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 pulse a laser photolysis-resonance fluorescence technique. Absolute O(3P) q uantum yields were determined at selected wavelengths using 03 photoly sis to normalize for laser energy and detection sensitivity; the measu red 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, th e O(3P) yield was found to be unity between 570 and 585 nm and to decr ease in essentially linear fashion from 585 nm to near zero at 640 nm. Anomalously low O(3P) yields were noted in the strong absorption band s 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 b een used to calculate atmospheric photolysis rates for (1) NO3 + hnu - -> NO2+ O(3P), j1 = 0.19 s-1 and (2) NO3 + hnu --> NO+02, j2 = 0.016 s -1. From the wavelength threshold for process 1, the DELTAH(f,298) for NO3 was estimated to be 18 +/- 1 kcal/mol.