Laser Measurements of the H Atom + Ozone Rate Constant at

May 18, 2016 - The exothermic H + O3 reaction produces OH(v) Meinel band emissions, used to derive mesospheric H concentrations and chemical heating r...
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Laser Measurements of the H Atom + Ozone Rate Constant at Mesospheric Temperatures Yingdi Liu, Jian Peng,† Kelsey Reppert,‡ Sara Callahan,§ and Gregory P. Smith* SRI International, 333 Ravenswood Avenue, Menlo Park, California 94025, United States S Supporting Information *

ABSTRACT: The exothermic H + O3 reaction produces OH(v) Meinel band emissions, used to derive mesospheric H concentrations and chemical heating rates. We remeasured its rate constant to reduce its uncertainty and extended the measurements to lower mesospheric temperatures using modern laser-induced fluorescence (LIF) techniques. H atoms were produced by pulsed ultraviolet laser trace photolysis of O3, followed by reaction of O(1D) with added H2. A second, delayed, frequency-mixed dye laser measured the reaction decay rate with the remaining ozone using LIF. We monitored either the H atom decay by two photon excitation at 205 nm and detection of red fluorescence, or the OH (v = 9) product time evolution with excitation of the B2Σ+−X2Π (0,9) band at 237 nm and emission in the blue B2Σ+−A2Σ+ (0,7) band. By cooling the enclosed low pressure flow cell we obtained measurements from 140 to 305 K at 20 to 200 Torr in Ar. Small kinetic modeling corrections were made for secondary regeneration of H atoms. The results are consistent with the current NASA JPL recommendation for this rate constant and establish its extrapolation down to the lower temperatures of the mesosphere.

1. INTRODUCTION The reaction H + O3 → OH(v = 5−9) + O2 (R1) is an important process in the upper atmosphere. Near 90 km altitude, where H atoms peak and a secondary ozone maximum occurs, this step is mainly responsible for kinetic loss of both species.1 The reaction produces the infrared emissions of the Meinel bands from the vibrationally excited OH, a valuable observable for diagnosing this remote region of the upper atmosphere. The SABER instrument aboard the TIMED satellite has provided a large data set of mesospheric Meinel emission observations.1 Coupled with ozone concentrations determined from its infrared emissions and the rate constant for reaction R1, this data has led to derived (previously scarce) H atom concentration compilations.1 Reaction R1 is 77 kcal/mol exothermic,2 and provides the main chemical heat release path in the mesosphere. Thus, the Meinel data also has provided a means to compute local and average heating rates, but this does critically depend on an accurate rate constant for reaction R1 according to the algorithm used.3,4 There are several previous studies for the titled rate constant. Five room temperature values agree within 10%.5−9 Only 2 studies were performed below room temperature, on millisecond time scales. Lee et al.8 performed a VUV flash photolysis resonance lamp fluorescence study extending to 219 K, which agrees with Keyser’s9 discharge flow resonance fluorescence measurement down to 196 K. A similar experiment by Clyne and Monkhouse10 to higher temperatures, however, gives lower rates. This consensus (with just one exception) leads to a small estimated uncertainty in recent NASA JPL evaluations.2 © XXXX American Chemical Society

In light of this rate constant’s importance to data reduction and with only 2 previous low temperature studies, we have employed modern laser techniques and diagnostics methods to remeasure its reaction rate and temperature dependence, with much faster time resolution. This study also extends measurements down to the lowest mesospheric temperatures.

2. EXPERIMENTAL METHOD We have employed two time-resolved laser photolysis−laserinduced fluorescence (LP−LIF) methods to measure the rate constant of reaction R1. Both H reactant and OH(v = 9) product were measured, in separate experiments. In this study, the main kinetic reaction scheme employed is shown as follows: O3 + hυ(248nm, 266nm) → O(1D) + O2 (a) 90%

initiation O(3P) + O2 10%

quenching O(1D) + Ar → O + Ar

(R2)

formation O(1D) + H 2 → H + OH

(R3)

Received: March 22, 2016 Revised: May 13, 2016

A

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After a variable delay, a second LIF laser was used to excite the H or OH(v = 9) to generate the fluorescence signal. The LIF laser beam was concentrated by a 50 cm focal length lens to a central detection zone of 0.5 mm diameter or less, which is necessary for two photon H atom excitation in H measurement experiments. The H method involves absorption of two photons at 205.1 nm to excite H to the 3s state, which then fluoresces at 656 nm (3s−2p).13,14 The LIF radiation was generated by frequency tripling the 615 nm output of a dye laser with doubling and mixing crystals. The third harmonic (355 nm) output beam of a pulsed Nd:YAG laser (Quanta-Ray GCR-4, 10 Hz) pumped a dye laser (Lambda LPD-3000) to deliver radiation around 615 nm with dye solution mixture (sulforhodamine 640/rhodamine R = 1/4 by weight). A KDP crystal is used to frequency double the dye laser output to generate a 307.5 nm beam. Then the polarization of the 307.5 nm beam was rotated to coincide with the polarization of the 615 nm beam. Both laser beams were input to a BBO crystal to generate a 205 nm UV laser beam through a sum-frequency process. Both crystals were electronically angle tuned by Inrad autotrackers to provide constant output energy. In OH(v = 9) method,12 the Q11 line of OH B2Σ+−X2Π (0,9) band was excited at 237 nm by the same frequency-doubled YAGpumped dye laser using dye Coumarin 102. Fluorescence was then focused (5 cm f.l.) and detected from H at 656 nm (3s-2p) and OH B2Σ+−A2Σ+ (0,7) at 510 nm by an amplified R928 or 1P28 photomultiplier through interference filters (fwhm ∼10 nm). A Labview programmed computer controlled the delay and triggering of the lasers and signal collection and averaging from the short-gate boxcar integrator that collected the LIF signal. Each experimental run took about 3 min for data acquisition and averaging. Gas flows of argon and hydrogen were regulated and measured by calibrated mass flow controllers, with typical partial pressures of 60 and 1 Torr, respectively. (This generated comparable initial amounts of H, O, and OH.) The reaction cell pressure was directly measured by calibrated capacitance manometer. Ozone is generated by static electric discharge of oxygen gas from an ozone generator (Welsbach T408, ∼5% O3 in O2). The O3−O2 mixture from the ozone generator is passed through a silica gel trap at dry ice temperature, and O3 is adsorbed on the silica gel. Ozone was transported to the reaction cell by part of the argon flow through the cooled precollected ozone silica-gel trap; Ar is allowed to flow for at least 1 h to purge out the residual O2 in the trap and enrich O3 before the experiment. The ozone partial pressure was measured by the absorption of the gas mixture at 253.7 nm using a Hg Pen-Ray lamp, in a 92 or 43 cm tube located before the reaction cell and at the cell pressure (O3 cross-section is 1.15 × 10−17 cm2 at 298 K2). Experimental ozone partial pressures were varied, and range from 15 to 140 mTorr. The crossed-tube reaction cell is suspended in a second differentially pumped stainless steel apparatus, also with windows and gas connections. The gas flow speed through the photolysis zone in a typical experiment is about 2.5 cm/s, replacing the sample between laser shots. A coldfinger Dewar at the top is connected to the gas tube upstream and provides the means to cool the reaction cell using a dry ice/isopropanol bath or liquid nitrogen. A thermocouple suspended in the gas flow above the photolysis zone measured the experimental temperatures during the operation. Rate constants for reaction R1 were measured over the temperature range 140−305 K in Ar bath gas. The lowest

reaction H + O3 → OH(v = 5−9) + O2

(R1)

relaxation OH(v = 9) + M → OH(v < 9) + M

(R4)

secondary kinetics OH(v) + O → H + O2

(R5)

Following laser photolysis of a small fraction of the ozone, excited O(1D) atoms rapidly produce H or are quenched by the argon bath gas, as shown in reactions R3 and R2. Reaction R1 then proceeds and is monitored by either H reactant or OH(v = 9) product using LIF temporal profiles. Reactions of OH and O in the system can regenerate H atoms (5), particularly at longer time (usually longer than 100 μs, dependent on conditions) and higher initial dissociation/concentration. Small corrections based on detailed kinetic modeling are needed. With well controlled experiments and proper corrections, the effects of secondary chemistry can be minimized, at the expense of signal intensity. Dissociation fractions under 5% were used in order to minimize the correction. A detail description of the photodissociation and secondary chemical kinetics correction is presented later. 2.1. Apparatus. The apparatus and procedures, used and described in previous work,11,12 are discussed briefly here. A schematic illustration is shown in Figure 1. The experiments are

Figure 1. Schematic diagram of the experimental apparatus.

conducted in a reaction cell with crossed 1 cm diameter aluminum tubes of 20 cm length. Pumped gas flows through one tube, and counter-propagating coaxial photolysis and detection laser beams gain optical access via Brewster angle windows through the other perpendicular tube. The generated fluorescence is then detected by a filtered photomultiplier tube (PMT) along the third axis. To study the rate constant of reaction R1, the attenuated 248 nm beam of a KrF excimer laser (Lambda Physik LPX-100) was used for ozone photolysis, similar to our previous work.11,12 Subsequent reaction of the O(1D) product with added H2 produced the H reactant. An alternate photolysis laser (QuantaRay GCR-11) at 266 nm was used for most of the H atom measurement experiments. The photolysis laser beams were apertured and slightly focused to provide a ∼2 mm diameter reaction zone. B

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The Journal of Physical Chemistry A temperature was achieved using liquid N2, where the value actually reached is limited by the heat transfer of the apparatus. Measurements at low temperatures were more difficult due to a lower rate constant for reaction R1 vs R5, and thus larger model corrections. Becasue of its large quenching of the O(1D),12 N2 is not used as bath gas and we only used Ar as bath gas in this study. 2.2. Experimental Photodissociation Estimation. To minimize the effects of secondary H kinetics from reaction R5 on the measurement and to provide an accurate modeling correction for this H regeneration, one must determine accurately the fraction of ozone dissociation in each experiment. For the excimer photolysis experiments, we employed our previous method11 of measuring OH(v = 4) prompt yields by LIF following O3 photolysis and the O(1D) + H2 → H + OH(v = 0−4) reaction as a function of laser power. This gives a good saturation curve that then can be applied to compute dissociation at low measured excimer powers. The fit to LIF = A(1 − e−BP), where LIF is the signal and P is the laser power, becomes measurably nonlinear by 30−40% dissociation, and thus a sensitive dissociative calibration. The excimer laser photodissociation fractions were also directly calculated from the cross-section, measured power, and beam area, and agree within 40% with the values from the power-dependent saturation curve. For the H experiments using the lower power 266 nm YAG photolysis laser, dissociation fractions were calculated from the measured laser power and beam area using the known ozone absorption cross section.2 This is less accurate than the excimer procedure, and the beam is less uniform. We thus estimate potential uncertainty from the modeling correction to be up to 50% of its amount, which is the dominant nonstatistical uncertainty in this study. The agreement between calculated dissociation and the saturation curve for the excimer, and the general agreement of results, endorse the validity of these dissociation estimates. 2.3. Modeling Correction for Secondary Regeneration of H Atom. The regeneration of H during the measurement period (reaction R5) slows the decay from that caused by reaction R1, and must be corrected for. Since the magnitude depends on OH and O concentrations, the correction increases with ozone dissociation fraction, and it also increases with ozone concentration but to a lesser extent. The problem is greater at low temperature because reaction R1 is getting slower but reaction R5 is not at lower temperature. The experiments were modeled using a detailed 90 step kinetic mechanism including specific OH vibrational levels and their reactions and relaxation, given in the Supporting Information. We used the Chemkin modeling code Senkin15 to simulate the kinetics at each experimental condition for each decay. Exact details of the model-based correction factors are given in the Results and Discussion.

Figure 2. H atom decay temporal profile from the H + O3 reaction in a typical H LIF experiment at 297 K and 70 Torr with a photodissociation of 4% and O3 concentration of 7.9 × 1014 molecules cm−3 and H2 partial pressure of 1 Torr. The open squares are experimental data and the red line is the fit using eq 1.

was fitted to an exponential function to obtain a pseudo-firstorder rate constant, k′, from the following equation, as shown in Figure 2: H signal = A exp(−k′t ) + constant

(1)

The measured H decay rate k′ is from exponential part of the fit of experiment results. The constant of eq 1 reflects the secondary chemistry. Typically, the first-order H decays were measured at 8−20 different O3 concentrations for each temperature at constant pressure and photolysis power. Because of the photodissociation-caused secondary chemistry, it is necessary to correct k′ to only represent the decay caused by the H + O3 reaction. The ratio of the final k′corrected to the measured k′ is obtained through the modeling study as described below. In this study, the k′ values were corrected by running the kinetic model with the NASA-JPL rate constants under the same experimental conditions. The model simulated H atom concentration is then plotted and fit from its highest point to the experimental ending time (400 μs) using input model parameters taken from individual experimental conditions. The fitted decay rate is recorded as kmodel ′ , and represents the effects of all the reactions including the secondary chemistry. The computed rate kNASA [O3] represents the decay caused by H + O3 reaction. Therefore, equating experiment and model equivalents ′ ′ ) kcorrected /k′ = (kNASA[O3]/k model

and our corrected rate constant is ′ ′ ) kcorrected = k′ × (kNASA[O3]/k model

(2)

where kNASA is the H + O3 reaction rate constant calculated from the NASA-JPL evaluation2 at experimental conditions, which is used for the modeling input. The ratio of decay rates shows how much the loss rate is retarded by the secondary chemistry regeneration of H over this time range. The bimolecular rate constant k is then obtained, using two alternate statistical methods. The first method is to plot the pseudo-first order decay rate k′corrected as a function of the corresponding initial postphotolysis O3 concentration. Figure 3 shows a typical example of kcorrected ′ values at 228 K in Ar at 80 Torr. The bimolecular reaction rate constant k was determined

3. RESULTS AND DISCUSSION 3.1. H Measurements. A typical H decay profile is shown in Figure 2 with prephotolysis laser scatter background subtraction. The initial decay of H concentration reflects the reaction rate of reaction R1, with some longer time signal representing a near steady-state (slowly decaying) balance between reaction R1 and R5, which gives a nearly constant tail as shown in Figure 2. A correction for this secondary chemistry is carried out using a kinetic model. To determine the bimolecular rate constants of H + O3, each H temporal profile C

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The Journal of Physical Chemistry A Table 1. Summary of Rate Constant Resultsa H measurements

Figure 3. A typical plot for the corrected H decay rate kcorrected ′ as a function of [O3] at a total pressure of 80 Torr in Ar at 228 K with a H2 partial pressure of 0.85 Torr and photodissociation of 5%.

from the slope of the linear least-squares fits through the ([O3], k′corrected) data points. Under current experimental conditions, the removal of H radicals by reaction with other species and diffusion outside the viewing zone is too slow to show as a significant y-intercept. So the small y-intercept is attributed mainly to statistical uncertainty. This zero intercept assumption is born out by most method 1 fits. Thus, k can also be calculated using a second method, direct calculation from k = k′corrected/[O3]. In this method, a value for k is obtained from each k′corrected and initial postphotolysis [O3] value, and then presented as the statistical average for each set. The resulting H + O3 rate constants from both methods are given in Table 1 with statistical uncertainties and experimental conditions, for 17 separate data sets. It also shows the ozone dissociation fraction for each run as determined from the photolysis power or the OH(v = 4) saturation curve calibration, and the size of the modeling correction. The individual set statistical uncertainties range from (2−10)% using the first method to (5−20)% using the second method, 1σ, precision only. Additional contributions to the total error include the uncertainty in the measurement of the O3 concentration (1%), calibration of the pressure gauge (1%) and calibration of the flow controllers (1%). The dominant additional uncertainties are due to the photolysis model correction, as previously described. Corrections average ∼5−10%, uncertain by about half. In the lower portion of Table 1, we have averaged together runs of the same temperature. The estimated total uncertainties for these averages, from random and systematic errors, are ∼20%, 1σ. Values are only 1−10% different from the NASAJPL results. 3.2. OH(v = 9) Experiments. The behavior for OH(v = 9) product signal (Figure 4) is more complicated and at early times is governed by formation step reaction R1 and removal step reaction R4. The differential equation solution16 is

140 159 159 159 159 159 173 219 228 228 228 228 235 297 297 298 303

4 9 15 11 13 11 10 8 16 14 15 15 5 12 10 9 6

T (K)

no. of O3 pts

146 146 146 146 246 246 303 304 304 305 305

11 9 13 9 10 8 11 11 5 8 7

T (K)

no. of O3 pts

159 228 298

O3 dissociation (%)

correction range (%)

k (av)

σk

k (slope)

4 25−46 0.43 0.03 0.55 3 8−10 0.56 0.05 0.56 3 8−10 0.70 0.09 0.66 2 9−13 0.78 0.12 0.62 2 9−13 0.76 0.10 0.73 2 10−13 0.67 0.09 0.73 3 7−9 0.81 0.16 0.89 4 5−17 1.35 0.20 1.66 5 3−20 2.07 0.24 1.34 5 3−20 1.82 0.40 1.68 2 1.1−4.4 2.06 0.40 1.40 3 1.1−4.3 1.92 0.32 1.46 4 14 2.14 0.11 1.88 4 0−7 3.06 0.50 2.88 4 4−9 2.98 0.18 2.82 1 0−23 2.42 0.33 2.79 2 3−17 2.77 0.33 2.29 OH(v = 9) measurements using average results O3 dissociation (%)

correction range (%)

1.9 1 0.3 0.6 1.5 0.5 1.3 2 0.9 5.6 5.6 H averaged all runs of the same O3 dissociation (%)

45 20 10 25 14 6 14 12 7 33 25 temperature

correction range (%)

k (av)

σk

0.78 0.68 0.67 0.78 1.64 1.75 2.94 3.14 2.89 4.06 4.79

0.10 0.16 0.14 0.13 0.27 0.11 0.29 0.26 0.19 0.42 0.31

k (av)

σk

73 0.70 73 1.97 37 2.86 OH(v = 9) averaged all runs of the same temperature

T (K)

no. of O3 pts

146 246 304 304

36 18 41 27

O3 dissociation (%)

all ≤2

correction range (%)

σk 0.06 0.04 0.06 0.03 0.08 0.05 0.10 0.04 0.05 0.06 0.07 0.04 0.11 0.18 0.06 0.13 0.33

0.14 0.38 0.47

k (av)

σk

0.75 1.69 3.40 3.10

0.10 0.22 0.66 0.35

a

Error limits are one standard deviation (statistical only). Units for both k and σk are 10−11 cm3 molecule−1 s−1.

this case, from prior studies, the faster step reaction R4 is responsible for the signal rise, and the slower step reaction R1 is responsible for the signal decay. Therefore, process reaction R4 is rapid as measured rates12 for O and O3 indicate, and the OH(v = 9) signal decay will measure the desired rate of reaction R1. Because OH(v = 9) is the highest level formed in reaction R1, it cannot also be produced by later secondary quenching reactions from other vibrational levels. Eleven sets of experiments were conducted with the OH(v = 9) diagnostic at 3 temperatures by varying ozone concen-

[OH(v = 9)] = [H]0 k1/(k1 − k4) × (exp( −k1t ) − exp( −k4t ))

T (K)

no. of O3 pts

(3)

where k1 and k4 are rate constants for reactions R1 and R4, and [H]0 is the initial concentration of H. Note the two steps are not a priori distinguishable; the two parenthetical terms of (eq 3) are either both positive or both negative; the faster step is responsible for the signal rise and the slower for the decay. In D

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Figure 5. Rate constants on an Arrhenius plot for the H + O3 reaction from this work compared with previous literature results on a log scale. Current literature data are in open symbols and this work’s data are in solid symbols. The blue solid line is the current NASA-JPL recommendation, while the dashed line is its extrapolation to lower temperatures. Error limits are one standard deviation. The error for the present work includes both statistics and modeling correction. The embedded figure enlarges the section around room temperature (gray region), with a linear y-axis.

Figure 4. OH(v = 9) signal vs laser delay time. Experiment conducted at 145 K in 58 Torr Ar, with 0.6 Torr H2, and 1.8% dissociation of 57 mTorr (3.8 × 1015 molecules cm−3) O3. Data analysis fit is shown by the dashed line. Main controlling reactions at various times are noted on the figure.

trations, while keeping constant the total pressure, hydrogen concentration, and photolysis laser power. A sample decay trace is shown in Figure 4 for the analyzed conditions subject to the largest interference correction. The signal rises to a near-steady state peak as H slowly reacts with ozone and OH(v = 9) is removed by relaxation. The rise reflects this quenching time scale. As H is removed by reaction, the OH(v = 9) decays. Finally at a longer time (>150 μs) we see the steady-state regenerated H atoms from secondary chemistry, as shown in Figure 4. Since the middle time behavior is most sensitive to reaction R1, we analyzed the data by fitting this decay from the 90% to 20% intensity points, after subtracting the small prephotolysis scattering baseline, using OH signal = A exp( −k′t )

3.3. OH(v = 9) Rise Time Removal Rates. A separate fit of the rise time, using the dual exponential function (eq 3), can provide rates for OH(v = 9) relaxation and removal if sufficient time resolution is employed in the data acquisition. Under our conditions of low dissociation and high H2, O3 and H are the chief removal gases. A graph of the rise time versus ozone concentration has a slope giving the OH(v = 9) + O3 rate constant. At room temperature our result exactly matches the 1.4 × 10−10 cm3 molecule−1 s−1 rate constant measured previously by steady-state kinetics.12 Some rise time measurements were performed at ∼75% dissociation to measure removal rates by H. After small corrections for removal by O and O3, a very rapid rate constant of 1.8 × 10−9 cm3 molecule−1 s−1 was determined for removal of OH(v = 9) by H, which confirms the value of 2 × 10−9 used in ref 12. Note this may be lower if OH is a significant quencher of OH(v = 9) since it is present in similar amounts. Approximate results suggest rates may be twice as fast at 146 K. 3.4. Arrhenius Expression. Using all rate constants from both OH and H experiments data sets (Table 1, first and second sections), an Arrhenius expression for this bimolecular reaction was obtained. The derived values from our experiments for the A-factor and Ea/R are (1.32 ± 0.12) × 10−10 cm3 molecule−1 s−1 and (460 ± 19) K, respectively, with a statistical uncertainty of one standard deviation. The calculated Ea/R produced a positive temperature dependence for the reaction, and the results are consistent with the results of the NASA-JPL recommendation2 as shown in Table 2. Figure 5 gives a summary of current literature data compared with our average results from individual decays grouped by temperature. The blue solid line is the current NASA-JPL recommendation, while

(4)

The OH decay rate k′ is from the exponential part of fitting the experiment results. Besides using the first-order exponential fit, a dual exponential fit using eq 3 with the entire trace to the 20% point was also used and gave the same decay rate. To perform the model correction for the OH(v = 9) measuement experiments, the model simulated OH(v = 9) decay rate was fit the same way as the experimental results, over the same 90%−20% range using eq 4 to provide a kmodel ′ . Similar to the H data model correction, kcorrected ′ is then also calculated using eq 2. The OH experimental results are given in Table 1, where we have averaged the different ozone concentration results in each data set. Slopes of corrected decay rate plots vs ozone concentration give similar values (as was the case for H), that is, negligible intercepts. Table 1 also shows the ozone dissociation fraction and modeling correction for OH measurements. Standard deviations for the averages are shown in the final column. The final entries show overall averages for the 3 temperatures. For the lower temperature runs and low dissociation runs at room temperature, statistical uncertainty is ∼13%. If we include half the model correction as the main additional error term, ∼7%, we estimate about 20% (1σ) uncertainty, which is included in Figure 5. The OH(v = 9) values at 304 and 246 K are only 4% above and 18% below, and consistent with, the NASA evaluation. The new 146 K measurement is 34% above an extrapolation of that expression.

Table 2. H + O3 Reaction Rate Constant Compared with NASA-JPL Evaluation2

NASA-JPL this work E

A (cm3 molecule−1 s−1)

E/R (K)

(1.40 ± 0.14) × 10−10 (1.32 ± 0.12) × 10−10

470 ± 40 460 ± 19

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(4) Smith, A. K.; Lopez-Puertas, M.; Xu, J.; Mlynczak, M. G. The Heating Efficiency of the Exothermic Reaction H + O3 in the Mesosphere. J. Geophys. Res. Atmos. 2015, 120, D024061. (5) Seeley, J. W.; Jayne, J. T.; Molina, M. J. High Pressure Fast Flow Technique for Gas Phase Kinetics Studies. Int. J. Chem. Kinet. 1993, 25, 571−594. (6) Phillips, L. F.; Schiff, H. I. Mass Spectrometric Studies of Atomic Reactions III. Reactions of Hydrogen Atoms with Nitrogen Dioxide and With Ozone. J. Chem. Phys. 1962, 37, 1233−1238. (7) Force, A. P.; Wiesenfeld, J. R. Laser Photolysis Of O3/H2 Mixtures: The Yield of The H + O3 →HO2 + O Reaction. J. Chem. Phys. 1981, 74, 1718−1723. (8) Lee, J. H.; Michael, J. V.; Payne, W. A.; Stief, L. J. Absolute Rate of the Reaction of Hydrogen Atoms with Ozone from 219−360 K. J. Chem. Phys. 1978, 69, 350−354. (9) Keyser, L. F. Absolute Rate Constant and Temperature Dependence of the Reaction between Hydrogen Atoms and Ozone. J. Phys. Chem. 1979, 83, 645−648. (10) Clyne, M. A. A.; Monkhouse, P. B. Atomic Resonance Fluorescence for Rate Constants of Rapid Bimolecular Reactions 5. Hydrogen Atom Reactions; H + NO2 and H + O3. J. Chem. Soc., Faraday Trans. 2 1977, 73, 298−309. (11) Robertson, R.; Smith, G. P. Temperature Dependence of O + OH at 136−377 K Using Ozone Photolysis. J. Phys. Chem. A 2006, 110, 6673−6679. (12) Kalogerakis, K. S.; Smith, G. P.; Copeland, R. A. Collisional Removal of OH(X2Π, ν = 9) by O, O2, O3, N2, and CO2. J. Geophys. Res. 2011, 116, D20307. (13) Bokor, J.; Freeman, R. R.; White, J. C.; Storz, R. H. Two Photon Excitation of the N = 3 Level in H and D Atoms. Phys. Rev. A: At., Mol., Opt. Phys. 1981, 24, 612−614. (14) Lucht, R. P.; Salmon, J. T.; King, G. B.; Sweeney, D. W.; Laurendeau, N. M. Two Photon Excited Fluorescence Measurement of Hydrogen Atoms in Flames. Opt. Lett. 1983, 8, 365−367. (15) Lutz, A. E.; Kee, R. J.; Miller, J. A. SENKIN: A Fortran Program for Predicting Homogeneous Gas Phase Chemical Kinetics with Sensitivity Analysis, Sandia Report: SAND87-8248, 1987. (16) Laidler, K. J. Chemical Kinetics; McGraw-Hill: New York, 1965, p. 323.

the dashed line is its extrapolation to lower temperatures. Since most literature results are at higher temperatures, our results clearly fill the missing low temperature range, which is very important for understanding the upper atmosphere.

4. CONCLUSION This study measured rate constants for the bimolecular reaction H + O3 over 140−305 K in 20−200 Torr Ar. Two methods, monitoring both H atom and OH(v = 9) radical in separate experiments, were combined to provide reliable results. The resulting rate constant results are consistent with the NASAJPL evaluation, its extrapolation, and most other literature data, while our studies provide new reliable results in the low temperature range. Laboratory decays were corrected for the effects of secondary reactions using kinetic model simulations (∼10%). To minimize corrections, the photolytic O 3 dissociation needs to be less than 5%. Our results further reduce the uncertainty in this rate constant from previously studies, and fill the need for low temperature measurements under conditions representative of earth’s mesosphere.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpca.6b02986. Reactions and rate constants used in kinetics simulations and model correction (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: 650-859-3494. Present Addresses †

J.P.: Coherent Inc., Mountain View, CA. K.R.: North Carolina State University, Raleigh, NC. § S.C.: Smith College, Northampton, MA. ‡

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the Aeronomy Program of the National Science Foundation under Grant AGS-1256568. Summer research by KR and CS was supported by a Research Experiences for Undergraduates Program sponsored by the NSF, Grant PHY-1359410. Opinions, findings, and conclusions are those of the authors and do not necessarily reflect the views of the NSF.

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REFERENCES

(1) Mlynczak, M. G.; Hunt, L. A.; Marshall, B. T.; Mertens, C. J.; Marsh, D. R.; Smith, A. K.; Russell, J. M.; Siskind, D. E.; Gordley, L. L. Atomic Hydrogen In The Mesopause Region Derived From SABER: Algorithm Theoretical Basis, Measurement Uncertainty, and Results. J. Geophys. Res. Atmos. 2014, 119, 3516−3526. (2) Sander, S. P.; Friedl, R. R.; Barker, J. R.; Golden, D. M.; Kurylo, M. J.; Wine, P. H.; Abbatt, J. P. D.; Burkholder, J. B.; Kolb, C. E.; Moortgat, G. K. et al. Chemical Kinetics and Photochemical Data for Use in Stratospheric Modeling, Evaluation Number 17, JPL Publication 10-6; Jet Propulsion Laboratory: Pasadena, CA, 2011. (3) Mlynczak, M. G.; Zhou, D. K.; Adler-Golden, S. M. Kinetic and Spectroscopic Requirements For The Inference of Chemical Heating Rates and Atomic Hydrogen Densities From OH Meinel Band Measurements. Geophys. Res. Lett. 1998, 25, 647−650. F

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