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.
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