced into Eq. (16), a function F(E) can be derived, which expresses the way the efficiency of phase space exploration varies with the internal energy of the molecular ion [40,42,48]. The results will be discussed in Section 5.4.…”

Section: Energy Dependencementioning

confidence: 99%

“…We may, however, already note that intramolecular energy flow among oscillators resulting from the anharmonic character of the potential energy surface of the molecular ion in its ground electronic state is not the only mechanism by which energy gets redistributed. Very fast radiationless transitions that result from the numerous crossings among potential energy surfaces also contribute to energy randomization [40,42,55,56]. The higher the internal energy E, the more extended and intricate the pattern of surface crossings.…”

Section: A Very Interesting Question Concerns the Energy-dependence Omentioning

confidence: 99%

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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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Section: A Very Interesting Question Concerns the Energy-dependence Omentioning

confidence: 84%

Section: Mem Expression Of the Actual Kerdsmentioning

confidence: 99%

Section: Energy Dependencementioning

confidence: 99%

Section: Energy Dependencementioning

confidence: 99%

Section: A Very Interesting Question Concerns the Energy-dependence Omentioning

confidence: 99%

See 3 more Smart Citations

Analysis of kinetic energy release distributions by the maximum entropy method

Leyh¹,

Gridelet²,

Locht³

et al. 2006

International Journal of Mass Spectrometry

Self Cite

View full text Add to dashboard Cite

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Current literature in mass spectrometry

2004

J. Mass Spectrom.

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In order to keep subscribers up‐to‐date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of mass spectrometry. Each bibliography is divided into 11 sections: 1 Books, Reviews & Symposia; 2 Instrumental Techniques & Methods; 3 Gas Phase Ion Chemistry; 4 Biology/Biochemistry: Amino Acids, Peptides & Proteins; Carbohydrates; Lipids; Nucleic Acids; 5 Pharmacology/Toxicology; 6 Natural Products; 7 Analysis of Organic Compounds; 8 Analysis of Inorganics/Organometallics; 9 Surface Analysis; 10 Environmental Analysis; 11 Elemental Analysis. Within each section, articles are listed in alphabetical order with respect to author (4 Weeks journals ‐ Search completed at 17th. Mar. 2004)

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