Hydroxyl Radical Quantum Yields from Isopropyl Nitrite Photolysis in Air

Alkyl nitrites photolyze in air to yield alkoxy radicals and NO which, through secondary reactions, generate OH radicals. This photochemistry is important in the atmosphere and in laboratory studies where nitrites are often used as a source of OH. The overall quantum yield for hydroxyl radical formation from irradiation of isopropyl nitrite (i-C3H7ONO) between 300 and 425 nm in 1 atm air at 296 ± 2 K is reported for the first time. The OH radical was scavenged by reaction with CF3CF═CF2 and the formation of CF3CFO and CF2O monitored as a function of time using Fourier transform infrared spectrometry. The quantum yield was found to be 0.54 ± 0.07 (2σ) and is independent of whether or not NO was added (up to 3 × 1014 molecules cm−3) prior to photolysis to increase NO concentrations above those due to the photolysis of the nitrite. Ultraviolet−visible and infrared cross sections of i-C3H7ONO are also reported. These data on the OH quantum yields as well as the UV−visible and infrared cross sections for isopropyl nitrite are critical for quantitatively interpreting the results of laboratory studies where i-C3H7ONO is employed as an OH source as well as for assessing the role of alkyl nitrites in the chemistry of the troposphere.