Richard F. Porter

Stability of the ammonium and methylammonium radicals from neutralized ion‐beam spectroscopy

The stability of the ammonium radical (NH4) was determined from measurements of the kinetic energy released in its fragmentation products following formation in a fast electron capture process: NH4++Na → NH4*+Na+. Scattering profiles for heavy (NH3) and light (H) dissociation products were obtained from beam measurements with 5–16 keV NH4+ ions. The existence of a predissociative barrier in the radical is inferred from edge structure and scattering continua in H atom profiles. The radical is bound with respect to a potential minimum but all of the isotopic species NH4, NH3D, NH2D2, and NHD3 undergo rapid loss of H atoms and have ground states lying above their dissociation limits. The radical ND4 has unusual stability with its ground state lying close to or below its dissociation limit. Dissociative lifetimes for stable and unstable states of ND4 differ by at least two orders of magnitude. The possible significance of these observations on the interpretation of optical transitions involving the ground sta...

Energetics of fragmentation of CH5, H3O, and NH4 from neutralized ion‐beam experiments

Fragmentation energies for radicals of the type RH2 (RH=CH4, NH3, and H2O) produced by electron capture interactions of 5 keV RH2+ ion with Na or K atoms are reported. The experimental technique involves measurement of spatial beam profiles resulting from dissociation of neutral radicals following their formation in a near resonant electron transfer process. Cross sections for RH2+–Na capture reactions are typically 1x10−14 cm2. Fragmentation energies from measurements with Na target atoms are −2.65±0.14, −0.22±0.03, and −1.12±0.07 eV for CH5, NH4, and H3O, respectively. From our results with Na and K targets and published values for proton affinities, the vertical electron affinities of CH5+ and H3O+ are calculated to be 5.3±0.2 eV and 5.1±0.3 eV, respectively. Beam profiles for ND4 show this species to be metastable with a lifetime of about 1 μs. From this we estimate a potential barrier to dissociation in NH4(ND4) between 0.36 and 0.48 eV, indicating this species should be stable at low temperatures. C...

Mass Spectrometric and Thermodynamic Study of Gaseous Transition Metal (II) Halides

Mass spectrometric and Knudsen effusion techniques have been used to study the vaporization of several transition metal (II) halides. The systems studied include FeI2 and the chlorides and bromides of Cr, Mn, Co, and Ni. The over‐all temperature range was between 440 and 700°C. For all systems the monomer is the major vapor species in the temperature range studied. Dimeric species have also been detected in the vapor phase for all systems, except NiCl2 and NiBr2. Vapor pressure data have been combined with mass spectrometric and entropy data to give heats for the dimerization reaction, 2MX2 (g)=M2X4 (g).

Molecular Structure of Lithium Chloride Dimer. Thermodynamic Functions of Li2X2 (X = Cl, Br, I)

Our electron diffraction apparatus has been suitably modified for the study of vapors at high temperatures. A furnace and auxiliary power supply have been constructed, and a serviceable design for a sample container, with a nozzle, has been developed.Data on two systems have been obtained. The diffraction pattern produced by cesium chloride vapor is that expected for a diatomic molecule; the interatomic distance determined in this experiment checks with the microwave value. In lithium chloride vapor, dimers predominate. Their structure is diamond shape (planar) with Li–Cl=2.23±0.03 ACl–Cl=3.61±0.03 A∠ClLiCl=108∘±4∘.The dimensions of the lithium halide dimers are compared and their thermodynamic functions tabulated.

The molecular structures of perfluorocyclobutane and perfluorocyclobutene, determined by electron diffraction

Abstract As part of our current program to establish relationships between the geometries of low molecular weight hydrocarbons and the corresponding F-substituted analogs, the molecular structure of perfluorocyclobutane and perfluoro-cyclobutene were investigated byelectron diffraction. The geometrical parameters obtained by least squares refinements of the intensity data are: the carbon atoms in C 4 F 8 are not coplanar; symmetry D 2d , with (C-F) = 1.333 ±0.002 A, (C-C) = 1.566±0.008 A, ∠FCF = 109.9±0.3°, ∠CCC = 89.3±0.3°, the dihedral angle = 17.4° and tilt angle for CF 2 = −5.4°. The carbon atoms in C 4 Fe 6 are coplanar; (C-C) = 1.342 ±0.006 A, (C-C) = 1.508 ±0.003 A, (C-C) = 1.595 A, (C-F) = 1.319±0.012 A, (-C-F) = 1.336±0.006 A, ∠C(1)C(2)C(3) = 94.8 ±0.3°, ∠C(2)C(3)C(4) = 85.2°, ∠C(2)C(1)F(5) = 133.6 ±2.9° and ∠C(2)C(3) F(7) = 115.9±0.5°. These results are compared with the available structural data for various substituted cyclobutenes and cyclobutanes.

Experimental evidence for metastable states of D3O and its monohydrate by neutralized ion beam spectroscopy

The oxonium radical (H3O) has been generated in its ground state by neutralizing a fast beam of ions in the near resonant electron transfer reaction H3O++K(g)→H3O*+K+. Analysis of neutral beam scattering profiles and collisionally reionized mass spectra indicate that the fully deuterated species (D3O) can be formed in a distribution of dissociative and metastable states (τ>0.6 μs). Thermalization of the precursor D3O+, prior to electron transfer, is required for production of metastable D3O. Neither H3O nor D2HO is observed in metastable states. These isotope effects support earlier theoretical predictions of a shallow local minimum on the oxonium potential surface. The ionization potential of D3O is calculated to be 4.3±0.1 eV. Some spectroscopic implications for this radical are discussed. The oxonium monohydrates (H3O⋅H2O) are also observed to exist in metastable states for several H/D isotopic variants. The ionization potential of D3O⋅D2O is estimated to be ≥3.4 eV.

Mass Spectrometric Study of the Reactions of BF3(g) with BCl3(g), B(OH)3(g), and B2O3(1)

Exchange reactions of halogen and hydroxyl with BX3(g) have been studied mass spectrometrically. The major product produced by the reaction of BF3(g) with boric acid at 25°C and pressures of the order of 10—6 atm is B(OH)F2(g). The species B(OH)2F(g) is also formed at higher temperatures when B(OH)3(g) is observable. Equilibria involving the reactions 13BF3(g)+23BCl3(g)=BFCl2(g),23BF3(g)+13BCl3(g)=BF2Cl(g),13BF3(g)+23B(OH)3(g)=B(OH)2F(g), and 23BF3(g)+13B(OH)3(g)=B(OH)F2(g), have been studied as a function of temperature. Heats of formation at 298°K for BFCl2(g), BF2Cl(g), B(OH)2F(g), and B(OH)F2(g) are found to be —154.1±1.0, —211.9±2.0, —249.8±2.5, and —260.2±2.5 kcal/mole, respectively.Reactions of BF3(g) with B2O3(l) have also been studied at pressures between 10—6 and 10—3 atm and temperatures between 400 and 1000°K. Results are consistent with published data from studies with BF3 at pressures near 1 atm and show that (BOF)3(g) is the primary product at both pressure extremities. For the reaction BF3...

Experimental observations of excited dissociative and metastable states of H3 in neutralized ion beams

Electron transfer reactions for a fast beam of H3+ ions with Mg and K atoms have been investigated by neutral beam scattering techniques. Reactions with Mg and K targets form H3 molecules in the dissociative 2p 2E′ ground state and predissociative 2s 2A1′ and 2p 2A2″ excited states, respectively. Fragmentation energies, obtained from beam scattering measurements, allow the scaling of these electronic states of H3 with respect to their dissociation products. A metastable form of H3 observed in the H3+/K reaction is identified as the nonpredissociating, nonrotating molecule in the 2p 2A2″ electronic state. The cross section for the state‐to‐state process H3+(X 1A1′, N=1, K=0)+K(g)→H3*(2p 2A2″, N=K=0)+K+ for a 6 keV ion beam is 7.0±1.0 A2. Total ion beam attenuation cross sections for the species H3+, H2D+, D2H+, and D3+ with K targets are in the relative order 1.0, 0.59, 0.58, 0.53. The higher cross section observed for the H3+/K reaction is partially accounted for by an usually high cross section for the n...

Mass Spectrometric Study of the Vaporization of LiF, NaF, and LiF–NaF Mixtures

Vapors effusing from Knudsen cells containing LiF, NaF, and LiF–NaF mixtures have been analyzed mass spectrometrically. The over‐all temperature range studied is between 900 and 1150°K. Monomers, dimers, and trimers of LiF and NaF are observed. The LiF system has the higher concentration of dimers and trimers. In the LiF–NaF system at 50 mole percent LiF the mixed dimer, LiNaF2, is the major polymeric vapor species. Thermochemical data for LiF(g), NaF(g), Li2F2(g), Na2F2(g) and Li3F3(g) have been obtained. For the reaction Li2F2(g)+Na2F2(g)=2LiNaF2(g), ΔH° is approximately zero.

Mass Spectra of Aluminum(III) Halides and the Heats of Dissociation of Al2F6(g) and LiF·AlF3(g)

Mass spectra of gaseous aluminum(III) chloride and bromide have been obtained and interpreted quanitatively in terms of the degree of association in the vapor phase. Ion currents indicative of a molecular trimer of AlCl3 have been observed. Mass spectra of the vapors effusing from a Knudsen cell containing AlF3 have been obtained and the stability of the molecular dimer of AlF3(g) has been determined quantitatively. Mass spectra of vapors from LiF–AlF3 mixtures indicate the existence of a stable LiF·AlF3(g) molecule. Ion current data have been obtained as a function of condensed phase composition. A second complex molecular species which appears to be either (LiF)2·AlF3(g) or (LiF·AlF3)2(g) has been observed. For the reaction Al2F6(g)=2AlF3(g), ΔH°1000=48.0±4.0 kcal/mole dimer, and for LiF·AlF3(g)=LiF(g)+AlF3(g), ΔH°1000=73±4 kcal/mole.