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The energy dependence of reaction cross sections has been observed for various ion-molecule reactions. The secondary ions C4HI0Br2+, C4HsBr+, CIHloRr+, CpHaBr2-and CHRr2' from C2H5Br; CsH1412+ from n-CaH71 and C6HI4C1+ from s-C3117C1 indicate low energy limits of stability. Tropylium and substituted tropylium ions appear to result from reactions of CHI+, CD3+, CHC12T and CC13* with C&; they give evidence of transitions in reaction cross sections a t cn. 1.3-2.0 ev. inn energy which are identified with instability resulting from head-on collisions.

Ion cyclotron resonance techniques have been used to determine the thermal energy rate constants for the ion-molecule reactions: (H2+)v+H2 → lim k1H3++H,(H2+)v+ He → lim k2HeH+ + H,→ lim kv (H2+)v′ + He lim →He+ + H2 → lim k3HeH+ + H,HeH+ + H2 → lim k4H3+ + He.For a near-Franck-Condon distribution of initial vibrational states in H2+ k1 = 2.08 ± 0.03, k2 =0.13 ± 0.01, k3 < 0.002, and k4 = 1.83 ± 0.06×10−9 cm3/molecule· sec. Collisional deactivation of vibrationally excited H2+ ions is also shown to occur in nonreactive encounters with He atoms. The rate constant kν for this process increases with increasing vibrational quantum number ν and is approximately equal to k2v for H2+ ions in vibrational state ν.

Ion cyclotron resonance methods are used to identify and to measure the rate constants for the abstraction of a hydrogen atom from H2 by CH+, CH2+, CH4+, N+, NH+, NH2+, NH3+, O+, OH+, H2O+, CO+, N2+, C2+, and C2H+ ions. Although in most cases hydrogen atom abstraction is the only available exothermic pathway for these reactions at thermal energies, the rate constants measured show that except for O+, CO+, and N2+, a large fraction of collisions between these ions and H2 are not reactive. The rate constants measured range from a low of (3±1) × 10−13 cm3/sec for the NH3+−H2 reaction to (1.73±0.04) × 10−9 cm3/sec for the N2+−H2 reaction. These values compare to the Langevin value of about 1.5 × 10−9 cm3/sec for collisions between these ions and H2. An examination was also made for possible thermoneutral hydrogen atom exchange reactions for those ions which do not react with H2 (CH5+, CH3+, NH4+, H3O+, H2S+, H3S+). The only exchange reaction observed was for collisions between CD3+ ions and H2, for which a rate constant of (5.1±0.5) × 10−10 cm3/sec was measured.

A mass spectrometer was used to study gaseous equilibria in the Be–Al–Cl system by passing HCl(g) over a Be–Al mixture in a Knudsen cell molecular source. For the reactions Be(g) + AlCl(g) = BeCl(g) + Al(g) and Be(g) + BeCl2(g) = 2 BeCl(g), ΔH298 values of 26.2 ± 2 and 36.1 ± 2 kcal, respectively, are derived. Also, the sublimation of BeCl2 was studied by torsion-effusion and mass-spectrometric techniques, from which the heat of sublimation ΔH298 = 32.5 ± 0.5 kcal/mole is derived for β-BeCl2. These data yield the dissociation energies D0°(BeCl) = 91.9 kcal (3.98 eV) and D0°(BeCl2) = 219.4 kcal (9.51 eV). The results are discussed briefly in terms of the chemical bonding.

Mass spectrometric Knudsen effusion experiments have provided evidence for the existence of the suboxide species Be2O(g) in the equilibrium vapor above crystalline beryllium oxide at temperatures around 2300°K. Be2O+ ions appear to be formed both by simple ionization of Be2O(g) and by fragmentation of a larger molecule. The relative importance of the two processes has been shown to be temperature dependent. An average value of —8±10 kcal/mole was obtained for ΔHf°298[Be2O(g)] from third-law calculations for three equilibria. Mass spectral data are given for the equilibrium vapor above beryllium oxide at 2380°K in the presence of tungsten.

The reaction of BF3(g) with B2O3(l) was studied by the transpiration method in the temperature range 600° to 1100°K. Results indicate the reaction to be BF3(g)+B2O3(l)=(BOF)3(g).ΔH298° was found to be 4.2 kcal, and leads to ΔHf298°=—566.8±1 kcal/mole for (BOF)3(g). The vapor above mixtures of MgF2 and B2O3 contained in a Knudsen cell was analyzed with a mass spectrometer and was found to contain BF3(g), (BOF)3(g), and BOF(g) in the range 980° to 1230°K. From studies of the temperature dependence of appropriate ion intensities the heat of the reaction (BOF)3(g)=3BOF(g)was derived as 131 kcal at 1125°K. Use of low ionizing electron energies was required to avoid fragmentation effects. The heat of formation of BOF(g) at 298°K was calculated to be —144±3 kcal/mole.

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