Lyman‐α absorption photometry at high pressure and atom density kinetic results for H recombination

Rate coefficients of the title reaction have been measured in a high-temperature photochemistry (HTP) reactor using Ar as the bath gas. H atoms were generated by flash photolysis of NH 3 and their relative concentrations were monitored by resonance fluorescence. The data are best fitted by k(295-905 K) = 6.5 × 10 −34 (T/K) 0.206 exp(780 K/T) cm 6 molecule −2 s −1 , with ±2σ precision values varying from 16 to 36% and corresponding suggested accuracy levels of 29-42%. Using a literature value for the relative collision efficiencies of N 2 and Ar indicates that for N 2 as the third body the above rate coefficient expression should be multiplied by 1.6. This leads to good agreement with two recent near 1000 K measurements.

Section: Resultssupporting

confidence: 85%

The H+NO recombination reaction over a wide temperature range

Riley

Cosic

Fontijn

2003

“…Data were generally obtained from transmittances of 0.98-0.35 which corresponds to a concentration range of 1-50 X 1O1O atoms/cm3. However, since second-order volume termination is not totally negligible under the higher concentration in comparison to the first-order decay [7], the range of transmittances reported here were limited to the long time tail (5-7 sec). Generally ten points were taken from 0.80 to 0.98 transmittance.…”

Section: Methodsmentioning

confidence: 70%

“…Separate calibration experiments [7] have shown that operation of this lamp with tank He (C.D. grade from Airco) produces (3 f 1) X lo1' atoms/cm3 in the plasma.…”

Section: Methodsmentioning

confidence: 99%

“…Plots of In [HI against time show no curvature and are first order. Even under the highest pressure (1500 torr), the maximum instantaneous equivalent first-order rate constant due to second-order volume termination [7],2izr[H][M], is only 0.10 f 0.04 sec-' and decreases to 0.007 f 0.003 sec-l at the lowest [HI.…”

Section: Methodsmentioning

confidence: 99%

“…It should be noted that i i is the average concentration in the sphere, but the quantity actually observed is nabs = 2/a j-i n dr. For the dark period case substitution of n [eq. (7)] into this expression gives rise to the tabulated (CRC Handbook) exponential sine integrals which have to be numerically evaluated. Evaluation for the present cases explicitly shows [as does the closed-form equation for 5, eq.…”

Section: Case Ii: No Irradiation (Dark Period)mentioning

confidence: 99%

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Diffusion of hydrogen atoms in spherical vessels

Lynch

Michael

1978

Self Cite

A previously developed model for active species concentration profiles in infinite cylindrical systems has been extended to include the spherical system. The model couples the processes of diffusion to and reaction a t the wall. Predictions of time buildup under conditions of homogeneous production by light, and time decay after extinguishing the light source, are made for H atoms. Such predictions require a knowledge of the wall recombination coefficient and the binary diffusion coefficient for H in heat bath gas. The model is experimentally tested by measuring the first-order decay constants of H at room temperature in various pressures (10-1500 tom) of six heat bath gases. The atomic concentration is monitored by Lyman-a absorption photometry. The results show good agreement with model predictions in the various heat bath gases up to -400 torr and depend only on one parameter, y, the recombination coefficient. This should be contrasted with the earlier work where slight variation in y was invoked. The rate constants at pressures higher than 400 torr are consistently higher than model predictions.

The flash photolysis—shock tube technique using atomic resonance absorption for kinetic studies at high temperatures

Michael

Sutherland

Klemm

1985

Self Cite

A flash photolysis-shock tube technique is described for making kinetic measurements a t high temperature. Coupled with sensitive atomic resonance absorption detection, this method allows bimolecular rate constants for atom-molecule reactions to be measured directly under conditions free from kinetic complications. Experiments were performed in the reflected shock regime, and the temperature and density were calculated using ideal shock wave theory in this initial work. Results for the reaction of atomic hydrogen with ammonia are presented to illustrate the potential of the technique. The values of the Arrhenius rate parameters found in these experiments, 900 K 5 T 5 1850 K , were A = (1.14 t 0.121 x 10 '" cmB molecule s ' and E , = 13,216 2 242 cal mol-'. This result gives rate constants t h a t a r e about five times larger than those from previous studies. Although corrections for nonidealities in the reflected shock region are anticipated and under investigation, the expected changes will be relatively small and thus the large discrepancy noted here will remain