Colin G. Freeman

Visible and near-ultraviolet absorption spectrum of liquid water

The optical absorption of pure liquid water in the 300-700-nm region has been measured by use of a long (1.5-m) path-length cell. The absorption spectrum coincides well with the edge of previous data in the 200-320-nm region and provides reliable data in the 320-420-nm region that has until now been a region of considerable unreliability. The data obtained for the 420-700-nm region agree quite well with the means of the existing literature in that well-studied region. The absorptions in the 550-700-nm region show evidence for the overtones and combination tones of the well-known OH stretching frequency at 3500 cm(-1).

Gas-phase reactions of some positive ions with atomic and molecular nitrogen

The reactions of the cations CN+, HCN+, HCNH+, HC3N+, HC3NH+, H3+, H2O+, H3O+, N2+, CO+, HCO+, O2+, CO2+, HCO2+, and C2H2+ with atomic and molecular nitrogen have been characterized using a selected ion flow tube (SIFT) operating at room temperature. Rate coefficient and branching ratio data are reported for all ion–neutral reactions studied. Constraints arising from spin conservation considerations are found to be unimportant in cation-N atom processes.

Emission of nitrogen oxides and ammonia from varying rates of applied synthetic urine and correlations with soil chemistry

Synthetic urine was applied at 5 rates, from 0 to 1000 kg synthetic urine-N/ha, to a pasture soil under controlled laboratory conditions. Gaseous emissions of NOx and NH3 were monitored for up to 21 days following application using selected ion flow tube mass spectrometry with N2O measured using electron-capture gas chromatography. During this period soil replicates were destructively sampled to measure changes in soil pH and inorganic-N concentrations. Comparisons were made between measured soil variables, calculated soil concentrations of NH3(g), HNO2, and the measured gas fluxes. At N rates up to 500 kg N/ha, inorganic-N concentrations increased as nitrification progressed over time. With the exception of the 1000 kg N/ha treatment, NO production followed the pattern of increasing nitrification, reaching a maximum of 905 ng NO-N/cm2.h in the 500 kg N/ha treatment 14 days after synthetic urine application. At this time the NO flux was associated best with soil pH, NH4+, and NO2– levels. Over 21 days the maximum cumulative loss as NO-N and N2O-N occurred under the 100 kg N/ha urine treatment, with 6.6 and 6.4% of N applied lost as gas, respectively. NO2 gas fluxes paralleled the NO emissions but were an order of magnitude smaller. Nitrification was inhibited in the 1000 kg N/ha treatment due to the sustained high ammoniacal-N and pH conditions present. These conditions prolonged the NH3 volatilisation from this treatment. NH3 volatilisation, as determined by selected ion flow tube-mass spectrometry, was linearly related to calculated soil NH3 gas concentrations up to 500 kg N/ha on Day 1.

Quantitative analysis of trace gases of breath during exercise using the new SIFT–MS technique

Abstract We show how the concentration of the breath gases ammonia, acetone, and isoprene vary with time during exercise using the new selected ion flow tube mass spectrometry (SIFT–MS) technique. The expired breath concentrations of ammonia, acetone and isoprene were observed within the range of 50–500, 100–1400 and 5–400 ppb, respectively. Increasing acetone levels were observed for most subjects during the exercise period. However, isoprene levels decreased with time during exercise. Older subjects showed higher levels of isoprene compared with younger subjects. The ammonia time profile with exercise showed both decreasing and increasing patterns for different subjects.

The reactivity of HOC+ and the proton affinity of CO at O

Abstract Two ion/molecule reactions were observed to produce the isoformyl ion, HOC+, as a product in conjunction with the structural isomer, HCO+. These two reactions are C+ + H2O and CO+ + H2. The reaction mainly used in this study to produce an HOC+/HCO+ mixture in the flow tube was CO+ + H2 and the branching ratio for the production of HOC+ was 0.48. A technique based on the very different proton affinity of CO at O compared with CO at C, was used to distinguish between the isomers. The rates of proton transfer from HOC+ to O2, H2, Kr, Xe, NO, CO, CO2, CH4, and N2O were measured at room temperature. In addition, the reaction with H2 was also observed to isomerize HOC+ into HCO+. The proton affinity of CO at O that best fits these results is 427 kJ mol−1 which yields a value of ΔHf[HOC+] = 990 kJ mol−1.

Fluorescence of aliphatic amines

Abstract Fluorescence of several tertiary aliphatic amines has been excited in the gas phase by absorption of 206.2 nm radiation, i.e. in the band corresponding to the A - X transition of NH3. No fluorescence was obtained from molecules having hydrogen or deuterium bonded directly to the nitrogen atom. The experiments support the view that quantum-mechanical tunnelling is the major factor governing the rates of predissociation of the excited states of NH3, ND3, and simple amines.

A flowing afterglow selected ion flow tube (FA/SIFT) comparison of SIFT injector flanges and H3+ + N revisited

Abstract The performances of two different but interchangeable Venturi injectors (an annulus and a hole injector) have been compared in a new flowing afterglow source-selected ion flow tube (FA/SIFT) instrument built at the University of Canterbury. The tests applied compared the relative “pumping efficiencies” of the two injectors; their ion transmission using (O 2 + ); the relative ease of injecting cluster ions subject to collision induced dissociation (H 3 O · + H 2 O); and the extent of isomerization of ions sensitive to structural changes during the injection process (C 3 H 5 + ). The annulus injector was clearly superior to the hole injector in pumping efficiency. Thereafter the improvement in performance was only marginal. The greater difficulty of construction and maintenance of the annulus injector needs to be balanced against the slightly less versatile hole injector. It was necessary to direct a significant fraction of the total helium buffer gas flow through an outer, noncritical orifice to maintain satisfactory performance in the hole injector when injecting ions susceptible to collision induced dissociation. Finally, the new instrument was used to reexamine the reaction of H 3 + and N atoms, which was found to be a nonreactive system, k −11 cm 3 s −1 .

Real time analysis of breath volatiles using SIFT-MS in cigarette smoking.

Abstract The selected ion flow tube mass spectrometry (SIFT-MS) technique enables real time analysis of trace volatiles at ppb levels without preconcentration steps or chemical derivatization. Most previous studies of trace compounds on the breath were analyzed using gas chromatography where enhanced detection sensitivity was achieved by concentrating the breath using cryogenic or adsorption trapping techniques. In this paper, we have examined volatile organic substances, isoprene, acetone, ammonia and ethanol in breath before and after smoking a cigarette. It is interesting that isoprene levels increased in all the subjects after smoking one cigarette with a mean increase of 70%. The mean increase for acetone was found to be 22%. In contrast to isoprene, a decreasing ethanol level was observed in all the subjects except one with the negative mean decrease of 28%. Further SIFT-MS studies also have high-lighted some organic substances produced even by unburned cigarettes, US and New Zealand products. Certain US brands have shown much higher levels of volatile species than cigarettes produced in New Zealand.

Gas phase reactions of some positive ions with atomic and molecular hydrogen at 300 K

The reactions of CO+, CO2+, SO2+, NO2+, CS2+, CN+, C2N2+, and C2H3+ with H atoms and H2 molecules have been studied in a selected ion flow tube operated at (300±5) K. The H atom reactions proceed variously by the processes of atom exchange and charge transfer (when allowed), none proceed at the Langevin rate, and the rates of several of them appear to be influenced by the spin states of the product species. Most of the H2 reactions proceed by H atom abstraction and at a large fraction of the Langevin rate.The reactions of CO+, CO2+, SO2+, NO2+, CS2+, CN+, C2N2+, and C2H3+ with H atoms and H2 molecules have been studied in a selected ion flow tube operated at (300±5) K. The H atom reactions proceed variously by the processes of atom exchange and charge transfer (when allowed), none proceed at the Langevin rate, and the rates of several of them appear to be influenced by the spin states of the product species. Most of the H2 reactions proceed by H atom abstraction and at a large fraction of the Langevin rate.

COMPETITIVE ASSOCIATION AND CHARGE TRANSFER IN THE REACTIONS OF NO+ WITH SOME KETONES : A SELECTED ION FLOW DRIFT TUBE STUDY

The rate coefficients and product ion branching ratios have been determined for reactions between NO+ and three ketones, acetone, 2-butanone, and 3-pentanone, as a function of NO+/reactant ketone centre-of-mass energy, Er, and NO+/helium carrier gas atom centre-of-mass energy, Ec, in a flowing afterglow selected ion flow drift tube apparatus. In these experiments, the helium carrier gas was maintained at a temperature of 300 K. At zero drift field, association was the dominant channel occurring at close to the collision rate forming NO·+ ketone adduct ions. At higher drift fields (Er, Ec < 1 eV), charge transfer and dissociative charge transfer channels became the major channels forming fragment ions of the ketones. The decrease in the association rate coefficient with increasing Ec exhibits an inverse power law dependence k3 ∝ Ec−n where n ∼ 2.5 for all three ketones. This dependence is much larger than predicted by simple theory and may be indicative of low energy vibrations contributing to the total energy pool in the (NO· ketone)+∗ excited complex. Keywords: Ion/molecule association; SIFT; Drift tube; Charge transfer