INTERNAL ENERGY-DISTRIBUTIONS FROM NITROGEN-DIOXIDE FLUORESCENCE .3. PHOTOLYSIS OF JET-COOLED N2O4

A supersonic jet of N2O4 is photolyzed at three wavelengths: 351, 248, and 193 nm. The resultant NO2 fluorescence is dispersed, the fluoresc ence spectrum is folded into a cumulative sum, and the internal energy distribution of almost nascent photolysis products is found by the me thod of article 1 of this series. The spread of these product internal energy distributions increases as the photolysis energy increases fro m 351 to 248 to 193 nm. The most probable internal energy increases be tween 351- and 248-nm photolysis, but at 193-nm photolysis it is about the same as, or somewhat lower than, that at 248 nm. This apparent an omaly is explained in terms of the electronic states of the products. The internal energy distribution derived from 351-nm data is examined by the method of prior distribution, and the photolysis products are f ound to be one NO2 molecule in the ground electronic state and the oth er in the B-2(1) electronic state with 3 or 4 quanta of bending vibrat ion excitation. The internal energy distributions at 193 and 248 nm ar e combined with Kawasaki's time-of-flight translational energy distrib utions at 193 and 248 nm, and upon adding considerations of molecular orbitals the product states are assigned for photolysis at 193 and 248 nm. From these considerations, it is concluded that the most probable N2O4 photodissociation channels are as follows: N2O4 + hnu (lambda = 351 nm) --> NO2 (B B-2(1), v2 = 3-4) + NO2 (X 2A1), N2O4 + hnu (lambd a = 193 nm) --> NO2 (B-2(2)) + NO2* (B-2(2)), and N2O4 + hnu (lambda = 248 nm) --> NO2 (B-2(1)) + NO2* (B-2(2)).