On the hydrogen loss from protonated nucleobases after electronic excitation or collisional electron capture

摘要

In this work, we have subjected protonated nucleobases MH+ (M = guanine, adenine, thymine, uracil and cytosine) to a range of experiments that involve high-energy (50 keV) collision-induced dissociation (CID) and electron capture-induced dissociation. In the tatter case, both neutralisation reionisation and charge reversal were done. For the CID experiments, the ions interacted with O-2. In neutral reionisation, caesium atoms were used as the target gas and the protonated nucleobases captured electrons to give neutrals. These were reionised to cations a microsecond later in collisions with O-2. In choosing Cs as the target gas, we have ensured that the first electron transfer process is favourable (by about 0.1-0.8 eV depending on the base). In the case of protonated adenine, charge reversal experiments (two Cs collisions) were also carried out, with the results corroborating those from the neutralisation-reionisation experiments. We find that white collisional excitation of protonated nucleobases in O-2 may lead to hydrogen loss with limited probabilities, this channel becomes dominant for electron capture events. Indeed, when sampling reionised neutrals on a microsecond timescale, we see that the ratio between MH+ and M+ is 0.2-0.4 when one electron is captured from Cs. There are differences in these ratios between the bases but no obvious correlation with recombination energies was found.