Figure 7: Photodepletion kinetics of dicyanoacetylene ice.
From Photochemical activity of Titan’s low-altitude condensed haze
- Journal name:
- Nature Communications
- Volume:
- 4,
- Article number:
- 1648
- DOI:
- doi:10.1038/ncomms2649
Time variation of change in absorption at 2,244 cm−1 when C4N2 film at 100 K is photolysed at 355 nm (inset) and 266 nm. As expected for a forbidden and weak singlet-triplet absorption-induced photochemistry, the depletion of C4N2 is linearly proportion to the irradiation time when exposed at 355 nm, representing initial stages of an exponential process. Only 14% of C4N2 was depleted after ~1,400 min irradiation at ~50 mW cm−2. The last three points on the lower curve (filled squares) were obtained using higher laser power (160 mW cm−2 or 8 mJ per pulse), whereas the rest of the data were derived using a 50 mW cm−2 (2.5 mJ per pulse) laser power. Linearity of this curve when fluence is converted to time clearly indicates that the 355 nm photochemistry is a one-photon process. We also plotted these three points with 160 mW cm−2 laser power separately (filled circles). As discussed in the text, the slopes of these two curves scale linearly with the laser fluencies—confirming that the 355 nm photochemistry is indeed a one-photon process. The 266 nm photolysis through singlet-singlet excitation follows a monoexponential curve with over 35% depletion within the first 800 min of irradiation at 120 mW cm−2. Extrapolation towards the longer durations of the 266 nm photolysis may not be accurate due to simultaneous increase in extinction of the film at this wavelength from the formation of new products.