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Real-time detection of air toxics is becoming increasingly important in understanding the sources and constituents of air pollution. The detection of low levels of air contaminants requires reliable sampling and calibration techniques, as well as sophisticated analytical instrumentation. Recently, a new low pressure chemical ionization (LPCI) source was developed for ambient air monitoring of benzene, toluene, xylene (BTX) and gas-phase polycyclic aromatic hydrocarbons (PAH) in real-time. This ion source in conjunction with a triple quadrupole (Q1, Q2, Q3) mass spectrometer (trace atmospheric gas analyzer (TAGA IIe)) has been proven highly useful for measuring selected air pollutants. The ion chemistry under LPCI conditions involves charge transfer reactions yielding parent ions which are selected in the first quadrupole, Q1, dissociated in the second quadrupole, Q2, and the resultant daughter ions are then identified by the third quadrupole, Q3. Monitoring of specific parent/daughter (P/D) ion pairs is used to measure concentrations of BTX and selected PAH. The response of the TAGA IIe is characterized through multi-point calibration curves. Detection limits (DL) as low as 0.5 microg/m(3) for BTX and PAH were accomplished by optimizing various TAGA IIe operating parameters. This unique method was applied in November 1999 to monitor emissions released during the cleanup of a historical coal tar site in Kingston, Ontario. This information was used by local officials for enhancing abatement activities or in some cases temporarily halting the excavation when levels of air toxics were higher than allowable provincial guidelines.

Ab initio molecular orbital calculations are reported for small neutral molecules and cations containing magnesium, nitrogen and hydrogen. Structures have been optimized using gradient techniques at B3LYP/6-31+G(d) and at MP2(full)/6-311++G(d,p). Single-point calculations are reported at QCISD(T)(full)/6-311++G(2df,p) and at CCSD(T)(full)/6-311++G(2df,p) levels using geometries optimized at MP2(full)/6-311++G(d,p). Standard enthalpies of formation at 298 K have been calculated at these two higher levels of theory. Other thermochemical properties calculated include ionization energies and proton affinities. The binding enthalpies of ammonia to Mg+, MgNH2+ and MgNH3+ are also reported.

Density functional calculations at B3LYP/6-31+G(d) and B3LYP/DZVP are reported for Mg(NH 3 ) n +· , where n = 1–6 and for some solvated ions Mg(NH 3 ) n +· … NH 3 ( n = 1–3, 6). After correction for basis set superposition errors, the enthalpies for sequential addition of NH 3 to Mg +· resulting from direct coordination to the metal are 38.1, 26.6, 21.2, 13.7, 12.1, and 11.3 kcal mol −1 . The free energies for these same addition reactions are all negative, although for complexes with n ≥ 4 the values are very small. Attempts at optimising structures with higher coordination numbers all resulted in the formation of solvated octahedral complexes. Enthalpies for solvation through hydrogen bonding to one of the ligated NH 3 molecules are all less than 16 kcal mol −1 and decrease rapidly as the number of ligated NH 3 molecules increases. Molecular orbital calculations at B3LYP/DZVP have been used to optimise structures for ions Ag(NH 3 ) n + , where n = 1–6. The five-coordinate and six-coordinate structures have very small binding enthalpies (4.3 and 2.6 kcal mol −1 ) and the free energies for formation of these ions are positive. The binding energies for the addition of the first and second NH 3 molecules added to Ag + are 40.1 and 36.1 kcal mol −1 , while those for the third and fourth additions are much smaller (15.1 and 11.0 kcal mol −1 ). Adducts up to n = 3 have been detected in electrospray experiments. The first three adducts of Ag + with NH 3 have been formed in the selected ion flow tube apparatus and multicollision induced dissociation experiments show Ag(NH 3 ) 3 + to have a lower binding enthalpy than both Ag(NH 3 ) 2 + and Ag(NH 3 ) + .

The coordination of the electronic ground states of Mg+, (c-C5H5)Mg+, and (c-C5H5)2Mg+ with the straight-chain saturated hydrocarbons methane, ethane, n-propane, n-butane, n-pentane, n-hexane, and n-heptane has been investigated in the gas phase in helium at room temperature and moderate pressures. Reaction rate coefficients and product distributions were measured with the selected-ion flow tube (SIFT) technique operating at 294 ± 3 K and a helium buffer-gas pressure of 0.35 ± 0.01 Torr. Rate coefficients were measured for all observed ligation steps (or upper limits in the case of nonreactions), and bond connectivities in the coordinated ions were probed with multicollision-induced dissociation. Only single ligation was observed. The rate of ligation was found to depend on the size of the saturated hydrocarbon, increasing with increasing size until the collision rate is reached, and on the degree of ligation with c-C5H5. Mg+ was found to be unreactive with methane and ethane, k < 10-13 cm3 molecule-1 s-1...

Calculations at B3LYP/6-31+G(d) show c-C4H3+ to have a singlet ground state, with the triplet being 19.5 kcal mol−1 higher in energy. Singlet c-C4H3+ has a puckered ring structure (Cs symmetry) with an out-of-plane angle of 51.4°. The barrier to inversion via the planar ring structure (C2v symmetry) is 29.1 kcal mol−1. In the puckered ring the cross–ring distance between CH groups is 1.793 A and the Wiberg bond order is 0.436, indicating considerable interaction. The stability of the singlet state then is attributed to homoaromaticity. Ion c-C4H3+ in its triplet state is planar, but with alternate bonds being long and short, reminiscent of the geometries of c-C4H4 and c-C4H4+. Substitution of H atoms by CN groups stabilises the triplet state relative to the singlet, and for C4(CN)3+ the triplet is only 8.4 kcal mol−1 higher. Substitution also reduces the out-of-plane angle of the ions in the singlet state, going from 51.4° in the unsubstituted ion c-C4H3+ to 43.4 kcal mol−1 in C4(CN)3+. A CN group adjacent (α) to the carbene centre reduces the barrier by ∼7 kcal mol−1 whereas substitution at the opposite carbon (β position) reduces it by ∼2 kcal mol−1. These effects are roughly additive, with C4(CN)3+ having a barrier to inversion of only 12.9 kcal mol−1.

A combined experimental and theoretical approach has been employed to establish the basicity and proton affinity of SiF4 and the structure of SiF4H 1 . The kinetics and energetics for the transfer of a proton between SiF4 ,N 2, and Xe have been explored experimentally in helium at 0.35 6 0.02 torr and 297 6 3 K with a selected-ion flow tube apparatus. The results of equilibrium constant measurements are reported that provide a basicity and proton affinity for SiF4 at 297 6 3 K of 111.4 6 1.0 and 117.7 6 1.2 kcal mol 21 , respectively. These values are more than 2.5 kcal mol 21 lower than currently recommended values. The basicity order was determined to be GB(Xe) . GB(SiF4) . GB(N2), while the proton-affinity order was shown to be PA(Xe) . PA(N2) . PA (SiF4). Ab initio molecular orbital computations at MP4SDTQ(fc)/ 6-31111G(3df,3pd) using geometries from B3LYP/6-311G(d,p) indicate a value for PA(SiF4) 5 118.7 kcal mol 21 that is in good agreement with experiment. Also, the most stable structure of SiF4H 1 is shown to correspond to a core SiF3 cation solvated by HF with a binding energy of 43.9 kcal mol 21 . Support for this structure is found in separate SIFT collision induced dissociation (CID) measurements that indicate exclusive loss of HF. (J Am Soc Mass

The coordination of the electronic ground states of Mg+, (c-C5H5)Mg+, and (c-C5H5)2Mg+ with the inorganic molecules H2, NH3, H2O, N2, CO, NO, O2, CO2, N2O, and NO2 has been investigated in the gas phase at room temperature and moderate pressures. Reaction rate coefficients and product distributions were measured with the selected-ion flow tube (SIFT) technique operating at 294 ± 3 K and a helium buffer-gas pressure of 0.35 ± 0.01 Torr. Rate coefficients were measured for all observed ligation steps (or upper limits in the case of nonreactions), and bond connectivities in the coordinated ions were probed with multicollision-induced dissociation. The rates and extent of ligation were found to depend on the degree of ligation with c-C5H5 and the nature and size of the inorganic ligand. Mg+ was found to be unreactive except with ammonia, which was found to add slowly (k = 4 × 10-12 cm3 molecule-1 s-1). Single ligation of Mg+ with c-C5H5 substantially enhances the efficiency of ligation; the initial ligation i...

Molecular orbital calculations were carried out for the neutral and ionic species that occur in the gas-phase chemistry of magnesium in the presence of oxygen and hydrogen including Mg 1 , MgO, MgOH, MgOH 1 , MgOH2 , Mg(OH)2, HOMgOH2 , and the hydrate structure MgOH 1 ...( OH 2). Standard enthalpies of formation for these species were obtained from single-point calculations at the QCISD(T)(full)/6-31111G(2df,p) and CCSD(T)(full)/6-31111G(2df,p) levels of theory using geometrical parameters obtained from MP2(full)/6-31111G(d,p) optimizations. These DHf values provide a recommended and self-consistent set with uncertainties as small as 612.6 kJ mol 21 (63 kcal mol 21 ) for deriving thermodynamic properties. The properties of interest include the proton affinities PA298 of MgO, MgOH, and Mg(OH)2, ionization energy IE0 of MgOH, bond dissociation energies D0 of Mg‐O, Mg‐OH, MgO‐H, HOMg‐OH, Mg‐OH 1 , H2O‐Mg 1 , and H2O‐MgOH 1 ; the latter two are hydration energies. Values in the literature, both experimental and theoretical, for many of these quantities show considerable scatter and a detailed comparison is made. Magnesium ions in fuel-rich, H2‐O2‐N2 flames at atmospheric pressure in the temperature range 1820 ‐2400 K were investigated experimentally by sampling the flames doped with magnesium through a nozzle into a mass spectrometer. It was shown that the interconversion of Mg 1 and MgOH 1 proceeds by way of the three-body reaction of Mg 1 with OH, in support of Sugden’s criterion that this occurs in flames if the weak HO‐Mg 1 bond has a dissociation energy less than 335 kJ mol 21 . The proton affinity PA 298 (MgO) was measured to be 1056 6 29 kJ mol 21 (252 6 7 kcal mol 21 ) along with approximate values for PA298 (MgOH) 5 919 kJ mol 21 (220 kcal mol 21 ) and PA298 [Mg(OH)2] 5 878 kJ mol 21 (210 kcal mol 21 ). Values were estimated for the electron‐ion recombination coefficient for MgH mOn molecular ions of 2 3 10 27 cm 3 molecule 21 s 21 , and for Mg 1 of 4 3 10 224 T 21 cm 6 molecule 22 s 21 similar to those for alkali metal ions. Finally, small rate coefficients for the chemi-ionization of magnesium via the reactions of Mg 1 OH and MgO 1 H to give MgOH 1 were estimated to be 4.832 3 10 29 exp(255 700/T) and 3.341 3 10 29 exp(232 970/T )c m 3 molecule 21 s 21 , respectively. (Int J Mass Spectrom 184 (1999) 153‐173) © 1999 Elsevier Science B.V.

Experimental results are reported that track the kinetics of the sequential ligation of Mg+, Fe+, (c-C5H5)Mg+, and (c-C5H5)Fe+ with ammonia in the gas phase as a function of the number of ligands added. The energetics of the sequential ligation of Mg+ with ammonia has also been followed theoretically. Molecular orbital calculations with density functional theory (DFT) performed at the B3LYP/6-31+G(d) level have been used to compute the binding energies for direct coordination of the ammonia molecules with Mg+ and for solvation that involves N−H···N interactions. Single-point calculations were also done using the optimized geometries from B3LYP/6-31+G(d) at B3LYP/6-311++G(2df,p) and MP4SDTQ(fc)/6-311++G(2df,p). Relative binding energies and standard enthalpies of formation (ΔH°f,298) have been calculated at all three levels of theory investigated. The experiments were performed with a selected-ion flow tube (SIFT) apparatus in helium buffer gas at 0.35 ± 0.01 Torr and 294 ± 3 K. The measured rate coefficie...

Ab initio molecular orbital calculations at the HF/6–31G(d,p) and MP2(full)/6–311G(d,p) levels are reported for the C2H4NO+ and C2H4NS+ potential energy surfaces. All structures have been subjected to geometry optimisations at both levels of theory and have been characterised by harmonic frequency calculations. On the C2H4NS+ surface the S-bridged thioformamidylmethyl cation, 3a, has the lowest energy while on the C2H4NO+ surface the ‘solvated ion’ H2CNH2+…CO, 8b, is lowest. On each surface the formamidylmethyl cation, 3, is in a deep well. On both surfaces there is an ion (structure 7) in which a three-membered ring contains both heteroatoms. On the C2H4NS+ surface 7a is 39.3 kcal mol−1 above 3 and there is a substantial barrier (25.8 kcal mol−1) for rearrangement of 7a to 3a. The oxygen analogue, 7b, is 62.6 kcal mol−1 above 3b. Dissociation of the α-aminothioacetyl cation, 6a, is endothermic (by 29.0 kcal mol−1) whereas dissociation of the α-aminoacetyl cation is exothermic by 12.1 kcal mol−1.

Ab initio molecular orbital calculations are reported for all neutrals, anions, and cations of the formula NHm (m = 1−3) and for their chlorinated analogues NHmCln (m + n = 1, 2, or 3). Structures ...

Laboratory measurements with the SIFT technique have shown that magnesium radical cations in a helium bath gas at 0.35 Torr and 294 K are unreactive with hydrogen cyanide but initiate a chemical sequence in cyanoacetylene that leads to the formation of Mg(HC3N)n+• cluster ions with n up to 7. Rate‐coefficient measurements for sequential addition of cyanoacetylene to Mg+• indicate an extraordinary pattern in alternating chemical reactivity while multiple‐collision induced dissociation experiments revealed an extraordinary stability for the Mg(HC3N)4+• cluster radical cation. Molecular orbital calculations with density functional theory (DFT) have provided structures and energies for the observed Mg(HC3N)1–4+• cations. These calculations indicate that the path of formation of Mg(HC3N)4+• appears to involve ligand‐ligand interactions mediated by Mg+• to form 2,4,6,8‐tetracyanosemibullvalene‐Mg+• or 1,2,5,6‐tetracyano‐1,3,5,7‐cyclooctatetraene‐Mg+• cations. A case is made for the formation of similar complex ...

Experimental results are reported that track the kinetics of gas-phase reactions initiated by Mg+*, (c-C5H5)Mg+ and (c-C5H5)2Mg+* in hydrogen cyanide and cyanoacetylene. The experiments were performed with a selected-ion flow tube (SIFT) tandem mass spectrometer at a helium buffer-gas pressure of 0.35 +/- 0.01 Torr and at 294 +/- 3 K. The observed chemistries of Mg+* and (c-C5H5)Mg+ are dominated by sequential ligation, while that of (c-C5H5)2Mg+* is by ligand switching. The rate-coefficient measurements for sequential addition of cyanoacetylene to Mg+* indicate an extraordinary pattern in alternating chemical reactivity while multiple-collision induced dissociation experiments revealed an extraordinary stability for the Mg(HC3N)4+* cluster ion. Molecular orbital calculations with density functional theory (DFT) at the B3LYP level, Hartree-Fock (HF) and second-order Mphiller-Plesset (MP2) levels, all performed with a 6-31+G(d) basis set, have been used to calculate structures and energies for the observed Mg(HC3N)1-4(+)* cations. These calculations indicate that the path of formation of Mg(HC3N)4+* involves ligand-ligand interactions leading to two cyclic (HC3N)2 ligands which then interact to form 2,4,6,8-tetracyanosemibullvalene-Mg+ or 1,2,5,6-tetracyano-1,3,5,7-cyclooctatetraene-Mg+ cations. A case is made for the formation of similar complex organomagnesium ions in the upper atmosphere of Titan where subsequent electron-ion recombination may produce cyano derivatives of large unsaturated hydrocarbons. In contrast, circumstellar environments with their much higher relative content of free electrons are less likely to give rise to such chemistry.

The low level detection of air pollutants requires reliable sampling and calibration techniques, as well as using sophisticated analytical instrumentation. Incorporating these requirements into a mobile platform allows for accurate, curb side measurement of airborne ambient chemicals in real time. In this case study, air emissions from two manufacturing facilities in close proximity to each other were monitored with a mobile unit to chemically characterize and differentiate the emissions from each facility. Based upon the downwind fingerprinting and concentration levels, the mobile unit was able to isolate the source of the emissions to the responsible facility. A few chemicals which were detected by the TAGA had never been reported by the companies. Real time proximity monitoring was accomplished by using a triple quadrupole mass spectrometer (TAGA IIe). The TAGA IIe interfaces with a low pressure chemical ionization source that operates at 3 Torr and 100 microA. By monitoring the response of specific parent/daughter ion pairs, the TAGA IIe unit was able to determine the point-of-impingement concentrations of styrene and other ambient airborne chemicals. Positive identification and quantitation of styrene was accomplished by multiple measurements of the following ion pairs: 104/78, 104/77, 104/65 and 104/52. By optimizing various parameters of the TAGA IIe a method detection limit of 1.1 microg/m(3) was achieved for styrene. A daily multi-point calibration was performed using a liquid standard. The maximum half-hour average concentration of styrene measured downwind of the two facilities was 2300 microg/m(3) and the maximum instantaneous level was measured at 15,000 microg/m(3). The mobile capability of the unit was also utilized in determining the ambient airborne concentration of styrene at various distances from the companies with the maximum levels measured at close proximity to the emission sources.

On 9 August 2000 a fire started at a facility that manufactures pool chemicals in Guelph, Ontario. A mobile trace atmospheric gas analyzer (TAGA) unit was summoned to provide on-site air monitoring operated by the Ontario Ministry of the Environment (OMOE). The responsibility of the TAGA unit was to monitor in real time the airborne contaminants released through the combustion of pool chemicals. This was accomplished by using an atmospheric pressure chemical ionization (APCI) source with the newest TAGA (model IIe): a triple quadrupole mass spectrometer which allows for the direct sampling and real time analysis of air for a wide range of toxics at low parts-per-billion (ppb) levels. The ionization mechanism under negative APCI conditions is dominated by charge transfer reactions, yielding parent ions which are selected in Q1, dissociated in Q2 and the resultant daughter ions are identified in Q3. By monitoring specific parent/daughter (P/D) ion pairs, the TAGA IIe was able to simultaneously measure, in real time, levels of hydrogen chloride (HCl) and chlorine (Cl2) present in the air. The response of the TAGA IIe was characterized by multi-point calibration curves which were linear up to 250 microg/m3 for HCl and up to 600 microg/m3 for Cl2. The average detection limit (DL) for this application was 0.50 microg/m3 for both HCl and Cl2. On-site measurements of HCl and Cl2 were made at several locations upwind and downwind of the fire site over a period of 3 days. The data collected by the TAGA unit was used by the local officials for a real time assessment of the airborne levels of HCl and Cl2.

Given the increasing number of English Language Learners (ELLs) in post-secondary environments (Roessingh & Douglas, 2012), educational practices such as availability of language support for mathematics should be assessed to ensure that all students’ needs are met. To explore the effects of language on mathematics in ELLs, mathematical test items were presented in four language contexts: vocabulary knowledge, negation, preposition use, and atypical sentence structure. Sixty students enrolled in mathematics courses volunteered to complete the mathematics task. Results suggest that math items falling into each of the four language contexts disadvantage ELLs, highlighting that the needs of ELLs should be considered at all levels, from classroom practices to educational policy.