Kinetics of the reaction of hydroxyl radicals with nitric acid

Journal Article · Thu Sep 16 04:00:00 EDT 1982 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100216a022· OSTI ID:6446863

Margitan, J J; Watson, R T

The gas-phase reaction of hydroxyl radicals with nitric acid was studied in a flash photolysis system utilizing uv resonance fluorescence detection of the OH radicals formed by 266-nm laser photolysis of HNO/sub 3/ over the temperature range 225 to 415 K and pressures from 20 to 300 torr. The data were found to exhibit a slight pressure dependence, which increased in importance at lower temperatures. Room-temperature rate constants increased from 1.1 x 10/sup -13/ cm/sup 3/s/sup -1/ at 20 torr to 1.22 x 10 /sup -13/ cm/sup 3/s/sup -1/ at 100 torr and 1.3 x 10/sup -13/ cm/sup 3/s/sup -1/ at 300 torr. At 238 K, however, the observed rate constants increased from 2.05 x 10/sup -13/ cm/sup 3/s/sup -1/ at 20 torr to 2.8 x 10/sup -13/ cm/sup 3/s/sup -1/ at 100 torr. An Arrhenius plot over the entire 225 to 415 K temperature range is curved, with a negative T dependence below room temperature characterized by E/R = -800 K at 40 torr and E/R = -700 K for the purely bimolecular reaction component (extrapolated to zero pressure). At temperatures above 298 K, the T dependence is significantly weaker. These results are in excellent agreement with two recent flash photolysis studies but differ from a recent flow study and two older investigations. The negative T dependence and the pressure dependence are consistent with a reaction that proceeds through an intermediate complex. Additionally, the quantum yields for the production of O and H atoms from 266-nm HNO/sub 3/ photolysis were determined by direct observation as Phi(0) = 3 x 10/sup -2/ and Phi(H) < 2 x 10/sup -3/. 7 figures, 2 tables.

• Research Organization: California Inst. of Tech., Pasadena
• OSTI ID: 6446863
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 86:19; ISSN JPCHA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400500 -- Photochemistry
400600* -- Radiation Chemistry
ACTIVATION ENERGY
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
DATA
DECOMPOSITION
ELECTROMAGNETIC RADIATION
ENERGY
ENERGY-LEVEL TRANSITIONS
EXCITATION
EXPERIMENTAL DATA
HIGH TEMPERATURE
HYDROGEN COMPOUNDS
HYDROXYL RADICALS
INFORMATION
INORGANIC ACIDS
IONIZATION
KINETICS
LASER RADIATION
LOW PRESSURE
LOW TEMPERATURE
MEDIUM TEMPERATURE
NITRIC ACID
NUMERICAL DATA
PHOTOCHEMICAL REACTIONS
PHOTOIONIZATION
PHOTOLYSIS
PRESSURE DEPENDENCE
RADIATIONS
RADICALS
REACTION INTERMEDIATES
REACTION KINETICS
TEMPERATURE DEPENDENCE
TIME DEPENDENCE