Benzene Ions Research Articles

Ion nucleation as a detector: application of REMPI to generate selected ions in supersaturated vapors

Resonance enhanced multiphoton ionization (REMPI) of aromatic molecules present in a small concentration within a supersaturated host vapor is demonstrated. The method is applied to the study of ion nucleation in supersaturated vapors of methanol, acetonitrile and nonane induced by the molecular ions of benzene, toluene, and p-xylene. With this method it is now possible to selectively and unambiguously generate specific ions of interest and study their nucleating behavior. Furthermore, the selectivity of REMPI combined with the amplification and detection capabilities of nucleation and growth offer valuable analytical features for the identification of trace components in supersaturated vapors.

Examination of Sputtered Ion Mechanisms Leading to the Formation of C7H7+ during Surface Induced Dissociation (SID) Tandem Mass Spectrometry (MS/MS) of Benzene Molecular Cations

Recent work reported in the literature has shown new evidence of a sputtered ion mechanism for associative ion surface reactions occurring during surface induced dissociation (SID) tandem mass spectrometry (MS/MS). In the context of a sputtered ion mechanism, we have studied selected routes to the formation of C7H7+ during the low-energy collision (ca. 30 eV) of benzene molecular ions with surfaces covered with a hydrocarbon overlayer. A key approach utilized in this work is the use of gas phase ion molecule chemistry to model reactive ion surface collisions. Benzene, 2H6-labeled benzene, and 13C6-labeled benzene have been examined by SID and collision activated dissociation (CAD). The CAD experiments have been used to investigate the fragmentation of hydrocarbon adducts of benzene and labeled benzene formed by methane and isobutane chemical ionization (CI) as models of those ions which may be formed via a sputtered ion mechanism during SID. In addition, the thermodynamics of many of the possible sputtered ion routes to the formation of C7H7+ have been compared using experimental heats of formation as well as total energies and zero-point vibrational energies (ZPVE) obtained by ab initio (MP2 6-31G*//HF 6-31G*) calculations. While there are several seemingly viable sputtered ion routes to the formation of C7H7+ during SID of benzene molecular ions, the combination of thermodynamic considerations and experimental results suggest that a likely sputtered ion route involves the reaction of neutralized benzene ions with C3H5+ ions (sputtered from the hydrocarbon overlayer) followed by the loss of ethene.

Chemical Reactivity in Microscopic Systems: The Nucleophilic Substitution of Halogenated Benzene Ions by Ammonia Studied in Molecular Clusters

Chemical Reactivity in Microscopic Systems: The Nucleophilic Substitution of Halogenated Benzene Ions by Ammonia Studied in Molecular Clusters

Ionization of Benzene and Toluene Molecules with Kinetic Energy on Metal Surfaces

Ionization of Benzene and Toluene Molecules with Kinetic Energy on Metal Surfaces

Radiative Association Kinetics of Methyl-Substituted Benzene Ions

Radiative Association Kinetics of Methyl-Substituted Benzene Ions

Condensation of Supersaturated Vapors on Benzene Ions Generated by Resonant Two-Photon Ionization: A New Technique for Ion Nucleation

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCondensation of Supersaturated Vapors on Benzene Ions Generated by Resonant Two-Photon Ionization: A New Technique for Ion NucleationDavid Kane, George M. Daly, and M. Samy El-ShallCite this: J. Phys. Chem. 1995, 99, 20, 7867–7870Publication Date (Print):May 1, 1995Publication History Published online1 May 2002Published inissue 1 May 1995https://doi.org/10.1021/j100020a006RIGHTS & PERMISSIONSArticle Views105Altmetric-Citations47LEARN 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 (445 KB) Get e-Alerts

Mass shifts due to ion/ion interactions in a quadrupole ion‐trap mass spectrometer

AbstractMass spectra recorded using a Paul ion trap, operated in the mass‐selective instability scan mode, give peak positions which are shown to depend on ion abundance. The isolated molecular ions of benzene, anisole, cresol, and n‐butylbenzene are ejected during the mass selective instability scan at times which display a linear dependence on ion abundance for low populations of trapped ions. Remarkably, the degree to which the peaks are shifted is also compound dependent. Mass shifts are also influenced by the presence of other ions in the trap and this effect is amplified as the mass difference between the analyte and matrix ions decreases. Mass shifts are also affected by the helium pressure which controls the ion density. Extrapolation to zero ion abundance and to zero helium pressure is suggested as a method of eliminating these effects and hence of improving the mass measurement accuracy attainable using the ion trap.

Cationic polymerization within clusters composed of unsaturated molecules

Abstract Electron impact ionization of large neutral clusters composed of simple olefinic molecules (ethene, 1,1-difluoroethene and propene) display highly anomalous ion intensity distributions. These cluster ion distributions typically exhibit a magic number at n = 4, for cluster ions of the type {M}+, where M is an olefinic molecule. The explanation which best explains this observation is that these small ‘cluster’ ions are in actuality covalently bound molecular ions formed by sequential ion-molecule association (polymerization) reactions which have occurred within the cluster ion. This size dependent cluster chemistry is accounted for by kinetic bottlenecks which occur in the ionic chain growth reactions and which terminate with the formation of cyclic molecular ions (i.e. cyclopentanes and cyclohexanes ions). The condensed phase counterparts of these intracluster reactions are the free cationic polymerization reactions initiated by radiolysis of bulk samples of the olefins. In addition to reviewing our own efforts in this field, we will discuss previous work on cationic polymerization which is relevant to the new chemistry we have observed within clusters of olefinic molecules. We also will present work concerning acetylene and methylacetylene cluster ions where we also observe similar intracluster ion-molecule reactions giving rise to what are most likely benzene and trimethylbenzene ions. Lastly, we will show how mixed cluster of acetylene-acetone also are capable of producing covalently bonded cyclic molecular ions again via intracluster ion-molecule polymerization reactions. We therefore feel that these new cluster condensation reactions constitutes a more general family of chemical reactions for all cluster ions containing unsaturated molecules.

The isomerization of C 6H 6 radical cations. A comparison of photodissociation results with semi-empirical molecular orbital calculations

Semi-empirical calculations on the isomerization of C 6H + 6 radical cations give a clear picture of the relevant processes, which is in good agreement with previous experiments. For the 1,3-hexadien-5-yne radical cation the barrier for isomerization to the benzene structure is well below the dissociation limit. For all other linear benzene isomers the barrier is much closer to the dissociation threshold but sufficiently low for an isomerization of part of the ions to stable benzene ions. The very low barrier for isomerization of the 1,5-hexadiyne radical cation to the benzene structure is ascribed to the very weak-nature of the central bond in this ion which leads to a low-energy isomerization to the 1,2,4,5-hexatetraene structure and from there to the benzene structure. The calculations furthermore show that many non-classical ion structures have heats of formation comparable to or lower than that of classical ion structures. The calculated barrier for an isomerization to the fulvene structure shows that the barrier for carbon scrambling in the benzene ion is well below the dissociation limit.

High-efficiency surface-induced dissociation on a rhenium oxide surface

We report on the high-efficiency surface-induced dissociation of benzene and cyclohexane polyatomic ions after scattering from a rhenium oxide surface with a kinetic energy of 5-290 eV. Rhenium oxide was prepared by directly heating a rhenium metal foil, under 10 −5 mbar partial oxygen pressure, at about 1000 K. Rhenium oxide is characterized by a very high work function of 6.4 eV and thus minimizes ion reneutralization probabilities. The catalytic combustion of surface organic impurities with oxygen ensures good long-term stability. We found that the surface-induced dissociation ion current is 70 times larger on rhenium oxide than on bare rhenium or stainless steel. Absolute scattered ion yields of about 50% were measured. The implications of surface-induced dissociation on mass spectrometry in supersonic molecular beams are mentioned.

Radiative and collisional association of mesitylene ion with parent neutral at 196 K

The dimerization of mesitylene (1,3,5-trimethylbenzene) ion was measured at 196 and 300 K in the ICR ion trap. Radiative association at 196 K had a rate constant 7×10 −12 cm 3 molecule −1 s −1. Analysis gave a collisional efficiency of 0.006, an IR photon emission rate of 29 s −1 and a complex redissociation rate of 5×10 3 s −1. The three-body association rate was 2.9×10 −22 cm 6 molecule −2 s −1 at 196 K and 9×10 −25 at 300 K. Mesitylene ion radiative association kinetics at 196 K should be a good analog for benzene ion association at interstellar cloud temperatures around 50 K.

Collision-induced dissociation of Ag (C 6H 6) +

Collision-induced dissociation (CID) of Ag (C 6H 6) + is studied by using guided ion beam mass spectrometry. A flow tube source is used to produce thermalized silver benzene ions. Ag + is the only observed ionic product; no charge transfer product C 6H + 6 is found, in contrast with previous photodissociation results. Careful analysis of the CID threshold yields a 0 K bond dissociation energy of D(Ag +−C 6H 6) = 1.62 ± 0.07 eV (37.4 ± 1.7 kcal/mol). This value is compared with several literature values.

Reactive collisions of benzene ion C6H6.bul.+ and C6D6.bul.+ at self-assembled monolayer films prepared on gold from n-alkane thiols and a fluorinated alkanethiol: the influence of chain length on the reactivity of the films and the neutralization of the projectile

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTReactive collisions of benzene ion C6H6.bul.+ and C6D6.bul.+ at self-assembled monolayer films prepared on gold from n-alkane thiols and a fluorinated alkanethiol: the influence of chain length on the reactivity of the films and the neutralization of the projectileArpad Somogyi, Thomas E. Kane, Jian Mei Ding, and Vicki H. WysockiCite this: J. Am. Chem. Soc. 1993, 115, 12, 5275–5283Publication Date (Print):June 1, 1993Publication History Published online1 May 2002Published inissue 1 June 1993https://doi.org/10.1021/ja00065a044RIGHTS & PERMISSIONSArticle Views249Altmetric-Citations79LEARN 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 (1 MB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

The photoionization and dissociation dynamics of energy-selected acetylene dimers, trimers, and tetramers

The photoionization and dissociation characteristics of (C2H2)n (n=2, 3, and 4) have been studied by the threshold photoelectron–photoion coincidence technique applied to a molecular beam. For photon energies between 10.20 and 11.27 eV, only dissociative ionization pathways were observed for the clusters; no direct ionization of (C2H2)2, (C2H2)3, and (C2H2)4 to the stable ions C4H4+, C6H6+, and C8H8+ was observed. The shape of the time of flight peaks is consistent with statistical dissociation dynamics, and statistical analysis of the fragment peak shapes suggests that the dimer, trimer, and tetramer produce the fragments C4H2+/C4H3+, C4H4+, and C6H6+, respectively. Consistent with these observations, ab initio calculations are presented which indicate that the neutral T-shaped dimer and triangular trimer geometries are unstable on the ionic potential energy surface, and indeed have vertical ionization energies well above the dissociation limits of many of their possible product channels. The statistical modeling of the C4H4+ peak width is consistent with a process in which the trimer neutral produces a C4H4+–C2H2 complex, which then dissociates via monomer evaporation without exploring any of the covalent C6H6+ potential energy surface, i.e., benzene ion is not formed. The heat of formation of the observed C4H4+ daughter is estimated to be 1240±15 kJ/mol, indicating that it is cyclobutadiene, butatriene, or vinylacetylene ion. The peak width of C6H6+ is also analyzed, and suggests a process whereby the tetramer produces a C6H6+–C2H2 complex, which dissociates via monomer evaporation without exploring any of the covalent C8H8+ potential energy surface. The heat of formation of the C6H6+ daughter fragment is estimated as 1160±15 kJ/mol, which is consistent with the formation of benzvalene ion.

Formation of long-lived benzene ions during charge exchange ionization of 1,5-hexadiyne in an ion cyclotron resonance spectrometer

Although it is generally accepted that C 6H + 6 ions from 1,5-hexadiyne have a heat of formation above the dissociation limit, charge exchange ionization of 1,5-hexadiyne in an ion cyclotron resonance spectrometer produces significant fractions of C 6H + 6 ions, having the benzene structure, which survive for at least a few hundred milliseconds. Stabilization of the excited C 6H + 6 ions before they dissociate is believed to be due to IR radiative emission. Using the rates of dissociation and radiative emission from recent measurements, the expected fraction of stabilized parent ions is calculated for the present conditions, and is found to agree with the observed results with near-quantitative accuracy. This indicates that the energy deposition in the charge transfer ionizations used here is complete to within one or two tenths of an electronvolt.

Intracluster polymerization reactions within acetylene and methylacetylene clusters ions

Abstract. We report the observation of laige (n up to -25) acetylene and methy-lacetylene cluster ions- the largest yet reported from ionization of neutral(C2H 2 )n or (CH 3 CCH)n clusters. The cluster ion intensity distributions of bothsystems display prominent magic numbers at n = 3. This finding is indicativeof Intracluster ion-molecule reactions giving rise to what are most likely ben-zene and trlmethylbenzene ions from (C2H2)n+ and (CH3CCH)n + cluster ions,respectively. The acetylene cluster Ion intensity distributions observed underefficient clustering conditions are further characterized by unexpected fea-tures, most notably a sharp break at n = 7 and a strong magic number at n= 14. The mass spectra of methylacetylene display a less dramatic break at n = 7and a weak magic number around n = 10. These surprising structures mayarise as a result of the formation of particularly stable covalently bondedmolecular ions. In view of the unique properties of carbon it is possible thatthese ions possess spherical cage geometries reminiscent of the fullerenes.t Alfred P Sloan Fbundation Fellow 1991-3.

Experimental and theoretical characterization of isomeric adduct ions of silicon radical cation and benzene and their neutral counterparts

Results of gas-phase experiments and theoretical investigations are reported which provide evidence for the stability of the π-complex Si .+ -C 6 H 6 and the C-H insertion complex C 6 H 5 SiH .+ . Theory also predicts the stability of the ring-insertion complex for which the experiments could not provide unambiguous experimental evidence. The π-complex and C-H insertion complex are distinguished with neutralization-reionization (NR) mass spectrometry experiments at 8 keV which also provide evidence for the stability of the corresponding neutral molecules

ESR “in situ” studies of photostimulated formation of benzene cation-radicals over ZSM-5 zeolites

Photostimulated formation of stabilized benzene cationradicals over ZSM-5 zeolite has been found. Benzene ionization follows a monophotonic mechanism starting from photon energy hν=2.8 eV. The formation of donor-acceptor complexes of adsorbed benzene molecules with strong accepting sites on zeolite is suggested. Irradiation within the charge-transfer band is accompanied by photodissociation of these complexes and generation of benzene cation radicals.

A striking solvent effect on the photochemical reaction of naphthalene with 2-(diethylamino)ethanol

Photochemical reaction of naphthalene with 2-(diethylamino)ethanol shows a striking effect of solvent polarity on the reaction course, which is explained in terms of the intermediacy of a geminate radical ion pair in benzene and free radical ions in acetonitrile.

Multiphoton ionization and dissociation of mixed van der Waals clusters in a linear reflectron time-of-flight mass spectrometer

Slow metastable fragmentation of benzene/toluene and benzene/para-difluorobenzene clusters is observed in a newly developed linear reflectron time-of-flight mass spectrometer after two-photon ionization. The breakdown of the metastable intensity with decreasing two-photon energy is measured and yields the appearance potential for the main dissociation channels of the homo- and the heterodimers. Based on these values, the dissociation energies of the neutral dimers are obtained and shown to be consistent with the changes of the polarizability and dipole moment of the components. In addition, from the appearance potentials and the measured ionization potentials, the dissociation energies of the charged dimer clusters are found. The binding energies of the heterocluster ions and the para-difluorobenzene homodimer ion are smaller than the respective binding energies in the benzene and toluene homodimer ions. This is explained by a larger contribution of charge transfer resonance interaction to the binding energy of the latter homodimer ions. On the basis of these results we present an energetic scheme for prediction of the dissociation pathways of the trimer ions in agreement with the measured results.