Additional Time-of-Flight Mass Spectrometry Experiments

Additional Time-of-Flight Mass Spectrometry Experiments 

The previously described results were obtained with 248-nm irradiation which is close to an absorption minimum, while 308 nm (351 nm) which was used for most other studies is close to an absorption maximum. A comparison of these two irradiation wavelengths, one corresponding to the absorption of the photochemically active triazene group (308 nm), the other to the photochemically more stable aromatic system (248 nm), could give valuable information about the influence of these structural units on the ablation mechanism. 

For a direct comparison between the two irradiation wavelengths, the relative maximum peak intensities of different fragments are compared. In Fig. 47 the response of the most intense mass (i.e., 28 amu from N2) at the two different irradiation wavelengths is shown. The data taken after irradiation at 308 nm exhibit a linear increase of the signal intensities at low flu-ences ( 40 mj cm 2), as shown in the insert in Fig. 47. At higher fluences a fast increase is observed. This is an indication that at fluences above 

After irradiation at 248 nm a much faster increase of the signal was detected and no linear range can be observed (see insert in Fig. 47). At higher fluences the signal intensity reaches a maximum. This is probably due to absorption of the incoming photons by aromatic fragments (e.g., radicals, which are produced during ablation). In Fig. 48 the observations for other analyzed masses after irradiation at 308 nm are summarized. 

In comparison, pronounced differences between the signal intensities at 248- and 308-nm irradiation are observed. The fragments with masses high- 

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