Gas-phase thermochemical information from triple quadrupole mass spectrometers: Relative proton affinities of amines

McLuckey, Scott A.; Cooks, R. Graham; Fulford, J.E.

doi:10.1016/0020-7381(83)85037-2

Cited by 59 publications

(51 citation statements)

References 12 publications

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“…This means that the more highly activated ions, with internal energy well above the dissociation threshold, fragment more readily under multiple collision conditions. By contrast to expectation based on the behavior of ions with large number of degrees of freedom [52], the experimentally measured effective temperature T eff under multiple collision conditions (Table 3) is lower than that obtained under single collision conditions (Table 2). Normally, more collisions should result in ions acquiring more internal energy, resulting in the higher effective temperatures [52], although collisional relaxation effects under multiple collision conditions [47] complicate this picture.…”

Section: Effective Temperature Decrease Under Multiple Collision Condcontrasting

confidence: 84%

“…By contrast to expectation based on the behavior of ions with large number of degrees of freedom [52], the experimentally measured effective temperature T eff under multiple collision conditions (Table 3) is lower than that obtained under single collision conditions (Table 2). Normally, more collisions should result in ions acquiring more internal energy, resulting in the higher effective temperatures [52], although collisional relaxation effects under multiple collision conditions [47] complicate this picture. In the simple salt clusters under study, however, the kinetic shift is negligible (only four vibrators), so internal energy can be stored in the ions only up to the critical energy, above which the ion dissociates very rapidly.…”

Section: Effective Temperature Decrease Under Multiple Collision Condcontrasting

confidence: 84%

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Alkali chloride cluster ion dissociation examined by the kinetic method: Heterolytic bond dissociation energies, effective temperatures, and entropic effects

Denault

Cooks

et al. 2002

J. Am. Soc. Mass Spectrom.

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Branching ratios have been measured as a function of collision energy for the dissociation of mass-selected chloride-bound salt cluster ions, Cl-M i ] ϩ , where M i ϭ Na, K, Cs. The extended version of the kinetic method was used to determine the heterolytic bond dissociation energy (HBDE) of Rb-Cl. The measured value of 480.8 Ϯ 8.5 kJ/mol, obtained under single collision conditions, agrees with the HBDE value (482.0 Ϯ 8.0 kJ/mol), calculated from a thermochemical cycle. The observed effective temperature of the collisionally activated salt clusters increases with laboratory-frame collision energy under both single-and multiplecollision conditions. Remarkably, the effective temperatures under multiple collision conditions are lower than those recorded under single-collision conditions at the same collision energy, a consequence of the inability of the triatomic ions to store significant amounts of internal energy. Laboratory-frame kinetic energy to internal energy transfer (T3 V) efficiencies range from 3.8 to 13.5%. For a given cluster ion, the T3 V efficiency decreases with increasing collision energy. Many features of the experimental results are accounted for using . Not only is this information useful in the interpretation and prediction of ionic reactivities and ion/molecule mechanisms, but the paucity of alternative sources of this information has made its acquisition an important application of ion/molecule reactions [2,3]. Methods for determining absolute values of thermochemical quantities are rarely applicable, so relative values are typically measured by kinetic and equilibrium measurements on gas-phase ions. Theoretical calculations serve a special reference function [4]. Under appropriate conditions, the kinetics of the dissociation of molecular cluster ions can yield relative, but quantitative, thermochemical information on the constituent species [5]. The kinetic method, based on this concept, has been widely used for estimating thermochemical properties [5,6]. Cluster ions bound via protons (eq 1), as well as other atomic or polyatomic anions or cations can be isolated and their dissociations followed in a tandem mass spectrometry experiment [7]. In eq 1, k 1 and k 2 represent the rate constants for two competitive dissociation channels of the proton-bound dimer to yield B 1 H ϩ and B 2 H ϩ , respectively. The ratio of rate constants, viz. the branching ratio of two fragment ion abundances, is related logarithmically to the gas-phase basicities of B 1 and B 2 , in the standard form of the kinetic method:In eq 2, ⌬(⌬G) is the difference in gas-phase basicities of B 1 and B 2 , R is the gas constant, and T eff is the effective temperature (the parameter in the kinetic method which connects the degree of fragmentation of

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Section: Effective Temperature Decrease Under Multiple Collision Condcontrasting

confidence: 84%

Section: Effective Temperature Decrease Under Multiple Collision Condcontrasting

confidence: 84%

Alkali chloride cluster ion dissociation examined by the kinetic method: Heterolytic bond dissociation energies, effective temperatures, and entropic effects

Denault

Cooks

et al. 2002

J. Am. Soc. Mass Spectrom.

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“…From the ratios of the ionic fragments of a loosely bound dimer, the difference in ion affinity of the neutrals can be calculated by Eqn (2) if T eff is known. McLuckey et al 24 demonstrated that, in the multiple collisions condition, the T eff of proton dimers increases with the collision energy. At 5 eV the T eff is 544 K; at 35 eV it is 757 K. Assuming a linear variation of T eff within the 5–35 eV range, a T eff at 15 eV of 615 K is calculated, and Table 1 lists the absolute differences in PA (ΔPA) for the pairs of isotopomers employed as calculated using the T eff of 615 K. This value is certainly a rough estimation for T eff , but one should note that imprecisions in the T eff would affect little the relative affinities; for instance, an error of 50% in T eff results in an error of only 0.01 kcal mol −1 in the final relative ion affinities.…”

Section: Resultsmentioning

confidence: 99%

Primary and secondary kinetic isotope effects in proton (H⁺/D⁺) and chloronium ion (³⁵Cl⁺/³⁷Cl⁺) affinities

Gozzo

Eberlin

2001

J. Mass Spectrom.

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The Cooks' kinetic method and tandem-in-space pentaquadrupole QqQqQ mass spectrometry were used to measure primary and secondary kinetic isotope effects (KIEs) in H(+) and Cl(+) (X(+)) affinity for a series of A/A(') isotopomeric pairs. Gaseous, isotopomeric, and loosely bound dimers [A...X(+)...A(')] were formed in combinations in which X = H(+), D(+), (35)Cl(+) or (37)Cl(+) and A/A(') = acetonitrile/acetonitrile - d(3), acetonitrile/acetonitrile-(15)N, acetonitrile-d(3)/acetonitrile-(15)N, acetone/acetone-d(6), acetone/acetone-(18)O, acetone-d(6)/acetone-(18)O, pyridine/pyridine-d(5), pyridine/pyridine-(15)N, pyridine-d(5)/pyridine-(15)N, or 3-((35)Cl)chloropyridine/3-((37)Cl)chloropyridine. Under nearly the same experimental conditions, the dimers were mass-selected and then dissociated by low-energy collisions with argon, yielding AX(+) and A(')X(+) as the fragment ions. KIEs were measured from the changes in ion affinities of the neutrals (DeltaX(+)) as estimated by the AX(+)/A(')X(+) abundance ratios. Using [A...H(+)(D(+))...A(')] and [A...(35)Cl(+)((37)Cl(+))...A(')] dimers and by comparing their extent of dissociation under nearly identical collision-induced dissociation conditions, the kinetic method was also applied, for the first time, to measure primary KIEs of the central ion as well as their influence on secondary KIEs. Becke3LYP/6-311++G(2df,2p) calculations were found to provide Delta(DeltaZPE)s for the competitive dissociation reactions that accurately predict the nature (normal or inverse) of the measured KIEs.

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“…The Ðrst point has been made repeatedly in the literature of the kinetic method, from very early experiments. 45,46 The second point is emphasized by Drahos and Ve key,44 but also appears in the early experiments by McLuckey et al 45 Evidence for the third point has been discussed qualitatively in various recent experimental studies. 28,47 The elegant work of Drahos and Ve key44 enhances the understanding of e †ective temperature provided by Brauman and co-workers.…”

Section: Temperatures and Internal Energy Distributionsmentioning

confidence: 87%

The kinetic method of making thermochemical determinations

1999

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Gas-phase thermochemical information from triple quadrupole mass spectrometers: Relative proton affinities of amines

Cited by 59 publications

References 12 publications

Alkali chloride cluster ion dissociation examined by the kinetic method: Heterolytic bond dissociation energies, effective temperatures, and entropic effects

Alkali chloride cluster ion dissociation examined by the kinetic method: Heterolytic bond dissociation energies, effective temperatures, and entropic effects

Primary and secondary kinetic isotope effects in proton (H⁺/D⁺) and chloronium ion (³⁵Cl⁺/³⁷Cl⁺) affinities

The kinetic method of making thermochemical determinations

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Gas-phase thermochemical information from triple quadrupole mass spectrometers: Relative proton affinities of amines

Cited by 59 publications

References 12 publications

Alkali chloride cluster ion dissociation examined by the kinetic method: Heterolytic bond dissociation energies, effective temperatures, and entropic effects

Alkali chloride cluster ion dissociation examined by the kinetic method: Heterolytic bond dissociation energies, effective temperatures, and entropic effects

Primary and secondary kinetic isotope effects in proton (H+/D+) and chloronium ion (35Cl+/37Cl+) affinities

The kinetic method of making thermochemical determinations

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Primary and secondary kinetic isotope effects in proton (H⁺/D⁺) and chloronium ion (³⁵Cl⁺/³⁷Cl⁺) affinities