Whither the statistical theory of mass spectra?

Lorquet, Jean-Claude

doi:10.1002/mas.1280130304

Cited by 60 publications

(29 citation statements)

References 121 publications

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“…Thus, just as in the case of thermal reactions, energy randomization is greatly facilitated by the fact that the initial conditions are already scattered all over phase space. 11,71,72 Since, in addition, the efficiency of anharmonic coupling increases with E, a nearly uniform distribution of trajectories in phase space can be achieved at high internal energies, even if the lifetime is very short.…”

Section: B Mechanism Of Phase Space Samplingmentioning

confidence: 99%

“…The distributions of kinetic energy released during the fragmentation process ͑KERDs͒ contain information about the reaction dynamics [1][2][3][4][5][6][7][8][9][10] and provide a complementary and more severe test for the validity of the statistical theories of mass spectra than the measurement of the unimolecular reaction rate constants. 11 The maximum entropy method [12][13][14][15] has seldom been used for the analysis of the KERD data of ionic systems, mainly in the form of a surprisal analysis. 5,[16][17][18][19][20][21][22] Only recently have detailed maximum entropy analyses of KERDs of ionic systems been reported.…”

Section: Introductionmentioning

confidence: 99%

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Unimolecular dynamics from kinetic energy release distributions. V. How does the efficiency of phase space sampling vary with internal energy?

Hoxha

Locht

Lorquet

et al. 1999

The Journal of Chemical Physics

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A retarding field technique coupled with a quadrupole mass analyzer has been used to obtain the kinetic energy release distributions ͑KERDs͒ for the C 2 H 3 Br ϩ →͓C 2 H 3 ͔ ϩ ϩBr dissociation as a function of internal energy. The KERDs obtained by dissociative photoionization using the He͑I͒, Ne͑I͒, and Ar͑II͒ resonance lines were analyzed by the maximum entropy method and were found to be well described by introducing a single dynamical constraint, namely the relative translational momentum of the fragments. Ab initio calculations reveal the highly fluxional character of the C 2 H 3 ϩ ion. As the energy increases, several vibrational modes are converted in turn into large-amplitude motions. Our main result is that, upon increasing internal energy, the fraction of phase space sampled by the pair of dissociating fragments is shown to first decrease, pass through a shallow minimum around 75%, and then increase again, reaching almost 100% at high internal energies ͑8 eV͒. This behavior at high internal energies is interpreted as resulting from the conjugated effect of intramolecular vibrational redistribution ͑IVR͒ and radiationless transitions among potential energy surfaces. Our findings are consistent with the coincidence data of Miller and Baer, reanalyzed here, and with the KERD of the metastable dissociation.

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Section: B Mechanism Of Phase Space Samplingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Unimolecular dynamics from kinetic energy release distributions. V. How does the efficiency of phase space sampling vary with internal energy?

Hoxha

Locht

Lorquet

et al. 1999

The Journal of Chemical Physics

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“…The usual picture is based on the RRKM [22][23][24][25][26] (Rice-Rampsberger-Kassel-Marcus) statistical theory of unimolecular dissociation. The expression of the rate constant k(E) depends on an enthalpic term (the critical energy E 0 ), and on the activation entropy (through a degeneracy factor and the density of states of the reactant and the transition state).…”

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confidence: 99%

Comparison of the collision-induced dissociation of duplex DNA at different collision regimes: Evidence for a multistep dissociation mechanism

Gabelica

Pauw

2002

J. Am. Soc. Mass Spectrom.

104

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The dissociation mechanism of duplex DNA has been investigated in detail by collisioninduced dissociation experiments at different collision regimes. MS/MS experiments were performed either in a quadrupole collision cell (hybrid quadrupole-TOF instrument) or in a quadrupole ion trap with different activation times and energies. In addition to the noncovalent dissociation of the duplex into the single strands, other covalent bond fragmentation channels were observed. Neutral base loss from the duplex is favored by slow activation. In fast activation conditions, however, the major reaction channel is the noncovalent dissociation into single strands, which is highly entropy-favored. Fast activation regimes can favor the entropy-driven noncovalent dissociation, while in slow heating conditions the competition with enthalpy-driven covalent fragmentation can completely hinder the dissociation of the complex. We also evidence that the noncovalent dissociation of DNA duplex is a multistep process involving a progressive unzipping, preferentially at terminal positions. This is proposed to be a general feature for complexes containing a high number of contributing interactions organized at the interface of the ligands. The overall (observed) dissociation kinetics of noncovalent complexes can therefore depend on a complicated mechanism for which a single transition state description of the kinetics is too simplistic. [1][2][3][4] led to tremendous development of the study of noncovalent complexes by mass spectrometry. ESI gently transfers the complexes from the solution to the gas phase by a progressive desolvation assisted by collisions in the source [5], by heating in a capillary [6], or both. Once the intact complexes have been obtained in the gas phase, they can be studied by MS/MS collision-induced dissociation (CID) in quadrupoles [7][8][9], in ion traps [10,11], in ICR cells [12,13], blackbody radiation in ICR cells [14, 15, . . .], or in-source dissociation techniques (heated capillary dissociation [16,17], in-source CID [13, 18 -20]. All these methods give access to the relative dissociation kinetics of the complexes [21], which depends on the nature and the strength of the interactions between the constitutive units. Tandem mass spectrometry has therefore the potency to become a method of choice to probe the intrinsic interactions between biomolecules in the absence of solvent.Currently, the interpretation of the MS/MS on large complexes is still based on a simplistic view inherited from earlier studies on small molecules. The usual picture is based on the RRKM [22-26] (Rice-Rampsberger-Kassel-Marcus) statistical theory of unimolecular dissociation. The expression of the rate constant k(E) depends on an enthalpic term (the critical energy E 0 ), and on the activation entropy (through a degeneracy factor and the density of states of the reactant and the transition state). For large molecules, the link between the observed fragmentation yield and the microscopic characteristics of the complex is difficult to make ...

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“…Lorquet suggested that the future research into the ergodic nature of chemical reactions should be directed to the analysis of kinetic energy release distributions. 45 The results of the present study provide another merit of such an analysis. Namely, valuable fundamental information such as the symmetry of the reaction path and the tunneling through the barrier may also be obtained from the kinetic energy release data.…”

Section: Discussionmentioning

confidence: 70%