Search

Absolute rate constants are reported for the deactivation of O(1D) by five trace atmospheric constituents for the temperature range 200–350 K. O(1D) atoms produced by photolyzing ozone with a frequency quadrupled pulse from a Nd‐YAG laser are monitored directly by means of the O(1D) →O(3P) emission at 630 nm. All the gases studied here are thought to deactivate O(1D) primarily through reactive channels. Their rate constants exhibit no detectable temperature dependence. The rate constants are (in units of 10−10 cm3/molecule⋅s) N2O: 1.1,±0.2, H2: 0.99±0.3, HCl: 1.4±0.4, NH3: 2.5±0.5, CH4: 1.4±0.4. The present results and those of our previous studies are compared with rate constants obtained using the time‐resolved attenuation of resonance absorption technique.

Absolute rate constants and their temperature dependencies for the deactivation of O(1D) by five important atmospheric gases are reported. O(1D) atoms are produced by photolysis of ozone at 266 nm and the atoms are directly observed in time resolved decay of the O(1D) →O(3P) radiation at 630 nm. Gases which only quench O(1D) (O2, N2, and CO2) are observed to have a small negative temperature dependence while O3 and H2O, which also have a reactive channel, display no temperature dependence. Arrhenius expressions for the reactions measured are (A in units of 10−10 cm3/molecule⋅ s, E in cal/mole) O2(T=104–354 K) 0.29 exp(134/RT), N2(T=104–354 K) 0.20 exp(214/RT), CO2(T=139–200 K) 1.2 and (T=200–354 K) 0.68 exp(233/RT). The rate constants for O3 and H2O are 2.4×10−10 and 2.3×10−10 cm3/molecule⋅ s over ranges of 103–393 K and 253–353 K, respectively. The results are compared with other energy dependent measurements and with the theories reported in the literature.

The relative rate constants for the reaction channels were determined using chemical‐ionization mass spectrometry to measure the products of Reaction (1). O(1D2) atoms were produced by the photodissociation of N2O at wavelengths greater than 1950 A. The measurements were carried out in mixtures of N2O with helium added to remove the excess kinetic energy carried by the O(1D2). We find the ratio k1a/k1b is sensitive to the presence of helium increasing from a value of 0.68 in pure N2O to a value of 0.80 with [He]/[N2O]?10. In addition, at 300 K we find that (1a) and (1b) consititute the only significant channels for the reaction with (k1c+k1d+k1e)/(k1a+k1b ) ?0.038. The ratio k1a/k1b is found to decrease slowly with increasing temperature over the range 170–434 K. These data can be fitted by the expression k1a/k1b= (0.72±0.11) +(21.6±7.0)/T.

The flowing afterglow and selected ion flow tube techniques are applied in a room temperature study of the kinetics of proton‐transfer reactions of the type XH++Y?YH++X for X or Y=He, H2, O2, Kr, O, N2, Xe, CO2, CH4, CD4, N2O, OH, and CO, and for the deuteration of O2 by D3+. Equilibrium constants are determined and changes in thermodynamic state properties (ΔG°, ΔH°, ΔS°) are derived for the reactions with X/Y=H2/O2, O2/Kr, H2/Kr, H2/N2, O/N2, N2/Xe, Xe/CO2, CO2/CH4, CH4/N2O, and N2O/CO. Proton affinities are reported for O2, H2, Kr, O, N2, Xe, CO2, CH4, N2O, and CO, together with the heats of formation of their protonated species. Also a correlation is presented between the kinetic and thermodynamic results obtained in this study.

Absolute rate constants for the deactivation of O(1D) atoms by some atmospheric gases have been determined by observing the time-resolved emission of O(1D) at 630 nm. O(1D) atoms were produced by the dissociation of ozone via repetitive laser pulses at 266 nm. Absolute rate constants for the relaxation of O(1D) at 298 K are reported for N2, O2, CO2, O3, H2, D2, CH4, HCl, NH3, H2O, N2O, and Ne. The results obtained are compared with previous relative and absolute measurements reported in the literature.

The spectral distribution of the chemiluminescent reactions O+NO→NO2+hv has been determined over the wavelength region 3875–14 000 A. The absolute rate constant was determined by a method of chemical actinometry which required only relative intensity measurements and which is virtually free from geometry errors. The rate constant over this spectral region was found to be 6.4×10—17 cm3 molecule—1 sec—1 within an accuracy of 30%. This reaction can be used as a standard from which the rate constants for other chemiluminescent reactions can be readily obtained without requiring detector calibration or geometry corrections.

The conductance of NaCl and KCl in 50‐mole percent methanol‐water mixtures has been measured at concentrations from 0.0005 to 0.01 N. The data can be represented within experimental error by the Onsager‐Shedlovsky equation, the limiting conductances being 66.62 and 75.10, respectively. The limiting conductances of chloride ion, obtained from these values, and the limiting transference numbers reported in the accompanying paper, satisfy the rule of independent ionic mobilities, but at finite concentrations the chloride ion conductance is less for the potassium salt than for the sodium. The decrease in limiting ion conductances as compared with those in water is greater than can be accounted for by viscosity alone. The results are also in disagreement with the Bjerrum theory of ion pair formation if the mean ionic diameter, determined thermodynamically, is significant in transport processes.

A pulsed, flowing afterglow has been utilized to measure rate constants at room temperature for the following reactions involving NO: N2++NO→NO++N2,k1≈5(+1,−3)×10−10cm3/sec,N++NO→NO++N,k2=8(+1,−4)×10−10cm3/sec,O2++NO→NO++O2,k3≈8(+2,−5)×10−10cm3/sec,O++NO→NO++O,k4≤2.4×10−11cm3/sec. In addition the following related reactions have been measured: N++O2↗NO++O↘N+O2+,k5≈1(+0.1,−0.6)×10−9cm3/sec,N2++O2→O2++N2,k6≈1(+0.2,−0.6)×10−10cm3/sec,O2++N→NO++O,k7≈1.8(+0.2,−0.9)×10−10cm3/sec. Some additional information concerning the end products of N++O2 is offered.

A small, central portion of an active nitrogen stream was continuously sampled into a mass spectrometer. The ratio of ion intensities at masses 14 to 28 was found to be higher than that for normal nitrogen at the same pressure. The ionization efficiency curves at mass 28, in the presence and in the absence of the discharge were superimposable, but those at mass 14 were quite different. The difference Δ14, between these two curves was plotted against the applied electron voltage. A discontinuity in this Δ14 curve showed that it resulted from two processes. The appearance potentials for these two processes were 14.72±0.26 ev and 16.1±0.3 ev. The lower value clearly indicated the presence of ground state atoms in active nitrogen. Several processes capable of producing the higher value are discussed. The concentration of active species is estimated to be between 0.1 and 1%.

A mass spectrometric method was used to show that 75±5% of the nitrogen formed by the reaction N+NO→N2*+O has more than the 24 kcal/mole of excess energy required to decompose ozone. The rate constant for the reaction N2*+O3→O2+O+N2 was found to be (5.4±1.1)×10—13 cm3 molecule—1 sec—1. The rate of collisional deactivation of N2* to vibrational levels below the fourth was found to be 3.5×10—16 cm3 molecule—1 sec—1 with unexcited N2 and 1.3×10—15 cm3 molecule—1 sec—1 with N2O as the collision partners. If loss of vibrational energy occurs mainly by single quantum jumps, the measured deactivation rate constant is less than that for a single quantum jump by the ratio of the number of molecules in the fourth level to those in all levels above the third.

A method has been developed for following the kinetics of fast atomic reactions with a mass spectrometer. The method has been used to determine separately the rate constants for the following reactions which are relevant to an atomic nitrogen‐ozone system. N+O3→NO+O2k1=(5.7±1.4)×10−13 cm3molec−1sec−1N+NO→N2+Ok2=(2.2±0.6)×10−11 cm3molec−1sec−1O3+NO→NO2+O2k3=(2.1±0.5)×10−14 cm3molec−1sec−1O3+O→2O2k4=(2.5±0.5)×10−14 cm3molec−1sec−1O+NO2→O2+NOk5=(2.5±0.6)×10−12 cm3molec−1sec−1 These reactions have been used to interpret the observed changes of concentration with time for reactants and products of the N–O3 reaction. The concentrations of N2O and NO2 in the system were below the detection limits of the mass spectrometer, which is consistent with predictions based on the above rate constants. Evidence was obtained for the production by reaction (2) of vibrationally excited N2 molecules having energies greater than 23.4 kcal/mole. Such energetic molecules are not present in significant quantities in discharged O2...

The recombination of oxygen atoms has been studied in an O2‐free system containing a known initial atom concentration. The value of the rate constant for the reaction O+O+N2→O2+N2 was found to be 2.8×10−33 cm6 molecule−2 sec−1. Failure to remove condensable products from the gas stream resulted in a 40% increase in the recombination rate. The efficiencies of other third bodies relative to N2 are: Ar, ≤0.3; He, 0.3; N2O, 1.4; CO2, 3.0; SF6, 3.0. The presence of vibrationally excited N2 did not affect the recombination rate. The wall recombination coefficient γ was found to be 1.65×10−5. Comparison of these results with high‐temperature shock‐tube results indicates that the temperature coefficient of the recombination is small.

The reaction of H atoms with excess NO2 results in the production of one NO molecule for every NO2 molecule consumed and the consumption of 1.5±0.1 NO2 molecules per H atom initially present. The secondary reactions are rapid and make the over‐all reaction very suitable for H‐atom titration. A mechanism is proposed to explain these results. The reaction of H atoms with excess O3 results in the consumption of 3.1±0.2 O3 molecules for each H atom initially present. Addition of H2 and N2O to the system showed that vibrationally excited OH formed in the initial reaction decomposes O3. Other mechanisms for the additional O3 consumption are discussed. The rate constant for the primary step was found to be (4.8±0.5) × 10—11 cm3 molecule—1 sec—1 for the NO2 reaction and (2.6±0.5) × 10—11 cm3 molecule—1 sec—1 for the O3 reaction.

A simple analysis is presented for the perturbation of a stream of partially dissociated gas by a catalytic probe capable of completely removing all the atoms from the stream. The results of this analysis were confirmed by experiments on discharged O2, which showed that for linear flow rates of several meters per second the atom concentration reaches 99% of the unperturbed value within 2.5 cm upstream from the probe. It is shown that such a probe can be used to measure atom concentrations, since the flux to the probe remains finite even though the atom concentration at its surface is virtually zero. No appreciable errors are introduced into relative concentration measurements required to obtain first order rate constants. Under suitable experimental conditions, absolute concentrations can be obtained which are negligibly different from the unperturbed values regardless of the order of the recombination processes. A method is described for using such a probe to obtain accurate values of atomic diffusion coefficients which does not require accurate knowledge of heterogeneous or homogeneous recombination rates.

The catalytic sink technique previously described was used to measure the diffusion coefficients of H atoms in H2 over the temperature range 202°–364°K and in H2–He and H2–Ar mixtures at 275°K. The rigid‐sphere collision diameters of H atoms in H2, He, and Ar were 1.89, 1.94, and 1.84, respectively. However, the temperature dependence of the H–H2 diffusion coefficients does not fit the rigid‐sphere equation but can be represented by the use of the Lennard‐Jones parameters e / k = 85°K and σ′H,H2 = 2.32 A. Comparisons are made with values derived from viscosity data and with theoretical calculations.

A flowing, steady‐state afterglow system has been utilized to measure room‐temperature ion—neutral reaction rates. A description of the apparatus and technique is given. Measured rate constants for He+ reactions with O2, N2, CO, NO, and CO2 are reported, as well as upper limits for the reactions of He+ with H2, Ne, and Ar, and an estimate for the reaction of He2+ with Ne and N2.The reactions of He+ with O2, N2, CO, NO, and CO2 are all rapid, the rate constants all being ≈10−9 cm3 sec−1, implying essentially a reaction per collision.

The reaction of N atoms with NO2 has been studied in a fast flow system, using a mass spectrometer to monitor the composition of the reaction mixture. The rate constant for removal of NO2 by N was found to be (1.85±0.22)×10−11 cm3 molecule−1·sec−1. By a combined mass‐spectrometric and photometric method the relative contributions of the different primary reactions have been determined as follows (errors shown are standard deviations): N+NO2→N2O+O (0.43±0.04),N+NO2→2NO (0.33±0.07),N+NO2→N2+O2 (0.10±0.12),N+NO2→N2+2O (0.13±0.11).

The ultraviolet photolysis of O3 in the presence and in the absence of O2 has been investigated in the wavelength region ∼ 2375–2625 A using flash photolysis and kinetic emission spectroscopy with a time resolution high enough to allow unambiguous identification of photodissociation products. The production of O(1D) was established by observing the forbidden 1D → 3P emission at 6300 A. The decay of the emission provided a value of the rate constant for the O(1D)–O3 reaction of (2.5 ± 1) × 10−10 cm3 molecule−1·sec−1 at 25°C. Analysis of the O(1D) decay showed that the rate of chain reactions in which O(1D) could be reproduced must be smaller than the O(1D)–O3 quenching rate by more than an order of magnitude. No emission was observed from O2(1Σg+) when O3 alone was photolyzed, indicating that the primary yield for O2(1Σg+) production is smaller than 1/20 of the O(1D) production. O(1D) was very efficiently quenched when N2 and O2 were added. O2(1Σg+) was observed by the 1Σg+ → 3Σg− emission when O3–O2 mixtures were photolyzed. The emission disappeared when N2 was added. The O2(1Σg+) production and decay rates were measured at various O3 and O2 concentrations. The results indicated that O2(1Σg+) was formed by energy transfer from O(1D) to ground state O2. The decay of the 1Σg+ emission provided a value of the rate constant for the O2(1Σg+)–O3 quenching of (2.5 ± 0.5) × 10−11 cm3 molecule−1·sec−1. The relative quenching rate of O(1D) by O3 and O2 was about 5, yieding an O(1D)–O2 rate constant of 5 × 10−11 cm3 molecule−1·sec−1 with an uncertainty of a factor of 2. The dependence of the 1Σg+ emission on the O2 pressure showed that the primary quantum yield of O2(1Σg+) is at least 20 times smaller than that of O(1D), in agreement with the previous result.

An electron impact study of NO was made using the retarding potential difference method for producing the effect of a monoenergetic electron beam. In this modification of the method the electron retarding potential is provided by the potential minimum which exists between the anode and cathode of a space‐charge limited diode.The ionization potential of NO was found to be 9.25±0.02 ev and the ionization efficiency curve for NO+ to be nonlinear near the onset. This curvature can be attributed to the difference in the equilibrium internuclear distances of NO and NO+. Appearance potentials were obtained for the formation of N+, O+, and O‐ ions from a number of processes. With the exception of O‐ ions formed by electron capture, it was not necessary to postulate that any of the ions are formed with excess kinetic energy. The appearance potentials of all the processes are consistent, within experimental error, with a value of 6.50 ev for the dissociation energy of NO. The shape of the resonance capture curve fo...

The laser emission of vibrationally excited OH in the electronic ground state, produced in pulsed electric discharges through O3–H2 gas mixtures, has been studied using two transverse discharge systems. Discharges were produced in two electrode and multipin transverse configurations. Stimulated emission between the ν = 3→ν = 2 and ν = 2→ν = 1 levels was observed in the 3 μ wavelength region. The output has been investigated as a function of composition and pressure of O3–H2 mixtures, addition of foreign gases, and discharge energy. Output intensities were compared to that of the HF laser emission produced from H2–SF6 in the same discharge system. The two discharge configurations gave similar intensities; this OH laser was shown to have approximately 10−2 times the power of the HF† laser.

Results are reported for an experimental study of the reactions of O(1D) with CCl4, CFCl3, CF2Cl2, CHFCl2, CHF2Cl, and CF2ClCFCl2 over the temperature range from 173 to 343 K, based on the time-resolved emission of O(1D) at 630 nm. The experiments involved photolysis of O3 by Nd-YAG laser pulses and measurements of 630-nm emission intensity in mixtures with He and the various halocarbons. Pseudo-first-order rate constants are derived from plots of the logarithms of the 630-nm emission intensities as a function of time for particular He/O3/halocarbon mixtures, and second-order rate constants are then obtained from plots of these pseudo-first-order rate constants as a function of halocarbon concentration at constant He and O3 concentrations. No temperature dependence of the second-order rate constants is observed over the range studied, within the precision of the measurements. It is found that the rate constants decrease as H is substituted for Cl in a halocarbon molecule and as F is substituted for H or Cl.

The conductance of sodium and potassium chlorides has been determined in anhydrous methanol for concentrations from 0.0002 N to 0.01 N. For trace amounts of water, the decrease in equivalent conductance for a given electrolyte concentration is proportional to the water content, the proportionality factor being a function of the ionic strength. The results up to 0.002 N satisfy the Onsager‐Shedlovsky equation. The limiting conductances, when combined with the transference data of the preceding paper, give the first precise limiting ionic conductances in an anhydrous solvent. The limiting values for chloride ion are the same for the two salts within experimental precision; but with increasing concentration, there are deviations from the Kohlrausch rule of independent ionic mobilities which are considerably greater than is the case in aqueous solution. The equivalent conductance data are in definite disagreement with Frazer and Hartley's results for the two salts in this solvent.

The ``vapor snake'' phenomenon, originally reported for cyclohexane, has been found to occur with some twenty compounds. The ease of occurrence increases with the triple point pressure of the compound. The tubule tip was always at the freezing point of the compound although the surrounding liquid may be above the freezing point. Although the presence of a crust on the surface of the liquid is not essential for the occurrence of the phenomenon, transport of heat by vapor to a cold portion of the sample must occur in order to produce a tubule sheath of the thickness observed.

The normal impulse accommodation coefficient is measured with a torsion balance. Data for Ar, N2, O2, H2, N2O, CO2, stainless steel, and glass are given. The absolute error of the relative method used is Δσ′=0.05. The measurements occur at room temperature.

The rate constants for the deactivation of O(1D) by Xe, Kr, and Ar were measured over the range 110-330 K. Only Xe had a significant temperature dependence. Its Arrhenius expression is (8.5 + or - 1.7) times 10 to the -11th power exp(-103 + or - 52)/RT cu cm/molecule-sec. The rate constants for Kr and Ar are (6.4 + or - 1.3) times 10 to the -12th power and (5.0 + or - 1.5) times 10 to the -13th power cu cm/molecule-sec, respectively. The observed trend in deactivation efficiency, Xe (greatest), Kr, Ar (least), and the observed temperature effects support the results and the spin-orbit interaction mechanism for deactivation given by Husain and co-workers.

Absolute rate constants for the deactivation of O(1D) by CO have been measured at temperatures between 113 and 333 K. A very small temperature dependence is observed and is described by the Arrhenius expression (4.7 + or - 0.9) times 10 to the -11th power exp(126 + or 33)/RT cu cm/molecule-sec, where E is in cal/mol.