Flow Drift Tube Research Articles

The reactions of the highly polar ion ArD 3+ with C 3H 8 and C 4H 10

A Selected Ion Flow Drift Tube (SIFDT) operated at 300 K with helium buffer gas has been used to obtain rate coefficients for the reactions of the highly polar ion ArD 3 + with C 3H 8 and C 4H 10. The rate coefficients, k(C 3H 8) = (1.46 ± 0.15) × 10 −9 cm 3 s −1 and k(C 4H 10) = (1.49 ± 0.15) × 10 −9 cm 3 s −1 are higher than the respective Langevin limiting values k L(C 3H 8) = 1.24 × 10 −9 cm 3 s −1 and k L(C 4H 10) = 1.32 × 10 −9 cm 3 s −1 by 18 and 13 percent, respectively, an effect which is quantitatively explained on the basis of the interaction between the ion-dipole and the induced dipole of the neutral reactants.

Proton transfer reaction mass spectrometry (PTR-MS): propanol in human breath

Proton transfer reaction mass spectrometry (PTR-MS) based on reactions of H 3O + ions has been used to measure the concentrations of propanol in 46 healthy persons, yielding an average concentration of about 150 ppb. That the measurements were not obscured by other components of the same mass as propanol was proven by comparison of PTR-MS data with separate selected-ion flow-drift tube (SIFDT) investigations of the energy dependences of reactions of H 3O + and H 3O +·H 2O with isopropanol, n-propanol, acetic acid and methyl formate.

Rotational and Vibrational Energy Effects on Ion−Molecule Reactivity As Studied by the VT-SIFDT Technique

A method is described for measuring internal energy dependences of gas phase ion−molecule reactions in a variable temperature-selected ion flow drift tube (VT-SIFDT) instrument. Numerous studies have been conducted to examine the effects of both rotational and vibrational excitation on rate constants and branching ratios. Rotational and translational energy are found to be equally efficient at driving endothermic reactions. For exothermic reactions, large rotational effects are found only when one or both of the reagents have a large rotational constant. This indicates that changing from a low to moderate J value can affect reactivity but that changing from moderate to high J has little influence on reactivity. Vibrational effects are more varied. In some reactions, vibrational excitation in the anticipated reaction coordinate strongly affects reactivity, while in other cases it does not. Vibrational effects are often observed in charge transfer reactions, presumably due to energy resonances and Franck−Condon arguments. For the SN2 reactions studied to date, vibrations play no role in governing reactivity for halide ions reacting with methyl halides, while vibrations are equivalent to other types of energy in influencing the reactivity of non-methyl halide systems.

Mobilities of Aromatic Ions Drifting in Helium

Aromatic ions are produced in an electron impact ion source and injected into the flow tube section of a selected-ion flow-drift tube (SIFDT) apparatus. The reduced mobilities of C6H5+, C6H6+, C6H7+, C12H12+, C12H11+, naphthalene (C10H8+) cation, and biphenyl (C12H10+) cation drifting in helium are measured as a function of the characteristic parameter E/N (the ratio of the electric field to the number density of the helium buffer gas atoms in the drift tube). The reduced mobilities of the benzene dimer ions (C12H12+ and C12H11+) are compared with the measured mobilities of naphthalene and biphenyl cations to correlate the mobilities with ionic structures. An angle-averaged collision cross section of the ions drifting in helium is obtained from the geometric structure of these ions and is used to compute the zero-field mobility. The predicted zero-field mobilities are found to compare well with the experimentally measured mobilities.

Selected ion flow drift tube studies of the kinetics of the reactions of Si +( 2P) with C 2H 2 and C 6H 6

The reaction rate coefficients, k, for the reactions of ground state Si +( 2P) with C 2H 2 and C 6H 6 have been measured as a function of reactant ion/reactant neutral centre-of-mass kinetic energy, KE CM, in a selected-ion flow drift tube (SIFDT) apparatus, operated with helium at a temperature 298 ± 2 K. The values k of the studied reactions have very pronounced negative energy dependences; k decreases by about one order of magnitude when KE CM increases from near thermal values to about 2 eV. The results are interpreted in terms of a simple model assuming that the reactions proceed via the formation of long-lived complexes. These intermediate complexes decompose back to reactants or forward to products, the unimolecular decomposition rate coefficients for these reactions being k −1 and k 2 respectively. It is found that a power law of the form k −1/ k 2 = constant ( KE CM) m closely describes each reaction. The negative energy dependence of the reaction rate coefficient of the reaction of Si +( 2P) with C 2H 2 is rationalized in terms of the negative entropy change in the reaction. The dependence of the reaction rate coefficient of the reaction of Ar + with C 6H 6 on KE CM is also reported.

Selected ion flow drift tube studies of the reactions of Si+(2P) with HCl, H2O, H2S, and NH3: Reactions which produce atomic hydrogen

The reaction rate coefficients, k, for the reactions of ground-state Si+(2P) with HCl, H2O, H2S, and NH3, have been measured as a function of reactant ion/reactant neutral center-of-mass kinetic energy, KECM, in a selected ion flow drift tube (SIFDT) apparatus, operated with helium at a temperature 298±2 K. The values k of the studied reactions have very pronounced, negative energy dependencies; the rate coefficients decrease by about 1 order of magnitude as KECM increase from near thermal values to ∼2 eV. The results are interpreted in terms of a simple model assuming the reactions to proceed via the formation of long-lived complexes. These intermediate complexes decompose back to reactants or forward to products, the unimolecular decomposition rate coefficients for these reactions being k1 and k2, respectively. It is found that a power law of the form k−1/k2=const(KECM)m closely describes each reaction.

Selected ion flow drift tube studies of the reactions of S+(4S) with CH4, C2H2, C2H4, and C3H8

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSelected ion flow drift tube studies of the reactions of S+(4S) with CH4, C2H2, C2H4, and C3H8P. Zakouril, J. Glosik, V. Skalsky, and W. LindingerCite this: J. Phys. Chem. 1995, 99, 43, 15890–15898Publication Date (Print):October 1, 1995Publication History Published online1 May 2002Published inissue 1 October 1995https://doi.org/10.1021/j100043a030RIGHTS & PERMISSIONSArticle Views59Altmetric-Citations12LEARN 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 (913 KB) Get e-Alerts

Selected ion flow drift tube studies of the reaction of Si + ( 2P) with C 2H 4. Observation of the ternary reaction with two channels: collisional stabilization and collisional dissociation

A selected ion flow drift tube study on the reaction of ground state Si +( 2P) with C 2H 4 has been carried out in the pressure range from 0.14 to 0.52 Torr for average relative centre-of-mass kinetic energies, KE CM, from near thermal to ≈ 2 eV. Two product ions have been observed, SiC 2H 3 + and SiC 2H 4 +. The apparent binary (“effective”) rate coefficient, k eff, and the product distribution have been determined as functions of KE CM. The reaction rate coefficients of the binary ( k BIN) and ternary ( k 3) channels have been determined by two procedures, from the pressure dependence of k eff (indicated by index “PRESSURE”) and by using the observed product distribution (indicated by index “PROD”). For KE CM < 0.1 eV k 3 obtained by both methods, k 3-PRESSURE and k 3-PROD, are equal and their dependence on KE CM can be expressed in the form: k 3-PROD = k 3-PRESSURE ∝ ( KE CM) −0.5. It was observed that dependence of the reaction rate coefficient of the binary channel can be expressed also in the form k BIN-PRESSURE ∝ ( KE CM) −0.5. This similarity in the dependence on KE CM may indicate that both binary and ternary channels are proceeding via the same rate-determining process prior to separation into two channels. The situation is different for KE CM > 0.1 eV. Here k 3-PROD decreased more rapidly with KE CM than k 3-PRESSURE, indicating that in the collisions of He atoms with the excited intermediate collision complex the dissociation of (SiC 2H 4) +∗ to SiC 2H 3 + takes place. Here we report the first observation of a ternary reaction having two product channels—collisional stabilization (product (SiC 2H 4 +) and “collision induced dissociation” (product SiC 2H 3) with probabilities α 1 and α 2 (where α 2 = 1 - α 1), respectively. α 1 and α 2 have been determined from k 3-PROD and k 3-PRESSURE. For KE CM < 0.1 eV the stabilization channel is dominant ( α 1 ⪢ α 2), for KE CM ≈ 0.2 eV both channels have the same probability ( α 1 = α 2), and for KE CM > 0.2 eV the “collision induced dissociation” of the intermediate complex, producing SiC 2H 3 +, is dominant ( α 2 > α 1).

Vibrational relaxation in the NO+–He collision system: Implication of the Gislason–Ferguson model

The rate constants for vibrational relaxation of NO+ in collisions with He are calculated using the semiclassical (classical path) approach of Billing and the interaction potentials, constructed by us on the base of the model of Gislason and Ferguson. An encouraging agreement of the theoretical results with near thermal selected ion flow drift tube data is achieved. The role of the anisotropy of the interaction potential in the vibrational relaxation process is also investigated.

Gas phase reactions of the sulfur-34 anion with CS2, OCS, and H2S as a function of kinetic energy

We have measured rate coefficients and product branching ratios for the reactions of labeled and unlabeled sulfur anions with CS2, OCS, and H2S. These studies were carried out as a function of kinetic energy in the range between 298 K and ∼1 eV using a tandem flowing afterglow-selected ion flow drift tube instrument. For the reaction of S−+CS2 as a function of increasing kinetic energy, the total rate coefficient initially decreases, reaches a minimum at about 0.4 eV, and then increases. Thermoneutral isotope exchange is responsible for the negative energy dependence at lower energies and endothermic sulfur abstraction is responsible for the positive energy dependence at higher energies. For the reaction of S−+OCS vs kinetic energy, the total rate coefficient initially decreases, reaches a plateau, and then increases slightly. Thermoneutral isotope exchange and exothermic sulfur atom abstraction are responsible for the negative energy dependence. For the reaction of S−+H2S, the total rate coefficient has a very weak energy dependence. The strong negative energy dependence of the thermoneutral isotope exchange is counterbalanced by the positive energy dependence of the slightly endothermic hydrogen and proton transfer channels. For these reactions isotope exchange may proceed by formation of an intermediate collision complex, whereas sulfur abstraction may proceed by two different mechanisms, complex formation at lower energies and direct attack on sulfur at higher energies.

Effects of O −2 and SF 6 vibrational energy on the rate constant for charge transfer between O −2 and SF 61

Rate constants for the charge-transfer reaction of O − 2 with SF 6 have been measured as a function of the average kinetic energy (KE cm) at several temperatures in a selected-ion flow-drift tube. Increasing kinetic energy is found generally to decrease the reactivity. In the temperature range below 300 K, increasing temperature is found to decrease the rate constants; above 300 K the rate constants increase with temperature. Information on the internal energy dependences of the reactions is derived from the data. The data indicate that neither rotations nor low-frequency vibrations measurably affect the reactivity. Higher-frequency vibrations and/or overtones are found to enhance the reactivity greatly, presumably by distorting the geometry of SF 6 to match more closely that of SF − 6. Vibrations of O − 2 are found to increase the reactivity by a factor of 2.9 at 162 K.

Interaction between the ion dipole and the ion-induced dipole in reactions of the polar ion ArH+3

The reactions of the highly polar ion ArH+3 with the nonpolar neutrals Xe, Kr, CH4, CO, NO, O2, and N2 and with the polar neutrals SO2, H2O, NH3, CH3I, and C2H5I have been investigated in a selected ion flow drift tube experiment at near thermal conditions. The rate coefficients obtained have typically 15%–35% larger values than the collisional limiting values kL and kADO obtained by the Langevin and ADO (average dipole orientation) theory, respectively. These data are explained on the basis of the interaction between the dipole of ArH+3 and the ion-induced dipole and the permanent dipole, respectively, of the neutral reactants. Rate coefficients for the reactions of H+3 with the above neutrals were also obtained for comparison, as well as the zero field mobility of ArH+3 in helium being (18.5±1.5) cm2/V s. The ion KrD+3 (KrH+3) was detected unambiguously for the first time. Its dissociation energy is larger than 0.29 eV which is the lower limit of the dissociation energy of ArH+3.

Applications of proton transfer reactions to gas analysis

The applicability of proton transfer reactions involving H 3O + ions to trace gas analysis of methanol, ethanol and acetone in human breath is demonstrated, using a conventional Selected ion flow drift tube (SIFDT). The potential of H 3O + for trace gas analysis lies in the slightly smaller proton affinity of H 2O as compared to those of many organic compounds, thus allowing for non-dissociative proton transfer to these neutrals resulting in only one product ion for each neutral trace component to be analysed.

Kinetics of the Reactions of F- with CF3Br and CF3I as a Function of Temperature, Kinetic Energy, Internal Temperature, and Pressure

Abstract : The reactions of F- with CF3Br and CF3I have been studied at several temperatures as functions of pressure and ion-neutral average center-of-mass kinetic energy ((KE sub cm)). Rate constants and product branching fractions were measured by using a variable temperature-selected ion flow drift tube apparatus. Both title reactions involve two product pathways: displacement and association, the latter being the major channel under most experimental conditions. The rate constants for displacement are governed by total energy, regardless of the relative contributions by translational and internal energy, indicating that the displacement reactions behave statistically. In contrast, the rate constants for association depend strongly on the internal energy of CF3X (rotations and vibrations) compared with the relatively weak effect of translational collision energy. For CF3Br the rate constants for the association channel increase with increasing pressure while those for displacement are independent of pressure, indicating that the additional reactivity leading to more association at higher pressure appears not to compete with the displacement pathway. This lack of competition may be the result of two different reaction intermediates. The more efficient CF3I reaction is at or near the high-pressure limit for association, showing no pressure dependence in both the association and displacement channels. Therefore, there appears to be no competition between these channels for CF3I as well, but the data are less definitive in this case.

Collision induced dissociation of the isometric ions H 2COOH + and HC(OH) +12

The dissociation of two isomeric forms of the ion CH 3O + 2 induced by collisions with the helium buffer gas atoms has been studied in a selected ion flow drift tube (SIFDT) experiment. When CH 2OOH + is formed via the reaction of O 2 + with CH 4, the product ions from collision induced dissociation (CID) are HCO + (60%) and H 3O + (40%) respectively, independent of the mean relative collision energy E c between the buffer gas and the ions, from thermal to 0.2 eV. The Arrhenius activation energy obtained is 24 kcal mol −1. Protonation of formic acid leads to HC(OH) + 2 ions, the CID of which yields 50% HCO + and 50% H 3O +, also independent of E c. The Arrhenius activation energy is 38.4 kcal mol −1. When formic acid is protonated in reaction with D 3O + to form CH 2DO + 2, the products of CID of this ion are HCO + and DH 2O + only, showing that deuteration occurs on the oxygen alone and not on the carbon HC(OH) + 2 performs fast isotope exchange in collisions with D 2O to form HC(OD) + 2 in two consecutive steps and, again, deuteration on the carbon atom is not observed HC(OH) + 2 also rapidly collisionally associates with H 2O( k≈10 −27 cm 6 s −1 at 300 K).

Relaxation of vibrationally excited ions O +2( v) and NO + ( v) in collisions with He

Vibrational quenching rate coefficients k q have been measured from thermal energy to 0.3 eV mean relative kinetic energy KE cm for NO + ( v=1 or 4) and O + 2( v=1 or 2) ions in collisions with He by using a monitor ion technique in a selected ion flow drift tube. All these values for k q increase dramatically with increasing KE cm. These quenching processes have also been investigated theoretically by using simple collinear models which yield rate coefficients in good agreement with the measured values.

Reactions of Kr +2 with various neutrals

Earlier studies performed by Shul and co-workers [R.J. Schul, B.L. Upschulte, R. Pasarella, R.G. Keesee and A.W. Castleman, Jr., J. Chem. Phys. 91 (1987) 2557; R.J. Schul, R. Pasarella, B.L. Upschulte, R.G. Keesee and A.W. Castleman, Jr., J. Chem. Phys., 86 (1987) 4446] reporting room temperature data on 14 reactions of Kr + 2 have been extended by investigating the energy dependences of the overall rate coefficients and the branching ratios of Kr + 2 reactions with 11 neutral reactants using a selected ion flow drift tube. Switching is the main reaction channel in parallel with charge transfer in many of the reactions investigated. The charge transfer observed in these reactions is discussed using a Franck—Condon model, due to Bearman . [G.H. Bearman, J.D. Earl, R.J. Pieper, H.H. Harris and J.J. Leventhal, Phys. Rev. A, 13 (1976) 1734]. The binding energies obtained for KrCO + and KrCO + 2 are (1.07±0.08) eV and (0.82±0.03) eV respectively, and that obtained for (CO 2) + 2 is (0.65±0.03) eV. The reduced mobility of Kr + 2 in He in the range 10 Td ⩽ E/N⩽ 150 Td is also reported.

SIFDT studies of the reactions of C +, CH + and CH +2 with HCl and CO 2, and CH +3 with HCl

The rate coefficients k have been determined as a function of reactant ion/reactant molecule centre-of-mass energy E r for the reactions of C +, CH + and CH + 2 with both HCl and CO 2 in a selected ion flow drift tube (SIFDT) apparatus. In these experiments, the carrier gas was pure helium at a temperature of 300 K. For low values of E r, the k values are close to the respective collisional rate coefficients k c but the k decreases with increasing E r. These results are interpreted in terms of a simple model by which the reactions are considered to proceed via the formation of long-lived complexes which decompose back to the reactants or forward to products, the unimolecular decomposition rate coefficients for these reactions being k −1 and k 2 respectively. It is found that a power law relation of the form k −1/ k 2=const × E m t closely describes each reaction. An attempt is made to rationalise the values of the indices m obtained for each reaction in terms of the number of rotational degrees of freedom in the separated reactants, and then some support is apparently evident for the theoretical indication that CO 2 is a “bent” molecule. The k for the slower reaction of CH + 3 with HCl was measured in the SIFDT in both helium and argon carrier gas, and the results compared with previous results obtained in a VT-SIFT apparatus under truly thermalised conditions. The combined results of these studies are used to indicate which form of energy in the reactants (internal or translational) influences the rate at which the reaction proceeds.

The reaction SF +5 + H 2S at near thermal energies: competition between association and binary reactions

The reaction between SF + 5 has been investigated in the energy from 0.052 to 1.7 eV, KE cm, using a selected ion flow drift tube (SIFDT) operating with helium buffer gas. At low energies a slow binary reactions channel into SF 4HS + occurs in parallel with a fast association reaction. Both rate coefficients decline from 3×10 −11 cm 3 s −1 and 3×10 −27 cm 6 s −1 respectively at 0.052 eV to <5×10 −12 cm 3 s −1 and < 5×10 −28 cm 6 s −1 respectively at 0.3 eV, KE cm. Above 0.3 eV the endoergic charge transfer channel becomes dominant, the rate coefficient increasing to 9×10 −12 cm 3s −1 at 1.7 eV, KE cm. SF + 5·H 2S was found to react fast with H 2S, the rate coefficient being 1.4×10 −9 cm 3 s −1.

A further investigation of the reaction of C 2H +2 with H 2

The reactions of C 2H + 2 with H 2 and C 2D + 2 + D 2 have been studied in a selected ion flow drift tube (SIFDT) over a range of centre-of-mass energies E c from thermal (300K) to a few tenths of an electron volt. The reactions proceed along parallel bimolecular and termolecular channels producing C 2H + 3 (C 2D + 3) and C 2H + 4 (C 2D + 4). The relative importance of the bimolecular channel increases and that of the termolecular channel decreases with increasing E c in accordance with previous data. The rates for the bimolecular reactions increase as the C=C stretching vibrations in the reactant ion are excited in collisions with the helium carrier gas atoms in the SIFDT at higher E c values, consistent with other work in which these vibration modes are selectively excited using laser ionisation. The question is addressed as to whether the atom abstraction reactions are exothermic or endothermic. Based on the new experimental data, some recent ion trap data and previous data on the reaction of C 2H + 2 with H atoms, it is concluded that the reactions are slightly endothermic, and it is tentatively suggested that a potential barrier also exists to the reactions. The interstellar implications of these results are briefly referred to.