Photofragmentation in selected tautomers of protonated adenine.

The photofragmentation by UV excitation of selectively prepared 1(+) and 3(+) tautomers of protonated adenine is studied after excitation at a 266 and 263 nm wavelengths with two different experimental set-ups located in Seoul and Orsay. While the production of 1(+) tautomers with an electrospray ion source is now well accepted, calculations were used to ascribe the preparation of 3(+) tautomers from cold adenine dimers. The fragmentation patterns are rather similar for both tautomers, suggesting similar mechanisms as a statistical fragmentation in the ground electronic state after internal conversion.

Photoinduced evaporation of mass-selected aniline+(water)n (n=4-20) clusters.

Photofragmentation of mass-selected aniline(+)(water)n (An(+)Wn, n=4-20) clusters is investigated over photon energies ranging from 1.65 to 4.66 eV by linear tandem time-of-flight mass spectrometry. The aniline ring turns out to survive irradiation of photons, and most of the absorbed photon energy flows to the hydrogen-bonding networks to be used up for liberation of water molecules. The average number of ejected water molecules measured as a function of photon energy reveals that the loss of water molecules is a photoevaporation process. The distributions of internal energies for parent ions and binding energies of water molecules are estimated from the plots of photofragment branching ratio versus photon energy, which give nice Gaussian fits. Also, density functional theory calculations are performed to obtain optimized structures of isomers for An(+)Wn clusters and binding energies. The authors find that the An(+)W6 cluster has a highly symmetric structure and its binding energy in An(+)W6-->An(+)W5+W stands out. This is in line with the experimental results showing that n=6 is a magic number in the mass distribution and An(+)W6 is relatively stable in metastable decay.