64 research outputs found
Observation of the Unimolecular Decomposition Pathways of Chemically Activated Acetic Acid by Fourier Transform Infrared Emission Spectrometry
Formation of Nitric Acid in the Gas-Phase HO2 + NO Reaction: Effects of Temperature and Water Vapor
International audienc
Infrared Chemiluminescence Study of the Reaction of Hydroxyl Radical with Formamide and the Secondary Unimolecular Reaction of Chemically Activated Carbamic Acid
Reactions of OH and OD radicals with
NH<sub>2</sub>CHO and ND<sub>2</sub>CHO were studied by Fourier transform
infrared emission spectroscopy of the product molecules from a fast-flow
reactor at 298 K. Vibrational distributions of the HOD and H<sub>2</sub>O molecules from the primary reactions with the C–H bond were
obtained by computer simulation of the emission spectra. The vibrational
distributions resemble those for other direct H atom abstraction reactions,
such as with acetaldehyde. The highest observed level gives an estimate
of the C–H bond dissociation energy in formamide of 90.5 ±
1.3 kcal mol<sup>–1</sup>. Observation of CO<sub>2</sub>, ammonia,
and secondary water chemiluminescence gave evidence that recombination
of OH and NH<sub>2</sub>CO forms carbamic acid (NH<sub>2</sub>COOH)
with excitation energy of 103 kcal mol<sup>–1</sup>, which
decomposes through two pathways forming either NH<sub>3</sub> + CO<sub>2</sub> or H<sub>2</sub>O + HNCO. The branching fraction for ammonia
formation was estimated to be 2–3 times larger than formation
of water. This observation was confirmed by RRKM calculation of the
decomposition rate constants. A new simulation method was developed
to analyze infrared emission from NH<sub>3</sub>, NH<sub>2</sub>D,
ND<sub>2</sub>H, and ND<sub>3</sub>. Dynamical aspects of the primary
and secondary reactions are discussed based on the vibrational distributions
of CO<sub>2</sub> and those of H/D isotopes of water and ammonia
Branching Ratios and Vibrational Distributions in Water-Forming Reactions of OH and OD Radicals with Methylamines
Reactions
of OH and OD radicals with (CH<sub>3</sub>)<sub>3</sub>N, (CH<sub>3</sub>)<sub>2</sub>NH, and CH<sub>3</sub>NH<sub>2</sub> were studied
by Fourier transform infrared emission spectroscopy
(FTIR) of the water product molecules from a fast-flow reactor at
298 K. The rate constants (4.4 ± 0.5) × 10<sup>–11</sup>, (5.2 ± 0.8) × 10<sup>–11</sup>, and (2.0 ±
0.4) × 10<sup>–11</sup> cm<sup>3</sup> molecule<sup>–1</sup> s<sup>–1</sup> were determined for OD + (CH<sub>3</sub>)<sub>3</sub>N, (CH<sub>3</sub>)<sub>2</sub>NH, and CH<sub>3</sub>NH<sub>2</sub>, respectively, by comparing the HOD emission intensities
to the HOD intensity from the OD reaction with H<sub>2</sub>S. Abstraction
from the nitrogen site competes with abstraction from the methyl group,
as obtained from an analysis of the HOD and D<sub>2</sub>O emission
intensities from the OD reactions with the deuterated reactants, (CD<sub>3</sub>)<sub>2</sub>NH and CD<sub>3</sub>NH<sub>2</sub>. After adjustment
for the hydrogen–deuterium kinetic isotope effect, the product
branching fractions of the hydrogen abstraction from the nitrogen
for di- and monomethylamine were found to be 0.34 ± 0.04 and
0.26 ± 0.05, respectively. Vibrational distributions of the H<sub>2</sub>O, HOD, and D<sub>2</sub>O molecules are typical for direct
hydrogen atom abstraction from polar molecules, even though activation
energies are negative because of the formation of pre-transition-state
complexes. Comparison is made to the reactions of hydroxyl radicals
with ammonia and with other compounds with primary C–H bonds
to discuss specific features of disposal of energy to water product
Rate Constant and Mechanism of the Reaction of OH Radicals with Acetic Acid in the Temperature Range of 229−300 K
Product Branching Fractions and Kinetic Isotope Effects for the Reactions of OH and OD Radicals with CH 3
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