Quantum yields for NO₃ photolysis between 570 and 635 nm

Quantum yields for the production of O(³P) from the photolysis of NO₃ have been measured over the wavelength range 570-635 nm, using a pulsed laser photolysis-resonance fluorescence technique. Absolute O(³P) quantum yields were determined at selected wavelengths using O₃ photolysis to normalize for laser energy and detection sensitivity; the measured quantum yields were 1.06 ± 0.26 at 582 nm, 0.72 ± 0.18 at 590 nm, and 0.52 ± 0.13 at 603 nm. Combining these absolute yields with a series of relative measurements made as a function of wavelength, the O(³P) yield was found to be unity between 570 and 585 nm and to decrease in essentially linear fashion from 585 nm to near zero at 640 nm. Anomalously low O(³P) yields were noted in the strong absorption bands near 623 nm. In addition, NO has been detected as a minor product of NO₃ photolysis (quantum yield about 20%) near 590 nm. The data have been used to calculate atmospheric photolysis rates for (1) NO₃ + hv → NO₂ + O(³P),j₁ = 0.19 s^-1 and (2) NO₃ + hv → NO + O₂,j₂ = 0.016 s^-1. From the wavelength threshold for process 1, the ΔH_f,298 for NO₃ was estimated to be 18 ± 1 kcal/mol.