Aufbau eines Oktopol-Ionenführungssystems zur Untersuchung von Ionen-Molekül-Reaktionen - Rotationsabhängigkeit der Reaktion HBr+(DBr+) mit CO2

The proton-transfer reaction of state selected HBr+- and DBr+-ions, respectively, to carbon dioxide under formation of HOCO+ and DOCO+, respectively, and Br was investigated in an octopole ion guide. For both endothermic reactions studies of the influence of the ion rotation on the cross section were done for different collision energies. The state selected ions were created in a (2+1)-REMPI process in the electronic, spin-orbit and vibrational ground state of the ion and with a narrow distribution in the rotational states. The mean rotational energies of the HBr+-ion were varied from 1.4 to 66.3 meV and of the DBr+-ion from 0.7 to 43.0 meV. Furthermore the collision energies ranged from 0.32 to 1.00 eV. For both, the proton and deuteron transfer, decreasing cross sections with increasing rotational energy were determined for all collision energies. However, the dependence on the rotation is stronger for the higher collision energies than for the lower ones. For example, the cross section for the collision energy Ec.m. = 1.00 eV drops by about 50% for both reactions in the investigated range of Erot. Compared with Ec.m. = 0.35 eV the cross section of the proton transfer is decreased by 30% whereas the deuteron transfer is only decreased by 20%. Measured absolute cross sections range from 0.9 to 3.5 Å2. With increasing collision energy the efficiencies of the reactions are enhanced as expected for endothermic reactions. For the higher collision energies the cross section shows a level-off behavior. A comparison of the rotational dependences of the proton and the deuteron transfer shows that the cross section might be dominated more probable by effects of the rotational energy than the angular momentum.