Sidney W. Benson

Chemiluminescence studies. IV. Pressure‐dependent photon yields for Ba, Sm, and Eu reactions with N2O, O3, O2, F2, and NF3

Chemiluminescence spectra and photon yields are presented for reactions of Ba, Sm, and Eu with N2O, O3, O2, F2, and NF3 for the pressure range 0.5–20 torr. Peak yields range from 2.5% to 70%, with the reactions of Sm with NF3 and F2 having the highest yields. These latter reactions put from 12% to 16% of their available thermal energy into luminous output. The pressure dependence of the photon yields deduced from these and other recent measurements suggests that the initial exothermic reaction primarily populates high vibrational levels of the ground electronic state of the newly formed diatomic. Radiating states would then be populated mainly by collision‐induced vibrational‐to‐electronic internal conversion.

Theory of the Low‐Temperature Chromatographic Separation of the Hydrogen Isotopes

A new electrostatic theory is presented which quantitatively explains the chromatographic separation of the hydrogen isotopes on an alumina column at low temperatures. The theory is based on the interaction of the surface electric fields of the alumina with the polarizable hydrogen isotopes. By calculating the electric fields over an adopted Al2O3 surface, it is found that there are two active adsorption sites at 77.4°K, one over a vacancy in the Al2O3 structure, and the other over an Al3+. The total interaction potential over either site is a function of the polarizabilities of the adsorbed molecules and the distance the molecules are from the surface. A 5–9 potential over a vacancy site gives results which favorably agree with experimental values. The rotational barrier, necessary to explain the separation of the ortho and para species, is shown to arise from the difference in the parallel and perpendicular components of the molecular polarizability of the hydrogen molecule.

Vibrational Energy Exchange of Highly Excited Anharmonic Oscillators

The probabilities of dissociation Pdis, excitation Pex, de‐excitation Pde, and the associated average energy exchanges were calculated theoretically for a highly energized, anharmonic oscillator (I2 or Br2) colliding classically with an inert gas atom C through a Morse‐type potential. The effect of varying mass and well depth was investigated.It was found that the effect of anharmonicity is to favor excitation and dissociation. However, the average ΔEv for these processes is about the same for harmonic and anharmonic oscillators and not much bigger than 1 to 2 RT. Pdis increases markedly with increasing mass. The well depth (V0) does not seem to have much effect in the range 0.004<V0/D0<0.14, where D0 is the bond dissociation energy. Exchange reactions are observed, but for shallow well depths they are rare events. From the results, it is possible to calculate λ, the probability of stabilizing an atom pair by a third‐body collision. This turns out to be independent of temperature but depends strongly on t...

Thermochemistry of the gas phase equilibria i-C3H7I C3H6 + HI, n-C3H7I i-C3H7I, and C3H6 + 2HI C3H8 + I2

Abstract Equilibrium constants of the reactions given in the title were measured spectrophotometrically in the gas phase between 241.8 K and 342.5 K. These results and others were used to obtain the entropies and enthalpies of formation of n - and i -propyl iodide, as well as to point out the possibility of a small discrepancy in the values for propane and propylene. The group values [see reference 2] carried over from the thermochemical properties of 1,2-di-iodoethane and 1,2-di-iodopropane would fit the above thermochemical quantities well, indicating the absence of any 1,2-I—I interaction. The best values are: n -C 3 H 7 I i -C 3 H 7 I C -(C)(H) 2 (I) C -(C) 2 (H)(I) ΔH f o (298.15 K)/kcal mol −1 −7.4 −9.4 8.0 10.5 S o (298.15 K)/cal K −1 mol −1 81.0 77.6 43.0 21.3 Measured values of the equilibrium constants for n -PrI and i -PrI formation from HI + C 3 H 6 allow “best” values to be selected for forward and reverse rate constants for these reactions and also for the I-atom catalyzed reactions.

Vibrational Relaxation of Diatomic Molecules

A one‐dimensional model is explored and rigorous solutions are obtained to the classical equations of motion yielding transition probabilities between low‐lying vibrational levels of diatomic molecules. Results are listed for four halogens, O2, N2, and CO colliding in pure gases and O2 with Ar or He as a collision partner. Selecting a single variable ``a (the range term of the Morse potential function), excellent agreement was found with the available experimental data over a 30‐fold temperature range. The validity of the Landau—Teller theory is discussed; in particular, the effect of the consideration of an attractive potential and the simplification involved in its explicit treatment. Transitions involving double quantum jumps are considered. Some preliminary results of a two‐dimensional model are discussed.

Kinetics and Mechanism of Hydrogenolyses. The Addition of Hydrogen Atoms to Propylene, Toluene, and Xylene

Previously measured rates of hydrogenolysis of propylene, toluene, and xylene fit −d[RCH3]/dt=10(11.5±1)−(55±3)/θ[RCH3][H2]1/2u2009moleu2009liter−1·sec−1 (where θ is 2.3RT kcal mole−1) over an unusually wide range of conditions. In the case of toluene, for example, the range is 107 in rate, 105 in hydrogen pressure, and 500°C in temperature. We propose the mechanism H2⇄2H, H+RCH3⇄RH+CH3, CH3+H2⇄CH4+H, giving −d[RCH3]/dt=K11/2k2[RCH3][H2]1/2. Substitution of values for K1 and k2 gives rate constants and Arrhenius parameters in excellent agreement with all reliable data.

Vibrational and Rotational Excitation of Diatomic Molecules. Two‐Dimensional Model

The change of energy of a diatomic molecule upon collision with an atom in two dimensions was calculated. The energy contributed to the various internal degrees of freedom of the molecule was evaluated. The vibrational transition probabilities obtained were compared to experimental data for the case of O2→Ar collisions. By contrasting these results with those of a one‐dimensional treatment, the form of a realistic three‐dimensional potential function was predicted. It was found that at lower initial rotational energies, transfer of energy from rotational to vibrational degrees of freedom is as effective as translational→vibrational transfer. For higher initial rotational energy, rotational→vibrational transfer is shown to be less probable.

Kinetic and Spectroscopic Constraints on the Origin of the N2 Afterglow

The large transition probability (10−1 to 10−2) for curve crossing such as that which occurs in N2 pre‐dissociation, N2u2009(3B)u2009⇆N2(5Σ), guarantees that the rotationally hot members of the 12th vibrational level of the B state (3B(12))* will always be in equilibrium with free N atoms without the intervention of a third body. A kinetic scheme is suggested for these species that includes rotational and vibrational quenching in competition with electronic quenching. Fast rotational quenching gives rise to pseudoequilibrium population of normal 3B(12) species. The equilibrium constant KB for 2N⇆N2(2B(12)) is estimated at 10−1.2 liter/moleu2009=u200910−22.9 cc/particle at 300°K with a negative activation energy of −u20092.2 kcal/mole, in good accord with recent data. Using 105.0±0.3 sec−1 as the measured radiative rate constant of the 12‐8 transition yields an absolute emission intensity for this band of 102.9±0.3 liter/mole·secu2009=u200910−17.9±0.3 cc/molecule·sec, again in good accord with observation. It appears from this that t...

Classical Theory of Rotational Relaxation of Diatomic Molecules

The classical equations of motion of colliding diatomic molecules are solved rigorously in two dimensions to obtain the energy transferred to the internal degrees of freedom during collision. The model considers up to four atoms bound by six atom‐centered Morse potentials. The effect of varying range parameters is noted. The relaxation of H2 with He and H2 collision partners, D2 with He, and pure N2 and O2 is studied. The vibration—rotation energy exchange is evaluated and accounted for. The resulting relaxation times and average collision numbers agree well with empirical findings. In the temperature range 100°—700°K, except for N2 and O2, a negative temperature dependence was obtained. The contrary is expected at higher temperatures where the relaxation times are functions of the inverse collision frequency only.

Heat‐pipe‐oven reactor (HPOR): I. A new device for flame studies; photon yields in the reaction of Na with CCl4 and N2O

A new device based on the heat‐pipe oven has been demonstrated to have a unique capability for studying reactions of metal atoms with oxidizers. This device allows spherical diffusion flame studies under known, uniform, and easily adjustable, metal atom concentration. low gas pumping rate, clean window operation, and minimized problems of reactive solid disposal. The reactor was used for the study of chemiluminescence of the reactions of sodium vapors with CCl4, with N2O, and with both CCl4 and N2O. The emission from these reactions in the range 2000–9000 A was identified to be from various excited atomic levels of sodium and from excited C2, mostly in the Swan bands. Even though the emission was very intense, especially in the case of Na+N2O+CCl4 (photon yields of about 10%), it was found that the Na excited‐state populations had a Boltzmann distribution corresponding to an electron temperature of 2260u2009°K. This suggests that the emission of sodium radiation from both the Na+CCl4 and Na+CCl4+N2O flames re...