Collision-Induced Dissociation of Diatomic Ions

Los, J.; Govers, T.R.

doi:10.1007/978-1-4613-3955-7_7

Cited by 17 publications

(12 citation statements)

References 90 publications

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“…Equation (3) is a simple consequence of conservation of mass, momentum and translational energy under the restrictive assumptions that AT, (2), is zero, and that there is zero conversion of the internal energy of M f " to translational energy of the fragments in step (ii), (1). The latter assumption may be shown' to introduce negligible error to the assignment of fragment ion mass mF from measured values of TF, although this effect does result in the ' NRCC No.…”

Section: A T G ( T ( ) -T ) = a E And + A E~+ Tgmentioning

confidence: 99%

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Are Derrick shifts real? An investigation by tandem mass spectrometry

Guevremont

Boyd

1988

Rapid Comm Mass Spectrometry

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The phenomenon of collision-induced dissociation (CID) of fast ions, prompted by collisions with thermal gas molecules, has been known since the earliest days of mass spectrometry.' It has since become well established2 that the overall CID process can be meaningfully separated into two consecutive steps occurring on well-separated timescales. The first is a fast (-10-'s-10-'4s) collisional activation (CA) step in which some portion of the initial translational energy To of the fast ion is converted into internal energy of both projectile and target, as well as into translational energy of the latter. The second step is the dissociation of the now energized (and isolated) projectile ion, and is often considered in terms of statistical theories of unimolecular reaction rates:The energized projectile ions M+" which emerge from the CA step (i) have lost translational energy AT, given by: A T G ( T ( ) -T ) = A E & + A E~+ TG (2)where T and TG are the post-collision translational energies of Mf and of the (formerly thermal) target G, respectively. AE" represents a change in internal energy resulting from the collision. Study of CID processes of fast ions (keV energy range) has been conducted in mass spectrometers using techniques such as mass analysed ion kinetic energy spectroscopy (MIKES) .3 Such translational energy spectra are commonly transformed to mass spectra (masses of fragment ions F' ) via the simple relationship:where m denotes mass and TF is the translational energy of fragment F' . Equation (3) is a simple consequence of conservation of mass, momentum and translational energy under the restrictive assumptions that AT, (2), is zero, and that there is zero conversion of the internal energy of M f " to translational energy of the fragments in step (ii), (1). The latter assumption may be shown' to introduce negligible error to the assignment of fragment ion mass mF from measured values of TF, although this effect does result in the ' NRCC No. 28467i Author to whom correspondence should be addressed well-known broadening of the peaks in translational energy spectra. The first assumption ( A T = ( ) ) is almost always made in work of this kind, although it is clear that it cannot, in principle, be exactly valid for CID reactions. Early examples of appreciable translational energy shifts (defined as shifts from peaks arising from unimolecular reaction ( A T = 0 by definition) to peaks due to the corresponding CID reaction) have been published (e.g. Fig. 80 of Ref. 3). Nonetheless, interpretation of translational energy spectra of fragment ions formed by CID reactions has almost invariably employed (3). In the case of small organic ions, such mass assignments are unlikely to be in serious error since (3) can be corrected and then differentiated to give:For the typical values T,, = 8000 eV and mM = 100 Da, AT, (for AmF=lDa) is about 80eV. Such a large translational energy loss is impossible4 if the resulting trajectory is to fall within the acceptance aperture of the analysing sector, even if the mass of the t...

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Section: A T G ( T ( ) -T ) = a E And + A E~+ Tgmentioning

confidence: 99%

“…The energized projectile ions M+" which emerge from the CA step (i) have lost translational energy AT, given by: (2) where T and TG are the post-collision translational energies of Mf and of the (formerly thermal) target G, respectively. AE" represents a change in internal energy resulting from the collision.…”

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confidence: 99%

Are Derrick shifts real? An investigation by tandem mass spectrometry

Guevremont

Boyd

1988

Rapid Comm Mass Spectrometry

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“…Termed "translational spectroscopy," this technique allows for such an accuracy, owing to the magnification introduced by the laboratory-to-center-of-mass (CM) transformation of the momentum distribution of the fragments. Our knowledge of this field is well summarized in the review of Los and Govers [2]. In the keV energy range and for the investigated systems, the collision time is much shorter than the dissociation time of the molecule, allowing approximations in terms of "two step" mechanisms.…”

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confidence: 99%

“…Notice that most of the previous CID experiments were focused on the spectroscopy of the predissociating molecular states relevant of the EM mechanism [2] and did not pay much attention to the quantitative importance of the relative contribution of IM. The present results suggest new measurements of the relative contributions of both types of CID processes.…”

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Analysis of Collision Induced Dissociation ofNa2+Molecular Ions

et al. 1996

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A full analysis of the collision induced dissociation of a diatomic molecular ion is presented for the first time. The experiment is essentially based on the simultaneous measurement of the momenta of the two fragments. This technique applied to the collision of Na 2 1 with a helium target reveals, at keV collision energies, the competition between two dissociation mechanisms: an impulsive mechanism when the target hits one Na 1 core in a close encounter and an electronic mechanism when dissociation occurs after excitation of repulsive or weakly bound states. [S0031-9007(96)00952-0] PACS numbers: 34.50.Pi, 34.50.LfCollision induced dissociation (CID) of diatomic molecules is an example of a three body interaction which is not yet fully understood. Back in the sixties, the study of CID of H 2 1 molecules was initially motivated by the need to produce fast H atoms for heating plasma of interest for thermonuclear fusion. Then, during the seventies, an intense activity developed when it was demonstrated that accurate measurements of momentum distributions of dissociation fragments produced in fast collisions were a powerful tool to access the spectroscopy of molecular ions with meV accuracy [1]. Termed "translational spectroscopy," this technique allows for such an accuracy, owing to the magnification introduced by the laboratory-to-center-of-mass (CM) transformation of the momentum distribution of the fragments. Our knowledge of this field is well summarized in the review of Los and Govers [2]. In the keV energy range and for the investigated systems, the collision time is much shorter than the dissociation time of the molecule, allowing approximations in terms of "two step" mechanisms. In the first step, the molecule is excited into an unstable state. In the second step, dissociation occurs far from the perturbing partner of the collision. As first proposed by Durup [3], two classes of mechanisms have been considered, depending on the first step of the collision.(i) A close encounter between one atomic core of the molecule and the target atom, the other atomic core remaining spectator, leads to a large stretching of the molecule resulting in vibrational excitation, increasing with the scattering angle [4]. Such a mechanism, hereafter referred to as the impulse mechanism (IM), has been identified by measuring the energy losses undergone by a molecular projectile as a function of the scattering angle [5]. In such a collision induced vibrational excitation, the molecule dissociates when the energy transfer is large enough. Although often invoked, this dissociation mechanism has never been directly observed. Notice that such a binary impulse mechanism has already been invoked as an initial step for reactive collision processes at moderate energy [6].(ii) In a more distant collision, the target may primarily interact with the electron cloud of the molecule which can be electronically excited into a dissociative state. In fact, in most of the investigated cases, this excitation results from an electron capture by the mol...

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“…It has been shown that the nature of the target gas will influence the relative proportion of electronic excitation versus vibrational and rotational excitation into the ground state continuum. 20 The tendency is for helium to transfer greater amounts of energy (and thus a greater proportion of electronic excitation) than most other target gases. Conversely, more massive target gases tend to favor vibrational and rotational excitation.…”

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Metastable and collision induced fragmentation of some small cluster ions: Ar₂⁺ Ar₃⁺, ArN₂⁺ and N₄⁺

Illies

Bowers

1983

Org. Mass Spectrom.

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The results of a study on collision induced dissociation and a search for metastabIe reactions of four gas phase ion-molecule clusters, Ar2+, AI3+, ArN2+ and N,+, are presented. The ionic clusters were formed in a high pressure mass spectrometer ion source which was cooled to enhance the association products. Subsequent fragmentations were studied using mass analyzed ion kinetic energy spectrometry. Decomposition pathways consistent with experimental collision induced dissociation peak shapes and ab initio potential diagrams are

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Collision-Induced Dissociation of Diatomic Ions

Cited by 17 publications

References 90 publications

Are Derrick shifts real? An investigation by tandem mass spectrometry

Are Derrick shifts real? An investigation by tandem mass spectrometry

Analysis of Collision Induced Dissociation ofNa2+Molecular Ions

Metastable and collision induced fragmentation of some small cluster ions: Ar₂⁺ Ar₃⁺, ArN₂⁺ and N₄⁺

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Collision-Induced Dissociation of Diatomic Ions

Cited by 17 publications

References 90 publications

Are Derrick shifts real? An investigation by tandem mass spectrometry

Are Derrick shifts real? An investigation by tandem mass spectrometry

Analysis of Collision Induced Dissociation ofNa2+Molecular Ions

Metastable and collision induced fragmentation of some small cluster ions: Ar2+ Ar3+, ArN2+ and N4+

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Metastable and collision induced fragmentation of some small cluster ions: Ar₂⁺ Ar₃⁺, ArN₂⁺ and N₄⁺