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The electron impact ionization and dissociative ionization cross section data of CO, CO2, CH4, NH3, and SO2, measured in the laboratory, were parameterized utilizing an empirical formula based on the Born approximation. For this purpose an chi squared minimization technique was employed which provided an excellent fit to the experimental data.
Differential and momentum-transfer cross sections for the elastic scattering of electrons by NH3 have been obtained for collision energies of between 2.5 and 20 eV using the fixed-nuclei static-exchange approximation of the Schwinger variational principle. At intermediate and large scattering angles, good agreement is found between calculated and relative experimental cross sections. The differential cross sections reveal evidence of a weak d-wave enhancement around 8 eV.
An attempt is made to infer the abundance and distribution of ammonia from RF emission measurements more accurately than heretofore, on the basis of the results of laboratory measurements for the mm-wave opacity of gaseous ammonia under simulated Jovian atmosphere conditions. The measurements were conducted at various frequencies in the 32-40 GHz range at 2 atm and 203 K; the atmospheric mixture was 88.34 percent H2, 9.81 percent He, and 1.85 percent NH3. Experimental results are found to be readily modeled by the Gross (1955) line-shape factor, rather than that of Van Vleck and Weisskopf (1945).
The successive binding energies of up to four H2O and NH3 ligands to Cu(+) are computed at the self-consistent-field and modified coupled-pair functional levels. The most stable structures are those where all ligands are equivalent. Replacing Cu(+) by a point charge gives binding energies that are in good agreement with ab initio and experimental results, and is consistent with bonding that is largely charge dipole in nature. About two-thirds of the large reduction in ligand binding energy between the second and third ligand is due to ligand-ligand repulsion, while one-third is due to increased metal-ligand repulsion resulting from a loss of sd-sigma hybridization. The first and second ligand binding energies increase substantially at the correlated level due to an improved description of sd-sigma hybridization.
The structure and binding energies are determined for many of the M(H2O)n(+) and M(H2O)n(2+) species, for n = 1-3 and M = Mg, Ca, or Sr. The trends are explained in terms of metal sp or sd-sigma hybridization and core polarization. The M(NH3)n(+) systems, with M = Mg or Sr, are also studied. For the positive ions, the low-lying excited states are also studied and compared with experiment. The calculations suggest an alternative interpretation of the SrNH3(+) spectrum.
Intensities have been measured for individual transitions in the Q and R branches of the nu(sub 1) band of NH3 using a difference-frequency laser spectrometer. The data yield an integrated band strength of S(sup 0 sub v) = 219.36 +/- 1.03/sq cm/MPa at 297 K, corresponding to a transition moment of absolute value of mu(sub v) = 8.535(20) x 10(exp -32) C x m, and a Herman-Wallis correction factor,(1 + alpha(sub J)m), where alpha(sub J) = 0.0209(20). The intensities of a few lines for K greater than or equal to 7 were noticeably perturbed by a perpendicular Coriolis interaction with 2nu(sub 4)(E, l = 2), so were excluded from the fit. A small sample of nu(sub 3) band lines occurring in the nu(sub 1) band scans also yields a rough estimate of the nu(sub 3) band intensity with evident irregular perturbations.
The two-body recombination of NH4(+)(NH3)(sub 2,3) cluster-ions with electrons has been studied in an afterglow experiment in which the electron temperature T, was elevated by radio-frequency heating from 300 K up to 900 K. The recombination coefficients for the n = 2 and n = 3 cluster ions were found to be equal, alpha(sub 2, sup(2)) = alpha(sub 3, sup(2)) = (4.8 +/- 0.5) x 10(exp - 6)cu cm/s, and to vary with electron temperature as T(sub c, sup -0.65) rather than to be nearly temperature-independent as had been inferred from measurements in microwave-heated plasmas.
The Robert-Bonamy formalism has been commonly used to calculate half-widths and shifts of spectral lines for decades. This formalism is based on several approximations. Among them, two have not been fully addressed: the isolated line approximation and the neglect of coupling between the translational and internal motions. Recently, we have shown that the isolated line approximation is not necessary in developing semi-classical line shape theories. Based on this progress, we have been able to develop a new formalism that enables not only to reduce uncertainties on calculated half-widths and shifts, but also to model line mixing effects on spectra starting from the knowledge of the intermolecular potential. In our previous studies, the new formalism had been applied to linear and asymmetric-top molecules. In the present study, the method has been extended to symmetric-top molecules with inversion symmetry. As expected, the inversion splitting induces a complete failure of the isolated line approximation. We have calculated the complex relaxation matrices of selfbroadened NH3. The half-widths and shifts in the ν1 and the pure rotational bands are reported in the present paper. When compared with measurements, the calculated half-widths match the experimental data very well, since the inapplicable isolated line approximation has been removed. With respect to the shifts, only qualitative results are obtained and discussed. Calculated off-diagonal elements of the relaxation matrix and a comparison with the observed line mixing effects are reported in the companion paper (Paper II).
Line mixing effects have been calculated in the ν1 parallel band of self-broadened NH3. The theoretical approach is an extension of a semi-classical model to symmetric-top molecules with inversion symmetry developed in the companion paper [Q. Ma and C. Boulet, J. Chem. Phys. 144, 224303 (2016)]. This model takes into account line coupling effects and hence enables the calculation of the entire relaxation matrix. A detailed analysis of the various coupling mechanisms is carried out for Q and R inversion doublets. The model has been applied to the calculation of the shape of the Q branch and of some R manifolds for which an obvious signature of line mixing effects has been experimentally demonstrated. Comparisons with measurements show that the present formalism leads to an accurate prediction of the available experimental line shapes. Discrepancies between the experimental and theoretical sets of first order mixing parameters are discussed as well as some extensions of both theory and experiment.
Line coupling and line mixing effects have been calculated for several self-broadened NH3 lines in parallel bands involving an excited v2 mode. It is well known that once the v2 mode is excited, the inversion splitting quickly increases as this quantum number increases. In the present study, we have shown that the v2 dependence of the inversion splitting plays a dominant role in the calculated line-shape parameters. For the v2 band with a 36 cm-1 splitting, the intra-doublet couplings practically disappear and for the 2v2 and 2v2 - v2 bands with much higher splitting values, they are completely absent. With respect to the inter-doublet coupling, it becomes the most efficient coupling mechanism for the v2 band, but it is also completely absent for bands with higher v2 quantum numbers. Because line mixing is caused by line coupling, the above conclusions on line coupling are also applicable for line mixing. Concerning the check of our calculated line mixing effects, while the present formalism has well explained the line mixing signatures observed in the v1 band, there are large discrepancies between the measured Rosenkranz mixing parameters and our calculated results for the v2 and 2v2 bands. In order to clarify these discrepancies, we propose to make some new measurements. In addition, we have calculated self-broadened half-widths in the v2 and 2v2 bands and made comparisons with several measurements and with the values listed in HITRAN 2012. In general, the agreements with measurements are very good. In contrast, the agreement with HITRAN 2012 is poor, indicating that the empirical formula used to predict the HITRAN 2012 data has to be updated.
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in many astrophysical environments, and are likely present in interstellar clouds and protostellar disks [1]. In dense molecular clouds,PAHs and other gas-phase species are expected tocondense onto grains to form mixed molecular ice mantles dominated by small molecules like H2O, CH3OH, NH3, CO, and CO2 [2]. These icy mantleslikely undergo energetic processing from ionizing radiation in the form of cosmic rays and high-energy photons.
While dual-fuel ammonia engines are starting to be commercialized for the large low-speed 2-stroke marine engine market, there are still challenges with utilizing ammonia on 4-stroke engines used as auxiliary engines for ocean going vessels and within inland and coastal marine applications. The shorter timescales for high-speed engines pose a particular challenge for low-cetane, high ignition energy fuels like ammonia. In addition to achieving maximum ammonia substitution levels, N2O emissions are a key factor that needs to be understood. This paper reports the results of experiments using a single-cylinder 107mm bore Cummins B-series diesel engine modified for port-fuel injection of gaseous anhydrous ammonia with a direct injection of diesel fuel near-TDC to ignite the premixed ammonia. Combustion data as well as emissions data from an FTIR including NO, NO2, N2O, and unburned ammonia are presented for selected operating points with a focus on high-load operation at 1200rpm with high ammonia energy substitution (over 95% by fuel energy). Several air/fuel ratio conditions are included, sweeping from diesel-like airflow to stoichiometric conditions. The impact of biofuels (biodiesel and renewable diesel) as pilot fuels is also considered. Comparisons for emissions, greenhouse gas performance, and efficiency are made with a conventional diesel combustion baseline. The impact of fuel injection strategy on NOx, N2O, and NH3 emissions is quantified, and the dual-fuel ammonia results on this high-speed 4-stroke engine are expected to provide fundamental insights into further combustion development opportunities for the larger engines used across marine applications.
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Mass spectrometric analysis of oxygen atom reaction with hydrogen and ammonia
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Applicability of vacuum ultraviolet spectrometry to detecting neutral atom and molecule constituents in exhaust streams
Comparative numerical capture and experimental reaction cross sections for ion-molecule ammonia