Ion-molecule Studies Research Articles

Ion-molecule studies of energetic oxygen allotropes in flow tubes: .

Starting in the 1960s, flow tube apparatuses have played a central role in the study of ion-molecule kinetics, allowing for immense chemical diversity of cationic, anionic, and neutral reactants. Here, we review studies of oxygen allotropes, excluding ground state O2 ( ), and focusing instead on reactions of cations, anions, and metal chemi-ionization reactions with ground state atomic oxygen (O 3 P), vibrationally excited molecular oxygen (O2 (v)), electronically excited molecular oxygen (O2 ( )), and ozone (O3 ). Historical outlines of work over several decades are given along with a focus on more recent work by our group at the Air Force Research Laboratory.

Selective Reagent Ion-Time-of-Flight-Mass Spectrometric Investigations of the Intravenous Anaesthetic Propofol and Its Major Metabolite 2,6-Diisopropyl-1,4-benzoquinone

The first detailed selected reagent ion-time-of-flight-mass spectrometric fundamental investigations of 2,6-diisopropylphenol, more commonly known as propofol (C12H18O), and its metabolite 2,6-diisopropyl-1,4-benzoquinone (C12H16O2) using the reagent ions H3O+, H3O+.H2O, O2+• and NO+ are reported. Protonated propofol is the dominant product ion resulting from the reaction of H3O+ with propofol up to a reduced electric field strength (E/N) of about 170 Td. After 170 Td, collision-induced dissociation leads to protonated 2-(1-methylethyl)-phenol (C9H13O+), resulting from the elimination of C3H6 from protonated propofol. A sequential loss of C3H6 from C9H13O+ also through collision-induced processes leads to protonated phenol (C6H7O+), which becomes the dominant ionic species at E/N values exceeding 170 Td. H3O+.H2O does not react with propofol via a proton transfer process. This is in agreement with our calculated proton affinity of propofol being 770 kJ mol−1. Both O2+• and NO+ react with propofol via a charge transfer process leading to two product ions, C12H18O+ (resulting from non-dissociative charge transfer) and C11H15O+ that results from the elimination of one of the methyl groups from C12H18O+. This dissociative pathway is more pronounced for O2+• than for NO+ throughout the E/N range investigated (approximately 60–210 Td), which reflects the higher recombination energy of O2+• (12.07 eV) compared to that of NO+ (9.3 eV), and hence the higher internal energy deposited into the singly charged propofol. Of the four reagent ions investigated, only H3O+ and H3O+.H2O react with 2,6-diisopropyl-1,4-benzoquinone, resulting in only the protonated parent at all E/N values investigated. The fundamental ion-molecule studies reported here provide underpinning information that is of use for the development of soft chemical ionisation mass spectrometric analytical techniques to monitor propofol and its major metabolite in the breath. The detection of propofol in breath has potential applications for determining propofol blood concentrations during surgery and for elucidating metabolic processes in real time.

A SIFT ion-molecule study of some reactions in Titan's atmosphere. reactions of N +, N 2+, and HCN + with CH 4, C 2H 2, and C 2H 4

The results of a study of the ion-molecule reactions of N +, N 2 +, and HCN + with methane, acetylene, and ethylene are reported. These studies were performed using the FA-SIFT at the University of Canterbury. The reactions studied here are important to understanding the ion chemistry in Titan's atmosphere. N + and N 2 + are the primary ions formed by photo-ionization and electron impact in Titan's ionosphere and drive Titan's ion chemistry. It is therefore very important to know how these ions react with the principal trace neutral species in Titan's atmosphere: Methane, acetylene, and ethylene. While these reactions have been studied before the product channels have been difficult to define as several potential isobaric products make a definitive answer difficult. Mass overlap causes difficulties in making unambiguous species assignments in these systems. Two discriminators have been used in this study to resolve the mass overlap problem. They are deuterium labeling and also the differences in reactivities of each isobar with various neutral reactants. Several differences have been found from the products in previous work. The HCN + ion is important in both Titan's atmosphere and in the laboratory.

A SIFT ion-molecule study of some reactions in Titan's atmosphere. reactions of N+, N2+, and HCN+ with CH4, C2H2, and C2H4

A SIFT ion-molecule study of some reactions in Titan's atmosphere. reactions of N+, N2+, and HCN+ with CH4, C2H2, and C2H4

Selective gas-phase ion–molecule reactions of the benzoyl ion

Gas phase ion–molecule studies using ion trap mass spectrometry show that the benzoyl ion, [C6H5CO]+, undergoes selective reactions with hydroxy functional groups; the formation of product ions [M + 105]+, [M – H]+ and [M – OH]+ is characteristic of the hydroxy group environment.

Endothermic ion molecule reactions

Endothermic ion-molecule reactions in a tandem mass spectrometer have been used for a number of years for determining thermodynamic quantities, such as heats of formation and proton affinities, for gaseous ions. Recently, the reactive, endothermic collision has been exploited as an analytical technique for the structural analysis of peptides and other biomolecules. The technique is based upon the endothermic transfer of protons associated with amide bonds to ammonia. This reaction proceeds via a long-lived collision complex. When additional beam energy is supplied, other dissociation channels are opened up, leading to the production of sequence ions for the mass-selected, protonated analyte that are normally observed in high energy collision-induced dissociation spectra. The advantage, however, is that such spectra can be produced at very low beam energies. In this article, the rationale for developing this scheme, and its roots in previous ion-molecule studies, are explored.

Mass and energy selective ion partitioning in a two-section Fourier-transform ion cyclotron resonance spectrometer cell

A method for ion isolation due to selective partitioning in a two-section Fourier transform ion cyclotron resonance cell is described. The limitation on ion cyclotron radius imposed by the conductance limit aperture is exploited to isolate ions. This method allows ions to be isolated according to: (i) mass, (ii) translational energy in the cyclotron orbit, and (iii) spatial location. The general utility of the technique for ion-molecule studies is discussed, and extension to analytical applications is straightforward.

Mass spectrometric investigation of NH 3 and CO 2 cluster ions: appearance potentials and stability

Electron impact ionization of (CO 2) x and (NH 3) y (x up to 5, y up to 10) was investigated in a molecular beam experiment coupled with a double focusing mass spectrometer. A special ion optical system and operating mode (deflection method) was used to discriminate between beam species and background species. For both neat and seeded (He, Ar, Kr) beams we have studied neutral cluster beam properties. The following cluster ion appearance potentials were obtained: (CO 2) 2+e→(CO 2) + 2 AP=13.1±0.2 eV (NH 3) 2+e→NH 4 + AP=9.95±0.3 eV (NH 3) 3+e→(NH 3) 2H + AP=9.50±0.3 eV The exothermicity of the reaction of CO + 2 with CO 2 to form (CO 2) + 2 was found to be 17.1±5 kcal/mole in good agreement with previous high pressure mass spectrometry determination. The dissociation energy for the proton bound dimer to NH 4 ++NH 3 was found to be 0.60±0.2 eV in good agreement with a previous photoionization result of 0.60 eV, in contrast to a number of recent ion molecule studies supporting a value of about 1.1 eV. In addition, metastable transitions occurring in the mass spectrum of C 3H 8, N 2O and (CO 2) x, (NH 3) y were investigated by means of decoupling the acceleration and deflection fields of the mass spectrometer, yielding the first results on the stability of cluster ions.

Monoisotopic mass spectra

A computer technique which calculates a least-squares fit monoisotopic mass spectrum, restricted to positive solutions, from polyisotopic measurements, is described. Any combination of elements, sets of isotopes or isotopic abundances can be handled. Partial or complete spectra may be analyzed. The method is also useful to determine the fractional abundance of isotopes, calculate the cluster of isotope peaks due to any formula, handle the data from ion—molecule studies, and detect impurities in mass spectral data. As examples the mass spectra of (CH 3) 2Hg, (CH 3) 4Pb, SiCl 4 and SOCl 2 are resolved.

Implications of ion-molecule reactions observed in silane for recoil silicon atom studies

Ion-molecule reaction sequences in silane, producing tertiary product ions, are reported. A mechanism is presented by which trisilane can be producted from Si+ ions in recoil silicon studies. It is also reported that Si+ ions can be efficiently neutralized by charge exchange with triethylamine. Preliminary studies indicate that the addition of triethylamine to recoil silicon experiments results in a decrease in the absolute yield of trisilane without affecting the yields of other products. In addition, information obtained from ion-molecule studies in silane is applied to radiolysis studies of silane. A mechanism is presented by which higher homologues are produced by hydride ion transfer.

Effect of water on the radiolysis of liquid acetone

Liquid acetone is quickly and efficiently dried with 4 Å molecular sieve. Small concentrations (up to 0·4% v/v) of water greatly affect the radiolysis of liquid acetone; the yields of hydrogen, methane, and hexane-2,5-dione are increased and the yields of ethyl methyl ketone and 4-hydroxy-4-methylpentan-2-one are decreased. These effects are interpreted in terms of ionic reactions, for which there exists evidence from ion–molecule studies and from spectroscopic work with low temperature glasses.