Document Detail

Kinetics of the NCN + NO Reaction Over a Broad Temperature and Pressure Range.
MedLine Citation:
PMID:  22694482     Owner:  NLM     Status:  Publisher    
Rate coefficients for the reaction 3NCN + NO -> products (R3) were measured in the temperature range 251 - 487 K at pressures from 10 mbar up to 50 bar with helium as the bath gas. The experiments were carried out in slow-flow reactors by using pulsed excimer laser photolysis of NCN3 at 193 or 248 nm for the production of NCN. Pseudo-first order conditions with respect to NO were applied, and NCN was detected time-resolved by resonant laser-induced fluorescence excited near 329 nm. The measurements at the highest pressures yielded values of k3 ~ 8 x 10-12 cm3 s 1 virtually independent of temperature and pressure, which indicates a substantially smaller high-pressure limiting value of k3 than predicted in earlier works. Our experiments at pressures below 1 bar confirm the negative temperature and positive pressure dependence of the rate coefficient k3 found in previous investigations. The falloff behavior of k3 was rationalized by a master equation analysis based on a barrierless association step 3NCN + NO <-> NCNNO(2A") followed by a fast internal conversion NCNNO(2A") <-> NCNNO(2A'). From 251 - 487 K and above 30 mbar the rate coefficient k3 is well represented by a Troe parameterization for a recombination/dissociation reaction, k3(T, P) = k4(inf)k40[M]F(k40[M] + k4(inf))-1, where k4 represents the rate coefficient for the recombination reaction 3NCN + NO. The following parameters were determined (30% estimated error of the absolute value of k3): k40[M = He] = 1.91 x 10-30 (T/300 K)-3.3 cm6 s-1[He], k4(inf) = 1.12 x 10-11 exp(-23 K/T) cm3 s 1, and Fcent = 0.28 exp (173 K/T).
Oliver Welz; Matthias Olzmann
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-6-13
Journal Detail:
Title:  The journal of physical chemistry. A     Volume:  -     ISSN:  1520-5215     ISO Abbreviation:  -     Publication Date:  2012 Jun 
Date Detail:
Created Date:  2012-6-14     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9890903     Medline TA:  J Phys Chem A     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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