FIG. 6.
The absorption cross sections for CH4 (Mount et al., 1977; Kameta et al., 2002; Chen and Wu, 2004) and N2 (Chan et al., 1993) show that direct dissociation of N2 is not expected in the FUV. The vertical dashed line indicates the lower limit of our lamp emission. Huffman (1969) does report a cross-section measurement at Ly-α of 6×10−23 cm2 (open circle) but provides this only as an upper bound based on the detection limit of the instrumentation. As demonstrated by the graph, even with this upper limit the absorption of N2 is not competitive as compared to CH4, and direct dissociation cannot explain the high percentage of N2 incorporated into the aerosol material.