Thomas J. Buckley

Proton affinities of diacetylene, cyanoacetylene, and cyanogen

The proton affinity of cyanoacetylene HCCCN was determined by pulsed high pressure mass spectrometric equilibrium measurements as 180.1±1 kcal/mol. Ion cyclotron resonance (ICR) bracketing experiments yielded the proton affinity of diacetylene HCCCCH as 180±1 kcal/mol and of cyanogen NCCN as 161±2 kcal/mol. Ab initio calculations at the 6‐31+G** level are used to evaluate the heats of formation of HCCCCH as 105 and of HCCCN as 87 kcal/mol. The ab initio results show also that protonation of diacetylene on a terminal carbon converts a destabilizing antibonding interaction between the triple bonds in the neutral molecule into an attractive interaction, leading to a significant shortening of the C2–C3 bond.

Concerning the formation and the kinetics of phenylium ions

Abstract Kinetic measurements carried out in a pulsed ion cyclotron spectrometer show that C6H+5 ions formed in unimolecular and bimolecular processes consist of two populations of different reactivities. As expected, ground-state singlet phenylium ions are predominantly formed in low-energy processes, whereas higher-energy isomeric (mainly acyclic) ions appear in the high-energy electron impact fragmentation of C6H6 and halobenzenes, as well as products in highly exothermic ion/molecule reactions. The energy barrier for ring opening was estimated to be 2.0±0.3 eV, in reasonably good agreement with theory. Phenylium ions react readily with hydrocarbons and polar molecules. By means of isotopic labelling it was shown that alkanes transfer H2 via a two-stage process consisting of the transfer of H− to the phenylium ion followed by a transfer in the complex of H+ to the resulting benzene moiety. Cyclopropane was found to transfer CH2 to the phenylium ion in a direct concerted process. In contrast, reaction with unsaturated hydrocarbons involves extensive hydrogen and carbon atom scrambling. Contrary to earlier findings, phenylium ions were found to react at least ten times faster with acetylene than did the other C6H+5 isomer(s).

Toroidal cross capacitor for measuring the dielectric constant of gases

We describe toroidal cross capacitors built to accurately measure the dielectric constant of gases. We tested the capacitors by measuring the dielectric polarizability of helium and argon at 7 and 50 °C at pressures up to 3 MPa. For helium, the results are consistent with the ab initio calculation of the molar polarizability and are limited by the uncertainties of the capacitance measurements. For argon, the results are consistent with the best previously published measurements of the polarizability and are limited by the uncertainties of the pressure measurements. Lessons learned are provided.

Calculation of higher heating values of biomass materials and waste components from elemental analyses.

Abstract Higher heating values on a dry basis (HHV2), measured and calculated from elemental analyses, of more than 140 biomass and waste component materials have been compared. The data were evaluated by six higher heating value formulas. The Vondracek formula was found to give the best agreement between calculated and measured heating values over a wide range (10–47 MJ/kg), judged by good linear correlation between measured and calculated HHV2 values. Standard reference materials also have been evaluated and shown generally to give good agreement. The calculation of higher heating values form elemental analyses is a good check for the reliability of a materials composition and heating value measurements in most cases. Materials with differences between calculated and measured higher heating values in excess of 6% should be considered suspect and examined closely.

Structures and reactions of C3H6+ ions generated in cyclopropane

Abstract Ions of the formula C 3 H 6 + have been generated by charge transfer to cyclopropane from C 6 F 6 + (recombination energy, 9.91 eV), CS 2 + (recombination energy, 10.08 eV), COS + (recombination energy, 11.18 eV), and Xe + (recombination energy, 12.127 eV). From a determination of the charge transfer equilibrium constant in the c-C 3 H 6 : C 6 F 6 mixture, a value for the 300 K ionization energy of cyclopropane of 9.86 eV is obtained. In addition to the characteristic CH 2 NH 2 + and CH 2 NH 3 + products formed in reactions of c-C 3 H 6 + with ammonia, ions formed with no excess energy transfer a proton to ammonia. The probability of the occurrence of the proton transfer channel is about 30% for ions formed by charge transfer from C 6 F 6 + , CS 2 + , or COS + , but increases to 50% for ions formed by charge transfer from Xe + , which indicates that about 30% of the C 3 H 6 + ions formed by charge transfer from Xe + have undergone the isomerization process c-C 3 H 6 + → CH 3 CHCH 2 + . Thus the barrier associated with the rearrangement is >1.3 eV. The c-C 3 H 6 + ion reacts with PH 3 to give CH 2 PH 3 + and PH 4 + as products. Proton transfer reactions of the C 3 H 6 + ion generated by charge transfer from COS + with a series of bases of known proton affinity leads to a value for the apparent proton affinity of the C 3 H 5 conjugate base of ∼ 179 kcal mol −1 , which is lower than that which would be predicted for the cyclopropyl radical (187–192 kcal mol −1 ). It is suggested that the anomalously low value observed for the proton affinity indicates the occurrence of the process c-C 3 H 6 + + B→ BH + + CH 2 CHCH 2 .

Pulsed Electron-Beam Ionization of Humid Air and Humid Air/Toluene Mixtures: Time-Resolved Cationic Kinetics and Comparisons with Predictive Models

The technique of pulsed electron-beam high-pressure mass spectrometry wasused to investigate the sequential cationic chemistry in humid air streamsat 4.2×102 Pa and 380 K. The system was then modeled usingthe ACUCHEM program, incorporating thirty-five reactions taken from theformulations given in Part I of the new National Institute of Standards andTechnology (NIST) Chemical Kinetics Database for Humid Air Plasmas. Theresulting temporal ion profiles were found to be in qualitative agreementwith the laboratory data. Analogous pulsed electron-beam measurements werealso carried out with humid air samples containing low levels of toluene,and these results were also reproduced qualitatively by a model incorporatingforty-eight reactions after the inclusion of an unexpected, but crucial,channel involving the reaction of an intermediate air-generated cluster ionwith toluene. The benefits of laboratory validation of predictive databasesin systems for which the literature data are incomplete are emphasized.

Consecutive ion/molecule condensation reactions and photodissociation mechanisms of condensation ions in polyacetylenic compounds

Consecutive ion/molecule condensation and condensation/dissociation reactions in diacetylene, cyanoacetylene, and cyanogen have been examined in an ion cyclotron resonance spectrometer at pressures of ∼ 10−6 torr and in a high pressure photoionization mass spectrometer at pressures of ∼ 10−2 torr. The initial reaction of the diacetylene radical cation with diacetylene generates C6H2+ and C8H4+ ions which react further with neutral diacetylene, initiating the parallel series of reactions C6H2+ → C10H4+ → C14H6+ → C18H8+ and C8H4+ → C12H6+ → C16H8+ → C20H10+. The ions of the second sequence all show two populations, one of which is reactive and one unreactive with diacetylene. At lower pressures, the C8H4+ ions dissociate to give C8H2+ + H2 and the second sequence is replaced by the sequence C8H2+ → C12H4+ → C16H6+. The C12 and C10 ions are dissociated by 600 nm photons through loss of acetylene or diacetylene. Parent radical cations generated in cyanoacetylene and cyanogen mainly undergo simple consecutive addition processes with their respective parent molecules: M+ → M2+ → M3+ → etc. Rate constants are reported for the first few steps of the condensation sequences in all systems and inferences are made about the heats of formation of observed ions.

Temperature dependence of the gas and liquid phase ultraviolet absorption cross sections of HCFC-123 (CF3CHCl2) and HCFC-142b (CH3CF2Cl)

The absorption cross sections for HCFC-123 (CF3CHCl2) and HCFC-142b (CH3CF2Cl) have been measured in the gas and liquid phases over the temperature range of about 220–330 K. The liquid phase results were converted into effective gas phase cross sections using a wavelength shift procedure, thereby extending the gas phase cross sections to longer wavelengths. The results are compared with other available data and lend increased confidence in atmospheric lifetime calculations for these important industrial alternatives to the fully halogenated chlorofluorocarbons.

All-metal collection system for preparative-scale gas chromatography purification of low-boiling-point compounds

Abstract We describe a purification system based on a commercial preparative-scale gas chromatograph with a custom-designed condenser, collector, and fraction handling system. In our fraction collector design, all the wetted surfaces were either 316 stainless-steel or nickel. The collectors and the integrated gas-handling manifold were designed to be used down to liquid nitrogen temperature and up to 7 MPa of pressure to accommodate low-boiling-point compounds, such as refrigerants. The design, operation, and performance of this apparatus are presented.