Vibrational relaxation of HOD by collisions with Ar atoms.

Vibrational relaxation of HOD(v12, v3) molecules by collisions with Ar was studied at 298 K (v12 denotes coupled bending, v2, and OD stretching, v1, vibrational modes and v3 denotes OH stretching mode). The vibrationally excited HOD molecules were generated by exothermic abstraction reactions of OD radicals with 13 different RH reactants and observed by infrared emission from a fast-flow reactor as a function of Ar pressure and reaction time. State-specific relaxation rate constants were obtained by comparison of the time evolution of the experimental vibrational distributions with numerical kinetic calculations for vibrational populations.

Vibrational relaxation of high levels of HO by collisions with Ar as studied by infrared chemiluminescence.

Vibrational relaxation of HO(v,v) molecules by collisions with Ar was studied at 298 K (v denotes the bending vibrational mode and v denotes the sum of the symmetric, v, and asymmetric, v, vibrational modes). The HO molecules from 14 different exothermic reactions of H-atom abstraction by OH radicals were observed by infrared emission from a fast flow reactor as a function of Ar pressure and reaction time. Numerical kinetic calculations were used to obtain rate constants for stretch-to-bend energy conversion, (v,v) → (v + 2,v - 1), and pure bend relaxation, (v,v) → (v - 1,v).

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 NHCHO and NDCHO 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 HO 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.

Branching Ratios and Vibrational Distributions in Water-Forming Reactions of OH and OD Radicals with Methylamines.

Reactions of OH and OD radicals with (CH3)3N, (CH3)2NH, and CH3NH2 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.

Pressure dependence of butyl nitrate formation in the reaction of butylperoxy radicals with nitrogen oxide.

The yield of 1- and 2-butyl nitrates in the gas-phase reactions of NO with n-C4H9O2 and sec-C4H9O2, obtained from the reaction of F atoms with n-butane in the presence of O2, was determined over the pressure range of 100-600 Torr at 298 K using a high-pressure turbulent flow reactor coupled with a chemical ionization quadrupole mass spectrometer. The yield of butyl nitrates was found to increase linearly with pressure from about 3% at 100 Torr to about 8% at 600 Torr. The results obtained are compared with the available data concerning nitrate formation from NO reaction with other small alkylperoxy radicals.

Pressure and temperature dependence of methyl nitrate formation in the CH3O2 + NO reaction.

The branching ratio β = k(1b)/k(1a) for the formation of methyl nitrate, CH(3)ONO(2), in the gas-phase CH(3)O(2) + NO reaction, CH(3)O(2) + NO → CH(3)O + NO(2) (1a), CH(3)O(2) + NO → CH(3)ONO(2) (1b), has been determined over the pressure and temperature ranges 50-500 Torr and 223-300 K, respectively, using a turbulent flow reactor coupled with a chemical ionization mass spectrometer. At 298 K, the CH(3)ONO(2) yield has been found to increase linearly with pressure from 0.33 ± 0.

Branching ratios in the hydroxyl reaction with propene.

The branching ratios for the reactions of attachment of hydroxyl radical to propene and hydrogen-atom abstraction were measured at 298 K over the buffer gas pressure range 60-400 Torr (N(2)) using a subatmospheric pressure turbulent flow reactor coupled with a chemical ionization quadrupole mass spectrometer. Isotopically enriched water H(2)(18)O was used to produce (18)O-labeled hydroxyl radicals in reaction with fluorine atoms. The β-hydroxypropyl radicals formed in the attachment reactions 1a and 1b , OH + C(3)H(6) → CH(2)(OH)C(•)HCH(3) (eq 1a ) and OH + C(3)H(6) → C(•)H(2)CH(OH)CH(3) (eq 1b ), were converted to formaldehyde and acetaldehyde in a sequence of secondary reactions in O(2)- and NO-containing environment.

Pressure and temperature dependence of ethyl nitrate formation in the C(2)H(5)O(2) + NO reaction.

The branching ratio beta = k(1b)/k(1a) for the formation of ethyl nitrate, C(2)H(5)ONO(2), in the gas-phase C(2)H(5)O(2) + NO reaction, C(2)H(5)O(2) + NO --> C(2)H(5)O + NO(2) (1a), C(2)H(5)O(2) + NO --> C(2)H(5)ONO(2) (1b), was determined over the pressure and temperature ranges 100-600 Torr and 223-298 K, respectively, using a turbulent flow reactor coupled with a chemical ionization mass spectrometer. At 298 K the C(2)H(5)ONO(2) yield was found to increase linearly with pressure from about 0.7% at 100 Torr to about 3% at 600 Torr.

Water vapor effect on the HNO3 yield in the HO2 + NO reaction: experimental and theoretical evidence.

The influence of water vapor on the production of nitric acid in the gas-phase HO(2) + NO reaction was determined at 298 K and 200 Torr using a high-pressure turbulent flow reactor coupled with a chemical ionization mass spectrometer. The yield of HNO(3) was found to increase linearly with the increase of water concentration reaching an enhancement factor of about 8 at [H(2)O] = 4 x 10(17) molecules cm(-3) ( approximately 50% relative humidity). A rate constant value k(1bw) = 6 x 10(-13) cm(3) molecule(-1) s(-1) was derived for the reaction involving the HO(2)xH(2)O complex: HO(2)xH(2)O + NO --> HNO(3) (1bw), assuming that the water enhancement is due to this reaction.

HNO3 forming channel of the HO2 + NO reaction as a function of pressure and temperature in the ranges of 72-600 Torr and 223-323 K.

A high-pressure turbulent flow reactor coupled with a chemical ionization mass-spectrometer was used to determine the branching ratio of the HO(2) + NO reaction: HO(2) + NO --> OH + NO(2) (1a), HO(2) + NO --> HNO(3) (1b). The branching ratio, beta = k(1b)/k(1a), was derived from the measurements of "chemically amplified" concentrations of the NO(2) and HNO(3) products in the presence of O(2) and CO. The pressure and temperature dependence of beta was determined in the pressure range of 72-600 Torr of N(2) carrier gas between 323 and 223 K.

Mechanism of the OH-initiated oxidation of glycolaldehyde over the temperature range 233-296 K.

The mechanism of the gas-phase OH-initiated oxidation of glycolaldehyde (HOCH(2)CHO) was studied in the 233-296 K temperature range using a turbulent flow reactor coupled with a chemical ionization mass spectrometer. In the presence of O2, formaldehyde, CO2, formic acid, and glyoxal were observed at room temperature with the yields of 80, 34, 18, and 14%, respectively. Decrease of temperature to 233 K led to significant changes in the yields of the stable products: those of formaldehyde and glyoxal decreased to 50 and 4%, respectively, whereas that of formic acid increased to 52%.

Formation of nitric acid in the gas-phase HO2 + NO reaction: effects of temperature and water vapor.

A high-pressure turbulent flow reactor coupled with a chemical ionization mass spectrometer was used to investigate the minor channel (1b) producing nitric acid, HNO3, in the HO2 + NO reaction for which only one channel (1a) is known so far: HO2 + NO --> OH + NO2 (1a), HO2 + NO --> HNO3 (1b). The reaction has been investigated in the temperature range 223-298 K at a pressure of 200 Torr of N2 carrier gas. The influence of water vapor has been studied at 298 K.

Mechanism of the OH-initiated oxidation of hydroxyacetone over the temperature range 236-298 K.

The mechanism of the gas-phase reaction of OH radicals with hydroxyacetone (CH3C(O)CH2OH) was studied at 200 Torr over the temperature range 236-298 K in a turbulent flow reactor coupled to a chemical ionization mass-spectrometer. The product yields and kinetics were measured in the presence of O2 to simulate the atmospheric conditions. The major stable product at all temperatures is methylglyoxal.