F. Kaufman

Reactions of Metastable Nitrogen Atoms

The line absorption technique was applied to the kinetic study of the two metastable atomic nitrogen states N (22D) and N (22P) in a flowing afterglow system. The optical absorptions of the NI 1493‐A (2p32D−3s2P) and 1743‐A (2p32D−3s2P) transitions were used for the quantitative measurement of N (22D) and N (22P) concentrations. Deactivation of N (2D) and N (2P) by the Pyrex tube wall was found to be very efficient, i.e., occurs at nearly every collision. The second‐order rate constants at 300°K for the removal of N (2D) by O2, N2O, CO2, NO, N2, Ar, and He were found to be (6±2)×10−12, (3.5±1.2)×10−12, (5±2)×10−13, (7±2.5)×10−11, (1.6±0.7)×10−14, (1±0.6)×10−16, and ≤ 1.6×10−16 cm3 sec−1, respectively. It was established that the process for the first three reactant gases results in chemical reaction rather than physical quenching.

Kinetics of the isotope exchange reaction of 18O with NO and O2 at 298 K

The rates of 18O isotope exchange reactions were measured at 298 K using a discharge‐flow, modulated molecular beam mass spectrometer apparatus whose detection limit for NO and O was in the 109–1010 cm−3 range. The NO exchange is very fast, k1, x=(3.7±0.5)×10−11 cm3 s−1, and, assuming statistical breakdown of a long‐lived complex, the rate constant for the formation of the NO°2 complex, k1, c f is (7.4±1.0)×10−11 cm3 s−1. The slower O2 exchange was measured three different ways, yielding three rate constants whose average is k2, x=(2.9±0.5)×10−12 cm3 s−1. The results are compared with earlier isotope exchange experiments and discussed in the context of measured and calculated high pressure recombination and vibrational relaxation rate constants.

Gas phase recombination of hydrogen and deuterium atoms

Rate constants for the reaction H+H+M → H2 + M, with M = H2, He, and Ar were measured over the temperature range 77–298°K. Hydrogen atoms were produced by thermal dissociation and absolute atom concentrations were measured through use of a self‐balancing, isothermal catalytic probe detector. The specific rate constants were 8.1 ± 0.4 × 10−33, 7.0 ± 0.4 × 10−33, and 9.2 ± 0.6 × 10−33 cm6 molecules−2 · sec−1 at 298°K for M = H2, He, and Ar, respectively; these values rising to 18.5 ± 2.2 × 10−33, 12.0 ± 1.5 × 10−33, and 27.4 ± 4.6 × 10−33 cm6 molecules−2 · sec−1 at 77°K. For the equivalent deuterium atom process with D2 as the third body, the rate constants are 6.1 ± 0.3 × 10−33 cm6 molecules−2 · sec−1 at 298°K and 15.1 ± 1.0 × 10−33 cm6 molecules−2 · sec−1 at 77°K. These values are compared with previous experimental measurements and with recent theoretical calculations.

Kinetics and mechanism of NO2 fluorescence

NO2 fluorescence experiments with steady or modulated (8 and 20 kHz), monochromatic excitation at 4000–6000 A and monochromatic observation have shown the process to be interpretable in terms of a single electronically excited state undergoing vibrational relaxation at gas‐kinetic rate and electronic quenching about 100 times more slowly. An apparent radiative lifetime of about 55 μsec was found, independent of excitation frequency, but the possibility of mixing with vibrationally excited ground state makes this an upper limit to the lifetime of the hypothetical unperturbed 2B1 state. The average amount of vibrational energy transferred per collision was found to be 1000 · 500 cm−1 based on a simplified step‐ladder model for the relaxation.

Kinetics and Mechanism of the Formation of Water Cluster Ions from O2+ and H2O

The reaction sequence leading from O2+ to H3O+· H2O was examined in He, Ar, N2, and O2 carrier gases in a flowing afterglow system. The rate constants for the reactions were measured and the kinetic analysis for their determination is presented. For M=N2, two new steps involving the formation and reaction of O2+· N2 were proposed and examined. The rate constants are discussed and compared with other experimental values.

Thermal Decomposition of Nitric Oxide

The decomposition of pure nitric oxide and of mixtures with nitrogen or helium was studied at T = 1170 to 1530°K in quartz vessels. Above about T = 1400°K, the reaction is homogeneous and cleanly second order in NO throughout the course of decomposition. A change in the surface to volume ratio leaves the rate unchanged as does the addition of a fourfold excess of nitrogen or helium. Above 1400°K, the activation energy is constant at 63.8±0.6 kcal. The effect of added oxygen was investigated and a mechanism is discussed which reconciles much of the available data.

Fluorescence lifetime studies of NO2. I. Excitation of the perturbed 2B2 state near 600 nm

A pulsed, tunable dye laser (0.05 or 0.005 nm FWHM) was used to measure NO2 fluorescence lifetimes in the 578–612 nm absorption region at pressures of 0.01 to 25 mtorr. When relatively strong absorption features at 585, 593, and 612 nm are excited, the decay of total fluorescence is highly nonexponential, even at pressures as low as 0.01 mtorr, with radiative lifetimes ranging about 20 to 260 μsec, as determined from biexponential fits. In more weakly absorbing regions at 578, 594, and 603 nm, the decays are nearly exponential, with lifetimes of about 200 μsec. Experiments with 0.005 nm bandwidth in the 593 nm region show that there is a one to one correspondence between strong features in the high resolution fluorescence excitation spectrum and the most highly nonexponential decays. These results are explained in terms of a single excited electronic state (2B2) variably vibronically coupled to upper vibrational levels of the ground state. States with a larger fraction of 2B2 parentage have shorter lifeti...

Gas phase recombination of OH with NO and NO2

The termolecular recombination of OH with NO and with NO2 is studied for M=He, Ar, and N2 at pressures from 1–10 torr and temperatures from 230–450°K in a flow tube using resonance fluorescence detection of OH radicals. The reactions are in their low pressure, third-order limit. The rate constants for the NO reaction at 295°K are 3.3, 3.4, and 5.8×10−31 cm6 sec−1 in the above order of M gases. For the NO2 reaction the corresponding values are 1.0, 1.0, and 2.3×10−30, all with σ=±20% including estimates of systematic errors. Both recombinations show the expected negative temperature dependence, the Arrhenius activation energies being −1.7 kcal for NO and −1.8 kcal for NO2. These results are compared with all other published data and with RRKM unimolecular calculations.

Fluorescence lifetime studies of NO2. III. Mechanism of fluorescence quenching

NO2 fluorescence, excited by fixed visible frequencies of a Nd‐YAG laser, was measured as a function of time, pressure, and fluorescence wavelength. The low resolution fluorescence spectrum at all excitation wavelengths consists of strong banded features, assignable to ground state vibrational progressions, superimposed on an apparent continuum. The ratio of banded‐to‐continuum intensity decreases with increasing pressure, indicating that the continuum is partially of collisional origin at high pressures. There is also a red shift of fluorescence at high pressures, indicative of vibrational relaxation within the emitting state. A residual continuum is found under collision‐free conditions (0.1–0.01 mtorr) and ascribed to violation of the ΔK=0 selection rules in the initially excited levels of the highly perturbed 2B2 state. The time dependent decay of fluorescence excited at the banded features contains a fast component kB and a weaker, long‐lived component kC, identified with the underlying continuum. Ra...

Experimental Oscillator Strength of OH, 2Σ+→2Π, by a Chemical Method

The line absorption method is used to determine the oscillator strength of OH, 2Σ—2Π, in a discharge‐flow system. OH is made quantitatively by the rapid reaction H+NO2→OH+NO. f values for the unresolved Q1—4 doublet and P1—2 line are calculated from the measured absorption of these lines. On the well‐supported assumption of Doppler‐shaped emission and absorption lines and on the basis of experimental information on the translational temperature of emitting and absorbing OH molecules, a band oscillator strength, f00, of 7.1±1.1×10—4 is reported for the (0, 0) band. Application of corrections for thermochemistry and for vibration—rotation interaction to reported f values leads to improved agreement and suggests an f00 near 8×10—4.