Thermal Ion-molecule Reactions Research Articles

Effect of Intersystem Crossings on the Kinetics of Thermal Ion-Molecule Reactions: Ti+ + O2, CO2, and N2O.

A selected-ion flow tube apparatus has been used to measure rate constants and product branching fractions of 2Ti+ reacting with O2, CO2, and N2O over the range of 200-600 K. Ti+ + O2 proceeds at near the Langevin capture rate constant of 6-7 × 10-10 cm3 s-1 at all temperatures to yield 4TiO+ + O. Reactions initiated on doublet or quartet surfaces are formally spin-allowed; however, the 50% of reactions initiated on sextet surfaces must undergo an intersystem crossing (ISC). Statistical theory is used to calculate the energy and angular momentum dependences of the specific rate constants for the competing isomerization and dissociation channels. This acts as an internal clock on the lifetime to ISC, setting an upper limit on the order of τISC < 1e-11 s. 2Ti+ + CO2 produces 4TiO+ + CO less efficiently, with a rate constant fit as 5.5 ± 1.3 × 10-11 (T/300)-1.1±0.2 cm3 s-1. The reaction is formally spin-prohibited, and statistical modeling shows that ISC, not a submerged transition state, is rate-limiting, occurring with a lifetime on the order of 10-7 s. Ti+ + N2O proceeds at near the capture rate constant. In this case, both Ti+ON2 and Ti+N2O entrance channel complexes are formed and can interconvert over a barrier. The main product is >90% TiO+ + N2, and the remainder is TiN+ + NO. Both channels need to undergo ISC to form ground-state products but TiO+ can be formed in an excited state exothermically. Therefore, kinetic information is obtained only for the TiN+ channel, where ISC occurs with a lifetime on the order of 10-9 s. Statistical modeling indicates that the dipole-preferred Ti+ON2 complex is formed in ∼80% of collisions, and this value is reproduced using a capture model based on the generic ion-dipole + quadrupole long-range potential.

C-C Bond Formation of Mg- and Zn-Activated Carbon Dioxide.

Gas-phase activation of CO2 by chloride tagged metal atoms, [ClM]- (M=Mg, Zn), has been investigated by mass spectrometry and high-level quantum chemistry. Both metals activate CO2 with significant bending of the CO2 moiety to form complexes with the general formula [ClM,CO2 ]- . The structure of the metal-CO2 complex depends on the method of formation, and the energy landscapes and reaction dynamics have been probed by collisional induced dissociation and thermal ion molecule reactions with isotopically labeled species. Having established these structural relationships, the gas-phase reactivity of [ClM(κ2 -O2 C)]- with acetaldehyde (here considered a carbohydrate mimic) was then studied. Formation of lactate and enolate-pyruvate complexes are observed, showing that CO2 fixation by C-C bond formation takes place. For M=Zn, even formation of free pyruvate ([C3 H3 O3 ]- ) is observed. Implications of the observed CO2 reactivity for the electrochemical conversion of carbon dioxide, and to biochemical and artificial photosynthesis is briefly discussed. Detailed potential energy diagrams obtained by the quantum chemical calculations offer models consistent with experimental observation.

Highly Charged Protein Ions: The Strongest Organic Acids to Date

AbstractThe basicity of highly protonated cytochrome c (cyt c) and myoglobin (myo) ions were investigated using tandem mass spectrometry, ion–molecule reactions (IMRs), and theoretical calculations as a function of charge state. Surprisingly, highly charged protein ions (HCPI) can readily protonate non‐polar molecules and inert gases, including Ar, O2, and N2 in thermal IMRs. The most HCPIs that can be observed are over 130 kJ mol−1 less basic than the least basic neutral organic molecules known (tetrafluoromethane and methane). Based on theoretical calculations, it is predicted that protonated cyt c and myo ions should spontaneously lose a proton to vacuum for charge states in which every third residue is protonated. In this study, HCPIs are formed where every fourth residue on average is protonated. These results indicate that protein ions in higher charge states can be formed using a low‐pressure ion source to reduce proton‐transfer reactions between protein ions and gases from the atmosphere.

Highly Charged Protein Ions: The Strongest Organic Acids to Date

The basicity of highly protonated cytochrome c (cyt c) and myoglobin (myo) ions were investigated using tandem mass spectrometry, ion-molecule reactions (IMRs), and theoretical calculations as a function of charge state. Surprisingly, highly charged protein ions (HCPI) can readily protonate non-polar molecules and inert gases, including Ar, O2 , and N2 in thermal IMRs. The most HCPIs that can be observed are over 130 kJ mol-1 less basic than the least basic neutral organic molecules known (tetrafluoromethane and methane). Based on theoretical calculations, it is predicted that protonated cyt c and myo ions should spontaneously lose a proton to vacuum for charge states in which every third residue is protonated. In this study, HCPIs are formed where every fourth residue on average is protonated. These results indicate that protein ions in higher charge states can be formed using a low-pressure ion source to reduce proton-transfer reactions between protein ions and gases from the atmosphere.

Kinetic energy release in thermal ion-molecule reactions: single charge-transfer reactions of vanadium(2+) and tantalum(2+) with benzene

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTKinetic energy release in thermal ion-molecule reactions: single charge-transfer reactions of vanadium(2+) and tantalum(2+) with benzeneJames R. Gord, Ben S. Freiser, and Steven W. BucknerCite this: J. Phys. Chem. 1991, 95, 21, 8274–8279Publication Date (Print):October 1, 1991Publication History Published online1 May 2002Published inissue 1 October 1991https://doi.org/10.1021/j100174a048RIGHTS & PERMISSIONSArticle Views46Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (771 KB) Get e-Alerts

Formation of thermodynamically stable dications in the gas phase by thermal ion-molecule reactions: tantalum(2+) and zirconium(2+) with small alkanes

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFormation of thermodynamically stable dications in the gas phase by thermal ion-molecule reactions: tantalum(2+) and zirconium(2+) with small alkanesYasmin A. Ranasinghe, Timothy J. MacMahon, and Ben S. FreiserCite this: J. Phys. Chem. 1991, 95, 20, 7721–7726Publication Date (Print):October 1, 1991Publication History Published online1 May 2002Published inissue 1 October 1991https://doi.org/10.1021/j100173a032RIGHTS & PERMISSIONSArticle Views157Altmetric-Citations81LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (689 KB) Get e-Alerts

Kinetic energy release in thermal ion–molecule reactions: The Nb2+–(benzene) single charge–transfer reaction

We have adapted the techniques originally developed to measure ion kinetic energies in ion cyclotron resonance (ICR) spectrometry to study the single charge–transfer reaction of Nb2+ with benzene under thermal conditions in a Fourier transform ion cyclotron resonance mass spectrometer (FTICRMS). The partitioning of reaction exothermicity among the internal and translational modes available is consistent with a long-distance electron-transfer mechanism, in which the reactants approach on an ion-induced dipole attractive potential and cross to a repulsive potential at a critical separation of ∼7.5 Å when electron transfer occurs. The reaction exothermicity, 5.08 eV, is partitioned to translation of Nb+, 0.81±0.25 eV, translation of C6 H6+, 1.22±0.25 eV, and internal excitation of C6 H6+ to produce the la2u electronic state, which is ∼3 eV above the ground state of the ion. We have also studied the kinetics of the reaction of Nb2+ with benzene and determined the rate constant, k = 1.4×10−9 cm3 molecule−1 s−1, and the efficiency, 0.60, of the process. These also support the proposed charge–transfer mechanism. In addition to the charge–transfer pathway, which accounts for 95% of the reaction products, Nb2+ is observed to dehydrogenate benzene to form Nb2+ (benzyne). This process implies D(Nb2+ –benzyne)≥79 kcal/mol.

Formation of thermodynamically stable dications in the gas phase by thermal ion–molecule reactions: Nb2+ with small alkanes

The gas-phase reactions of Nb2+ with small alkanes at thermal energies are reported. For methane and ethane, dehydrogenation is a prominent reaction pathway. For propane and butane, charge transfer is virtually the only reaction pathway observed (&amp;gt;99%). NbCH2+2 and NbC2H2+2 formed in the reactions of Nb2+ with methane and ethane are thermodynamically stable with D(Nb2+–CH2)=197±10 kcal/mol, D(Nb+–CH+2)=107±10 kcal/mol, D(Nb2+–C2H2)≥74 kcal/mol, and D(Nb+–C2H+2)≥7 kcal/mol. The stability of these ions is most likely due to the charge-stabilizing effect of the metal center. Collision-induced dissociation of these ions results in charge-splitting reactions as well as reactions in which both charges remain on the metal center. Hydride transfer is observed to be competitive in the primary reactions of Nb2+ with alkanes. The hydride- and charge-transfer results are in qualitative agreement with a simple curve-crossing model.

Formation of primary amide complexes of Fe +, Co + and Rh + in the gas phase

Primary amide complexes, M +-NH 2, of Fe +, Co + and Rh + are formed in thermal ion-molecule reactions using a Fourier transform mass spectrometer. Contrary to previous belief, these complexes have relatively high MN bond strengths. These complexes were generated in reactions of various metal-ligand cations with NH 3. Collision-induced dissociation was used to probe the structures of these complexes. Mechanisms for the formation reactions are all proposed to proceed via oxidative addition of NH bonds in NH 3 to the various metal centres, followed by reductive elimination of either H 2O or H 2.

Statistical adiabatic channel model of ion-neutral dipole capture rate constants

The statistical adiabatic channel model is applied to thermal ion-molecule reactions, which are determined by capture rates, and to ion-molecule association reactions in the high-pressure limit. The radial part of the long-range potential leads to the known ion-locked-dipole rate expression. The anisotropy of the potential introduces rigidity described by an ion-dipole locking constant C. To a first approximation one derives, for dominant permanent dipole contributions. C = 1 − 0.614exp[−( B/kT) 2], where B denotes the rotational constant of the dipolar molecule. This result is often close to recent approximate quantum scattering and classical trajectory calculations.

Thermal ion—molecule reactions in oxygen-containing molecules. Ion—molecule clustering reactions in trioxane

The ion—molecule clustering reactions in trioxane have been studied with a time-of-flight mass spectrometer. The cluster ions, (CH 2O) n H + ( n = 3—9), were formed at long delay times. The first steps of the clustering reactions initiated by CH 2OH + and (CH 2O) 2H + were third-order reaction mechanisms and the second steps were second order. Similarly, the first step of the clustering reaction initiated by the protonated molecular ion, (CH 2O) 3H +, was a third-order reaction mechanism and the second step was second-order. However, the reaction order of the first step of the reaction with CH 2OH + changed with increasing delay time. The rate constants of the third-order clustering reactions observed in trioxane were very much arger than those reported in other simple molecules, and agreed with the values calculated theoretically using an empirical rate constant equation. It was found that the cluster ions formed in the clustering reactions of a polyatomic oxygen-containing molecule, such as trioxane, have a long life-time and are relatively stable owing to the large number of degrees of freedom of these ions. In addition, it was shown that the stability and reactivity of the cluster ion correlates with the structure of the ion.

ChemInform Abstract: THERMAL ION‐MOLECULE REACTIONS IN OXYGEN‐CONTAINING MOLECULES. INVERSE ISOTOPE EFFECT IN THE ION‐MOLECULE DIMERIZATION REACTIONS OF PROTONATED PROPYL ACETATE IONS

Chemischer InformationsdienstVolume 10, Issue 19 Physical Organic Chemistry ChemInform Abstract: THERMAL ION-MOLECULE REACTIONS IN OXYGEN-CONTAINING MOLECULES. INVERSE ISOTOPE EFFECT IN THE ION-MOLECULE DIMERIZATION REACTIONS OF PROTONATED PROPYL ACETATE IONS M. KUMAKURA, M. KUMAKURASearch for more papers by this authorK. ARAKAWA, K. ARAKAWASearch for more papers by this authorT. SUGIURA, T. SUGIURASearch for more papers by this author M. KUMAKURA, M. KUMAKURASearch for more papers by this authorK. ARAKAWA, K. ARAKAWASearch for more papers by this authorT. SUGIURA, T. SUGIURASearch for more papers by this author First published: May 8, 1979 https://doi.org/10.1002/chin.197919065AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume10, Issue19May 8, 1979 RelatedInformation

Thermal ion-molecule reactions in oxygen-containing molecules. Proton and acetyl ion transfer reactions in n-Propyl acetate-acetaldehyde mixtures

Thermal ion-molecule reactions in n-propyl acetate-acetaldehyde mixtures have been studied using a time-of-flight mass spectrometer. As cross-reaction product ions, CH 3CHOH +, CH 3COOC 3H 7H +, and CH 3CHOCH 3CO + were observed. CH 3COOH 2 + and CH 3CO + from n-propyl acetate undergo proton and acetyl ion transfer reactions in which CH 3COOH 2 + leads to the formation of CH 3CHOCH 3CO + by condensation-elimination reaction via a homo-elimination mechanism. The rate constants for the formation of CH 3CHOCH 3CO + by both CH 3COOH 2 + and CH 3CO + from n-propyl acetate were larger than those for CH 3COOC 3H 7CH 3CO + by a factor of four. CH 3CHO + and CH 3CO + from acetaldehyde did not participate in the acetyl ion transfer reaction leading to the formation of CH 3COOC 3H 7CH 3CO +.

Thermal ion–molecule reactions in oxygen-containing molecules. Inverse isotope effect in the ion–molecule dimerization reactions of protonated propyl acetate ions

Thermal ion–molecule dimerization reactions of protonated molecular ions in [2H3]n- and [2H3]iso-propylacetate have been studied with a time-of-flight mass spectrometer. CD3COOH+2 and CD3CO+ ions react with the neutral molecules to form CD3COOC3H7H+ and CD3COOC3H7D+ ions. These CD3COOC3H7H+ and CD3COOC3H7D+ ions subsequently react with the neutral molecules to form (CD3COOC3H7)2D+ ions by bimolecular dimerization reactions in which an inverse isotope effect is observed. The effect of various reaction conditions on the isotope effect has been studied and the relation between the isotope effect and the dimerization reaction mechanism is discussed.

Thermal ion–molecule reactions in oxygen-containing molecules. Formation of long-lived intermediate ions in acetyl chloride

The thermal ion–molecule reactions in acetyl chloride have been studied. The dissociation reaction of long-lived intermediate ions (CH3COClH+*) leading to the formation of CH3CO+ was observed. The formation of CH3COClH+ was confirmed from the detection of the metastable ions, and CH3COClH+* results from the reaction of CH3CO+ with acetyl chloride. CH3CO+ reacts with acetyl chloride to form CH3COClH+. In n-propyl acetate–acetyl chloride mixtures, the ion–molecule reactions involving CH3CO+ and CH3COOH+2 have been investigated to clarify the effect of reactant ions on the formation of CH3COClH+*. The reaction channel of CH3CO+ from n-propyl acetate with acetyl chloride to form CH3COClH+ is more probable than that of CH3CO+ from acetyl chloride. CH3CO+ from acetyl chloride led preferentially to the formation of CH3COClH+* in comparison with reactions of CH3CO+ from n-propyl acetate. The measurement of the translational energies of both CH3CO+ ions allows a clear elucidation of the detailed mechanism of dissociation of CH3COClH+* ions formed in the mixtures.

Thermal ion—molecule reactions in oxygen-containing molecules. Condensation—elimination reactions in n-propyl formate

The condensation—elimination reactions involving CH 2OH + and CH 2CHCH 3 + in n-propyl formate have been studied using a time-of-flight mass spectrometer. CH 2OH + reacts with the neutral molecule to form HCOOC 3H 7H +, HCOOC 3H 7CH + and HCOOC 3H 7CHO +; CH 2CHCH 3 + reacts to form HCOOC 3H 7H + and HCOOC 3H 7CH 2CHCH 2 +. The condensation—elimination reactions leading to the formation of these ions were studied using n-propyl formate- d. The product ions are formed by the dissociation of the intermediate complex in which extensive scrambling does not take place. The rate constants for the product ions resulting from the condensation—elimination and dimerization reactions were obtained. The rate constant of the proton transfer reaction by CH 2OH + is larger than that by CH 2CHCH 3 +, and thus it was found that the proton donor activity of an oxonium ion such as CH 2OH + is greater than that of a carbonium ion such as CH 2CHCH 3 +.

Thermal ion-molecule reactions in oxygen-containing molecules. Condensation-elimination reactions in n-propyl acetate

Thermal ion-molecule reactions in n-propyl acetate have been studied using a time-of-flight mass spectrometer. The appearance potentials and ionization efficiency curves of the fragment and product ions were measured by an RPD technique and the fine structures in the curves were clarified. The protonated molecular ion resulted from the proton transfer reactions of CH 3COOH 2 + and CH 3CO + with n-propyl acetate, and the protonated dimer ion from the condensation reaction of the protonated molecular ion with an n-propyl acetate molecule. In the proton transfer reaction by CH 3COOH 2 +, the transfer of the carboxyl group proton predominates as compared with that of the acetyl group proton. The acetylated ions were formed by the condensation and condensation-elimination reactions, and the condensation-elimination reaction involving CH 3COOH 2 + is via a cross-elimination mechanism which eliminates a water molecule.

Thermal ion-molecule reactions in oxygen-containing molecules. Condensation-elimination and addition reactions in simple aliphatic ketones

Thermal ion-molecule reactions in oxygen-containing molecules. Condensation-elimination and addition reactions in simple aliphatic ketones

Thermal ion-molecule reactions in oxygen-containing molecules. Condensation-elimination reactions involving CH 3+ and C 2H 4O + in acetaldehyde and ethylene oxide

The condensation-elimination reactions involving CH 3 + and C 2H 4O + in acetaldehyde and ethylene oxide have been studied using a time-of-flight mass spectrometer. The CH 3 + ions react with acetaldehyde and ethylene oxide to form C 2H 3 +, C 2H 4 +, C 2H 5 + and CH 3O +. Further studies in the reactions of CH 3 + were made in methane-acetaldehyde (or ethylene oxide) mixtures, and the formation mechanism of C 2H 5 + and CH 3O + was elucidated. The C 2H 4O + ions react with acetaldehyde and ethylene oxide to form C 3H 5O +, C 3H 6O +, and C 3H 7O +. Mechanistic studies in the ionic reactions involving the isomeric ions (CH 3CHO + and CH 2CH 2O +) was also made in acetaldehyde-d 4-ethylene oxide mixtures. From the distribution of isotopic product ions, the structures of the product ions and the condensation-elimination reaction mechanism were examined. In addition, the rate constants for the product ions were obtained.

Thermal ion–molecule reactions in oxygen-containing molecules. Proton and hydride ion transfer reactions in acetaldehyde

The proton and hydride ion transfer reactions in acetaldehyde have been studied on a modified time-of-flight mass spectrometer. The appearance potentials and the ionization efficiency curves of fragment and product ions were measured by the r.p.d. technique and the precursors of the product ions were determined from an analysis of the shapes of these curves. Rate constants for the formation reactions of CH3CHOH+ and CH3CO+ were obtained. The positions from which proton and/or hydrogen atom transfer occur were clarified using [2H3]2,2,2-acetaldehyde. The rate constant of proton and/or hydrogen atom transfer from the formyl group is larger than that from the methyl group by a factor of two. It was also confirmed that CH+3 abstracts only the hydrogen of the formyl group in the hydride ion transfer reaction. The hydride ion transfer involving CH+3 from methane was studied in acetaldehyde + methane mixtures and its rate constant is larger than that in pure acetaldehyde.