Statistical modeling of collision-induced dissociation thresholds

Rodgers, M. T.; Ervin, Kent M.; Armentrout, P. B.

doi:10.1063/1.473494

Cited by 448 publications

(965 citation statements)

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“…Modeling parameters for each of the single pathway reactions are given in Table 1. For these reactions, the cross section data were modeled by assuming loose, dissociative variational transition states, typical for direct cleavage processes [65]. Overall uncertainties were determined as described in the Experimental section.…”

Section: Resultsmentioning

confidence: 99%

“…For direct dissociation reactions, product-like transition states were assumed, corresponding to the phase-space limit [65]. Activation entropies for direct dissociation reactions are generally ϩ10 -20 cal/ mol · K, indicating loose transition states.…”

Section: Instrumental Description and Data Analysismentioning

confidence: 99%

“…Activation entropies for direct dissociation reactions are generally ϩ10 -20 cal/ mol · K, indicating loose transition states. Data analysis and modeling were carried out using the CRUNCH 4D program developed by Armentrout and coworkers [59,60,[65][66][67]. In the absence of reverse activation barriers, threshold energies can be equated with 0 K ⌬E values and converted to 298 K bond dissociation enthalpies by using the integrated heat capacities of reactants and products.…”

Section: Instrumental Description and Data Analysismentioning

confidence: 99%

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Fluorotrimethylsilane affinities of anionic nucleophiles: A study of fluoride-induced desilylation

Krouse

Wenthold

2005

J. Am. Soc. Mass Spectrom.

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In this study, preparation and decomposition of five novel pentavalent fluorosiliconates, RSi(CH 3 ) 3 F Ϫ (R ϭ CH 3 CH 2 O, CF 3 CH 2 O, (CH 3 ) 2 CHO, (CH 3 ) 3 SiO, and (CH 3 ) 3 SiNH) is used to investigate the process of fluoride-induced desilylation. The siliconates were characterized by collision-induced dissociation and energy-resolved mass spectrometry. Decomposition of RSi(CH 3 ) 3 F Ϫ leads to loss of the nucleophile R Ϫ and FSi(CH 3 ) 3 , except in the case of (CH 3 ) 3 SiNHSi(CH 3 ) 3 F Ϫ , where HF loss is also observed. Ion affinities for FSi(CH 3 ) 3 have been measured for all five nucleophiles, and compare well with computational predictions. The observed trend of the bond dissociation energies resembles the trend of ⌬H acid values for the corresponding conjugate acids, RH. Additionally, this data has been incorporated with existing thermochemistry to derive fluoride affinities for four of the silanes (R ϭ CH 3 CH 2 O, (CH 3 ) 2 CHO, (CH 3 ) 3 SiO, and (CH 3 ) 3 SiNH). We use the fluoride affinity of the silanes and the FSi(CH 3 ) 3 affinity of the departing nucleophilic anion to assess the feasibility of fluorideinduced desilylation of the silanes examined in this work. (J Am Soc Mass Spectrom 2005, 16, 697-707)

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Section: Resultsmentioning

confidence: 99%

Section: Instrumental Description and Data Analysismentioning

confidence: 99%

Section: Instrumental Description and Data Analysismentioning

confidence: 99%

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Fluorotrimethylsilane affinities of anionic nucleophiles: A study of fluoride-induced desilylation

Krouse

Wenthold

2005

J. Am. Soc. Mass Spectrom.

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“…This first became obvious to us in our studies of the CID of transition metal cluster cations [8]. Subsequently, we have refined our treatment upon several occasions [67,68]. Presently, we use eq 11, which incorporates integration over a unimolecular dissociation probability.…”

Section: Kinetic Shiftsmentioning

confidence: 99%

“…Information necessary to utilize this model are molecular parameters for the energized molecules (for CID reactions, this is the same information needed to assess the internal energies of the reactant ions) and for the transition state (TS) leading to products. For many processes, we have argued [68] that the latter can be accurately assessed assuming that the TS is loose and located at the centrifugal barrier for product formation, a so-called orbiting TS or phase space limit TS. This should be true as long as the threshold for dissociation corresponds to the asymptotic products, which is generally true for ion-molecule systems for the reasons discussed above.…”

Section: Kinetic Shiftsmentioning

confidence: 99%

Mass spectrometry—Not just a structural tool: The use of guided ion beam tandem mass spectrometry to determine thermochemistry

Armentrout

2002

J. Am. Soc. Mass Spectrom.

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Guided ion beam tandem mass spectrometry has proved to be a robust tool for the measurement of thermodynamic information. Over the past twenty years, we have elucidated a number of factors necessary to make such thermochemistry accurate. Careful attention must be paid to the reduction of the raw data, ion intensities versus laboratory ion energies, to a more useful form, reaction cross sections versus relative kinetic energy. Analysis of the kinetic energy dependence of cross sections for endothermic reactions can then reveal thermodynamic data for both bimolecular and collision-induced dissociation (CID) processes. Such analyses need to include consideration of the explicit kinetic and internal energy distributions of the reactants, the effects of multiple collisions, the identity of the collision partner in CID processes, the kinetics of the reaction being studied, and competition between parallel reactions. This work provides examples illustrating the need to consider this multitude of effects along with details of the procedures developed in our group for handling each of them. ( W hen does a mass spectrometer become an ion beam instrument? Is this defined by the instrument, by whether the operator is an analytical or physical chemist, or by the experiments done? All mass spectrometers utilize ion beams, but the unspoken definition of an ion beam instrument is an apparatus that can be used to make quantitative physical measurements. In this regard, the capabilities of the instrumentation and the intent and training of the operator are all important factors. Whereas a mass spectrometer is often used as an identification tool through the use of mass spectral patterns, by taking advantage of the ability to easily change the kinetic energy of ions, it can also be a powerful instrument for the determination of thermodynamic data.In this article, I lay down some of the founding principles behind our use of tandem mass spectrometry, and in particular, so-called guided ion beam mass spectrometry to elucidate thermochemical information. This is achieved primarily by examining the kinetic energy dependence of endothermic ion-molecule reactions and determining their energy thresholds.Although many types of instruments have been used to perform such measurements, the link between such studies and guided ion beam techniques is a strong one. Indeed, the NIST Webbook [1] states in its section on Determinations of Reaction Endothermicity that "more commonly a so-called guided-beam apparatus is utilized for such determinations." Considering that there are only about a dozen such laboratories worldwide, this is a testament to the ability of this particular kind of apparatus to provide a plethora of high quality information. However, such information requires attention to myriad details, which are outlined in this article.Two fundamental types of reactions can be used to acquire thermodynamic information: Bimolecular exchange reactions, process 1, and collision-induced dissociation (CID), process 2.Reactions 1 can be either ex...

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